Preparation method for ultrahigh-strength thermoforming steel for car

The invention discloses a preparation method for ultrahigh-strength thermoforming steel for a car, and belongs to the technical field of high-strength steel. The preparation method comprises the following steps of: combining stamping forming with low-temperature bainite isothermal treatment; comprehensively utilizing refining technologies such as micro-alloy refining, controlled-rolling controlled-cooling refining, pre-deforming and low-temperature bainite isothermal treatment, thereby obtaining an ultra-fine structure which consists of carbide-free bainite, a little blocky type retained austenite and martensite with volume fraction smaller than 10%, and the ultra-fine structure has tensile strength of 1500-2200 MPa, and ductility of 10-20%. A preparation process for ultrahigh-strength steel comprises the following technological process: smelting, continuous casting, hot rolling, cutting, thermal stamping forming and low-temperature bainite isothermal treatment. During thermal stamping forming, a cut hot-roll