HIGH STRENGTH AIR HARDENABLE MULTI PHASE STEEL WITH EXCELLENT WORKABILITY AND SHEET MANUFACTURING PROCESS THEREOF

An ultra-high-strength air-hardenable multiphase steel having minimal tensile strengths in a non air hardened state of 950 MPa and excellent processing properties, includes the following elements in % by weight: C≥0.075 to ≤0.115; Si≥0.400 to ≤0.500; Mn≥1,900 to ≤2,350; Cr≥0.200 to ≤0.500; Al≥0.005 to ≤0.060; N≥0.0020 to ≤0.0120; S≤0.0030; Nb≥0.005 to ≤0.060; Ti≥0.005 to ≤0.060; B≥0.0005 to ≤0.0030; Mo≥0.200 to ≤0.300; Ca≥0.0005 to ≤0.0060; Cu≤0.050; Ni≤0.050; remainder iron, including usual steel accompanying smelting related impurities, wherein for a widest possible process window during continuous annealing of hot rolled or cold rolled strips made from said steel a sum content of M+Si+Cr in said steel is a function of a thickness of the steel strips according to the following relationship: for strip thicknesses of up to 1.00 mm the sum content of M+Si+Cr is ≥2.800 and ≤3.000%, for strip thicknesses of over 1.00 to 2.00 mm the sum of Mn+Si+Cr is ≥2.850 and ≤3.100%, and for strip thicknesses of over 2.00 mm the sum of Mn+Si+Cr is ≥2.900 and ≤3.200%.