Welding Training 101: Welding Materials (2)

Welding Training Series:

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

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The melting electrode coated with coating for arc welding is called electrode;

The electrode is composed of welding core and coating (coating).

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1. Welding core

The metal core covered by the coating in the electrode is called the welding core.

The welding core is both an electrode (conducting current) and a filler metal (combining with the melted base metal to form a weld).

2. Coating

The coating is a layer of coating on the surface of the welding core after the raw materials such as ore powder, ferroalloy powder, organic matter and chemical products are prepared in a certain proportion.

Coating function:

1) Mechanical protection (combined gas and slag protection)

Gas and slag are generated to isolate air and prevent contact between molten droplets and molten pool metal and air;

The solidified slag shell is covered on the weld surface, which can prevent the high-temperature weld metal from being oxidized and nitrided;

2) Metallurgical treatment (deoxidation, dephosphorization, desulfurization, alloying)

Remove harmful elements and supplement alloy elements.

3) Improve welding process performance (arc stabilization)

The electric arc is easy to ignite, the combustion is stable, the spatter is small, the weld shape is beautiful, the slag is easy to fall off, and it is suitable for all position welding.

Composition of coating:

NameEffectCommon raw materials
Arc stabilizerContains materials that are easy to ionize, improving the stability of the arcPotassium carbonate, marble, sodium silicate, feldspar, rutile, etc
Investigational agentFormation of slag to protect the melter and bathIlmenite, rutile, marble, quartzite, mica, etc
GasifierGenerate gas and isolate the air to protect the welding areaOrganic matter (such as starch, dextrin, sawdust, etc.) and carbonate (marble, dolomite, etc.)
binderMake each component of the coating bond and bond around the coreSodium silicate, potassium sodium silicate
DeoxidizerReduce the oxidizability of coating and slag, and remove oxygen from metalFerromanganese, ferrosilicon, ferrotitanium and aluminum
Alloying agentThe elements that compensate for the loss can obtain the necessary ingredients to make the drug skin have certain plasticity, elasticity and flowFerroalloy 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 crackingWhite 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 many acid oxides in the drug skin, such as FeO, SiO2, TiO2, etc;

(2) Good processability, beautiful weld formation, and fine ripples;

(3) The oxidation of slag is strong;

(4) Both AC and DC.

b. Basic electrode (low hydrogen electrode)

Characteristic:

(1) The drug skin contains more alkaline oxides. Such as marble (CaCO3) and fluorite (CaF2);

(2) CO2 and HF are produced during welding, which reduces the hydrogen content of the weld, so it is also called low hydrogen electrode;

(3) The weld has high plasticity and toughness, and its processability and shape are not as good as those of acid electrode. Generally, DC reverse connection is adopted.

2) Classification according to the use of welding rods

Structural steel electrode, heat-resistant steel electrode, stainless steel electrode, surfacing electrode, low temperature steel electrode, cast iron electrode, nickel and nickel alloy electrode, copper and copper alloy electrode, aluminum and aluminum alloy electrode, and special purpose electrode.

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 based on the national standard of welding rod, and it is a representation method of main characteristics of 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.

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Grade

Welding rod grade is a specific name for welding rod products according to its main use and performance characteristics.

The grades of welding electrodes are divided into ten categories, such as structural steel electrodes, heat-resistant steel electrodes, stainless steel electrodes, etc.

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How to determine whether the welding rod used is reasonable?

How to judge whether the selection of welding rod is reasonable or not, it needs to be measured according to the technical performance indicators of the welding rod.

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.

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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. Equal strength principle refers to that the tensile strength of the deposited metal of the selected electrode is equal to or similar to that of the base metal to be welded.

b. Equal toughness principle refers to that the toughness of the deposited metal of the selected electrode is equal to or similar to that of the base metal to be welded.

c. Equal composition principle refers to that the chemical composition of the deposited metal of the selected electrode conforms to or is close to the base metal.

Use and storage of welding rod

1. Drying of welding rod

The welding rod is easy to absorb moisture from the air, which will affect the process performance and weld quality.

Therefore, the welding rod (especially alkaline welding rod) must be dried before use.

Generally, the drying temperature of acid electrode is 75~150 ℃, and the heat preservation is 1~2h;

Alkaline electrode is 350~400 ℃, and the heat preservation is 1~2h.

The accumulative drying times of welding rods shall not exceed 3.

2. Storage of welding rods

1) Welding rods must be stored by category, model and specification to avoid confusion.

2) It must be stored in a well ventilated and dry warehouse.

Electrodes used for important welding structures, especially low hydrogen electrodes, should preferably be stored in a special warehouse, with a temperature of more than 5 ℃ and a relative humidity of no more than 60%.

3) The welding rod must be placed on a wooden frame with a distance of more than 0.3m from the ground and the wall to prevent deterioration due to moisture.

3.2 Welding wire

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Nowadays, with the progress of welding technology, in the welding field, the continuous development towards mechanization and automation can not only achieve higher production efficiency and better welding quality, but also greatly improve the production and labor conditions.

In order to better realize the mechanization and automation of welding, welding wires are used as welding materials.

What welding materials are called welding wires?

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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.

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1.1 Production process of solid welding wire

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1.2 Model of solid welding wire

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1.3 Brand of solid welding wire

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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.

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2.1 Model of flux cored wire

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2.2 Brand of flux cored wire

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According to the wire structure, flux cored wire can be divided into: seam and seamless.

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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

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b. Steel tube method

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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 beautiful weld formation;

Large welding current can be used for all position welding.

Disadvantages:

The welding wire manufacturing process is complex and the cost is high;

The surface of welding wire is easy to rust, and the powder is easy to absorb moisture;

When welding, wire feeding is more difficult than solid wire, and the smoke is large.

3.3 Flux

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Seeing this picture, we must know that this is the welding process of submerged arc welding.

I want to ask you, do you see the “sand” above?

It is an indispensable welding material — flux in submerged arc welding process.

What is flux?

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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 divided into submerged arc welding flux, electroslag welding flux and surfacing flux;

(2) Classification by manufacturing method

It can be divided into smelting flux and non smelting flux.

(3) Classification by slag alkalinity

It can be divided into acid flux, neutral flux and basic flux.

a. Melting flux

The flux is made by melting various ingredients in a certain proportion in the furnace, granulating, drying and screening with water cooling.

Characteristic:

1) It is not easy to absorb moisture and usually does not need to be dried before use;

2) The unmelted flux can be reused;

3) After melting, it is cooled rapidly, usually in the form of glass;

4) A large amount of alloy elements cannot be added to the molten pool in the melting flux, and only a small amount can be transferred.

Melting flux

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Main components:

  • SiO2:40~44%;
  • MnO:32~38%;
  • CaF2:3~7%;    
  • CaO:≤8%.

b. Unmelted flux

The flux obtained by mixing various powders according to the formula and adding the binder to make small particles of a certain size, and baking or sintering is called non melting flux.

The flux baked at low temperature (below 400 ℃) is called bonding flux;

The flux sintered at high temperature (700~1000 ℃) is called sintered flux.

Characteristic:

1) The moisture absorption is relatively large, and it must be dried again before use;

2) Simple manufacturing and strong applicability.

Sintered flux

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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 mainly acid oxide, with good welding process performance and beautiful weld formation;

The weld metal has high oxygen content and low low-temperature impact toughness.

(2) Neutral flux (alkalinity 1.0 ~ 1.5)

The chemical composition of the deposited metal is similar to that of the welding wire, and the oxygen content of the weld metal is reduced.

(3) Alkaline flux (alkalinity B>1.5)

The slag is mainly alkaline oxide and calcium fluoride. The weld metal has low oxygen content, high impact toughness and good tensile property.

3.4 Solder

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In modern cutting-edge scientific and technological projects, such as aircraft plate fin radiator, rocket shell, engine nozzle, etc., they are all high, precise and sharp scientific and technological products, which can not tolerate any defects, and almost all products must be perfect in quality.

In this regard, because brazing technology has the advantages of small thermal impact, high precision, wide applicability, high welding efficiency, etc., it can realize the connection of multiple welds, high-precision, complex parts, and is widely used in the welding of high-tech cutting-edge fields.

In the brazing process, brazing filler metal plays a decisive role.

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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) Suitable melting point (dozens of degrees lower than the base metal);

(2) Good wettability;

(3) Fully dissolved and diffused with base metal;

(4) The composition is uniform and stable;

(5) It is economical and safe (less precious metals and toxic metals).

2. Classification of filler metals

1) Classification by melting point

Soft solder (fusible solder) — solder with melting point lower than 450 ℃, such as tin lead solder, cadmium silver solder, lead silver solder, etc;

Brazing filler metal (refractory filler metal) — brazing filler metal with melting point higher than 450 ℃, such as aluminum base, copper base, silver base, nickel base brazing filler metal, etc.

 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 mainly used to weld workpieces with low stress and low working temperature, such as the connection of various electrical wires and the soldering of instruments and instrument components 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

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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.

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2. What is the function of flux?

1) Remove the oxides on the surface of solder and base metal;

2) Improve the wettability of liquid solder to weldments;

3) Protect the weldment and liquid solder from oxidation during brazing.

3. Requirements for flux

1) Have sufficient ability to remove oxides on the surface of base metal and filler metal;

2) The melting point and minimum active temperature of the brazing flux shall be lower than the melting point of the brazing filler metal;

3) Sufficient wettability at brazing temperature;

4) The volatiles of the flux shall be non-toxic;

5) The corrosion of the flux and its residue to the solder and base metal shall be small and easy to remove.

4. Classification of flux

1) Soft soldering flux

The soldering flux used for brazing below 450 ℃, which can be divided into inorganic soft soldering flux and organic soft soldering flux.

a. Inorganic soft solder (corrosive soft solder) – The component is inorganic salt and inorganic acid, which has strong chemical activity and good thermal stability, and can significantly promote the wetting of liquid solder to the base metal, but the residue of this solder has a strong corrosion effect.

b. Organic soldering flux (non corrosive soldering flux) – its chemical activity is relatively weak, and it has almost no corrosion effect on the base metal. Such as rosin, amine, organic halide, etc. are non corrosive soldering fluxes.

2) Brazing flux

The flux used for brazing above 450 ℃ has high viscosity and high activity temperature.

It must be used above 800 ℃, and the flux residue is difficult to remove.

The commonly used brazing fluxes are borax, boric acid and their mixtures.

Adding fluoride and chloride of alkali metal and alkaline earth metal in boride can improve the wettability of borax and boric acid brazing fluxes, improve the ability to remove oxides, and reduce the melting temperature and active temperature of brazing fluxes.

3.6 Gas

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Welding gas mainly refers to the protective gas used in gas shielded welding (CO2 gas shielded welding, inert gas shielded welding) and the gas used in gas welding and cutting.

When welding, the shielding gas is not only the protective medium of the welding area, but also the gas medium for generating the arc;

Gas welding and cutting are mainly completed by high temperature flame with concentrated heat generated during gas combustion.

1. Common shielding gas

Emotional gasMolecular gasCompound gas
Argon, ammoniaOxygen, nitrogen, hydrogencarbon 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

GasSymbolMain propertiesApplication in welding
carbon dioxideCO2It 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 iceWelding 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
argonArEmotional gas, not active in chemical property, does not react with other elements at room temperature and high temperatureAs a protective gas for mechanical protection during arc welding, plasma welding and cutting
oxygenO2Colorless 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 roleIt 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 fastCH2Commonly 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 lightFor oxyacetylene flame welding and cutting
hydrogenH2It 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 poresWhen 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
nitrogenN2The 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 gasDuring 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
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GascomponentArc column potential gradientArc stabilityMetal transition characteristicsChemical propertiesWeld penetration shapeHeating characteristics
CO299.9% purityhighsatisfiedSatisfied, but some splashesStrong oxidationFlat shape with large penetration
ArPurity 99.995%lowgoodsatisfiedMushroom shape
He99.99% purityhighsatisfiedsatisfiedFlatThe heat input of butt weldment is higher than that of pure Ar
N299.9% purityhighdifferencedifferenceProduce porosity and nitride in steelFlat

4. Application of mixed gas in welding

1)Ar + He

It can improve weld penetration, reduce porosity, and improve production efficiency.

It is applicable to copper, aluminum and their alloys as well as titanium, zirconium and other metals.

2)Ar + H2

The addition of hydrogen can increase the arc temperature, increase the heat input of the base metal, and inhibit CO porosity.

The mixed gas is a reducing gas, which is suitable for nickel and its alloys, as well as stainless steel pipes.

3)Ar + N2

Add N2 to increase the arc temperature. Adding a small amount of N2 can improve the arc stiffness and weld formation.

It is applicable to the welding of non-ferrous metals such as copper and aluminum.

4)Ar + O2

Ar+O2 (low content) oxygen content is 1-5%, which can improve the wettability of the solution, reduce porosity, and stabilize the arc.

It is applicable to stainless steel (including welding of low carbon steel and low alloy steel)

The oxygen content of Ar+O2 (high content) is about 20%, which can improve production efficiency, reduce porosity, and improve the impact toughness of welds.

It is applicable to carbon steel and low alloy structural steel.

5)Ar + CO2

Stable arc, small spatter, easy to obtain axial spray transfer, good weld formation, wide application range (can be used for spray transfer or short circuit transfer)

6)Ar + CO2 + O2

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It is verified that 80% Ar+15% CO2+5% O2 mixed gas is the best for welding low carbon and low alloy steel, and it is very satisfactory in terms of weld formation, joint quality, metal droplet transfer and arc stability.

7)CO2 + O2

High deposition speed, large penetration, low hydrogen content of weld metal, strong specification (large current) welding, stable arc and small spatter.

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