Mechanical Property and Formability of 580DP and 700DP Hot-Rolled Dual Phase Steel

The tensile properties, hole-expansion properties and forming limit curves of 580DP and 700DP hot-rolled dual phase steel were studied and compared with those of QStE550TM hot-rolled microalloyed high strength steel. The forming limit curves were predicted by forming limit empirical formulas and MK model, and compared with test results. The main strains at valley point of forming limit curves for hot-rolled dual phase steels were fitting to modify the forming limit empirical formula. The results show that compared with QStE550TM steel, 580DP and 700DP steel had higher percentage elongation after fracture and work-hardening index and lower yield ratios, indicating better processability. The hole-expansion ratios of 580DP and 700DP steel were smaller than that of QStE550TM steel, and the hole-expansion properties were worse. The forming limit curve of 580DP steel was higher than that of 700DP steel, and both were higher than that of QStE550TM steel, indicating hot-rolled dual phase steel had better formability. The empirical formulas and MK model did not predict the forming limit curves of 580DP and 700DP steel well. The forming limit curves of hot-rolled dual phase steels calculated by modified forming limit empirical formula agreed with the test results; the relative error was less than 5.6% for 580DP steel, and less than 9.4% in plane strain region and less than 6.5% in other regions for 700DP steel.