Abstract: A cold rolled and galvannealed steel sheet having a composition including, by weight percent: C 0.15-0.25%, Mn 2.4-3.5%, Si 0.30-0.90%, Cr 0.30-0.70%, Mo 0.05-0.35%, Al 0.001-0.09%, Ti 0.01-0.06, B 0.0010-0.0040%, Nb 0.01-0.05%, P?0.020%, S?0.010% and N?0.008%, the remainder of the composition being iron and unavoidable impurities resulting from the smelting, and having a microstructure consisting of, in surface fraction, between 80% and 90% of martensite, the balance being ferrite and bainite.

Abstract: A steel sheet has a composition comprising 0.060%?C?0.085%, 1.8%?Mn?2.0%, 0.4%?Cr?0.6%, 0.1%?Si?0.5%, 0.010%?Nb?0.025%, 3.42N?Ti?0.035%, 0?Mo?0.030%, 0.020%?Al?0.060%, 0.0012%?B?0.0030%, S?0.005%, P?0.050%, 0.002%?N?0.007% and optionally 0.0005%?Ca?0.005%, the remainder of the composition being iron and unavoidable impurities. The microstructure consists of 34% to 80% bainite, 10% to 16% martensite, and 10% to 50% of ferrite. The surface fraction of unrecrystallized ferrite, with respect to the whole structure, is of less than 30%. The martensite consists of self-tempered martensite and fresh martensite, the surface fraction of self-tempered martensite being comprised between 4% and 10%.

Abstract: A cold-rolled and annealed steel sheet is provided, the chemical composition of which comprises, the contents being expressed by weight percent: 0.10?C?0.13% 2.4?Mn?2.8% 0.30?Si?0.55% 0.30?Cr?0.56% 0.020?Ti?0.050% 0.0020?B?0.0040% 0.005?Al?0.050% Mo?0.010% Nb?0.040% 0.002?N?0.008% S?0.005% P?0.020%, the remainder consisting of iron and unavoidable impurities resulting from the smelting, the steel sheet having a microstructure consisting of, in surface proportion, martensite and/or lower bainite, said martensite comprising fresh martensite and/or self-tempered martensite, the sum of the surface proportions of martensite and lower bainite being comprised between 60 to 95%, 4 to 35% of low carbide containing bainite, 0 to 5% of ferrite, and less than 5% of retained austenite in island form.

Abstract: A cold-rolled and annealed ferritic steel sheet is provided. The steel has a composition comprising, expressed by weight: 0.001?C?0.15%; Mn?1%; Si?1.5%; 7.5%?AI?10%; 0.020%?Ti?0.5%; S?0.050%; and P?0.1%. A balance of the composition includes iron and inevitable impurities resulting from the smelting. The structure includes kappa (?) precipitates and equiaxed ferrite, an average grain size d? of the equiaxed ferrite is less than 50 microns, and a linear fraction f of intergranular ? precipitates is less than 30%. The linear fraction f is defined by f = ? ( A ) ? di ? ( A ) ? Li . ?(A)di denotes the total length of grain boundaries containing ? precipitates relative to an area (A) and ?(A)Li denotes the total length of the grain boundaries relative to the area (A). A content of carbon in solid solution is less than 0.005% by weight, and the cold-rolled and annealed ferritic steel sheet has a thickness between 0.6 mm and 1.5 mm.

Abstract: A cold-rolled and annealed ferritic steel sheet is provided. The steel has a composition comprising, expressed by weight: 0.001?C?0.15%; Mn?1%; Si?1.5%; 7.5%?AI?10%; 0.020%?Ti?0.5%; S?0.050%; and P?0.1%. A balance of the composition includes iron and inevitable impurities resulting from the smelting. The structure includes kappa (?) precipitates and equiaxed ferrite, an average grain size d? of the equiaxed ferrite is less than 50 microns, and a linear fraction f of intergranular ? precipitates is less than 30%. The linear fraction f is defined by f = ? ( A ) ? di ? ( A ) ? Li . ?(A)di denotes the total length of grain boundaries containing ? precipitates relative to an area (A) and ?(A)Li denotes the total length of the grain boundaries relative to the area (A). A content of carbon in solid solution is less than 0.005% by weight, and the cold-rolled and annealed ferritic steel sheet has a thickness between 0.6 mm and 1.5 mm.

Abstract: A cold-rolled and annealed steel sheet is provided, the chemical composition of which comprises, the contents being expressed by weight percent: 0.10?C?0.13% 2.4?Mn?2.8% 0.30?Si?0.55% 0.30?Cr?0.56% 0.020?Ti?0.050% 0.0020?B?0.0040% 0.005?Al?0.050% Mo?0.010% Nb?0.040% 0.002?N?0.008% S?0.005% P?0.020%, the remainder consisting of iron and unavoidable impurities resulting from the smelting, the steel sheet having a microstructure consisting of, in surface proportion, martensite and/or lower bainite, said martensite comprising fresh martensite and/or self-tempered martensite, the sum of the surface proportions of martensite and lower bainite being comprised between 60 to 95%, 4 to 35% of low carbide containing bainite, 0 to 5% of ferrite, and less than 5% of retained austenite in island form.