Warped metal, carbon black color welds and setbacks; These are some of the things that can happen when welding stainless steel. Although stainless steel contains elements similar to carbon steel, it also adds alloy elements such as chromium and molybdenum, which brings completely different challenges to melting two or more pieces of stainless steel instead of carbon steel. Oxygen must be kept to an absolute minimum around the stainless steel bath. The weld pool will behave differently from aluminum or carbon steel. The thermal conductivity of stainless steel is much smaller, which makes deformation and heat input a big problem. There are many things to consider when welding stainless steel, and one of the most important decisions is what welding process to use.
Below we discuss the most popular welding processes used for stainless steel.
MIG welding, or more formally gas metal arc welding, is a more popular method of welding stainless steel. MIG welded stainless steel has many similarities with welded carbon steel. Special drive rollers are not required, and the polarity remains unchanged. However, the composition of the shielding gas is usually different. When welding stainless steel, the allowable oxygen content is low, so the oxygen or carbon dioxide level should be maintained at about 2% or less. When MIG welding stainless steel, tri blend shielding gas containing argon, helium, carbon dioxide or oxygen is common. Stainless steel welding wire must be used because the weld and base metal are usually required to have corrosion resistance. In addition, to prevent cracking, the filler wire and base stainless steel should be low carbon version or have stabilizers such as tantalum or niobium. Using pulse welding waveform can also help users weld MIG stainless steel more successfully.
TIG welding, more formally known as TIG welding, is another process often used to weld stainless steel. This process also has similarities when it is used to weld carbon steel and when it is used to weld stainless steel. Both of these materials need DC electrode negative polarity (CEN). Generally, argon or helium shielding gas is used almost 100%. As with MIG welding, TIG welding requires stainless steel filler metal to prevent the weld from being easily corroded. Stainless steel of low carbon or stable grade shall be used as filler metal, and base metal shall also be low carbon or stable. When welding stainless steel, deformation may be a major problem. Therefore, it is important to maintain a certain speed and low heat input when TIG welding stainless steel.
Generally speaking, the welding process using flux is not the best process for welding stainless steel. In other words, it is possible to weld stainless steel with flux cored process. Special gas mixtures are required. Compared with flux cored welding, gas shielded flux cored welding is usually a better choice for stainless steel welding process, because it relies less on flux cored welding than the latter process to protect the welding metal from the atmosphere.
A better alternative to self shielded flux cored welding and gas shielded flux cored welding is metal flux cored welding. This is mainly because metal core arc welding is completely independent of flux. The metal core of the filling material, although it has a specific kind of deoxidizer, is mainly filled with powder metal to increase deposition. Using proper shielding gas and wire feeding system, metal core arc welding can obtain high-quality stainless steel welds. High quality metal core arc welding of stainless steel needs pulse waveform or spray transfer arc to a great extent.
Laser welding is often used to connect very fast stainless steel and very low heat input. When using laser welding, care must be taken to avoid air holes and cracks. Cracks and pores can be avoided by reducing the amount of oxygen through the optimization of shielding gas and welding parameters. Laser welding is never carried out manually. Therefore, if laser welding is selected as the stainless steel welding process, it must be automated.
The above process is probably the most common process for welding stainless steel. There are many other, some less popular processes in industry that can be used to weld stainless steel. They include plasma arc welding (PAW), electron beam welding (EBW), shielded metal arc welding (SMAW), friction stir welding (FSW) and resistance welding (RW). This list is not exhaustive. There are more welding processes that can weld stainless steel together and achieve varying degrees of success.