ULTRAHIGH STRENGTH MULTIPHASE STEEL AND METHOD FOR PRODUCING A COLD-ROLLED STEEL STRIP THEREFROM

The invention relates to an ultrahigh strength multiphase steel with a dual-phase microstructure or a complex-phase microstructure and with a low content of residual austenite in particular for lightweight vehicle construction, to a method for producing cold-rolled steel strips from such a steel, and to steel strips produced using said method. The aim of the invention is a novel alloy concept with which the processing window for the continuous annealing of cold strips can be extended. According to the invention, this is achieved by a multiphase steel with a minimum tensile strength of 980 MPa containing (contents in wt. %): C≥0.075 to ≤0.115, Si≥0.400 to ≤0.500, Mn≥1.900 to ≤2.350, Cr≥0.250 to ≤0.400, Al≥0.005 to ≤0.060, N≥0.0020 to ≤0.0120, S≤0.0020, Nb≥0.005 to ≤0.060, Ti≥0.005 to ≤0.060, B>0.0005 to ≤0.0010, Mo>0.200 to ≤0.300, Ca>0.0010 to ≤0.0060, Cu≤0.050, Ni≤0.050, and residual iron, including customary steel-accompanying smelting-related impurities, wherein the total content of Mn+Si+Cr is ≥2.500 to ≤3.250 with a view to a processing window which is as wide as possible during the annealing process, in particular during the continuous annealing process, of cold strips of said steel.