In situ research of partial melt in as-cast H13 steel at elevated temperature

Abstract

ABSTRACTIn situ experimental investigations of partial melt phenomenon in as-cast H13 steel at elevated temperatures between 1150°C and 1300°C was carried out using a confocal laser scanning microscope (CLSM) observation. Stripy primary carbides composed of Cr, Mo, V and Ti were observed in the interdendritic zone of as-cast H13 steel. In the interdendritic zone there existed obvious Cr and Mo segregation and slightly C and V segregation. At temperatures above 1150°C, the liquid phase was observed at the primary carbides-matrix boundary, even though this temperature is much lower than the solidus temperature of H13 steel. A higher heat temperature and longer holding time result in the generation of an increased amount of liquid phase. The maximum fraction of the liquid phase in the present investigation was 6%. Two effects are responsible for the premature appearance of the liquid phase, namely the alloying elements segregation in the interdendritic zone and the decomposition of primary carbides. The presence of the liquid phase accelerates alloying elements diffusion in the interdendritic zone, and cavities will be generated because of the shrinkage of the liquid phase during rapid cooling.