Research Of Solidification Characteristics And Process Optimization For Continuous Casting With 26CrMoVTiB Steel

26CrMoVTiB steel is a kind of oil casting steel for the production of a large domestic iron and steel enterprise,which is much more stringent on the billet quality.The defects such as internal shrinkage,central porosity and segregation and low center equiaxial crystal seriously affect the qualified products rate of 26CrMoVTiB steel,and reduced the corrosion resistance of the oil casing steel.In this thesis,the solidification characteristics of 26CrMoVTiB steel was studied,and the solidification process of ?178 mm round billet are simulated with the ProCAST simulation software.Based on these,the technological parameters of round billet continuous casting are optimized,and the reasonable continuous casting technological scheme for the end electromagnetic stirring and feasible suggestions are put forward.In the study of solidification characteristics of 26CrMoVTiB steel,the results reveal a general fluidity,which lead to poor filling capacity;it also indicate volume shrinkage and linear shrinkage are in large quantities,which is likely to produce solidification shrinkage cavity,porosity,and other defects in the procedure of solidification;the phase transition point of the steel is determined,and the CCT curves are draw,which provide the basis for improving the quality of round billet continuous casting and heat transfer process.With the utilization of ProCAST simulation software,the mathematical model of the solidification and heat transfer of round billet continuous casting is established based on finite difference methods.The error between the slab surface temperature and the measured temperature is ?1.81%,the accuracy of the solidification heat transfer model is higher.The CAFE model is built on the basis of the temperature field of solidification and heat transfer,and the relative error of the center equiaxial crystal rate of the simulation results is 0.8%,which indicates that the CAFE model is in agreement with the actual situation.Combined with field process simulation,it is found that the superheat fluctuation greatly,which leads to high columnar crystal and aggravates the macro-segregation of continuous casting billet;the surface temperature of the continuous casting billet is too low(T<900?),the billet surface temperature rebound rate is too high in secondary cooling zone;the solidification rate of the billet is too high at the end of the stirring position,and the electromagnetic stirrer is not stirring.Simulation results of microstructure of 26CrMoVTiB steel continuous casting billet show that,as the other conditions remain unchanged,the number of grain and the equiaxed crystal ratio increase with the superheat decreases;the center equiaxial crystal rate changes less with the increase of casting speed;it can significantly improve the center equiaxial crystal rate to decrease cooling intensity of secondary cold water appropriately.The continuous casting technology is optimized to the problems existing in the current 26CrMoVTiB steel continuous casting process.After optimization,the surface temperature distribution of 26CrMoVTiB steel continuous casting billet is reasonable,and the center equiaxial crystal rate increases.The solidification rate of casting billet at the end of the stirring position meets the requirement of the electromagnetic stirring on continuous casting billet core diameter.