Microstructure and hardness of 4Cr5Mo2V steel at different cooling rates were observed and measured by using thermal expansion meter,resistance meter and hardness tester,combined with scanning electron microscope and energy dispersive spectroscopy.CCT curves of the tested steel were plotted,and the temperature of carbide intergranular precipitation in the steel was determined.The results show that as the cooling rate decreases,the hardness decreases and the microstructure transforms into martensite,bainite and pearlite in sequence.The critical cooling rates for pearlite and bainite transformation are 0.015 ℃/s and 0.25 ℃/s,respectively.When the cooling rate is not greater than 0.25 ℃/s,carbides precipitate along the grain in the steel,and as the cooling rate decreases,the temperature of carbide precipitation along the grain increases.At a cooling rate of 0.01 ℃/s,the highest precipitation temperature is 1022 ℃.
4Cr5Mo2V hot-working die steelcooling rateCCT curveintergranular carbidesprecipitation temperature
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