Method of producing austenitic iron/carbon/manganese steel sheets having a high strength and excellent toughness and being suitable for cold forming, and sheets thus produced

摘要

The invention relates to a hot rolled sheet which is made from austenitic iron/carbon/manganese steel and which has a resistance of greater than 900 MPa, whereby: resistance (MPa) x elongation at rupture (%) is greater than 45000. The chemical composition of the inventive sheet comprises the following concentrations expressed as weight: 0.5%=C=0.7%, 17%=Mn=24%, Si=3%, Al=0.05%, S=0.03%, P=0.08%, N=0.1% and, optionally, one or more elements such as Cr=1%, Mo=0.4%, Ni=1%, Ti=0.5%, Nb=0.5%, V=0.5%, Cu=5%, Cu=5%, the rest of the composition comprising iron and impurities resulting from production. According to the invention, the recrystallised fraction of the steel is greater than 75% and the surface fraction of precipitated carbides of the steel is less than 1.5%, the average grain size of the steel being less than 18 micrometers.

主权项

1. A process for manufacturing a hot-rolled sheet made of iron/carbon/manganese steel, in which:
providing a semifinished product cast from a steel whose chemical composition comprises, the contents being expressed by weight:
0.5%≦C≦0.7%17%≦Mn≦24%Si≦3%Al≦0.050%S≦0.030%P≦0.080%N≦0.1%,and, optionally, one or more elements such that:
Cr≦1%Mo≦0.40%Ni≦1%Cu≦5%Ti≦0.50%Nb≦0.50%V≦0.50%,the composition further comprising iron and inevitable impurities resulting from the smelting;
heating the semifinished product to a temperature between 1100 and 1300° C.; hot rolling the semifinished product so an end-of-rolling temperature is 890° C. or higher and precipitation of AIN is prevented; observing a time delay between said end of rolling and a subsequent rapid cooling operation, in such a way that the point defined by said time delay and said end-of-rolling temperature lies within an area defined by the ABCD′E′F′A plot of FIG. 1; coiling said sheet at a temperature below 580° C. to obtain a coiled hot-rolled sheet; cold deforming said coiled hot-rolled sheet with an equivalent deformation ratio of 30% or less, without further annealing.