DoITPoMS

Full Record for Micrograph 238

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Micrograph no
238
Brief description
Hypoeutectoid steel, normalised at 950°C
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 (wt%)
Standard codes
Reaction
Processing
Normalised 950°C
Applications
Sample preparation
Nital
Technique
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.
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
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