GB832562A - Improvements in the heat treatment of stainless steel - Google Patents

Abstract

A method of producing heat treated stainless steel comprises selecting a steel containing 0.03%-0.15% C., 0.25%-2.0% Mn, up to 0.5% Si, 14.5%-18% Cr, 3.5%-7.0% Ni, 2.0%-3.5% Mo, 0.05%-0.15% N, the balance being iron and unavoidable impurities, e.g. 0.04% max. P, 0.04% max. S, and 0.25% max. Cu, and having a stability factor D , in accordance with the formul D = % Ni - 1/12 [% Cr + 1.5 (% Mo) - 20]2 + 1/2 (% Mn) + 35 (% C + % N) - 14 where [% Cr + 1.5 (% Mo)] < 20 and D = % Ni + 1/12 [% Cr + 1.5 (% Mo) - 20]2 + 1/2 (% Mn) + 35 (% C + % N) - 14 where [% Cr + 1.5 (% Mo)] > 20 of - 3.82 to - 4.65 where (C + N) < 0.2 and Cr = 16-18% or of - 0.10 to - 1.0 where (C + N) > 0.2 and Cr = 14.5-16% austenizing the steel at 1675-1950 DEG F., cooling at a rate fast enough to retain at least 70% austenite, cooling to between - 80 DEG F. and - 110 DEG F., working the cooled steel at room temperature to produce a reduction in cross-sectional area of 10% to 30% and then tempering at 750 DEG F. to 950 DEG F. The sub-zero cooling may be for 1/2 to 2 hours and the final tempering for from 2 to 50 hours. Specification 824,031 is referred to.