Effects of hydrogen on the properties of bainitic steel crossing

The microstructures on the damaged surfaces of two served bainitic steel crossings were investigated using optical microscope and scanning electron microscope (SEM). The tensile properties of the bainitic steel with different contents of hydrogen were measured. The results showed that the plasticity of the bainitic steel, such as the reduction of area and elongation, decreases sharply with the increase of hydrogen content. There was a critical content of hydrogen without the hydrogen embrittlement for the commercial bainitic steel used for crossing, which was 7 × 10−5 wt%. When the content of hydrogen in a bainitic steel was lower than the critical value, during the used process of the crossings, the wear failure appeared during the early stage; however, the fatigue spalling appeared in the end of the process. When the content of hydrogen was higher than the critical, brittle fracture was responsible for the failure of the crossing in a short time during use.