Effects Of Heat Treatment On Microstructure And Rolling Wear Properties Of High Vanadium High Speed Steel

One type of high vanadium high speed steel, which has been researched by Henan Engineering Research Center for Wear Resistant Material, was selected. On the condition of quenching temperature at 900℃to 1100℃and tempering temperature at 250℃to 600℃, mechanism properties were measured. By WM-1 rolling wear machine, which can simulate work condition of the cold roll, the rolling wear properties were measured after different heat treatment. The scanning electron microscope was used to analysis the effects of heat treatment on their microstructure. Also, retained austenite amounts of high vanadium of high speed steel were measured by X-ray diffraction instrument. By the scanning electron microscope and the transmission electron microscope, the rolling wear mechanisms of high vanadium high speed steel were discussed.By researched and analyzed, some conclusions can be drawn as follows:After heat treatment, the effects on morphology, types and distribution of carbide is very little; but for their matrix, the comparatively amounts of the martensite and the retained austenite have greater effects. When quenching temperature increases, the amounts of retained austenite increase and correspondingly martensite decrease. When tempering temperature increases, the retained austenite amounts decrease.Hardness of high vanadium high speed steel fluctuates between 51 HRC and 66.5 HRC after heat treatment. High quenching temperature (above 1050℃) and high tempering temperature (above 500℃), hardness is higher. Impact toughness of high vanadium high speed steel fluctuates between 6 J/cm~2 and 12 J/cm~2 after heat treatment. Lower quenching temperature (under 950℃), tempering at any temperature, the impact toughness is lower. Quenching at 1050℃to 1100℃and tempering at 250℃, their impact toughness is highest. Quenching at 1050℃to 1100℃and tempering at 450℃to 550℃, impact toughness is higher. The effects of quenching temperature on rolling wear properties are important. When quenching temperature increases, the rolling wear properties increase too, but fluctuation bound of wear resistance data increases. At the quenching temperature of 900～1000℃, the effects of tempering temperature on wear resistance are little; when quenching at 1050～1100℃, their effects are important. The best wear resistance is quenching at 1100℃and tempering at 450℃, the better one is quenching at 1100℃and tempering at 550℃, and quenching at 1050℃and tempering at 550℃, its wear resistance also raises. Considering the effects of heat treatment on hardness, impact toughness, wear resistance, equipment loss and production costs, the proper heat treatment is quenching at 1050℃and tempering from 450℃to 550℃.In this paper, X-ray diffraction instrument was used to measure retained austenite, the effects of retained austenite amounts on hardness, impact toughness and rolling wear properties were analyzed. Retained austenite amounts and hardness are in curvilinear regression of second degree of shedding down. Retained austenite amounts at 40 to 60 volume fraction, hardness reaches peak value. More or less amounts of retained austenite all reduced the hardness of high vanadium high speed steel Retained austenite amounts and impact toughness are in approximately linear regression. Along with retained austenite amounts increase, their wear resistance gradually increases. The amounts of retained austenite and rolling wear resistance are in curvilinear regression of second degree of shedding up. Followed the retained austenite amounts increasing, wear resistance increases. Simultaneously, the fluctuation range of rolling wear resistance obviously increases. Considering the effects of retained austenite on its rolling wear resistance, the range of rolling wear resistance, hardness and impact toughness, proper volume fraction of retained austenite at 45 to 55 is propitious to their rolling wear properties, and its corresponding quenching temperature at 1050℃and tempering temperature at 450℃to 550℃.Retained austenite amounts of before tested and after tested samples were measured. It has been discovered that after rolling wear certain austenite of high vanadium high speed steel has been translated into martensite, which makes the material intensity improved near the crack source, increases cracks extension resistance, prolongs contact fatigue life. These can make foundation for further demonstration of contact fatigue mechanisms.