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

DoITPoMS Micrograph Library Full Record for Micrograph 239

Full Record for Micrograph 239

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Micrograph no
239
Brief description
Fe, C 0.4, Mn 0.8 (wt%) steel, normalised
Keywords
alloy Link to MATTER Glossary entry for alloy, carbon, hypoeutectoid Link to MATTER Glossary entry for hypoeutectoid, iron, metal, pearlite Link to MATTER Glossary entry for pearlite, steel Link to MATTER Glossary entry for steel
Categories
Metal or alloy
System
Fe-C-X   Link to phase diagram
Composition
Fe, C 0.4, Mn 0.8 (wt%)
Standard codes
BS 080M40, formerly En 8
Reaction
Processing
Normalised 800 ºC
Applications
Sample preparation
Nital
Technique
Reflected light microscopy
Length bar
400 μm
Further information
A hypoeutectoid alloy (carbon composition less than eutectoid). The first phase formed upon cooling from the austenite phase field is proeutectoid ferrite. Due to the lower solubility of carbon in ferrite, carbon is partitioned into the remaining austenite. At the eutectoid point the remaining carbon enriched austenite transforms to pearlite (a mixture of ferrite and cementite) which is the darker region of the micrograph. The proportion of pearlite is dependent upon the overall composition.

The ferrite (light areas) is a good example of an allotriomorphic ferrite. This means that its shape does not reflect its internal crystalline symmetry as it nucleates on the austenite grain boundaries and hence follows the shape of the boundaries, the remaining austenite within the ferrite then transforms to pearlite, and is surrounded by the ferrite.
Contributor
Dr R F Cochrane
Organisation
Department of Materials, University of Leeds
Date
04/09/02
Licence for re-use
Attribution-NonCommercial-ShareAlike 4.0 International
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