Study On Hot Stamping Technology Of Boron Steel Based On Property Gradient Distribution

As a kind of advanced forming technology, hot forming technology can achieve car lightweight well, it has received great attention and becomes more and more widely application in automotive industry. With the technology deep development, people realize that hot forming parts with high strength and high hardness has poor ductility, the body of this kind structure part has no collision energy absorption, occupant safety can not guarantee. In order to achieve better crashworthiness, this kind of parts need to obtain tailored properties. Because of this reason, researchers begin to study the realization method of property gradient distribution on the traditional hot forming technology.The key problem of the technology is to realize different cooling speed or starting forming temperature in the part’s different area. With the deepening of research, the methods of solving the problem also present diversification, but the mainly methods are sheet partial austenitizing, and change of mold materials, mold contact surface or mold temperature. Due to control the mold temperature can more effectively control the cooling speed of the sheet metal, the continuous change of the mold temperature can realize the continuous change of the material’s microstructure and properties, thereby this make it easier to achieve parts have required material properties. This method obtained the further research and wide attention of researchers at our country and abroad, and has become the main method to achieve property gradient distribution in the hot stamping.Based on this method, this paper researched this forming technology in depth by cartridge heaters mold which can control temperature. The main research contents are as follows:(1) First of all, this paper explored the mold temperature impact trend of material microstructure performance without deformation. By using tensile testing machine, microhardness tester, optical microscope, scanning electron microscope (SEM), this paper made the observation of mechanical properties test, fracture scanning, microstructure observation and analysis, the result provides data guide for hot forming experiments with partitioned heating mold.(2) Using partitioned heating mold, we made austenitizing sheet hot forming experiment by making hot area mold under different temperature, and got U-shaped part with gradient performance at last. Then this paper made mechanical properties experiment, microstructure observation by using the corresponding experimental equipment to explore the change trend of cold and hot area structure performance and transition region in the different mold temperature.(3) For hot forming experiments with partitioned heating mold, this paper established FEM models including transfer, hot forming, quenching and cooling in the air. Using simulative results, this paper predicted different regions’cooling curve, cold and hot area hardness transition trend, the change of microstructure contents under different mold temperature. By comparing with actual test results, this paper verified the feasibility and accuracy of simulation modeling.