Influence of alloy elements in welding wire on weldability

CO2 gas shielded welding copper plated wire is a kind of welding material with high efficiency, energy saving and material saving. It is suitable for the welding of low carbon steel and low alloy steel. The carbon content of CO2 welding wire is low, mostly below 0.1%, and contains Si, Mn, s, P, Cr, AI, Ti, Mo, V and other alloy elements.

The influence of these alloy elements on welding performance is described as follows:

What is the effect of Si on weldability?

Silicon is the most commonly used deoxidizing element in welding wire. It can prevent iron from combining with oxide and reduce FeO in molten pool. However, with silicon deoxidation alone, the resulting SiO2 has a high melting point (about 1710 ℃), and the particles of the product are small, so it is difficult to float out of the molten pool, which is easy to cause slag inclusion in the weld metal.

What is the effect of manganese on weldability?

The effect of manganese is similar to that of silicon, but its deoxidation ability is slightly worse than that of silicon. The density of MnO is 15.11g/cm3, and it is not easy to float out of the solution pool. In addition to deoxidation, manganese in welding wire can also combine with sulfide to form manganese sulfide (MNS), which is removed (desulfurization), so the tendency of hot cracking caused by sulfur can be reduced. It is difficult to remove the deoxidation products because of the deoxidation by silicon and manganese alone. So at present, silicon manganese combined deoxidation is often used to make SiO2 and MnO compound into silicate (MnO. SiO2). Mno.sio2 has low melting point (about 1270 ℃) and low density (about 3.6 g / cm3). It can agglomerate into large slag and float out in the molten pool, achieving good deoxidation effect. Manganese is also an important alloying element and hardenability element in steel, which has a great influence on the toughness of weld metal. When Mn content is less than 0.05%, the toughness of weld metal is very high; When Mn content is more than 3%, it is brittle again; When Mn content is 0.6-1.8%, the weld metal has higher strength and toughness.

What is the effect of sulfur (s) on weldability?

Sulfur is usually present in the form of iron sulfide in steel and distributed in the grain boundary as a network, thus significantly reducing the toughness of steel. The eutectic temperature of iron plus iron sulfide is relatively low (985 ℃). Therefore, during hot working, because the starting temperature of processing is generally 1150-1200 ℃, the eutectic of iron and iron sulfide has melted, which leads to cracking during processing. This phenomenon is called “hot brittleness of sulfur”. This property of sulfur causes hot cracks in steel during welding. Therefore, the sulfur content in steel is generally strictly controlled. The main difference between ordinary carbon steel, high quality carbon steel and high quality steel is the content of sulfur and phosphorus. As mentioned above, manganese has desulfurization effect, because manganese and sulfur can form manganese sulfide (MNS) with high melting point (1600 ℃), which is distributed in grains in granular form. During hot working, manganese sulfide has enough plasticity to eliminate the harmful effect of sulfur. Therefore, it is beneficial to keep a certain manganese content in steel.

What is the effect of phosphorus (P) on weldability?

Phosphorus can be completely dissolved in ferrite in steel. Its strengthening effect on steel is only inferior to that of carbon, which increases the strength and hardness of steel. Phosphorus can improve the corrosion resistance of steel, while the plasticity and toughness decrease significantly. Especially at low temperature, the effect is more serious, which is called the cold brittle tendency of phosphorus. So it is disadvantageous to welding and increases the crack sensitivity of steel. As an impurity, the content of phosphorus in steel should also be limited.

What is the effect of chromium (CR) on weldability?

Chromium can improve the strength and hardness of the steel, but the plasticity and toughness decrease little. Chromium has strong corrosion resistance and acid resistance, so austenitic stainless steel generally contains more chromium (more than 13%). Chromium also has strong antioxidant capacity and heat resistance. Therefore, chromium is widely used in heat-resistant steel, such as 12CrMo, 15crmo5crmo and so on. Chromium is an important constituent element of austenitic steel and ferrite element. It can improve the oxidation resistance and mechanical properties at high temperature in alloy steel. In austenitic stainless steel, when the total amount of Cr and Ni is 40%, Cr / Ni = 1, there is a tendency of hot cracking; When Cr / Ni = 2.7, there is no tendency of hot cracking. Therefore, when Cr / Ni = 2.2-2.3 in 18-8 type steel, chromium is easy to produce carbide in alloy steel, which makes heat conduction of alloy steel worse and chromium oxide easy to produce, which makes welding difficult.

What is the effect of aluminum (AI) on weldability?

Aluminum is one of the strong deoxidizing elements, so using aluminum as deoxidizer can not only reduce the production of FeO, but also reduce FeO easily, effectively inhibit the chemical reaction of CO gas produced in the molten pool, and improve the ability of resisting CO porosity. In addition, aluminum can combine with nitrogen to fix nitrogen, so it can also reduce nitrogen pores. However, the melting point of AI2O3 formed by aluminum deoxidation is very high (about 2050 ℃), and it exists in the molten pool as a solid state, which is easy to cause slag inclusion in the weld. At the same time, the welding wire containing aluminum is easy to cause spatter, and the high aluminum content will reduce the hot cracking resistance of weld metal, so the aluminum content in welding wire must be strictly controlled, not too much. If the aluminum content in the welding wire is controlled properly, the hardness, yield point and tensile strength of the weld metal will be slightly improved.

What is the effect of titanium on weldability?

Titanium is also a strong deoxidizing element, and it can also fix nitrogen with tin synthesized by nitriding, so as to improve the resistance of weld metal to nitrogen porosity. If the content of Ti and B (b) is appropriate in the weld microstructure, the weld microstructure can be refined.

What is the effect of molybdenum on weldability?

Molybdenum in alloy steel can improve the strength and hardness of the steel, refine the grain, prevent temper brittleness and overheating tendency, improve the high temperature strength, creep strength and rupture strength. When the content of molybdenum is less than 0.6%, it can improve the plasticity, reduce the tendency of cracks and improve the impact toughness. Molybdenum tends to promote graphitization. Therefore, the molybdenum content of general heat-resistant steels such as 16mo, 12CrMo and 15CrMo is about 0.5%. When the content of molybdenum in alloy steel is 0.6-1.0%, the plasticity and toughness of alloy steel will decrease and the quenching tendency of alloy steel will increase.

What is the effect of vanadium (V) on weldability?

Vanadium can improve the strength of the steel, refine the grain, reduce the tendency of grain growth and improve the hardenability. Vanadium is a strong carbide forming element, and the carbides formed are stable below 650 ℃. It has age hardening effect. The carbide of vanadium has high temperature stability, so it can improve the high temperature hardness of steel. Vanadium can change the distribution of carbides in steel, but vanadium is easy to form refractory oxides, which increases the difficulty of gas welding and gas cutting. In general, when the vanadium content in the weld is about 0.11%, it can play a role of nitrogen fixation, and become favorable.

Source: China Steel Pipes Manufacturer – Yaang Pipe Industry (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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