淬回火工艺对Cr20高铬铸铁组织及力学性能的影响

Effects of Quenching and Tempering Process on Microstructure and Mechanical Properties of Cr20 High Chromium Cast Iron

采用金相显微镜、XRD、洛氏硬度计、冲击试验机研究了淬回火工艺对Cr20高铬铸铁组织和力学性能的影响。结果表明:随空淬温度在980~1070℃升高,基体中M7C3二次碳化物逐步溶解,提高了合金淬透性,硬度由铸态时44 HRC提升至1025℃时的63 HRC,继续升高温度,残余奥氏体量过大,硬度低至43 HRC。随回火温度在400~650℃升高,马氏体逐步转变为回火马氏体,残余奥氏体发生二次淬火而部分转变为马氏体,同时M7C3碳化物析出造成二次硬化效应;550℃以上回火,组织转变为回火索氏体,硬度急剧下降。最佳淬回火工艺为(1025±10)℃保温1 h空淬后进行(500±10)℃保温1 h空冷回火。

The effects of quenching and tempering on the microstructure and mechanical properties of Cr20 high chromium cast iron were studied by means of metallographic microscope, XRD, Rockwell hardness tester and impact tester. The results sho w that, with the increase of the quenching temperature in 980 ℃-1070 ℃, the secondary carbides of M7C3 in the matrix gradually dissolve and improve the hardenability of the alloy, and the hardness of the alloy increases from 44 HRC in cast state to 63 HRC at 1025 ℃. If the temperature continues to rise, the amount of retained austenite is too larg e, which causes the hardness to decrease to 43 HRC. With the tempering temperature rising in 400 ℃-650 ℃, the martensite is gradually transformed into tempered martensite. The residual austenite is partially transformed into martensite after secondary quenching. At the same time, the precipitation of M7C3 carbides results in secondary hardening effect. When tempering above550 ℃, the microstructure changes to tempering sorbite, and the hardness decreases sharply. The optimum quenching and tempering technology is holding at(1025±10) ℃ for 1 h and then air quenching, tempering at(500±10) ℃ for 1 h.