Welding Training Series:
- Welding Training 101: Welding Method (1)
- Welding Training 101: Welding Materials (2)
- Welding Training 101: Welding Defects, Symbol, Deformation, Cracks, Inspection (3)
3. Welding materials
What is welding material?
The general name of the materials consumed during welding is called welding materials; such as welding rod, welding wire, metal powder, welding flux, gas, etc.
Common welding materials
3.1 Welding rod
The electrode used in arc welding, which is coated with a protective coating, is referred to as the “electrode.”
The electrode is made up of a welding core and a coating.
1. Welding core
The core of the electrode, covered by the coating, is referred to as the welding core.
The welding core serves dual purposes: as an electrode that conducts current, and as a filler metal that joins with the melted base metal to create the weld.
2. Coating
The coating is a layer applied to the surface of the welding core after the raw materials, such as ore powder, ferroalloy powder, organic matter, and chemical products, have been prepared in a specific proportion.
Coating function:
1) Mechanical Protection (Combined Gas and Slag Protection)
Gas and slag are used to shield the air and prevent contact between the molten droplets, the molten pool metal, and the air.
The solidified slag forms a protective layer over the weld surface, which helps to prevent oxidation and nitriding of the high-temperature weld metal.
2) Metallurgical Treatment (Deoxidation, Dephosphorization, Desulfurization, Alloying)
This process removes harmful elements and adds alloying elements.
3) Improving Welding Process Performance (Arc Stabilization)
The electric arc ignites easily and burns steadily, resulting in less spatter, a better-looking weld shape, and slag that is easy to remove. This process is suitable for all welding positions.
Composition of coating:
| Name | Effect | Common raw materials |
| Arc stabilizer | Contains materials that are easy to ionize, improving the stability of the arc | Potassium carbonate, marble, sodium silicate, feldspar, rutile, etc |
| Investigational agent | Formation of slag to protect the melter and bath | Ilmenite, rutile, marble, quartzite, mica, etc |
| Gasifier | Generate gas and isolate the air to protect the welding area | Organic matter (such as starch, dextrin, sawdust, etc.) and carbonate (marble, dolomite, etc.) |
| binder | Make each component of the coating bond and bond around the core | Sodium silicate, potassium sodium silicate |
| Deoxidizer | Reduce the oxidizability of coating and slag, and remove oxygen from metal | Ferromanganese, ferrosilicon, ferrotitanium and aluminum |
| Alloying agent | The elements that compensate for the loss can obtain the necessary ingredients to make the drug skin have certain plasticity, elasticity and flow | Ferroalloy or metal powder, such as ferromanganese, ferrosilicon, ferromolybdenum, ferrotitanium, etc |
| Formant | The coating has certain plasticity, elasticity and fluidity, which is convenient for electrode pressing, and makes the surface smooth without cracking | White mud, mica, titanium dioxide, dextrin, etc |
Classification of welding rod
What are the types of welding rods?
1) Classification by slag alkalinity
a. Acid electrode
Characteristic:
(1) There are several oxide acids present in the drug skin, including FeO, SiO2, and TiO2, among others.
(2) The processability is good, and the weld formation is attractive with fine ripples.
(3) The slag exhibits strong oxidation.
(4) It works with both AC and DC power.
b. Basic electrode (low hydrogen electrode)
Characteristic:
(1) The skin of the drug contains higher levels of alkaline oxides, such as marble (CaCO3) and fluorite (CaF2).
(2) During welding, CO2 and HF are produced, which decreases the hydrogen content in the weld, earning it the nickname “low hydrogen electrode.”
(3) The weld is characterized by its high plasticity and toughness, although its processability and shape are not as good as those of the acid electrode. Typically, a DC reverse connection is used.
2) Classification according to the use of welding rods
Structural steel electrodes, heat-resistant steel electrodes, stainless steel electrodes, surfacing electrodes, low temperature steel electrodes, cast iron electrodes, nickel and nickel alloy electrodes, copper and copper alloy electrodes, aluminum and aluminum alloy electrodes, and special-purpose electrodes.
3) Classification according to chemical composition of drug skin
Titanium Oxide Electrode, Calcium Titanate Electrode, Ilmenite Electrode, Iron Oxide Electrode, Cellulose Electrode, Low Hydrogen Electrode, Graphite Electrode, and Base Electrode.
Model
The type of welding rod is determined based on the national standard for welding rods, and it is a means of expressing the primary characteristics of the reaction welding rod.
The model of welding rod includes the following meanings: type of welding rod, characteristics of welding rod (type of core metal, service temperature, chemical composition of deposited metal, tensile strength, etc.), coating type and welding power source.
Grade
Welding rod grade refers to the specific classification of welding rod products based on their intended use and performance characteristics.
The grades of welding electrodes are categorized into ten groups, including structural steel electrodes, heat-resistant steel electrodes, stainless steel electrodes, among others.
How to determine whether the welding rod used is reasonable?
To determine the appropriateness of the welding rod selection, it should be evaluated based on its technical performance indicators.
Process performance index
1) Arc stability
The arc is easy to ignite, and the degree of stable combustion (no arc break, drift, magnetic bias blow, etc.) is maintained.
2) Weld formation
Good forming means that the surface is smooth, the ripple is fine and beautiful, and the geometric shape and size of the weld are correct.
3) Adaptability of welding at various positions
All position welding adaptability – all electrodes can be used for flat welding, but some electrodes are not suitable for horizontal welding, vertical welding and overhead welding, so their all position welding performance is poor.
4) Spatter
The metal particles flying out of the droplet or molten pool during welding are called spatter.
Spatter rate = Mass of splash/(Welding rod quality before welding – welding rod quality after welding)*100%
5) Deslagging property
It refers to the difficulty of removing slag shells from the weld surface after welding.
6) Welding rod melting speed
It refers to the quality and length of the melted core in unit time when the electrode is applied; Relatively speaking, the greater the melting speed, the better.
7) Redness of electrode coating
It refers to the phenomenon that when the electrode is used in the second half, the coating becomes red, cracked or falls off due to the high temperature of the coating.
8) Welding fume
Selection principle of welding rod
a. The Equal Strength Principle states that the tensile strength of the metal deposited from the chosen electrode should be equal to or similar to that of the base metal being welded.
b. The Equal Toughness Principle states that the toughness of the metal deposited from the chosen electrode should be equal to or similar to that of the base metal being welded.
c. The Equal Composition Principle states that the chemical composition of the metal deposited from the chosen electrode should conform to or be close to that of the base metal.
Use and storage of welding rod
1. Drying of welding rod
The welding rod is prone to absorbing moisture from the atmosphere, which can negatively impact its performance and the quality of the weld.
Therefore, it is important to dry the welding rod (especially alkaline welding rods) prior to use.
Typically, the drying temperature for an acid electrode is between 75-150°C, and it should be kept at this temperature for 1-2 hours.
For an alkaline electrode, the drying temperature should be between 350-400°C, and it should be kept at this temperature for 1-2 hours.
It is important to note that the cumulative drying time of the welding rods should not exceed 3.
2. Storage of welding rods
1) Welding rods should be organized and stored by type, model, and specifications to prevent confusion.
2) The storage area should be well-ventilated and kept dry.
3) Low hydrogen electrodes, which are essential for critical welding structures, should be stored in a dedicated warehouse with a temperature above 5°C and relative humidity no higher than 60%.
4) To protect against moisture damage, the welding rods should be placed on a wooden rack with a minimum distance of 0.3 meters from the ground and walls.
3.2 Welding wire
The welding field has seen continuous advancements in technology, leading to an increase in mechanization and automation. This has resulted in higher production efficiency, improved welding quality, and better working conditions.
To further advance the mechanization and automation of welding, welding wires are utilized as the welding material.
What are welding wires referred to as in terms of welding materials?
The wire used as filler metal or for conducting electricity during welding is called welding wire.
Classification of welding wires
a. Classification according to manufacturing method and welding wire shape
It can be divided into solid wire and flux cored wire.
b. Classification according to the applicable welding method
It can be divided into submerged arc welding wire, gas shielded welding wire, electroslag welding wire, surfacing welding wire and gas welding wire.
c. Classification according to the properties of the metal materials to be welded
It can be divided into carbon steel welding wire, low alloy steel welding wire, stainless steel welding wire, nickel base alloy welding wire, cast iron welding wire and special alloy welding wire.
d. Classified by copper plating or not
Copper plated wire and non copper plated wire.
1. What kind of welding wire is called solid welding wire?
The wire is directly drawn to the target wire diameter. The welding wire without powder is called solid welding wire.
1.1 Production process of solid welding wire
1.2 Model of solid welding wire
1.3 Brand of solid welding wire
2. What kind of welding wire is flux cored?
The thin steel strip is rolled into different sectional shapes, filled with powder, and then drawn into a kind of welding wire called flux cored wire.
The filled powder is called the core, and its effect is similar to that of the electrode coating.
2.1 Model of flux cored wire
2.2 Brand of flux cored wire
According to the wire structure, flux cored wire can be divided into: seam and seamless.
Seamless flux cored wire can be copper plated, with good performance and low cost, which has become the development direction in the future.
2.3 Production process of flux cored wire
For the production of seam flux cored wire, the “steel strip method” is commonly used;
For the production of seamless flux cored wire, the “steel pipe method” is commonly used.
a. Steel strip method
b. Steel tube method
3. Advantages and disadvantages of flux cored wire (compared with solid wire)
Advantages:
Small spatter, fast deposition speed, and high production efficiency.
Welding of various steels with strong adaptability.
Good process performance and a beautiful weld formation.
A large welding current can be used for welding in all positions.
Disadvantages:
The manufacturing process of welding wire is intricate and expensive.
The surface of the welding wire is prone to rusting and the powder is susceptible to moisture absorption.
Wire feeding during the welding process is more challenging compared to using solid wire, resulting in a large amount of smoke.
3.3 Flux
This picture depicts the process of submerged arc welding.
Do you notice the “sand” on top?
It is an essential welding material, known as the flux, in the submerged arc welding process.
What is flux?
Flux is a granular material that melts to form slag and gas during welding and plays a protective and metallurgical role in molten metal.
Effect:
1) Protect the molten pool metal;
2) Add alloy elements to the molten pool.
Classification of flux
(1) Classification by Use
It can be categorized into three types: Submerged Arc Welding Flux, Electroslag Welding Flux, and Surfacing Flux.
(2) Classification by Manufacturing Method
It can be divided into two categories: Smelting Flux and Non-Smelting Flux.
(3) Classification by Slag Alkalinity
It can be classified into three categories: Acid Flux, Neutral Flux, and Basic Flux.
a. Melting flux
The flux is created by melting various ingredients in a precise proportion in a furnace. The mixture is then granulated, dried, and screened while being cooled with water.
Characteristic:
1) It is not difficult to absorb moisture and typically does not require drying prior to use.
2) The flux that has not melted can be utilized again.
3) After being melted, it is cooled quickly, often taking the form of glass.
4) Only a limited amount of alloy elements can be added to the flux in the molten pool, as a large quantity cannot be transferred.
Melting flux
Main components:
- SiO2：40~44%;
- MnO：32~38%;
- CaF2：3~7%;
- CaO：≤8%.
b. Unmelted flux
The non-melting flux is obtained by mixing various powders according to a specific formula, adding a binder to form particles of a specific size, and then baking or sintering.
Bonding flux is a type of flux that is baked at low temperatures (below 400 ℃).
Sintered flux, on the other hand, is produced by sintering the flux at high temperatures (700 to 1000 ℃).
Characteristic:
1) The moisture absorption is relatively high, and it must be re-dried before use.
2) Easy to manufacture and highly applicable.
Sintered flux
Essential component（SJ101）:SJ102
- SiO2+TiO2:20~30% , 10~15%
- CaO+MgO:25~35%, 35~45%
- Al2O3+MnO:20~30%, 15~25%
- CaF2:15~25%, 20~30%
Classification according to slag alkalinity:
(1) Acid flux (alkalinity B<1.0)
The slag is primarily composed of acid oxides and has excellent welding performance, resulting in a visually appealing weld formation. However, the weld metal has a high oxygen content, which results in low low-temperature impact toughness.
(2) Neutral flux (alkalinity 1.0 ～ 1.5)
The composition of the deposited metal is similar to that of the welding wire, with a reduced oxygen content in the weld metal.
(3) Alkaline flux (alkalinity B>1.5)
The primary components of slag are alkaline oxides and calcium fluoride. The weld metal is characterized by a low oxygen content, high impact toughness, and good tensile properties.
3.4 Solder
In modern, cutting-edge scientific and technological projects, such as aircraft plate fin radiators, rocket shells, engine nozzles, and others, they all require high precision and sharpness and cannot tolerate any defects. Almost all products must be of impeccable quality.
Brazing technology is widely used in these fields due to its advantages of low thermal impact, high precision, wide applicability, and high welding efficiency. It allows for the connection of multiple, complex, high-precision parts.
The brazing filler metal plays a crucial role in the brazing process.
In order to realize the combination of two materials (or parts), the filler added in or beside the gap is called filler metal.
1. What are the requirements for filler metal?
(1) A melting point that is appropriate (several tens of degrees lower than the base metal);
(2) Excellent wettability;
(3) Completely dissolved and integrated with the base metal;
(4) A uniform and stable composition;
(5) It is cost-effective and safe (containing fewer precious metals and toxic metals).
2. Classification of filler metals
1) Classification by melting point
“Soft solder” (also known as “fusible solder”) refers to solders with melting points lower than 450°C, including tin-lead solder, cadmium-silver solder, and lead-silver solder, among others.
“Brazing filler metal” (also referred to as “refractory filler metal”) refers to brazing fillers with melting points higher than 450°C, including aluminum-based, copper-based, silver-based, and nickel-based brazing fillers, among others.
2) Classification by main chemical components
According to the main metal elements of solder, it is called × base solder, such as brazing base solder, zinc base solder, etc.
3) Sort by shape
It can be divided into wire, rod, sheet, foil, powder or solder with special shape (such as annular solder or paste solder).
3. Application of filler metal
(1) Soft solder
It is primarily used for welding workpieces with low stress and low operating temperatures, such as connecting various electrical wires and soldering instruments, components of instruments, and other electronic circuits.
(2) Brazing filler metal
It is mainly used to weld workpieces with large force and high working temperature, such as bicycle frame, carbide cutter, drilling bit and other mechanical parts.
3.5 Flux
In order to obtain a better welding joint, it is necessary to reasonably match the brazing flux according to the different brazing filler metals to jointly use as the welding materials in the brazing process.
1. What is flux?
The flux used in brazing is called brazing flux, including paste, powder, etc.
2. What is the function of flux?
1) Remove the oxide layers from the surface of the solder and base metal.
2) Enhance the ability of the liquid solder to wet the weldments.
3) Prevent the weldment and liquid solder from being oxidized during the brazing process.
3. Requirements for flux
1) Ensure that there is enough capability to eliminate oxides from the surface of the base metal and filler metal.
2) The brazing flux’s melting point and minimum active temperature should be lower than the melting point of the brazing filler metal.
3) Ensure adequate wetting ability at the brazing temperature.
4) The volatiles in the flux should be non-toxic.
5) The flux and its residue should have minimal corrosion to the solder and base metal and should be easily removable.
4. Classification of flux
1) Soft Soldering Flux
The soldering flux used for brazing at temperatures below 450 ℃ can be divided into two types: inorganic and organic.
a. Inorganic Soft Solder (Corrosive Soft Solder) – It is composed of inorganic salts and acids and has strong chemical activity and thermal stability. This type of solder promotes the wetting of liquid solder to the base metal effectively, but its residue has a strong corrosive effect.
b. Organic Soldering Flux (Non-Corrosive Soldering Flux) – Its chemical activity is relatively weak and does not corrode the base metal. Examples of non-corrosive soldering fluxes include rosin, amine, and organic halides.
2) Brazing Flux
The flux used for brazing at temperatures above 450 ℃ has a high viscosity and requires high temperature activation.
It must be used at temperatures above 800 ℃, and its residue is difficult to remove.
Common brazing fluxes include borax, boric acid, and their mixtures. Adding fluoride and chloride of alkali and alkaline earth metals to borides can improve the wettability of borax and boric acid brazing fluxes, enhance oxide removal, and lower the melting and activation temperature of the brazing fluxes.
3.6 Gas
Welding gas primarily refers to the protective gas utilized in gas shielded welding processes, such as CO2 gas shielded welding and inert gas shielded welding, as well as the gas used in gas welding and cutting.
When welding, the shielding gas serves not only as a protective medium for the welding area, but also as the gas medium that generates the arc.
Gas welding and cutting are typically performed using a high-temperature flame generated from the combustion of gas, which provides a concentrated source of heat.
1. Common shielding gas
| Emotional gas | Molecular gas | Compound gas |
| Argon, ammonia | Oxygen, nitrogen, hydrogen | carbon dioxide |
2. Common gas for gas welding and cutting
That is, combustion supporting gas (O2) and combustible gas (acetylene C2H2).
3. Characteristics and uses of common welding gases
| Gas | Symbol | Main properties | Application in welding |
| carbon dioxide | CO2 | It has stable chemical property, does not burn or support combustion, can be decomposed into C0 and 0 at high temperature, and has certain oxidizability to metals. It can liquefy liquid CO2, absorb a lot of heat when evaporating, and solidify into solid CO2, commonly known as dry ice | Welding wire can be used as shielding gas during welding, such as CO2 gas shielded welding and C02+O2, C02+A and other mixed gas shielded welding |
| argon | Ar | Emotional gas, not active in chemical property, does not react with other elements at room temperature and high temperature | As a protective gas for mechanical protection during arc welding, plasma welding and cutting |
| oxygen | O2 | Colorless gas, combustion supporting, very active under high temperature, directly combined with various elements. During welding, oxygen will oxidize metal elements when it enters the molten pool, which will play a harmful role | It can obtain extremely high temperature when mixed with combustible gas for welding and cutting, such as oxygen acetylene flame and hydrogen oxygen flame. Mix with argon, carbon dioxide, etc. in proportion, and conduct mixed gas shielded welding |
| B fast | CH2 | Commonly known as calcium carbide gas, it is less soluble in water, soluble in alcohol, and largely soluble in acetone. It mixes with air and oxygen to form an explosive gas mixture. It burns in oxygen and emits high temperature and strong light | For oxyacetylene flame welding and cutting |
| hydrogen | H2 | It can burn, is not active at normal temperature, and is very active at high temperature. It can be used as a reducing agent for metal ores and metal oxides. It can be melted in liquid metal during welding and precipitated when cooling, which is easy to form pores | When welding, it can be used as a reducing shielding gas, mixed with oxygen for combustion, and can be used as a heat source for gas welding |
| nitrogen | N2 | The chemical property is not active, and it can be directly combined with hydrogen and oxygen at high temperature. It is harmful to enter the molten pool during welding. It does not react with copper basically and can be used as protective gas | During nitrogen arc welding, nitrogen is used as the shielding gas to weld copper and stainless steel. Nitrogen is also commonly used in plasma arc cutting as the outer protective gas |
| Gas | component | Arc column potential gradient | Arc stability | Metal transition characteristics | Chemical properties | Weld penetration shape | Heating characteristics |
| CO2 | 99.9% purity | high | satisfied | Satisfied, but some splashes | Strong oxidation | Flat shape with large penetration | – |
| Ar | Purity 99.995% | low | good | satisfied | – | Mushroom shape | – |
| He | 99.99% purity | high | satisfied | satisfied | – | Flat | The heat input of butt weldment is higher than that of pure Ar |
| N2 | 99.9% purity | high | difference | difference | Produce porosity and nitride in steel | Flat | – |
4. Application of mixed gas in welding
1）Ar + He
It can enhance weld penetration, decrease porosity, and enhance production efficiency.
It can be used on copper, aluminum, and their alloys, as well as titanium, zirconium, and other metals.
2）Ar + H2
The addition of hydrogen can raise the arc temperature, increase the heat input to the base metal, and reduce the formation of CO porosity.
The blended gas is a reducing agent and is ideal for welding nickel and its alloys, as well as stainless steel pipes.
3）Ar + N2
To enhance the arc temperature, you should add N2. A slight addition of N2 can enhance the arc rigidity and enhance the weld formation.
This technique is suitable for welding non-ferrous metals, such as copper and aluminum.
4）Ar + O2
The oxygen content in Ar+O2 (low content) is in the range of 1-5%, which enhances the wettability of the solution, minimizes porosity, and stabilizes the arc. This method is suitable for welding stainless steel, including low carbon steel and low alloy steel.
Ar+O2 (high content) has an oxygen content of approximately 20%, which increases production efficiency, reduces porosity, and enhances the impact toughness of welds. This method is appropriate for welding carbon steel and low alloy structural steel.
5）Ar + CO2
Stable arc, minimal spatter, simple to attain axial spray transfer, optimal weld formation, and a broad range of applications (suitable for both spray transfer and short circuit transfer).
6）Ar + CO2 + O2
It has been confirmed that the optimal gas mixture for welding low carbon and low alloy steel is 80% Argon, 15% Carbon Dioxide, and 5% Oxygen. This mixture provides excellent results in terms of weld formation, joint quality, metal transfer, and arc stability, and is highly satisfactory.
7）CO2 + O2
High deposition rate, deep penetration, low hydrogen content in the weld metal, strong welding with high current specifications, stable arc, and minimal spatter.
