| 摘要 |
[Problem to be Solved] A method for producing a duplex stainless steel pipe that has not only a corrosion resistance required for the oil well pipes used in deep oil wells or in severe corrosive environments but also a targeted strength is provided. [Solution] A method for producing a duplex stainless steel pipe having a minimum yield strength of 758.3 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: 0 to 6%, W: 0 to 6%, Cu: 0 to 3% and N: 0.15 to 0.60%, and the balance being Fe and impurities, by a hot working optionally followed 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 ln MYS ˆ’ ln �¢ 14.5 × Cr + 48.3 × Mo + 20.7 × W + 6.9 × N / 0.195
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. |
