Static CCT Curve Measurement and Microstructure Analysis of 18CrNiMo7-6 Steel
The continuous cooling expansion curve of 18CrNiMo7-6 wind power steel was tested by using a Gleeble-3800 thermal 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 Ac1 phase transition temperature of 18CrNiMo7-6 wind power steel is 765℃,and the Ac3 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.
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