Image icon  Fe, C 0.1 (wt%), hypoeutectoid alloy

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Description: This is a hypoeutectoid alloy, which has been air cooled from the austenite phase field at 950 °C. The first solid to form is proeutectoid ferrite, its morphology being determined by the cooling rate. At slow cooling rates (furnace cooling) there is sufficient time for the carbon rejected from the austenite to diffuse and equilibrium solidification occurs. With faster cooling the microstructure also depends on the original austenite grain size.

Fast cooling and large grain size favours ferrite forming as Widmanstätten side plates from the grain boundaries. Small grain sizes imply a high number of nuclei and hence the ferrite grows as grain boundary allotriomorphs. In this case air cooling is sufficiently slow to produce allotriomorphic ferrite. The majority of the austenite has changed to ferrite leaving only a small amount to be transformed to pearlite, therefore the microstructure shows large ferrite grains with small islands of pearlite.
Keywords: allotriomorph • alloy • austenite • carbon • ferrite • hypoeutectoid • iron • metal • pearlite • proeutectoid steel • steel
Categories: Science approaches > Microstructure
Materials > Metals & alloys > Carbon steels
Testing, analysis & experimentation > Metallography
Scale > Micro
Created by: DoITPoMS, University of Cambridge
Prof T W Clyne, Department of Materials Science and Metallurgy, University of Cambridge
Published by: DoITPoMS, University of Cambridge
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Date created: 25 October 2001
Date added: 21 August 2009
Resource ID: 1082