Dissemination of IT for the Promotion of Materials Science (DoITPoMS)

DoITPoMS Micrograph Library Full Record for Micrograph 268

Full Record for Micrograph 268

Link to full size image of micrograph 268
[252 KB]

View micrograph
.. in new window

View micrograph and record
.. in new window


You can also view and download the micrographs on Flickr
Micrograph no
268
Brief description
Fe, C 0.5 (wt%) steel, near a decarburised surface
Keywords
alloy Link to MATTER Glossary entry for alloy, carbon, decarburisation Link to MATTER Glossary entry for decarburisation, hypoeutectoid Link to MATTER Glossary entry for hypoeutectoid, iron, metal, steel Link to MATTER Glossary entry for steel
Categories
Metal or alloy
System
Fe-C-X   Link to phase diagram
Composition
Fe, C 0.5 (wt%)
Standard codes
Reaction
Processing
Decarburised
Applications
Sample preparation
Nital
Technique
Reflected light microscopy
Length bar
400 μm
Further information
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.
Contributor
Dr R F Cochrane
Organisation
Department of Materials, University of Leeds
Date
04/09/02
Licence for re-use
Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales