Modified Type 316 Stainless Steel with Low Tendency to form Sigma

Abstract

A study was made to determine whether decreasing the chromium or the chromium and molybdenum contents of AISI Type 316 stainless steels would decrease the tendency for sigma-phase formation without impairing the elevated-temperature strength of the steel. The results of this study showed that in comparison with AISI Type 316, a modified Type 316 steel with about 14 per cent chromium instead of the normal 16 to 18 per cent chromium had about the same coefficient of thermal expansion, similar room- and elevated-temperature tensile properties, similar creep and creep-rupture strengths, and slightly better hot workability. Moreover, the impact strength of modified Type 316 steel after exposure for 6000 hr at 1100, 1300, and 1500 F was markedly superior to that of AISI Type 316 steel. The results of X-ray and metallographic studies indicated that the superior impact strength of the modified Type 316 was the result of lesser amounts of sigma formed in the new steel.