Study Of Carbon Spring Steel Heat Treatment Process Of High-strength 50CrV4

In this paper, the medium-carbon high strength spring steel of50CrV4was taken for the subject of the research. In order to find out the best spheroidization annealing process of the50CrV4steel, the subcritical spheroidization, isothermal spheroidization, periodic spheroidization and continuous annealing process were studied. Results are as follows:The strength and hardness of the steel is reduced and the toughness is enhanced by the spheroidization experiments. The nodularity of experimental steel increases with the increasing of the soaking time of subcritical spheroidization and isothermal spheroidization, also increases with the increasing of the cycles of periodic spheroidization. The50CrV4steel can be obtained the spheroidization rate over98%by12hours of soaking time of the subcritical spheroidization. And the steel can be obtained the spheroidization rate over95%by6hours of isothermal spheroidization, while after four cycles the spheroidization rate of the steel is still under95%.The results of continuous annealing experiment showed that the best continuous annealing process parameters of50CrV4steel are as follows:the soaking temperature is875℃, the soaking time is120s, the slow cooling rate is5℃/s, the slow cooling temperature is705℃and the slow cooling time is300s. The50CrV4steel can get good spheroidized microstructure by this continuous annealing process.Considering the best combination of strength and ductility of the50CrV4steel, the best process is holding at850℃for30min then oil quenching and tempering at475-525℃for45-60min and air-cooling. The50CrV4steel can get fine tempering sorbite, good strength and ductility by this heat treatment process.