Known as 300 series, austenitic stainless steels are the most commonly welded. These chrome nickel steels, in contrast to lower-cost stainless have more alloys and are “non magnetic” (Exception, types 310 – 330).
Austenitic grades of stainless steel typically contain a minimum of 16-26% chromium and 6-22% nickel.
308 Grade stainless steel, for example, is also referred to as 18-8 stainless steel and contains about 18% chromium and 8% nickel.
Austenitic stainless steel can be hardened by cold working, but not by heat treatment. In the annealed condition, all are nonmagnetic, although some may become slightly magnetic by cold working. At room temperature, the 300 Series stainless steels retain an austenitic microstructure. While resistance to corrosion is their principal attribute, they are also selected for their excellent strength properties at high or extremely low temperatures. They are considered to be the most weldable of the high-alloy steels. Comparatively, little trouble is experienced in making satisfactory welded joints if their inherent physical characteristics and mechanical properties are given proper consideration.
The principal criteria for selecting stainless steel is usually resistance to corrosion, and while most consideration is given to the corrosion resistance of the base metal, additional consideration should be given to the filler material and to the base metal immediately adjacent to the weld zone. Welding naturally produces a temperature gradient in the metal being welded, ranging from the melting temperature of the fused weld metal to ambient temperature at some distance from the weld.
Because of the long-term cost-effectiveness and inherent corrosion resistance of stainless steel, it has become a staple material across many industries. TIG welding stainless steel poses a number of distinct challenges, the greatest of which are carbide precipitation and distortion. The key to preventing these issues is good heat control, correct travel speeds, and adequate gas coverage.