Abstract
Equiaxed solidification contributes to the ridging defect resistance of ferritic stainless steel. Ti2O3 accelerating TiN formation to nucleate δ-ferrite was recently recognized as an effective method to promote equiaxed solidification. However, the acceleration mechanism of Ti2O3 is still unclear, and there lacks direct nucleation evidence. Therefore, in this study, the initial solidification state was preserved using a newly designed droplet experiment. The orientation relationship calibrated disregistry calculation was carried out to understand the nucleation phenomena. It is novel to find that the formation of Ti2O3-TiN originates from the Ti-O-N particle, which forms before solidification of steel. The sequenced precipitation in the order of Ti2O3 and TiN from the Ti-O-N particle follows the orientation relationship of {0001} Ti2O3 // {111} TiN and finally constitutes the Ti2O3-TiN. Afterward, the δ-ferrite nucleation will be promoted on the surface of the as-formed Ti2O3-TiN following {001} δ-Fe // {001} TiN. The primary δ-ferrite dendrite preserved in the droplet experiment affirmed the proposed mechanism. These findings will expand the knowledge of oxide accelerating nucleation and could contribute to suitable compositional design for equiaxed solidification.
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