Mn-Si-Cr系Q&P钢的准静态、动态力学行为对比

Comparison of quasi-static and dynamic mechanical behavior of Mn-Si-Cr (Q&P) steel

利用万能试验机和分离式霍普金森压杆装置(SHPB)对Mn-Si-Cr系Q&P钢分别进行了准静态和动态压缩试验。在应变速率为0.001、0.01、0.1 s^(-1)和900、1 500、2 200、3 000 s^(-1)情况下分别得到了准静态和动态压缩真应力-真应变曲线,并利用扫描电子显微镜进行压缩后的显微组织和断口分析,利用X射线衍射仪(XRD)对压缩变形试样进行物相分析。结果表明,准静态和动态压缩变形条件下,试验钢的真应力-真应变曲线均可大致分为弹性变形和塑性变形2个阶段,且没有明显的屈服平台。准静态压缩条件下应变速率强化效果不明显但应变强化效应较显著。动态压缩条件下应变强化效应不明显,但展现出一定的应变速率强化效应。准静态变形后,试样中心区域板条组织倾向沿近水平方向(垂直于压缩方向)定向排布。动态变形后,约有1/3试样发生了断裂,未发生断裂的试样中心出现45°方向剪切带,其附近板条组织发生了“屈曲”。准静态变形后残余奥氏体含量下降明显,而动态压缩试样中,残余奥氏体含量只有略微下降,且块状M/A岛内部出现扭曲变形与开裂,这可能是导致部分试样断裂的诱因。动态压缩破坏试样断口整体呈现45°剪切断裂,一端发生微孔聚集性断裂,另外一端发生剪切断裂。

The quasi-static and dynamic compression experiments of Mn-Si-Cr quenching-partitioning(Q&P) steel were carried out by universal testing machine and Split Hopkinson Pressure Bar(SHPB),respectively.The true stress-strain curves were obtained at the strain rate of 0.001,0.01,0.1 s^(-1) and 900,1 500,2 200,3 000 s^(-1),respectively.Scanning electron microscopy(SEM) was employed to observe microstructure and fracture surface after compression.Phase analysis of specimens under the two conditions was conducted by XRD.The results show that under both quasi-static and dynamic deformation conditions,the true stress-strain curves of steel can be roughly divided into two stages,i.e.,elastic and plastic deformation,and no obvious yield platform is observed.Under quasi-static condition,the strain rate strengthening effect is not obvious while the strain hardening effect is remarkable.In contrast,under dynamic deformation,the strain hardening effect is not obvious but shows a certain strain rate strengthening effect.After quasi-static deformation,directional arrangement of lath structure occurs along nearly horizontal direction(i.e.perpendicular to compression direction) in the central region of sample.After dynamic deformation,about 1/3 of samples are fractured and 45° shearing band appears in the central region of unfractured sample with twisting lath structure near this region.There is a significant decrease in residual austenite content of specimens after quasi-static deformation,while only small decrease of retained austenite is found after dynamic deformation.Meanwhile,the serious deformation and microcracking are observed in the blocky M/A island,which may be the cause of fracture for some samples.On the damage fracture of dynamic deformation specimens,the whole sample undergoes 45° shearing fracture with microvoid coalescence fracture on one end and shearing fracture on the other end.