The solidification structure of peritectic steels (15CrMo and 20CrMo) was studied using directional solidification experiments. An island dendrite structure was observed in the hypoperitectic steel (15CrMo) at growth velocities of 15, 50, and 80 μm·s−1. While a traditional peritectic dendritic structure was observed in the hyperperitectic steel (20CrMo) at growth velocities of 15 and 50 μm·s−1, an island dendrite structure was observed at a growth velocity of 80 μm·s−1. An analysis of the solute distributions near the liquid-solid interface during solidification revealed the role of the steel grade and cooling velocity on the formation of island dendrite structures. Higher cooling velocities caused higher carbon concentration gradients in the liquid phase near the liquid-solid interface, leading to a stronger driving force for the peritectic reaction and, consequently, a more favourable formation of island dendrite structures. Hypoperitectic steel is more prone to the formation of island dendrite structures than hyperperitectic steel.
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