High strength steel sheet having high young's modulus and method for manufacturing the same
A high strength steel sheet having a high Young's modulus, the steel sheet having a chemical composition including, by mass %, C: 0.060% or more and 0.150% or less, Si: 0.50% or more and 2.20% or less, Mn: 1.00% or more and 3.00% or less, Nb: 0.001% or more and 0.200% or less, and V: 0.001% or more and 0.200% or less, in which the contents of C, Nb, and V satisfy the equation 500≤C*≤1300. The steel sheet has a microstructure including ferrite in an amount of 20% or more and martensite in an amount of 5% or more, in terms of area ratio, such that the average grain size of the ferrite is 20.0 μm or less and the inverse intensity ratio of γ-fiber for α-fiber is 1.00 or more in each of the ferrite and the martensite.
1. A high strength steel sheet having a high Young's modulus, the steel sheet having a chemical composition comprising:
C: 0.060% or more and 0.150% or less, by mass %;
Si: 0.50% or more and 2.20% or less, by mass %;
Mn: 1.00% or more and 3.00% or less, by mass %;
P: 0.100% or less, by mass %;
S: 0.0100% or less, by mass %;
Al: 0.010% or more and 2.500% or less, by mass %;
N: 0.0100% or less, by mass %;
Nb: 0.001% or more and 0.200% or less, by mass %;
V: 0.001% or more and 0.200% or less, by mass %; and
Fe and inevitable impurities,
wherein:
the contents of C, Nb, and V satisfy relational expression (1):
500≤C*≤1300 (1),
where C*=(C−(12.0/92.9)×Nb−(12.0/50.9)×V)×10000, where atomic symbols in the relational expression respectively represent the contents (mass %) of the corresponding chemical elements, and where C* is represented in units of mass ppm, and
the steel sheet has a microstructure including ferrite in an amount of 20% or more in terms of area ratio and martensite in an amount of 5% or more in terms of area ratio, the average grain size of the ferrite being 20.0 μm or less, and the inverse intensity ratio of γ-fiber for α-fiber is 1.00 or more in each of the ferrite and the martensite, and
the chemical composition excludes Cr.
2. The high strength steel sheet having a high Young's modulus according to claim 1 , the steel sheet further having an average r value of 1.05 or more and a limiting drawing ratio (LDR) of 2.03 or more.
3. The high strength steel sheet having a high Young's modulus according to claim 1 , wherein the chemical composition of the steel sheet further comprises at least one chemical element selected from the group consisting of Mo: 0.05% or more and 1.00% or less, by mass %; Ni: 0.05% or more and 1.00% or less, by mass %; and Cu: 0.05% or more and 1.00% or less, by mass %.
4. The high strength steel sheet having a high Young's modulus according to claim 1 , wherein the chemical composition of the steel sheet further comprises B: 0.0003% or more and 0.0050% or less, by mass %.
5. The high strength steel sheet having a high Young's modulus according to claim 1 , wherein the chemical composition of the steel sheet further comprises at least one chemical element selected from the group consisting of Ca: 0.0010% or more and 0.0050% or less, by mass %; Mg: 0.0005% or more and 0.0100% or less, by mass %; and REM: 0.0003% or more and 0.0050% or less, by mass %.
6. The high strength steel sheet having a high Young's modulus according to claim 1 , wherein the chemical composition of the steel sheet further comprises at least one chemical element selected from the group consisting of Sn: 0.0020% or more and 0.2000% or less, by mass %; and Sb: 0.0020% or more and 0.2000% or less, by mass %.
7. The high strength steel sheet having a high Young's modulus according to claim 1 , wherein the steel sheet is a cold-rolled steel sheet.
8. The high strength steel sheet having a high Young's modulus according to claim 1 , wherein the steel sheet is a coated steel sheet having a coating film on the surface thereof.
9. The high strength steel sheet having a high Young's modulus according to claim 8 , the coating film being a galvanizing film and the coated steel sheet being a galvanized steel sheet.
10. The high strength steel sheet having a high Young's modulus according to claim 8 , the coating film being a galvannealing film and the coated steel sheet being a galvannealed steel sheet.
11. The high strength steel sheet having a high Young's modulus according to claim 1 , wherein the steel sheet has a Young's modulus of 205 GPa or more in a rolling direction and in direction at an angle of 45° to the rolling direction.
12. The high strength steel sheet having a high Young's modulus according to claim 11 , wherein the steel sheet has a Young's modulus of 220 GPa or more in a direction at a right angle to the rolling direction.
13. The high strength steel sheet having a high Young's modulus according to claim 1 , the steel sheet further having a tensile strength (TS) of 780 MPa or more.
14. The high strength steel sheet having a high Young's modulus according to claim 1 , wherein the chemical composition of the steel sheet further comprises Sn: 0.0020% or more and 0.2000% or less, by mass %.
15. A high strength steel sheet having a high Young's modulus, the steel sheet having a chemical composition comprising:
C: 0.060% or more and 0.150% or less, by mass %;
Si: 0.50% or more and 2.20% or less, by mass %;
Mn: 1.00% or more and 3.00% or less, by mass %;
P: 0.100% or less, by mass %;
S: 0.0100% or less, by mass %;
Al: 0.010% or more and 2.500% or less, by mass %;
N: 0.0100% or less, by mass %;
Nb: 0.001% or more and 0.200% or less, by mass %;
V: 0.001% or more and 0.200% or less, by mass %;
Ta: 0.0010% or more and 0.1000% or less, by mass %; and
Fe and inevitable impurities,
wherein:
the contents of C, Nb, V, and Ta satisfy relational expression (2):
500≤C*≤1300 (2),
where C*=(C−(12.0/92.9)×Nb−(12.0/50.9)×V−(12.0/180.9)×Ta)×10000, where atomic symbols in the relational expression respectively represent the contents (mass %) of the corresponding chemical elements, and where C* is represented in units of mass ppm, and
the steel sheet has a microstructure including ferrite in an amount of 20% or more in terms of area ratio and martensite in an amount of 5% or more in terms of area ratio, the average grain size of the ferrite being 20.0 μm or less, and the inverse intensity ratio of γ-fiber for α-fiber is 1.00 or more in each of the ferrite and the martensite.
16. A method for manufacturing the high strength steel sheet having a high Young's modulus according to claim 1 , the method comprising:
heating a steel slab to a temperature range of 1150° C. or higher and 1300° C. or lower,
after heating the steel slab, hot-rolling the heated steel slab in a finishing temperature range of 850° C. or higher and 1000° C. or lower to produce a hot-rolled steel sheet,
coiling the hot-rolled steel sheet in a coiling temperature range of 500° C. or higher and 800° C. or lower,
after coiling the hot-rolled steel sheet, cold-rolling the coiled steel sheet with a cold rolling reduction of 40% or more in order to obtain a cold-rolled steel sheet,
heating the cold-rolled steel sheet to a temperature range of 450° C. or higher and 800° C. or lower,
holding the heated steel sheet in the heating temperature range for 300 seconds or more,
subsequently, after holding the heated steel sheet, heating the held steel sheet to a temperature of 750° C. or higher and 950° C. or lower, and
after heating the held steel sheet, cooling the heated steel sheet at an average cooling rate of 3° C./sec or more in a temperature range of 300° C. or higher and 700° C. or lower in order to obtain a cold-rolled steel sheet.
17. A method for manufacturing the high strength steel sheet having a high Young's modulus according to claim 1 , the method comprising:
heating a steel slab to a temperature range of 1150° C. or higher and 1300° C. or lower,
after heating the steel slab, hot-rolling the heated steel slab in a finishing temperature range of 850° C. or higher and 1000° C. or lower to produce a hot-rolled steel sheet,
coiling the hot-rolled steel sheet in a coiling temperature range of 500° C. or higher and 800° C. or lower,
after coiling the hot-rolled steel sheet, cold-rolling the coiled steel sheet with a cold rolling reduction of 40% or more in order to obtain a cold-rolled steel sheet,
heating the cold-rolled steel sheet to a temperature range of 450° C. or higher and 800° C. or lower,
holding the heated steel sheet in the heating temperature range for 300 seconds or more,
subsequently, after holding the heated steel sheet, heating the held steel sheet to a temperature of 750° C. or higher and 950° C. or lower,
cooling the heated steel sheet at an average cooling rate of 3° C./sec or more in a temperature range of 550° C. or higher and 700° C. or lower, and
after cooling the heated steel sheet, performing a galvanizing treatment in order to obtain a galvanized steel sheet.
18. A method for manufacturing the high strength steel sheet having a high Young's modulus according to claim 1 , the method comprising:
heating a steel slab to a temperature range of 1150° C. or higher and 1300° C. or lower,
after heating the steel slab, hot-rolling the heated steel slab in a finishing temperature range of 850° C. or higher and 1000° C. or lower to produce a hot-rolled steel sheet,
coiling the hot-rolled steel sheet in a coiling temperature range of 500° C. or higher and 800° C. or lower,
after coiling the hot-rolled steel sheet, cold-rolling the coiled steel sheet with a cold rolling reduction of 40% or more in order to obtain a cold-rolled steel sheet,
heating the cold-rolled steel sheet to a temperature range of 450° C. or higher and 800° C. or lower,
holding the heated steel sheet in the heating temperature range for 300 seconds or more,
subsequently, after holding the heated steel sheet, heating the held steel sheet to a temperature of 750° C. or higher and 950° C. or lower,
cooling the heated steel sheet at an average cooling rate of 3° C./sec or more in a temperature range of 550° C. or higher and 700° C. or lower,
after cooling the heated steel sheet, performing a galvanizing treatment, and
after performing the galvanizing treatment, performing a galvannealing treatment in a temperature range of 470° C. or higher and 600° C. or lower in order to obtain a galvannealed steel sheet.