A method, which allows high-tensile flat steel products to be manufactured with less effort, includes a steel that forms a complex phase microstructure and contains (in wt. %) C: 0.08-0.11%, Mn: 1.00-1.30%, P: ≦0.030%, S: ≦0.004%, Si: 0.60-0.80%, Al: ≦0.05%, N: ≦0.0060%, Cr: 0.30-0.80%, Ti: 0.060-0.120%, remainder iron and unavoidable impurities, being cast into a cast strip having a thickness of 1-4 mm. The cast strip is hot-rolled in-line into a hot-rolled strip having a thickness of 0.5-3.2 mm in a continuous process at a final hot-rolling temperature ranging from 900 to 1100° C., the deformation degree being greater than 20%. The hot-rolled strip is coiled at a coiling temperature ranging from 550 to 620° C., so as to obtain a hot-rolled strip, which has a minimum tensile strength Rm of 800 MPa at a minimum breaking elongation A80 of 10%.