论文部分内容阅读
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。
Effect of niobium microalloying on the austenite reverse transformation of ferrite-pearlite precursors was investigated for carbon steel with carbon mass fraction of 0.47%. The results show that the reverse phase transformation of ferrite - pearlite steel is controlled by diffusion of carbon atoms. The austenite preferentially nucleates at the interface of ferrite and cementite (α / Fe3C) in the pearlite , And the growth rate along the direction parallel to the pearlite sheet is faster than perpendicular to the pearlite sheet. The refined pearlite structure with niobium wheel steel can improve the nucleation rate of austenite and refine the austenite grains. As the reheating temperature increases, the austenite miscible temperature of the niobium-containing wheel steel (960 ℃) is 80 ℃ higher than that of the niobium-free steel. Therefore, the reheating austenitization temperature window can be expanded by niobium microalloying. Combined with thermal-calc thermodynamic calculation and transmission electron microscopy, niobium mainly exists as precipitates in medium-carbon steel. The pinning effect is the main mechanism of refining austenite grains and delaying the phenomenon of mixed crystal.