Stainless steel alloys are widely used in many important applications but their production presents difficulties because they contain expensive chromium, which can be extensively oxidised during decarburisation to the very low carbon levels required. Modern stainless steelmaking largely avoids this problem by having two distinct stages and is therefore described as duplex practice. Molten high carbon stainless steel is produced in an electric arc furnace and then the melt is decarburised in an argon-oxygen converter or a vacuum oxygen decarburising converter. In this work, computational thermodynamics has been used to examine the major reactions occurring in the electric arc furnace and to show the effect of various process variables on chromium recovery. It was shown that significant oxidation of the scrap must occur during melting, and that subsequent carbon/oxygen injection initially oxidises some chromium, but then mostly oxidises the added carbon. Chromium was predicted to exist in the slag as CrO and CrO 1?5 in almost equal proportions. Increasing the temperature should improve chromium recovery but results in less benefit than expected due to the decreasing activity coefficients of CrO and CrO 1?5 and the increasing oxygen partial pressure. Ferrosilicon additions reduce chromium oxides from the slag, but much of the silicon simply dissolves into the steel. Computational thermodynamics is seen to be a very effective educational tool for gaining an understanding of smelting processes.

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Most manganese used in the world is consumed as ferroalloys by the steelmaking industry. Submerged arc electric furnace smelting using the manganese-rich slag method is widely used to produce ferromanganese. This process has been modelled using the HSC computational thermodynamics package. It was assumed that higher manganese and iron oxides are reduced to MnO and FeO before entering the zone where molten slag and alloy form and equilibrate. The model predictions were compared to data from Thermit Alloys (P) Limited, an Indian ferroalloy smelter, and the agreement was found to be good. It was then used to examine the affects of changing the amount of carbon reductant and temperature on several performance indicators. The results of this modelling are discussed and it is concluded that the model is useful as an aid to understanding ferromanganese smelting.CO CO2 = 1 whereas Fe 3 O 4 reduction to FeO requires either carbon or a gas mixture with a higher CO(g)

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