Double-pass compression tests of 18CrNiMo7-6 wind power gear steel with 30％deformation at 1150 and 1050 ℃ were carried out by Gleeble-3800 thermal simulator.The thermal expansion curves of the steel at cooling rates of 0.1-30 ℃/s were measured,and the dynamic continuous cooling transformation curves of the steel were drawn by metallographic-hardness method.The microstructure transformation of the steel at different cooling rates was analyzed,and the influence of cooling rate on its microstructure evolution and hardness was explored.The results show that the phase transition temperature of the 18CrNiMo7-6 wind power gear steel is Ac1=759 ℃,Ac3=835 ℃.Under the experimental conditions of double-pass rolling at high temperature,when the cooling rate is less than 0.5 ℃/s,the microstructure of the tested steel is ferrite+pearlite and a small amount of bainite.When the cooling rate is 0.5-1 ℃/s,ferrite gradually disappears and lath bainite begins to appear in the steel.As the cooling rate continues to increase,the content of bainite in the steel increases first and then decreases.When the cooling rate is greater than 10 ℃/s,the microstructure of the tested steel is full martensite.With the increase of cooling rate,the hardness of the tested steel gradually increases from 295 HV to 449 HV.
18CrNiMo7-6 wind power steeldynamic continuous cooling transformation curvemicrostructurehardness
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