Patent ID: 8293037

Claim:
A method for producing a duplex stainless steel pipe having a minimum yield strength of 861.8 to 965.2 MPa, comprising: preparing a duplex stainless steel material pipe for cold working, having a chemical composition consisting, by mass %, of C: 0.03% or less, Si: 1% or less, Mn: 0.1 to 4%, Cr: 20 to 35%, Ni: 3 to 10%, Mo: 2 to 6%, W: 1.5 to 6%, Cu: 0 to 3% and N: more than 0.17% and not more than 0.60%, and the balance being Fe and impurities, by a hot working and optionally by a solid-solution heat treatment; and producing the duplex stainless steel pipe by subsequently subjecting the material pipe to a cold rolling, wherein the cold rolling is performed under the conditions that the working ratio Rd, in terms of the reduction of area, in the final cold rolling step falls within a range from 10 to 80%, and the following formula (1) is satisfied: Rd =exp[{In( MYS )−In(14.5×Cr+48.3×Mo+20.7×W+6.9×N)}/0.195] (1) wherein Rd and MYS signify the working ratio (%) in terms of the reduction of area and the targeted yield strength (MPa), respectively, and Cr, Mo, W and N signify the contents (mass %) of the individual elements, respectively.