High strength steel sheet having high young's modulus and method for manufacturing the same

Abstract

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.

The invention claimed is: 
     
       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.