Research Of Heat Treatment Process In High Chromium White Cast (Cr15Mn5Si3)

Although high chromium white iron (Cr15Mo3) has an excellent wear-resisting property,the rising price of ferro-molybdenum limits its application. Wang Jingjing[56]has developedCr15Mn5Si3white iron using the way of Mn replacing Mo. The structure and performance ofCr15Mn5Si3has been close to that of Cr15Mo3white iron, while more retained austeniteexist in the structure. In this paper, Cr15Mn5Si3white iron is taken as the object, and theeffects of heat treatment technology on the structure and performances of Cr15Mn5Si3isstudied in order to decrease the quantity of retained austenite. The influences of quenchingtemperature, holding time, tempering temperature, cooling methods on the quantity ofretained austenite has been researched. The phase is analyzed by using the XRD ans theretained austenite is quantificationally calculated. The structure of Cr15Mn5Si3is observedthrough the optical microscope and its toughness and hardness are tested. The white iron ofCr15Mo3is taken as the referenced target, the optimum heat treatment parameters ofCr15Mn5Si3have been obtained. The results show that:(1) The quantity of the retained austenite is increased with the rise of the quenchingtemperature in the structure of Cr15Mn5Si3white iron. When the quenching temperature isvaries from930℃to980℃, the quantity of the retained austenite is increased from22.41%to39.74%.(2) When the low temperature quenching is adopted, sufficient holding time is requiredto reduce the quantity of the retained austenite of Cr15Mn5Si3white cast iron. When theholding time is increased from0.5h to4h at900℃quenching, the quantity of the retainedaustenite is decreased from25.86%to7.66%.(3) When the quenching temperature is below900℃, the effect of decreasing theretained austenite is not obvious applying the method of reducing the quenching temperature.When the quenching temperature is860℃and900℃, respectively, the quantity of theretained austenite is6.8%and7.8%. There is a difference of only1%.(4) The quantity of the retained austenite is decreased with the rise of the temperingtemperature in the structure of Cr15Mn5Si3white iron as a whole. The higher the quenchingtemperature is, the more the quantity of the martensite which is transformed from the retainedaustenite is after tempering. At930℃quenching, the quantity of the retained austenite isreduced from41%to10%when the tempering temperature is increased from400℃to520℃, which is reduced by30%. At860℃quenching, the quantity of the retained austeniteis reduced from9.4%to4.2%, which is reduced by52%.(5) The hardness is increased from47.7HRC to55.5HRC and the impact toughness isdecreased from5.2J/cm2to4.6J/cm2when the quenching temperature is enhanced from900℃to980℃for Cr15Mn5Si3white cast iron.(6) The impact toughness is dropped with the rise of the tempering temperature. Under the condition that the tempering temperature is increased from400℃to580℃, the impacttoughness is declined from5.6J/cm2to4.1J/cm2At900℃quenching, whereas the theimpact toughness is declined from4.7J/cm2to3.6J/cm2At930℃quenching.(7) The highest hardness value of Cr15Mn5Si3high chromium white iron is52.5HRC at900℃q uenchingand520℃tempering. The highest hardness value of Cr15Mn5Si3highchromium white iron is59HRC at930℃q uenchingand480℃tempering.(8) For Cr15Mn5Si3white cast iron, the optimum heat treatment technology is930℃quenching (air cooling) and480℃tempering. The obtained hardness and impact toughness is59HRC and4.1J/cm2, respectively.