Enhancing the hydrogen embrittlement resistance of 304 steel by grain boundary engineering

Grain boundary engineering has been widely applied to improve grain boundary-related properties such as intergranular corrosion, radiation damage and cracking in face-centered cubic metals with low to medium stacking fault energy. However, only a few investigations have been conducted to reduce the susceptibility to intergranular hydrogen embrittlement. Hydrogen embrittlement has severe effects on applications of engineering materials. In this study, grain boundary engineering was successfully applied to enhance the hydrogen embrittlement resistance of 304 austenitic stainless steel. Optimum grain boundary character distribution was acquired through thermomechanical treatments of 7% cold-rolling reduction and subsequent annealing at 1 0758C for 7 min, which reduced the two hydrogen embrittlement sensitivity indices, Id from 13.5 to 5.2 and Iw from 7.2 to 1.6. The effect of grain boundary character distribution comes from two aspects. On the one hand, special boundaries have some positive effects on the alleviation of hydrogen charging. Under the same charging condition, the charged hydrogen concentration decreases with increasing fraction of low-R CSL boundaries. On the other hand, special boundaries, especially R3 boundaries, could help to hinder the initiation and propagation of hydrogen- induced cracks. Therefore, the resistance of hydrogen embrittlement increases with increasing fraction of low-R CSL boundaries.