| 摘要 |
A process for the production of a duplex stainless steel pipe having a minimum yield strength of 758.3 to 965.2MPa, which comprises: subjecting a duplex stainless steel material having a chemical composition that contains by mass C: 0.03% or less, Si: 1% or less, Mn: 0.1 to 4%, Cr: 20 to 35%, Ni: 3 to 10%, Mo: 0 to 6%, W: 0 to 6%, Cu: 0 to 3%, N: 0.15 to 0.60% with the balance being Fe and impurities to hot working either alone or followed by solution treatment to produce a pipe stock for cold working; and then cold-rolling the pipe stock into a duplex stainless steel pipe, characterized in that the cold rolling is conducted under such conditions that the reduction ratio (Rd) (in terms of reduction in area) in the final cold rolling step falls within the range of 10 to 80% and satisfies the relationship (1): Rd=exp[{ln(MYS)-ln(14.5×Cr+48.3×Mo+20.7×W+6.9×N)}/0.195]···(1) wherein Rd and MYS represent reduction ratio (%) (in terms of reduction in area) and desired yield strength (MPa) respectively; and Cr, Mo, W, and N represent their respective contents (mass%). |
