Study On Quenching And Tempering Of Cr8Steel Applied For Cold Roller

The equilibrium crystallization process for Cr8steel was studied in this article bycalculating phase diagram with Thermo-Calc thermodynamic calculation software.Meanwhile X-ray diffraction, metallographic microscope and Rockwell hardness testerwere used to research the influence of quenching and tempering processes on themicrostructure and mechanical properties.The results indicate that the equilibrium phase is comprised of ferrite, MC carbide,M23C6carbide, and their contents were about85.7%,3.5%and10.8%respectively. Theequilibrium transformation of MC carbide and M23C6carbide were precipitated at1338℃and925℃respectively. When the austenitizing temperature was1125℃, a largenumber of alloying elements were dissolved in austenite, and the content of carbonelement in austenite was about0.6%.The quenching hardness presents the trend of increase first then decrease with thequenching temperature from975℃to1025℃for1hour, and it came to the maximumcounts63HRC when the quenching temperature reach about1025℃, and61HRC for1125℃. The grain sizes were9μm and16μm respectively when quenching temperaturewere1025℃and1125℃, besides the content of residual austenite were25.7%and50.4%respectively.The amount of carbide increase first then decrease when tempering temperatureincrease, and the amount of residual austenite reduced. At the quenching temperature of1025℃when the tempering temperature at515℃, the amount of carbide reached peak,;and at the quenching temperature of1125℃when the tempering temperature at525℃,the amount of carbide reached peak. At the quenching temperature of1025℃when thetempering temperature is lower than515℃, the amount of carbide increased withtempering temperature increase. At the quenching temperature of1025℃when thetempering temperature above515℃, the amount of carbide reduced with temperingtemperature increase. At the quenching temperature of1125℃when the temperingtemperature is lower than525℃, the amount of carbide rised with tempering temperature increase. At the quenching temperature of1125℃when the tempering temperatureabove525℃, the amount of carbide reduced with tempering temperature increase.