Ferrite massively transforms to austenite during solidification

A massive-like transformation from ferrite to austenite in the dendrite arms (Carbon steel)

炭素の凝固過程で、フェライト（BCC、δ）がマッシブ的にオーステナイト（FCC、γ）に変態する様子。固相変態であり、微細なオーステナイトが形成し、すぐに粗大化が起こっている様子。広く使われている炭素鋼でも、観察が困難な融液からの凝固には未知・未踏の領域が残っており、これらの解明が組織制御やプロセス開発に結びつくと期待しています。

The transformation from ferrite to austenite occurred during solidification at 20K below the peritectic temperature. Fine austenite grains were produced in a single arm and coarsening occurred.
We have not fully understood the solidification phenomena of steel, which took place at 1400-1500C, because of difficulties for time-resolved and in-situ observation / measurement.

"Dendrite fragmentation induced by massive-like δ–γ transformation in Fe–C alloys", H. Yasuda, K. Morishita, N. Nakatsuka, T. Nishimura, M. Yoshiya, A. Sugiyama, K. Uesugi, A. Takeuchi, Nature Communications 10 (2019) 1–5. DOI:10.1038/s41467-019-11079-y