What Is Stainless Steel?
Austenitic Stainless Steel
Austenitic stainless steels typically have 16 ¨C 26% chromium (Cr) and 8 ¨C 22% nickel (Ni). Alloy 304, which contains approximately 18% Cr and 10% Ni, is a commonly used alloy for welded fabrications, and these alloys can be readily welded using any of the arc welding processes (TIG, MIG, MMA, and SA). They exhibit good toughness because they are non-hardenable on cooling, and there is no need for pre- or post-weld heat treatment.
Avoiding weld imperfections ¨C Austenitic stainless steel is readily welded, but weld metal and HAZ cracking can occur. Weld metal solidification cracking is more likely to occur in fully austenitic structures, which are more crack sensitive than those containing a small amount of ferrite as ferrite has the capacity to dissolve harmful impurities which would otherwise form low melting point segregates and interdendritic cracks. The presence of 5 - 10% ferrite in the microstructure is extremely beneficial so the choice of filler material composition is crucial in suppressing the risk of cracking. An indication of the ferrite-austenite balance for different compositions is provided by the Schaeffler diagram. For example, when welding Alloy 304 stainless steel, an Alloy 308 filler material, which has a slightly different alloy content, is used.
