Abstract: A cold-rolled and heat-treated steel sheet, having a composition comprising, by weight percent: 0.10%?C?0.40%, 3.5%?Mn?8.0%, 0.5%?Si?2.5%, 0.003%?Al?3.0%, with Si+Al?0.8%, 0.001%?Mo?0.5%, S?0.010%, P?0.020%, N?0.008%, and optionally one or more elements selected from amongst Cr, Ti, Nb, V and B, such that: 0.01%?Cr?2.0%, 0.010%?Ti?0.080%, 0.010%?Nb?0.080%, 0.010%?V?0.30%, 0.0005%?B?0.003%, A remainder of the composition being iron and unavoidable impurities resulting from the smelting. The microstructure consists of, in surface fraction, between 10% and 50% of retained austenite, at most 8% of fresh martensite, and tempered martensite. The retained austenite comprises Mn-enriched austenite, having a Mn content higher than 1.3*Mn %, Mn % designating the Mn content of the steel sheet, the surface fraction of said Mn-enriched austenite with respect to the whole microstructure being comprised between 2% and 12%; and Mn-poor austenite, having a Mn content comprised between 0.5*Mn % and 1.3*Mn %.

Abstract: A cold-rolled and heat-treated steel sheet, having a composition including, by weight percent: 0.10%?C?0.40%, 3.5%?Mn?8.0%, 0.5%?Si?2.5%, 0.003%?Al?3.0%, with Si+Al?0.8%, 0.001%?Mo?0.5%, S?0.010%, P?0.020%, N?0.008%, and optionally one or more elements selected from a group comprising Cr, Ti, Nb, V and B, such that: 0.01%?Cr?2.0%, 0.010%?Ti?0.080%, 0.010%?Nb?0.080%, 0.010%?V?0.30%, 0.0005%?B?0.003%, the remainder of the composition being iron and unavoidable impurities resulting from the smelting. The microstructure includes, in surface fraction, between 10% and 50% of retained austenite, at most 8% of fresh martensite, and tempered martensite. The retained austenite includes Mn-enriched austenite, having a Mn content higher than 1.3*Mn %, Mn % designating the Mn content of the steel sheet, a surface fraction of the Mn-enriched austenite with respect to the whole microstructure is between 2% and 12%, and Mn-poor austenite, having an Mn content between 0.5*Mn % and 1.3*Mn %.

Abstract: A cold-rolled and heat-treated steel sheet, having a composition including, by weight percent: 0.10%?C?0.40%, 3.5%?Mn?8.0%, 0.5%?Si?2.5%, 0.003%?Al?3.0%, with Si+Al?0.8%, 0.001%?Mo?0.5%, S?0.010%, P?0.020%, N?0.008%, and optionally one or more elements selected from a group comprising Cr, Ti, Nb, V and B, such that: 0.01%?Cr?2.0%, 0.010%?Ti?0.080%, 0.010%?Nb?0.080%, 0.010%?V?0.30%, 0.0005%?B?0.003%, the remainder of the composition being iron and unavoidable impurities resulting from the smelting. The microstructure includes, in surface fraction, between 10% and 50% of retained austenite, at most 8% of fresh martensite, and tempered martensite. The retained austenite includes Mn-enriched austenite, having a Mn content higher than 1.3*Mn %, Mn % designating the Mn content of the steel sheet, a surface fraction of the Mn-enriched austenite with respect to the whole microstructure is between 2% and 12%, and Mn-poor austenite, having an Mn content between 0.5*Mn % and 1.3*Mn %.