Ferrous- From the Latin word ferrum, meaning iron. Describes an
alloy containing a significant amount of iron.
Slide 4
Cementite- Fe3C. Also known as iron carbide, a compound of iron
and carbon.
Slide 5
Anneal- In general, the heating of metal to soften it or reduce
its strength.
Slide 6
Figure 1.14 Schematic illustration of the effects of recovery,
recrystallization, and grain growth on mechanical properties and on
the shape and size of grains. Note the formation of small new
grains during recrystallization. Source: G. Sachs. Annealing
Slide 7
Allotropy- The ability of a material to exist in several
crystalline forms.
Slide 8
Austenite- A solid solution of iron and carbon and sometimes
other elements in which gamma iron, characterized by a face-
centered crystal structure, is the solvent.
Slide 9
Ferrite- A magnetic form of iron. A solid solution in which
alpha iron is the solvent, characterized by a body- centered cubic
crystal structure.
Slide 10
Figure 4.9 The unit cells for (a) austenite, (b) ferrite, and
(c) martensite. The effect of percentage of carbon (by weight) on
the lattice dimensions for martensite is shown in (d). Note the
interstitial position of the carbon atoms (see Fig. 1.9). Note,
also, the increase in dimension c with increasing carbon content;
this effect causes the unit cell of martensite to be in the shape
of a rectangular prism. Austenite, Ferrite, and Martensite
Slide 11
Curie temperature- The temperature above which metals are no
longer magnetic. For iron this temperature is 1414F. (It is named
for Pierre Curie, husband of Marie Curie.)
Slide 12
Phase- A portion of an alloy, physically homogeneous
throughout, that is separated from the rest of the alloy by
distinct boundary surfaces. The following phases occur in the
iron-carbon alloy: molten alloy austenite ferrite cementite
graphite
Slide 13
Figure 4.3 (a) Schematic illustration of grains, grain
boundaries, and particles dispersed throughout the structure of a
two-phase system, such as a lead-copper alloy. The grains represent
lead in solid solution in copper, and the particles are lead as a
second phase. (b) Schematic illustration of a two-phase system
consisting of two sets of grains: dark, and light. The dark and the
light grains have separate compositions and properties. Two-Phase
System
Slide 14
Phase change- The transformation of a substance from one
distinct, separate form to another. When a molten metal solidifies
it has changed phase, and depending on the alloy system, it may
solidify as one phase (a single phase) or as two phases (a
mixture).
Slide 15
Phase diagram- For binary (two metals) alloy systems, a diagram
of temperature versus percent composition, with 100 percent of one
metal on one axis and 100 percent of the second on the other. Lines
on the diagram separate single phases from mixtures of phases.
Slide 16
Phase diagram- Additional time is required to change from one
phase to another. In the construction of a phase diagram all the
time necessary for phase changes to occur is assumed available; it
is thus often termed an equilibrium phase diagram.
Slide 17
Figure 4.5 Phase diagram for nickel-copper alloy system
obtained at a slow rate of solidification. Note that pure nickel
and pure copper each has one freezing or melting temperature. The
top circle on the right depicts the nucleation of crystals. The
second circle shows the formation of dendrites (see Section 10.2).
The bottom circle shows the solidified alloy, with grain
boundaries. Nickel-Copper Alloy Phase Diagram
Slide 18
Figure 4.7 The lead-tin phase diagram. Note that the
composition of the eutectic point for this alloy is 61.9% Sn-38.1%
Pb. A composition either lower or higher than this ratio will have
a higher liquidus temperature. Lead-Tin Phase Diagram
Slide 19
Figure 4.8 The iron-iron carbide phase diagram. Because of the
importance of steel as an engineering material, this diagram is one
of the most important of all phase diagrams. Iron-Iron Carbide
Phase Diagram
Slide 20
Figure 4.12 Phase diagram for the iron-carbon system with
graphite (instead of cementite) as the stable phase. Note that this
figure is an extended version of Fig. 4.8. Extended Iron-Carbon
Phase Diagram
Slide 21
Aluminum-Copper Phase Diagram Figure 4.21 (a) Phase diagram for
the aluminum-copper alloy system. (b) Various micro- structures
obtained during the age-hardening process. Source: L. H. Van Vlack;
Materials for Engineering. Addison-Wesley Publishing Co., Inc.,
1982.
Slide 22
Figure 3.4 Cooling curve for the solidification of pure metals.
Note that freezing takes place at a constant temperature; during
freezing the latent heat of solidification is given off. Cooling
Curve
Slide 23
Liquidus- The temperature at which freezing begins during
cooling and ends during heating under equilibrium conditions,
represented by a line on a two-phase diagram.
Slide 24
Solidus- Seen as a line on a two-phase diagram, it represents
the temperatures at which freezing ends when cooling, or melting
begins when heating under equilibrium conditions.
Slide 25
Eutectic- The alloy composition that freezes at the lowest
constant temperature, causing a discrete mixture to form in
definite proportions.
Slide 26
Solubility- The degree to which one substance will dissolve in
another.
Slide 27
Eutectoid- The alloy composition that transforms from a high
temperature solid into new phases at the lowest constant
temperature. In binary (double) alloy systems, it is a mechanical
mixture of two phases that forms simultaneously from a solid
solution as it cools through the eutectoid (A1/A3,1 in steels)
temperature.
Slide 28
Eutectoid Steel Microstructure Figure 4.17 Microstructure of
eutectoid steel. Spheroidite is formed by tempering the steel at
700 C (1292 F). Magnification: 1000X. Source: Courtesy of USX
Corporation.
Slide 29
Pearlite- The lamellar mixture of ferrite and cementite in
slowly cooled iron-carbon alloys as found in steel and cast
iron.
Slide 30
Pearlite Microstructure Figure 4.11 Microstructure of pearlite
in 1080 steel, formed from austenite of eutectoid composition. In
this lamellar structure, the lighter regions are ferrite, and the
darker regions are carbide. Magnification: 2500X. Source: Courtesy
of USX Corporation.
Slide 31
Hypoeutectoid- Used to identify those metallic alloys that have
a composition less than that of the eutectoid composition.
Slide 32
Hypereutectoid- Used to identify metallic alloys that have a
composition greater than that of the eutectoid composition.
Slide 33
Quenching- The process of rapid cooling of metal alloys for the
purpose of hardening. Quenching media include air, oil, water,
molten metals, and fused salts.
Slide 34
Time-temperature transformation, or TTT, or IT- A diagram that
shows the transformation of austenite at one temperature when the
time for transformation is taken into account. Because the
transformation occurs at one temperature it is also termed an IT or
isothermal transformation diagram.
Slide 35
Martensite- Iron phase supersaturated in carbon that is a
nonequilibrium product of austenite transformation.
Slide 36
Martensite (b) Figure 4.18 (a) Hardness of martensite, as a
function of carbon content. (b) Micrograph of martensite containing
0.8% carbon. The gray platelike regions are martensite; they have
the same composition as the original austenite (white regions).
Magnification: 1000X. Source: Courtesy of USX Corporation.
Slide 37
Bainite- An austenitic transformation found in some steels and
cast irons. The microstructure consists of ferrite and a fine
dispersion of cementite that has the needlelike appearance of
martensite.
Slide 38
Induction-Hardened Surface Figure 4.1 Cross-section of gear
teeth showing induction-hardened surfaces. Source: TOCCO Div.,
Park-Ohio Industries, Inc.
Slide 39
Outline of Heat Treatment Processes for Surface Hardening
Slide 40
Figure 4.23 Heat-treating temperature ranges for plain-carbon
steels, as indicated on the iron-iron carbide phase diagram.
Source: ASM International. Figure 4.24 Hardness of steels in the
quenched and normalized conditions, as a function of carbon
content. Heat Treatment Processes
Slide 41
Surface hardening- Usually refers to the hardening of the
surface of steel; this can be accomplished two ways: using a steel
with sufficient carbon to achieve the hardness desired heat
treating just the surface, or raising the carbon content of the
surface and heat treating the whole part Surface peening will also
harden the surface of most metals.
Slide 42
Precipitation hardening- A process of hardening an alloy by
heat treatment in which a constituent precipitates from a
supersaturated solid solution while at room temperature or at some
slightly elevated temperature.
Slide 43
Plastic deformation- Deformation that occurs when so much
stress is applied to a solid that it does not return to its
original condition.
Slide 44
Work hardening- Also called strain hardening and cold working,
in which the grains become distorted and elongated in the direction
of working (e.g., rolling).
Slide 45
Full annealing- Heating a metal to an elevated temperature for
a long enough time that any evidence of prior cold working or heat
treating is removed, and then cooling at a slow rate; the cooling
is often accomplished by letting the metal cool in the furnace with
the burners off. Under these conditions the metal will approximate
the condition predicted by the phase diagram.
Slide 46
Figure 1.14 Schematic illustration of the effects of recovery,
recrystallization, and grain growth on mechanical properties and on
the shape and size of grains. Note the formation of small new
grains during recrystallization. Source: G. Sachs. Annealing
Slide 47
Stress relief anneal- The reduction of residual stress in a
metal part by heating it to a given temperature and holding it
there for a suitable length of time. This treatment is used to
relieve elastic stresses caused by welding, cold working,
machining, casting, and quenching.
Slide 48
Process anneal- An annealing process used within a sequence of
cold-working operations that causes the metal to recrystallize, so
that additional cold working can be done.
Slide 49
Normalize- To homogenize and produce a uniform structure in
alloy steels by heating above the transformation range and cooling
in air.
Slide 50
Spheroidizing- Consists of holding carbon steel for a period of
time at just under the transformation temperature. An aggregate of
globular carbide is formed from other microstructure such as
pearlite.
Slide 51
Recrystallization- A process in which the distorted grain
structure of metals that are subjected to mechanical deformation is
replaced by a new strain-free grain structure during
annealing.
Slide 52
Residual stress- Stresses induced within the structure of a
metal by cold working, machining, and heat treatments and remaining
in the metal after the treatment is completed.