Selection of solid welding wire

(1) Submerged arc welding wire

During submerged arc welding, the flux plays a protective and metallurgical role on the weld metal. The welding wire is mainly used as filler metal, while adding alloy elements to the weld and participating in the metallurgical reaction.

1) Welding wire for low carbon steel and low alloy steel The common welding wires for submerged arc welding of low carbon steel and low alloy steel are as follows.

A. Low-manganese welding wire (such as H08A): It is often used with high-manganese welding flux for welding low carbon steel and low alloy steel with low strength.

B. Medium manganese welding wire (such as H08MnA, H10MnS): mainly used for low alloy steel welding, but also used for low carbon steel welding with low manganese flux.

C. High manganese welding wire (such as H10Mn2 H08Mn2Si): used for low alloy steel welding

2) Wire for high-strength steel

This type of welding wire contains more than 1% of Mn and 0.3%~0.8% of Mo, such as H08MnMoA and H08Mn2MoA, and is used for welding low alloy high strength steel with high strength. In addition, elements such as NI, CR, V and Re can also be added to the welding wire according to the composition and performance requirements of high-strength steel to improve the weld performance. The weld metal with tensile strength of 590Mpa mostly adopts MN-MO welding wire, such as H08MNMOA, etc.

3) Welding wire for stainless steel

The composition of the welding wire used shall be basically the same as that of the stainless steel to be welded. When welding chromium stainless steel, HoCr14 H1Cr13 H1Cr17 and other welding wires shall be used; When welding chromium-nickel stainless steel, H0Cr19Ni9 HoCr19Ni9 HoCr19Ni9Ti and other welding wires shall be used; When welding ultra-low carbon stainless steel, the corresponding ultra-low carbon welding wire should be used, such as HOOCr19Ni9, etc. The flux can be melted or sintered, and the oxidizability of the flux should be small to reduce the burning loss of alloy elements. At present, sintered flux is mainly used to weld stainless steel in foreign countries, while melting flux is still the main method in China, but sintered flux is being developed and popularized.

 

(2) Welding wire for gas shielded welding

Gas shielded welding includes inert gas shielded welding (TIG welding and MIG welding), active gas shielded welding (MAG welding) and self-shielded welding. Pure Ar is used for TIG welding, and Ar+2% O2 or Ar+5% CO2 is generally used for MIG welding. CO2 gas is mainly used in MAG welding. In order to improve the process performance of CO2 welding, CO2+Ar or CO2+Ar+O2 mixed gas or flux-cored wire can also be used.

1) TIG welding wire

TIG welding sometimes does not add filler wire, which is directly connected after being heated and melted by the welding base metal, and sometimes adds filler wire. Because the shielding gas is pure Ar and non-oxidizing, the composition of the welding wire will not change after melting, so the composition of the welding wire is the weld composition. Some also use the base metal composition as the welding wire composition to make the weld composition consistent with the base metal. TIG welding has low welding energy, good weld strength, plasticity and toughness, and is easy to meet the performance requirements.

2) MIG and MAG welding wires

MIG method is mainly used for welding high alloy steel such as stainless steel. In order to improve the arc characteristics, add appropriate amount of O2 or CO2 gas into Ar gas, which is the MAG method. When welding alloy steel, Ar+5% CO2 can improve the blowhole resistance of the weld. However, Ar+5% CO2 mixed gas can not be used when welding ultra-low carbon stainless steel, only Ar+2% O2 mixed gas can be used to prevent weld carburization. At present, MIG welding of low alloy steel is gradually replaced by MAG welding of Ar+20% CO2. Due to the oxidation of the shielding gas during MAG welding, the content of deoxidizing elements such as Si and Mn in the welding wire should be appropriately increased. Other components can be consistent with or different from the base metal. When welding high-strength steel, the content of C in the weld is usually lower than that of the base metal, and the content of Mn should be higher than that of the base metal. This is not only for deoxidation, but also the requirement of the weld alloy composition. In order to improve low-temperature toughness, the content of Si in the weld should not be too high,

3) CO2 welding wire

CO2 is an active gas with strong oxidizability, so the welding wire used for CO2 welding must contain high deoxidizing elements such as Mn and Si. CO2 welding usually adopts C-Mn-Si welding wires, such as H08MnSiA, H08Mn2SiA, H04Mn2SiA, etc. The diameter of CO2 welding wire is generally 0.89 1.0 1.2 1.6 2.0 mm. Welding wire diameter ≤ 1.2mm belongs to fine wire CO2 welding, and welding wire diameter ≥ 1.6mm belongs to thick wire CO2 welding.

H08Mn2SiA welding wire is a widely used CO2 welding wire. It has good process performance and is suitable for welding low alloy steel below 500Mpa.

 

(3) Electroslag welding wire

Electroslag welding is suitable for medium plate and thick plate welding. The electroslag welding wire mainly plays the role of filler metal and alloying.

 

(4) Non-ferrous metal and cast iron welding wire

The first two letters of the trademark "HS" indicate nonferrous metal and cast iron welding wires; The first digit in the brand name represents the learned composition type of welding wire, and the second and third digits in the brand name represent different brands of the same type of welding wire.

1) Surfacing wire

At present, there are two main types of cemented carbide welding wires for surfacing: high-chromium alloy cast iron (Solmayte) and cobalt-based (Stellite) alloy. High chromium alloy cast iron has good oxidation resistance and cavitation resistance, high hardness and good wear resistance. Cobalt-based alloys can also maintain high hardness and good corrosion resistance at 650 ℃. The toughness of low carbon and low tungsten is good; High carbon and high tungsten have high hardness, but poor impact resistance.

The hardmetal surfacing welding wire can be overlayed by oxygen-acetylene, gas-electric welding and other methods. Although the production efficiency of oxygen-acetylene surfacing is low, the equipment is simple, the depth of penetration is shallow, the amount of base metal melting is small, and the surfacing quality is high, because it is widely used.

2) Copper and copper alloy welding wire

Copper and copper alloy welding wires are often used to weld copper and copper alloy, and brass welding wires are also widely used to braze carbon steel, cast iron and cemented carbide tools. For the welding of copper and copper alloy, various welding methods can be used, and the correct selection of filler metal is the necessary condition to obtain high-quality welds. Oxygen-acetylene gas welding shall be used together with gas welding flux.

3) Aluminum and aluminum alloy welding wire

Aluminum and aluminum alloy welding wires are used as filler materials for aluminum alloy argon arc welding and oxygen-acetylene gas welding. The selection of welding wire is mainly based on the requirements of the type of base metal, crack resistance, mechanical properties and corrosion resistance of butt joints. Generally, welding wires with the same or similar grade as the base metal are used for welding aluminum and aluminum alloy, which can obtain better corrosion resistance; However, when welding aluminum alloy with high tendency of hot cracking, the selection of welding wire is mainly based on solving the crack resistance. At this time, the composition of welding wire is very different from that of base metal.

4) Cast iron welding wire

It is mainly used for repairing cast iron by gas welding. Because the oxygen-acetylene flame temperature (less than 3400 ℃) is much lower than the arc temperature (6000 ℃) and the hot spots are not concentrated, it is more suitable for welding repair of gray cast iron thin-wall castings. In addition, the lower flame temperature of gas welding can reduce the evaporation of spheroidizing agent, which is beneficial to ensure the nodular cast iron structure of the weld. At present, ductile iron welding wires for gas welding mainly include magnesium alloy with rare earth and yttrium-based heavy rare earth. Due to the high boiling point of yttrium, its ability to resist spheroidization decay is stronger than that of magnesium, which is more conducive to ensure the spheroidization of weld, so it has been widely used in recent years.

 

Selection of flux-cored welding wire

(1) Types and characteristics of flux-cored wire

According to the structure of the welding wire, the flux-cored welding wire can be divided into two types: seam welding wire and seamless welding wire. Seamless welding wire can be copper plated, with good performance and low cost, and has become the future development direction.

According to whether there is shielding gas, flux-cored wire can be divided into gas shielded wire and self-shielded wire; The composition of the core powder of flux-cored wire is similar to that of the electrode coating, including arc stabilizer, deoxidizer, slagging agent and alloying agent. According to whether there is slagging agent in the inner filler powder of flux-cored wire, it can be divided into "powder type" wire and "metal powder type" wire; According to the basicity of slag, it can be divided into titanium type, titanium-calcium type and calcium type welding wires.

The weld bead of titanium slag flux-cored wire is beautiful, the all-position welding process performance is good, the arc is stable, and the spatter is small, but the toughness and crack resistance of the weld metal are poor. On the contrary, calcium slag flux-cored wire has excellent weld toughness and crack resistance, but its weld bead formation and welding process performance are slightly poor. The titanium-calcium slag system is between the above two.

The welding process performance of "metal powder type" flux-cored wire is similar to that of solid core wire, and its deposition efficiency and crack resistance are better than that of "powder type" wire. Most of the powder core is metal powder (iron powder, deoxidizer, etc.), and special arc stabilizer is added to ensure less slag formation, high efficiency, small spatter, stable arc, low diffusible hydrogen content of the weld, and improved crack resistance.

The section shape of flux-cored wire has a great influence on the welding process and metallurgical properties. According to the section shape of flux-cored wire, it can be divided into simple O shape and complex section folding shape. The folding shape can also be divided into plum shape, T shape, E shape and middle wire filling shape.

The more complex and symmetrical the cross-section shape of the flux-cored wire is, the more stable the arc is, and the more sufficient the metallurgical reaction and protective effect of the flux-cored wire is. However, with the reduction of the diameter of the welding wire, the difference gradually decreases. When the diameter of the welding wire is less than 2mm, the influence of the cutting shape is not obvious.

Flux-cored wire has good welding process performance, good weld quality and strong adaptability to steel, and can be used to weld various types of steel structures, including low carbon steel, low alloy high strength steel, low temperature steel, heat resistant steel, stainless steel and wear-resistant surfacing. The shielding gases used include CO2 and Ar+CO2. The former is used for common structures and the latter is used for important structures. Flux-cored wire is suitable for automatic or semi-automatic welding, both DC and AC arc welding.

1) Flux-cored wire for low carbon steel and high strength steel

Most of these welding wires are titanium slag system with good welding process and high welding productivity. They are mainly used in shipbuilding, bridge, construction, vehicle manufacturing, etc. There are many kinds of flux-cored wires for low carbon steel and high strength steel, and the flux-cored wires with tensile strength of 490MPa and 590Mpa have been widely used in terms of weld strength; In terms of performance, some focus on the process performance, some focus on the mechanical properties and crack resistance of the weld, some are applicable to all position welding including vertical downward welding, and some are dedicated to fillet welding.

2) Stainless steel flux-cored wire

There are more than 20 types of stainless steel flux-cored wire, including chromium-nickel stainless steel flux-cored wire and chromium-nickel stainless steel flux-cored wire. The diameter of welding wire is 0.8, 1.2 and 1.6 mm, which can meet the welding requirements of stainless steel sheet, medium plate and thick plate. Most of the shielding gases used are CO2, and the mixture of Ar+(20%~50%) CO2 can also be used.

3) Wear-resistant surfacing flux-cored wire

In order to increase the wear resistance or obtain some special properties on the metal surface, it is necessary to transfer a certain amount of alloy elements from the welding wire. However, the welding wire is difficult to process because of its high carbon content and alloy elements. With the advent of flux-cored wire, these alloy elements can be added to the flux core, and the processing and manufacturing are convenient. Therefore, it is a common method to use flux-cored wire for submerged arc surfacing wear-resistant surface, and has been widely used. In addition, by adding alloy elements into the sintered flux, the surfacing layer with corresponding components can also be obtained after surfacing. It can meet different surfacing requirements when combined with solid or flux-cored wires.

The common methods of CO2 surfacing with flux-cored wire and submerged arc surfacing with flux-cored wire are as follows.

Fine wire CO2 flux-cored wire surfacing This method has high welding efficiency, and the production efficiency is 3-4 times of that of manual arc welding; The welding process performance is excellent, the arc is stable, the spatter is small, the slag removal is easy, and the surfacing formation is beautiful. This method can only transfer alloy elements with flux-cored wire, and is mostly used for surfacing layer with low alloy composition.

Flux-cored wire submerged arc surfacing adopts large-diameter (3.2, 4.0 mm) flux-cored wire, with large welding current and significantly improved welding productivity. When the welding flux is used, the alloy elements can also be transferred by the flux to make the surfacing layer obtain higher alloy composition, and its alloy content can vary from 14% to 20% to meet different use requirements. This method is mainly used for surfacing wear-resistant and corrosion-resistant parts such as rolling roll, feeding roll and continuous casting roll.

 

(2) Self-shielded flux-cored wire

Self-shielded welding wire refers to the welding wire that can be used for arc welding without shielding gas or flux to obtain qualified welds. Self-shielded flux-cored welding wire refers to the powder and metal powder used for slagging, gas making and deoxidation placed in the steel sheet or coated on the surface of the welding wire. During welding, the powder turns into slag and gas under the action of the arc, which plays the role of slagging and gas making protection without additional gas protection.

The deposition efficiency of self-shielded flux-cored wire is significantly higher than that of electrode, and the flexibility and wind-resistance of field welding are better than that of gas shielded welding. Generally, welding can be carried out under four levels of wind. Because there is no need for protective gas, it is suitable for outdoor or high-altitude operations, so it is mostly used at installation sites and construction sites.

The weld metal plasticity and toughness of self-shielded wire are generally lower than that of flux-cored wire using shielding gas. Self-shielded welding wire is currently mainly used for low carbon steel welding structures, and is not suitable for welding important structures such as high strength steel. In addition, the self-shielded welding wire has a large amount of smoke and dust during welding. When working in a narrow space, pay attention to strengthening ventilation.