Patent ID: 7794552

Claim:
A hot-rolled austenitic iron/carbon/manganese steel sheet, wherein a strength of the steel sheet is greater than 1200 MPa; a product P of a strength in MPa×an elongation at break in % of the steel sheet is greater than 65000 MPa %; a nominal chemical composition of the steel sheet comprises iron and inevitable impurities and, by weight: 0.85% ≦ C ≦ 1.05% 16% ≦ Mn ≦ 19% Si ≦ 2% Al ≦ 0.050% S ≦ 0.030% P ≦ 0.050% N ≦ 0.1%, and, optionally, one or more elements selected from the group consisting of: Cr ≦ 1% Mo ≦ 1.50% Ni ≦ 1% Cu ≦ 5% Ti ≦ 0.50% Nb ≦ 0.50% V ≦ 0.50%; a recrystallized surface fraction of said steel is equal to 100%; a surface fraction of precipitated carbides of said steel sheet is equal to 0%; a mean grain size of the steel sheet is less than or equal to 10 microns; and, at any point in said steel sheet, a local carbon content C L and a local manganese content Mn L , expressed by weight, satisfy % Mn L +9.7% C L ≧21.66.