Disclosed is a stainless steel containing, by mass, 0.05% or less carbon, 1.5 to smaller than 3.5% Si, 3.0% or less Mn, 6.0 to 12.0% Cr, 4.0 to 10.0% Ni, 10.0% or less Co, 6.0% or less Cu, 0.5 to 3.0% Ti, 0 to 2.0% Al, not more than 1.0% Mo, not more than 0.01% nitrogen, and the balance of Fe and unavoidable impurities. Preferably, it has a hardness of not lower than 59 HRC and may contain not more than 1.0% Nb and/or not more than 1.0% Ta. Alternatively, the stainless steel may further contain not more than 0.1% of Zr. The process for producing the steel includes producing a steel having a composition as described above by a consumable electrode remelting process, and then subjecting the steel to a solution treatment at a temperature of 1000 to 1150.degree. C. and an aging treatment at a temperature of 400 to 550.degree. C., thereby aging the stainless steel to a hardness of not lower than 59 HRC.