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+(3×Mo)≥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%.