Roles of hydrogen content and pre-strain on damage evolution of TRIP-aided bainitic ferrite steel

From the aspect of crack/void initiation and growth characteristics, the effects of pre-strain on the hydrogen embrittlement resistance of a transformation-induced plasticity-aided bainitic ferrite steel were examined. The hydrogen uptake in the specimens without pre-strain caused degradation of crack growth resistance, but the crack initiation probability did not change significantly. It is noteworthy that the degree of degradation was independent of the hydrogen content in the present hydrogen charging condition. Pre-straining to 3% and 6% improved the crack growth resistance of the hydrogen-charged specimens because of a reduction in the probability of austenite presence at the crack tip. Furthermore, a high level of pre-strain provided high hydrogen concentration and resulted in strain-age-hardening, which caused an acceleration of quasi-cleavage fracture, an increase in yield strength, and a stress/strain concentration associated with Lüders deformation. These factors diminished the crack initiation resistance and crack growth resistance.