MODELLING CORED WIRE INJECTION IN STEEL MELTS

摘要

Cored wire injection is an essential feature of liquid steel processing. An estimation of the time for melting of the wire sheath (casing) and the subsequent release of the filling material cannot be done without resorting to an elaborate mathematical model due to the complexity of the heat transfer from the bath to the wire. In particular, the formation of a solid shell around the wire and the consequent lowering of the heat transfer needs to be addressed accurately. A mathematical model developed for calculating the melting time of the casing at the Research & Development Division of Tata Steel describes the freezing and melting process during the travel of the cored wire in the steel bath. The model has been validated against both published information as well as plant data. However, owing to the complexity of obtaining a direct validation in the operating plant, a novel indirect method has been adopted. Several new findings with respect to the casing thickness, wire diameter and the speed of injection have been obtained. It has been shown that the impact of different grades of liquid steel on the melting behaviour of the cored wire both on account of different superheat as well as the melting temperatures of the solidifying shells, is significant. In order to ensure that the wire releases powder at the same depth, the casing thickness of the wire used for injection into low carbon grade steel needs to be twice as much compared to that required for a high-carbon grade steel. Apart from providing deeper insight into the melting behaviour of cored wire, the model has also helped in formulating new specification of cored wire for Tata Steel.