Influence of Grain Size on Hydrogen-induced Cracking Behavior of 35CrMo Steel

The grain size of 35CrMo steel was increased by heat treatment method. The influence of grain size on hydrogen embrittlement sensitivity was studied in the environment of dynamic electrochemical hydrogen charging by slow strain rate test (SSRT) technique and modern micro-analysis method. The results showed that the grain size of 35CrMo steel reached 10.8 μm by complete quenching at 850 ℃ for 15 min (oil cold), subcritical quenching at 780 ℃ for 25 min (oil cold) and high temperature tempering at 740 ℃ for 120 min (air cooling) in order. When the current density of dynamic hydrogen charging was 150 mA/cm2, the breaking strength, elongation and reduction in area of 35CrMo steel were 569.875 MPa, 12.90% and 38.96% respectively, indicating that increasing grain size is an effective way to improve the resistance to hydrogen induced cracking of 35CrMo steel.