The invention discloses an ultrafine-grain hot-rolling
dual phase steel plate for automobiles and a production method thereof. The chemical constituent of the steel plate comprises, by
mass, 0.07%-0.09% of C, 0.2%-0.5% of Si, 1.3%-1.5% of Mn, 0.03%-0.05% of Nb, less than 0.02% of P, and less than 0.01% of S, and the balance being iron and ineluctable impurities, wherein the
volume fraction of ferrite is between 60% and 80%, the
volume fraction of
bainite is between 20% and 40%, the average grain
diameter is between 2-3 mu m. The production method comprises that:
continuous casting blanks are heated to 1150-1300 DEG C and insulated for 2-3 h. The rolling temperature is between 1100-1200 DEG C and the finishing temperature>950 DEG C during rough rolling. During finish rolling, the initial rolling temperature is between 890-950 DEG C and the final rolling temperature>800 DEG C. A laminar flow cooling technology is utilized and rapid cooling is carried out. The
cooling speed is controlled between 25-35 DEG C / s and coiling is carried out when the temperature is between 400-450 DEG C finally. The steel plate and the production method thereof have the advantages of low cost without adding noble metals such as Cr, Mo; simple technology without subsection cooling, easy
production control; uniform and consistent product performance and good
formability. The steel plate and the production method thereof are mainly used for
stamping workpieces of automobile wheels and girders.