CEMM 260/261
Review for Test #2
Spring 2005
From Chapter 8 Mostly, just know the definitions of the major phenomena described in
this chapter. Section 8.1 Impact Energy, (Fig 1 for Charpy test), Ductile to Brittle
Transition Temperature (Figure 8.3)
Section 8.3, Fatigue. Fatigue strength (Figure 8.10).
Creep was covered in Chapter 6, section 6.5.
From Chapter 9 Phase diagrams.
9.1 Gibbs Phase Rule. Thermodynamic equilibrium for phases
F = C – P + 2 (C – P + 1 for a system at constant pressure)
Phase diagrams for binary systems. At any temperature and composition be able to read:
1. The number of phases at equilibrium, 2. The identity of the phases, 3. The
composition of the phases, 4. From the lever rule (covered in Section 9.3) the amount of
each phase X = (Co-C)/(C-C)
2. Temperature invariant transformation: 3 phases in equilibrium in binary system.
Appears as a horizontal line on a phase diagram.
Types
On cooling
Eutectic (Fig 9.14, 9.16)
L => 
Peritectic
L + 
Eutectoid
(Solid State)

Peritectoid
(Solid State)


Eutectic and eutectoid transformation produce a characteristic laminated structure (see
front of chapter figure (Pb-Sn eutectic) and Figure 9.2 (Fe –C eutectoid)
Intermediate compounds may be congruent melting (Fig 9.24) or form by peritectic (Fig
9.22). They may be line compounds (ie no solid solubility) or may have solid solubility
and finite width in phase diagram.
Microstructure development during slow cooling. See Figure 9.35. Especially for
eutectic systems and alloys higher or lower than eutectic composition. Cool through L +
 region and develop proeutectic (primary ) . This forms above eutectic T, and will be
visible in final structure. Remaining liquid will have approximately the eutectic
composition and will freeze into the eutectic structure.
Chapter 10 Kinetics and heat treatment. Issue is how quickly the system moves to
equilibrium.
Section 10.2 TTT diagrams in steel (Fe-C) Uses eutectoid transformation (0.8% C) =>
 (0.02%C) + Fe3C (6.7%C) at 727oC. Lowering transformation temperature raises
thermodynamic driving force for transformation, speeding it up, but also lowers diffusion
coefficient, slowing it down. Results in C shaped curve. (Figure 10.11)
Transformation at high temperature results in coarse, soft structure, and transformation at
lower temperature results in fine, harder structure. Coarse Pearlite softer than fine
pearlite softer than bainite. Hardest phase is Martensite, a body centered tetragonal
structure formed by quenching austenite to room temperature. May temper (reheat to
bainite T range to soften slightly, but improve toughness.
Section 10.3 Hardenability Add alloy elements to steel to slow formation of ferrite +
cementite, making it easier to form martensite. Jominy end quench test.
Section 10.4 Precipitation Hardening
1. Choose an ally that is one phase at high T, but 2 phase at room T (Figure 10.26)
2. Solutionize (ie. Heat to 1 phase T range and dissolve second phase.
3. Quench to room T, producing soft, metastable phase.
4. Form phase into shape
5. Age Heat to T in 2 phase region where second phase particles can form. Hold for
prescribed time to obtain optimum hardness. If hold too long can overage and
soften. Note that aging kinetics change with T.
Section 10.5 and Fig 11.13. Cold work and annealing
Cold work = %CW = (Ao – Af)/Ao x 100 Equation 10.2
Hardness up as %CW up, due to dislocations in worked metal. To remove CW, anneal at
T ~(1/3 – ½) of melting point. Forms new grains without dislocations and removes cold
work. Use Fig 11.13 or equivalent to design cold work and annealing sequence to obtain
desired metal properties and dimensions for brass.
Note 10xx steel is plain carbon steel containing 0.xx %C.