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用金相法测定了18CrMnTi与18CrMnMo钢高温氰化层经860℃奥氏体化后的恒温C-曲线与马氏体开始转变温度M_H,同时也测定了A_1温度。为了探索氮对过冷奥氏体转变特性的影响,还将这两种钢进行了固体渗碳处理,使渗碳试样具有和高温氰化试样实际上相同的含碳量,然后将二者进行了平行试验。实验结果指出:氰化试样较渗碳试样具有较低的A_1温度、高得多的M_H点、和过冷奥氏体在珠光体与异茵体区间转变时较短的孕育期。实验中发现,在珠光体及上贝茵体形成之前,氰化试样中均有一种过剩相沿奥氏体晶粒边界析出。这种先析相可能是一种含氮的化合物,其析出为珠光体及上贝茵体的非自发形核提供了现成的有利界面,并使奥氏体合金化程度降低,因而加速了转变。
Metallographic method was used to determine the C-curve and martensitic transformation temperature M_H of the high-temperature cyanidation layer of 18CrMnTi and 18CrMnMo steel after being austenitized at 860 ℃. The A_1 temperature was also measured. In order to explore the effect of nitrogen on the transformation characteristics of undercooled austenite, both steels were also subjected to a solid carburizing treatment so that the carburized sample had substantially the same carbon content as that of the high-temperature cyanidation sample, and then two Who conducted a parallel test. The experimental results show that cyanidation samples have lower A_1 temperature and much higher M_H than carburized samples, and shorter incubation period when the supercooled austenite changes between pearlite and the different body. It was found in the experiment that before the formation of pearlite and bainite, there was an excess phase in the cyanide sample precipitated along the austenite grain boundary. This pre-phase may be a nitrogen-containing compound that precipitates as a pearlite and a non-spontaneous nucleation of the upper bainite, provides a ready-made, advantageous interface and reduces austenite alloying, thus accelerating the transformation .