Cr对20MnSiV门架型钢动态CCT曲线和性能的影响

利用热膨胀相变仪研究了不含Cr和含0.3%(质量分数)Cr的叉车门架用20MnSiV钢的连续冷却转变行为,通过光学显微镜观察试验钢在不同冷速下的显微组织,并检测其维氏硬度,得到了试验钢的动态连续冷却转变(CCT)曲线。结果表明,0.1~10 ℃/s的冷速范围内,试验钢在添加0.3%Cr后,贝氏体转变的临界冷速降低,综合力学性能提高,但易在偏析严重区域生成贝氏体和马氏体混合相,使-20 ℃低温冲击性能稳定性下降。通过采取末端电磁搅拌、降低终轧温度、加大末道次变形量、减小轧件空冷间距等措施,能够消除成品异常显微组织,提高低温冲击稳定性。

Effect of Cr on dynamic CCT curves and properties of 20 MnSiV gantry steel

The continuous cooling transformation behavior of forklift gantry 20MnSiV steel without Cr and with 0.3% (mass fraction) Cr was studied by thermal expansion instrument. The microstructure of the tested steel at different cooling rates was observed by optical microscope, and its Vickers hardness was measured. The dynamic continuous cooling transformation (CCT) curves of the tested steel was obtained. The results show that at the cooling rate of 0.1-10 ℃/s, the critical cooling rate of bainite transformation is decreased and the comprehensive mechanical properties are improved with the addition of 0.3% Cr. However, the mixed microstructure of bainite and martensite is easy to form in the severe segregation area, which reduces the stability of Charpy V-notch impact test value at -20 ℃. The abnormal microstructure of the finished product can be eliminated and the low temperature impact stability can be improved by taking steps of end electromagnetic stirring, reducing the final rolling temperature, increasing the deformation of the last pass and reducing the air cooling distance.