Stainless steels are iron based alloys which have outstanding resistance to corrosion. The stainless steel has the resistance against the gases, liquids and chemicals. Most of the stainless steels have better low temperature ductility and toughness. All stainless steels do not possess the same properties but the stainless steel having the similar formation contain same properties.
Welding for stainless steel is done by adopting various procedures like gas tungsten arc welding, shielded metal arc welding and gas metal arc welding. Stainless steels are difficult to melt as compared to mild carbon steels. The welding procedure is different for both of them because of their difference in physical properties. Stainless steels are grouped under the same metallurgical structure for welding.
Austenitic Stainless Steels
All the austenitic stainless steels are welded following the different welding processes excluding Type 303 which includes high sulphur and Type 303Se which includes selenium to develop machinability. This type of stainless steel requires travel speed welding which decreases carbide precipitation and heat input and diminishes distortion.
Ferritic Stainless Steels
All the ferritic grades of stainless steel are weldable with the help of various welding processes except 430F which includes high sulphur content. Welding procedures which raises the carbon are not suggested. The welding procedures for ferritic stainless steels include carbon arc process, oxy-fuel gas process and gas metal arc welding along with carbon dioxide shielding gas. On welding, this reduces the toughness, ductility and corrosion resistance.
Martensitic Stainless Steels
The welding for low carbon type can be done without following any particular precautions. This type of stainless steel requires preheating and postheating welding procedures. Austenitic stainless steel filler is recommended in case if preheating and postheating cannot be done. Type 416Se cannot be welded.
Welding Filler Metals
The choice of the filler metal alloy for welding the stainless steels depend on the work of the stainless steel. These filler metal alloys made up of stainless steel are available as bare solid wires and covered electrodes. To weld the stainless steels, the expansion of flux cored electrode wires has been done.
Welding Procedures for Stainless Steel
Gas Tungsten Arc Welding Process
This process is largely used for leaner parts of stainless steel. About 2 percent of tungsten is suggested. Argon is generally used for gas shielding and mixture of helium and argon is used for mechanical applications.
Gas Metal Arc Welding Process
This process is considered as the quicker welding process. The spray transfer mode is useful for smooth position welding and this needs the use of argon for shielding.