Researching About Hot Working Process Of The Spray FDormed M42 Steel

Nowadays, in order to obtain fine microstructure and high mechanicalproperties, most of the high speed steel produced by conventional casttechnique and then treated by complex heat treatment. But segregation ofcarbides in matrix is still existence, which can lead to invalidation,deterioration of mechanical properties, and aberration of heat treatment oftools.The key issue of uneven distribution of carbides can be solved by thespray forming process,which have advantages of simple process,low costand so on. However,the as-sprayed M42 steel can't meet the actual use ofmaterials and there are a small amount of holes in the as-sprayed M42 steel,so it need further heat processing to break the carbide and eliminate holes,then to get a good organization and improve the material's density.This paper's aim is to study the thermal deformation behavior through analyzingthermal simulation experiments, we can set the hot rolling and forgingprocess parameters according to the results of thermal simulationexperiments, and then determine parameters through the observatingorganization,the size and distribution of the carbide and so on,then throughthe ball annealing treatment get ideal spheroidizing organization,the last getreasonable parameters of the modulation processing.The thermal compression experimental results show that the stress andpeak stress of as-sprayed M42 steel increased with decreasing deformationtemperature and increasing strain rate. Stress did not increase with the strainincreases, but quickly achieved the peak stress about the true strain at 0.1.After the peak stress, then the stress of a downward trend and reached arelatively stable value, indicating that the recrystallization occurred in thedeformation process.The hot tensile test results show that the percentage of area reduction ofas-sprayed M42 steel reached a maximum value at 1050℃, and then declinedwith the deformation temperature; in the deformation temperature of 1000℃～1100℃, the steel has good plasticity and dynamic recrystallizationoccurs easily. Therefore, the spray forming of steel M42's final forging temperature should be above 1000℃.It was found that the M42 steel produced by spray forming technologyhas fine grains (about 20μm), the macro-segregation was reduced greatly, themorphology and distribution of carbides were refined greatly. Microstructureis composed of martensite,retained austenite,MC,M2C and M6C carbides；M2C will decompose into M6C and MC, when heated at high temperatures.The microstructure of the annealed as-sprayed M42 steel is pearlite andcircinal carbides. Hardness of the annealed as-sprayed high speed steel ismostly influenced by temperature; 880℃is the best annealing temperature.The microstructure of the quenched as-sprayed high speed steel isquench martensite,retained austenite and carbides. Sample has higherhardness, the fine carbides has dissolved in matrix, grains and carbides still inquondam size, after 1180℃quenching, which is a good quenchingtemperature.The microstructure of the tempered as-sprayed high speed steel istemper martensite,carbides and fine particles. Sample has higher hardness,fine carbides separate out and distribute homogenously after tempered twiceat 550℃, this microstructure avail to integrate higher hardness andtoughness.