18CrNiMo7-6钢静态CCT曲线测定与组织分析

Static CCT Curve Measurement and Microstructure Analysis of 18CrNiMo7-6 Steel

利用Gleeble-3800热模拟机对0.1~30℃/s冷却速度下18CrNiMo7-6风电钢连续冷却膨胀曲线进行测试。结合金相-硬度法绘制了18CrNiMo7-6风电钢静态连续冷却转变曲线(CCT曲线),分析了不同冷却速率条件下18CrNiMo7-6风电钢组织转变规律。实验结果表明,18CrNiMo7-6风电钢奥氏体相变点Ac1相变温度为765℃,Ac3相变温度843℃。当冷却速度小于0.5℃/s时,试验钢组织为铁素体和珠光体,发生高温相变;冷却速度0.5~1℃/s时,试验钢中铁素体逐渐减少,开始出现板条状马氏体组织;冷速大于2℃/s时,试验钢组织主要为贝氏体及马氏体,同时发生中温相变和低温相变;随冷速增加钢中贝氏体组织含量减少,马氏体组织含量增多;冷速大于20℃/s,组织全部为马氏体,只发生低温相变;冷速由0.1℃/s增加至30℃/s过程中,风电钢试样硬度逐渐增加。

The continuous cooling expansion curve of 18CrNiMo7-6 wind power steel was tested by using a Gleeble-3800thermal simulator at a cooling rate of 0.1-30℃/s.The static continuous cooling transformation curve(CCT curve)of 18CrNiMo7-6 wind power steel was plotted by using metallographic hardness method.The microstructure transformation law of 18CrNiMo7-6 wind power steel under different cooling rate conditions was analyzed.The experimental results show that the Ac_1 phase transition temperature of 18CrNiMo7-6 wind power steel is 765℃,and the Ac_3 phase transition temperature is 843℃.When the cooling rate is less than 0.5℃/s,the microstructure of the experimental steel is ferrite and pearlite,and high-temperature phase transformation occurs;At a cooling rate of 0.5-1℃/s,ferrite disappears and plate-like martensite is initially formed;Starting from 2℃/s,the microstructure is mainly bainite and martensite,with both medium temperature and low temperature phase transformations occurring simultaneously;After 10℃/s,the bainite content decreases and the martensite content increases with the increase of cooling rate;When the cooling rate is greater than 20℃/s,the microstructure is entirely martensitic with only low-temperature phase transformation occurring;During the process of increasing the cooling rate from 0.1℃/s to 30℃/s,the hardness of the wind power steel shows an upward trend.