Study On The Hot Deformation Behavior Of Ultrahigh Strength Steel BR1500HS

As the global problem such as environmental pollution, energy crisis and automobile safety are more and more serious, there is no doubt that the light weight and securitization of automobile become an important research target for scientific research institution and industry. As the billets of hot stamping are processed under high temperature,the shape and size of them are very fine. The strength of hot stamping is also excellent due to the process of quenching. Therefore, the hot stamping can relieve the above global problem to a certain extent. The ultrahigh strength steel BR1500 HS is the only commercial hot stamping steel that can be supplied in China, so it has an important significant to do some research on the hot deformation behaviors of ultrahigh strength steel BR1500 HS. In this paper, the hot deformation behaviors of ultrahigh strength steel were studied in the way of hot tensile test、metallographic test、processing map and Deform-3D simulation software. The work in this study can be described as follows.The true stress-strain curves of ultrahigh strength steel BR1500 HS at elevated temperature were obtained by performing hot tension tests at temperatures of 773, 873, 1023, 1123, 1223 K and strain rates of 0.01, 0.1, 1s-1 on a Gleeble3500 thermo-mechanical simulator. The activation energy, hardening exponent and other material constants were determined by the basic theory of creep and experimental true stress-strain curves, the Zener-Hollomon parameter was also introduced to establish the relationship between steady stress and deformation conditions. The effects of work hardening and dynamic recovery on the flow stress were described through the dislocation evolution model, and the constitutive model considering work hardening and dynamic recovery was solved. Then,the kinetic of dynamic recovery for ultrahigh strength steel BR1500 HS was deduced based on the established constitutive model.The microstructure evolution of ultrahigh strength steel BR1500 HS at different deformation conditions was analyzed on account of the processing map of ultrahigh strength steel BR1500 HS, and then the microstructure of ultrahigh strength steel BR1500 HS was observed in the way of metallographic test. As a result, it can be found that better microstructure can be achieved under the forming temperature of 1123 K to 1223 K with the strain rate of 0.01s-1 to 0.02s-1.The fracture criterion was revised according to the hot tensile test and finite element simulation. The revised fracture criterion can be applied under the forming temperature of 873 K to 1223 K with the strain rate of 0.01s-1 to 1s-1. Based on the established dynamic recovery kinetics and the revised fracture criterion, the dynamic recovery extent and damage of ultrahigh strength steel BR1500 HS during the process of hot deformation were simulated through the secondary development of Deform-3D.