Martensitic stainless steel material for hydrogen gas environment and manufacturing method therefor

Abstract

Disclosed is a martensitic stainless steel material for a hydrogen gas environment, having a composition consisting of: 0.03 mass %≤C≤1.20 mass %, Si≤1.00 mass %, Mn≤1.50 mass %, P≤0.060 mass %, S≤0.250 mass %, Cu≤0.50 mass %, 8.0 mass %≤Cr≤22.0 mass %, Ni≤1.00 mass %, and N≤0.40 mass %, and optionally at least one selected from the group consisting of: Mo≤3.00 mass %, V≤1.50 mass %, Nb≤1.00 mass %, Pb≤0.30 mass %, and B≤0.0500 mass %, with the balance being Fe and inevitable impurities; having: a content of a precipitate of 1.50 mass % or more, a crystal grain size number of prior austenite grains of 2.0 or more, a metal structure including a martensite structure, a tensile strength of 1,800 MPa or less, and satisfying D H2(0.7) /D air ≥0.8.

What is claimed is: 
     
         1 . A martensitic stainless steel material for a hydrogen gas environment,
 having a composition consisting of:
 0.03 mass %≤C≤1.20 mass %, 
 Si≤1.00 mass %, 
 Mn≤1.50 mass %, 
 P≤0.060 mass %, 
 S≤0.250 mass %, 
 Cu≤0.50 mass %, 
 8.0 mass %≤Cr≤22.0 mass %, 
 Ni≤1.00 mass %, and 
 N≤0.40 mass %, and 
 optionally at least one selected from the group consisting of:
 Mo≤3.00 mass %, 
 V≤1.50 mass %, 
 Nb≤1.00 mass %, 
 Pb≤0.30 mass %, and 
 B≤0.0500 mass %, 
 
 with the balance being Fe and inevitable impurities; 
   having:
 a content of a precipitate of 1.50 mass % or more, 
 a crystal grain size number of prior austenite grains of 2.0 or more, 
 a metal structure including a martensite structure, 
 a tensile strength of 1,800 MPa or less, and 
   satisfying the following formula (1):
     D   H2(0.7)   /D   air ≥0.8  (1)
 
   here, D air  represents a displacement at a time point when stress shows a local maximum in a stress-displacement curve obtained by performing a tensile test under a condition of a strain rate of 5×10 −5 /s in the atmosphere at normal temperature (25° C.), and   D H2(0.7)  represents a displacement at a time point when stress shows a local maximum or a maximum value in a stress-displacement curve obtained by performing a tensile test under a condition of a strain rate of 5×10 −5 /s in hydrogen gas of 0.7 MPa at normal temperature (25° C.).   
     
     
         2 . The martensitic stainless steel material for a hydrogen gas environment according to  claim 1 , wherein the composition further satisfies at least one elected from the group consisting of:
 0.01 mass %≤V≤1.50 mass %,   0.01 mass %≤Nb≤1.00 mass %, and   0.05 mass %≤Pb≤0.30 mass %.   
     
     
         3 . The martensitic stainless steel material for a hydrogen gas environment according to  claim 1 , wherein the precipitate contains a branched carbonitride. 
     
     
         4 . A manufacturing method for a martensitic stainless steel material for a hydrogen gas environment, comprising:
 a step A of subjecting a material A1 having the same composition as that of the martensitic stainless steel material for a hydrogen gas environment according to  claim 1 , to a hot working and/or a heat treatment to obtain a material A2 containing a spheroidized precipitate,   a step C1 of subjecting the material A2 to a quenching or the quenching and a sub-zero treatment to obtain a material C1 having a retained austenite of 10.0 vol % or less, and   a step D1 of subjecting the material C1 to a tempering.   
     
     
         5 . A manufacturing method for a martensitic stainless steel material for a hydrogen gas environment, comprising:
 a step A of subjecting a material A1 having the same composition as that of the martensitic stainless steel material for a hydrogen gas environment according to  claim 1 , to a hot working and/or a heat treatment to obtain a material A2 containing a spheroidized precipitate,   a step B of subjecting the material A2 to a cold working to obtain a material B,   a step C2 of subjecting the material B to a quenching or the quenching and a sub-zero treatment to obtain a material C2 having a retained austenite of 10.0 vol % or less, and   a step D2 of subjecting the material C2 to a tempering.