Based on theoretical formulae for medium and heavy plate straightening force and measured data in production of steel Q345 22 〜40 mm plate straightening at 500 ~ 630 T

taking undetermined coefficients in math models of deformation force and elastic modulus as optimized variables

minimum error of straightening force calculation as objective function

the math models of deformation resistance and elastic modulus of steel Q345 medium and heavy plate during straightening process is established by using simplex algorithm to optimized calculate the undetermined coefficients. It is obtained that in straightening process of steel Q345 medium and heavy plate at 500 ~ 630 °C

with increasing temperature (T) the deformation resistance (as) decreases: as = - 1 080. 1 +4. 854 7 T - 0. 004 811 5 尸；and with increasing temperature (T) the elastic modulus (E) increases earlier and decreases later： E = ( -6. 480 7 x 105) + 2 576. 5 T - 2. 387 5 T2. Results show that the relative error between calculated and measured value is less than 5%.