Effect of Starting Microstructure in High Speed Steel on the Grain Refinement Potency of Electropulsing Treatment

Abstract

High speed steels (HSSs) are widely used materials for tools production, which grab a third part of the global cutting tool market. Heat treatment is an indespensable process for the fabrication of HSS tools. Modifications of carbides and grain size of the matrix are two main aspects for the heat treatment of HSSs. In order to obtain better wear property, hardness or red hardness, modification of carbides attracts more researchers’ attention, but grain refinement benefits to the toughness and tool life. Compared with the grain refinement methods used for other steels, such as controlled rolling, available method for grain refinement of HSSs seems deficient. Our previous study provided a new method to produce ultrafine grained M2 steel, but the effect of the starting structures on the grain refinement potential of electropulsing treatment (EPT) was not involved. Results in this work show that the grain size can both be refined or even ultra-refined by EPT, whatever the difference in the starting structures. But the austenite transformation of the matrix was completed at lower peak temperature when using starting tempered structure. And the pre-tempered M2 samples have higher hardness than that obtained after heat treatment or EPT when using the starting annealed structures.