Study On Deformation Enhanced Carbide Decomposition And Spheroidization In High Speed Steel

High-speed steel is widely used in the manufacture of various high-speed cutting tools,high-load molds,aviation high-temperature bearings and special heat-resistant wear-resistant parts,etc.,and plays an important role in the manufacturing industry.Due to the composition characteristics of high-carbon and high-alloy alloys,high-speed steel is prone to produce structural quality problems characterized by coarse carbide size and uneven distribution,which deteriorates the performance of high-speed steel.For large-scale high-speed steel forgings,the above-mentioned problems are particularly prominent because the amount of deformation is greatly limited.In this paper,the M2 high-speed steel with the largest output and the most application is taken as the research object.The high-speed steel was pre-deformed before the carbide decomposition heat treatment.The influence of room temperature deformation and high temperature deformation on the decomposition and spheroidization of carbides was studied in order to provide theoretical guidance for overcoming the problem of coarse carbide size of high-speed steel.Deformation studies at room temperature indicated that the deformation induced defects such as dislocations and stacking faults in M₂C carbides.The M₂C carbide decomposition mechanism was changed from a single phase interface nucleation manner alone to phase interface nucleation and dislocation nucleation,which accelerated the decomposition of carbides and produced deformation-enhancing carbide decomposition effects.Deformation improved the nucleation rate and number density of decomposition products,the carbide phase interface increased,the spheroidization driving force increased,and the spheroidization and size refinement of carbide were significantly promoted.As the temperature and time of spheroidizing heat treatment increased,the size of carbide gradually grew.The optimal spheroidizing heat treatment process is 1160?for 20 minutes.Due to the effect of deformation enhancement carbide decomposition and spheroidization on the refinement of carbide size,the number of undissolved carbides after quenching of high-speed steel was reduced,the supersaturation of martensite was increased,and the hardness of quenching and tempering was increased by 0.5?1.5HRC,wear resistance improved.The deformation-enhancing carbide decomposition effect also existed during the high-temperature deformation process.Studies had shown that with the increase of high-temperature compression ratio,the promotion of deformation on carbide decomposition and spheroidization was enhanced,and the effect of carbide size refinement was more obvious.Deformation-enhanced carbide decomposition is dependent on the deformation temperature.When deformed at 1050?,the effect of deformation on M₂C carbide decomposition was most significant.High temperature deformation promoteed carbide spheroidization,refined carbide size,increased the quenching and tempering hardness of high-speed steel by?1HRC,and improved wear resistance.As the deformation temperature increased,the quenching and tempering hardness of high-speed steel gradually decreased,and the wear type changed from abrasive wear to oxidative wear.Comprehensive consideration of carbide,martensite grain size and high-speed steel use,processing performance,the best deformation temperature is 1050?.