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-rolled plate is re-heated to Ac3+50 DEG C for austenization, and heat is preserved for 0.5-1 hour, and then, the plate is immediately moved onto thermal stamping equipment to perform stamping forming; the quick cooling and
quenching effect of a thermal stamping mould is utilized for cooling super-cooled
austenite to a temperature lower than Ms point, is subjected to isothermal treatment for 0.5-1 minute, is quickly put into a salt-bath furnace or a resistance furnace of 200-300 DEG C to perform isothermal treatment for 4-6 hours, is subjected to isothermal bainite transformation, and is taken out for being air-cooled to the
room temperature.