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采用箱式电阻炉对试验工具钢进行了不同工艺的回火处理。用扫描电镜对钢中碳化物的形貌进行了观察,用化学方法对析出的碳化物的含量和成分进行了分析。结果表明,试验钢在900℃淬火后的组织为马氏体+碳化物,有较多未溶碳化物在原奥氏体均匀分布;200℃×2 h回火对于组织中碳化物的析出不明显,300℃×2 h回火时析出相严重粗化,造成性能明显下降,而当采用160℃×10 h低温回火工艺时,析出相含量大大增加,呈细小弥散分布,性能得到明显提高;在各种工艺回火后,组织中M_3C的含量均较淬火态明显增加,而MC含量较淬火态无明显差别,M_3C析出相中主要以Fe、C、Cr三种元素为主,MC析出相中主要以V、C、N三种元素为主,还含有少量的Nb、Ti、Cr、Mo等元素。
The use of box-type resistance furnace test tool steel was tempered by different processes. The morphology of the carbides in the steel was observed by SEM, and the content and composition of the precipitated carbides were analyzed by chemical methods. The results show that the microstructure of the test steel after quenching at 900 ℃ is martensite + carbide with more undissolved carbides uniformly distributed in the original austenite. The precipitation of carbides at 200 ℃ for 2 h is not obvious , The precipitated phase coarsens extensively during tempering at 300 ℃ for 2 h, resulting in a significant drop in performance. However, when the tempering process at 160 ℃ × 10 h is used, the content of precipitated phase increases greatly, showing a small and diffuse distribution, and the performance is obviously improved. After tempering in a variety of processes, the contents of M_3C in the microstructure were obviously increased compared with the quenched state, while the MC content was not significantly different from that in the quenched state. The main precipitated phases in the M_3C were mainly Fe, C and Cr, and MC precipitated In the main V, C, N three main elements, but also contains a small amount of Nb, Ti, Cr, Mo and other elements.