CHAPTER 2

Metals
2.1
Classification of Metals Alloy; Ferrous
and Nonferrous Alloy
2.1 Classification of Metals Alloy;
Ferrous and Nonferrous Alloy
 What is METAL?
• Metals are solid at room temperature,
except mercury (liquid)
• Metals have very high melting point
• Metals are shiny when they cut
• Metals are good conductor of heat and
electricity
• Metals are usually strong and malleable so
they can be hammered into
shape
 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

ferrous alloys
Tool
2.1.1 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 earth’s 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.
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
in specific concentrations).
 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).
 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.
 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.
 High-Carbon Steels
 Carbon contain : 0.60 wt% - 1.4 wt%
 Other alloying elements : chromium, vanadium, tungsten and
molybdenum.
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.).
 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.
 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

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

White Malleable

Cast Iron Microstructure

Table 2.1 : 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
-mech. properties -rollers
approaching steel -crankshafts etc.
 There are some distinct limitations in the usage of ferrous
metals:
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.
APPLICATIONS OF FERROUS METALS

Paper clip Toaster

Fork-lift truck
2.1.2 NON-FERROUS ALLOYS
Metal Alloys

Ferrous Nonferrous

Copper & Its Alloys

Aluminium & Its Alloys

Magnesium & Its Alloys

Titanium & Its Alloys

Refractory Metals, Noble

Metals & Super Alloys
 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
resistance
– 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
 Limitation – low melting temperature (660C); 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.
 Magnesium And Its Alloys
 Properties :
i) lowest density compared to all
structural metals
ii) low melting temperature (651C)
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)
 Titanium And Its Alloys

 Properties :
i) low density
ii) high melting point (1668C)
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.
Titanium:
MEDICAL APPLICATION
 APPLICATIONS OF NON-FERROUS METALS

Aluminium can

Awning

Satellite

Lead sculpture
2.1.3 FABRICATION OF METALS
Metal Fabrication
Techniques

Forming Operations Casting Miscellaneous

Forging Sand Powder Metallurgy

Rolling Die Welding

Extrusion Investment

Drawing Continuous

Classification scheme of metal fabrication techniques

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

a) 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.
Metal deformation during (a) rolling, (b) forging, (c) extrusion
and (d) drawing
b) 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.
Four typical casting
processes:
(a) and (b) Green
sand molding where
clay-bonded sand is
packed around a
pattern. Sand cores
can produce internal
cavities in the casting.
(c) The permanent
mold process where
metal is poured into an
iron or steel mold.
(d) Die casting where
metal is injected at
high pressure into a
steel die.
(e) Investment casting
where a wax pattern is
surrounded by a
ceramic; after the wax
is melted and drained,
metal is poured into
the mold. Casting
Methods
c) MISCELLANEOUS
Powder Metallurgy
Welding

• In welding, two or more metal parts are joined to form a

single piece when one-part fabrication is expensive or
inconvenient.
• Both similar and dissimilar metals may be welded.
• The joining bond is metallurgical (involving some diffusion)
rather than just mechanical, as with riveting and bolting.
• A variety of welding methods exist, including arc and gas
welding, as well as brazing and soldering.