Prediction of dissolution time of gerromanganese in hot metal and steel bath

Abstract

Mathematical models enable us to study metallurgical processes in depth. Significant improvements in plant operation cannot, in general, be brought about without quantification of the impact of the operating parameters on the end product. It is for this reason that mathemati-cal models have become popular in the steel industry, particularly with the advent of low-cost, high speed personal computers. Another reason why modelling is necessary is because increasingly alterations in operating parameters have to be made to bring about changes in heat or mass transfer. The gut-feelings of the plant operator are no longer able to deliver the goods because such feelings are developed by repeated exposure to quanti-fiable changes in the process brought about by alterat-ions, deliberate or otherwise, in the operating parameters. Some of these basic parameters are not measured, for example heat transfer coefficient in case of a solid particle dissolving in a liquid bath, and therefore it would be futile to expect gut-feelings to offer solutions as to how dissolution time would be effected by a change in the type of ferroalloy or by change in its size. The deter-mination of the dissolution time of ferroalloys is import-ant as it indicates to the process control engineer the minimum time necessary before the bath can be subjected to the next step of processing. Changes in the bath superheat; the size and the initial temperature of the ferroalloy and the bath hydrodynamics influence the dissolution time. Determining this dissolution time by experimentation is extremely difficult and would involve a series of experi-ments with different types of ferroalloys under varying conditions. On the other hand, the dissolution time can be obtained using a mathematical model of the dissolution kinetics of ferroalloys which after proper validation can be used to assess the dissolution behaviour of the ferro-alloy under a variety of conditions. At TATA STEEL blast furnace hot metal is used to cast ingot molds. The com-position of the blast furnace hot metal desired for making ingot moulds demands the addition of 20 kg each of ferro-manganese & ferro-silicon in the 12 tonne transfer ladles into which the blast furnace metal is poured at the ingot mould foundry (IMF). Owing to the low temperature of hot metal at IMF, casting commences immediately and a complete dissolution of the ferroalloy is often not possible. A mathematical model for calculating dissolution time for a solid particle in a liquid metal has been developed at R&D Division of Tata Steel. The model has been developed with the feasibility of predicting dissolution times for eases where the ferroalloy has a melting point lower as well as higher than the bath temperature. The model has been validated against data published in literature and applied to predict dissolution times of ferroalloys in steel and blast furnace hot metal. This model was used to study dissolution of ferroalloys in foundry and to evolve suitable corrective measures. On the basis of this study additions are being optimized at the IMF in' Tata Steel.