A cold rolled and heat treated steel sheet having a composition including the following elements, expressed in % by weight: 0.1%≤carbon≤0.6% 4%≤manganese≤20% 5%≤aluminum≤15% 0≤silicon≤2% aluminium+silicon+nickel≥6.5% and can possibly contain one or more of the following optional elements: 0.01%≤niobium≤0.3%, 0.01%≤titanium≤0.2% 0.01%≤vanadium≤0.6% 0.01%≤copper≤2.0% 0.01%≤nickel≤2.0% cerium≤0.1% boron≤0.01% magnesium≤0.05% zirconium≤0.05% molybdenum≤2.0% tantalum≤2.0% tungsten≤2.0% the remainder being composed of iron and unavoidable impurities caused by elaboration, wherein the microstructure of said steel sheet includes in area fraction, 10 to 50% of austenite, the austenite phase optionally including intragranular kappa carbides, the remainder being regular ferrite and ordered ferrite of D03 structure (Fe,Mn,X)3Al, optionally including up to 2% of intragranular kappa carbides (Fe,Mn)3AlCx said steel sheet presenting a ultimate tensile strength higher than or equal to 900 MPa. It also deals with a manufacturing method and with use of such grade for making vehicle parts.