Phase Diagram

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Phase Diagram

• MSE 201 Lab III

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Overview

• Examine microstructures of the selected carbon
  steels
• Correlate chemical composition and temperature
  with microstructure of the steel samples using
  equilibrium Fe-C phase diagram
• Hardness testing of the steels of equilibrium and
  non-equilibrium cooling

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Samples Conditions

• AISI-SAE 1018 0.18 C
• AISI-SAE 1045 0.45 C
• AISI-SAE 1095 0.95 C
• Austenitized at 870C for 2 hours followed by
• Slow cooling (furnace cool)
• Fast cooling (water quench)

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Iron-Carbon Phase Diagram
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Its All Greek To Me

• Alpha
• Ferrite, BCC Iron
• Room Temperature
• Gamma
• Austenite, FCC Iron
• Elevated Temperatures
• These are PHASES of iron. Adding carbon changes
  the phase transformation temperature.

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Where Does the Carbon Go?

• Interstitial Sites

FCC (Austenite)
BCC (Ferrite) BCT (Martensite)
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Solubility Limits
BCC (? or Ferrite) Iron cant hold much Carbon,
it has a low solubility limit (0.022)
But, FCC (? or Austenite) Iron can hold up to
2.14 Carbon!
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Eutectoid Reaction (Pearlite Formation)

• Austenite precipitates Fe3C at Eutectoid
  Transformation Temperature (727C).
• When cooled slowly, forms Pearlite, which is a
  microcontituent made of ferrite (?) and Cementite
  (Fe3C), looks like Mother of Pearl.

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Microstructure of Pearlite
Photomicrographs of (a) coarse pearlite and (b)
fine pearlite. 3000X
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Hypo-Eutectoid
Proeutectoid means it formed ABOVE or BEFORE
the Eutectoid Temperature!
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Microstructure of Hypo-Eutectoid
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Hyper-Eutectoid
Proeutectoid means it formed ABOVE or BEFORE
the Eutectoid Temperature!
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Microstructure of Hyper-Eutectoid
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Exercise with Lever Rule

• Figure out what type of reaction of the
  transformation and the phases/microconstituents
  involved
• Construct a tie line at the temperature of alloy
• Project the intersections to determine
  concentration
• C0 C ? f? (1- f? ) C Liq

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Exercise with Lever Rule Hypo-eutectoid

• 4. Microconstituents Primary Ferrite, Pearlite
• 5. C in each microconstituent
• Ferrite - 0.022
• Pearlite 0.76
• Amount of each microconstituent
• f? - fraction of ?
• Then C0 C ? f? (1- f? ) C Pearlite
• f? (C0 - C Pearlite)/(C ? - C Pearlite)
• f Pearlite 1- f?

• Phase(s) present ?, Fe3C
• C ? - 0.022, Fe3C 6.7
• Amount of each phase
• f? - fraction of ?
• Then C0 C ? f? (1- f? ) C Fe3C
• f? (C0 - C Fe3C)/(C ? - C Fe3C)
• f Fe3C 1- f?

You will figure out how to work it out for
hyper-eutectoid compositions
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What if cooled really fast?

• Faster cooling gives non-equilibrium
  microconstituents Martensite, and more!
• Lets measure the hardness of slow and fast
  cooled samples and compare

NEXT LAB 11/03/06 NO GROUP REPORTS FOR THIS
LAB!!!!