冷处理对马氏体不锈钢组织和硬度的影响

Effect of cryogenic treatment on microstructure and hardness of martensitic stainless steel

将传统马氏体不锈钢9Cr18Mo和新型含氮马氏体不锈钢SV30钢进行1050℃淬火、-80℃低温冷处理和180℃回火。对比不同热处理状态下两种钢的硬度,用光学显微镜、扫描电子显微镜、X射线衍射分析了显微组织及相组成。采用原位纳米力学测试系统Triboindenter测试了SV30钢中马氏体、残留奥氏体的纳米硬度。结果表明:SV30钢淬火后硬度仅为39.8 HRC,残留奥氏体含量高达67%;经冷处理后SV30钢残留奥氏体含量略微降低,但硬度显著提高至58 HRC。与冷处理促进传统马氏体不锈钢9Cr18Mo残留奥氏体继续转变导致硬度提高不同,冷处理促进了SV30钢中马氏体相内部的弥散析出强化,而大幅度提高了硬度。

Two martensitic stainless steels,traditional 9 Cr18 Mo and the novel SV30 steel,were quenched at 1050 ℃,then cryogenic treated at-80 ℃ and subsequently tempered at 180 ℃. Hardness of 9 Cr18 Mo and SV30 steel at different heat treatment conditions were compared.Phase constituent and microstructures were characterized by means of OM,SEM and XRD. Meanwhile,the nanohardness of martensite and retained austenite in SV30 steel were tested by Triboindenter. The results show that the hardness of quenched SV30 steel is only 39. 8 HRC,while the content of retained austenite is up to 67%. The content of retained austenite is slightly reduced after cryogenic treatment,however the hardness is significantly increased to 58 HRC. Different from that the hardness of traditional 9 Cr18 Mo steel is due to retained austenite transforming to martensite,the hardness of SV30 steel increasing significantly after cryogenic treatment is closely related to dispersive precipitation which strongly strengthens the internal martensite phase during cryogenic treatment.