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

DoITPoMS Micrograph Library Full Record for Micrograph 240

Full Record for Micrograph 240

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Micrograph no
Brief description
Fe, C 0.4, Mn 0.8 (wt%) steel, normalised
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
Metal or alloy
Fe-C-X   Link to phase diagram
Fe, C 0.4, Mn 0.8 (wt%)
Standard codes
BS 080M40, formerly En 8
Normalised 800 ºC
Sample preparation
Reflected light microscopy
Length bar
100 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.
Dr R F Cochrane
Department of Materials, University of Leeds
Licence for re-use
Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales
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