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采用OM、SEM、TEM和XRD等分析方法,研究了90CrMnTi钢经780℃淬火(1~3)次和180℃回火处理后的组织和性能,分析了循环淬火-回火处理对冲击韧性的影响。研究表明,循环淬火显著改善了90CrMnTi钢的冲击韧性,但对其硬度的影响较小。经3次淬火后其晶粒尺寸从1次淬火的约18μm减小到3μm,马氏体片的宽度明显变窄,未溶碳化物减少和残留奥氏体量增加。宽度20~70 nm的薄膜状残留奥氏体分布于马氏体片间或马氏体片与碳化物的交界处,且与相邻马氏体满足K-S或NW位向关系。90CrMnTi钢冲击韧性显著提高的根本原因是循环淬火-回火处理所致的晶粒超细化、马氏体片细化和碳化物减少及残留奥氏体量增加的综合作用的结果。
The microstructure and properties of 90CrMnTi steel after tempering at 780 ℃ for 1 ~ 3 times and tempering at 180 ℃ were studied by OM, SEM, TEM and XRD. The effects of cyclic quenching - tempering on impact toughness influences. Studies have shown that the cyclic quenching significantly improves the impact toughness of 90CrMnTi steel, but its hardness is less affected. After three quenching, the grain size decreases from about 18μm to about 3μm in primary quenching, and the width of martensite sheet is obviously narrower, the amount of undissolved carbides and the amount of retained austenite increase. The film-like residual austenite with a width of 20-70 nm is distributed between the martensite sheets or between the martensite sheet and the carbide and satisfies the K-S or NW orientation relationship with the adjacent martensite. The fundamental reason for the significant increase in impact toughness of 90CrMnTi steel is the result of a combination of grain refinement, martensite refinement, reduction of carbides and retained austenite due to recirculation-tempering.