ISIJ International
Online ISSN : 1347-5460
Print ISSN : 0915-1559
ISSN-L : 0915-1559
Time-resolved and In-situ Observation of δγ Transformation during Unidirectional Solidification in Fe–C Alloys
Tomohiro NishimuraKohei MorishitaMasato YoshiyaTomoya NagiraHideyuki Yasuda
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JOURNALS OPEN ACCESS Advance online publication

Article ID: ISIJINT-2019-636

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Abstract

Time-resolved and in-situ observations using synchrotron radiation X-rays successfully proved that a massive-like transformation, in which the γ phase was produced through the solid–solid transformation and partitioning of substitute elements such as Mn and Si at the δγ interface was negligible, was selected in the unidirectional solidification of 0.3 mass% C steel at a pulling rate of 50 μm/s. The massive-like transformation produced fine γ grains near the front of the δγ interface. The coarse γ grains also grew behind the fine γ grains along the temperature gradient. Distance between the δγ front and the advancing front of coarse γ grains was as short as 200 μm. Namely, the fine γ grains disappeared within 10 s owing to growth of coarse γ grains. In addition, the observation of the δγ interface confirmed that a transition from the diffusion-controlled γ growth to the massive-like γ growth occurred at a growth velocity of 5 μm/s. Thus, the massive-like transformation is dominantly selected in the carbon steel during conventional solidification processes.

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