Stainless steel pipe and method for manufacturing the same

Abstract

Provided are a stainless steel pipe and a method for manufacturing the same. The stainless steel pipe has a chemical composition containing, by mass %, C: 0.05% or less, Si: 1.0% or less, Mn: 0.10% to 2.0%, P: 0.05% or less, S: less than 0.005%, Cr: 16.0% to 20.0%, Mo: 0.6% to 1.4%, Ni: 3.0% to 5.0%, Al: 0.001% to 0.10%, N: 0.010% to 0.100%, O: 0.01% or less, Cu: 0.3% to 3.5%, and a balance of Fe and incidental impurities, in which predetermined relational expressions are satisfied by Cr, Ni, Mo, W, Cu, and C, a microstructure including, in terms of volume fraction, 45% or more of a tempered martensitic phase, 20% to 40% of a ferrite phase, and 5% to 25% of a retained austenite phase, a yield strength of 758 MPa or higher, and an absorbed energy at a temperature of −10° C. vE−10 of 40 J or more.

1 . A stainless steel pipe having
 a chemical composition comprising, by mass %,
 C: 0.05% or less, 
 Si: 1.0% or less, 
 Mn: 0.10% to 2.0%, 
 P: 0.05% or less, 
 S: less than 0.005%, 
 Cr: 16.0% (not inclusive) to 20.0%, 
 Mo: 0.6% (not inclusive) to 1.4% (not inclusive), 
 Ni: 3.0% to 5.0% (not inclusive), 
 Al: 0.001% to 0.10%, 
 N: 0.010% to 0.100%, 
 O: 0.01% or less, 
 Cu: 0.3% to 3.5%, and 
 a balance of Fe and incidental impurities, in which relational expression (1) and relational expression (2) are satisfied, 
   a microstructure including, in terms of volume fraction, 45% or more of a tempered martensitic phase, 20% to 40% of a ferrite phase, and 5% to 25% of a retained austenite phase,   a yield strength of 758 MPa or higher, and   an absorbed energy at a temperature of −10° C. vE −10  of 40 J or more:
   Cr+0.65×Ni+0.6×(Mo+0.5×W)+0.55×Cu−20×C≥21.7  (1),
 
   Cr+3.3×(Mo+0.5×W)−17×C≥21.0  (2),
 
   where, in both relational expressions, each of Cr, Ni, Mo, W, Cu, and C denotes the content (mass %) of the corresponding element and is assigned a value of zero when the corresponding element is not added.   
     
     
         2 . The stainless steel pipe according to  claim 1 , wherein the chemical composition further comprises, by mass %, one, two, or more selected from group A to group E below:
 group A: one, two, or more selected from Ti: 0.3% or less, Nb: 0.5% or less, V: 0.5% or less, and Ta: 0.5% or less,   group B: one, two, or all selected from B: 0.0050% or less, Ca: 0.0050% or less, and REM: 0.010% or less,   group C: one or both selected from Mg: 0.010% or less and Zr: 0.2% or less,   group D: one or both selected from Sn: 0.20% or less and Sb: 0.20% or less, and   group E: one or both selected from Co: 1.0% or less and W: 3.0% or less.   
     
     
         3 . A method for manufacturing the stainless steel pipe according to  claim 1 , the method comprising
 heating a steel pipe material to a heating temperature of 1100° C. to 1350° C. and performing hot working on the heated material to obtain a seamless steel pipe having a predetermined shape,   performing a quenching treatment of reheating the seamless steel pipe after the hot working to a temperature of 850° C. to 1150° C. and cooling the heated steel pipe to a cooling stop temperature of 0° C. (not inclusive) to 50° C. in terms of surface temperature at a cooling rate equal to or higher than a cooling rate corresponding to natural cooling, and   performing a tempering treatment of heating the quenched steel pipe to a tempering temperature of 500° C. to 650° C.   
     
     
         4 . A method for manufacturing the stainless steel pipe according to  claim 2 , the method comprising
 heating a steel pipe material to a heating temperature of 1100° C. to 1350° C. and performing hot working on the heated material to obtain a seamless steel pipe having a predetermined shape,   performing a quenching treatment of reheating the seamless steel pipe after the hot working to a temperature of 850° C. to 1150° C. and cooling the heated steel pipe to a cooling stop temperature of 0° C. (not inclusive) to 50° C. in terms of surface temperature at a cooling rate equal to or higher than a cooling rate corresponding to natural cooling, and   performing a tempering treatment of heating the quenched steel pipe to a tempering temperature of 500° C. to 650° C.