Effect Of Ti,RE In-situ Microalloying Of Electroslag Remelting On Solidification Structure Of H13 Steel

H13 steel is one of the high strength and heat resistance hot work die steel.It has good comprehensive mechanical properties and is widely used at home and abroad.Due to the high alloy content of H13 steel and the large size of billet and components,the problem of severe element segregation and coarse primary carbide precipitation during the solidification of the steel ingot is prone to occur.This has a significant influence on the subsequent forging,heat treatment process control and the comprehensive mechanical properties of the material.In this study,based on the traditional H13 die steel ingot casting process,in-situ Ti,RE microalloying during the electroslag remelting was performed.The effect of in-situ Ti,RE microalloying during electroslag remelting on the solidification structure of H13 steel was systematically studied.And through hot compression simulation experiments,the effect of Ti,RE microalloying during the electroslag remelting process on the hot deformation characteristics of H13 steel as-cast structure was explored in depth.The study results show that after the addition of Ti element,massive Ti and V-rich MNtype precipitation phases precipitated in the H13 steel structure,and the growth trend of dendrites in the area near the core of the steel ingot was significantly weakened.The study found that the excessively high Ti content will cause the precipitation of MN-type precipitates in the structure to advance,the size and number of precipitates increase significantly,and the element segregation between dendrites aggravates significantly.In addition,it is found that Ti microalloying significantly decreases the number of large-size MC-type primary carbides in the as-cast structure of H13 steel.The Clyne-Kurz segregation model and the calculation of carbide precipitation thermodynamics also verify that in-situ addition of Ti element delays the precipitation of primary carbides during the solidification and reduces the amount of carbides.The study results show that after the addition of RE element,the dendrite growth trend was weakened in the area near the core of H13 steel ingot,and the microsegregation of elements was significantly ameliorated.At the same time,it is found that the precipitation number of large-size MC-type primary carbides significantly decreases,and M2C-type primary carbides tend to appear in the eutectic state.In addition,it is found that RE element microalloying modified the inclusions in the steel ingot into fine rare earth inclusions,the number of which decreases by more than 50 %,and the proportion of Mn S-type inclusions decreases to 7 %.The study results show that excessive addition of RE element will cause the precipitation of larger-sized O and S-rich rare earth inclusions,and the ameliorating effect of dendrite segregation is weakened.This paper further explored the effect of Ti,RE microalloying on the thermal deformation characteristics of H13 steel as-cast structure.The experimental results show that H13 steel as-cast structure of Ti,RE in-situ microalloying by electroslag remelting shows high deformation resistance during hot deformation.The rate at which dynamic recrystallization occurs gets promotion and dynamic recrystallization is more sensitive to strain rate.Compared with the addition of RE element,the addition of Ti element has more significant promotion effect on dynamic recrystallization during hot deformation,and the dynamic recrystallization of ingot after Ti microalloying is less sensitive to deformation direction.