A Study of Hot Stamping Process for Producing Ultra-High Strength Steel Part 2014-01-2014

Ultra-High Strength Steels (UHSSs) have been widely used to reduce car body weight and to increase crashworthiness of new generation vehicles. To manufacture such components, hot stamping or press hardening process was developed, in which sheet metal forming at high temperature and quenching procedure were performed successively in a single step. Generally, hot stamped parts exhibit exceptionally high strength properties and low springback effect. In this work, a direct hot stamping process of boron-alloyed steel with a thickness of 1.4 mm was investigated. Temperature evolutions on blank and tools were determined during the experiments. Afterwards, microstructure analysis, hardness measurement and tensile test for different locations, namely, at the bottom and flange of the formed samples were carried out. It was found that final parts after the hot forming mostly showed a fully martensitic microstructure. Yield strength and tensile strength up to 1100 and 1500 MPa, respectively, could be obtained. Moreover, FE simulations of the investigated hot stamping test were performed. The temperature developments of the blank and tools, local distributed hardness values as well as emerged microstructures of the formed parts were predicted. The results of the numerical simulations were acceptable when comparing with the experiments.