Effects Of Forging And Heattreatment Process Of MC5Cold Roll Blank Defects And Structure Property

With the rapid development of steel industry, modernized rolling mill is in acontinuous improvement, which results in increasingly high requirements on thematerials and quality of rolling. Cold roll blank has the highest quality requirementamong a wide range of roll products, thus it is a high technology product with extremelyhigh requirement on the materials and complicated manufacturing process. Thematerials of forged steel cold roll develop toward high-content chrome direction in aprogressive way thanks to the development of craftsmanship, increasing from only1.5%Cr in the initial cold roll to5%Cr after getting through many years’development.Today, the study focuses on the improvement through the application of micro-alloyingtechnology based on5%Cr. However, as a large number of alloy elements exist in Cr5steel and carbon content is relatively high, which causes to easily produce compositionsegregation when steel ingot solidifies, block or eutectic skeleton-shape liquationcarbide will be produced. Such carbide has high hardness and tremendous brittleness,and it will usually become fatigue source of crack or leads peeling in the superficiallayer or in large area under the rolling load in the steel rolling process when it exists inthe surface of roll barrel. In view of the above questions,this paper conducts a collectionof experimental researches on MC5electroslag steel roll blank and analyzes the defectsof roll and their causes. Based on above causes, the experimental plan is designed withaim to eradicate or improve those defects arising from the roll blank.Based on the particle overburning experiment, high temperature homogenizationexperiment and forging experiments of different forging ratios, analyze the impact offorging process on roll performance and carbide. Accordion to the particle overburningexperiment, the area where confronts with severe particle segregation has a temperatureapproximating1200℃, which shall not be exceed in order to prevent from particleoverburning; according to the high temperature homogenization experiment, theliquation level of carbide within the roll decreases with the increase of high temperaturehomogenization experimental temperature and heat preservation time, generally,long-time high temperature diffusion is applied under1190℃with the heatpreservation time of ranging from14to36hours; according to the forging experimentsof different forging ratios, no significant change occurs in the hardness and ductility with the increase of forging ratio, but the yield strength and tensile strength increasesaccordingly in a insignificant range, the impact has a dramatic increase along with theincrease of forging ratio.Under different temperature，heat preservation time and heat treatment afterforging，research the impacts of post-forging heat treatment on the carbide andband-type carbide. The study on the spheroidizing annealing process reveals that theheating temperature of spheroidizing annealing has a wide range (820℃-900℃). Thespheroidizing annealing isothermy shall be between700℃and740℃and theisothermy temperature should be high in the case of low hardness requirement. Theprocess of hardening and tempering is applied for quenching under910℃to930℃,with appropriate tempering temperature under690℃to720℃. Induction hardeningensures the power frequency and intermediate frequency outlet temperature falls intothe category between930℃and950℃in a decreasing speed of0.5mm/s for roll.