Process for producing high strength stainless steel of duplex structure having excellent spring limit value

A process for the production of a high strength stainless steel strip of a duplex structure having an excellent spring limit value, which comprises:

• conventional hot rolling and cold rolling steps to provide a cold rolled strip of a stainless steel, said stainless steel further comprising from 10.0 to 20.0% by weight of Cr, from 0.01 to 0.15% by weight of C, up to 1.39% by weight of Si, up to 0.032% by weight of N and at least one of Ni, Mn and Cu in an amount of from 0.1 to 4.0% by weight, the balance being Fe and impurities;
• a step of heat treatment for forming a duplex structure in which the cold rolled strip is continuously passed through a continuous heat treatment furnace where it is heated to a temperature range for a two-phase of ferrite and austenite, and thereafter the strip is rapidly cooled to provide a strip of a duplex structure, consisting essentially of ferrite and martensite;
• a step of temper rolling the strip of the duplex structure at a rolling reduction of an effective amount not more than 10%;
• and
• a step of continuous aging the strip for a period of time of not longer than 10 minutes in which the temper rolled strip is continuously passed through a continuous heat treatment furnace where the strip is heated to a temperature ranging from 300.degree. to 650.degree. C., the aged strip having a hardness (HV) of not higher than 450 and a spring limit value Kb, in both the rolling direction and the direction perpendicular thereto, of at least 65 kgf/mm.sup.2.