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Q500钢在不同应变速率下的氢致裂纹研究

Investigation on hydrogen-induced cracks of Q500 steel under different strain rates

  • 摘要: 本文采用氢微印技术,对Q500实验钢内氢分布状态展开观察;同时,开展慢应变速率拉伸实验,分析实验钢充氢后不同应变速率下拉伸断口形貌以及裂纹扩展情况,研究应变速率对Q500钢氢致裂纹形核、扩展的影响。结果表明,氢原子主要在M/A岛上及其边界、夹杂物与基体的界面和晶界(原奥氏体晶界、块状贝氏体铁素体和板条状贝氏体铁素体界面、板条束界、板条界)处富集。充氢后,随着应变速率的降低,实验钢的屈服强度、抗拉强度和伸长率均下降,氢脆指数升高;拉伸断口边缘的微观形貌从韧窝逐渐转变为河流状花样;裂纹源数量增加,裂纹源萌发位置从M/A岛边界、M/A岛边界和板条束界,转变为M/A岛边界和板条界;裂纹扩展方式逐渐由沿晶扩展转变为穿晶扩展。

     

    Abstract: In this study, hydrogen microprinting was employed to characterize the distribution of hydrogen in the Q500 experimental steel. Slow strain rate tensile (SSRT) tests were also conducted at various strain rates on the hydrogen-charged steel to examine fracture morphology and crack propagation behavior, aiming to clarify the influence of strain rate on hydrogen-induced crack nucleation and growth. The results show that hydrogen atoms preferentially segregated at M/A islands and their boundaries, at inclusion-matrix interfaces, and at various grain boundaries, including prior austenite grain boundaries, interfaces between granular and lath bainitic ferrite, as well as packet and lath boundaries. After hydrogen charging, with decreasing strain rate, the yield strength, tensile strength, and elongation all decreased, whereas the hydrogen embrittlement index increased correspondingly. The microscopic fracture morphology at the tensile specimen edge gradually transitioned from dimples to river-like patterns. Meanwhile, the number of crack initiation sites increased, and the initiation locations shifted from M/A island boundaries (or M/A island boundaries plus packet boundaries) to M/A island boundaries and lath boundaries. Furthermore, the dominant crack propagation mode gradually changed from intergranular to transgranular fracture.

     

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