Study On Evolution Rule Of Carbides In High Speed Steel M2

In order to further improve the quality and performance of high-speed steel,it is particularly important to study the influence of carbides on the cracks and refinement of large-particle carbides in the application and production of high-speed steel.This article takes M2 high-speed steel as the research object,and explores the influence of different production processes on the precipitation and transformation of carbides in high-speed steel during the smelting production process,thereby affecting the number,size and transformation of carbides in high-speed steel.The composition is controlled to obtain high-quality high-speed steel products.Firstly,use the thermodynamic software JMatPro to simulate the precipitation type of M2high-speed steel carbides and its alloying element composition,and use thermodynamics to calculate the precipitation of M₂C carbides with different compositions in the liquid phase,solid-liquid front liquid phase and solid phase,and explore M₂C Decomposition and transformation of carbides.Then the forged M2 high-speed steel is heat treated,and the effect on carbides is explored through pre-heat treatment and strengthening heat treatment.Finally,the influence of the cooling rate at different positions in the intermediate frequency furnace and the electroslag remelting process and the different deformation amount in the subsequent rolling process on the carbide are studied.Through research,the following conclusions are obtained:（1）Using JMatPro simulation found that the carbide types of M2 high-speed steel are mainly MC,M₆C and M₂₃C₆type carbides.The most component of MC carbide is V,and it contains a certain amount of Mo and W;the most component of M₆C carbide is W,which contains a certain amount of Fe and Mo;the most component of M₂₃C₆carbide is Fe and Cr,and it also contains a certain amount of The amount of Mo,with the temperature change,the composition of the carbide will also change.（2）The thermodynamic calculations of unsteady M₂C carbides show that when M2high-speed steel is solidified and cooled,neither Mo₂C nor W₂C can be formed in the liquid phase region.When the temperature is in the solid-liquid two-phase region,the thermodynamic temperature that Mo₂C can generate is 1526K,while W₂C does not have the thermodynamic conditions for generation.When the temperature drops below the solidus line,secondary carbides are formed.Mo₂C starts to form at 550K,and W₂C starts to form at 340K.The order of formation is Mo₂C,W₂C.During the heating and holding process,M₂C will decompose to form M₆C and MC carbides.（3）After quenching and tempering,after tempering at 520℃,560℃,and 600℃,the hardness and carbide content are reduced,and the lowest is at 600℃.After spheroidizing annealing,700℃,750℃,800℃,the carbides are mostly distributed in spheres,and the distribution of carbides is significantly improved.As the isothermal temperature increases,the carbide content decreases and the hardness also decreases.At 800°C isothermal,the carbide dispersion is the best.After quenching and tempering and annealing,SEM and EDS analysis found that there are mainly two kinds of carbides,one mainly contains W and Mo elements,and the other mainly contains V elements.（4）When quenching at different temperatures,the grains gradually increase with the increase of temperature.At 1160℃,the grains are the smallest,but contain a lot of undissolved carbides;at 1240℃,the grains are the largest,and the carbides are mainly distributed along the grain boundaries.After three times of high temperature tempering after quenching,the quenching temperature increases and the hardness increases.The hardness is the highest at1240℃,reaching HRC65.The structure after tempering is carbide,martensite and a small amount of retained austenite,and the martensite becomes coarser as the quenching temperature increases.After XRD analysis,after heat treatment,the carbides are mainly three types:M₆C,MC and M₇C₃carbides.There is basically no change in the types of carbides at different temperatures.（5）The carbides in the M2 high-speed steel intermediate frequency furnace and electroslag remelting ingots mainly exist as network carbides.From the edge to the center of the ingot,the thickness of the carbide network gradually increases,and the cooling rate becomes slower and slower.（6）After forging,the network carbides are broken and decomposed by heating.They are mainly distributed in the grain boundary in a circular shape,but the spherical carbides in the matrix increase.After annealing,the carbide aggregation has improved and the size is uniform.By comparing the morphology of carbides at different stages of rolling,it can be found that with the increase of rolling deformation,the size of carbides gradually becomes smaller.The greater the deformation,the fewer large-sized carbides,and the largest number of carbides with a size of 0.2～0.5μm.