Image icon  Fe, C 3.6, Si 2.1 (wt%), hypereutectic grey cast iron

Use this resource: Use this resource icon
Link to this page:
View at:            
Resource type: Image
Description: The carbon equivalent of this alloy (4.37 wt%) is greater than the eutectic composition (4.3 wt% C) so this alloy is known as a hypereutectic grey cast iron. Si has a very low solubility in cementite and therefore its presence favours the formation of graphite in preference to cementite. Therefore, upon cooling from the liquid, the primary phase to solidify is free graphite. Graphite forms directly from the melt as flakes (black) rather than dendrites. These flakes are interconnected and align themselves in the heat flow direction. Upon further cooling the remaining liquid forms initially as a eutectic mixture of austenite and cementite, known as ledeburite. The austenite within the eutectic further transforms to a mixture of pearlite and cementite. The graphite is eventually embedded in a complex mixture known as 'transformed ledeburite'. The graphite flakes are very soft and have low density so compensate for freezing contraction upon solidification, however they also act effectively as cracks making the cast iron is brittle.
Keywords: alloy • carbon • cast iron • graphite • hypereutectic • iron • metal • silicon
Categories: Science approaches > Microstructure
Materials > Metals & alloys > Cast irons
Processes > Shaping > Casting
Testing, analysis & experimentation > Metallography
Scale > Micro
Created by: Prof T W Clyne, Department of Materials Science and Metallurgy, University of Cambridge
DoITPoMS, University of Cambridge
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).
Creative Commons Attribution Non-Commercial Share Alike logo
You are free:
  • to share – to copy, distribute and transmit the work
  • to remix – to adapt the work
Under the following conditions:
  • attribution – You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work).
  • noncommercial – You may not use this work for commercial purposes.
  • share alike – If you alter, transform, or build upon this work, you may distribute the resulting work only under the same or similar license to this one.
View the full legal code here.
Date created: 25 October 2001
Date added: 21 August 2009
Resource ID: 1129