Ch4 alloys heat threatment Erdi Karaçal Mechanical Engineer University of Gaziantep

Chapter 4
Metal Alloys: Structure and
Strengthening by Heat Treatment
Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.
ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Gear Teeth Cross-section
Figure 4.1 Cross-section of gear teeth showing induction-hardened
surfaces. Source: Courtesy of TOCCO Div., Park-Ohio Industries, Inc.

Chapter 4 Topics
Figure 4.2 Outline of topics described in Chapter 4.

Two Phase Systems
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.

Cooling of Metals
Figure 4.4 (a) 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. (b) Change in density during the cooling of pure metals.

Phase Diagram for Nickel-copper Alloy System
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.

Mechanical Properties of Copper Alloys
Figure 4.6 Mechanical properties of copper-nickel and copper-zinc
alloys as a function of their composition. The curves for zinc are short,
because zinc has a maximum solid solubility of 40% in copper.

Lead-tin Phase Diagram
Figure 4.7 The lead-tin phase diagram. Note that the composition of 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.

Iron-iron Carbide Phase Diagram
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.

Unit Cells
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). Also
note, 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.

Microstructures for an Iron-Carbon Alloy
Figure 4.10 Schematic illustration of
the microstructures for an iron-carbon
alloy of eutectoid
composition (0.77% carbon) above
and below the eutectoid temperature
of 727°C (1341°F).

Microstructure of Steel Formed from Eutectoid Composition
Figure 4.11 Microstructure of pearlite in 1080 steel formed from austenite
of a eutectoid composition. In this lamellar structure, the lighter regions
are ferrite, and the darker regions are carbide. Magnification: 2500x.

Iron-Carbon Phase Diagram with Graphite
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.

Microstructure for Cast Irons
Figure 4.13 Microstructure for cast irons. Magnification: 100x. (a) Ferritic gray iron
with graphite flakes. (b) Ferritic ductile iron (nodular iron) with graphite in nodular
form. (c) Ferritic malleable iron. This cast iron solidified as white cast iron with the
carbon present as cementite and was heat treated to graphitize the carbon.

Microstructure of Eutectoid Steel
Figure 4.14
Microstructure of eutectoid
steel. Spheroidite is
formed by tempering the
steel at 700°C (1292°F).
Magnification: 1000x.

Martensite
Figure 4.15 (a) Hardness of martensite as a function of carbon content. (b)
Micrograph of martensite containing 0.8% carbon. The gray plate-like regions are
martensite; they have the same composition as the original austenite (white
regions). Magnification: 1000x.

Hardness of Tempered Martensite
Figure 4.16 Hardness of tempered martensite as a function of
tempering time for the 1080 steel quenched to 65 HRC. Hardness
decreases because the carbide particles coalesce and grow in size,
thereby increasing the interparticle distance of the softer ferrite.

Time-temperature-transformation
diagrams
Figure 4.17 (a) Austenite-to-
pearlite transformation
of iron-carbon alloy as a
function of time and
temperature. (b)
Isothermal transformation
diagram obtained from (a)
for a transformation
temperature of 675°C
(1274°F). (c)
Microstructures obtained
for a eutectoid iron-carbon
alloy as a function of
cooling rate.

Hardness and Toughness in Steel as a Function of Carbide Shape
Figure 4.18 (a) and (b) Hardness and (c) toughness for annealed plain-carbon steel as a
function of a carbide shape. Carbides in the pearlite are lamellar. Fine pearlite is obtained
by increasing the cooling rate. The spheroidite structure has sphere-like carbide particles.

Mechanical Properties of Steel as a Function of
Composition and Microstructure
Figure 4.19 Mechanical properties of annealed steels as a function of composition and
microstructure. Note in (a) the increase in hardness and strength and in (b) the decrease
in ductility and toughness with increasing amounts of pearlite and iron carbide.

End-Quench
Hardenability
Test
Figure 4.20 (a) End-quench
test and cooling
rate. (b) Hardenability
curves for five different
steels, as obtained from the
end-quench test. Small
variations in composition
can change the shape of
these curves. Each curve is
actually a band, and its
exact determination is
important in the heat
treatment of metals for
better control of properties.

Phase Diagram for Aluminum-copper Alloy
and Obtained Microstructures
Figure 4.21 (a) Phase diagram for the aluminum-copper alloy system.
(b) Various microstructures obtained during the age-hardening process.

Effect of Time and Temperature on Yield Stress
Figure 4.22 The effect of again time and temperature on the yield
stress of 2014-T4 aluminum alloy. Note that, for each
temperature, there is an optimal aging time for maximum strength.

Outline of Heat Treatment Processes for Surface Hardening

Outline of Heat Treatment Processes for Surface Hardening, con’t.

Heat-treating Temperature Ranges for Plain-Carbon Steels
Figure 4.23 Heat-treating temperature ranges for plain-carbon
steels, as indicated on the iron-iron carbide phase diagram.

Hardness of Steel as a Function of Carbon Content
Figure 4.24 Hardness of steels in the quenched and
normalized conditions as a function of carbon content.

Mechanical Properties of Steel as a Function of
Tempering Temperature
Figure 4.25 Mechanical
properties of oil-quenched
4340 steel as
a function of tempering
temperature.

Ch4 alloys heat threatment Erdi Karaçal Mechanical Engineer University of Gaziantep

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