Research on grain refinement mechanism in undercooled Fe₇₅Ni₂₅ alloy

The grain refinement mechanisms of undercooled Fe₇₅Ni₂₅ alloys were investigated by fluxing and cyclic superheating. Within the undercooling, △T, range achieved, two kinds of grain refinement were observed. In combination with the calculation and the analysis of experiment results, the grain refinement mechanisms were elucidated. The results indicate that the first grain refinement, occurring at 56 K< △t <145 K, can be ascribed to the breakup of dendrite-skeleton owing to remelting, and the second grain refinement at △T > 209 K, was due to the recrystallization induced by the stress originating from the rapid solidification contraction.