Steel product and manufacturing method of the same
View Patent ↗A steel product has: a chemical composition represented by, in mass %, C: 0.050% to 0.35%, Si: 0.50% to 3.0%, Mn: exceeding 3.0% to 7.5% or less, P: 0.05% or less, S: 0.01% or less, sol. Al: 0.001% to 3.0%, N: 0.01% or less, V: 0% to 1.0%, Ti: 0% to 1.0%, Nb: 0% to 1.0%, Cr: 0% to 1.0%, Mo: 0% to 1.0%, Cu: 0% to 1.0%, Ni: 0% to 1.0%, Ca: 0% to 0.01%, Mg: 0% to 0.01%, REM: 0% to 0.01%, Zr: 0% to 0.01%, B: 0% to 0.01%, Bi: 0% to 0.01%, and the balance: Fe and impurities; and a metal structure in which a thickness of a decarburized ferrite layer is 5 μm or less and a volume ratio of retained austenite is 10% to 40%, wherein tensile strength is 980 MPa or more.
1. A steel product comprising:
a chemical composition represented by, in mass %,
C: 0.050% to 0.35%,
Si: 0.50% to 3.0%,
Mn: exceeding 3.0% to 7.5% or less,
P: 0.05% or less,
S: 0.01% or less,
sol. Al: 0.001% to 3.0%,
N: 0.01% or less,
V: 0% to 1.0%,
Ti: 0% to 1.0%,
Nb: 0% to 1.0%,
Cr: 0% to 1.0%,
Mo: 0% to 1.0%,
Cu: 0% to 1.0%,
Ni: 0% to 1.0%,
Ca: 0% to 0.01%,
Mg: 0% to 0.01%,
REM: 0% to 0.01%,
Zr: 0% to 0.01%,
B: 0% to 0.01%,
Bi: 0% to 0.01%, and
the balance: Fe and impurities; and
a metal structure in which a thickness of a decarburized ferrite layer is 5 μm or less and a volume ratio of retained austenite is 10% to 40%,
wherein tensile strength is 980 MPa or more, and
wherein an average C concentration in the retained austenite is 0.6% or less in mass %.
2. The steel product according to claim 1 ,
wherein, in the metal structure, a number density of cementite is less than 2/μm 2 .
3. The steel product according to claim 1 ,
wherein, in the chemical composition,
V: 0.05% to 1.0%
is satisfied.
4. The steel product according to claim 2 ,
wherein, in the chemical composition,
V: 0.05% to 1.0%
is satisfied.
5. The steel product according to claim 1 ,
wherein, in the chemical composition,
Ti: 0.003% to 1.0%,
Nb: 0.003% to 1.0%,
Cr: 0.01% to 1.0%,
Mo: 0.01% to 1.0%,
Cu: 0.01% to 1.0%, or
Ni: 0.01% to 1.0%,
or arbitrary combination of the above is satisfied.
6. The steel product according to claim 2 ,
wherein, in the chemical composition,
Ti: 0.003% to 1.0%,
Nb: 0.003% to 1.0%,
Cr: 0.01% to 1.0%,
Mo: 0.01% to 1.0%,
Cu: 0.01% to 1.0%, or
Ni: 0.01% to 1.0%,
or arbitrary combination of the above is satisfied.
7. The steel product according to claim 3 ,
wherein, in the chemical composition,
Ti: 0.003% to 1.0%,
Nb: 0.003% to 1.0%,
Cr: 0.01% to 1.0%,
Mo: 0.01% to 1.0%,
Cu: 0.01% to 1.0%, or
Ni: 0.01% to 1.0%,
or arbitrary combination of the above is satisfied.
8. The steel product according to claim 4 ,
wherein, in the chemical composition,
Ti: 0.003% to 1.0%,
Nb: 0.003% to 1.0%,
Cr: 0.01% to 1.0%,
Mo: 0.01% to 1.0%,
Cu: 0.01% to 1.0%, or
Ni: 0.01% to 1.0%,
or arbitrary combination of the above is satisfied.
9. The steel product according to claim 1 ,
wherein, in the chemical composition,
Ca: 0.0003% to 0.01%,
Mg: 0.0003% to 0.01%,
REM: 0.0003% to 0.01%,
Zr: 0.0003% to 0.01%,
B: 0.0003% to 0.01%, or
Bi: 0.0003% to 0.01%,
or arbitrary combination of the above is satisfied.
10. The steel product according to claim 2 ,
wherein, in the chemical composition,
Ca: 0.0003% to 0.01%,
Mg: 0.0003% to 0.01%,
REM: 0.0003% to 0.01%,
Zr: 0.0003% to 0.01%,
B: 0.0003% to 0.01%, or
Bi: 0.0003% to 0.01%,
or arbitrary combination of the above is satisfied.
11. The steel product according to claim 3 ,
wherein, in the chemical composition,
Ca: 0.0003% to 0.01%,
Mg: 0.0003% to 0.01%,
REM: 0.0003% to 0.01%,
Zr: 0.0003% to 0.01%,
B: 0.0003% to 0.01%, or
Bi: 0.0003% to 0.01%,
or arbitrary combination of the above is satisfied.
12. The steel product according to claim 4 ,
wherein, in the chemical composition,
Ca: 0.0003% to 0.01%,
Mg: 0.0003% to 0.01%,
REM: 0.0003% to 0.01%,
Zr: 0.0003% to 0.01%,
B: 0.0003% to 0.01%, or
Bi: 0.0003% to 0.01%,
or arbitrary combination of the above is satisfied.
13. A manufacturing method of the steel product according to claim 1 , comprising the steps of:
heating a steel material to a temperature of 670° C. or more in a manner that an average heating speed between 500° C. to 670° C. is 1° C./s to 5° C./s, which steel material has a chemical composition represented by, in mass %,
C: 0.050% to 0.35%,
Si: 0.50% to 3.0%,
Mn: exceeding 3.0% to 7.5% or less,
P: 0.05% or less,
S: 0.01% or less,
sol. Al: 0.001% to 3.0%,
N: 0.01% or less,
V: 0% to 1.0%,
Ti: 0% to 1.0%,
Nb: 0% to 1.0%,
Cr: 0% to 1.0%,
Mo: 0% to 1.0%,
Cu: 0% to 1.0%,
Ni: 0% to 1.0%,
Ca: 0% to 0.01%,
Mg: 0% to 0.01%,
REM: 0% to 0.01%,
Zr: 0% to 0.01%,
B: 0% to 0.01%,
Bi: 0% to 0.01%, and
the balance: Fe and impurities, and has a metal structure in which volume ratios of bainite and martensite are 90% or more in total and an average value of aspect ratios of bainite and martensite is 1.5 or more;
holding the temperature in a temperature range of 670° C. to 780° C. for 60 s to 1200 s after the heating; and
performing cooling to a temperature of 150° C. or less in a manner that an average cooling speed between the temperature range and 150° C. is 5° C./s to 500° C./s, after the holding.
14. The manufacturing method of the steel product according to claim 13 ,
wherein, in the chemical composition,
V: 0.05% to 1.0%
is satisfied, and
wherein 70% or more of V contained in the steel material is solid-solved.