1.School of Mechanical Engineering & Automation,Northeastern University,Shenyang 110819,China
2.State Key Laboratory of Vanadium and Titanium Resources Comprehensive Utilization,Panzhihua Iron and Steel Research Institute Co. ,Ltd. ,Panzhihua 617000,China.
The effect of hydrogen charging time on the hydrogen embrittlement (HE) of the multiphase microstructure of QP980 steel was studied by electrochemical hydrogen charging and slow strain rate tensile (SSRT) tests. The stress-strain curve shows that the tensile strength and elongation decrease significantly with the increase of hydrogen charging time, but the presence of hydrogen does not affect the work hardening rate before fracture. The fracture morphology analysis shows that in the absence of hydrogen, the fracture mode at the center of the specimen is a mixed dimple and quasi-cleavage, and the edge region exhibits a dimple fracture morphology. After hydrogen charging, the mixed fracture zone of the specimen expands, and the unit facet size of quasi-cleavage increases with prolonged hydrogen charging time. Observations of secondary cracks and microstructure revealed that at lower hydrogen concentrations, the phase interfaces between ferrite and martensite served as the primary sites for crack initiation. These cracks propagated along the ferrite-martensite interfaces but were blunted by the ferrite phase, resulting in microvoid-coalescence type cracks. This indicates that the hydrogen-enhanced localized plasticity (HELP) mechanism was the dominant hydrogen embrittlement mechanism under these conditions. When hydrogen concentration is high, the cracks transform into hairline cracks and pass through the matrix ferrite structure, indicating that the hydrogen-enhanced decohesion (HEDE) is the dominant mechanism.
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