Image icon  Fe, C 0.5 (wt%) steel, near a decarburised surface

 
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Description: This is a hypoeutectoid steel (one that has a carbon composition below that of the eutectoid). During original cooling from high temperature, some ferrite was formed first on the prior austenite grain boundaries and the remaining carbon-enriched austenite then transformed to pearlite in a eutectoid reaction. The specimen was then exposed to a decarburising atmosphere (just air in this case). This might happen inadvertently, or it could be done deliberately if a softer surface is required for some reason. Material near the top of the micrograph, which was close to the free surface, is depleted in carbon and has become almost entirely ferritic. The depth to which there is significant carbon depletion depends on the time and temperature of the decarburisation treatment. It is given approximately by the square root of the product of the diffusivity of the carbon at the temperature concerned and the treatment time.
Keywords: alloy • carbon • decarburisation • hypoeutectoid • iron • metal • steel
Categories: Science approaches > Microstructure
Materials > Metals & alloys > Carbon steels
Testing, analysis & experimentation > Metallography
Scale > Micro
Created by: DoITPoMS, University of Cambridge
Dr R F Cochrane, Department of Materials, University of Leeds
Published by: DoITPoMS, University of Cambridge
License: This resource is released under the Creative Commons Attribution Non-Commercial Share Alike license (2.0 UK: England & Wales).
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Date created: 04 September 2002
Date added: 21 August 2009
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Resource ID: 1305