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3726511 
Journal Article 
Difference in transformation behavior between ferrite and austenite formations in medium manganese steel 
Nakada, N; Mizutani, K; Tsuchiyama, T; Takaki, S 
2014 
Yes 
Acta Materialia
ISSN: 1359-6454 
65 
251-258 
WOS:000331347600024 
The difference in transformation behavior between the gamma -> alpha and alpha'-> gamma transformations at the transition temperature T-0 was investigated in 0.1%C-5%Mn steel. The gamma -> alpha transformation was very slow, and so little ferrite phase formed at T-0, even after a lengthy annealing time of 50 h. However, the alpha'-> gamma transformation was relatively fast and rapidly proceeded at T-0. In the dual-phase structure formed by the alpha'-> gamma transformation, thin film-shaped reversed austenite grains with sufficient thermal stability formed along the lath boundaries of the tempered martensite matrix. The simulation using diffusion-controlled transformations (DICTRA) software confirmed that the rapid austenite formation in medium manganese steel is attributed to: (1) the high density of austenite nucleation sites derived from the hierarchical lath martensitic structure; (2) the negligible-partitioning local equilibrium growth controlled by very fast carbon diffusion at the initial stage; and (3) the relatively higher diffusivity of Mn within the martensite matrix under the partitioning local equilibrium growth that occurred at a subsequent stage. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. 
Medium Mn steel; Reversed austenite; Martensite; Local equilibrium; Growth kinetics