| abstract |
A cold-rolled heat-treated steel sheet having a composition containing the following elements in % by weight: 0.10%≤carbon≤0.5%, 1%≤manganese≤3.4%, 0.5%≤silicon≤2.5%, 0.03%≤aluminum≤1.5% , 0%≤sulfur≤0.003%, 0.002%≤phosphorus≤0.02%, 0%≤nitrogen≤0.01%, and may contain one or more of the following optional elements: 0.05%≤chromium≤1%, 0.001%≤molybdenum≤0.5%, 0.001%≤niobium≤0.1%, 0.001%≤titanium≤0.1%, 0.01%≤copper≤2%, 0.01%≤nickel≤3%, 0.0001%≤calcium≤0.005%, 0% ≤vanadium≤0.1%, 0%≤boron≤0.003%, 0%≤cerium≤0.1%, 0%≤magnesium≤0.010%, 0%≤zirconium≤0.010%, the balance is composed of iron and impermissibility caused by processing. Avoided impurity composition, the microstructure of the steel sheet comprises, in area fractions, 10% to 30% retained austenite, 10% to 40% bainite, 5% to 50% annealed martensite, 1 % to 20% quenched martensite and less than 30% tempered martensite with a cumulative amount of bainite and retained austenite greater than or equal to 25%. |