Effect of secondary cracks on hydrogen embrittlement of bainitic steels

Hydrogen embrittlement and secondary cracks of bainitic steels were studied by means of the slow strain rate test (SSRT), in situ tension in transmission electron microscopy (TEM) analysis and scanning electron microscopy (SEM). The results showed that the microstructure of the bainitic steels became finer, the phase interfaces as irreversible hydrogen traps significantly were increased, the nano-scale carbides were precipitated from retained austenite, and hydrogen embrittlement was decreased greatly with Al addition. Lots of secondary cracks were formed with Al addition. The stress concentration was relaxed and the hydrogen embrittlement was reduced significantly because of the presence of secondary cracks. Due to hydrogen, the dislocation emission and motion were enhanced and the formation of secondary cracks was reduced.