HIGH STRENGTH STEEL SHEET HAVING EXCELLENT FORMABILITY

Abstract

A high strength steel sheet contains, in percent by mass, 0.03 to 0.2% of C, 0.5 to 2.5% of Si, 1 to 3.0% of Mn, 0.01 to 0.5% of Cr, 0.01 to 0.5% of Mo, 0.02 to 0.15% of Al, 0.15% or less of Ti, 0.15% or less of No, and 0.15% or less of V; wherein the remainder includes Fe and inevitable impurities, and the content of Si satisfies the following formula (1),

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a view showing a relationship between values of ([Si]−α) and TS×El.

Claims

1. A high strength steel sheet comprising, in percent by mass: C: 0.03 to 0.2%;Si: 0.5 to 2.5%;Mn: 1 to 3.0%;Cr: 0.01 to 0.5%;Mo: 0.01 to 0.5%;Al: 0.02 to 0.15%;Ti: 0.15% or less;Nb: 0.15% or less; andV: 0.15% or less,wherein a metal structure of the steel sheet includes ferrite and a second phase, a fraction of ferrite is 10% to 90%, and a fraction of the second phase is 10% to 90%, andthe content of Si satisfies the following formula (1), α−4.1≦[Si]≦α−2.4  (1),provided, α=6.9×([C]+[Mn]/6+[Cr]/5+[Mo]/4+[Ti]/15+[Nb]/17+[V]/14)1/2

2. The high strength steel sheet according to claim 1, wherein the steel sheet contains at least one selected from a group including Ti: 0.01 to 0.15%, Nb: 0.01 to 0.15%, and V: 0.01 to 0.15%.

3. The high strength steel sheet according to claim 1, wherein the steel sheet contains B: 0.0005 to 0.01%.

4. The high strength steel sheet according to claim 1, wherein the steel sheet contains Ca: 0.0005 to 0.01%.

5. The high strength steel sheet according to claim 1, wherein the steel sheet contains at least one of Cu: 0.0005 to 0.5% and Ni: 0.0005 to 0.5%.

6. The high strength steel sheet according to claim 1, wherein a surface of the high strength steel sheet has a galvanizing layer formed thereon.

7. The high strength steel sheet according to claim 1, wherein a surface of the high strength steel sheet has an alloyed galvanizing layer formed thereon.

8. The high strength steel sheet according to claim 1, wherein a metal structure of the high strength steel sheet includes a mixed structure of ferrite and a second phase, and an area ratio (Sc) of an intermediate transformation structure in the second phase is 0.3 or less.