In-Situ study of the early stages of solidification

摘要

The late Keith Brimacombe not only had a passion to link processing conditions with product quality but also to apply fundamental knowledge to problems on the shop floor. This study has been driven by these same sentiments and it is befitting that he be honoured for the influence the had in shaping research on continuous casting. Continuous casting has emerged as one of the great technological developments of this century and increasingly, emphasis has focused on the attainment of quality. Of central importance is a fundamental understanding of the events occurring in the meniscus region, which determines the quality of cast product. Recent developments in the strip casting of carbon steels point to the potential impact of this process upon the steel industry. Fundamental studies into nucleation and growth in strip casting are reviewed. Laser scanning high temperature metallography in combination with infrared heating has been developed to such a level of sophistication that in-situ observation of the early stages of solidification can be made. This technique has been used to study solidification at the liquid metal/liquid slag interface when a thin layer of slag is formed on the surface of the liquid metal. The interfacial surface tension plays a dominant role and the study has been extended to the observation of early solidification phenomena. Using a laser scanning confocal microscope, high temperature phase transformations have also been observed. Diffusional phase transformations of delta-to-gamma and gamma to delta in low carbon steel have been studied. Massive types of these transformation have also been observed at high temperature in carbon as well as stainless steels. For example, diffusionless transformation of dlta-to-gamma has been observed at temperatures just below the transformation temperature and at relatively low cooling rates in a 0.06percentC Steel.