淬火介质对离子渗氮42CrMo钢冲击性能的影响

Effect of quenching media on impact property of ion-nitrided 42CrMo steel

为研究淬火介质对42CrMo钢离子渗氮后的组织与冲击性能的影响,分别用PAG水基淬火液和淬火油两种介质对42CrMo钢进行调质处理(850℃×1 h淬火+580℃×1.5 h回火),然后进行540℃×60 h离子渗氮,利用光学显微镜(OM)、扫描电镜(SEM)、拉伸试验、冲击试验、显微硬度计等研究了42CrMo钢渗氮前后的组织与强韧性。结果表明,采用PAG水基淬火液淬火后42CrMo钢的组织为全马氏体,而经油淬后的组织为马氏体+下贝氏体;两种淬火介质下的调质态组织均为细小均匀的回火索氏体;离子渗氮后,采用PAG水基淬火液时42CrMo钢的渗氮层较油淬时更深,心部基体组织与调质态相差不大,而油淬的心部基体组织中出现比较明显的游离铁素体;油淬42CrMo钢调质态的-20℃冲击吸收能量较高,而PAG水基淬火液淬火的42CrMo钢渗氮后的-20℃冲击吸收能量更高,比油淬试样高13.8%。

In order to investigate the effect of quenching media on microstructure and impact property of the ion-nitrided 42CrMo steel,PAG aqueous solution and quenching oil was used respectively for quenching at 850 ℃ for 1 h and tempering at 580℃for 1.5 h,and then ionnitriding at 540 ℃ for 60 h was carried out.The microstructure,strength and toughness before and after ion-nitriding were studied by means of optical microscope(OM),scanning electron microscope(SEM),tensile test,impact test and microhardness tester.The results show that the microstructure of the 42CrMo steel is all martensite after quenching with PAG aqueous solution,while the oil quenched microstructure is a mixture of martensite and lower bainite,however,both of the microstructure of the steel after quenching and tempering with two quenching medias is fine and uniform tempered sorbite.After ion-nitriding,the nitriding layer of the 42CrMo steel with PAG aqueous solution quenching is thicker than that with oil quenching,and the microstructure at the core is not different from that after quenching and tempering,while the microstructure at the core of that with oil quenching shows obvious free ferrite.The impact absorbed energy at-20 ℃ of the 42CrMo steel after quenching and tempering with oil quenching is higher,while the impact absorbed energy at-20 ℃ of the nitrided 42CrMo steel with PAG aqueous solution is 13.8%higher than that with oil quenching.