回火对新型机械工具钢碳化物析出行为的影响研究

Effect of Tempering on Precipitation Behavior of Carbides in New-type Machine Tool Steel

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 tempering treatments of the test tool steel under different processes were carded out by using the box type electric resistance furnace. The morphology of the carbides was observed by scanning electron microscope, and the chemical composition of the carbides was analyzed by the chemical method. The results show that, the microstructure of test steel after quenching at 900 ℃ is martensite and carbides, and many un-dissolved carbides uniformly distribute in the original austenite; during tempering at 200 ℃ for 2 h, the precipitation of carbide in the microstructure is not obvious; during tempering at 300 ℃ for 2 h, the precipitated phase seriously coarsens to cause a significant decline in performance; and during tempering at 160 ℃ for 10 h, the precipitated phase contents greatly increase and fine dispersion distribution appears, and the perfo^nance is obviously improved; compared with quenching state, the M3C content in microstrueture is significantly increased while the MC content has no significant difference after tempering at each process, M3C precipitate consists of three major elements Fe, C and Cr, and MC precipitate consists of V, C, N, and a small amount ofNb, Ti, Cr and Mo.