Effect of solidification pressure on growth mode of eutectic carbide in chromium white cast iron

The distance of the maximum degree subcooling and interface

Besides discussing the interface structure, which is the mechanism of atom stacking and crystal morphology, we also need to discuss the temperature condition at the interface front, which is the solidification region. As shown in the figure, when the primary phase solidifies, its front edge is metal melt, and the ambient temperature is higher, so both temperature supercooling and solute supercooling have no significant effect on it. Therefore, the impact of pressure is also very limited. However, in the process of eutectic solidification, the pressure increases the nucleation rate, which makes the eutectic spacing narrow obviously, and forces the width of component supercooling zone narrow obviously. However, the component supercooling degree increases obviously, and the area of component supercooling zone increases. When the component undercooling is greater than the critical nucleation undercooling, new nuclei will be formed, which makes the free dendrite appear in the front of the original growing crystal instead of cellular structure.

To sum up, whether the growth mode of carbides changes needs to be divided into eutectic carbides and primary carbides. It is caused by the difference of solid-liquid front in the growth process of two kinds of carbides. For eutectic carbides, the growth mode changes from facet to non facet and from smooth to rough under pressure. However, for primary carbides, there is no substantial change in their growth mode except for their size and inclusion rate.