PROCESS FOR MANUFACTURING STEEL SHEET HAVING VERY HIGH STRENGTH, DUCTILITY AND TOUGHNESS CHARACTERI

文件类型：PDF文档
文件大小：1639K
The invention relates to a hot-rolled steel sheet having a strength 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 comprises, 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% and Cr+(3 ſ Mo) ⿥ 0.3%, the balance ofthe composition consisting of iron and inevitable impurities resulting from the smelting, and the microstructure of the steel consisting of at least 75% bainite, residual austenite in an amount equal to 5% or higher, and martensite in an amount equal to 2% or higher.