Patent ID: 11466335

Abstract:
A cold rolled and heat treated steel sheet is provided. The steel sheet includes a composition including 0.17%≤carbon≤0.24%, 1.9%≤manganese≤2.2%, 0.5%≤aluminum≤1.2%, 0.5%≤silicon≤1%, Si+Al≥1.3%, 0.05%≤chromium≤0.2%, 0.015%≤niobium≤0.03%, sulphur≤0.003%, phosphorus≤0.03% and optionally 0.005%≤titanium≤0.05%, 0.001%≤molybdenum≤0.05%, a remainder of the composition including iron and the unavoidable impurities. A microstructure of the coated steel sheet includes, in area fraction, 10 to 20% residual austenite, said austenite phase having a carbon content between 0.9 to 1.1%, 40 to 55% polygonal ferrite, 15 to 40% granular bainite and at least 5% tempered martensite, a sum of tempered martensite and residual austenite being between 20 to 30%. A method is also provided.