Abstract: A cold rolled and coated steel sheet having a composition including of the following elements, expressed in percentage by weight: 0.140%?Carbon?0.2%, 1.5%?Manganese?2.15%, 0.5%?Silicon?0.8%, 0.4%?Aluminum?0.8%, 0%?Phosphorus?0.09%, 0%?Sulfur?0.09%, 0%?Nitrogen?0.09%, 0.01%?Niobium?0.1%, 0.01%?Titanium?0.1%, and can contain one or more of the following optional elements 0%?Chromium?0.1%, 0%?Nickel?0%, 0%?Calcium?0.005%, 0%?Copper?2%, 0%?Molybdenum?0.5%, 0%?Vanadium?0.1%, 0%?Boron?0.003%, 0%?Cerium?0.1%, 0%?Magnesium?0.010%, 0%?Zirconium?0.010% the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of the steel sheet including in area fraction, 40 to 60% Inter-critical Ferrite, 25 to 45% Transformed Ferrite, 8% to 20% and 5% to 20% Fresh Martensite, 0 to 10% Bainite, wherein the cumulated amount of Inter-critical and Transformed Ferrite is between 75% and 85%.

Abstract: A cold rolled and annealed martensitic steel sheet is provided. The steel sheet includes by weight percent, 0.30?C?0.5%, 0.2?Mn?1.5%, 0.5?Si?3.0%, 0.02?Ti?0.05%, 0.001?N?0.008%, 0.0010?B?0.0030%, 0.01?Nb?0.1%, 0.2?Cr?2.0%, P?0.02%, S?0.005%, Al?1%, Mo?1% and Ni?0.5%. The remainder of the composition includes iron and unavoidable impurities resulting from melting. The microstructure is 100% martensitic and a prior austenite grain size is lower than 20 ?m. The steel sheet has a delayed fracture resistance of at least 24 hours during an acid immersion U-bend test. A method, part, structural member and vehicle are also provided.

Abstract: A cold rolled and annealed martensitic steel sheet is provided. The steel sheet includes by weight percent, 0.30?C?0.5%, 0.2?Mn?1.5%, 0.5?Si?3.0%, 0.02?Ti?0.05%, 0.001?N?0.008%, 0.0010?B?0.0030%, 0.01?Nb?0.1%, 0.2?Cr?2.0%, P?0.02%, S?0.005%, Al?1%, Mo?1% and Ni?0.5%. The remainder of the composition includes iron and unavoidable impurities resulting from melting. The microstructure is 100% martensitic and a prior austenite grain size is lower than 20 ?m. The steel sheet has a delayed fracture resistance of at least 24 hours during an acid immersion U-bend test. A method, part, structural member and vehicle are also provided.