Effect of isothermal temperature on phase transformation,microstructure and properties of Ti-Mo microalloyed high strength dual phase steel
Effect of isothermal temperature on phase transformation,microstructure and properties of Ti-Mo microalloyed high strength dual phase steel was studied by means of thermal simulation experiments,optical microscope,microhardness tester and transmission electron microscopy.The results show that when the isothermal temperature is between 750-725 ℃,the microstructure of the experimental steel is mainly martensite+a small amount of bainite or ferrite.As the isothermal temperature decreases(≤700 ℃),the ferrite content increases,and the carbon removal behavior increases the stability of undercooled austenite,inhibiting the bainite transformation in the medium and low temperature zone.In the subsequent cooling stage,undercooled austenite tends to transform into martensite.The microhardness of both ferrite and martensite increases with the decrease of isothermal temperature,but when the temperature is further reduced,the hardness of martensite remains basically stable(361 HV0.1),the highest microhardness of ferrite is achieved at 650 ℃(242 HV0.1),mainly due to the generation of a large number of fine interphase precipitates inside the ferrite.At the same time,the strengthening effect of precipitates reduces the hardness difference between the ferrite and the martensite,reducing the dependence of dual phase steel strength on the martensite volume fraction.When the isothermal temperature is high,the formation of interphase precipitates is inhibited.
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