Abstract: Quenching-partitioning (QP) steel has the combination of ultrahigh-strength and good ductility properties due to the martensitic transformation during plastic deformation. However, the formability of the QP1180 steel is still unclear. The ultimate strains of the QP1180 steel under different strain paths were obtained by Nakajima experiment. The effects of the texture evolution and phase transformation on the forming limit of QP1180 steel were analyzed by using the crystal plastic finite element model coupled with the MK theory (CPFEM-PT-MK). The results show that the ultimate principal strain of QP1180 steel is the lowest under the strain path ζ=0.1, and the established CPFEM-PT-MK model can successfully predict the forming limit of QP1180 steel sheet. The texture evolutions of the constituent phases in the QP1180 steel are different under various strain paths. According to simulation, the texture evolutions enhance the forming limit of the QP1180 steel under various strain paths. Without phase transformation, the minimum limited major strain of the QP1180 steel is located under the strain path of ζ=0, which is significantly different from that when phase transformation occurs. And the effect of phase transformation on the forming limit of the QP1180 steel is related to the strain paths.

Key words: crystal plasticity finite element, martensitic transformation, Marciniak-Kuczynski theory, texture evolution, forming limit