Study On The Hot Deformation Characteristics Of M35 High Speed Steel By Electron Beam Smelting

The electron beam smelting is a cutting-edge smelting process.Due to the concentrated energy of the electron beam gun and the high vacuum of the smelting equipment,the water-cooled copper crucible used does not introduce impurities and can provide a greater cooling rate.Therefore,it has a very broad prospect in the field of preparing high-purity,high-performance materials.High speed steel is a cutting tool material widely used in the production process.Due to its high alloy content and high carbon content,there are continuous coarse network eutectic carbide structure,which improves the network eutectic carbide structure.It is very important to improve the performance of high speed steel.The subject uses the Gleeble-3500 thermal compression simulation tester to conduct electron beam melting M35 high-speed steel with strain rates of 0.01 s^-1,0.1 s^-1,1 s^-1,10 s^-1,and deformation temperatures of 1273 K,1323 K,1373 K and 1423 K,totally sixteen sets of experiments under these conditions,to study the hot deformation characteristics of M35 high-speed steel by electron beam melting.The effect of thermal deformation process parameters on the evolution of carbides in M35 high speed steel smelted by electron beam is studied,and the carbide structure is observed at low and high magnifications.The main types of carbides in electron beam smelting M35 high speed steel are M₂C type carbides,M₆C type carbides and MC type carbides.The higher the deformation temperature,the more fully the decomposition of M₂C type carbides,the more obvious the spheroidization of carbides,and the more fully the fracture of the eutectic carbide network;the faster the strain rate,the greater the mechanical force on the carbides on the eutectic ledeburite network,and the more fully fractured the carbide network.At the same time,the hardness of electron beam smelting M35 high speed steel increases and increases significantly with the increase of the hot compression deformation temperature,and slightly increases with the increase of the strain rate.The flow stress curve of electron beam smelting M35 high-speed steel is unimodal,which has the characteristics of rapidly increasing and reaching the peak and then slowly decreasing,which conforms to the characteristics of the dynamic recrystallization curve,and the curve has a sawtooth characteristic at high strain rates.The peak stress value increases with the increase of the strain rate and the decrease of the temperature,and the peak stress under each deformation parameter is generally higher than the peak stress under the corresponding deformation parameter of ordinary smelted M35 high-speed steel.The hot deformation constitutive equation of electron beam smelting M35 high speed steel is established,and the average thermal activation energy is calculated to be 504.624 k J/mol,which is significantly higher than the hot deformation activation energy of ordinary smelting M35 high speed steel.Use the Dynamic Material Model(DMM)to establish the hot processing map of the electron beam melting M35high speed steel.The hot processing map can show the hot deformation instability area of the M35 high-speed steel.The area where the best deformation conditions for the hot processing is obtained is:the deformation temperature is 1400-1423 K,the strain rate is 0.01-1 s^-1,and its hot working window is wider than that of ordinary smelted M35 high-speed steel.The dynamic recrystallization behavior of electron beam smelting M35 high speed steel was studied,and it was found that with the increase of temperature and the decrease of strain rate,the dynamic recrystallization of electron beam smelting M35 high speed steel occurred more fully.Dynamic recrystallization in electron beam melting M35 high-speed steel first occurs around carbides.The mechanism of dynamic recrystallization is the nucleation and growth of dynamic recrystallized grains where more dislocations are likely to accumulate.