Rearch On Enhancing Qualification Rate Of Billet Cast

The billet of the factory mainly supply Heavy Section Plant,Wire and Rod Plant and Seamless Tube Plant as raw materials,and the quality requirements is very strict.In this dissertation,the problems of 120 mm × 120 mm billet continuous casting process in Ansteel are studied.The microstructure,segregation,inclusion and equiaxed crystal ratio of the cast billets in experiment are examined.The results show that the porosity of the casting slab is loose,the shrinkage is serious,the equiaxed grain rate is low,and large inclusions are found.In this paper,Ansys and Procast software are used to simulate the mold and the secondary cooling section.And the optimum parameters of electromagnetic stirring,tundish flow field,primary cooling and secondary cooling are determined.The actual production shows that the residence time of molten steel in the ladle increases when the number of gas curtain changed from 2 to 4.And thus,the inclusions fully floating.The number of inclusions below 5 ?m accounted for more than 75%,and the number of above 10 ?m is few,only up to 3.And the cleanliness of molten steel is improved.According to the simulation results of electromagnetic stirring,the electromagnetic stirring parameters of the mold are set to 285 A and 3.3Hz,and the equiaxed crystal ratio of the billet is increased from 10% below to 15~20%,which greatly improves the internal quality of the slab.When the superheat is less than 35 ?,the casting speed is 3 m/ min,and the cooling intensity is controlled at 0.4~0.5 L/kg,the low multiple inspection showed that casting billet porosity,shrinkage and crack were less than 0.5,the inner quality of billet is improved.After a year of the production withthe optimum parameters above,the casting machine runs well and the billet quality increases month by month.Compared with the experiment period,the failure flow rate is reduced to less than 0.1%,the rate of choose materials before rolling has been down to below 0.05%,and the rejection rate after rolling is reduced to less than 0.1%.As of November 2016,the billet quality qualification rate reached 99.8%.