Accurate determination of deformation resistance for thin-hard steel strip in tandem cold rolling process

In the tandem cold rolling of thin-hard steel strip, the calculated value of rolling force is often smaller than the measured value in the back stands (e.g. the fourth and fifth stand), and the unbalanced load distribution appears with inaccurate rolling force, which significantly disturbs the stability of rolling process. Strip deformation resistance is an important factor affecting the calculation of rolling force, which is commonly determined via the uniaxial stress test of incoming material, however, the deformation state of material in uniaxial stress test is different from that in actual rolling, especially for the thin-hard strip with severe work-hardening, the effect of rolling strengthening may be more obvious than tensile strengthening. Here, combined the sampling of industrial multi-stand rolled strip with the tensile test, a method to accurately determine deformation resistance of thin-hard strip is proposed, which considers the rolling deformation state. It is found that the stress-strain data in plastic deformation stage of thin-hard specimens from the fourth and fifth stand are difficult to be obtained, so the size effect theory is used for prediction. By comparing the calculated rolling force with the measured rolling force, the accuracy of proposed method is proved. This work builds a solid foundation for accurate calculation of rolling force and balanced load distribution for thin-hard strip in routine five-stand cold rolling mill, and provides a significant reference for solution of similar problem for other types of thin-hard strips and the process improvement of emerging six-stand mill with smaller roll diameter.