Theoretical Prediction of Forming Limit Diagrams for B1500HS Steel at Elevated Temperature Based on Modified Arrhenius and M-K Models

Boron steel B1500HS deforms at elevated temperature under the complete austenite state, and it accords with the 0-angle necking type, irrespective of the strain state on the left- or right-hand side of the forming limit diagram (FLD), which is in accordance with the M-K simplified model. However, the constitutive equation significantly affects the prediction of the FLD of the sheet metal. In this study, the modified Arrhenius model, including the deformation activation energy and the deformation temperature, describing the hot deformation of the sample with austenitic microstructure combined with the Logan-Hosford yield criterion and the Von Mises yield criterion, was used to predict the forming limits of boron steel B1500HS. The theoretical calculation of the forming limits for B1500HS steel at elevated temperature and under different conditions was carried out, and the FLD predicted by the theoretical calculation was found to be in good agreement with the experimental results. It was concluded that with decrease in the initial inhomogeneity of the material, the hot forming limit curves for B1500HS steel at elevated temperature decreased, and the initial inhomogeneity coefficient f(0) = 0.997 was better for the accurate prediction of the hot forming limits of boron steel. With increasing forming temperature, the forming limit curves calculated for B1500HS steel at elevated temperature increased. With increasing mean strain rate, the forming limit curves of B1500HS steel at elevated temperature increased slightly.