MC5 Cold Roll Secondary Electroslag Remelting And Carbide Refining Technology Development

Roll is an important part of rolling mill and also is main consumption parts.According to production scale integrated computation at present,about 50?60 ten thousand tons of metallurgical rolls are consumed every year.Therefore it is very important to develop new roll using voided roll.Some voided MC5 rolls from baosteel company are used for the ESR trial.The relationship between technology process and microstructure has been studied in detail based on the ESR.The findings provided theoretical basis for making new rolls using voided rolls and improving the roll performance by secondary ESR.In order to reduce loss of the main alloying elements,the gas shielding is used in the process of ESR.The experiment slag is CAF60 whose composition is 60 mass%CaF2,20 mass%CaO and 20 mass%Al2O3.In addition a certain deoxidizer is used for reducing oxygen content.The experimental results show that the main alloying element Mo,V,Mn is not burning lost,the loss amount of C and Cr is between 0.01%?0.02%after secondary ESR.Electroslag composition is fully appropriate for the requirement of new roll.The purity of steel is increased remarkably after secondary ESR.The rating results show that the A,B,C,D and Ds inclusions are all far below the level of roll standard requirement.Because of select crystallization,there are some large size eutectic carbides in middle and core of ESR ingot but a little in surface.The adopted process route for the secondary ESR ingot includes forging--high temperature difusion—forging,normalizing at 1030? and spheroidizing annealing.The results show that there is little eutectic and zonal carbide no matter in the surface,1/3R,middle and core of the forging stock.The net carbide level is 0 in the surface,2 in 1/3R and middle,2.5 in the core.The spheroidizing annealing microstructure is 2 grade.It is very good for the requirements about roll blank.The high temperature solution treatment + high tempering process and the high temperature solution treatment+austenitizing circulation+high tempering process are all adopted for the ultrafine processing of MC5 steel carbide.The carbide is obviously refined,but the structure uniformity is poor after high temperature solid solution at 1050?+tempering at 740?.However the structure uniformity is good but there are a few large size undissolve carbides when the temperature of solid solution is 950?.After high temperature solid solution at 1050? and cycle different times at 800?,840? respectively,the size of more than 80%of the generated carbides are within 0.3 ?m,and the largest size is less than 0.5 ?m.This suggests that the carbides get through ultrafine processing are more tiny and uniform than that of ordinary heat treatment.Considering the size of the carbide and the structure uniformity,the best process of carbide refining is high temperature solution at 1050?+cycling three times at 840?+740? high temperature tempering.The experiments found that with the increasing of cycling time,carbide has a tendency to grow up,this phenomenon is caused due to Ostwald ripening.