Preparation method of low-carbon Q and P steel for 1400 MPa grade bainite/martensite multiphase vehicle

The invention relates to a preparation method of low-carbon Q and P steel for a 1400 MPa grade bainite/martensite multiphase vehicle. The low-carbon Q and P steel is prepared from the following chemical components including C, Si, Mn, Ni, Ti, Nb, Cr, Al, V, P, N, S, B and the like. According to a given composition formula of the invention, the preparation method comprises the following steps of after burdening, performing smelt with a converter, then performing secondary refining with a vacuum furnace, adding trace alloy elements, performing continuous casting to obtain a casting billet, performing heating and thermal insulation, removing phosphorus with high-pressure water, performing hot rolling, and performing water quenching to a room temperature; performing pickling and multi-pass cold rolling to acquire a steel plate with a target thickness; and heating the steel plate to A3 or above for thermal insulation, performing water quenching to T0 between MS and Mf for thermal insulation, and then performing ai