Steel material for high-pressure hydrogen gas environment, steel structure for high-pressure hydrogen gas environment, and methods for producing steel material for high-pressure hydrogen gas environment
A steel material and methods for producing the same. The steel material exhibits excellent hydrogen embrittlement resistance in a high-pressure hydrogen gas environment and is, therefore, suitable for use in hydrogen storage tanks, hydrogen line pipes, and the like. The steel material has a specified chemical composition, a tensile strength of 560 MPa or higher, and a fracture toughness value K IH exhibited by the steel material in a high-pressure hydrogen gas atmosphere is 40 MPa·m 1/2 or higher.
1. A steel material having a chemical composition comprising, by mass %:
C: 0.04 to 0.50%;
Si: 0.5 to 2.0%;
Mn: 0.5 to 2.0%;
P: 0.05% or less;
S: 0.010% or less;
N: 0.0005 to 0.0080%;
Al: 0.5% to 2.0%;
O: 0.0100% or less;
Cu: 0.5 to 2.0%; and
the balance being Fe and incidental impurities,
wherein:
the steel material has a tensile strength of 560 MPa or higher and 1097 MPa or lower, and
a fracture toughness value K IH exhibited by the steel material in a hydrogen gas atmosphere at 115 MPa is 40 MPa·m 1/2 or higher.
2. The steel material according to claim 1 , wherein the chemical composition further comprises at least one group selected from the following groups:
Group A: at least one element selected from the group consisting of, by mass %, Ni: 0.05 to 2.00%, Cr: 0.10 to 2.50%, Mo: 0.05 to 2.00%, W: 0.05 to 2.00%, Nb: 0.005 to 0.100%, V: 0.005 to 0.200%, Ti: 0.005 to 0.100%, and B: 0.0005 to 0.0050%, and
Group B: at least one element selected from the group consisting of, by mass %, Nd: 0.005 to 1.000%, Ca: 0.0005 to 0.0050%, Mg: 0.0005 to 0.0050%, and REM: 0.0005 to 0.0050%.
3. A steel structure comprising the steel material according to claim 2 .
4. The steel structure according to claim 3 , wherein the steel structure is a storage tank or a line pipe.
5. A steel structure comprising the steel material according to claim 1 .
6. The steel structure according to claim 5 , wherein the steel structure is a storage tank or a line pipe.
7. A method for producing the steel material according to claim 1 , the method comprising:
heating a steel starting material having the chemical composition to a temperature of Ac 3 transformation temperature or higher and then hot-rolling the steel starting material to form the steel material having a predetermined shape; and
thereafter subjecting the steel material to an accelerated cooling process, in which the steel material is cooled from a temperature of (Ar 3 transformation temperature-50° C.) or higher to a cooling stop temperature of 600° C. or lower at a cooling rate in a range of 1 to 200° C./s.
8. The method according to claim 7 , wherein the chemical composition further comprises at least one group selected from the following groups:
Group A: at least one element selected from the group consisting of, by mass %, Ni: 0.05 to 2.00%, Cr: 0.10 to 2.50%, Mo: 0.05 to 2.00%, W: 0.05 to 2.00%, Nb: 0.005 to 0.100%, V: 0.005 to 0.200%, Ti: 0.005 to 0.100%, and B: 0.0005 to 0.0050%, and
Group B: at least one element selected from the group consisting of, by mass %, Nd: 0.005 to 1.000%, Ca: 0.0005 to 0.0050%, Mg: 0.0005 to 0.0050%, and REM: 0.0005 to 0.0050%.
9. A method for producing the steel material according to claim 1 , the method comprising:
heating a steel starting material having the chemical composition to a temperature of Ac 3 transformation temperature or higher and then hot-rolling the steel starting material to form the steel material having a predetermined shape;
thereafter subjecting the steel material to a direct quenching-tempering process, in which the steel material is cooled from a temperature of (Ar 3 transformation temperature −50° C.) or higher to a cooling stop temperature of 250° C. or lower at a cooling rate in a range of 1 to 200° C./s; and
tempering the steel material at a temperature of Ac 1 transformation temperature or lower.
10. A method for producing the steel material according to claim 1 , the method comprising:
subjecting the steel material having the chemical composition and being formed to have a predetermined shape, to a reheating-quenching-tempering process, in which the steel material is heated to a temperature of Ac 3 transformation temperature or higher;
subsequently subjecting the steel material to water quenching or oil quenching; and
tempering the steel material at a temperature of Ac 1 transformation temperature or lower.