Enrichment characteristic of carbon atoms in solid-liquid zone of high carbon steel under different directional solidification rates

Abstract

To reveal the formation mechanism and main influencing factors of C-segregation in high carbon steel under different solidification rates (40, 80, 160, 200 and 320 µm·s−1), the enrichment characteristics of carbon atoms in the solid-liquid zone of Fe-0.61%C steel were studied using a zone melting liquid metal cooling apparatus and electron probe microanalysis. The relationships among micro-segregation of carbon atoms, solid-liquid interface morphology and solidification rate were fully discussed. The results show that large dendrite spacing and a slow-moving dendritic interface create less resistance and more time for the migration of interdendritic carbon atoms to liquid zone. This results in the continuous enrichment of carbon atoms in liquid zone, further expands the solid-liquid temperature range, prolongs the solidification time of molten steel, and causes the formation of carbon micro-segregation at the solidification end as the solidification rate is 40 µm·s−1. Conversely, abundant and elongated secondary dendrite arms with small spacing seriously impede the diffusion of interdendritic carbon-rich molten steel to liquid zone. As a result, there is only obvious dendrite segregation, but little difference in the carbon content along the solidification direction as solidification rate exceeds 200 µm·s−1.