ON THE SOLIDIFICATION OF STEEL INGOTS AND CONTINUOUSLY CAST STEEL BILLETS AND SLABS

The cast macrostructure in steel ingots and continuously cast steel billets is often divided into three zones, a chill zone at the surface, a columnar zone in the intermediate region. and large grained equiaxed zone in the centre. This paper discusses the formation of the three zones and attempts to theoretically describe their formation. The formation of the three crystal zones influences the macrosegregation in both ingots and continuously cast billets. The effect of the cast structure on macrosegregation is discussed. Centreline segregation in continuously cast billets and slabs is considered theoretically, and related to the macrosegregation in ingots. The different mechanisms leading to macrosegregation in continuously cast billets, slabs, and static cast ingots are considered. Pipe formation in ingots is primarily dependent on solidification shrinkage. A simple theoretical model of pipe formation in ingots is used to delineate the most important parameters for minimizing pipe formation. The same model is used to determine the extent of pipe formation at the end of solidification of a continuously cast billet. In this case it is shown that shrinkage of the solidified shell as it cools is more important than solidification shrinkage.