Study On Microstructure And Carbide Of M35 High Speed Steel By Electron Beam Smelting

High-speed steel has excellent comprehensive properties and can be adapted to the complex working environment.The structure of high-speed steel is composed of matrix and carbide.The fine and dispersed carbide is the guarantee of its excellent performance.It is generally obtained by melting+forging.During the development of high-speed steel,new elements are continuously added to enhance its comprehensive performance,and the complex composition leads to coarse carbides and severe segregation in the high-speed steel obtained by smelting.The double process of induction melting+electroslag remelting can improve the problem of coarse segregation of carbides to a certain extent.The water-cooled copper crucible used by Electron Beam Melting?EBM?technology can give liquid metals a high cooling rate after the melting is completed,and it has the advantages of high energy density and good controllability,which is beneficial to improve the carbide state in the high-speed steel and improve its performance.This paper proposes the preparation of M35?W6Mo5Cr4V2Co5?high-speed steel by electron beam melting,and explores the effect of electron beam melting on the carbides of M35high-speed steel.and performs high-temperature heat treatment on the prepared as-cast M35high-speed steel to achieve Refinement and improvement of carbides.By characterizing the composition,microstructure and carbide observation of M35 high-speed steel,the following conclusions were obtained:?1?The preparation of electron beam smelting does not change the main composition ratio of M35 high-speed steel,but due to the high saturated vapor pressure of Mn element in vacuum melting,the content of Mn element in high-speed steel ingot is significantly reduced.?2?The as-cast microstructure of EBM-M35 high speed steel is fine,the average dendrite spacing is 20?m,and the structure is similar in different regions;The types of carbides are mainly MC type and M₂C type carbides,and the morphology of M₂C carbides changed from lamellar to fibrous?3?During the high-temperature heat treatment of as-cast EBM-M35 high-speed steel,with the increase of heat treatment temperature and the extension of heat preservation time,the dendrite spacing continues to increase,The lamellar spacing of the lamellar M₂C type carbide and the fiber spacing of the fibrous M₂C type carbide become smaller.At the same time,At the same time,carbides will break and spheroidize,but too high temperature or too long holding time will lead to the growth of carbides.?4?The best process for heat treatment of as-cast EBM-M35 high-speed steel is at 1180?for 30 minutes.Under this process,the carbide network in the as-cast high-speed steel structure breaks,the carbide fractures and spheroidizes,and the fine carbides are more uniformly dispersed in the structure to obtain the best heat treatment structure.?5?During the heat treatment process of as-cast EBM-M35,the fracture and spheroidization of carbide can be completed with a lower heat treatment temperature or a shorter heat treatment time,and the structure optimization of as-cast high-speed steel can be completed at lower cost.