Patent ID: 8021502

Claim:
A method for producing a high-strength martensitic stainless steel pipe which comprises: heating the steel pipe, which is made by use of the martensitic steel, having a chemical composition comprising by mass percent, C: 0.18 to 0.22%, Si: 0.1 to 0.5%, Mn: 0.40 to 1.00%, P: 0.011 to 0.018%, S: 0.003% or less, Cr: 11.50 to 13.50%, Ni: 0.5% or less, Al: 0.0005 to 0.003%, N: 0.012 to 0.040%, Cu: 0.25% or less, Ti: 0.05% or less, V: 0.02 to 0.18%, Mo: 0 to 0.05%, Nb: 0 to 0.009%, B: 0.0010% or less, and Ca: 0.0050% or less, with the balance being Fe and impurities, as the material and cooled to room temperature by atmospheric cooling or air cooling, at a temperature T 1 , which exists in the temperature range of 930 to 980 degrees C., for 5 to 30 minutes; then cooling the steel pipe from the temperature T 1 to a temperature T 2 , which exists in the temperature range of 600 to 350 degrees C., at a cooling rate of 1 to 40 degrees C./sec; successively cooling the steel pipe from the temperature T 2 to a temperature T 3 , which exists in the temperature range of 300 to 150 degrees C., and from the temperature range lower than the temperature T 3 to room temperature at cooling rates of less than 1 degrees C./sec and of 5 to 40 degrees C./sec, respectively; and, performing a bend straightening treatment at a straightener outlet temperature of 510 degrees C. or higher successively to tempering treatment at 610 to 750 degrees C.