PowerPoint Presentation

•

Part I:

Thermal Processing of Metal

Alloys

–

Heat Treatment

–

Precipitation Hardening

•

Part II:

Metal Alloys and Fabrication of

Metals

Outline of Chapter 11

•

Ferrous Alloys: Alloys containing more than 50wt.%Fe

–

Classification of Steels

–

Designation of Steels

•

Nonferrous Alloys: Alloys containing less than 50wt.

%Fe

–

Aluminum

–

Copper

–

Magnesium

–

Titanium

–

Refractory metals

–

Superalloys

–

Noble metals

Metal Alloys

Ferrous

Nonferrous

Steels

Cast Irons

Low Alloy

Low-carbon Medium-

carbon

High-

carbon

High Alloy

Plai

High

strengt

h, low

alloy

Heat

treatab

Plai

Tool

Plai

Stainles
s

Gra

iron

Whit

iron

Malleabl

e iron

Ductil

e iron

Classification of Ferrous

Alloys

–

Steels

(0.008 ~ 2.14wt% C)

In most steels the microstructure consists of both  and

C phases.

Carbon concentrations in commercial steels rarely

exceed 1.0 wt%.

–

Cast irons

(2.14 ~ 6.70wt% C)

Commercial cast irons normally contain less than 4.5wt
% C

Classification of Ferrous

Alloys

•

Based on carbon

content

–

Pure iron

0.008wt% C)
From the phase

diagram, it is

composed almost

exclusively of the

ferrite phase at room

temperature.

•

The carbon content is normally less than
1.0 wt%.

•

Plain carbon steels:

containing only

residual concentrations of impurities other
than carbon and a little manganese

About 90% of all steel made is carbon steel.

•

Alloy steels:

more alloying elements are

intentionally added in specific
concentrations.

•

Stainless steels

Ferrous Alloys — Steels

•

Low-carbon steels

–

Less than 0.25 wt%C

•

Medium-carbon steels

–

0.25 ~ 0.60 wt%C

•

High-carbon steels

–

0.60 ~ 1.4 wt%C

Classification of Steels

According to Their Carbon Contents

•

four-digit number:

–

the first two digits indicate the alloy
content;

–

the last two, the carbon concentration

•

For plain carbon steels, the first two digits
are 1 and 0;

alloy steels are designated by

other initial two-digit combinations (e.g., 13,
41, 43)

•

The third and fourth digits represent the
weight percent carbon multiplied by 100

For example, a 1040 steel is a plain carbon
steel containing 0.40 wt% C.

The Designation of Steels

•

four-digit number

: the first two digits

indicate the alloy content; the last two,
the carbon concentration

Identifies
major
alloying
element(s)

Percentag
e of
carbon

The Designation of Steels

•

AISI:

merican

ron and

teel

nstitute

•

SAE:

ociety of

utomotive

ngineers

•

UNS:

niform

umbering

ystem

Table 11.2a AISI/SAE and UNS Designation

Systems

Steel Alloys

Steel Numerical Name

Key Alloys

10XX, 11 XX

Carbon only

13XX

Manganese

23XX, 25 XX

Nickel

31XX, 33XX, 303XX

Nickel-Chromium

40XX

41XX

Cr-Mo

43XX & 47XX

Ni-Cr-Mo

44XX

Mn-Mo

48XX

Ni-Mo

50XX, 51XX, 501XX, 521XX,

514XX, 515XX

61XX

Cr-V

81XX, 86XX, 87XX, 88XX

Ni-Cr-Mo

92XX

Si-Mn

93XX, 98XX

Ni-Cr-Mo

94XX

Ni-Cr-Mo-Mn

XXBXX

Boron

XXLXX

Lead

94XX Ni-

•

Less than 0.25 wt%C

•

Unresponsive to heat treatments intended to
form martensite;

strengthening is

accomplished by cold work

•

Microstructures:

ferrite and pearlite

•

Relatively soft and weak, but having
outstanding ductility and toughness

•

Typically, 

= 275 MPa, 

= 415~550 MPa,

and ductility = 25%EL

•

Machinable, weldable, and, of all steels, are
the least expensive to produce

•

Applications:

automobile body components,

structural shapes, and sheets used in
pipelines, buildings, bridges, etc.

Low-Carbon Steels

•

0.25 ~ 0.60 wt%C

•

May be

heat treated

by austenitizing,

quenching, and then tempering to improve
their mechanical properties

•

Stronger than low-carbon steels and weaker
than high-carbon steels

Classified as high-carbon steels

Typical Tensile Properties for Oil-Quenched and Tempered Plain

Carbon

Medium-Carbon Steels

•

0.60 ~ 1.4 wt%C

•

Used in a

hardened and tempered

condition

•

Hardest, strongest, and yet least ductile;
especially wear resistant and capable of
holding a sharp cutting edge

•

Containing Cr, V, W, and Mo; these alloying
elements combine with carbon to form very
hard and wear-resistant carbide compounds
(e.g., Cr

, V

, and WC)

•

Applications:

cutting tools and dies for

forming and shaping materials, knives,
razors, hacksaw blades, springs, and high-
strength wire

High-Carbon Steels

Carbon Steel

Alloy Steel

Lower cost

Higher strength

Greater availability

Better wear

Toughness

Special high temperature

behavior

Better corrosion

resistance

Special electrical

properties

94XX Ni-

•

Alloy steel is more expensive than carbon steel; it should
be used only when a special property is needed.

Comparison of the Advantages

Offered by Carbon Steels and Alloy

Steels

•

Stainless steels are selected for their
excellent resistance to corrosion.

•

Stainless steels are divided into three
classes: martensitic, ferritic, or austenitic

•

The predominant alloying element is

chromium

; a concentration of at least 11 wt%

Cr is required

–

It permits a thin, protective surface layer
of chromium oxide to form when the steel
is exposed to oxygen.

–

The chromium is what makes stainless
steel stainless!

Stainless Steels

•

Aluminum and aluminum alloys are the most widely
used nonferrous metals.

•

Aluminum alloys:

strengthened by cold working and

alloying (Cu, Mg, Si, Mn, and Zn)

–

Nonheat-treatable: single phase, solid solution strengthening

–

Heat treatable: precipitation hardening (MgZn

)

•

Properties

–

Low density (2.7 g/cm

), as compared to 7.9 g/cm

for steel

–

High electrical and thermal conductivity

–

Resistant to corrosion in some common environments

–

Easily formed and thin Al foil sheet may be rolled

–

Al has an FCC crystal structure; its ductility is retained even
at very low temperatures

–

Limitation: low melting temperature (660°C)

Aluminum and Its Alloys

Aluminum Alloy Desginations

Material

Number

Al (99.00% minimum and

greater)

1XXX

Al alloys are grouped by

major alloying elements

Copper

2XXX

Manganese

3XXX

Silicon

4XXX

Magnesium

5XXX

Magnesium and Silicon

6XXX

94XX Ni-

Aluminum’s use in vehicles is rapidly increasing

due to

the need for fuel efficient, environmentally friendly

vehicles

•

Al alloys can provide a
weight savings of up to
55% compared to an
equivalent steel
structure

•

It can match or exceed
crashworthiness
standards of similarly
sized steel structures

•

The Ford Motor
Company now has
aluminum-intensive test
vehicles on the road,
providing 46% weight
savings in the structure,
with no loss in crash
protection.

Aluminum plate is used in the

manufacture of aircraft and for fuel

tanks in spacecraft

•

Aircraft manufacturers use high-strength alloys

(principally alloy 7075)

to strengthen aluminum

aircraft structures.

•

Alloy 7075 has

zinc and copper

added for ultimate

strength, but because of the copper it is very
difficult to weld.

•

7075 has the best machinability and results in the
finest finish.

Lightweight aluminum is a

good material for conductor

cables

•

Electrical transmission
lines are the largest
users of aluminum
rod/bar/wire products.

•

In fact, this is the one
market in which
aluminum has virtually
no competition from
other metals.

•

Aluminum is simply
the most economical
way to deliver
electrical power.

•

Unalloyed copper:

–

So soft and ductile that it is difficult to machine

–

Unlimited capacity to be cold worked

–

Highly resistant to corrosion in diverse
environments

•

Copper alloys:

strengthened by cold working

and/or solid-solution alloying.

•

Bronze and brass

are two common copper alloys.

•

Applications:

costume jewelry, cartridge casings,

automotive radiators, musical instruments,
electronic packaging, and coins

Copper and Its Alloys

•

Bronze

is an alloy of

copper and tin

–

The first metal

purposely alloyed

by the smith

–

May contain up to

25% tin

•

Brass

is an alloy of

copper

and zinc

–

Contain 5-30% zinc

–

The zinc increases the strength of the

copper.

–

Ductility and formability are also

increased.

Bronz

Mask

Bronze and Brass

•

Relatively new engineering materials that
possess an extraordinary combination of
properties

–

Low density (4.5 g/cm

)

–

High melting temperature (1668°C), high elastic
modulus (107 GPa)

–

Extremely strong: 1400 MPa tensile strength at
room temperature, highly ductile and easily
forged and machined

–

Limitations



Chemical reactivity with other materials and
oxidation problem at elevated temperatures



Cost

•

Applications:

airplane structures, space vehicles,

and in the petroleum and chemical industries

Titanium and Its Alloys

Alloy

Type

Common

Name

(UNS

Numbser)

Composition

(wt%)

Condition

Tensile

Strength

(MPa)

Yield

Strength

(MPa)

Ductility

(%EL)

  Ti-6Al-4V

(R564000)

6Al, 4V,

balance Ti Annealed

947

877

94XX Ni-

•

Typical Applications:

High-strength prosthetic

implants, chemical-processing equipment,
airframe structural components

An Example of Titanium Alloy (Table

11.9)

•

Superlative combinations of

properties

–

Nickel-based alloys

–

Other alloying elements: Nb, Mo,

W, Ta, Cr, and Ti
IN792: Ni-12Cr-10Co-2Mo-4W-

3.5Al-4Ti-4Ta- 0.01B-0.09Zr-

0.1C-0.5Hf

•

Applications:

aircraft turbine

components

–

Turbine blades and discs, high

creep and oxidation resistance

at elevated temperatures

(1000°C)

–

Density

is an important

consideration because

centrifugal stresses are

diminished in rotating parts

when the density is reduced

Ni-Base Superalloys

•

Modern aeroengine design constantly seeks to increase
the engine operating temperature to improve overall
efficiency.

•

Materials for turbine blades are required to perform at
higher and higher temperatures.

•

Use of advanced nickel-based alloys, together with
innovative cooling design

Ni-Based Superalloys Used for Turbine

Blades

Polycrystalli
ne turbine
blade

Improvement in Creep Resistance of

Turbine Blades through Casting

Technologies

Columnar grain
structure produced
by a directional
solidification
technique

Creep resistance
is further
enhanced with
single-crystal
blades.

Thermal Barrier Coatings (TBCs)

•

Demands for higher efficiency and lower emission require

higher operating temperatures

in aeroengines

•

The typical melting points of the superalloys used for the
turbine components range from 1230-1315°C

•

The temp. in a combustion gas environment is > 1370°C

Thermally Grown

Oxide (TGO)

(1-10m)

Ceramic Top Coat (100-400m)

-Stabilized ZrO

)

Bond Coat (~100m)

Substrate

Cooling Air

Hot Gases

Thermally Grown

Oxide (TGO)

(1-10m)

Ceramic Top Coat (100-400m)

-Stabilized ZrO

)

Bond Coat (~100m)

Substrate

Cooling Air

Hot Gases

The key to meeting
the higher
temperature
requirements lies in
providing an
insulating ceramic

thermal barrier
coating (TBC)

lower the surface
temperature of
superalloy
underneath

•

Melting temperatures range between 2468°C for
niobium (Nb) and 3410°C for tungsten (W)

–

Interatomic bonding is extremely strong.

–

Large elastic moduli and high strength and
hardness at ambient and elevated
temperatures

•

Applications:

–

Ta and Mo are alloyed with stainless steel to
improve its corrosion resistance.

–

Molybdenum alloys: extrusion dies and
structural parts in space vehicles

–

Tungsten alloys: filaments, X-ray tubes,
welding electrodes

Refractory Metals

•

To select a steel alloy for a gearbox output shaft,

a 1-in diameter cylindrical shaft.

–

Surface hardness  38 HRC

–

Ductility >12%EL

•

Specify an alloy and treatment that meet these

criteria

•

Cost is always an important design consideration.

–

This would eliminate relatively expensive

steels, such as stainless steels.

–

Examine

plain-carbon and low-alloy steels

, and

what treatments are available to alter their

mechanical properties.

•

Two approaches

–

Cold work

–

Heat treatment  martensite

Design Example 11.1

Fig. 7.17

For 1040 steel, brass, and copper, (b) the increase

in tensile strength, and (c) the decrease in ductility (%EL)
with percent cold work

The Correlation between Cold Work and

Tensile Strength and Ductility for Various

Alloys

Design Example 11.1

•

1-in diameter cylindrical shaft.

•

Having a surface hardness of at least 38 HRC
and a minimum ductility of 12%EL

•

Cold work

–

From Fig. 6.19, a hardness of 38 HRC
corresponds to a tensile strength of 1200
MPa

–

From Fig. 7.17(b), at 50% cold work, a
tensile strength is only ~900 MPa and
the ductility is ~10%EL.

–

Both of these properties fall short of
those specified in the design.

•

Cold working other plain-carbon or low-alloy steels

would probably not achieve the required minimum

values.

•

To perform a series of heat treatments in which the

steel is austenitized, quenched (to form martensite),

and finally tempered.

–

Examine the mechanical properties of various

plain-carbon and low-alloy steels that have been

treated in this manner.

–

The surface hardness of the quenched material will

depend on both alloy content and shaft diameter.

Design Example 11.1

Table 11.10

Surface hardnesses for oil-quenched cylinders of

1060 steel having various diameters.

Design Example 11.1

Table 11.11

Rockwell hardness (surface) and percent

elongation values for 1-in. diameter cylinders of six steel
alloys, in the as-quenched condition and for various tempering
heat treatments.

•

The only alloy-heat treatment combinations that meet the

stipulated criteria are 4150/oil-540°C temper, 4340/oil-540°C

temper, and 6150/oil-540°C temper.

•

The costs of these three materials are probably comparable.

•

The 6150 alloy has the highest ductility (by a narrow

margin), which would give it a slight edge in the selection

process.

Steel Alloys

Steel Numerical Name

Key Alloys

10XX, 11 XX

Carbon only

13XX

Manganese

23XX, 25 XX

Nickel

31XX, 33XX, 303XX

Nickel-Chromium

40XX

41XX

Cr-Mo

43XX

& 47XX

Ni-Cr-Mo

44XX

Mn-Mo

48XX

Ni-Mo

50XX, 51XX, 501XX,

521XX, 514XX, 515XX

61XX

Cr-V

81XX, 86XX, 87XX, 88XX

Ni-Cr-Mo

92XX

Si-Mn

93XX, 98XX

Ni-Cr-Mo

94XX

Ni-Cr-Mo-Mn

94XX Ni-

Steel Alloys

Alloying

Element

4150

4340

6150

0.48-0.53

0.38-0.43

0.48-0.53

0.75-1.00

0.60-0.80

0.70-0.90

0.035

0.040

0.15-0.35

1.65-2.00

0.80-1.10

0.70-0.90

0.80-1.10

0.15-0.25

0.20-0.30

0.15 min

94X X Ni-

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