Numerical approach for predicting hydrogen diffusion in dual-phase hot stamped boron steel with hydrogen embrittlement

The hot stamped boron steel parts are developed quickly due to the increasing demands of light-weighting for cars. However, hydrogen embrittlement always bothers the manufacture and service process of the hot stamped parts. Although several numerical models have been developed to predict the hydrogen diffusion which determines the susceptibility of hydrogen embrittlement, but they are hard to calculate the hydrogen distribution for the hot stamped boron steel because of the possible existence of the dual-phase structure. In this article the hydrogen transport in the dual-phase hot stamped boron steel is studied by a modified numerical method. The present model is developed by introducing the mean-field homogenization method into the classical equation for hydrogen transport. In order to verify the validation of the present approach, a numerical simulation of the hydrogen diffusion near the blunting crack tip is conducted. The overall and local hydrogen concentration are both predicted in trapping sites and lattice sites respectively. In addition, the inconstant occupancy of the local hydrogen concentration per phase near the crack tip is found in both the trapping sites and lattice sites, which is due to the variation of the local mechanical responding under the macro boundary condition. Furthermore, the coupling effects of the microstructure and the mesomechanical behavior on the local hydrogen concentration are analyzed. The present model realizes to multiscale describe the hydrogen diffusion in the dual-phase microstructure under the macro mechanical behavior, which is meaningful to the prediction of hydrogen induced crack in dual-phase microstructure under different boundary conditions.