How to Weld Stainless Steel. Stainless steel represents a class of materials that can be characterized as iron-based metal alloys with at least 12 percent chromium. They have some resistance to rust because of a protective outer layer of chromium oxide, but the term "stainless steel" does not identify the specific type of metal and cannot be used for any practical purpose. Here's how to weld some major families of stainless steel.
Weld austenitic stainless steels. These steels are generally the most weldable because of low thermal conductivity and a high coefficient of expansion compared to other stainless steels. These properties produce greater distortion when welding and require specific strategies, including a base metal with low carbon content, a base metal with titanium or niobium or a solution heat treatment.
Identify ferritic stainless steels by their ferromagnetism and inability to be hardened by heat. These stainless steels are welded with austenitic or ferritic filler material using arc processes, although heat treatment may be required after the weld.
Consider stainless steels with a mixture of austenitic and ferritic properties to be Duplex steels. The most important factor in welding these steels is to limit their time at temperatures between 300 and 980 degrees C so as to minimize the degradation of their properties.
Analyze martensitic steels by their magnetism and ability to be fully hardened by heat. These steels are not readily weldable. The best results may be achieved with a very low carbon base metal and heat treatment before and after welding.
Use precise instructions to weld hardenable stainless steel. This class of metal is readily welded if the proper heat treatment is performed.