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

Patent metadata

Field	Value
Publication number	US-2016186283-A1
Application number	US-201414909253-A
Country	US
Kind code	A1
Filing date	Jul 16, 2014
Priority date	Aug 2, 2013
Publication date	Jun 30, 2016
Grant date	—

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, and one or both of Ti: 0.001% or more and 0.200% or less and Nb: 0.001% or more and 0.200% or less, in which the contents of C, N, S, Ti, and Nb 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 the ferrite and the martensite.

First claim

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 %; one or both of Ti: 0.001% or more and 0.200% or less and Nb: 0.001% or more and 0.200% or less, by mass %; and Fe and inevitable impurities, wherein:
the contents of C, N, S, Ti, and Nb satisfy relational expression (1):
500≦ C*≦ 1300  (1),

where C*=(C−(12.0/47.9)×(Ti−(47.9/14.0)×N−(47.9/32.1)×S)−(12.0/92.9)×Nb)×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.

2 . 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 N: 0.0100% or less, by mass %; Ti: 0.001% or more and 0.200% or less, by mass %; V: 0.001% or more and 0.200% or less, by mass %; and the balance being Fe and inevitable impurities, wherein:
the contents of C, N, S, Ti, and V satisfy relational expression (2);
500≦ C*≦ 1300  (2),

where C*=(C−(12.0/47.9)×(Ti−(47.9/14.0)×N−(47.9/32.1)×S)−(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.

3 . 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.

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 at least one chemical element selected from among Cr: 0.05% or more and 1.00% or less, by mass %; 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 %.

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 B: 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 among 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 %.

7 . 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 %; one or both of Ti: 0.001% or more and 0.200% or less and Nb: 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, N, S, Ti, Nb, and Ta satisfy relational expression (3):
500≦ C*≦ 1300  (3),

where C*=(C−(12.0/47.9)×(Ti−(47.9/14.0)×N−(47.9/32.1)×S)−(12.0/92.9)×Nb−(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.

8 . 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 among 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 %.

9 . 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.

10 . 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.

11 . The high strength steel sheet having a high Young's modulus according to claim 10 , the coating film being a galvanizing film and the coated steel sheet being a galvanized steel sheet.

12 . The high strength steel sheet having a high Young's modulus according to claim 10 , the coating film being a galvannealing film and the coated steel sheet being a galvannealed steel sheet.

13 . 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.

14 . 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

Assignees

• Jfe Steel Corp

Inventors

• Minami Hidekazu
• Yokota Takeshi
• Seto Kazuhiro

Classifications

• C21D8/02

  during manufacturing of plates or strips (C21D8/12 takes precedence) · CPC title

• C22C38/06

  containing aluminium · CPC title

• B32B15/013

  one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium · CPC title

• C21D2211/005

  Ferrite · CPC title

• C22C38/34

  with more than 1.5% by weight of silicon · CPC title