A rolled steel sheet is provided. The rolled steel sheet has a mechanical strength greater than or equal to 600 MPa and an elongation at fracture that is greater than or equal to 20%. A a method for its fabrication is also provided. The chemical composition of the steel sheet includes 0.10≤C≤0.30%, 6.0≤Mn≤15.0%, 6.0≤Al≤15.0%, and optionally one or more elements selected from among: Si≤2.0%, Ti≤0.2%, V≤0.6% and Nb≤0.3%. The remainder of the composition includes iron and the unavoidable impurities resulting from processing. The ratio of the weight of manganese to the weight of aluminum is such that Mn Al > 1.0 . The microstructure of the sheet includes ferrite, austenite and up to 5% Kappa precipitates in area fraction.