Mn-Si-Cr系Q&P钢的准静态、动态力学行为对比

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。

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

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.