CHAPTER 6

6.1 Types of Metals

6.1.1 Ferrous Alloys
6.1.2 Nonferrous Alloys
6.2 Fabrication of Metals
6.2.1 Forming Operations
6.2.2 Casting
6.2.3 Miscellaneous Techniques
 Metal Alloys

Ferrous Nonferrous

Steel Cast Iron

High Alloy Grey Iron

Tool Ductile(Nodular) Iron

Stainless White Iron

Low Alloy Malleable Iron

Low Carbon

Plain

High strength, low alloy

Medium Carbon

Plain

Heat treatable

High Carbon

Classification scheme for the various Plain

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ferrous alloys
Tool
 6.1.1 FERROUS ALLOYS
Those of which iron is the prime constituent.
They are especially important as engineering construction
materials.
Their widespread use is accounted for by three factors :
1. iron-containing compounds exist in abundant
quantities within the earths crust;
2. may be produced using relatively economical
extraction, refining, alloying and fabrication techniques
3. extremely versatile have wide range of mechanical and
physical properties.

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 STEELS
Steels are iron-carbon alloys.
Contains 0.01% - 2.00% wt carbon (C) + other alloying
elements.
The mechanical properties are sensitive to the content of
carbon.
Most common steels are classified according to carbon
concentration low- , medium- and high- carbon types.
Subclasses also exist according to the concentration of
other alloying elements plain carbon steels & alloy steels
i) Plain carbon steels contains carbon + a little
manganese.
ii) Alloy steels carbon + more alloying elements (added
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in specific concentrations).
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 Low-Carbon Steels

Contain < 0.25 wt % C + Mn

Plain low-carbon steels
a) Properties :
i) relatively soft and weak
ii) outstanding ductility
iii) outstanding toughness
iv) machinable and weldable
v) least expensive.
b) Applications : automobile body components, structural
shape (beam) and sheets (bridge, pipelines and
buildings).
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 High-strength, low alloy (HSLA)
a) Contains C + Mn + other alloying elements (copper,
nickel, vanadium & molybdenum).
b) Properties :
i) higher strength than plain low-carbon steels
ii) ductile
iii) formable
iv) machinable
v) more resistant to corrosion than plain carbon
steels
c) Applications : bridges, towers, pressure vessels etc.

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 Medium-Carbon Steels

Carbon contain : 0.25 wt% - 0.60 wt%

Properties :
i) high strength
ii) low ductility compared to low-carbon steels
iii) low toughness compared to low-carbon steels
Applications railway wheel & track, gears, crankshafts and
other high-strength structural components.

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 High-Carbon Steels

Carbon contain : 0.60 wt% - 1.4 wt%

Other alloying elements : chromium, vanadium, tungsten and
molybdenum.
combine with carbon form very hard and wear
resistance carbide compounds (e.g., Cr23C6, WC and V4C3).
Properties :
i) high hardness
ii) high strength
iii) good wear resistance
iv) low ductility
Applications : used as cutting tools & dies for forming and
shaping materials. (knives, razors, springs etc.).
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 Stainless Steels

A class of high alloy steels.

Major alloying elements : 11 wt% - 30 wt% chromium (Cr)
Other alloying elements : nickel & molybdenum.
Properties :
i) highly resistant to corrosion (rusting) in a variety of
environments.
ii) moderate ductility & formability
Applications : springs, knives, automotive exhaust
components, pressure vessels etc.

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 CAST IRONS
Carbon contains : > 2.14 wt% + other alloying elements.
The carbon exists as graphite.
The types of cast iron are normally name based on its
fracture surface.

CAST IRON

COMPACTED
NODULAR GRAPHITE
GREY WHITE MALLEABLE
(DUCTILE) (Graphite
Type IV)

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 Gray Nodule

White Malleable

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 Table 6.1 : Approximate Compositions, Mechanical Properties
and Typical Applications

Type Composition of major elements Mechanical Applications

Properties
C (%) Si (%)
White 1.8 3.6 0.5 1.9 -hard -rollers in rolling mills
-brittle -as intermediate
(unmachinable) product for malleable
-wear resistance iron
Malleable 2.2 2.9 0.9 1.9 -high strength -connecting rods
-appreciable -pipe fitting
ductility/malleability -flanges etc.

Gray 2.5 4.0 1.0 3.0 -Weak & brittle in -Piston

tension -Cylinders
-high resistance to -Diesel engine casting
wear -Clutch plates etc.
-least expensive
Ductile 3.0 4.0 1.8 2.8 -more ductile -valves
-much stronger -high-strength gears
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SCIENCE properties -rollers 12

approaching steel -crankshafts etc.

 There are some distinct limitations in the usage of ferrous
metals, chiefly :
1. a relatively high density
2. a comparatively low electrical conductivity
3. an inherent susceptibility to corrosion in some common
environments.

Thus, for many applications it is advantageous or even

necessary to utilize other alloys having more suitable property
combinations (nonferrous alloy).
a) Cast alloys so brittle that forming or shaping by
appreciable deformation is not possible.
b) Wrought alloys those that are amendable to mechanical
deformation.

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 6.1.2 NON-FERROUS ALLOYS
Metal Alloys

Ferrous Nonferrous

Copper & Its Alloys

Aluminium & Its Alloys

Magnesium & Its Alloys

Titanium & Its Alloys

Refractory Metals, Noble

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Metals & Super Alloys14
 The periodic table of the elements.

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 Copper And Its Alloys

Properties of unalloyed copper

soft, ductile, difficult to machine,
highly resistance to corrosion.
The mechanical and corrosion
resistance properties improved
by alloying.
Most copper alloys :
a) BRASS Cu & Zn (as predominant alloying element)
amount of Zn may be up to 35%.
applications : costume jewelry, automotive
radiators, musical instruments, electronic
packaging, coins etc.
b) BRONZE Cu + Sn (+Al, Si, Ni)
stronger than brass, high corrosion
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bearing, gears, springs, clutch disks etc.

 Aluminium And Its Alloys

Properties :
i) high electrical & thermal conductivities
ii) good corrosion resistance
iii) high ductility
iv) low density (refer Periodic Table)
Limitation low melting temperature (660C); restrict the
maximum temperature at which it can be used.
Alloying enhanced the mechanical strength of pure
aluminium.
elements : Cu, Mg, Si, Mn and Zn
Applications : food/chemical storage, cooking utensils,
automotive parts, aircraft structures etc.
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 Magnesium And Its Alloys

Properties :
i) lowest density compared to all
structural metals (refer Periodic Table)
ii) low melting temperature (651C)
iii) poor corrosion resistance
Alloying enhanced the mechanical properties (elements : Al,
Zn and Mn)
Applications :
hand-held devices ( chain saws, power tools etc)
automobile ( steering wheels, seat frames etc)
audio-video-computer-communications equipment
(laptop computers, TV sets, cellular telephones etc)
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 Magnesium metal burns with a very bright light.

DO NOT TRY THIS AT HOME...!!!

The picture shows the results of

setting off a mixture of magnesium
The picture below shows the color metal with solid silver nitrate with
arising from adding magnesium water
powder to a burning mixture of
potassium
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 Titanium And Its Alloys

Properties :
i) low density (refer Periodic Table)
ii) high melting point (1668C)
iii) high strength
iv) highly ductile easily machined
v) high corrosion resistance
Alloying elements : Al, Zn, V, Mo, Sn and Fe
Applications : airplane structures, space vehicles, surgical
implants, used in the petroleum & chemical industries.

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 Titanium:
MEDICAL APPLICATION
http://www.podassociates.net/podassociates_web_032.htm

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6.2 FABRICATION OF METALS
Metal Fabrication
Techniques

Forming Operations Casting Miscellaneous

Forging Sand Powder Metallurgy

Rolling Die Welding

Extrusion Investment

Drawing Continuous

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Classification scheme of metal fabrication techniques
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 The method chosen for the fabrication of metals
depend on several factors; most important are
i) the properties of the metal
ii) the size and shape of the finished piece
iii) cost

FORMING OPERATIONS
Operations in which the shape of a metal piece
is changed by plastic deformation.
The deformation must be induced by an external
force or stress.

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 2 types of deformations:
Deformation at T > Trecrystallisation =
Hot work
Deformation at T < Trecrstallisation/Tambient
Cold work

Hot working process include:

Rolling
Forging
Extrusion
Drawing
Spinning
Pipe Welding
Piercing
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FORGING

Forging is the plastic working of metal by means

of localised compressive forces exerted by
manual or power hammers, presses, or special
forging machines.

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 The metal may be
1) Drawn out, increasing its length and decreasing its cross
section
2) Upset, increasing the cross section and decreasing the
length
3) Squeezed in closed impression dies to produce
multidirectional flow

The state of stress in the work is primarily uniaxial or

multiaxial compression.

The common forging processes are:

1. Open-die hammer
2. Impression-die drop forging
3. Press forging
4. Upset forging
5. Roll forging
6. Swaging

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 Open-die hammer forging

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 Rolling

Rolling consists of passing metal between two rolls that

revolve in opposite directions, the space between the
rolls being somewhat less than the thickness of the
entering metal

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 2 types of rolling process
Metal heated at T > Trecrystallisation =
Hot rolling
Roller T < Trecrstallisation/Tambient =
Cold rolling

Important process : Soaking

Purpose to ensure entire metal is heated uniformly
throughout proper temperature

*Non uniform heating (hotter exterior flowing) results

cracking and tearing*
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 Extrusion

In the extrusion process metal is compressively

forced to flow through a suitably shaped die to
form a product with reduced cross section

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 2 types :
Hot Extrusion

Hot extrusion requires the metal to be heated

before it passes through the die

The heat of the metal should be over half of

the melting temperature of the metal

For metals and alloys that do not have

sufficient ductility at room temperature, or in
order to reduce the forces required
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 Cold Extrusion

Cold extrusions is done at room

temperature/ near room temperature

Advantages of this over hot extrusion are:

1) Lack of oxidation
2) Good control of dimensional tolerances
3) Fast extrusion speeds can be used

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 Drawing

Drawing is a process for forming sheet metal

between an edge-opposing punch and a die (draw
ring) to produce a cup, cone, box, or shell-like part.
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 Process:
1) The end of a round rod is squeezed to reduce
the cross-sectional area so that it can be fed into
the die
2) Material is then pulled through the die at high
speeds.
Most wire drawing involves several dies
in tandem to reduce the diameter to the
desired dimension.
Die materials are usually alloy steels,
carbides, and diamond.
Diamond dies are used for drawing fine
wires.
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CASTING
A fabrication process whereby a totally molten metal is
poured into a mold cavity having the desired shape
Upon solidification, the metal assumes the shape of the
mold but experiences some shrinkage.
Casting techniques are employed when:
1. the finished shape is so large or complicated that any
other method would be impractical
2. particular alloy is so low in ductility that forming would
be difficult
3. casting is the most economical fabrication process
compare to the others.
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 Casting processes are divided according to
the specific type of molding method used
in casting, as follows:
1. Sand
2. Centrifugal
3. Permanent
4. Die
5. Plaster-mold
6. Investment

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 Sand Casting Process
Sand casting consists basically of pouring
molten metal into appropriate cavities
formed in a sand mold

The sand may be natural, synthetic, or an

artificially blended material.
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 Continuous Casting Process

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 Molten metal is poured continuously into a
water-cooled mold from which the solidified
metal is continuously withdrawn in plate or rod
form

The slab or bar is typically cut to a length with a

flying saw or torch

Rate of withdrawal of metal from mold must be

such that sufficient solidification occurs to
prevent melt-through
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 Investment
Casting
Process

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 Casting processes in which the pattern is used
only once are variously referred to as lostwax or
precision-casting processes.
Pattern making
1) Wax pattern is produced by injecting wax into pattern
2) Several patterns are attached to a sprue to form a pattern
tree

Investment process
1) Pattern tree is coated with a refractory material slurry
2) Full mold is made by another coating with sufficient
refractory material stucco (Stucco or render is a material
made of an aggregate, a binder, and water) to make it
more rigid

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Dewax
Mold is heated to melt the wax and drip out of cavity (in an
autoclave (a device to sterilise equipment and supplies by
subjecting them to high pressure steam at 121 C or more)

Preheating
Mold is preheated to higher temperature to ease liquid metal
flow

Pouring
1) Molten metal is poured
2) Metal solidifies

Removal
1) Mold is broken away from sprue
2) Parts separated from sprue

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