What is 304 stainless steel?
304 stainless steel is a common material in stainless steel, with a density of 7.93 g/cm³；
It is also called 18/8 stainless steel in the industry, which means that it contains more than 18% chromium and more than 8% nickel;
It has high temperature resistance of 800 ℃, good processing performance and high toughness, and is widely used in industry, furniture decoration industry and food and medical industry.
However, it should be noted that the content index of food grade 304 stainless steel is more strict than that of ordinary 304 stainless steel.
For example, 304 stainless steel is basically defined internationally as mainly containing 18% – 20% chromium and 8% – 10% nickel, while food grade 304 stainless steel contains 18% chromium and 8% nickel, allowing fluctuations within a certain range, and limiting the content of various heavy metals.
In other words, 304 stainless steel is not necessarily food grade 304 stainless steel.
The common marking methods in the market are 06Cr19Ni10 and SUS304, in which 06Cr19Ni10 generally refers to the production of national standard, 304 generally refers to the production of ASTM standard, and SUS 304 refers to the production of Japanese standard.
304 is a universal stainless steel, which is widely used to make equipment and parts that require good comprehensive performance (corrosion resistance and formability).
In order to maintain the inherent corrosion resistance of stainless steel, the steel must contain more than 18% chromium and more than 8% nickel.
304 stainless steel is a grade of stainless steel produced according to American ASTM standards.
Types of 304 stainless steel
304 stainless steel is an alloy composed of iron, chromium, carbon and many different elements.
Iron is the main element, and chromium is the first main alloy element.
Generally speaking, only when the chromium content accounts for at least 11% can the stainless steel be called stainless steel, because if the chromium content is insufficient, the stainless steel surface will not be able to form that dense chromium oxide protective film, and will lose the function of rust prevention [corrosion].
If the content of chromium is enough, it will not rust in normal temperature atmosphere.
Generally, it can be divided into five categories according to its metallographic structure:
1. Austenitic stainless steel
The most common 304 stainless steel is this type, and its standard composition is 18% chromium plus 8% nickel, commonly known as 18-8 stainless steel.
This type of stainless steel is non-magnetic, cannot change its metallographic structure by heat treatment, and has good workability.
Because it contains nickel, the corrosion resistance is superior to the other two types of stainless steel containing only chromium (without nickel).
The main uses of 300 series stainless steel are:
General people’s livelihood uses, such as kitchen tableware, building materials, medical and health equipment, food processing materials, transportation tools, chemical equipment and pipe fittings, mechanical equipment and parts.
In the eyes of ordinary people, the so-called stainless steel refers to 300 series stainless steel (especially 304 stainless steel).
2. Martensitic stainless steel
The representative steel type of this type of stainless steel is 410, and its chemical composition contains 13% chromium, less than 0.15% carbon and a small amount of other element alloys.
The raw materials are cheap, magnetic, and can be hardened by heat treatment to increase strength.
However, because it does not contain nickel, its corrosion resistance is inferior to that of ordinary 304 stainless steel, so it can only be used in mildly corrosive environments.
General uses include bearings, medical appliances and knives.
3. Ferritic stainless steel
The representative steel type of this type of stainless steel is 430, its standard chemical composition is 16-18% chromium, and its carbon content is low.
This kind of stainless steel has magnetism. If the stainless steel plates we see can be adsorbed by magnets, it is likely to belong to this kind of stainless steel.
The price is relatively low due to nickel free, and the typical uses include kitchen appliances, weaving nets and accessories.
4. Precipitation hardening stainless steel
AISI number is 600 series stainless steel.
In addition to chromium and nickel, this type of stainless steel also contains precipitation hardening elements such as copper, aluminum and titanium, which harden the material and increase its strength.
The typical uses of this type of stainless steel are: valves, motor shafts, petrochemical equipment, golf heads, etc.
5. Duplex stainless steel
Typical grades of this type of stainless steel are 2205, i.e. 22% chromium and 5% nickel.
This type of steel is characterized by good strength (far better than 304) and corrosion resistance, so it is commonly used in petrochemical pipelines, pressure vessels and mandrels.
304 stainless steel is mainly composed of carbon ≤ 0.08%, silicon ≤ 1.00%, manganese ≤ 2.00%, phosphorus ≤ 0.045%, sulfur 0.03%, nickel 8.0-10.5% and chromium 18-20%.
Chemical composition of 304L stainless steel
SUS304l, C ≤ 0.08, Si ≤ 1.00, Mn ≤ 2.00, P ≤ 0.05, S ≤ 0.03, Cr18.00-20.00, Ni8.25-12.50
304L stainless steel is the most widely used chromium-nickel stainless steel with good corrosion resistance, heat resistance, low-temperature strength and mechanical properties.
It is resistant to corrosion in the atmosphere.
If it is an industrial atmosphere or a heavily polluted area, it needs to be cleaned in time to avoid corrosion.
Suitable for food processing, storage and transportation.
It has good processability and weldability.
Plate heat exchanger, corrugated pipe, household products, building materials, chemistry, food industry, etc.
304L is a universal stainless steel, which is widely used to make equipment and parts that require good comprehensive performance (corrosion resistance and formability).
304L stainless steel is a brand of stainless steel produced according to American ASTM standards.
304 is equivalent to 0Cr19Ni9 (0Cr18Ni9) stainless steel in China.
304 stainless steel contains 19% chromium and 9% nickel.