Study Of Phase Transformation Law Of CSP Hot Rolled 50CrV4 Spring Steel

50CrV4 spring steel which has good mechanical properties,high fatigue strength and hardenability is being used to manufacture the automotive clutch spring diaphragm and the automotive suspension spring etc.The domestic 50CrV4 hot rolled steel strip is usually produced by traditional hot rolling,but there are some quality problems.Compared with the traditional hot continuous rolling process,compact strip production?CSP?process has some advantages of quality improvement of medium and high carbon steel and energy saving which caused more attention from iron and steel enterprises and research institutions.In this paper,the phase transformation behavior of50CrV4 spring steel were systematically investigated by means of by means of Thermecmastor-Z thermal simulation testing machine,OM,SEM and Vickers hardness tester.The influence of deformation and coiling parameters on the phase transformation law was discussed.The results show that austenite deformation can promote ferrite-pearlite transformation and exaggerate bainite transformation interval during the continuous cooling process.And it also enhanced the mechanical stability of austenite that inhibited the martensite transformation and reduced the M_s point.When the cooling rate is less than 0.5 ^oC/s,the microstructure of ferrite and pearlite can be obtained in the experimental steel.Furthermore,a s the deformation temperature decreased from 920 ^oC to 860 ^oC and the strain rate increases from 1s^-1 to 30s^-1,the isothermal phase transfomation kinetic increases first and then slows down.And with the increasing of deformation,kinetic of isothermal phase transfomation shows a trend of gradual acceleration.When the coiling temperature is reduced from 700 ^oC to 550 ^oC,the phase transformation kinetic firstly accelerated and then slowed,the ferrite grains and lamellar pearlite were refined,the hardness increased gradually.According to the Johnson-Mehl-Avrami equation,the isothermal transformation kinetics equation was obtained,and the TTT curve of 50CrV4 spring steel was obtained.It provides a theoretical basis for process optimization and control of CSP hot rolled 50CrV4 spring steel.