NM400耐磨钢连续冷却过程相变研究

Study on Phase Transition of NM400 Wear-resistant Steel in Continuous Cooling

利用MMS-200热模拟试验机研究了NM400耐磨钢奥氏体化后连续冷却转变规律,当冷却速度<1℃/s时,组织为先共析铁素体和粒状贝氏体;1~3℃/s时,B+F;3~5℃/s时,针状贝氏体和少量M组织;5~10℃/s时,M+B;10℃/s以上时,组织为板条马氏体(含少量RA)。在CCT曲线中,相变区域主要分为3部分:铁素体区、贝氏体区、马氏体区。随冷却速度的增加,晶粒随之变细,合金元素使CCT曲线右移,降低了NM400耐磨钢的临界冷却速度。

With MMS-200 thermal simulator, the continuous cooling transformation of NM400 wear-resistant steel after austenizing was studied. When the cooling rate is less than 1 ℃/s, the microstructure is the first eutectoid ferrite and granular bainite. When the cooling rate is 1-3 ℃/s, the microstructure is the bainite and ferrite. When the cooling rate is 3-5 ℃/s, the microstructure is the needle bainite and a small amount of martensite. When the cooling rate is 5-10 ℃/s, the microstructure is martensite and bainite. When the cooling rate is 10 ℃/s or more, the microstructure is lath martensite （containing a small amount of retained austenite）. In the CCT curve, the phase change region is divided into three parts： the ferrite region, the bainite region and the martensite region. With the increasing of the cooling rate, the grain becomes thinner, the alloying elements shift the CCT curve to the right, and the critical cooling rate of the NM400 wear-resistant steel is reduced.