The effect of intercritical annealing time on the hydrogen embrittlement of dual-phase steel

The present study investigates the influence of annealing duration (30 min, 45 min, and 60 min, referred to as A30, A45, and A60) during intercritical annealing at 78 C-degrees on the hydrogen embrittlement (HE) of dual-phase (DP) steel. The results indicate that HE susceptibility experiences an initial increase and then a decrease with prolonged annealing time, showing its lowest value in A45. Post-mortem electron backscattered diffraction (EBSD) results indicate that HE cracking initiates from martensite or ferrite/martensite interface, and propagate along the ferrite/martensite interface or across the ferrite. Ex-situ EBSD results show that strain localization during tensile deformation is most severe in A30, resulting in the highest number of secondary cracks and rendering it more susceptible to HE. Meanwhile, the chain-networked distribution developed in A60 is considered advantageous for crack propagation, as evidenced by the longest average length of secondary cracks, making A60 also sensitive to HE. Our findings suggest that, in order to improve the HE resistance of DP steels, it is crucial to consider the hardness and distribution of martensite in addition to the volume fraction of martensite.