Welding Stainless Steel
What Is Stainless Steel?
Martensitic Stainless Steel
The most common martensitic alloys, i.e., Alloy 410, have a moderate chromium content of 12-18% with low Ni but, more importantly, have a relatively high carbon content. The principle difference compared with welding the austenitic and ferritic grades of stainless steel is the potentially hard HAZ martensitic structure and the matching composition weld metal. The material can be successfully welded providing precautions are taken to avoid cracking in the HAZ, especially in thick section components and highly restrained joints.
Avoiding weld imperfections – High hardness in the HAZ makes this type of stainless steel very prone to hydrogen cracking. The risk of cracking generally increases with the carbon content. Precautions must be taken to minimize the risk by: using low hydrogen process (TIG or MIG) and ensuring the flux or flux coated consumable are dried (MMA and SAW) according to the manufacturer's instructions; preheating to around 200 to 300°C — the actual temperature will depend on weld (especially Cr and C content), section thickness, and the amount of hydrogen entering the weld metal; maintaining the recommended minimum interpass temperature; and carrying out post-weld heat treatment, i.e., at 650-750°C. The time and temperature will be determined by chemical composition.
Thin section, low carbon material, typically less than 3 mm, can often be welded without preheat, providing that a low hydrogen process is used, the joints have low restraint, and attention is paid to cleaning the joint area. Thicker section and higher carbon (>0.1%) material will probably need preheat and post-weld heat treatment. The post-weld heat treatment should be carried out immediately after welding not only to temper (toughen) the structure but also to enable the hydrogen to diffuse away from the weld metal and HAZ.