In-Situ Observation of the Growth of Massive Ferrite in Very Low-Carbon Fe-Mn and Ni Alloys
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The growth of ferrite was observed in situ under confocal scanning laser microscope in Fe-Ni and Mn alloys containing less than 0.01 mass pct C. The advancements of α/γ boundary during cooling at 2 and 20 °C/s were measured in the paraequilibrium α single-phase region in Fe-2Ni and 2Mn alloys and near the paraequilibrium α/(α + γ) phase boundary in an Fe-5Ni alloy. The growth rates obtained from the boundary displacement vs time plots were almost constant and were considerably greater than those calculated under long-range carbon diffusion control, and thus, the ferrite growth is likely to have occurred in a massive manner, albeit a carbon spike may develop ahead of the boundary. The mobility of massive α/γ boundary was calculated to fall between those proposed by Hillert and Wits et al. irrespective of the assumption as to the formation of carbon spike in front of the boundary.
KeywordsFerrite Austenite Fast Cool Rate Boundary Mobility Ferrite Growth
The authors are deeply indebted to Dr. S. Fukumoto, Nippon Steel & Sumikin Stainless Steel Corp., for invaluable assistance in scanning laser microscopy.
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