22MnB5NbV热成形钢氢损伤与氢聚集的可视化研究

Visualization of Hydrogen Damage and Aggregation for22MnB5NbV Hot Stamped Steel

通过扫描电子显微镜(SEM)、电子背散射技术(EBSD)等手段及电化学充氢与氢微印等实验,表征分析22MnB5NbV热成形钢的组织结构、氢损伤形核临界条件、氢损伤与氢聚集可视化;建立氢损伤演变模型预测氢致裂纹演变方式,并通过充氢实验进一步观察氢致裂纹的形核与扩展,验证模型预测结果。结果表明:22MnB5NbV钢组织基本由马氏体组成,组织较细小,平均晶粒尺寸约7.81μm,小角度晶界占比高达35.34%;充氢4 h时,22MnB5NbV钢诱发氢鼓泡形核的临界电流密度为30 mA/cm^(2);氢原子首先在氢鼓泡内部大量聚集,随充氢时间的增加,氢原子复合为氢分子后在氢压的驱动下逐渐向外部扩散,充氢10 h后,氢原子聚集趋势消失,呈弥散状分布在氢鼓泡四周。长时间电化学充氢会使氢鼓泡的聚集状态呈方向性,在材料内部形成多个线性排列的氢鼓泡,最终连接为不连续氢致裂纹;高浓度氢原子在氢鼓泡内壁偏聚后使其周围基体发生局部软化,在氢压的作用下氢鼓泡易向一端或两端扩展,形成氢致裂纹。

The microstructure,critical conditions of hydrogen damage shaped nuclear,visualization of hydrogen damage and hydrogen aggregation of 22MnB5NbV hot stamped steel were characterized and analyzed by scanning electron microscopy(SEM)and electron back-scatter diffraction(EBSD)analysis,as well as the electrochemical hydrogen charging and hydrogen microprint tests.A hydrogen damage evolution model was established to predict the evolution mode of hydrogen induced cracks.The nucleation and growth of hydrogen induced cracks were further observed through the hydrogen charging experiments to verify the prediction results of the model.It is found that the microstructure of 22MnB5NbV steel is basically composed of martensite,and the microstructure is relatively small.The average grain size is about 7.81μm,and the proportion of small angle grain boundaries is up to 35.34%.The critical current density of hydrogen blister nucleation induced by 22MnB5NbV steel is 30 mA/cm^(2) at 4 h hydrogen charging.The hydrogen atoms first accumulate in a large number inside the hydrogen blister,with the increase of hydrogen charging time,the hydrogen atoms recombine into hydrogen molecules,and then gradually diffuse outwards under the hydrogen pressure.After 10 h of hydrogen charging,the hydrogen atom aggregation trend disappears and is distributed around the hydrogen bubble in a dispersion form.The aggregation state of hydrogen bubbles exhibits directivity under prolonged electrochemical hydrogen filling,the multiple linear arrangement of hydrogen bubbles form inside the material,which is eventually connected as discontinuous hydrogen-induced cracks.The local softening occurs in the surrounding matrix after the high concentration hydrogen atoms depolymerizes in the inner wall of hydrogen bubble.Under the action of hydrogen pressure,hydrogen bubbling is prone to expand to one or both ends,forming hydrogen induced cracks.