Have you ever wondered why stainless steel doesn’t rust like regular steel? This blog post will explore the fascinating world of stainless steel, its unique properties, and its critical role in modern industry. By the end, you’ll understand why this material is essential for everything from kitchen utensils to aerospace technology. Get ready to uncover the secrets behind stainless steel’s resilience and versatility!
Stainless steel is a kind of high-alloy steel that can resist corrosion in air or chemical corrosion medium.
Stainless steel has a beautiful surface and good corrosion resistance, and it does not require surface treatment such as color plating, allowing the inherent surface properties of stainless steel to be fully utilized.
It is used in many steel applications and is typically referred to as stainless steel.
Representative properties include 13-chromium steel, 18-chromium-nickel steel, and other high alloy steels.
From a metallographic perspective, stainless steel contains chromium, which forms a very thin chromium film on the surface that separates oxygen from the steel and plays a role in corrosion resistance.
To maintain the inherent corrosion resistance of stainless steel, the steel must contain more than 12% chromium.
China is the first country in the world to smelt iron and steel.
Their ancestors mastered some skills of iron smelting, steel making, casting and forging and heat treatment as far as 3000 years ago, more than 1700 years earlier than European countries, and made important contributions to world civilization and human progress.
Steel has become the most basic and important material for modern industrial and agricultural production, transportation, national defense and even people’s life.
At present, although various new inorganic materials and organic synthetic materials have been greatly developed.
However, from the aspects of production cost and wide application performance, they are far from replacing steel.
Therefore, the production capacity of steel is still one of the important symbols to measure a country’s national strength.
The reason why iron and steel materials are so widely used is that iron ore deposits are concentrated, the storage capacity is large, the mining and smelting are relatively economical, and the cold and hot deformation capacity of semi-finished steel products is strong.
The finished products have excellent mechanical properties (strength, plasticity and impact resistance) and processing properties (cutting, welding, cold deformation, etc.).
However, compared with silicic acid materials, polymer synthetic materials and some non-ferrous metals, its biggest disadvantage is that it is easy to lose weight and even completely destroy due to corrosion under the conditions of atmosphere or various media such as acid, alkali and salt.
Stainless steel can be roughly classified by use, chemical composition and metallographic structure.
The austenitic system steel is basically composed of 18% chromium-8% nickel, and the addition amount of each element changes differently, so as to develop steel grades for various purposes.
Classified by chemical composition:
① Cr series: ferrite series, martensite series.
② Cr Ni series: Austenitic series, abnormal series, precipitation hardening series.
Classification by metallographic structure:
① Austenitic stainless steel;
③ Martensitic stainless steel;
④ Duplex stainless steel;
⑤ Precipitation hardening stainless steel
From 1910 to 1914, stainless steel with martensite, ferrite and austenite was born.
From the perspective of chemical composition, it mainly belongs to two systems: Fe Cr and Fe Cr Ni.
In the nearly three decades from the end of World War I to the end of World War II (i.e. 1919 to 1945).
With the development of various industries, stainless steel has differentiated to adapt to working conditions, that is, on the basis of the original two systems and three organizational States, many new types of stainless steel have been derived by increasing or decreasing carbon content and adding a variety of other alloy elements.
For more than 30 years from the end of the second large station to now, pitting corrosion resistant stainless steel, stainless steel for atomic energy industry, precipitation hardening stainless steel and manganese nitrogen substituted nickel stainless steel have been developed mainly to meet the needs of resisting seawater or salt corrosion, absorbing y-rays and neutrons, obtaining ultra-high strength and saving nickel.
In recent years, in order to solve the problems of intergranular corrosion and stress corrosion of austenitic stainless steel, ultra-low carbon stainless steel and ultra-pure ferritic stainless steel have been developed respectively.
At present, there are more than 20 varieties of stainless steel, of which more than 20 varieties of chromium (chromium) have been used in the market, and the rest are about 80 varieties of stainless steel.
The main research and development of stainless steel grades are focused on two aspects:
The first aspect is to improve the corrosion resistance of steel.
The research on the intergranular corrosion of 18-8 steel not only develops the steel type, but also puts forward the process method to solve this problem.
It also promotes the research on the passivation and corrosion mechanism of stainless steel.
The second aspect is the development of high-strength stainless steel (precipitation hardening stainless steel), which was developed with the progress of aviation, aerospace and rocket technology after World War II.
Among them, semi austenitic precipitation hardening stainless steel has excellent process properties (17-7PH), which is easy to be processed and formed after solution treatment, and the subsequent enhanced heat treatment (aging treatment) temperature is not high, and the deformation is very small.
In the United States, this kind of steel is mostly used in aviation structure and has been mass produced, and similar steel types have been put into use in various countries
1. General characteristics
2. Quality characteristics and requirements of stainless steel
| Item | Basic organization | ||
| Representative steel grade | STS304 | STS430 | STS410 |
| heat treatment | Solid melt heat treatment | annealing | Quenching after annealing |
| Hardness | Work hardening | Micro hardenability | Small amount hardenability |
| Main purpose | Interior and exterior decoration of buildings, kitchen utensils, chemical scale, aviation machinery | Building materials, auto parts, electrical appliances, kitchen appliances, lunch boxes, etc | Drill and knife machine parts, hospital appliances, surgical appliances |
| Corrosion resistance | high | high | medium |
| strength | high | medium | high |
| Processability | high | medium | high |
| magnetic | Nonmagnetic | Magnetically | Upper magnetism |
| Weldability | high | medium | low |
2.1. Quality characteristics of stainless steel:
2.2. Quality characteristics and requirements of stainless steel
Due to different uses of products, their processing technology and quality requirements of raw materials are also different.
(1) Material:
① DDQ (deep drawing quality):
It refers to the material used for deep drawing (punching), that is, the so-called soft material.
The main characteristics of this material are high elongation (≥ 53%), low hardness (≤ 170%), internal grain grade between 7.0 ~ 8.0, and excellent deep drawing performance.
At present, the processing ratio (blank size / product diameter) of many enterprises producing thermos bottles and pots is generally high, and their processing ratios are 3.0, 1.96, 2.13 and 1.98 respectively.
SUS304 DDQ materials are mainly used for these products requiring high processing ratio.
Of course, products with processing ratio more than 2.0 generally need to be stretched for several times.
If the extension of raw materials cannot be reached, the products are easy to crack and pull through when processing deep drawn products, which will affect the qualified rate of finished products and, of course, increase the cost of manufacturers;
② General materials:
It is mainly used for materials other than DDQ.
This material is characterized by relatively low elongation (≥ 45%), relatively high hardness (≤ 180) and internal grain size grade of 8.0 ~ 9.0.
Compared with DDQ materials, its deep drawing performance is relatively poor.
It is mainly used for products that can be obtained without stretching, such as spoons, spoons, forks, electrical appliances, steel pipes, etc.
However, compared with DDQ material, it has an advantage that BQ property is relatively good, which is mainly due to its slightly higher hardness.
(2) Surface quality:
Stainless steel sheet is a very expensive material, and customers have very high requirements for its surface quality.
However, all kinds of defects, such as scratches, pitting, creases and pollution, will inevitably appear in the production process of stainless steel sheet, so its surface quality, such as scratches, creases and other defects, whether high-grade materials or low-grade materials, are not allowed, and pitting is also not allowed in spoon, spoon, fork and production, because it is difficult to throw it away during polishing.
| Purpose | Object product | Processing technology | Requirements, quality and characteristics | ||||||
| surface quality | BQ property | texture of material | shape | Thickness tolerance | Weldability | Corrosion resistance | |||
| Shallow processing | Knife, fork, etc | Blanking → transverse stretching → head cutting → forming → polishing + cleaning → packaging | High requirements, no pitting and other defects | good | General wood | commonly | -5% | Not required | good |
| Deep processing | Class II tableware, thermos cup, etc | Blanking → oiling → forming → (sometimes several times) trimming + crimping → cleaning → re bottoming → polishing → welding handle → packaging | High requirements, no scratch, crease and other defects | good | DDQ | High requirements | -3-~-5% | good | good |
| PIPE | Decorative pipe, etc | Narrow band → extrusion molding → butt welding → grinding weld + pipe cutting → grinding → polishing → packaging | High requirements, no creases and other defects | commonly | General wood | good | -8% | good | commonly |
| Kitchenware | Outer wall of freezer, etc | Blanking → folding → electric welding → grinding | High requirements, no creases and other defects | commonly | General wood | commonly | -8% | good | commonly |
| container | Water heater water dispenser liner | Narrow band → drum → welding → pipe cutting and bottom welding → grinding weld + Packaging | commonly | commonly | General wood | commonly | -10% | good | commonly |
We determine the surface quality grade according to the degree and frequency of various surface defects, so as to determine the product grade. (see table:)
(3) Thickness tolerance:
Generally speaking, different stainless steel products require different thickness tolerances of raw materials.
For example, class II tableware and thermos cups, the thickness tolerance is generally required to be – 3 ~ 5%, while class I tableware generally requires – 5%, steel pipes – 10%, hotel freezers – 8%, and dealers generally require – 4% ~ 6%.
At the same time, the difference of domestic and export products will also lead to different requirements of customers for the thickness tolerance of raw materials.
Generally, the thickness tolerance requirements of customers of export products are high, while the thickness tolerance requirements of domestic enterprises are relatively low (mostly due to cost considerations), and some customers even require – 15%.
(4) Weldability:
Different product uses have different requirements for welding performance.
Class I tableware generally does not require welding performance, even including some pot enterprises.
However, most products need raw materials with good welding performance, such as class II tableware, thermos cup, steel pipe, water heater, water dispenser, etc.
(5) Corrosion resistance:
Most stainless steel products require good corrosion resistance, such as class I and II tableware, kitchenware, water heater, water dispenser, etc.
Some foreign businessmen also test the corrosion resistance of the products: heat the NACL aqueous solution to boiling, pour out the solution after a period of time, wash and dry, and weigh the weight loss to determine the degree of corrosion (Note: when polishing the products, rust spots will appear on the surface during the test due to the content of Fe in abrasive cloth or sandpaper).
(6) Polishing performance (BQ):
At present, stainless steel products generally go through the process of polishing in production, and only a few products such as water heater and water dispenser liner do not need polishing.
Therefore, this requires good polishing performance of raw materials.
The main factors affecting the polishing performance are as follows:
① Surface defects of raw materials. Such as scratch, pitting, over pickling, etc.
② Material problem of raw materials. If the hardness is too low, it is not easy to polish (BQ is not good), and if the hardness is too low, orange peel is easy to appear on the surface during deep drawing, which affects BQ. BQ with high hardness is relatively good.
③ After deep stretching, small black spots and ridging will appear on the surface of the area with great deformation, which will affect the BQ property.
| Steel grade | Characteristic | Application |
| 301 | Compared with 304 steel, the content of Cr and Ni is less, the tensile strength and hardness are higher during cold working, non-magnetic, but magnetic after cold working. | Train, aircraft, conveyor belt, vehicle, bolt, spring, screen |
| 17Cr-7Ni carbon | ||
| 301L | It is to reduce the content of C and improve the grain boundary corrosion resistance of welded junction on the basis of 301 steel; | Railway vehicle frame and exterior decoration materials |
| 17Cr-7Ni-0.1N-low carbon | The strength deficiency caused by the reduction of C content is compensated by adding N element to ensure the strength of steel. | |
| 304 | As a widely used steel, it has good corrosion resistance, heat resistance, low temperature strength and mechanical properties; | Household products (Class 1 and 2 tableware, cabinets, indoor pipelines, water heaters, boilers, bathtubs), auto parts (windshield wipers, silencers, molded products), medical appliances, building materials, chemistry, food industry, agriculture, ship parts |
| 18Cr-8Ni | Stamping, bending and other hot workability is good, and there is no heat treatment hardening phenomenon (if there is no magnetism, use the temperature range of – 196 ℃ ~ 800 ℃) | |
| 304L | As a Low-C 304 steel, its corrosion resistance is similar to that of 304 steel in general, but its resistance to grain boundary corrosion is excellent after welding or stress relief; | It is applied to outdoor machines in chemical, coal and petroleum industries with high requirements for grain boundary corrosion resistance, heat-resistant parts of building materials and parts with difficulty in heat treatment. |
| 18Cr-8I-low carbon | It can also maintain good corrosion resistance without heat treatment, and the service temperature is – 196 ℃ ~ 800 ℃. | |
| 304 | Due to the addition of Cu, it has good formability, especially wire drawing and aging crack resistance, so it can form products with complex shapes; Its corrosion resistance is the same as 304· | Thermos bottle, kitchen sink, pot, pot, insulated lunch box, door handle, textile processing machine. |
| Cu13Cr-7.7Ni-2Cu | ||
| 304N | On the basis of 304 steel, the content of S and Mn is reduced, and N element is added to prevent the decrease of plasticity, improve the strength and reduce the thickness of steel. | Components, street lamps, water storage tanks, water pipes |
| 118Cr-8Ni-N | ||
| 304N | Compared with 304, N and MB are added as high-strength steel for structural members. | Components, street lamps, water storage tanks |
| 218Cr-8Ni-N | ||
| 316 | Due to the addition of M, its corrosion resistance, atmospheric corrosion resistance and high temperature strength are particularly good, and can be used under harsh conditions; Excellent work hardening (non-magnetic). | Equipment used in seawater, chemical, dye, papermaking, oxalic acid, fertilizer and other production equipment; Photography, food industry, coastal facilities, ropes, CD rods, bolts, nuts |
| 18Cr-12Ni-2.5Mo | ||
| 316L | As a Low-C series of 316 steel, in addition to having the same characteristics as 316 steel, it has excellent grain boundary corrosion resistance. | In the application of 316 steel, products with special requirements for grain boundary corrosion resistance |
| 18Cr-12Ni-2.5Mo low carbon | ||
| 321 | Adding Ti to 304 steel to prevent grain boundary corrosion; | Aircraft, exhaust pipe, boiler drum |
| 18Cr-9Ni-Ti | Suitable for use at 430 ℃ ~ 900 ℃. | |
| 409L | Due to the addition of Ti, it has good high temperature corrosion resistance and high temperature strength. | Automotive exhaust pipes, heat exchangers, containers and other products that are not heat treated after welding. |
| 11. 3Cr-0.17Ti-low C, n | ||
| 410L 13Cr low C | On the basis of 410 steel, the content of C is reduced, and its processability, welding deformation resistance and high temperature oxidation resistance are excellent. | Parts for mechanical structure, engine exhaust pipe, boiler combustion chamber, burner. |
| 410 13Cr low carbon | As a representative of martensitic steel, although it has high strength, it is not suitable for harsh corrosive environment; It has good workability and is hardened (magnetic) according to the heat treatment surface. | Blade, mechanical parts, oil refining unit, bolt and nut, pump rod, class 1 tableware (knife and fork). |
| 420J1 13Cr-0.2C | After quenching, it has high hardness and good corrosion resistance (magnetic). | Tableware (knife), turbine blade |
| 420J2 13Cr-0.3C | After quenching, the hardness is higher than that of 420J1 steel (magnetic). | Blade, nozzle, valve, ruler, tableware (scissors, blade). |
| 430J1L 18-Cx0. 5C Nb low C, n | In 430 steel, Cu, Nb and other elements are added; It has good corrosion resistance, formability, weldability and high temperature oxidation resistance. | Building exterior decoration materials, auto parts, cold and hot water supply equipment. |
| 436L 18Cr-1Mo-Ti wbzr low C, N | It has good heat resistance and abrasion resistance. Because it contains B and Zr elements, it has excellent processability and weldability. | Washing machine, automobile exhaust pipe, electronic products, 3-layer bottom pot. |
The physical properties of stainless steel are mainly expressed in the following aspects:
① Coefficient of thermal expansion
The change of material quality and elements caused by temperature change.
The expansion coefficient is the slope of the expansion temperature curve, the instantaneous expansion coefficient is the slope at a specific temperature, and the average slope between two specified temperatures is the average thermal expansion coefficient.
The coefficient of expansion can be expressed in volume or length, usually in length.
② Density
The density of a substance is the mass per unit volume of the substance, in kg / m3 or 1b / in3.
When the force applied to the two ends of the edge per unit length can cause the unit change of the object in length, the force required per unit area is called the elastic modulus.
The unit is 1b / in3 or N / m3.
④ Resistivity
The resistance measured between two opposite sides of cubic material per unit length, in Ω· m, μ Ω· cm or (discarded) Ω / (circular mil. Ft).
⑤ permeability
Dimensionless coefficient, which indicates the degree to which a substance is easily magnetized, is the ratio of magnetic induction intensity to magnetic field intensity.
⑥ melting temperature range
Determine the temperature at which the alloy begins to solidify and after solidification.
⑦ Specific heat
The amount of heat required to change the temperature of a substance per unit mass by 1 degree.
In the British system and the CGS system, the value of the specific heat is the same, because the unit of heat (BIU or CAL) depends on the amount of heat required for the increase of 1 degree per unit mass of water.
The value of specific heat in the international system of units is different from the British system or CGS system, because the unit of energy (J) is determined according to different definitions.
The unit of specific heat is Btu (1b · 0F) and J / (kg · K).
⑧ Thermal conductivity
A measure of the rate at which a substance conducts heat.
When the temperature gradient of 1 degree per unit length is established on the material per unit cross-sectional area, the thermal conductivity is defined as the heat conducted per unit time, and the unit of thermal conductivity is Btu / (h · ft · 0F) or w / (m · K).
⑨ Thermal diffusivity
It is a property to determine the temperature migration rate inside a material.
It is the ratio of thermal conductivity to the product of specific heat and density.
The unit of thermal diffusivity is Btu / (h · ft · 0F) or w / (m · K).
316 and 316L stainless steel
316 and 317 stainless steels (see the following for the properties of 317 stainless steel) are molybdenum containing stainless steels.
The molybdenum content of 317 stainless steel is slightly higher than that of 316 stainless steel Due to the molybdenum in the steel, the overall performance of this steel is better than 310 and 304 stainless steel.
Under high temperature conditions, when the concentration of sulfuric acid is lower than 15% and higher than 85%, 316 stainless steel has a wide range of applications.
316 stainless steel also has good chloride corrosion performance, so it is usually used in marine environment.
316L stainless steel has a maximum carbon content of 0.03 and can be used in applications where annealing cannot be carried out after welding and maximum corrosion resistance is required.
Corrosion resistance
The corrosion resistance is better than 304 stainless steel, and has good corrosion resistance in the production process of pulp and paper.
Moreover, 316 stainless steel is also resistant to marine and aggressive industrial atmosphere.
Heat resistance
316 stainless steel has good oxidation resistance in intermittent use below 1600 degrees and continuous use below 1700 degrees.
In the range of 800-1575 degrees, it is better not to continuously act on 316 stainless steel, but when 316 stainless steel is continuously used outside this temperature range, the stainless steel has good heat resistance.
The carbide precipitation resistance of 316L stainless steel is better than that of 316 stainless steel, and the above temperature range can be used.
Heat treatment
Annealing in the temperature range of 1850-2050 degrees, then rapid annealing, and then rapid cooling.
316 stainless steel cannot be hardened by overheating.
Welding
316 stainless steel has good weldability.
All standard welding methods can be used for welding. 316cb, 316L or 309cb stainless steel filler rods or electrodes can be used for welding according to the purpose. In order to obtain the best corrosion resistance, the welded section of 316 stainless steel needs post weld annealing. If 316L stainless steel is used, post weld annealing is not required.
Typical use
Pulp and paper equipment, heat exchangers, dyeing equipment, film processing equipment, pipelines, materials for the exterior of buildings in coastal areas.
Stainless steel not only has good corrosion resistance, but also has good appearance and other characteristics.
The application range of stainless steel is more and more extensive.
The following table is a simple example of the application of stainless steel:
| Industry | Main use cases | Industry | Main use cases |
| For automobile | Exterior parts | building material | Mirror (mirror material) |
| Hot parts | Regrinding | ||
| Flatware | Spoon, fork – export or domestic | Elevator. | |
| Knife export or domestic sales | Building interior and exterior decoration materials | ||
| Hollowware tableware (two kinds of utensils) | Deep drawing (DDQ) – drawing ratio greater than 1.5 | Window and door materials | |
| Drawing – draw ratio less than 1.5 | Chemical equipment | heat exchanger | |
| Press (press) | Boiler and tank | ||
| Spinning | Chemical industrial furnace | ||
| Kitchen equipment | Sink general tensile material (high surface requirements) | Chemical equipment components | |
| Gas range – high surface requirements | General purpose | Reroll (for re rolling) | |
| Refrigerator (freezer liner) | For high hardness | ||
| Electrical appliances | Washing machine, dryer | For processing plant | |
| Microwave Oven | Market flow general | ||
| Electronic components (non-magnetic) | Special purpose | ||
| For steel pipe | Decorative tube | Transportation equipment | Container |
| Structural pipe (industrial) | Railway vehicle | ||
| For drainage pipe |
Stainless steel
Generally speaking, stainless steel is steel that is not easy to rust.
In fact, some stainless steel has both rust resistance and acid resistance (corrosion resistance).
The rust resistance and corrosion resistance of stainless steel are due to the formation of chromium rich oxide film (passive film) on its surface.
This rust resistance and corrosion resistance are relative.
The test shows that the corrosion resistance of steel increases with the increase of chromium content in steel in weak media such as atmosphere and water and oxidizing media such as nitric acid.
When the chromium content reaches a certain percentage, the corrosion resistance of steel changes suddenly, that is, from easy to rust to not easy to rust, from non corrosion to corrosion resistance.
There are many ways to classify stainless steel.
According to the structure classification at room temperature, there are martensite, austenite, ferrite and duplex stainless steel;
According to the classification of main chemical components, it can be basically divided into two systems: chromium stainless steel and chromium nickel stainless steel;
According to the purpose, there are nitric acid resistant stainless steel, sulfuric acid resistant stainless steel, seawater resistant stainless steel and so on;
According to the type of corrosion resistance, it can be divided into pitting corrosion-resistant stainless steel, stress corrosion-resistant stainless steel, intergranular corrosion-resistant stainless steel, etc;
According to the functional characteristics, it can be divided into non-magnetic stainless steel, free cutting stainless steel, low-temperature stainless steel, high-strength stainless steel and so on.
Because stainless steel has excellent corrosion resistance, formability, compatibility and strength and toughness in a wide temperature range, it has been widely used in heavy industry, light industry, household goods industry, architectural decoration and other industries.
Austenitic stainless steel
Stainless steel with austenitic structure at room temperature. When the steel contains about 18% Cr, 8% ~ 10% Ni and 0.1% C, it has stable austenite structure.
Austenitic chromium nickel stainless steel includes the famous 18Cr-8Ni steel and the high Cr Ni series steel developed by increasing the content of Cr and Ni and adding Mo, Cu, Si, Nb, Ti and other elements.
Austenitic stainless steel is non-magnetic and has high toughness and plasticity, but its strength is low.
It can not be strengthened by phase transformation, but only by cold working.
If S, Ca, Se, Te and other elements are added, it has good machinability.
In addition to being resistant to oxidizing acid medium corrosion, this kind of steel can also be resistant to sulfuric acid, phosphoric acid, formic acid, acetic acid, urea and other corrosion if it contains Mo, Cu and other elements.
If the carbon content of this kind of steel is less than 0.03% or contains Ti and Ni, its intergranular corrosion resistance can be significantly improved.
Austenitic stainless steel with high silicon has good corrosion resistance with concentrated nitric acid.
Austenitic stainless steel has been widely used in all walks of life because of its comprehensive and good comprehensive properties.
Ferritic stainless steel
Stainless steel with ferrite structure in service.
The chromium content is 11% ~ 30%, with body centered cubic crystal structure.
This kind of steel generally does not contain nickel, and sometimes contains a small amount of Mo, Ti, Nb and other elements.
This kind of steel has the characteristics of high thermal conductivity, low expansion coefficient, good oxidation resistance and excellent stress corrosion resistance.
It is mostly used to manufacture parts resistant to atmospheric, steam, water and oxidizing acid corrosion.
This kind of steel has some disadvantages, such as poor plasticity, obvious reduction of plasticity and corrosion resistance after welding, which limits its application.
The application of out of furnace refining technology (AOD or VOD) can greatly reduce the interstitial elements such as carbon and nitrogen, so this kind of steel is widely used.
AUSTENITIC FERRITIC duplex stainless steel
It is a stainless steel with about half of austenite and half of ferrite. When the content of C is low, the content of Cr is 18% ~ 28%, and the content of Ni is 3% ~ 10%.
Some steels also contain Mo, Cu, Si, Nb, Ti, N and other alloy elements.
This kind of steel has the characteristics of both austenitic and ferritic stainless steel.
Compared with ferrite, it has higher plasticity and toughness, no room temperature brittleness, significantly improved intergranular corrosion resistance and welding performance.
At the same time, it also maintains the 475 ℃ brittleness, high thermal conductivity and Superplasticity of ferritic stainless steel.
Compared with austenitic stainless steel, it has high strength and significantly improved resistance to intergranular corrosion and chloride stress corrosion.
Duplex stainless steel has excellent pitting corrosion resistance and is also a nickel saving stainless steel.
Martensitic stainless steel
Stainless steel whose mechanical properties can be adjusted by heat treatment is a kind of hardenable stainless steel.
The typical brand is Cr13 type, such as 2Cr13, 3Cr13, 4Cr13, etc.
The hardness after heating is high, and different tempering temperatures have different strength and toughness combinations.
It is mainly used for steam turbine blades, tableware and surgical instruments.
According to the difference of chemical composition, martensitic stainless steel can be divided into martensitic chromium steel and martensitic chromium nickel steel.
According to the different structure and strengthening mechanism, it can also be divided into martensitic stainless steel, martensitic and semi austenitic (or semi martensitic) precipitation hardening stainless steel and maraging stainless steel.
1. Numbering and representation of steel
① International chemical element symbols and national symbols are used to represent chemical components, and Arabic letters are used to represent component content, such as China and Russia 12CrNi3A
② Use fixed digit numbers to represent steel series or numbers;
Such as: the United States, Japan, 300 series, 400 series, 200 series;
③ The serial number is composed of Latin letters and order, which only indicates the purpose.
2. Numbering rules in China
① Use element symbols
Purpose, Chinese Pinyin,
Open hearth steel: P
Boiling steel: F
Killed steel: B
Class a steel: A
T8: te8,
GCr15: Ball
◆ Bonded steel and spring steel, such as 20CrMnTi 60simn, (C content expressed in ten thousandths)
◆ Stainless steel and alloy tool steel (C content is expressed in thousands), such as one thousandth of 1Cr18Ni9 (i.e. 0.1% C), stainless C ≤ 0.08%, such as 0Cr18Ni9, ultra-low carbon C ≤ 0.03%, such as 0Cr17Ni13Mo.
3. International stainless steel identification method
The American Iron and Steel Institute uses three digits to identify various standard grades of malleable stainless steel.
Of which:
① Austenitic stainless steels are marked with numbers of 200 and 300 series.
For example, some more common austenitic stainless steels are marked with 201, 304, 316 and 310.
② Ferritic and martensitic stainless steels are represented by 400 series numbers.
③ Ferritic stainless steel is marked with 430 and 446, and martensitic stainless steel is marked with 410, 420 and 440C, two-phase (austenite ferrite).
④ Stainless steel, precipitation hardening stainless steel and high alloy with iron content less than 50% are usually named by patent name or trademark.
| Types | China | America | Japen | Europe |
| Martensitic stainless steel | Cr13 | 410 | SUS410 | SAF2301 |
| 1Cr17Ni2 | 431 | SUS431 | SAF2321 | |
| 9Cr18 | 440C | SUS440C | ||
| 0Cr17Ni4Cu4Nb | 17-4PH | SUH630 | ||
| 1Cr12Ni3MoWV | XM32 | DIN1.4313 | ||
| 2Cr12MoVNbN | SUH600 | |||
| 2Cr12NiMoWV | SUH616 | |||
| Dual phase steel | 00Cr18Ni5Mo3Si2 | S31500 | 3RE60 | |
| 00Cr22Ni5Mo3N | S31803 | 329J3L1 | SAF2205 | |
| 00Cr25Ni6Mo2N | 329J1L1R-4 | |||
| 00Cr25Ni7Mo3N | S31260 | 329J4L | SAF2507 | |
| 00Cr25Ni6Mo3CuN | S32550 | |||
| Special alloy | ZG40Cr25Ni20 | HK | ||
| ZG45Ni35Cr27N6 | KP | |||
| ZG50N148Cr28W5 | ||||
| ZGN136Cr26Co15W5 | ||||
| ZG10Ni32Cr20Nb | ||||
| ZG45Ni48Cr28W5Co5 | ||||
| Ferrite | 0Cr13 | 410S | SUS410S | |
| 00Cr17Ti | ||||
| 00Cr18Mo2Ti | ||||
| Austenitic stainless steel | 0Cr18Ni9Ti | 321 | SUS321 | SAF2337 |
| 00Cr19Ni10 | 304L | SUS304L | ||
| 0Cr17Ni12Mo2 | 316 | SUS316 | SAF2343 | |
| 0Cr17Ni14Mo2 | 316L | SUS312L | ||
| 00Cr19Ni13Mo3 | 317L | SUS317L | ||
| ZG00Cr19Ni10 | CF3 | SCS19A | ||
| ZG00Cr17Ni14Mo2 | CF3M | SCS16A | ||
| 0Cr25Ni20 | 310S | SUS310S | ||
| 00Cr20Ni18Mo6CuN | S31254 | 254SMO | ||
| 00Cr20Ni25Mo4.5Cu | 904L | 2RK65 | ||
| 00Cr25Ni22MoN | S31050 | 2RE69 | ||
| Alloy steel | All kinds of high-quality alloy steel, tool and die steel, low-temperature steel, pressure vessel steel, ASME code materials, wire rod, plate, TIG welding wire and covered electrode. | |||
| ChinaGB1220-92[84] GB3220-92[84] | Japan JIS | AmericaAISI UNS | Britain BS 970 Part4 BS 1449 Part2 | Germany DIN 17440 DIN 17224 | FranceNFA35-572 NFA35-576~582 NFA35-584 | Former Soviet Union TOCT5632 |
| 1Cr17Mn6Ni5N | SUS201 | 201 | — | — | — | — |
| 1Cr18Mn8Ni5N | SUS202 | 202 | — | — | — | 12×17.T9AH4 |
| — | — | S20200 | 284S16 | — | — | — |
| 2Cr13Mn9Ni4 | — | — | — | — | — | — |
| 1Cr17Ni7 | SUS301 | 301 | — | — | — | — |
| — | — | S30100 | 301S21 | X12CrNi177 | Z12CN17.07 | — |
| 1Cr17Ni8 | SUS301J1 | — | — | X12CrNi177 | — | — |
| 1Cr18Ni9 | SUS302 | 302 | 302S25 | X12CrNi188 | Z10CN18.09 | 12×18H9 |
| 1Cr18Ni9Si3 | SUS302B | 302B | — | — | — | — |
| Y1Cr18Ni9 | SUS303 | 303 | 303S21 | X12CrNiS188 | Z10CNF18.09 | — |
| Y1Cr18Ni9Se | SUS303Se | 303Se | 303S41 | — | — | — |
| 0Cr18Ni9 | SUS304 | 304 | 304S15 | X2CrNi89 | Z6CN18.09 | 08×18B10 |
| 00Cr19Ni10 | SUS304L | 304L | 304S12 | X2CrNi189 | Z2CN18.09 | 03×18H11 |
| 0Cr19Ni9N | SUS304N1 | 304N | — | — | Z5CN18.09A2 | — |
| 00Cr19Ni10NbN | SUS304N | XM21 | — | — | — | — |
| 00Cr18Ni10N | SUS304LN | — | — | X2CrNiN1810 | Z2CN18.10N | |
| 1Cr18Ni12 | SUS305 | S30500 | 305S19 | X5CrNi1911 | Z8CN18.12 | 12×18H12T |
| [0Cr20Ni10] | SUS308 | 308 | — | — | — | — |
| 0Cr23Ni13 | SUS309S | 309S | — | — | — | — |
| 0Cr25Ni20 | SUS310S | 310S | — | — | — | — |
| 0Cr17Ni12Mo2N | SUS315N | 316N,S31651 | — | — | — | — |
| 0Cr17Ni12Mo2 | SUS316 | 316 | 316S16 | X5CrNiMo1812 | Z6CND17.12 | 08×17H12M2T |
| 00Cr17Ni14Mo2 | SUS316L | 316L | 316S12 | X2CrNiMo1812 | Z2CND17.12 | 03×17H12M2 |
| 0Cr17Ni12Mo2N | SUS316N | 316N | — | — | — | — |
| 00Cr17Ni13Mo2N | SUS316LN | — | — | X2CrNiMoN1812 | Z2CND17.12N | — |
| 0Cr18Ni12Mo2Ti | — | — | 320S17 | X10CrNiMo1810 | Z6CND17.12 | — |
| 0Cr18Ni14Mo2Cu2 | SUS316J1 | — | — | — | — | — |
| 00Cr18Ni14Mo2Cu2 | SUS316J1L | — | — | — | — | — |
| 0Cr18Ni12Mo3Ti | — | — | — | — | — | — |
| 1Cr18Ni12Mo3Ti | — | — | — | — | — | — |
| 0Cr19Ni13Mo3 | SUS317 | 317 | 317S16 | — | — | 08X17H15M3T |
| 00Cr19Ni13Mo3 | SUS317L | 317L | 317S12 | X2CrNiMo1816 | — | 03X16H15M3 |
| 0Cr18Ni16Mo5 | SUS317J1 | — | — | — | — | — |
| 0Cr18Ni11Ti | SUS321 | 321 | — | X10CrNiTi189 | Z6CNT18.10 | 08X18H10T |
| 1Cr18Ni9Ti | — | — | — | — | — | 12X18H20T |
| 0Cr18Ni11Nb | SUS347 | 347 | 347S17 | X10CrNiNb189 | Z6CNNb18.10 | 08X18H12B |
| 0Cr18Ni13Si4 | SUSXM15J1 | XM15 | — | — | — | — |
| 0Cr18Ni9Cu3 | SUSXM7 | XM7 | — | — | Z6CNU18.10 | — |
| 1Cr18Mn10NiMo3N | — | — | — | — | — | — |
| 1Cr18Ni12Mo2Ti | — | — | 320S17 | X10CrNiMoTi1810 | Z8CND17.12 | — |
| 00Cr18Ni5Mo3Si2 | — | S31500 | — | 3RE60(Sweden) | — | — |
| 0Cr26Ni5Mo2 | SUS329J1 | — | — | — | — | — |
| 1Cr18Ni11Si4AlTi | — | — | — | — | — | — |
| 1Cr21Ni5Ti | — | — | — | — | — | — |
| 0Cr13 | SUS410S | S41000 | — | X7Cr13 | Z6C13 | 08X13 |
| 1Cr13 | SUS410 | 410 | 410S21 | X10Cr13 | Z12Cr13 | 12X13 |
| 2Cr13 | SUS420J1 | 420 | 420S29 | X20Cr13 | Z20Cr13 | 30X13 |
| — | — | S4200 | 420S27 | — | — | — |
| 3Cr13 | SUS420J2 | — | 420S45 | — | — | 14X17H2 |
| 3Cr13Mo | — | — | — | — | — | — |
| 3Cr16 | SUS429J1 | — | — | — | — | — |
| 1Cr17Ni2 | SUS431 | 431 | 431S29 | X22CrNi17 | Z15CN-02 | — |
| 7Cr17 | SUS440A | 440A | — | — | — | — |
| 11Cr17 | SUS440C | 440C | — | — | — | 95X18 |
| 8Cr17 | SUS440B | 44013 | — | — | — | — |
| 1Cr12 | — | — | — | — | — | — |
| 4Cr13 | SUS420J2 | — | — | X4DCr13 | Z40C13 | — |
| 9Cr18 | SUS440C | 440C | — | X105CrMo17 | Z100CD17 | — |
| 9Cr18Mo | SUS440C | 440C | — | — | — | — |
| 9Cr18MoV | SUS440B | 440B | — | X90CrMoV18 | Z6CN17.12 | — |
| 0Cr17Ni4Cu4Nb | SUS630 | 630 | — | — | — | — |
| 0Cr17Ni7Al | SUS631 | 631 | — | — | — | 09X17H710 |
| — | — | S17700 | — | X7CrNiAl177 | Z8CNA17.7 | — |
| 0Cr15Ni7Mo2Al | — | 632 | — | — | — | — |
| — | — | S15700 | — | — | Z8CND15.7 | — |
| 00Cr12 | SUS410 | — | — | — | — | — |
| 0Cr13Al[00Cr13Al] | SUS405 | 405 | — | — | — | — |
| — | — | S40500 | 405S17 | X7CrAl13 | Z6CA13 | — |
| 1Cr15 | SUS429 | 429 | — | — | — | — |
| 1Cr17 | SUS430 | 430 | — | — | — | 12X17 |
| — | — | S43000 | 430S15 | X8Cr17 | Z8C17 | — |
| [Y1Cr17] | SUS430F | 430F | — | — | — | — |
| — | — | S43020 | — | X12CrMoS17 | Z10CF17 | — |
| 00Cr17 | SUS430LX | — | — | — | — | — |
| 1Cr17Mo | SUS434 | 434 | — | — | — | — |
| — | — | S43400 | 434S19 | X6CrMo17 | Z8CD17.01 | — |
| 00Cr17Mo | SUS436L | — | — | — | — | — |
| 00Cr18Mo2 | SUS444 | — | — | — | — | — |
| 00Cr27Mo | SUSXM27 | XM27 | — | — | — | — |
| — | — | S44625 | — | — | Z01CD26.1 | — |
| 00Cr30Mo2 | SUS447J1 | — | — | — | — | — |
| 1Cr12 | SUS403 | 403,S40300 | 403S17 | — | — | — |
| 1Cr13Mo | SUS410J1 | — | — | — | — | — |
| China | Japan | Germany | America | Britain | Franch | Former Soviet Union | ||
| GB,YB | JIS | DIN(W-Nr.) | ASTM | AISI | SAE | BS | NF | ГОСТ |
| 0Cr13 | SUS405 | X7Cr13(1.4000) | 405 | 405S17 | 08X13(0X13) | |||
| SUS429 | 429 | |||||||
| SUS416 | 416 | 416S21 | Z12CF13 | |||||
| 1Cr17 | SUS430 | X8Cr17(1.4016) | 430 | 430S15 | Z8C17 | 12X17(X17) | ||
| SUS430F | X12CrMoS17(1.4104) | 430F | Z10CF17 | |||||
| SUS434 | X6CrMo17(1.4113) | 434 | 434S19 | Z8CD17-01 | ||||
| 1Cr28 | X8Cr28(1.4083) | 15X28(X28) | ||||||
| 0Cr17Ti | 08X17T(0X17T) | |||||||
| 1Cr17Ti | X8CrTi17(1.4510) | |||||||
| 1Cr25Ti | 25X25T(X25T) | |||||||
| 1Cr17Mo2Ti | X8CrMoTi17(1.4523) | |||||||
| 1Cr13 | SUS410, | X10Cr13(1.4006), | 410, | 410S21, | Z12C13 | 12X13(1X13) | ||
| SUS403 | X15Cr13(1.4024) | 403 | 403S17 | |||||
| SUS410S | X7Cr13(1.4000) | 410S | Z6C13 | 08X13(0X13) | ||||
| 2Cr13 | SUS420J1 | X20Cr13(1.4021) | 420 | 420S37 | Z20C13 | 20X13(2X13) | ||
| 420S29 | ||||||||
| SUS420F | 420F | Z30CF13 | ||||||
| 3Cr13 | SUS420J2 | 420S45 | Z30C13 | 30X13(3X13) | ||||
| 4Cr13 | X40Cr13(1.4034) | Z40C14 | 40X13(4X13) | |||||
| 1Cr17Ni2 | SUS431 | X22CrNi17(1.4057) | 431 | 431S29 | 14X17H2(1X17H2) | |||
| 9Cr18 | 95X18(9X18) | |||||||
| 9Cr18MoV | X90CrMoV18(1.4112) | |||||||
| SUS440A | 440A | |||||||
| SUS440B | 440B | |||||||
| SUS440C | 440C | Z100CD17 | ||||||
| SUS440F | 440F | |||||||
| SUS305 | X5CrNi19 11(1.4303) | 305 | 305S19 | Z8CN18-12 | ||||
| 00Cr18Ni10 | SUS304L | X2CrNi18 9(1.4306) | 304L | 304L12 | Z2CN18-10 | 03X18H11(000X18H11) | ||
| 0Cr18Ni9 | SUS304 | X5CrNi18 9(1.4301) | 304 | 304S15 | Z6CN18-09 | 08X18H10(0X18H10) | ||
| 1Cr18Ni9 | SUS302 | X12CrNi18 8(1.4300) | 302 | 302S25 | Z10CN18-09 | 12X18H9(X18H9) | ||
| 2Cr18Ni9 | 17X18H9(2X18H9) | |||||||
| SUS303 | X12CrNiS18 8(1.4305) | 303 | 303S12 | Z10CNF18-09 | ||||
| SUS303Se | 303Se | 303S14 | 12X18H10E(X18H10E) | |||||
| SUS201 | 201 | |||||||
| Standard | Standard name |
| GB | National standards of the people’s Republic of China (State Bureau of technical supervision) |
| KS | Korean Standard |
| AISI | America Iron and Steel Institute |
| SAE | Society of Automative Engineers |
| ASTM | American Society for Testing and Material |
| AWS | American Welding Society |
| ASME | American Society of Mechanical Engineers |
| BS | British Standard |
| DIN | Deutsch Industria Normen |
| CAS | Canadian Standard Associatoin |
| API | American Petroleum Association |
| KR | Korean Resister of Shipping |
| NK | Hihon Kanji Koki |
| LR | Llouds Register of Shipping |
| AB | American Bureau of Shipping |
| JIS | Japanese Standard |
| Project name | Key features |
| （EAF）Electric ArcFurnace | The alloy iron (ferrochrome and ferronickel) of the main raw material is melted by the heat generated by the electric arc in the electric furnace after being properly mixed with general steel. |
| A.O.D or V.O.D | The stainless steel melted in the electric furnace is rolled with refining agent to remove oxygen, and the inert gas argon is blown in to reduce the content of carbon and sulfur, and adjust the chemical composition at the same time. |
| Conting Casting | The stainless steel water refined in the refining furnace, the engineering of raw ingot, and the equipment for directly manufacturing flat billet. |
| Furnace | Equipment for heating flat billet (blank) to hot rolling temperature |
| Rough HotRolling | It is an equipment for producing profiled plate by one-time hot rolling of the blank (flat blank) heated by the heating furnace. |
| Finish Hot Rolling | After one hot rolling, the stainless steel plate is rolled again to form hot-rolled coil and equipment for controlling the final thickness. |
| H-APLAnnealing&Pickling Ling | Through annealing, the hot rolling stress caused by hot rolling is eliminated and the normal metal structure is restored. The impurities generated during hot rolling are washed away with acid and made into the final hot rolling coil. |
| CGLCoil GrindingLing | Different defects on the surface of products during hot rolling, especially corrosion pits caused by continuous annealing during hot rolling and pickling.A device that adjusts surface flatness by grinding. |
| （CBL）Coil Building-up Ling | The unit is specially designed to improve the yield of products. Another function of the unit is to check the surface quality of raw materials. |
| ZRM20-hi SendzimirMill | Like stainless steel, it is a rolling mill specially designed for cold rolling, which needs high-strength and high-precision products. At present, the rolling mill is the most advanced 20 high rolling mill in the world.The unit is equipped with the whole process automatic thickness control system AGC, with a control accuracy of 0.025mm. In addition to the screwdown device and system program, the system also has an industrial IBM 32-bit Pentium computer as the central control unit. Two thickness gauges are located on both sides of the strip steel. The thickness measurement system is connected with the process cycle calculation of AGC system and SPC system.Strip steel section measurement: this function allows the operator to move the thickness gauge over the whole strip steel width, and get the strip steel section diagram on the AGC display screen, which can be printed out.In this way, the operator can accurately set the parameters and control board type.The C-shaped frame and hydraulic cylinder of the thickness gauge can ensure the movement of the mobile thickness gauge. The selection of the thickness gauge is limited by the direction switch of the rolling mill. If the operator wants to see the section of the inlet strip steel, he can change the direction switch and press the move key. The thickness gauge will measure a point every 12.7mm, and then the thickness gauge will return to the middle, and the section of the strip steel will be displayed on the screen.The unit is also equipped with advanced emulsion filtration system, which can ensure the beautiful and smooth surface of the produced strip steel. |
| （APL）Annealing&Pickling Line | The internal structure of stainless steel during cold rolling is restored to normal through heat treatment. At the same time, the high-temperature oxide during heat treatment is pickled again to remove the high-temperature oxide in order to maintain the inherent surface of stainless steel.The unit is the equipment of American fata company. The total length of the unit is 299.89m. It is equipped with four annealing furnaces without open fire preheating section, preheating section, heating section and soaking section. It is equipped with neutral salt sodium sulfate electrolytic pickling to carry out the mixed pickling section of nitric acid and hydrofluoric acid, so as to finally ensure the surface finish of strip steel. |
| （SPM）Skin Pass Mill | The process of rolling the heat-treated products after cold rolling with very little reduction. Its purpose is to improve and correct the mechanical properties of the products, as well as to obtain the equipment of metallic luster. |
| （CPL）Coil Polishing ling | According to the surface state required by the user, the final surface grinding processing engineering.ZPSS produces products with NO2D, NO2B, NO3, NO4, HL and other surfaces. |
| （STL）Slitting Ling | The products processed in the previous project shall be cut according to the length and width determined by the user’s requirements.The shearing specification of the project is 45mm ~ 1000mm wide. |
| （SCL）Shearing Ling | The products processed in the previous project shall be cut according to the length and width determined by the user’s requirements.The specifications of the shearable section of the project are steel plates with a length of 1000mm ~ 4000mm and small steel coils with different weights. |
Cutting and stamping
Because stainless steel has higher strength than ordinary materials, higher pressure is required for stamping and shearing, and poor shear and work hardening can not occur when the gap between knives is accurate.
Plasma or laser cutting is best used. When gas cutting or arc cutting has to be used, grinding and necessary heat treatment shall be carried out for the heat affected zone.
The thin plate can be bent to 180.
However, in order to reduce the same radius of cracks on the bending surface, it is best to give a radius of 2 times the thickness of the plate when the thick plate is bent along the rolling direction and 4 times the thickness of the plate when it is bent perpendicular to the rolling direction.
Especially during welding, in order to prevent machining cracking, the surface of the welding area shall be ground.
Drawing is easy to generate friction heat during deep processing, so stainless steel with high pressure resistance and heat resistance shall be used for simultaneous forming.
After processing, the oil attached to the surface shall be removed.
Before welding, the rust, oil, moisture, paint, etc. harmful to welding shall be completely removed, and the welding rod suitable for steel grade shall be selected.
The time interval of spot welding is shorter than that of carbon steel. Stainless steel brush shall be used when removing welding slag.
After welding, in order to prevent local corrosion or strength reduction, the surface shall be ground or cleaned.
Construction and construction precautions
In order to prevent scratches and pollutants from adhering during construction, stainless steel construction shall be carried out under the film state.
However, with the extension of time, the residue of adhesive solution shall be cleaned according to the service life of the film.
When removing the film after construction, the surface shall be washed and special stainless steel tools shall be used.
When cleaning public tools with general steel, they shall be cleaned in order to prevent iron filings from sticking.
Attention shall be paid to prevent highly corrosive magnetic and stone luxury cleaning drugs from contacting the stainless steel surface.
If they contact, they shall be washed immediately.
After construction, neutral detergent and water shall be used to wash the cement, powder ash and other substances attached to the surface.
Stainless steel cutting: stainless steel pipes can be cut effortlessly during installation.
Manual pipe cutter, hand saw and electric saw, high-speed rotary cutting grinding wheel.
Appropriate cleaning cycle according to different environment
In order to keep the surface of stainless steel gorgeous and clean, it is necessary to wash and manage the long-term stainless steel periodically.
| Environment | Pastoral area | Urban, industrial and coastal areas | ||
| Position | structure | General environment | Corrosive environment | |
| Rain | No contaminant sediment residue | 1 – ~ 2 times / year | 2 ~ 3 times / year | 3 ~ 4 times / year |
| residual | 2-3 times / year | 3 ~ 4 times / year | 4-5 times / year | |
| Indoor | No contaminant sediment residue | 1 ~ 2 times / year | 3 ~ 4 times / year | 4-5 times / year |
| residual | 2 ~ 3 times / year | 4-5 times / year | 5-6 times / year | |
Determine the washing method according to the surface state
● General precautions
When washing, please pay attention not to scratch the surface.
Avoid using bleaching ingredients, washing liquid containing abrasive, steel wire ball (brush roller ball), grinding tools, etc.
In order to remove the washing liquid, wash the surface with clean water at the end of washing.
| Surface state | Washing method |
| Dust and easy to remove scale | Wash with soap, weak detergent or warm water |
| Label and film | Scrub with warm water and weak detergent, and use alcohol or organic solution as binder |
| Fat, oil and lubricating oil pollution | After drying with cloth or paper, wash with neutral detergent or special sea washing medicine |
| Bleach and acid attachment | Wash immediately with water, soak in high or neutral carbonated soda, and then wash with neutral detergent or warm water |
| Organic carbide adhesion | Soak in hot neutral detergent or ammonia solution and then wash with detergent containing weak grinding |
| fingerprint | Organic agent for polyester wine (B and), dry it with a soft cloth and then wash it with water |
| Rainbow pattern | It is caused by excessive use of detergent or oil. When washing, use warm water neutral detergent |
| Welding discoloration | After washing the sea with acid, neutralize it with water, acid and soda, and then wash it with water. It is specially used for washing drugs |
| Rust caused by surface contaminants | -Wash with nitric acid (10%) or abrasive detergent – use special washing drugs |
Safekeeping
During storage, pay attention to moisture, dust, oil, lubricating oil, etc., as well as rust on the surface, or poor welding and reduced corrosion resistance.
When water is immersed between the film and the steel substrate, the corrosion rate is faster than that without film.
The warehouse shall be kept in a clean, dry and ventilated place to maintain the original packaging state.
The stainless steel coated with film shall avoid direct light.
The film shall be inspected periodically.
If the film deteriorates (the service life of the film is 6 months), it shall be replaced immediately.
If the packaging material is soaked when adding pad paper, the pad paper shall be removed immediately to prevent surface corrosion.
Transportation
In order to avoid surface scratch during transportation, rubber or sleepers shall be used, and special materials for stainless steel protection shall be used as far as possible.
In order to avoid surface pollution caused by fingerprints, gloves shall be worn during operation.
At present, there are more than 100 known chemical elements, and about 20 kinds of chemical elements can be encountered in steel materials commonly used in industry.
For the special steel series of stainless steel formed by people’s long-term struggle against corrosion, there are more than a dozen commonly used elements.
In addition to the basic element iron, the elements that have the greatest impact on the performance and structure of stainless steel are carbon, chromium, nickel, manganese, silicon, molybdenum, titanium, niobium, titanium, manganese, nitrogen, copper, cobalt, etc.
In addition to carbon, silicon and nitrogen, these elements are elements in the transition group in the periodic table of chemical elements.
In fact, stainless steel used in industry has several or even more than a dozen elements at the same time.
When several elements coexist in the unity of stainless steel, their influence is much more complex than that when they exist alone, because in this case, we should not only consider the role of each element itself, but also pay attention to their mutual influence.
Therefore, the structure of stainless steel depends on the sum of the influence of various elements.
1) Effects of various elements on properties and microstructure of stainless steel
1-1. The decisive role of chromium in stainless steel:
There is only one element that determines the property of stainless steel, which is chromium. Each kind of stainless steel contains a certain amount of chromium.
So far, there is no stainless steel without chromium.
The fundamental reason why chromium has become the main element determining the performance of stainless steel is that after adding chromium to the steel as an alloy element, it promotes the internal contradiction movement to develop in favor of resisting corrosion damage.
This change can be explained from the following aspects:
① Chromium increases the electrode potential of iron-based solid solution
② Chromium absorbs electrons from iron and passivates it
Passivation is a phenomenon that the corrosion resistance of metals and alloys is improved due to the prevention of anodic reaction.
There are many theories that constitute the passivation of metals and alloys, mainly including film theory, adsorption theory and electron arrangement theory.
1-2. Duality of carbon in stainless steel
Carbon is one of the main elements of industrial steel.
The properties and microstructure of steel largely depend on the content and distribution of carbon in steel, especially in stainless steel.
The influence of carbon on the structure of stainless steel is mainly reflected in two aspects.
On the one hand, carbon is an element that stabilizes austenite and plays a great role (about 30 times that of nickel).
On the other hand, due to the great affinity between carbon and chromium, it forms a series of complex carbides with chromium.
Therefore, from the two aspects of strength and corrosion resistance, the role of carbon in stainless steel is contradictory.
Knowing the law of this influence, we can choose stainless steel with different carbon content from different use requirements.
For example, the standard chromium content of the five steel grades 0Crl3 ~ 4Cr13, the most widely used and minimum stainless steel in industry, is 12 ~ 14%, which is determined after taking into account the factors that carbon and chromium form chromium carbide.
The purpose is to make the chromium content in the solid solution not less than the minimum chromium content of 11.7% after the combination of carbon and chromium to form chromium carbide.
For these five steel grades, due to different carbon content, the strength and corrosion resistance are also different.
0Cr13 ~ 2Crl3 steel has good corrosion resistance, but the strength is lower than 3Crl3 and 4Cr13 steel.
They are mostly used to manufacture structural parts.
The latter two steel grades can obtain high strength due to high carbon content, and are mostly used to manufacture springs, cutting tools and other parts requiring high strength and wear resistance.
For another example, in order to overcome the intergranular corrosion of 18-8 chromium nickel stainless steel, the carbon content of the steel can be reduced to less than 0.03%, or elements with greater affinity than chromium and carbon (titanium or niobium) can be added to prevent the formation of chromium carbide.
For another example, when high hardness and wear resistance become the main requirements, we can appropriately increase the chromium content while increasing the carbon content of the steel to meet the requirements of hardness and wear resistance.
It also takes into account the certain corrosion resistance function.
In industry, 9Cr18 and 9cr17movco stainless steel are used as bearings, measuring tools and blades.
Although the carbon content is as high as 0.85 ~ 0.95%, their chromium content is also increased accordingly, so the requirements of corrosion resistance are still guaranteed.
Generally speaking, the carbon content of stainless steel used in industry is relatively low. The carbon content of most stainless steel is between 0.1 ~ 0.4%, while the carbon content of acid resistant steel is mostly 0.1 ~ 0.2%.
Stainless steel with carbon content greater than 0.4% accounts for only a small part of the total number of steel grades, because under most service conditions, stainless steel always takes corrosion resistance as the main purpose.
In addition, the lower carbon content is also due to some process requirements, such as easy welding and cold deformation.
1-3. The role of nickel in stainless steel is played only after it is matched with chromium
Nickel is an excellent corrosion-resistant material and an important alloying element of alloy steel.
Nickel is an element forming austenite in steel, but in order to obtain pure austenite structure in low-carbon nickel steel, the nickel content should reach 24%;
The corrosion resistance of steel in some media is significantly changed only when the nickel content is 27%.
Therefore, nickel cannot form stainless steel alone.
However, when nickel and chromium exist in stainless steel at the same time, stainless steel containing nickel has many valuable properties.
Based on the above situation, the function of nickel as an alloy element in stainless steel is that it changes the structure of high chromium steel, so as to improve the corrosion resistance and process performance of stainless steel.
1-4. Manganese and nitrogen can replace nickel in chromium nickel stainless steel
Although chromium nickel austenitic steel has many advantages, in recent decades, due to the large-scale development and application of nickel base heat-resistant alloy and heat strength steel containing less than 20% nickel, as well as the increasing development of chemical industry, there is an increasing demand for stainless steel, and the mineral reserves of nickel are small and concentrated in a few regions.
Therefore, there is a contradiction between supply and demand of nickel all over the world.
Therefore, in the fields of stainless steel and many other alloys (such as steel for large castings and forgings, tool steel, thermal strength steel, etc.), especially in countries with relatively lack of nickel resources, scientific research and production practice of saving nickel and replacing nickel with other elements have been widely carried out.
In this regard, manganese and nitrogen are mostly used to replace nickel in stainless steel and heat-resistant steel.
The effect of manganese on austenite is similar to that of nickel.
But to be exact, the role of manganese is not to form austenite, but to reduce the critical quenching speed of steel, increase the stability of austenite during cooling, inhibit the decomposition of austenite, and keep the austenite formed at high temperature to normal temperature.
Manganese has little effect on improving the corrosion resistance of steel.
For example, the change of manganese content in steel from 0 to 10.4% does not significantly change the corrosion resistance of steel in air and acid.
This is because manganese has little effect on improving the electrode potential of iron-based solid solution, and the protective effect of the formed oxide film is also very low.
Therefore, although there are austenitic steels alloyed with manganese in industry (such as 40Mn18Cr4, 50Mn18Cr4WN, ZGMn13 steel, etc.), they can not be used as stainless steel.
The role of manganese in stabilizing austenite in steel is about half that of nickel, that is, the role of 2% nitrogen in steel is also stabilizing austenite, and the degree of action is greater than that of nickel.
For example, in order to make the steel containing 18% chromium obtain austenite structure at room temperature, low nickel stainless steel with manganese and nitrogen instead of nickel and chromium manganese nitrogen free steel with elemental nickel have been applied in industry, and some have successfully replaced the classic 18-8 chromium nickel stainless steel.
1-5. Titanium or niobium is added to stainless steel to prevent intergranular corrosion.
1-6. Molybdenum and copper can improve the corrosion resistance of some stainless steels.
1-7. Effects of other elements on properties and microstructure of stainless steel.
The influence of the above nine main elements on the properties and microstructure of stainless steel.
In addition to the elements that have a great influence on the properties and microstructure of stainless steel, stainless steel also contains some other elements.
Some are common impurity elements like ordinary steel, such as silicon, sulfur, phosphorus, etc. others are added for some specific purposes, such as cobalt, boron, selenium, rare earth elements, etc.
From the main property of corrosion resistance of stainless steel, these elements are non main aspects relative to the nine elements discussed.
However, they can not be completely ignored, because they also affect the properties and microstructure of stainless steel.
Silicon is an element forming ferrite, which is a common impurity element in general stainless steel.
Cobalt is rarely used in steel as an alloying element because of its high price and more important applications in other aspects (such as high-speed steel, cemented carbide, cobalt based heat-resistant alloy, magnetic steel or hard magnetic alloy, etc.).
Cobalt is not often added as an alloy element in general stainless steel.
The purpose of adding cobalt to common stainless steel such as 9Crl7MoVCo steel (containing 1.2-1.8% cobalt) is not to improve the corrosion resistance, but to improve the hardness, because the main purpose of this kind of stainless steel is to manufacture slicing mechanical cutting tools, scissors and surgical blades.
Boron: adding 0.005% boron to high chromium ferritic stainless steel Crl7Mo2Ti steel can improve the corrosion resistance in boiling 65% acetic acid.
Adding a small amount of boron (0.0006 ~ 0.0007%) can improve the hot plasticity of austenitic stainless steel.
Due to the formation of eutectic with low melting point, a small amount of boron increases the tendency of hot cracks in austenitic steel welding, but when there is more boron (0.5 ~ 0.6%), it can prevent the generation of hot cracks.
Because when it contains 0.5 ~ 0.6% boron, austenite boride two-phase structure is formed, which reduces the melting point of the weld.
When the solidification temperature of the molten pool is lower than the semi melting zone, the tensile stress produced by the base metal during cooling.
It is borne by the weld metal in liquid and solid state, which will not cause cracks at this time. Even if a crack is formed in the near seam area, it can also be filled by the molten pool metal in liquid and solid state.
Chromium nickel austenitic stainless steel containing boron has special applications in atomic energy industry.
Phosphorus: it is an impurity element in general stainless steel, but its harmfulness in austenitic stainless steel is not as significant as that in general steel, so the content can be allowed to be higher.
If some data suggest that it can reach 0.06%, so as to facilitate smelting control.
The phosphorus content of individual manganese containing austenitic steel can reach 0.06% (such as 2Crl3NiMn9 steel) to 0.08% (such as Cr14Mnl4Ni steel).
The strengthening effect of phosphorus on steel is also used as the alloying element of age hardening stainless steel.
PH17-10P steel (containing 0.25% phosphorus) is ph-HNM steel (containing 0.30 phosphorus), etc.
Selenium and sulfur are also common impurities in stainless steel.
However, adding 0.2 ~ 0.4% sulfur to stainless steel can improve the cutting performance of stainless steel, and selenium also has the same effect.
Sulfur and selenium improve the cutting performance of stainless steel because they reduce the toughness of stainless steel.
For example, the impact value of 18-8 chromium nickel stainless steel can reach 30 kg / cm2.
The impact value of 18-8 steel containing 0.31% sulfur (0.084% C, 18.15% Cr, 9.25% Ni) is 1.8 kg / cm2; Including 0.
The impact value of 18-8 steel with 22% selenium (0.094% C, 18.4% Cr, 9% Ni) is 3.24 kg / cm2.
Sulfur and selenium reduce the corrosion resistance of stainless steel, so they are rarely used as alloying elements of stainless steel.
Rare earth elements: rare earth elements are used in stainless steel. At present, they are mainly used to improve process performance.
For example, adding a small amount of rare earth elements to Crl7Ti steel and Cr17Mo2Ti steel can eliminate bubbles caused by hydrogen in ingot and reduce cracks in billet.
The forging properties of austenitic and austenitic ferritic stainless steels can be significantly improved by adding 0.02 ~ 0.5% rare earth elements (cerium lanthanum alloy).
There was once an austenitic steel containing 19.5% chromium, 23% nickel and molybdenum, copper and manganese.
In the past, only castings could be produced due to the performance of hot working process. After adding rare earth elements, various profiles could be rolled.
2) Classification of stainless steel according to metallographic structure and general characteristics of all kinds of stainless steel
According to the chemical composition (mainly chromium content) and purpose, stainless steel is divided into two categories: stainless steel and acid resistance.
In industry, stainless steel is also classified according to the type of matrix structure of steel after heating and air cooling at high temperature (900-1100 ℃), which is determined based on the characteristics of the influence of carbon and alloy elements on the structure of stainless steel discussed above.
According to the metallographic structure, stainless steel used in industry can be divided into three categories: ferritic stainless steel, martensitic stainless steel and austenitic stainless steel. The characteristics of these three types of stainless steels can be summarized (as shown in the table below), but it should be noted that not all martensitic stainless steels can be welded, but they are limited by certain conditions, such as preheating before welding and high temperature tempering after welding, which makes the welding process more complex.
In actual production, some martensitic stainless steels such as 1Cr13, 2Cr13 and 2Cr13 are often welded with 45 steel.
| Classification | Approximate composition% | Quench | Corrosion resistance | Processability | Weldability | Magnetic | ||
| Cr | Ni | Fire | ||||||
| Ferritic system | Below 0.35 | 16-27 | one by one | nothing | good | passable | Fair | have |
| Martensitic system | Below 1.20 | 11-15 | Self hardening | can | can | must not | have | |
| Austenite system | Below 0.25 | Above 16 | More than 7 | nothing | excellent | excellent | excellent | nothing |
The above classification is only based on the matrix structure of steel, because the stable austenite and the elements forming ferrite in the steel can not balance each other, and a large amount of chromium makes the s point of the equilibrium diagram shift to the left.
In addition to the three basic types mentioned above, the structure of stainless steel used in industry also includes transition duplex stainless steel such as martensite ferrite, austenite ferrite and austenite martensite, as well as stainless steel with martensite carbide structure.
2-1. Ferritic steel
Low carbon chromium stainless steel containing more than 14% chromium, chromium stainless steel containing 27% chromium, and stainless steel added with molybdenum, titanium, niobium, silicon, aluminum,, tungsten, vanadium and other elements on the basis of the above components.
The elements forming ferrite in the chemical composition are absolutely dominant, and the matrix structure is ferrite.
The structure of this kind of steel is ferrite in quenched (solid solution) state, and a small amount of carbides and intermetallic compounds can be seen in the structure of annealed and aged state.
Crl7, Cr17Mo2Ti, Cr25, Cr25Mo3Ti, Cr28, etc. belong to this category.
Ferritic stainless steel has good corrosion resistance and oxidation resistance due to its high chromium content, but poor mechanical and process properties.
It is mostly used in acid resistant structure with little stress and as oxidation resistant steel.
2-2. Ferritic martensitic steel
This kind of steel is in y + a (or δ ) two-phase state at high temperature, y-m transformation occurs at rapid cooling, and ferrite is still retained.
The normal temperature structure is martensite and ferrite.
Due to different composition and heating temperature, the amount of ferrite in the structure can vary from a few percent to dozens.
0Cr13 steel, 1Cr13 steel, 2Cr13 steel with upper limit of chromium deviation and lower limit of carbon deviation, Cr17Ni2 steel and Cr17wn4 steel, as well as many steel grades in many modified 12% chromium thermal strength steels (also known as heat-resistant stainless steel) developed on the basis of ICrl3 steel, such as Cr11mov, Cr12WMoV, Crl2W4MoV, 18Crl2WoVNb, etc.
Ferritic martensitic steel can be partially quenched and strengthened, so it can obtain high mechanical properties.
However, their mechanical and technological properties are largely affected by the content and distribution of ferrite in the tissue.
According to the chromium content in the composition, this kind of steel belongs to two series: 12 ~ 14% and 15 ~ 18%.
The former has the ability to resist atmosphere and weak corrosive medium, and has good shock absorption and small coefficient of linear expansion;
The corrosion resistance of the latter is equivalent to that of ferritic acid resistant steel with the same chromium content, but it also retains some disadvantages of high chromium ferritic steel to a certain extent.
2-3. Martensitic steel
This kind of steel is in the y-phase region at normal quenching temperature, but their y-phase is stable only at high temperature, and the M-point is generally about 3oo ℃, so it changes to martensite during cooling.
This kind of steel includes 2Cr13, 2Cr13Ni2, 3Cr13 and some modified 12% chromium hot strength steel, such as 13Cr14NiWVBA, Cr11Ni2MoWVB steel, etc.
The mechanical properties, corrosion resistance, process properties and physical properties of martensitic stainless steel are similar to those of ferritic martensitic stainless steel containing 12 ~ 14% chromium.
Because there is no free ferrite in the structure, the mechanical properties are higher than those of the above steel, but the overheating sensitivity during heat treatment is low.
2-4. Martensite carbide steel
The carbon content of the eutectoid point of Fe-C alloy is 0.83%.
In stainless steel, the S-point moves to the left due to chromium.
The steel containing 12% chromium and more than 0.4% carbon (Fig. 11-3) and the steel containing 18% chromium and more than 0.3% carbon (Fig. 3) belong to hypereutectoid steel.
When this kind of steel is heated at normal quenching temperature, the secondary carbides cannot be completely dissolved in austenite, so the microstructure after quenching is composed of martensite and carbide.
There are not many stainless steels in this category, but some stainless steels with high carbon content, such as 4Crl3, 9Cr18, 9Crl8MoV, 9Crl7MoVCo steel, etc. 3Crl3 steel with upper carbon content may also have such structure when quenched at a lower temperature.
Due to the high carbon content, the above three steel grades such as 9Cr18 contain more chromium, but their corrosion resistance is only equivalent to that of stainless steel containing 12 ~ 14% germanium.
This kind of steel is mainly used for parts requiring high hardness and wear resistance, such as cutting tools, bearings, springs and medical instruments.
2-5. Austenitic steel
This kind of steel contains more elements that expand y zone and stabilize austenite. It is y phase at high temperature.
During cooling, because MS point is below room temperature, it has austenite structure at room temperature.
Chromium nickel stainless steels such as 18-8, 18-12, 25-20 and 20-25Mo, and low nickel stainless steels with manganese replacing part of nickel and adding nitrogen, such as Cr18Mn10Ni5, Cr13Ni4Mn9, Cr17Ni4Mn9N, Cr14Ni3Mn14Ti steel, all belong to this category.
Austenitic stainless steel has many advantages mentioned above.
Although its mechanical properties are relatively low and it cannot be strengthened by heat treatment like ferritic stainless steel, its strength can be improved by cold working deformation and work hardening.
The disadvantage of this kind of steel is that it is sensitive to intergranular corrosion and stress corrosion, which needs to be eliminated by appropriate alloy additives and process measures.
2-6. AUSTENITIC FERRITIC STEEL
Due to the expansion of Y zone and the stabilization of austenite elements, this kind of steel is not enough to make the steel have pure austenite structure at room temperature or very high temperature.
Therefore, it is in austenite ferrite multiphase state, and its ferrite content can change in a large range due to different composition and heating temperature.
There are many stainless steels belonging to this category, such as low-carbon 18-8 chromium nickel steel, 18-8 chromium nickel steel with titanium, niobium and molybdenum, especially ferrite can be seen in the structure of cast steel.
In addition, chromium manganese stainless steel with chromium greater than 14 ~ 15% and carbon less than 0.2% (such as cr17mnll), as well as most chromium manganese nitrogen stainless steels studied and applied at present.
Compared with pure austenitic stainless steel, this kind of steel has many advantages, such as high yield strength, high resistance to intergranular corrosion, low sensitivity to stress corrosion, less tendency to produce hot cracks during welding, good casting fluidity and so on.
The disadvantages are poor pressure processing performance, large tendency of pitting corrosion, easy to produce c-phase brittleness, weak magnetism under the action of strong magnetic field and so on.
All these advantages and disadvantages come from ferrite in the tissue.
2-7. Austenitic martensitic steel
The MS point of this kind of steel is lower than room temperature.
After solution treatment, it is austenitic structure, which is easy to form and weld.
Generally, two processes can be used to make it undergo martensitic transformation.
First, after solution treatment, after heating at 700 ~ 800 degrees, austenite changes to metastable state due to precipitation of chromium carbide, Ms point rises above room temperature and changes to martensite when cooling;
Second, after solution treatment, it is directly cooled to the point between MS and MF to transform austenite into martensite.
The latter method can obtain high corrosion resistance, but the interval from solution treatment to cryogenic treatment should not be too long, otherwise the strengthening effect of cryogenic treatment will be reduced due to the aging stability of austenite.
After the above treatment, the steel is aged at 400 ~ 500 degrees to further strengthen the precipitated intermetallic compounds.
The typical steel grades of this kind of steel are 17cr-7Ni-A1, 15Cr-9Ni-A1, 17Cr-5Ni-Mo, 15Cr-8Ni-Mo-A1, etc.
This kind of steel is also called austenitic maraging stainless steel.
In fact, in addition to austenite and martensite, there are different amounts of ferrite in the structure of these steels, so it is also called semi austenitic precipitation hardening stainless steel.
This kind of steel is a new type of stainless steel developed and applied in the late 1950s.
They are generally characterized by high strength (C up to 100-150) and good thermal strength. However, due to the low chromium content and chromium carbide precipitation during heat treatment, the corrosion resistance is lower than that of standard austenitic stainless steel.
It can also be said that the high strength of this kind of steel is obtained at the expense of some corrosion resistance and other properties (such as non-magnetic).
At present, this kind of steel is mainly used in aviation industry and rocket missile production.
It is not widely used in general machinery manufacturing, and there is also a series of ultra-high strength steel in classification.
1. Types and definitions of corrosion
A stainless steel can have good corrosion resistance in many media, but in some other media, it may be corroded due to low chemical stability.
Therefore, a kind of stainless steel can not resist corrosion to all media.
In many industrial applications, stainless steel can provide satisfactory corrosion resistance.
According to the application experience, in addition to mechanical failure, the corrosion of stainless steel is mainly manifested in: a serious form of corrosion of stainless steel is local corrosion (i.e. stress corrosion cracking, pitting corrosion, intergranular corrosion, corrosion fatigue and crevice corrosion).
These failure cases caused by local corrosion account for almost half of the failure cases.
In fact, many failure accidents can be avoided through reasonable material selection.
According to the mechanism, metal corrosion can be divided into three types: special corrosion, chemical corrosion and electrochemical corrosion.
The vast majority of metal corrosion in life and engineering practice belongs to electrochemical corrosion.
Stress corrosion cracking (SCC): a general term that refers to the mutual failure of stressed alloys due to the expansion of severe lines in corrosive environment.
Stress corrosion cracking has brittle fracture morphology, but it may also occur in materials with high toughness.
The necessary conditions for stress corrosion cracking are tensile stress (whether residual stress or applied stress, or both) and the existence of specific corrosion medium.
The formation and expansion of the pattern are roughly perpendicular to the direction of tensile stress.
The stress value leading to stress corrosion cracking is much smaller than the stress value required for material fracture in the absence of corrosive medium.
Microscopically, the crack passing through the grain is called transgranular crack, while the crack along the grain boundary expansion diagram is called intergranular crack.
When the stress corrosion crack extends to its depth (here, the stress on the section of the loaded material reaches its fracture stress in the air), the material will be broken according to the normal crack (in ductile materials, it is usually through the polymerization of microscopic defects).
Therefore, the cross-section of parts that fail due to stress corrosion cracking will contain the characteristic area of stress corrosion cracking and the “dimple” area associated with the polymerization of micro defects.
Pitting corrosion: pitting corrosion refers to the high degree of local corrosion that occurs when most of the metal material surface is not corroded or the corrosion is slight and scattered.
The size of common corrosion spots is less than 1.00mm, and the depth is often greater than the surface pore diameter.
Light ones have shallow corrosion pits, and serious ones even form perforation.
Intergranular corrosion: the intergranular boundaries are the boundary cities of disordered dislocation between grains with different crystallographic orientations.
Therefore, they are favorable areas for the segregation of various solute elements or the precipitation of metal compounds (such as carbides and phase δ) in steel.
Therefore, it is not surprising that the grain boundary may be corroded first in some corrosive media.
This type of corrosion is called intergranular corrosion.
Most metals and alloys may exhibit intergranular corrosion in specific corrosion media.
Intergranular corrosion is a kind of selective corrosion damage.
The difference between it and general selective corrosion is that the locality of corrosion is micro scale, but not necessarily local in macro scale.
Crevice corrosion: refers to the macroscopic pitting or ulceration at the crevices of metal components.
It is a form of local corrosion, which may occur in the crevices where the solution stagnates or in the shielded surface.
Such gaps can be formed at the junction of metal and metal or metal and non-metal, for example, at the junction with rivets, bolts, gaskets, valve seats, loose surface sediments and marine organisms.
Total corrosion: a term used to describe the corrosion phenomenon that occurs on the whole alloy surface in a relatively uniform manner.
When full-scale corrosion occurs, the village material gradually becomes thinner due to corrosion, and even the material corrosion fails.
Stainless steel may show overall corrosion in strong acid and alkali.
The failure problem caused by total corrosion is not very worrying, because this kind of corrosion can usually be predicted by simple immersion test or consulting the literature on corrosion.
Uniform corrosion: refers to the phenomenon of corrosion on all metal surfaces in contact with corrosive media.
Different index requirements for corrosion resistance are put forward according to different service conditions, which can be generally divided into two categories:
1. Stainless steel
It refers to the corrosion-resistant steel in the atmosphere and weak corrosive medium. Rot
If the corrosion rate is less than 0.01mm/year, it is considered as “complete corrosion resistance”;
If the corrosion rate is less than 0.1mm/year, it is considered as “corrosion resistant”.
2. Corrosion resistant steel
It refers to the steel that can resist corrosion in various strongly corrosive media.
2. Corrosion resistance of various stainless steels
301 stainless steel shows obvious work hardening phenomenon during deformation, which is used in various occasions requiring high strength.
302 stainless steel is essentially a variant of 304 stainless steel with higher carbon content. It can obtain higher strength by cold rolling.
302B is a stainless steel with high silicon content, which has high resistance to high temperature oxidation.
303 and 303Se are free cutting stainless steels containing sulfur and selenium respectively.
They are used in occasions where free cutting and surface gloss are mainly required.
303Se stainless steel is also used to make parts requiring hot upsetting because it has good hot workability under such conditions.
304 is a universal stainless steel, which is widely used to make equipment and parts requiring good comprehensive performance (corrosion resistance and formability).
304L is a variant of 304 stainless steel with low carbon content, which is used for occasions requiring welding.
The lower carbon content minimizes the precipitation of carbides in the heat affected zone close to the weld, which may lead to intergranular corrosion (welding corrosion) of stainless steel in some environments.
304N is a kind of stainless steel containing nitrogen. Nitrogen is added to improve the strength of steel.
305 and 384 stainless steels contain high nickel and have low work hardening rate.
They are suitable for various occasions with high requirements for cold formability.
308 stainless steel is used to make welding rods.
The nickel and chromium contents of 309, 310, 314 and 330 stainless steels are relatively high in order to improve the oxidation resistance and creep strength of the steel at high temperature.
30S5 and 310S are variants of 309 and 310 stainless steel.
The difference is that the carbon content is low in order to minimize the carbide precipitated near the weld.
330 stainless steel has particularly high carburizing resistance and thermal shock resistance
316 and 317 stainless steels contain aluminum, so their pitting corrosion resistance in marine and chemical industry environment is much better than 304 stainless steel.
Among them, 316 stainless steel is made of variants, including low-carbon stainless steel 316L, high-strength stainless steel 316N containing nitrogen and free cutting stainless steel 316F with high sulfur content.
321, 347 and 348 are stainless steels stabilized with titanium, niobium, tantalum and niobium respectively, which are suitable for welding components at high temperature.
348 is a kind of stainless steel suitable for nuclear power industry, which has a certain limit on the amount of tantalum and drill.
Original surface: the surface treated with heat treatment and pickling after No.1 hot rolling.
It is generally used for cold rolling materials, industrial tanks, chemical industrial devices, etc. and the thickness is 2.0mm-8.0mm.
Blunt surface: after NO.2D cold rolling and heat treatment and pickling, the material is soft and the surface is silvery white.
It is used for deep stamping processing, such as automobile components, water pipes, etc.
Fogged surface: NO.2B cold rolling, heat treatment, pickling, and finish rolling to make the surface moderately bright.
Because the surface is smooth and easy to regrind, it makes the surface brighter and has a wide range of uses, such as tableware, building materials and so on.
The surface treatment with improved mechanical properties can meet almost all applications.
Coarse sand NO.3 is the product ground with 100-120 grinding belt.
It has better gloss and discontinuous coarse grain.
Used for building interior and exterior decoration materials, electrical products and kitchen equipment.
Fine sand: NO.4 product ground with 150-180 abrasive belt.
It has better gloss, discontinuous coarse grain, and the stripe is thinner than NO.3.
It is used in baths, building interior and exterior decoration materials, electrical products, kitchen equipment and food equipment.
#320 product ground with NO. 320 grinding belt.
It has better gloss, discontinuous coarse grain, and the stripe is thinner than NO.4.
It is used for baths, building interior and exterior decoration materials, electrical products, kitchen equipment and food equipment.
Hairline: HL NO.4 product with grinding pattern generated by continuous grinding of polishing abrasive belt with appropriate particle size (subdivided into 150-320).
It is mainly used for architectural decoration, elevators, doors and panels of buildings, etc.
Bright surface: BA is the product obtained by bright annealing after cold rolling and leveling.
With excellent surface gloss and high reflectivity.
Like a mirror surface.
Used for household appliances, mirrors, kitchen equipment, decorative materials, etc.
SUS304: it has good corrosion resistance, heat resistance, low temperature strength and mechanical properties, good hot workability such as stamping and bending, no heat treatment hardening phenomenon and no magnetism.
It is widely used in household products (Class 1 and 2 tableware), cabinets, indoor pipelines, water heaters, boilers, bathtubs, auto parts, medical appliances, building materials, chemicals, food industry, agriculture and ship parts.
SUS304L: Austenitic basic steel, which is most widely used;
Excellent corrosion resistance and heat resistance;
Excellent low temperature strength and mechanical properties;
Single phase austenite structure, no heat treatment hardening phenomenon (non-magnetic, service temperature – 196-800 ℃).
SUS304Cu: austenitic stainless steel with 17Cr-7Ni-2Cu as the basic composition;
Excellent formability, especially good wire drawing and aging crack resistance;
The corrosion resistance is the same as 304.
SUS316: excellent corrosion resistance and high temperature strength.
It can be used under harsh conditions.
It has good work hardening and non-magnetic.
Suitable for seawater equipment, chemistry, dyes, papermaking, oxalic acid, fertilizer production equipment, photography, food industry and coastal facilities.
SUS316L: Mo (2-3%) is added to the steel, so it has excellent corrosion resistance and high temperature strength;
The carbon content of SUS316L is lower than SUS316, so the intergranular corrosion resistance is better than SUS316;
High creep strength at high temperature.
It can be used under harsh conditions, with good work hardening and non-magnetic.
Suitable for seawater equipment, chemistry, dyes, papermaking, oxalic acid, fertilizer production equipment, photography, food industry and coastal facilities.
SUS321: adding Ti to 304 steel, so it has excellent intergranular corrosion resistance;
Excellent high temperature strength and high temperature oxygen resistance;
The cost is high and the processability is worse than SUS304.
Heat resistant materials, automobile and aircraft exhaust pipes, boiler covers, pipes, chemical devices, heat exchangers.
SUH409H: good processability and welding performance, good high-temperature oxidation resistance, and can withstand the temperature range from room temperature to 575 ℃.
It is widely used in automobile exhaust system.
SUS409L: control the content of C and N in steel, so it has excellent weldability, formability and corrosion resistance;
Containing 11% Cr, ferritic stainless steel with BCC Structure at high temperature and normal temperature;
Due to the filling of Ti, there is air oxidation and corrosion resistance below 750 ℃.
SUS410: martensite represents steel with high strength and hardness (magnetic);
Poor corrosion resistance, not suitable for use in severely corrosive environment;
Low C content and good workability. The surface can be hardened by heat treatment.
SUS420J2: martensite represents steel, with high strength and hardness (magnetic);
Poor corrosion resistance, poor processing formability and good wear resistance;
Can carry out heat treatment to improve mechanical properties.
It is widely used to process cutting tools, nozzles, valves, board rulers and tableware.
SUS430: low thermal expansion rate, good molding and oxidation resistance.
It is suitable for heat-resistant appliances, burners, household appliances, class 2 tableware and kitchen sink.
With low price and good processability, it is an ideal substitute for SUS304;
Good corrosion resistance, typical non heat treatment hardening ferritic system stainless steel.
In particular, 316 and 317 stainless steels (see the following for the properties of 317 stainless steel) are molybdenum containing stainless steels.
The molybdenum content of 317 stainless steel is slightly higher than that of 316 stainless steel Due to the molybdenum in the steel, the overall performance of this steel is better than 310 and 304 stainless steel.
Under high temperature conditions, when the concentration of sulfuric acid is lower than 15% and higher than 85%, 316 stainless steel has a wide range of applications.
316 stainless steel also has good chloride corrosion performance, so it is usually used in marine environment.
316L stainless steel has a maximum carbon content of 0.03 and can be used in applications where annealing cannot be carried out after welding and maximum corrosion resistance is required.
Corrosion resistance: the corrosion resistance is better than 304 stainless steel.
It has good corrosion resistance in the production process of pulp and paper.
Moreover, 316 stainless steel is also resistant to marine and aggressive industrial atmosphere.
Heat resistance: 316 stainless steel has good oxidation resistance in intermittent use below 1600 degrees and continuous use below 1700 degrees: 316 stainless steel is best not to act continuously in the range of 800-1575 degrees, but when 316 stainless steel is used continuously outside this temperature range, the stainless steel has good heat resistance.
The carbide precipitation resistance of 316L stainless steel is better than that of 316 stainless steel, and the above temperature range can be used.
Heat treatment: annealing in the temperature range of 1850-2050 degrees, then rapid annealing, and then rapid cooling.
316 stainless steel cannot be hardened by overheating.
Welding: 316 stainless steel has good welding performance.
All standard welding methods can be used for welding.
316Cb, 316L or 309Cb stainless steel filler rods or electrodes can be used for welding according to the purpose.
In order to obtain the best corrosion resistance, the welded section of 316 stainless steel needs post weld annealing.
If 316L stainless steel is used, post weld annealing is not required.
Typical uses: pulp and paper equipment, heat exchangers, dyeing equipment, film processing equipment, pipelines, materials for the exterior of buildings in coastal areas.
Why is stainless steel rusty? When there are brown rust spots (spots) on the surface of stainless steel pipe, people are surprised: they think that “stainless steel is not rusty, rusty is not stainless steel, maybe there is a problem with the steel”.
In fact, this is a one-sided wrong view of the lack of understanding of stainless steel. Stainless steel will rust under certain conditions.
Stainless steel has the ability to resist atmospheric oxidation – that is, rust resistance.
At the same time, it also has the ability to corrode in the medium containing acid, alkali and salt – that is, corrosion resistance.
However, its corrosion resistance changes with the chemical composition of the steel itself, the state of interaction, the service conditions and the type of environmental medium.
For example, 304 steel pipe has absolutely excellent corrosion resistance in a dry and clean atmosphere, but if it is moved to the coastal area, it will soon rust in the sea fog containing a lot of salt;
The 316 steel pipe performs well.
Therefore, not any kind of stainless steel can resist corrosion and rust in any environment.
Stainless steel is a thin, firm, fine and stable chromium rich oxide film (protective film) formed on its surface to prevent the continuous infiltration and oxidation of oxygen atoms, so as to obtain the ability of anti-corrosion.
Once the film is continuously damaged for some reason, the oxygen atoms in the air or liquid will continuously penetrate or the iron atoms in the metal will continuously separate out, forming loose iron oxide, and the metal surface will be continuously corroded.
There are many forms of surface facial mask damage.
1. There are dust containing other metal elements or attachments of dissimilar metal particles on the surface of stainless steel.
In humid air, the condensate between the attachments and stainless steel connects them into a micro battery, which leads to electrochemical reaction and damage to the protective film, which is called electrochemical corrosion.
2. The surface of stainless steel adheres to organic juice (such as melons and vegetables, noodle soup, phlegm, etc.), which constitutes organic acid in the case of water and oxygen.
For a long time, the corrosion of organic acid on the metal surface will be reduced.
3. The stainless steel surface contains acid, alkali and salt substances (such as alkali water and lime water splashing on the decoration wall), causing local corrosion.
4. In polluted air (such as atmosphere containing a large amount of sulfide, carbon oxide and nitrogen oxide), sulfuric acid, nitric acid and acetic acid liquid points are formed in the presence of condensate, causing chemical corrosion.
The above conditions can cause the damage of the protective film on the surface of stainless steel and lead to corrosion.
Therefore, in order to ensure that the metal surface is permanently bright and not corroded, we suggest:
1. Clean the stainless steel surface frequently, and remove the external decorative factors.
2. 316 stainless steel shall be used in coastal areas, which can resist seawater corrosion.
3. The chemical composition of some stainless steel pipes in the market can not meet the corresponding national standards and can not meet the 304 material requirements.
Therefore, it will also cause rust, which requires users to carefully select the products of reputable manufacturers.
People often think that the magnet absorbs stainless steel to verify its advantages and disadvantages and authenticity.
If it does not absorb non-magnetic, it is considered to be good and genuine;
If the user is magnetic, it is considered to be a fake.
In fact, this is an extremely one-sided, impractical and wrong identification method.
There are many kinds of stainless steel, which can be divided into several types according to the organizational structure at room temperature:
1. Austenite type: such as 304, 321, 316, 310, etc;
2. Martensitic or ferritic type: such as 430, 420, 410, etc;
Austenite type is non-magnetic or weakly magnetic, while martensite or ferrite is magnetic.
Most of the stainless steel commonly used as decorative tubesheet is Austenitic 304 material, which is generally non-magnetic or weak magnetic.
However, magnetism may also occur due to fluctuations in chemical composition or different processing conditions caused by smelting, but this cannot be considered as counterfeit or unqualified.
What is the reason?
As mentioned above, austenite is non-magnetic or weakly magnetic, while martensite or ferrite is magnetic.
Due to component segregation or improper heat treatment during smelting, a small amount of martensite or ferrite in Austenitic 304 stainless steel will be caused.
In this way, 304 stainless steel will have weak magnetism.
In addition, after cold working, the microstructure of 304 stainless steel will also be transformed into martensite.
The greater the cold working deformation, the more martensite transformation, and the greater the magnetism of the steel.
Like the steel strip of the same batch number, 76 tubes are produced without obvious magnetic induction, and 9.5 tubes are produced.
Due to the large cold bending deformation, the magnetic induction is obvious.
The deformation of square rectangular pipe is larger than that of round pipe, especially the corner part, the deformation is more intense and the magnetism is more obvious.
In order to completely eliminate the magnetism of 304 steel caused by the above reasons, the stable austenite structure can be recovered through high-temperature solid solution treatment, so as to eliminate the magnetism.
In particular, the magnetism of 304 stainless steel caused by the above reasons is completely different from that of other stainless steels, such as 430 and carbon steel, that is, the magnetism of 304 steel always shows weak magnetism.
This tells us that if stainless steel has weak magnetism or no magnetism at all, it should be judged as 304 or 316 material;
If it is the same as the magnetism of carbon steel, it shows strong magnetism, because it is judged that it is not made of 304 material.
We suggest that stainless steel products should be purchased from reputable manufacturers. Don’t be greedy for cheap and beware of being cheated.
A. Hot rolled stainless steel plate
Stainless steel hot rolled steel plate is a kind of stainless steel plate produced by hot rolling process.
Thin plates with a thickness of no more than 3mm and thick plates with a thickness of more than 3mm are used to manufacture corrosion-resistant parts, containers and equipment in chemical, petroleum, machinery, shipbuilding and other industries.
Its classification and brand are as follows:
1. Austenitic steel
(1)1Cr17Mn6Ni15N；
(2)1Cr18Mn8Ni5N；
(3)1Cr18Ni9；
(4)1Cr18Ni9Si3；
(5)0Cr18Ni9；
(6)00Cr19Ni10；
(7)0Cr19Ni9N；
(8)0Cr19Ni10NbN；
(9)00Cr18Ni10N；
(10)1Cr18Ni12；
（11） 0Cr23Ni13；
(12)0Cr25Ni20；
(13) 0Cr17Ni12Mo2；
(14) 00Cr17Ni14Mo2；
(15) 0Cr17Ni12Mo2N；
(16) 00Cr17Ni13Mo2N；
(17) 1Cr18Ni12Mo2Ti；
(18) 0Cr18Ni12Mo2Ti；
(19) 1Cr18Ni12Mo3Ti；
(20) 0Cr18Ni12Mo3Ti；
(21) 0Cr18Ni12Mo2Cu2；
(22) 00Cr18Ni14Mo2Cu2；
(23) 0Cr19Ni13Mo3；
(24) 00Cr19Ni13Mo3；
(25) 0Cr18Ni16Mo5；
(26) 1Cr18Ni9Ti；
(27) 0Cr18Ni10Ti；
(28) 0Cr18Ni11Nb；
(29) 0Cr18Ni13Si4
2. AUSTENITIC FERRITIC STEEL
（30）0Cr26Ni5Mo2；
（31）00Cr18Ni5Mo3Si2；
3. Ferritic steel
（32）0Cr13Al；
(33) 00Cr12；
(34)1Cr15；
(35)1Cr17；
(36)1Cr17Mo；
(37)00Cr17Mo；
(38)00Cr18Mo2；
(39)00Cr30Mo2；
(40)00Cr27Mo
4. Martensitic steel
（41）1Cr12；
（42）0Cr13；
（43）；1Cr13；
（44）2Cr13；
（45）3Cr13；
（46）4Cr13；
（47）3Cr16；
（48）7Cr17
5. Precipitation hardening section steel
（49）0Cr17Ni7Al
B. Cold rolled stainless steel sheet
Stainless steel cold rolled steel plate is a stainless steel plate produced by cold rolling process. Thin plate with thickness no more than 3mm and thick plate with thickness more than 3mm.
It is used to make corrosion-resistant parts, petroleum and chemical pipelines, containers, medical instruments, marine equipment, etc.
Its classification and brand are as follows:
1. Austenitic steel
In addition to the same as the hot rolling part (29 kinds), there are:
（1）2Cr13Mn9Ni4
(2)1Cr17Ni7
(3) 1Cr17Ni8
2. AUSTENITIC FERRITIC STEEL
In addition to the same as the hot rolling part (2 kinds), there are:
(1)1Cr18Ni11Si4AlTi
(2) 1Cr21Ni5Ti
3. Ferritic steel
In addition to the same as the hot rolling part (9 kinds), there are:00Cr17
4. Martensitic steel
In addition to the same as the hot rolling part (8 kinds), there are 1Cr17Ni2
5. Precipitation hardening section steel: the same as the hot rolling part
C. Introduction to ferrite, austenite and martensite
As we all know, solid metals and alloys are crystals, that is, the atoms in them are arranged according to a certain law.
There are generally three ways of arrangement: body centered cubic lattice structure, face centered cubic lattice structure and closely arranged hexagonal lattice structure.
Metal is composed of polycrystalline, and its polycrystalline structure is formed in the process of metal crystallization.
The iron constituting the iron carbon alloy has two kinds of lattice structures: α-iron with body centered cubic lattice structure below 910 ℃ and a-iron with face centered cubic lattice structure above 910 ℃ Υ—— Iron.
If carbon atoms squeeze into the lattice of iron without destroying the lattice structure of iron, such a substance is called solid solution.
The solid solution formed by dissolving carbon into α-iron is called ferrite.
Its carbon dissolving ability is very low, and the maximum solubility is no more than 0.02%.
And carbon dissolves into Υ—— The solid solution formed in iron is called austenite, which has high carbon dissolving ability, up to 2%.
Austenite is the high temperature phase of iron carbon alloy.
The austenite formed by steel at high temperature becomes unstable undercooled austenite when it is undercooled below 727 ℃.
If it is supercooled below 230 ℃ at a great cooling rate, there is no possibility of diffusion of carbon atoms in austenite, and austenite will be directly transformed into a kind of carbon containing supersaturated carbon α Solid solution, called martensite.
Due to the supersaturation of carbon content, the strength and hardness of martensite are increased, the plasticity is reduced and the brittleness is increased.
The corrosion resistance of stainless steel mainly comes from chromium.
Experiments show that the corrosion resistance of steel can be greatly improved only when the chromium content exceeds 12%.
Therefore, the chromium content in stainless steel is generally not less than 12%.
Due to the increase of chromium content, it also has a great impact on the structure of steel. When the chromium content is high and the carbon content is small, chromium will balance iron and carbon, as shown in the fig. Υ, the phase region shrinks or even disappears.
This stainless steel is ferrite.
It is called ferritic stainless steel because of its structure and no phase transformation during heating.
When the chromium content is low (but higher than 12%), the carbon content is high, and the alloy is easy to form martensite when cooled from high temperature, so this kind of steel is called martensitic stainless steel.
Nickel can be expanded Υ Phase zone, so that the steel has austenite structure.
If the nickel content is enough to make the steel have austenitic structure at room temperature, the steel is called austenitic stainless steel.
D. Application fields of stainless steel
In the 40 years from 1960 to 1999, the output of stainless steel in western countries soared from 2.15 million tons to 17.28 million tons, an increase of about 8 times, with an average annual growth rate of about 5.5%.
Stainless steel is mainly used in kitchen, household appliances, transportation, construction and civil engineering.
In terms of kitchen appliances, there are mainly water washing tanks and electrical and gas water heaters, and household appliances mainly include the drum of full-automatic washing machine.
From the perspective of energy conservation and recycling and other environmental protection, the demand for stainless steel is expected to further expand.
In the field of transportation, there are mainly the exhaust systems of railway vehicles and vehicles.
The stainless steel used for the exhaust system is about 20-30kg in each vehicle, and the annual demand of the world is about 1 million tons, which is the largest application field of stainless steel.
In the construction field, the demand has increased sharply recently, such as the protective device of Singapore metro station, which uses about 5000 tons of stainless steel exterior decoration materials.
For another example, after 1980 in Japan, the stainless steel used in the construction industry increased by about four times, mainly used as roof, interior and exterior decoration of buildings and structural materials.
In the 1980s, 304 type unpainted materials were used as roof materials in the coastal areas of Japan, and the use of painted stainless steel was gradually changed from rust prevention.
In the 1990s, more than 20% high Cr ferritic stainless steel with high corrosion resistance was developed, which was used as roof material.
At the same time, various surface finishing technologies were developed for beauty.
In the field of civil engineering, Japan’s dam suction tower uses stainless steel.
In cold areas in Europe and America, salt needs to be sprinkled to prevent freezing of highways and bridges, which accelerates the corrosion of reinforcement, so stainless steel reinforcement is used.
About 40 roads in North America have adopted stainless steel reinforcement in recent three years, with the use of 200-1000 tons each.
In the future, stainless steel will make a difference in the market in this field.
2. The key to expanding the application of stainless steel in the future is environmental protection, long life and popularization of it.
In terms of environmental protection, first of all, from the perspective of atmospheric environmental protection, the demand for heat-resistant and high-temperature corrosion-resistant stainless steel for high-temperature waste incineration devices, LNG power generation devices and high-efficiency power generation devices using coal to inhibit the occurrence of dioxin will expand.
In addition, it is estimated that the battery shell of fuel cell vehicles that will be put into practical application in the early 21st century will also use stainless steel.
From the perspective of water quality and environmental protection, stainless steel with excellent corrosion resistance will also expand the demand in water supply and drainage treatment devices.
With regard to long life, the application of stainless steel is increasing in the existing bridges, highways, tunnels and other facilities in Europe.
It is expected that this trend will spread all over the world.
In addition, the service life of ordinary residential buildings in Japan is particularly short, 20-30 years, and the treatment of waste materials has become a major problem.
Recently, buildings with a service life of 100 years have begun to appear, so the demand for materials with excellent durability will increase.
From the perspective of environmental protection of the earth, while reducing civil engineering and construction waste materials, it is necessary to explore how to reduce maintenance costs from the design stage of introducing new concepts.
With regard to the popularization of it, in the process of it development and popularization, functional materials play a great role in equipment and hardware, and there are great requirements for high-precision and high-functional materials.
For example, in mobile phone and microcomputer components, the high strength, elasticity and non-magnetic properties of stainless steel are flexibly applied, which expands the application of stainless steel.
In addition, stainless steel with good cleanliness and durability plays an important role in the manufacturing equipment of semiconductors and various substrates.
Stainless steel has many excellent properties that other metals do not have. It is a material with excellent durability and recycling.
In the future, corresponding to the changes of the times, stainless steel will be widely used in various fields.
1. Overview of steel grade representation in China
The brand of steel, abbreviated as steel number, is the name of each specific steel product.
It is a common language for people to understand steel.
The steel grade representation method in China adopts the combination of Chinese phonetic alphabet, chemical element symbols and Arabic numerals according to the provisions of the national standard “steel product grade representation method” (gb221-79).
Namely:
① Chemical elements in steel grades are represented by international chemical symbols, such as Si, Mn, Cr. “Rare earth element” (or “XT”) is used to represent “rare earth element”.
② The product name, purpose, smelting and pouring method are generally represented by the abbreviations of Chinese Pinyin, as shown in the table.
③ The content (%) of main chemical elements in steel is expressed in Arabic numerals.
Table: abbreviations used in GB standard steel grades and their meanings
| Name | Chinese characters | Symbol | Typeface | Position |
| Yield point | Bend | Q | Capitalize | head |
| Boiling steel | boiling | F | Capitalize | tail |
| Semi killed steel | half | b | a lowercase letter | tail |
| Killed steel | town | z | Capitalize | tail |
| Special killed steel | Special town | TZ | Capitalize | tail |
| Oxygen converter (steel) | oxygen | Y | Capitalize | in |
| Alkaline air converter (steel) | alkali | J | Capitalize | in |
| Free cutting steel | easy | Y | Capitalize | head |
| Carbon tool steel | carbon | T | Capitalize | head |
| Rolling bearing steel | rolling | G | Capitalize | head |
| Steel for welding rod | weld | H | Capitalize | head |
| High grade (high quality steel) | high | A | Capitalize | tail |
| super | special | E | Capitalize | tail |
| Riveted screw steel | Rivet screw | ML | Capitalize | head |
| Anchor chain steel | anchor | M | Capitalize | head |
| Mining steel | mine | K | Capitalize | tail |
| Steel for automobile girder | beam | L | Capitalize | tail |
| Steel for pressure vessel | Allow | R | Capitalize | tail |
| Steel for multilayer or high pressure vessels | high-level | gc | a lowercase letter | tail |
| cast steel | cast steel | ZG | Capitalize | head |
| Cast steel for roll | Casting roll | ZU | Capitalize | head |
| Steel pipe for geological drilling | geology | DZ | Capitalize | head |
| Hot rolled silicon steel for electrical purposes | electrothermal | DR | Capitalize | head |
| Cold rolled non oriented silicon steel for electrical purposes | No electricity | DW | Capitalize | head |
| Cold rolled oriented silicon steel for electrical purposes | Electric extraction | DQ | Capitalize | head |
| Pure iron for electrical purposes | Electric iron | DT | Capitalize | head |
| super | exceed | C | Capitalize | tail |
| Marine steel | ship | C | Capitalize | tail |
| Bridge steel | Bridge | q | a lowercase letter | tail |
| Boiler steel | pot | g | a lowercase letter | tail |
| Rail steel | rail | U | a lowercase letter | head |
| Precision alloy | essence | J | Capitalize | in |
| Corrosion resistant alloy | Corrosion resistance | NS | Capitalize | head |
| Wrought superalloy | Gao He | GH | Capitalize | head |
| Cast superalloy | K | Capitalize | head |
1. Classification of steel plate (including strip steel):
1. Classification by thickness:
(1) Sheet
(2) Middle plate
(3) Thick plate
(4) Extra thick plate
2. Classification by production method:
(1) Hot rolled steel plate
(2) Cold rolled steel sheet
3. Classification by surface features:
(1) Galvanized sheet (hot dip galvanized sheet, electro galvanized sheet)
(2) Tinplate
(3) Composite steel plate
(4) Color coated steel plate
4. Classification by purpose:
(1) Bridge steel plate
(2) Boiler steel plate
(3) Shipbuilding steel plate
(4) Armor plate
(5) Automobile steel plate
(6) Roof steel plate
(7) Structural steel plate
(8) Electrical steel plate (silicon steel sheet)
(9) Spring steel plate
(10) Other
2. Common Japanese brands of steel plates for ordinary and mechanical structures
1. In the grades of Japanese steel (JIS Series), ordinary structural steel is mainly composed of three parts:
The first part represents the material, for example, S (steel) represents steel and F (ferrum) represents iron;
The second part represents different shapes, types and uses, such as P (plate) represents plate, T (tube) represents tube, and K (kogu) represents tool;
The third part represents the characteristic number, which is generally the minimum tensile strength.
For example: SS400 – the first S represents steel, the second S represents “structure”, 400 represents the lower limit tensile strength of 400MPa, and the whole represents ordinary structural steel with tensile strength of 400MPa.
2. SPHC – the first S is the abbreviation of steel, P is the abbreviation of plate, H is the abbreviation of hot heat, and C is the abbreviation of commercial.
It generally represents hot-rolled steel plate and strip.
3. SPHD — hot rolled steel plate and strip for stamping.
4. Sphe — hot rolled steel plate and strip for deep drawing.
5. SPCC – cold rolled carbon steel sheet and strip, equivalent to Chinese Q195-215A brand.
The third letter C is the abbreviation of cold.
When it is necessary to ensure the tensile test, add T at the end of the brand as spcct.
6. SPCD refers to cold-rolled carbon steel sheet and strip for stamping, which is equivalent to China 08Al (13237) high-quality carbon structural steel.
7. Spce – cold rolled carbon steel sheet and strip for deep drawing, equivalent to 08Al (5213) deep drawing steel in China.
When non timeliness is required, add n at the end of the brand as spcen.
Quenching and tempering code of cold rolled carbon steel sheet and strip: annealing state is a, standard quenching and tempering is s, 1 / 8 hard is 8, 1 / 4 hard is 4, 1 / 2 hard is 2, and hard is 1.
Surface processing code: D for matte finish rolling and B for bright finish rolling.
For example, spcc-sd refers to cold rolled carbon sheet commonly used for standard quenching and tempering and matte finish rolling.
Another example is spcct-sb, which means cold rolled carbon sheet with standard quenching and tempering, bright processing and mechanical properties.
8. JIS steel grades for mechanical structures are expressed as follows:
S + carbon content + letter code (C, CK), in which the carbon content is the middle value × 100 means, the letter C means carbon, and K means steel for carburizing.
For example, the carbon content of carbon coil S20C is 0.18-0.23%.
3. Designation of silicon steel sheet in China and Japan
1. Chinese brand representation:
(1) Cold rolled non oriented silicon steel strip (sheet)
Expression method: DW + iron loss value (iron loss value per unit weight with frequency of 50Hz and sinusoidal magnetic induction peak value of 1.5T.) 100 times + 100 times the thickness value.
For example, dw470-50 represents cold-rolled non oriented silicon steel with iron loss value of 4.7w/kg and thickness of 0.5mm. Now the new model is 50W470.
(2) Cold rolled oriented silicon steel strip (sheet)
Expression method: DQ + iron loss value (iron loss value per unit weight with frequency of 50Hz and sinusoidal magnetic induction peak value of 1.7t.) 100 times + 100 times the thickness value. Sometimes G is added after the iron loss value to indicate high magnetic induction.
For example, DQ133-30 represents cold-rolled oriented silicon steel strip (sheet) with iron loss value of 1.33 and thickness of 0.3mm. Now the new model is 30Q133.
(3) Hot rolled silicon steel plate
Hot rolled silicon steel plate is represented by DR, which is divided into low silicon steel (silicon content ≤ 2.8%) and high silicon steel (silicon content > 2.8%).
Expression method: Dr + 100 times of iron loss value (the maximum value of magnetic induction intensity with 50Hz repeated magnetization and sinusoidal variation is the iron loss value per unit weight when the maximum value is 1.5T) + 100 times of thickness value.
For example, DR510-50 represents hot-rolled silicon steel plate with iron loss value of 5.1 and thickness of 0.5mm.
The grade of hot-rolled silicon steel sheet for household appliances is expressed by JDR + iron loss value + thickness value, such as JDR540-50.
2. Japanese brand representation:
(1) Cold rolled non oriented silicon steel strip
From the nominal thickness (expanded by 100 times) + code a+ guaranteed value of iron loss (the value after expanding by 100 times the iron loss value when the frequency is 50Hz and the maximum magnetic flux density is 1.5T).
For example, 50A470 represents cold-rolled non oriented silicon steel strip with thickness of 0.5mm and iron loss guarantee value ≤ 4.7.
(2) Cold rolled oriented silicon steel strip
The nominal thickness (value expanded by 100 times) + code G: ordinary material, P: high orientation material + iron loss guarantee value (the value after expanding the iron loss value when the frequency is 50Hz and the maximum magnetic flux density is 1.7t by 100 times).
For example, 30G130 represents cold-rolled oriented silicon steel strip with thickness of 0.3mm and iron loss guarantee value ≤ 1.3.
4. Electroplated tin plate and hot-dip galvanized plate:
1. Electroplated tin plate
Electroplated tin sheet and steel strip, also known as tinplate, the surface of this steel plate (strip) is plated with tin, which has good corrosion resistance and is non-toxic.
It can be used as packaging material for cans, inner and outer sheath of cables, instrument and telecommunication parts, flashlight and other hardware.
The classification and symbols of tinned steel plates and strips are as follows:
| Classification method | Category | Symbol |
| According to tin plating quantity | Equal thickness tinning E1, e, e | |
| Differential thickness tin plating D1, D, D, D, D, D | ||
| According to hardness grade | T50、T52、T57、、T61、T65、T70 | |
| By surface condition | Smooth surface | G |
| Stone grain surface | s | |
| Pockmarked noodles | M | |
| By passivation method | Low chromium passivation | L |
| Chemical passivation | H | |
| Cathodic electrochemical passivation | Y | |
| According to the amount of oil applied | Lightly oiled | Q |
| Re oiling | Z | |
| By surface quality | a set | I |
| Two groups | II | |
The provisions of equal thickness tin plating amount and differential thickness tin plating amount are as follows:
| Symbol | Nominal tin plating amount, g / m2 | Minimum average tin plating amount, g / m2 |
| E1 | 5.6(2.8/2.8) | 4.9 |
| E2 | 11.2(5.6/5.6) | 10.5 |
| E3 | 16.8(8.4/8.4) | 15.7 |
| E4 | 22.4(11.2/11.2) | 20.2 |
| D1 | 5.6/2.8 | 5.05/2.25 |
| D2 | 8.4/2.8 | 7.85/2.25 |
| D3 | 8.4/5.6 | 7.85/5.05 |
| D4 | 11.2/2.8 | 10.1/2.25 |
| D5 | 11.2/5.6 | 10.1/5.05 |
| D6 | 11.2/8.4 | 10.1/7.85 |
| D7 | 15.1/5.6 | 13.4/5.05 |
2. Hot dip galvanized sheet
Zinc plating on the surface of steel sheet and steel strip by continuous hot plating can prevent corrosion and rust on the surface of steel sheet and steel strip.
Galvanized steel sheet and strip are widely used in machinery, light industry, construction, transportation, chemical industry, post and telecommunications and other industries.
The classification and symbols of galvanized steel sheet and strip are shown in the following table:
| Classification method | Typess | Symbol | |
| According to processing performance | General purpose | PT | |
| Mechanical occlusion | JY | ||
| Deep drawing | SC | ||
| Ultra deep drawing aging resistance | CS | ||
| Structure | JG | ||
| By weight of zinc layer | Zn | 1 | 1 |
| Zn | 100 | 100 | |
| Zn | 200 | 200 | |
| Zn | 275 | 275 | |
| Zn | 350 | 350 | |
| Zn | 450 | 450 | |
| Zn | 600 | 600 | |
| Zn | 1 | 1 | |
| Fe | 90 | 90 | |
| alloy | 120 | 120 | |
| 180 | 180 | ||
| By surface structure | Normal zinc flower | Z | |
| Small zinc flower | X | ||
| Finishing zinc flower | GZ | ||
| Zinc iron alloy | XT | ||
| By surface quality | Group I | Ⅰ | |
| Group II | Ⅱ | ||
| According to dimensional accuracy | Advanced precision | A | |
| General accuracy | B | ||
| By surface treatment | Chromate passivation | L | |
| Oiling | Y | ||
| Chromate passivation and oiling | LY | ||
5. Boiling steel plate and killed steel plate
1. Boiling steel plate is a hot rolled steel plate made of ordinary carbon structural steel boiling steel.
Boiling steel is a kind of steel with incomplete deoxidation.
Only a certain amount of weak deoxidizer is used to deoxidize the liquid steel, and the oxygen content of the liquid steel is high.
When the liquid steel is injected into the ingot mold, the carbon oxygen reaction produces a large amount of gas, resulting in the boiling of the liquid steel.
Therefore, boiling steel is named.
The carbon content of rimmed steel is low, and the silicon content in steel is also low (Si < 0.07%) due to the use of ferrosilicon deoxidation.
The outer layer of boiling steel is crystallized under the condition of violent stirring of liquid steel caused by boiling, so the surface layer is pure and dense, the surface quality is good, and has good plasticity and stamping performance.
There is no large centralized shrinkage cavity, less head cutting, high yield, simple production process of boiling steel, less ferroalloy consumption and low steel cost.
Boiling steel plate is widely used to manufacture all kinds of stamping parts, architectural and engineering structures and some less important machine structure parts.
However, there are many impurities in the core of boiling steel, serious segregation, non compact structure and uneven mechanical properties.
At the same time, due to the high gas content in the steel, the toughness is low, the cold brittleness and aging sensitivity are large, and the welding performance is also poor.
Therefore, boiling steel plate is not suitable for manufacturing welded structures and other important structures that bear impact load and work at low temperature.
2. Killed steel plate is a hot rolled steel plate made of ordinary carbon structural steel killed steel.
Killed steel is a steel with complete deoxidation.
The molten steel is fully deoxidized with ferromanganese, ferrosilicon and aluminum before pouring.
The oxygen content of the molten steel is low (generally 0.002-0.003%), and the molten steel is relatively calm in the ingot mold without boiling. Therefore, killed steel is named.
Under normal operating conditions, there are no bubbles in the killed steel, and the microstructure is uniform and dense;
Due to the low oxygen content, there are less oxide inclusions in the steel, the purity is high, and the tendency of cold embrittlement and aging is small;
At the same time, the segregation of killed steel is small, the performance is relatively uniform and the quality is high.
The disadvantages of killed steel are concentrated shrinkage, low yield and high price.
Therefore, killed steel is mainly used for components bearing impact at low temperature, welded structures and other components requiring high strength.
Low alloy steel plates are both killed and semi killed steel plates.
Due to its high strength and superior performance, it can save a lot of steel and reduce the weight of the structure. Its application has been more and more widely.
6. High quality carbon structural steel plate
High quality carbon structural steel is a carbon steel with carbon content less than 0.8%.
This steel contains less sulfur, phosphorus and non-metallic inclusions than carbon structural steel, and has excellent mechanical properties.
High quality carbon structural steel can be divided into three categories according to different carbon content: low carbon steel (C ≤ 0.25%), medium carbon steel (C = 0.25-0.6%) and high carbon steel (c > 0.6%).
High quality steels with manganese content of 1% – 0.0% and normal manganese content of 20.0% have better mechanical properties.
1. Hot rolled high quality carbon structural steel sheet and strip
High quality carbon structural steel hot-rolled steel sheets and strips are used in automobile, aviation industry and other departments.
Its steel grades are boiling steel: 08F, 10F, 15F;
Killed steel: 08, 08Al, 10, 15, 20, 25, 30, 35, 40, 45, 50. 25 and below are low carbon steel plates, and 30 and above are medium carbon steel plates.
2. High quality carbon structural steel hot rolled thick steel plate and wide steel strip
High quality carbon structural steel hot rolled thick steel plate and wide steel strip are used for various mechanical structural parts.
The grade of steel is low carbon steel, including 05F, 08F, 08, 10F, 10, 15F, 15, 20F, 20, 25, 20Mn, 25Mn, etc;
Medium carbon steel includes: 30, 35, 40, 45, 50, 55, 60, 30mn, 40Mn, 50Mn, 60Mn, etc;
High carbon steel includes: 65, 70, 65Mn, etc.
7. Special structural steel plate
1. Steel plate for pressure vessel: it is indicated by capital R at the end of the brand, and its brand can be expressed by yield point or carbon content or alloy element.
For example, Q345R and Q345 are yield points.
For another example, 20R, 16MnR, 15MnVR, 15MnVNR, 8MnMoNbR, MnNiMoNbR, 15CrMoR, etc. are expressed by carbon content or alloy elements.
2. Steel plate for welded gas cylinder: it is indicated by capital HP at the end of the brand, and its brand can be indicated by yield point, such as Q295HP and Q345HP;
It can also be expressed by alloying elements, such as 16MnREHP.
3. Steel plate for boiler: represented by lowercase g at the end of the brand.
Its brand can be expressed by yield point, such as Q390g;
It can also be expressed by carbon content or alloy elements, such as 20g, 22Mng, 15CrMoG, 16Mng, 19Mng, 13MnNiCrMoNbg, 12Cr1MoVG, etc.
4. Steel plate for bridge: represented by lowercase Q at the end of the brand, such as Q420q, 16Mnq, 14MnNbq, etc.
5. Steel plate for automobile girder: represented by capital l at the end of the brand, such as 09MnREL, 06til, 08til, 10TiL, 09SiVL, 16MnL, 16MnREL, etc.
8. Color coated steel plate
Color coated steel plate and strip are products based on metal strip and coated with various organic coatings on its surface.
They are used in the fields of construction, household appliances, steel furniture, transportation and so on.
The classification and code of steel plates and strips are as follows:
| Classification method | Types | Code |
| By purpose | External use of building | JW |
| Internal use of building | JN | |
| Household Electric Appliances | JD | |
| By surface state | Coated plate | TC |
| Printing board | YH | |
| matrix for embossing | YaH | |
| By coating type | External polyester | WZ |
| Internal polyester | NZ | |
| Silicon modified polyester | GZ | |
| Acrylic acid for external use | WB | |
| Acrylic acid for internal use | NB | |
| Plastisol | SJ | |
| Organic sol | YJ | |
| By base material category | Cold rolled low carbon steel strip | DL |
| Small zinc flower flat steel strip | XP | |
| Large zinc flower flat steel strip | DP | |
| Zinc iron alloy steel strip | XT | |
| Electro galvanized steel strip | DX |
9. Structural steel for hull
Shipbuilding steel generally refers to the steel used for hull structure.
It refers to the steel used for manufacturing hull structure produced according to the construction specifications of classification society.
It is often used for ordering, production scheduling and sales of special steel.
A ship includes ship plate, section steel, etc.
At present, several major iron and steel enterprises in China have production, and can produce marine steel with different national specifications according to the needs of users, such as the United States, Norway, Japan, Germany, France, etc. the specifications are as follows:
| Nationality | Standard |
| China | CCS |
| U.S.A | ABS |
| Germany | GL |
| France | BV |
| Norway | DNV |
| Japan | KDK |
| Britain | LR |
（1） Variety specification
According to the minimum yield point, the strength grade of structural steel for hull is divided into general strength structural steel and high strength structural steel.
The general strength structural steel according to the rules and standards of China Classification Society is divided into four quality grades: A, B, D and E;
The high-strength structural steel according to the rules and standards of China Classification Society has three strength levels and four quality levels:
| A32 | A36 | A40 |
| D32 | D36 | D40 |
| E32 | E36 | E40 |
| F32 | F36 | F40 |
（2） Mechanical properties and chemical composition
Mechanical properties and chemical composition of general strength hull structural steel
| Steel grade | yield point | tensile strength | elongationσ | C | Mn | Si | S | P |
| σ(MPa) not less than | σb(MPa) | % Not less than | ||||||
| A | 235 | 400-520 | 22 | ≤0.21 | ≥2.5 | ≤0.5 | ≤0.035 | ≤0.035 |
| B | ≤0.21 | ≥0.80 | ≤0.35 | |||||
| D | ≤0.21 | ≥0.60 | ≤0.35 | |||||
| E | ≤0.18 | ≥0.70 | ≤0.35 |
Mechanical properties and chemical composition of high strength hull structural steel
| Steel grade | yield point | tensile strengthσb(MPa) | elongationσ% | C | Mn | Si | S | P |
| σ(MPa)not less than | Not less than | |||||||
| A32 | 315 | 440-570 | 22 | ≤0.18 | ≥0.9-1.60 | ≤0.50 | ≤0.035 | ≤0.035 |
| D32 | ||||||||
| E32 | ||||||||
| F32 | ≤0.16 | ≤0.025 | ≤0.025 | |||||
| A36 | 355 | 490-630 | 21 | ≤0.18 | ≤0.035 | ≤0.035 | ||
| D36 | ||||||||
| E36 | ||||||||
| F36 | ≤0.16 | ≤0.025 | ≤0.025 | |||||
| A40 | 390 | 510-660 | 20 | ≤0.18 | ≤0.035 | ≤0.035 | ||
| D40 | ||||||||
| E40 | ||||||||
| F40 | ≤0.16 | ≤0.025 | ≤0.025 |
（3） Precautions for delivery and acceptance of marine steel:
1. Review of quality certificate:
The steel factory must deliver the goods according to the user’s requirements and the specifications agreed in the contract, and provide the original quality certificate.
The certificate must contain the following contents:
(1) Specification requirements;
(2) Quality record number and certificate number;
(3) Furnace batch number and technical grade;
(4) Chemical composition and mechanical properties;
(5) Certificate of approval of classification society and signature of surveyor.
2. Physical examination:
For the delivery of marine steel, the physical object shall have the manufacturer’s mark, etc. Specifically:
(1) Classification society approval mark;
(2) Frame or paste marks with paint, including technical parameters, such as furnace batch number, specification and standard grade, length and width, etc;
(3) The appearance is smooth and smooth without defects.
10. Naming method of 1550 cold rolling product brand number of Baosteel
（1） Designation method of cold continuous rolling steel strip for stamping
1. General stamping steel: BLC
B — abbreviation of Baosteel;
L — low carbon;
C – Commercial
2. Aging resistant low yield steel: BLD
B – Baosteel;
L — low carbon;
D – drawing.
3. Non aging ultra deep drawing steel: BUFD (BUSD)
B – Baosteel;
U – Ultra;
F – formability;
D – drawing
4. Non aging ultra deep drawing steel: BSUFD
B – Baosteel;
Su – Ultra advanced (Ultra + super);
F – formability;
D – drawing
（2） Designation method of high strength tandem cold rolled steel strip for cold forming
B ××× × ×
B – Baosteel;
×××—— Minimum yield point value;
×—— It is generally represented by V, X, Y and Z
V: High strength low alloy, the difference between yield point and tensile strength is not specified
X: The difference between the minimum value of yield point and the minimum value of tensile strength in V is 70MPa
Y: The difference between the minimum value of yield point and the minimum value of tensile strength in V is 100MPa
Z: The difference between the minimum value of yield point and the minimum value of tensile strength in V is 140MPa
×—— Oxide / sulfide inclusion control (K: sedation and fine grain; F: K + sulfide control; O: K and F)
Example: B240ZK, B340VK
（3） Designation method of sag resistant cold continuous rolled steel strip
B ××× × ×
B — abbreviation of Baosteel
×××—— Minimum yield point value
×—— Strengthening method (P: strengthening; H: baking hardening)
×—— Represented by 1 or 2 (1: ultra low carbon; 2: low carbon)
Example: B210P1: high strength steel for deep stamping;
B250P2: phosphorus containing high strength steel for general processing;
B180H1: bake hardened steel for deep drawing.
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