采用硬度计SEM, EDS, TEM和XRD研究了经深冷处理和未经深冷处理Cr8Mo2SiV钢的回火硬度、残余奥氏体含量和碳化物析出行为. 结果表明, Cr8Mo2SiV钢经1030℃淬火后,二次硬化峰值硬度出现在回火温度为520℃. 深冷处理能够显著减少残余奥氏体含量,进而提高二次硬化峰温度之前的回火硬度, 并使二次硬化峰向低温区移动20℃.在520℃回火处理, Cr8Mo2SiV钢的回火硬度随保温时间的延长而线性降低.Cr8Mo2SiV钢的二次硬化是残余奥氏体的转变和Mo2C的析出前期共同作用的结果,残余奥氏体的作用更大. Mo2C的析出前期合金元素Mo和C形成[Mo--C]偏聚团的G.P.区, 随回火时间延长, Mo2C析出并长大, 均匀弥分布于基体中.
Cr8–type cold work die steels, such as Cr8Mo2SiV steel have been widely used in recent years due to high strength and high toughness, These steels have obvious secondary hardening effect. It has been widely reported that the secondary hardening mechanism of these die steels resulted from the combination of retained austenite and carbide precipitation. However, less attention has been paid on the secondary hardening of Cr8Mo2SiV steel. In order to investigate the secondary hardening mechanism of Cr8Mo2SiV steel, the hardness, retained austenite and precipitation of Cr8Mo2SiV steel were investigated in this paper by SEM, EDS, TEM and XRD analysis. Experimental results indicate that the secondary hardening peak of Cr8Mo2SiV steel which was quenched at 1030 ℃ appears at 520 ℃. Deep cryogenic treatment observably reduces the content of retained austenite, and thus increases the tempering hardness before secondary hardening peak and the secondary hardening peak shifted to low temperature by about 20 ℃. The tempered hardness of Cr8Mo2SiV steel decreased linearly wth the increase of soaking time when tempering at 520 ℃. The secondary hardening mechanism of Cr8Mo2SiV steel is the combination of the transformation of retained austenite and the earlstage of Mo2C precipitation, and the role of transformation of retained austenite is more obvious. The early tage of Mo2C–carbide precipitation is likely to be G.P. zone which ormed y [Mo–C] segregation group. As the tempering time extended, Mo2C precipitated, and it ws dispersive and uniformly distributed.
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