High-strength stainless steel material and production process of the same

A production process of a high-strength stainless steel material comprising a step of subjecting, to a dual-phase formation treatment, a steel piece having a composition comprising, as essential components, greater than 0.00 mass % but not greater than 0.15 mass % of C, greater than 0.0 mass % but not greater than 2.0 mass % of Si, greater than 0.0 mass % but not greater than 4.0 mass % of Mn, greater than 0.00 mass % but not greater than 0.04 mass % of P, greater than 0.00 mass % but not greater than 0.03 mass % of S, greater than 0.0 mass % but not greater than 4.0 mass % of Ni, from 10.0 to 20.0 mass % of Cr, and greater than 0.00 mass % but not greater than 0.12 mass % of N with a balance of Fe and inevitable impurities;

• and having a γmax of from 50 to 85, the γmax being represented by the following equation (1):
• γmax=420Wc+470WN+23WNi+7WMn−11.5WCr−11.5WSi+189 (1)
• (in the equation (1), Wc, WN, WNi, WMn, WCr, and WSi represent contents (unit:
• mass %) of C, N, Ni, Mn, Cr, and Si relative to the total mass of the steel piece, respectively);
• and
• subjecting the steel piece obtained by the dual-phase formation treatment to an aging treatment,
• wherein the high-strength stainless steel material has a difference of 300 HV or less in hardness between a ferrite phase and a martensite phase and wherein the high-strength steel material has a hardness of 397 HV or less.