Image icon  Fe, C 0.3 (wt%) steel, spheroidised carbide

 
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Description: A hypoeutectoid alloy (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 eutectic 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.

Subsequent to casting the sample was annealed for a long period just below the transformation range. This induces the cementite to take on a spherical appearance. This results in a softer and more ductile alloy. This process is known as spheroidisation. The changes to the morphology of the cementite cannot be seen clearly in this micrograph, but they are more apparent at higher magnification (see micrograph 242).
Keywords: alloy • carbon • hypoeutectoid • iron • metal • pearlite • steel
Categories: Science approaches > Microstructure
Materials > Metals & alloys > Carbon steels
Processes > Thermal treatments > Annealing
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: 1278