Non-equilibrium Solidification of δ-TRIP Steel
- Non-equilibrium Solidification of δ-TRIP Steel
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- The solidification kinetics of TRIP-assisted steels with high-aluminum contents is investigated, which is characterized by the unique microstructures containing dendritic δ-ferrite. The as-cast specimens contain higher fractions of dendritic δ-ferrite than what expected from the equilibrium phase fraction, probably for kinetic reason. Numerical simulations using DICTRA software and unidirectional solidification experiment were conducted in order to analyze the kinetic effect. However, experimentally observed ferrite fractions were higher than simulated values. Several possible factors for the discrepancy were discussed. Based on the fact that the simulation showed little changes with the cooling rate while experimentally measured ferrite fraction is increased under higher cooling rates, the accuracy of diffusivity database or the cell size set for the simulation probably is not the reason. Also, the modification in liquid diffusivity has little influence on the phase evolution. It seems that γ phase formed between the liquid and δ-phase grows more into the liquid phase due to direct solidification, resulting in considerable amount of residual δ-ferrite. The characteristic of aluminum partition, which makes liquid phase solute-depleted, is attributed to the preferred growth of γ phase toward liquid.
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