Effect of slag properties and nitrogen addition on behaviour of alloying elements during ESR of AISI M41 tool steel

High speed tool steels are high alloyed high carbon steels. The processing of these grades is affected to a large extent, by the behaviour of the alloying elements. In this work, the effect of nitrogen alloying, physical properties and chemical composition of fluxes used in electroslag refining (ESR) on hardness, microstructure and alloying elements recovery and homogeneity of two grades, conventional and nitrogen alloyed AISI M41 high speed tool steel, were studied. One melt of each selected grade was melted in an induction furnace. The ingots were then used as consumable electrodes in ESR, where each steel grade was remelted under three different prefused CaF2 based fluxes. The alloying element behaviour was investigated. The highest recovery was obtained using ESR flux of high viscosity and low metal/slag interfacial tension. Increasing the nitrogen content of the steel results in an increase in alloying element recovery. Furthermore, the ESR process improved the shape, size and distribution of precipitates in the ingots. Also, hardness was improved by both ESR and nitrogen alloying.