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 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 di
sappears 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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