| 摘要 |
The invention relates to a hot-rolled steel sheet having a tensile strength of greater than 1200 MPa, an Re/Rm ratio of less than 0.75 and an elongation at break of greater than 10%, the composition of which contains, the contents being expressed by weight: 0.10%<=C<=0.25%; 1%<=Mn<=3%; Al>=0.015%; Si<=1.985%; Mo<=0.30%; Cr<=1.5%; S<=0.015%; P<=0.1%; Co<=1.5%; B<=0.005%; it being understood that 1%<=Si+Al<=2%; Cr+(3xMo)>=0.3%, the balance of the composition consisting of iron and inevitable impurities resulting from the smelting, the microstructure of the steel consisting of at least 75% bainite, residual austenite in an amount equal to or greater than 5% and martensite in an amount equal to or greater than 2%.
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