The Science and Engineering of Materials, 4th ed Donald R. Askeland

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Section 11.9 The Eutectoid
Reaction

• Austenite - The name given to the FCC crystal
  structure of iron.
• Ferrite - The name given to the BCC crystal
  structure of iron that can occur as a or d.
• Cementite - The hard, brittle ceramic-like
  compound Fe3C that, when properly dispersed,
  provides the strengthening in steels.
• Pearlite - A two-phase lamellar microconstituent,
  containing ferrite and cementite, that forms in
  steels cooled in a normal fashion or isothermally
  transformed at relatively high temperatures.

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Figure 11.15 The Fe-Fe3C phase diagram ( a
portion of the Fe-C diagram). The vertical line
at 6.67 C is the stoichiometric compound Fe3C.
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Figure 11.16 Growth and structure of pearlite
(a) redistribution of carbon and iron, and (b)
photomicrograph of the pearlite lamellae (2000).
(From ASM Handbook, Vol. 7, (1972), ASM
International, Materials Park, OH 44073.)
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Example 11.5
Phases and Composition of Pearlite
Calculate the amounts of ferrite and cementite
present in pearlite. Example 11.5 SOLUTION Since
pearlite must contain 0.77 C, using the lever
rule
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Figure 11.17 The evolution of the microstructure
of hypoeutectoid and hypoeutectoid steels during
cooling. In relationship to the Fe-Fe3C phase
diagram.
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Section 11.10 Controlling the
Eutectoid Reaction

• Controlling the Amount of the Eutectoid
• Controlling the Austenite Grain Size
• Controlling the Cooling Rate
• Controlling the Transformation Temperature
• TTT diagram - The time-temperature-transformation
  diagram describes the time required at any
  temperature for a phase transformation to begin
  and end.
• Isothermal transformation - When the amount of a
  transformation at a particular temperature
  depends on the time permitted for the
  transformation.

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Figure 11.21 The time-temperature-transformation
(TTT) diagram for an eutectoid steel.
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Figure 11.23 (a) Upper bainite (gray, feathery
plates) (? 600). (b) Lower bainite (dark needles)
(? 400). (From ASM Handbook, Vol. 8, (1973), ASM
International, Materials Park, OH 44073.)
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Figure 11.24 The effect of transformation
temperature on the properties of an eutectoid
steel.
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Figure 11.21 The time-temperature-transformation
(TTT) diagram for an eutectoid steel.
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Figure 11.25 (a) The unit cell of BCT martensite
is related to the FCC austenite unit cell. (b)
As the percentage of carbon increases, more
interstitial sites are filled by the carbon atoms
and the tetragonal structure of the martensite
becomes more pronounced.
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Section 11.11 The
Martensitic Reaction and Tempering

• Martensite - A metastable phase formed in steel
  and other materials by a diffusionless, athermal
  transformation.
• Displacive transformation - A phase
  transformation that occurs via small
  displacements of atoms or ions and without
  diffusion. Same as athermal or martensitic
  transformation.
• Tempering - A low-temperature heat treatment used
  to reduce the hardness of martensite by
  permitting the martensite to begin to decompose
  to the equilibrium phases.

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Figure 11.26 The effect of carbon content on the
hardness of martensite in steels.
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Figure 11.28 Effect of tempering temperature on
the properties of and eutectoid steel.
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Figure 11.29 Tempered martensite in steel (?
500). (From ASM Handbook, Vol. 9, Metallography
and Microstructure (1985), ASM International
Materials Park, OH 44073.)
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Figure 11.35 The eutectoid portion of the
Fe-Fe3C phase diagram (for Problems 11.78, 11.86,
11.87, and 11.88)
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