WELDING PROCESSES FOR STAINLESS STEEL
Warped metal, charcoal-colored welds, and frustration; these are some of the things that can happen when welding stainless steel. While it contains similar elements to that of carbon steel, stainless steel has the addition of alloying elements such as chromium and molybdenum, and that presents an altogether different set of challenges when fusing two or more pieces of stainless steel rather than carbon steel. The oxygen surrounding the molten pool of stainless steel must be kept to an absolute minimum. The weld pool will behave differently than aluminum or carbon steel. The thermal conductivity of stainless steel is much less, making distortion and heat input a large concern. While there are many items to consider when welding stainless steel, one of the most important decisions to make is what welding process to use.
Welding Processes for Stainless Steel
Below we discuss the most popular welding processes used for stainless steel.
Metal Inert Gas (MIG) Welding/Gas Metal Arc Welding (GMAW)
MIG welding, or gas metal arc welding as it is more formally known, is one of the more popular ways to weld stainless steel. There are many similarities between MIG welding stainless steel and welding carbon steel. No special drive rolls need to be used, and the electrical polarity remains the same. However, shielding gas compositions are typically different. Lower amounts of oxygen are allowable when welding stainless steel, so O2 or CO2 levels should be kept around 2% or lower. It is quite common for tri-blend shielding gases that contain argon, helium, and carbon dioxide or oxygen to be used when MIG welding stainless steel. Since corrosion resistance will typically be desired in the weld as well as the base material, stainless steel welding wire must be used. Furthermore, to prevent cracking, the filler wire and base stainless steel should be a low carbon version or have stabilizers in them such as tantalum or niobium. Using a pulsed welding waveform can also help users MIG weld stainless steel more successfully.
Tungsten Inert Gas (TIG) Welding/Gas Tungsten Arc Welding (GTAW)
TIG welding, more formally known as gas tungsten arc welding, is another process that is frequently used to weld stainless steel. This process also has similarities between when it is used to weld carbon steel and when it is used to weld stainless steel. Both materials require a direct current electrode negative (DCEN) polarity. Typically, nearly 100% argon or helium shielding gases are used. As with MIG welding, TIG welding requires stainless steel filler metal to prevent making a weld that will be easily susceptible to corrosion. Low carbon or stabilized grades of stainless steel should be used as filler metals, and the base metals should also be low carbon or stabilized. Distortion can be a major problem when welding stainless steel, so it is important to keep travel speeds somewhat fast and heat inputs low when TIG welding stainless steel.
Flux-Cored Arc Welding
In general, welding processes that use flux are not optimal for welding stainless steel. That being said, it is possible to weld stainless steel with the flux-cored process. Special gas mixtures need to be used. Gas-shielded flux-cored arc welding is typically a better choice of process to weld stainless steel than flux-cored arc welding since it relies less on flux than the latter process to shield the weld metal from the atmosphere.
Metal-Cored Arc Welding
A better cored wire alternative to both self-shielded flux-cored arc welding and gas-shielded flux-cored arc welding is metal-cored arc welding. This is mostly because metal-cored arc welding does not rely on flux at all. The metal core of the filler material, while it does have certain kinds of deoxidizers, is mostly packed with powdered metals to increase deposition. With the proper shielding gas and wire feeding system, metal-cored arc welding can be used to make high-quality welds on stainless steel. For the most part, a pulsed waveform or spray-transfer arc is required to make a high-quality stainless steel weld with metal-cored arc welding.
Laser Beam Welding (LBW)
Laser beam welding is frequently used to join together stainless steel at very fast travel speeds and with very low heat inputs. Care must be taken to avoid porosity and cracking when welding with lasers. Cracks and porosity can be avoided through reducing the amount of oxygen via a shielding gas and weld parameter optimization. Laser beam welding is never performed manually, and therefore, must be automated if it is selected as the process to be used for welding stainless steel.
Other Welding Processes Used on Stainless Steel
The above-mentioned processes are perhaps the most common processes used to weld stainless steel. There are many other, somewhat less popular processes out in the 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, and there are many more welding processes that can weld stainless steel together with varying levels of success.
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