The IronCarbon Phase Diagram

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The Iron-Carbon Phase Diagram

• Steven Shepherd
• December 06, 2005

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A Very Complex Iron-Carbon Phase Diagram (1992)
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A Slightly Less Complex Phase Diagram
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A Simple Iron-Carbon Phase Diagram
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A Very Simple Iron-Carbon Phase Diagram
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The Iron-Carbon Phase Diagram
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Why do We Care?

• Iron
• Properties of Iron
• Steel
• Ferrite, pearlite, cementite, austenite
• Can heat-treat so it can suit its application
• Good steel versus bad steel
• 1 C
• Bessemer Process

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Ferrite and Austenite

• Ferrite
• Known as a-iron
• Pure iron at room temperature
• Body-centered cubic structure
• Austenite
• Known as ?-iron
• 910C
• Face-centered cubic
• Much softer than ferrite
• More easily worked
• blacksmithing

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Pearlite and Cementite

• Pearlite (Perlite)
• Pearly lustre in the microscope
• Interference of light in its regular layers
• Most common constituent of steel
• Gives steel most of its strength
• layered mixture of ferrite and cementite of
  average composition 0.83 carbon
• Point D
• Cementite
• Hard, brittle, white
• melts at 1837C
• density of 7.4 g/cc
• On the phase diagram, cementite corresponds to a
  vertical line at 6.7 C
• Engineers only care about compounds with less
  carbon

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Interesting Information

• Left of point B a steel
• Heated ? uniform austenite phase
• Right of point B a cast-iron
• Point E eutectic
• Lowest fusing T (1130 C)
• Liquid left of E? austenite ledeburite
• Right of E?cementite ledeburite
• Eutectoids
• Like eutectic
• No melting
• Normalization of steel (723 C)
• No melting, just hot enough to become austenite
  (gt1130 C)

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More Interesting Information

• Around Point C
• looks like an inverted eutectoid--not a eutectoid
  
• What happens at point C is called a peritectic
  reaction, as d-iron is dissolved and austenite
  formed

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Interesting Sites Concerning Phase Diagrams

• Interactive Phase Diagram-- http//www.soton.ac.uk
  /pasr1/interact.htmmap3d
• Cellular Automata Phase Diagrams
  http//www.physics.emory.edu/weeks/ca/ca.html

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Works Cited

• http//www.tf.uni-kiel.de/matwis/amat/mw1_ge/kap_8
  /illustr/phasendiagramm_fe.gif
• http//www.roymech.co.uk/Useful_Tables/Matter/Phas
  e_diagram.html
• http//members.lycos.nl/cvdv/ironcarbondiagrams/Zh
  ukov1992.htm
• http//www.kuleuven.ac.be/bwk/materials/Teaching/m
  edia/wg02/f0100006.jpg
• http//www.du.edu/jcalvert/phys/phase.htm