Tetsu-to-Hagane
Online ISSN : 1883-2954
Print ISSN : 0021-1575
ISSN-L : 0021-1575
Regular Articles
Time-resolved and In-situ Observation of δ-γ Transformation during Unidirectional Solidification in Fe-C Alloys
Tomohiro NishimuraKohei MorishitaMasato YoshiyaTomoya NagiraHideyuki Yasuda
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2019 Volume 105 Issue 2 Pages 290-298

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Abstract

Time-resolved and in-situ observations using synchrotron radiation X-rays successfully proved that the massive-like transformation, in which the γ phase was produced through the solid – solid transformation and the partition of substitute elements such as Mn and Si at the δ/γ interface could be negligibly small, 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 in the vicinity of the front of δ/γ interface. The coarse γ grains also grew behind the fine γ grains along the temperature gradient. Distance between the δ/γ front and the advancing front of coarse γ grains was as short as 200 μm. Namely, the fine γ grains disappeared within 10 s by the growth of coarsen γ grains along the temperature gradient. In addition, the observation of the δ/γ interface confirmed that a transition from the diffusion-controlled γ growth to the massive-like growth of γ phase occurred at a growth rate of 5 μm/s. Thus, the massive-like transformation is dominantly selected in the carbon steel during conventional solidification processes.

Transmission images (left) and diffraction images (right) during steady growth state in Fe-0.3C-0.6Mn- 0.3Si. Pulling rate was 50 μm/s. Arrows on the left side (transmission images) indicate the growing front of γ phase. Pixel size for transmission image and diffraction image are 2.5 μm × 2.5 μm and 50 μm × 50 μm, respectively. Frame rate of transmission images was 1 fps. X-ray energy was 21 keV. Fullsize Image
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© 2019 The Iron and Steel Institute of Japan
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