The hot tensile test of Φ10 mm x 30 mm cylinder specimen of low alloy steel Q345B with true strain 0.15 and strain rate 0.001-0.1 s

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at 450-650 ℃ has been carried out by Gleeble-1500 thermal test machine. Results show that with low strain rate at lower temperature the deformation resistance is at elastic-piastic deformation stage and its linear section is longer

and as deformation is larger than 0. 06

the apparent plastic deformation of steel occurs and the change rule of deformation resistance is basically similar to that at higher temperature. Based on test data the math model for deformation resistance of steel Q345B is established by using Origin software with multivariate nonlinear regression. The straightening force of 9 rolls straightener for medium and heavy plate is calculated by using this model combined with straightening theoretical equation

the relative error of calculated results are 0.01%-6.17% .