module last prelim

Question 1

Metal alloys, by virtue of composition, are often grouped into two classes they are

Answer 1

classes—ferrous

and non-ferrous.

Question 2

those in which iron is the principal constituent include

steels and cast irons.

Answer 2

Ferrous alloys

Question 3

all alloys that are not iron based.

Answer 3

The nonferrous

Question 4

Another classification is made based on their formability. If materials are hard to
form, components with these materials are fabricated by casting, thus they are called

Answer 4

cast alloys.

Question 5

If material can be deformed, they are known as

Answer 5

wrought alloys.

Question 6

Materials are usually strengthened by two methods they are

Answer 6

cold work and heat treatment.

Question 7

involves either precipitation hardening or martensitic transformation,

Answer 7

Strengthening by

heat treatment

Question 8

When a material cannot be

strengthened by heat treatment, it is referred as

Answer 8

non-heat-treatable alloys.

Question 9

those in which iron is the prime constituent—are produced in

larger quantities than any other metal type.

Answer 9

Ferrous alloys

Question 10

exist in abundant quantities within the Earth’s crust;

Answer 10

iron containing compounds

Question 11

may be produced using relatively economical extraction,

refining, alloying, and fabrication techniques;

Answer 11

metallic iron and steel alloys

Question 12

may be tailored to have a wide

range of mechanical and physical properties

Answer 12

ferrous alloys are extremely versatile,

Question 13

The principal disadvantage of many ferrous alloys is their susceptibility

Answer 13

corrosion.

Question 14

are alloys of iron and carbon plus other alloying elements. carbon
present in atomic form, and occupies interstitial sites of Fe microstructure.

Answer 14

Steels

Question 15

Alloying

additions are necessary for many reasons including:

Answer 15

improving properties, improving

corrosion resistance, etc.

Question 16

Mechanical properties of steels are very sensitive to carbon content. Hence, it is
practical to classify steels based on their carbon content. Thus steels are basically three
kinds:

Answer 16

low-carbon steels medium carbon steels high-carbon steels

Question 17

The other parameter available for classification

of steels is amount of alloying additions, and based on this steels are two kinds:

Answer 17

(plain)

carbon steels and alloy-steels.

Question 18

These are arguably produced in the greatest quantities than other alloys. These are arguably produced in the greatest quantities than other alloys. Their microstructure
consists of ferrite and pearlite, and these alloys are thus relatively soft, ductile combined
with high toughness. Hence these materials are easily machinable and weldable. Typical
applications of these alloys include: structural shapes, tin cans, automobile body
components, buildings, etc.

Answer 18

Low Carbon Steels

Question 19

low carbon steels these alloys are strengthened by

Answer 19

cold work.

Question 20

These are stronger than low carbon steels. However these are of less ductile than
low carbon steels. These alloys can be heat treated to improve their strength. Usual heat
treatment cycle consists of austenitizing, quenching, and tempering at suitable conditions
to acquire required hardness. They are often used in tempered condition. As hardenability
of these alloys is low, only thin sections can be heat treated using very high quench rates.
Ni, Cr and Mo alloying additions improve their hardenability. Typical applications include:
railway tracks & wheels, gears, other machine parts which may require good combination
of strength and toughness.

Answer 20

Medium Carbon Steels

Question 21

These are strongest and hardest of carbon steels, and of course their ductility is
very limited. These are heat treatable, and mostly used in hardened and tempered
conditions. They possess very high wear resistance, and capable of holding sharp edges.
Thus these are used for tool application such as knives, razors, hacksaw blades, etc. With
addition of alloying element like Cr, V, Mo, W which forms hard carbides by reacting with
carbon present, wear resistance of high carbon steels can be improved considerably.

Answer 21

High Carbon Steels

Question 22

A special group of ferrous alloys with noticeable amount of alloying additions Common alloying elements are: Cu, V,
Ni, W, Cr, Mo, etc. These alloys can be strengthened by heat treatment, and yet the same
time they are ductile, formable. Typical applications of these steels include: support
columns, bridges, pressure vessels.

Answer 22

HSLA (High-Strength Low-Alloy) Steels

Question 23

The name comes from their high resistance to corrosion i.e. they are rust-less Steels are made highly corrosion resistant by addition of special alloying
elements, especially a minimum of 12% Cr along with Ni and Mo. Stainless steels are
mainly three kinds: ferritic & hardenable Cr steels, austenitic and precipitation hardenable
(martensitic, semi-austenitic) steels. This classification is based on prominent constituent
of the microstructure. Typical applications include cutlery, razor blades, surgical knives,
etc.Steels are made highly corrosion resistant by addition of special alloying
elements, especially a minimum of 12% Cr along with Ni and Mo. Stainless steels are
mainly three kinds: ferritic & hardenable Cr steels, austenitic and precipitation hardenable
(martensitic, semi-austenitic) steels. This classification is based on prominent constituent
of the microstructure. Typical applications include cutlery, razor blades, surgical knives,
etc.

Answer 23

Stainless Steels

Question 24

are principally Fe-Cr-C alloys with 12-14% Cr. They also

contain small additions of Mo, V, Nb, and Ni.

Answer 24

Ferritic Stainless Steels

Question 25

usually contain 18% Cr and 8% Ni in addition to other
minor alloying elements. Ni stabilizes the austenitic phase assisted by C and N. Other
alloying additions include Ti, Nb, Mo (prevent weld decay), Mn and Cu (helps in
stabilizing austenite).

Answer 25

Austenitic Stainless Steels

Question 26

is made to be above the room
temperature. These alloys are heat treatable. Major alloying elements are: Cr, Mn and
Mo.

Answer 26

Martensitic Steels

Question 27

steels are hardened and strengthened by cold work because

they are not heat treatable.

Answer 27

Ferritic and austenitic

Question 28

are heat treatable.

Answer 28

martensitic steels

Question 29

are most corrosion resistant, and they are produced in large quantities. are non-magnetic as against ferritic and martensitic steels, which are
magnetic.

Answer 29

Austenitic steels

Question 30

Though ferrous alloys with more than 2.14 wt.% C. Hard and brittle constituent presented in these alloys, cementite is a meta-stable
phase, and can readily decompose to form α-ferrite and graphite. In this way
disadvantages of brittle phase can easily be overcome.

Answer 30

CAST IRONS

Question 31

is the most used fabrication technique for these

alloys.

Answer 31

casting

Question 32

Tendency of cast irons to form

graphite is usually controlled by their

Answer 32

composition and cooling rate.

Question 33

Based on the form of

carbon present, cast irons are categorized as

Answer 33

gray, white, nodular and malleable cast

irons.

Question 34

These alloys consists carbon in form graphite flakes, which are surrounded by
either ferrite or pearlite. Because of presence of graphite, fractured surface of these alloys
look grayish, and so is the name for them. Alloying addition of Si (1-3wt.%) is responsible
for decomposition of cementite, and also high fluidity. Thus castings of intricate shapes
can be easily made. Due to graphite flakes, gray cast irons are weak and brittle. However
they possess good damping properties, and thus typical applications include: base
structures, bed for heavy machines, etc. they also show high resistance to wear.

Answer 34

Gray Cast Iron

Question 35

When Si content is low (< 1%) in combination with faster cooling rates, there is no
time left for cementite to get decomposed, thus most of the brittle cementite retains.
Because of presence of cementite, fractured surface appear white, hence the name. They
are very brittle and extremely difficult to machine. Hence their use is limited to wear
resistant applications such as rollers in rolling mills. Usually white cast iron is heat treated
to produce malleable iron.

Answer 35

White Cast Iron

Question 36

Alloying additions are of prime importance in producing these materials. Small
additions of Mg / Ce to the gray cast iron melt before casting can result in graphite to form _______. Matrix surrounding these particles can be either ferrite
or pearlite depending on the heat treatment. These are stronger and ductile than gray
cast irons. Typical applications include: pump bodies, crank shafts, automotive
components, etc.

Answer 36

Nodular (Or Ductile) Cast Iron

Question 37

These formed after heat treating white cast iron. Heat treatments involve heating
the material up to 800-900 deg. C, and keep it for long hours, before cooling it to room
temperature. High temperature incubation causes cementite to decompose and form
ferrite and graphite. Thus these materials are stronger with appreciable amount of ductility. Typical applications include: railroad, connecting rods, marine and other heavy-
duty services.

Answer 37

Malleable Cast Iron

Question 38

are consumed in exceedingly large quantities
because they have such a wide range of mechanical properties, may be fabricated with
relative ease, and are economical to produce.

Answer 38

Steel and other ferrous alloys

Question 39

have specific advantages over ferrous materials. They can be fabricated with ease, high relatively low density, and high electrical and thermal conductivities. However different materials have distinct characteristics, and are used for
specific purposes.

Answer 39

Non-ferrous materials

Question 40

These are characterized by low density, high thermal & electrical conductivities,
and good corrosion resistant characteristics. As Al has FCC crystal structure, these alloys
are ductile even at low temperatures and can be formed easily.

Answer 40

Aluminum Alloys

Question 41

One special feature of most of these alloys is their
corrosion resistant in diverse atmospheres. Most of these alloys are strengthened by

9
either cold work or solid solution method. Common most Cu alloys: Brass, alloys of Cu
and Zn where Zn is substitutional addition (e.g.: yellow brass, catridge brass, muntz
metal, gilding metal); Bronze, alloys of Cu and other alloying additions like Sn, Al, Si and
Ni. Bronzes are stronger and more corrosion resistant than brasses. Mention has to be
made about Beryllium coppers who possess combination of relatively high strength,
excellent electrical and corrosion properties, wear resistance, can be cast, hot worked
and cold worked. Applications of Cu alloys include: costume jewelry, coins, musical
instruments, electronics, springs, bushes, surgical and dental instruments, radiators, etc.

Answer 41

Copper Alloys

Question 42

is low density among all structural metals. has HCP structure, are difficult to form at room temperatures. are usually fabricated by casting or hot working. As in case of Al, alloys are cast or
wrought type, and some of them are heat treatable. Major alloying additions are: Al, Zn,
Mn and rare earths. Common applications of Mg alloys include: hand-held devices like
saws, tools, automotive parts like steering wheels, seat frames, electronics like casing for
laptops, camcorders, cell phones etc.

Answer 42

Magnesium Alloys

Question 43

are of relatively low density, high strength and have very high
melting point. At the same time they are easy to machine and forge. However the major
limitation is Ti’s chemical reactivity at high temperatures, which necessitated special
techniques to extract. Thus these alloys are expensive. They also possess excellent
corrosion resistance in diverse atmospheres, and wear properties. Common applications
include: space vehicles, airplane structures, surgical implants, and petroleum & chemical
industries.

Answer 43

Titanium Alloys

Question 44

These are metals of very high melting points. For example: Nb, Mo, W and Ta.
They also possess high strength and high elastic modulus. Common applications include:
space vehicles, x-ray tubes, welding electrodes, and where there is a need for corrosion
resistance.

Answer 44

Refractory Metals

Question 45

These are eight all together: Ag, Au, Pt, Pa, Rh, Ru, Ir and Os. All these possess
some common properties such as: expensive, soft and ductile, oxidation resistant. Ag, Au
and Pt are used extensively in jewelry, alloys are Ag and Au are employed as dental
restoration materials; Pt is used in chemical reactions as a catalyst and in thermo couples.

Answer 45

Noble Metals