In the study, the pre-strain effect on hydrogen embrittlement property of the ultra-high-strength transformation-induced plasticity (TRIP)-aided bainitic ferrite (TBF) steel was investigated towards application for automobile frame parts. Specifically, 3–10% tensile pre-strain suppressed hydrogen-induced mechanical degradation relative to total elongation (pre-strain + elongation after hydrogen charging) while 12–15% pre-strained specimen did not exhibit elongation after hydrogen charging. The advantageous effect of the 3–10% pre-strain was attributed to the suppression of crack initiation related to retained austenite. Specifically, the TRIP by pre-straining decreased the volume fraction of retained austenite before hydrogen charging, thereby reducing existing probabilities of preferential crack initiation sites and propagation paths. Conversely, high pre-strain such as 12–15% does not effectively work due to work hardening resulting in increases in hydrogen embrittlement susceptibility and a significant increase in hydrogen content due to the multiplication of dislocations.
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