Abstract: By Gleeble3500 thermomechanical simulator to determine the dilation curves at continuous cooling conditions, the critical transformation points of steel NM400 are Ac₁=719. 4 ℃ and Ac₃ =847. 8 ℃，and combined with the metallographic method, the continuous cooling transformation (CCT) curves of super cooling austenite of tested steel are plotted using Origin software. The results show that with the increase of cooling rate, the microhardness of steel increases gradually, and the phase transformation gradually changes from ferrite and pearlite to bainite and martensite, and the ferrite content decreases gradually ； when the cooling rate is less than 1 ℃/s, the pearlite content increases gradually, and the grain size gradually decreases; when the cooling rate is greater than 5 ℃/s, the ferrite and pearlite phase transition disappears ,and with the increase of the cooling rate the bainite phase decreases and martensitic phase is gradually increasing.

摘要： 用Gleeble3500热模拟试验机测定的连续冷却膨胀曲线,得出NM400钢临界相变点Ac₁=719.4 ℃, Ac₃=847.8℃,结合金相法,利用Origin软件绘制了试验钢的过冷奥氏体连续冷却转变（CCT）曲线。结果表明,随着冷却速度增大,钢的显微硬度逐渐增大,显微组织逐渐由铁素体和珠光体过渡为贝氏体和马氏体,铁素体量逐渐减少;冷速小于1℃/s珠光体含量逐渐增多,尺寸逐渐减小;冷速大于5 ℃/s,铁素体和珠光体逐渐消失,贝氏体相变量随冷速增加而减少,马氏体相变量逐渐增多。

关键词: NM400耐磨钢, CCT曲线, 热膨胀法, 相变点, 组织