针对碳质量分数为0.47%中碳高铁车轮钢，研究了铌微合金化对前驱体为铁素体-珠光体的组织发生奥氏体逆相变的影响。结果表明，铁素体-珠光体钢的逆相变是一个由碳原子扩散控制的过程，奥氏体优先在珠光体内的铁素体与渗碳体（α/Fe3C）片层界面处形核，并且沿平行于珠光体片层方向的长大速率比垂直于珠光体片层方向更快。含铌车轮钢细化的珠光体组织可以提高奥氏体的形核率，有利于细化奥氏体晶粒。随着再加热温度的提高，含铌车轮钢的奥氏体混晶温度（960℃）比不含铌的钢高80℃，因此通过铌微合金化可扩大再加热奥氏体化温度窗口。结合Thermal-Calc热力学计算和透射电镜分析，铌在中碳钢中主要以析出物的形式存在，析出钉扎作用是其细化奥氏体晶粒、推迟混晶现象出现的主要机制。
In allusion to high speed railway steel wheel,this papaer studied the influence of Nb micro-alloying on re-verse transformation of ferrite and pearlite mocro-structure,whose precursor is ferrite and pearlite. The results indicated that the reverse transformation of ferrite and pearlite was controlled by carbon atomic diffusion. The austenite preferential-ly nucleated at the interface ofα/Fe3C in pearlite and grew up faster in parallel with the direction of pearlite lamellae than perpendicular to that. The Nb micro-alloyed medium carbon steel with refined pearlite colonies could increase the nucle-ation rate of austenite and obtain smaller size austenite grains . The crystal mixture temperature of wheel steel with Nb is 80℃higher than that without Nb. Nb micro-alloying could expand the temperature range of austenite reheat. Thermal-Calc calculation and TEM observation indicated that Nb existed in the form of precipitates in railway wheel steels. Precipi-tation pinning contributes to refine the austenite grain and postpone crystal mixture is the main mechanism of Nb-alloying in railway wheel steels.
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