Stainless steel seamless pipe and production method therefor

Abstract

Provided is a stainless steel seamless pipe having high strength and excellent low-temperature toughness and corrosion resistance. The stainless steel seamless pipe comprises: a predetermined chemical composition; 30% or more martensite phase, 50% or less ferrite phase, and 40% or less retained austenite phase in volume fraction; a yield stress of 758 MPa or more; and a Charpy absorbed energy vE−10 at −10° C. of 40 J or more.

1 . A stainless steel seamless pipe comprising:
 a chemical composition containing, in mass %,   C: 0.06% or less,   Si: 1.0% or less,   Mn: 0.01% or more and 1.0% or less,   P: 0.05% or less,   S: 0.005% or less,   Cr: 15.2% or more and 18.0% or less,   Mo: 1.5% or more and 4.3% or less,   Cu: 1.2% or more and 3.5% or less,   Ni: 3.5% or more and 5.2% or less,   V: 0.5% or less,   Al: 0.10% or less,   N: 0.10% or less,   O: 0.010% or less,   Sb: 0.001% or more and 1.000% or less,   Co: 0.01% or more and 1.00% or less, and   Ca: 0.001% or more and 0.030% or less,   with a balance consisting of Fe and inevitable impurities;   30% or more martensite phase, 50% or less ferrite phase, and 40% or less retained austenite phase in volume fraction;   a yield stress of 758 MPa or more; and   a Charpy absorbed energy vE −10  at −10° C. of 40 J or more.   
     
     
         2 . The stainless steel seamless pipe according to  claim 1 , wherein the chemical composition further contains, in mass %, at least one selected from the group consisting of
 Nb: 0.07% or less,   Ti: 0.2% or less,   W: 0.9% or less,   B: 0.01% or less,   Ta: 0.3% or less,   Zr: 0.3% or less,   REM: 0.3% or less,   Mg: 0.01% or less, and   Sn: 1.0% or less.   
     
     
         3 . The stainless steel seamless pipe according to  claim 1 , comprising:
 50% or more martensite phase, 50% or less ferrite phase, and 25% or less retained austenite phase in volume fraction; and   a yield stress of 862 MPa or more.   
     
     
         4 . A production method for a stainless steel seamless pipe, the production method comprising:
 making a seamless steel pipe from a steel material having the chemical composition according to  claim 1 ;   heating the seamless steel pipe to a quenching temperature of 850° C. to 1150° C.;   cooling the seamless steel pipe after the heating to a cooling stop temperature of 50° C. or less at a cooling rate of 0.01° C./s or more; and   heating the seamless steel pipe after the cooling to a tempering temperature of 500° C. to 650° C., to produce a stainless steel seamless pipe having:   30% or more martensite phase, 50% or less ferrite phase, and 40% or less retained austenite phase in volume fraction; a yield stress of 758 MPa or more; and a Charpy absorbed energy vE −10  at −10° C. of 40 J or more.   
     
     
         5 . The production method for a stainless steel seamless pipe according to  claim 4 , wherein the stainless steel seamless pipe has: 50% or more martensite phase, 50% or less ferrite phase, and 25% or less retained austenite phase in volume fraction; and a yield stress of 862 MPa or more. 
     
     
         6 . The stainless steel seamless pipe according to  claim 2 , comprising:
 50% or more martensite phase, 50% or less ferrite phase, and 25% or less retained austenite phase in volume fraction; and   a yield stress of 862 MPa or more.   
     
     
         7 . A production method for a stainless steel seamless pipe, the production method comprising:
 making a seamless steel pipe from a steel material having the chemical composition according to  claim 2 ;   heating the seamless steel pipe to a quenching temperature of 850° C. to 1150° C.;   cooling the seamless steel pipe after the heating to a cooling stop temperature of 50° C. or less at a cooling rate of 0.01° C./s or more; and   heating the seamless steel pipe after the cooling to a tempering temperature of 500° C. to 650° C., to produce a stainless steel seamless pipe having:   30% or more martensite phase, 50% or less ferrite phase, and 40% or less retained austenite phase in volume fraction; a yield stress of 758 MPa or more; and a Charpy absorbed energy vE −10  at −10° C. of 40 J or more.   
     
     
         8 . The production method for a stainless steel seamless pipe according to  claim 7 , wherein the stainless steel seamless pipe has: 50% or more martensite phase, 50% or less ferrite phase, and 25% or less retained austenite phase in volume fraction; and a yield stress of 862 MPa or more.