ATI 15-7™ Precipitation Hardening Alloy (S15700, AISI Type 632) is a chromium-nickel-molybdenum-aluminium semi-austenitic precipitation hardening stainless steel used for applications requiring high strength and a moderate level of corrosion resistance.

The S15700 alloy is similar to ATI 17-7 Precipitation Hardening Alloy (S17700). The S15700 alloy is designed with substitution of approximately 2.0 percent molybdenum for 2.0 percent chromium in the S17700 alloy. This results in somewhat higher room and elevated temperature strength for the S15700 alloy. The S15700 alloy has been available for a number of years and has found application in aerospace and many spring type applications requiring high strength.

The ATI 15-7 precipitation hardening alloy may be formed in a soft austenitic condition and hardened to a high strength level by low temperature heat treatments. The low temperature heat treatment required for developing high strength allows minimum distortion compared to conventional quench and temper hardening processes. In addition to material produced by the standard refining procedures, material which has been vacuum arc or electroslag remelted is available for further increase in resistance to fatigue, for those applications subject to cyclic stresses.