Stainless steel seamless pipe and method for manufacturing same

Abstract

A stainless steel seamless pipe has a component composition containing, in terms of mass%, C: 0.06% or less, Si: 1.0% or less, Mn: 0.01% or more and 0.90% or less, P: 0.05% or less, S: 0.005% or less, Cr: 15.70% or more and 18.00% or less, Mo: 1.60% or more and 3.80% or less, Cu: 1.10% or more and 4.00% or less, Ni: 3.0% or more and 6.0% or less, AI: 0.10% or less, N: 0.10% or less, O: 0.010% or less, V: 0.120% or more and 1.000% or less, C, Si, Mn, Cr, Ni, Mo, Cu, and N satisfying a predetermined formula, and a remainder consisting of Fe and unavoidable impurities, and has a microstructure including 30% or more of a martensitic phase, 60% or less of a ferritic phase, and 40% or less of a retained austenitic phase, and a yield strength is 758 MPa or higher.

1 . A stainless steel seamless pipe having a component composition comprising, in terms of mass%:
 C: 0.06% or less;   Si: 1.0% or less;   Mn: 0.01% or more and 0.90% or less;   P: 0.05% or less;   S: 0.005% or less;   Cr: 15.70% or more and 18.00% or less;   Mo: 1.60% or more and 3.80% or less;   Cu: 1.10% or more and 4.00% or less;   Ni: 3.0% or more and 6.0% or less;   Al: 0.10% or less;   N: 0.10% or less;   O: 0.010% or less;   V: 0.120% or more and 1.000% or less,   C, Si, Mn, Cr, Ni, Mo, Cu, and N satisfying Formula (1) below; and   a remainder consisting of Fe and unavoidable impurities,   wherein the stainless steel seamless pipe has a microstructure including, in terms of volume fraction, 30% or more of a martensitic phase, 60% or less of a ferritic phase, and 40% or less of a retained austenitic phase, and   a yield strength is 758 MPa or higher,
                   13.0   ≤   −   5   .9   ×       7.82   +   27   C   −    0   .91Si   +   0   .21Mn   −   0   .9Cr   +               Ni   −   1   .1Mo +   0.2   Cu   +       11Ν       ≤   50.0               ­­­(1)               
   here, each of C, Si, Mn, Cr, Ni, Mo, Cu, and N is the content (mass%) of each element and is regarded as zero in a case of being not contained.   
     
     
         2 . The stainless steel seamless pipe according to  claim 1 , 
 wherein the volume fraction of the martensitic phase is 40% or more, the volume fraction of the retained austenitic phase is 30% or less, and the yield strength is 862 MPa or higher.   
     
     
         3 . The stainless steel seamless pipe according to  claim 1 , further comprises, in addition to the component composition, in terms of mass%, one group or two or more groups selected from Group A to Group D below:
 Group A: W: 3.0% or less,   Group B: Nb: less than 0.10%,   Group C: one or two or more selected from B: 0.010% or less, Ta: 0.3% or less, Co: 1.5% or less, Ti: 0.3% or less, and Zr: 0.3% or less, and   Group D: one or two or more selected from Ca: 0.01% or less, REM: 0.3% or less, Mg: 0.01% or less, Sn: 1.0% or less, and Sb: 1.0% or less.   
     
     
         4 .  The stainless steel seamless pipe according to  claim 2 , further comprises, in addition to the component composition, in terms of mass%, one group or two or more groups selected from Group A to Group D below: 
 Group A: W: 3.0% or less,   Group B: Nb: less than 0.10%,   Group C: one or two or more selected from B: 0.010% or less, Ta: 0.3% or less, Co: 1.5% or less, Ti: 0.3% or less, and Zr: 0.3% or less, and   Group D: one or two or more selected from Ca: 0.01% or less, REM: 0.3% or less, Mg: 0.01% or less, Sn: 1.0% or less, and Sb: 1.0% or less.   
     
     
         5 . A method for manufacturing the stainless steel seamless pipe according to  claim 1 , the method comprising:
 heating a steel pipe material having the component composition at a temperature within a heating temperature range of 1100° C. to 1350° C. to make the steel pipe material into a seamless steel pipe by hot-working;   subsequently, carrying out a quenching treatment by reheating the seamless steel pipe to a temperature within a heating temperature range of 850° C. to 1150° C. and cooling the seamless steel pipe to a cooling stop temperature of 50° C. or lower at a cooling rate for air cooling or faster; and   thereafter, carrying out a tempering treatment by heating the seamless steel pipe to a temperature within a tempering temperature range of 500° C. to 650° C.   
     
     
         6 . A method for manufacturing the stainless steel seamless pipe according to  claim 2 , the method comprising:
 heating a steel pipe material having the component composition at a temperature within a heating temperature range of 1100° C. to 1350° C. to make the steel pipe material into a seamless steel pipe by hot-working;   subsequently, carrying out a quenching treatment by reheating the seamless steel pipe to a temperature within a heating temperature range of 850° C. to 1150° C. and cooling the seamless steel pipe to a cooling stop temperature of 50° C. or lower at a cooling rate for air cooling or faster; and   thereafter, carrying out a tempering treatment by heating the seamless steel pipe to a temperature within a tempering temperature range of 500° C. to 650° C.   
     
     
         7 . A method for manufacturing the stainless steel seamless pipe according to  claim 3 , the method comprising:
 heating a steel pipe material having the component composition at a temperature within a heating temperature range of 1100° C. to 1350° C. to make the steel pipe material into a seamless steel pipe by hot-working;   subsequently, carrying out a quenching treatment by reheating the seamless steel pipe to a temperature within a heating temperature range of 850° C. to 1150° C. and cooling the seamless steel pipe to a cooling stop temperature of 50° C. or lower at a cooling rate for air cooling or faster; and   thereafter, carrying out a tempering treatment by heating the seamless steel pipe to a temperature within a tempering temperature range of 500° C. to 650° C.   
     
     
         8 . A method for manufacturing the stainless steel seamless pipe according to  claim 4 , the method comprising:
 heating a steel pipe material having the component composition at a temperature within a heating temperature range of 1100° C. to 1350° C. to make the steel pipe material into a seamless steel pipe by hot-working;   subsequently, carrying out a quenching treatment by reheating the seamless steel pipe to a temperature within a heating temperature range of 850° C. to 1150° C. and cooling the seamless steel pipe to a cooling stop temperature of 50° C. or lower at a cooling rate for air cooling or faster; and   thereafter, carrying out a tempering treatment by heating the seamless steel pipe to a temperature within a tempering temperature range of 500° C. to 650° C.