Iron and steel;their types,properties and formation.

1. IRON & STEEL

2. Extraction and processing of raw material develops: Efficient, cleaner and
systematic methods of raw- material extraction are developed.
Industrial growth takes place: New industries for manufacturing new
products are created.
Infrastructure Improves: Power, transport andcommunication improves.
Importance of Engineering
Materials

3. Technical education improves: To work in industry skilled man power is
required. Technical education improves.
Gross National Product of the country improves: Improvement in
material production leads to increase in GNP.
Standard of living of people improves: Salaries and wages of trained
personnel improves which leads improvement in overall living
standard of people.
Technological and economic development takes place.

4. Metal and their alloy
Non- Metals and
Composite materials

5. 1. Ferrous metals: In Ferrous metals Iron (Fe) is the major
constituent. Examples: Cast Irons and Steels. They are strongest
material available. They are used for making bridges, railway lines,
railway engines, railway wagons, strong parts of automobiles, steel
wires, rods, plates etc.
2. Non-Ferrous metals are those metals in which major constituent is
other than Iron (Example: Gold, Silver, Copper, Zinc, Brass, Tin,
Bronze, and Lead etc.). Their mechanical strength is less.

6. Synthetic Non-Metals such as plastics and adhesives do not exist in
nature, they are manufactured from natural substances such as oil,
coal and clay. They have good mechanical strength and can be easily
manufactured. Plastics are extensively used from utensils to structural
members. Synthetic adhesives are used for joining.
Natural Non-Metals: Some non-metals such as wood, rubber, glass,
emery, ceramic, diamonds, oils and silicon are naturally occurring.
They are obtained from nature and given desired shape for use

7. Composite materials are combination of
two or more materials. They exhibit
different properties then those materials
of which they are
example composite
made
material
of. Some
are fiber
glass, Clad metals, Cemented Carbides,
Reinforced plastics etc.

8. Ferrous materials are those materials in which chief constituent is
Iron. In these materials Iron is mixed with Carbon, Silicon,
Chromium, Nickel, Manganese etc. to form alloys such as
Steels and Cast Irons.
Ferrous materials are classified into two categories namely
Steels and Cast Irons based on Carbon content in them

9. Steels: Steels are those alloys of Iron and Carbon in which carbon content
is less than 2%. Depending upon % of other alloying elements, Steels are
further named as Carbon Steels, Stainless Steels or Tool steels.
Cast Iron: Cast Irons are those alloys of Iron and Carbon in which Carbon
content is 2% to 6.67%. Cast Irons are normally produced from cupola
furnace. Depending upon % of Carbon and other alloying elements various
Cast Irons are produced.

10. Carbon Steels and their classification based on % of Carbon:
Higher percentage of carbon in steel makes it harder and tougher.
Carbon Steels are classified into following four categories:
a) Low carbon steel , C %- 0.05-0.15
b) Mild steel,C %- 0.16-0.29
c) Medium carbon steel ,C %- 0.3-0.59
d) High carbon steel C %- 0.60-1.7

11. s.
no
Type of carbon steel %of carbon properties applications
1 Low carbon steel 0.05-0.15 soft, ductile , very
little hardenability,
Welded or
Seamless tubes,
good corrosion Thin sheets, Wire
resistance.,good
weld ability.
rods, Nails,
Rivets,
,Stampings etc.
2 Mild carbon steel 0.16-0.29 Soft, ductile,
Little
hardenability,go
od weladbility
Forgings,
Stampings,
Structural
sections (i.e.
Angles,
Channels,
Beams, wire
Rods, Ribbed
bars etc.), Plates,
Steel Castings

12. s. no Type of
carbon steel
%of carbon properties applications
3 Medium
carbon steel
0.30-0.59 Good strength and
ductility. good
hardenability and
Drop forgings,
Plates for boiler
drums, Marine
weldability. They Shafts and
can be hot or cold axles, High
worked. tensile wires
and tubes,
Locomotive
wheels, Wire
ropes, hammers
etc.
4 High carbon
steel
0.60- 1.7 good
hardenability,
ductility and
for making
Cutting Tools,
Punches & Dies
weldability are and high
low. strength Rails.

13. a) Low Carbon Steel or Dead mild steel: They have carbon content in
the range of 0.05 – 0.15%. These steels are very soft, ductile and have very
little hardenability. They have good corrosion resistance. They have good
weld ability. They can be easily cold worked and they acquire hardness
through cold working. They are used for making Welded or Seamless
tubes, Thin sheets, Wire rods, Nails, Rivets, and Stampings etc.
b) Mild Steel: They have Carbon Content from 0.16% - 0.29%. These
steels are soft, ductile and have very little hardenability. They acquire
hardness through cold working. They have good weldability. They are
used for making Forgings, Stampings, Structural sections (i.e. Angles,
Channels, Beams, wire Rods, Ribbed bars etc.), Plates, Steel Castings etc.

14. c) Medium Carbon Steel: They have Carbon Content from 0.3%-0.59%.
These steels have good strength and ductility. They have good hardenability
and weldability. They can be hot or cold worked. They get hardened quickly
while cold working, due to this they require frequent annealing while cold
working. They are suitable for making Drop forgings, Plates for boiler
drums, Marine Shafts and axles, High tensile wires and tubes, Locomotive
wheels, Wire ropes, hammers etc.
d) High Carbon Steel: They have Carbon Content from 0.6% to 1.7%.
These steels have very good hardenability. There ductility and weldability
are low. They become so hard after quenching that tempering is normally
required to reduce their brittleness and make them tougher. They are mostly
used for making Cutting Tools, Punches & Dies and high strength Rails.

15. It is purest form of iron which
contains 99.8 % of iron and
produced by melting pig iron in
puddling furnace.

16. Cast Iron: Cast Iron is produced by melting Pig Iron* in
Cupola furnaces or some other furnace (i.e. Induction
furnace etc.)
The chemistry of Pig Iron is suitably modified in cupola
furnace to produce different grades of Cast Iron.

17. Cast Iron has low tensile strength, but good compressive
strength and good corrosion resistance. Cast Irons are
very brittle and have no plasticity as a result they can
not be forged.
It has self lubricating properties due to presence of free
carbon and is therefore used for making surfaces over
which sliding takes place (such as lathe bed etc.)

18. a) Gray Cast Iron : In this Cast Iron most of the carbon is present
in the form of free graphite. Under microscope this carbon is
visible as flakes.
If a piece of this material is broken its fractured section shows the
grayish color and that is why it is known as Gray Cast Iron. The
gray color is due to presence of free carbon in the form of
graphite flakes. In Gray Cast Irons the Carbon content in
combined form (i.e. in the form of Fe3C) may vary from 0.3% to
0.9%.

19. Properties :
It is very brittle and posses no ductility or plasticity as a result it can not be
forged. High brittleness makes it unsuitable for making parts which are
subjected to shock loading.
It has good machinability.
It has good compression strength (1250 Kg/Sq.cm) and low tensile strength 650
Kg/ Sq. cm). Due to good compressive strength it is most suitable for making
Compressive load bearing members such legs and beds of heavy machinery.
It has good fusibility which makes it suitable for making castings.
Due to presence of free graphite it has self lubricating property and hence it is
suitable for making sliding surfaces.

20. White Cast Iron :
It is called white cast iron because its fractured section shows whitish color.
Most of the carbon present in this cast Iron is in the combined form (i.e.
iron carbide which is called Cementite). Cementite is white in color and
makes the structure white.
Cementite is very hard and brittle. Cenmentite is formed due to rapid
cooling of iron after melting. It is due to this reason that all the chilled parts
of castings are hard and brittle.
White cast iron is hard and brittle and highly wear resistant.

21. c) Malleable cast Iron :
It has fairly good amount of malleability. It is produced in two steps.
First cast iron castings are produced by melting white cast iron in
cupola furnace. These castings are packed in Iron boxes containing
material rich in O2. These boxes are kept for four days in annealing
furnaces at a temperature of 815oC to 1010oC and then allowed to
cool slowly along with the furnace. This allows Cementite to
decompose into iron and carbon.

22. d)Nodular Cast Iron : This is also known as Spheroidal Graphite (
or simply SG) Cast Iron, Ductile Cast Iron or High Strength Cast
Iron. For its production the shape of graphite present in cast iron is
changed from flakes to spheroids or nodules.
This is achieved by adding magnesium metal to the molten cast
iron just after tapping. This magnesium treated metal when cast
into moulds gives SG cast iron. This changed shape of graphite
prevents formation and propagation of cracks and enhances
ductility of Cast Iron. It has chemistry similar to gray cast iron

23. All steels in addition to Iron and Carbon contain other
elements like silicon, manganese, sulphur and phosphorous. In
some steels special elements like Nickel, Chromium,
Molybdenum, Vanadium and Tungsten etc. are added to enhance
their mechanical properties. These steels are called alloy steels.
They have their properties as per the alloying elements in them.
These steels are named normally on the basis of their principal
alloying element.

24. These are various types-
Stainless steel
Tool steel
Spring steel

25. Stainless steels: They are corrosion resistant steels. Their
principal alloying element is chromium, while other elements
like nickel, manganese can also be present in small amounts.
To impart high corrosion resistance to steels Chromium up to
12% is added.
The chromium present in steels reacts with O2 in air to form
a strong layer of chromium oxide on the surface of the metal.
This layer protects the metal from corrosion. Stainless steels
carrying more than 12% chromium are known as true
stainless steels.

26. These alloy steels have special application in
manufacture of cutting tools for those applications
where tools made of carbon steel will either fail to
perform or will have a very short life. They are put into
two categories namely :

27. High Speed Steel : It is a high alloy tool steel used for making cutting tools suitable
for high temperature applications.
Main Constituents in HSS are Carbon, tungsten, chromium, vanadium and molybdenum.
High Speed Steel has high wear resistance, high abrasion resistance and high red hardness.
They retain their hardness up to 620oC.
The most commonly used high speed steel is 18-4-1 which carries 18% Tungsten, 4%
Chromium, 1% Vanadium, 0.7% Carbon and rest Iron.
It has good red hardness, wear resistance shock resistance and widely used for making
cutting tools for lathe, shapers, slotters, milling machines, drill etc

28. Stainless Steel
 It is the alloy of iron and carbon
 This is a steel alloy with a minimum of 12% chromium
content that’s why called Stainless Steel.
 Stainless steel is more resistant to stains , corrosion,
and rust than ordinary steel.

29. Why Chromium is added?
 Chromium is added to Steel to increase
Resistance to Corrosion
 Chromium has self Passive Properties
 When react with Oxygen produce
Chromium Oxide layer on Stainless
Steel

30. Composition
Chromium>10%
Carbon<1.2%
Iron(base)
Other elements

31. Types
Stainless steel is used where the properties of steel as well
as the resistance to corrosion is required. there are about
150 grades
Two of them are very famous and use
Stainless 316 contain more nickel
Stainless 304 contain more Chromium

32. Stainless Steel 316
 Type 316 steel is an austenitic chromium-nickel stainless
steel that contains between two and three percent molybdenum.
 The molybdenum content increases corrosion-resistance,
improves resistance to putting in chloride ion solutions, and
increases strength at high temperatures

33. Composition of Steel 316
 Stainless 316 is made up of
16% chromium,
10% nickel
2% molybdenum.
 This Steel is durable and provide excellent
resistance to corrosion and rust.

34. Stainless Steel 306
 SAE 304 stainless steel is the most common used stainless steel.
 The steel contains
Chromium (between 15% and 20%)
Nickel (between 2% and 10.5%)
 It is an austenitic stainless steel. It is less electrically and
thermally conductive than 316 steel and is essentially non-magnetic.
 It has a higher corrosion resistance than regular steel and is widely
used because of the ease in which it is formed into various shapes.

35. What's the difference between 304 and
316 stainless steel?
 The simple answer is 304 contains 18% chromium and 8%
nickel and is Widely used.
 While 316 contains 16% chromium, 10% nickel and 2%
molybdenum. The molybdenum is added to help resist corrosion
to chlorides (like sea water and de-icing salts).

36. Uses of Stainless Steel
Stainless steel is commonly used
▪ Surgical Instruments
▪ Automomotive Industry
▪ Storage tanks
▪ Construction
▪ Food processing plant

37. Why we use stainless steel
▪ It service in very extreme eminent
▪ Minimum survival temperature -269 degree c
▪ Maximum survival temperature 1100 degree
▪ The amount of chromium make it unique
▪ It the most corrosion resistant because the layer of oxide make over the
surface of it

38. Types of Stainless Steel based on Structure
Ferrite
Austenite
Martensite
Duplex
Precipitation
hardning

39. Ferrite Stainless Steel
Ferrite is body center cube allotrope of iron.
 Formed on cooling low carbon concentrations in iron-carbon
alloys from the liquid state before transforming to austenite. In
highly alloyed steels, delta ferrite can be retained to room
temperature
The Maximum Solubility is 0.025% C at 723 °C
Dissolve 0.008% C at Room Temperature.

40.  This type contains chromium and trace amounts of carbon.
 It contains 10.5% to 20% chromium and are highly resistant
to scaling and cracking at elevated temperatures.
 The molecular structure resembles that of low carbon steel.
 It is not tough or hard, hence its applications are limited.
 It is characterized by its magnetic nature and by the ability to
resist cracking in the presence of stress and corrosion.
 It has also good Electrical Properties

41. Structure of Ferrite
Body Centered Cube
Microscopic Structure

42. Austenitic Stainless Steel
 It is Face Centered Cube
 This is the most common type of stainless steel.
 It contain 15% to 30% chromium and 2% to 20% nickel for enhanced surface
quality, formability and increased corrosion and wear resistance.
 The Maximum Solubility of Carbon is 2.13% at 1147 c
 It shows presence of nickel, manganese, and nitrogen.
 These elements impart the alloy with the ability to be welded and formed into
any desired shape.
 Known for their formability and resistance to corrosion, austenitic steels are
the most widely used grade of stainless steel.

43. Formation
 This is a face-centered cubic structure formed when iron
is heated above 910° C (1,670° F); gamma iron becomes
unstable at temperatures above 1,390° C (2,530° F).
 Austenite is an ingredient of a kind of stainless steel
used for making cutlery, hospital and food-service
equipment, and tableware.

45. Martensite Stainless Steel
 This is name given to very hard and brittle constituent
 Highly Saturated with dissolved Carbon.
 This type is similar to ferrite steel but has a higher carbon
content (almost 1%).
 It exhibits high strength and moderate corrosion resistance.
 It is also magnetic and has a low weldability

46. Formation of Martensite
 Martensite is formed in carbon steels by the rapid cooling
(quenching) of the austenite form of iron at such a high rate
that carbon atoms do not have time to diffuse out of the crystal
structure in large enough quantities to form cementite (Fe3C)

47. Duplex Stainless Steel
 Duplex stainless steel have a two-phase microstructure consisting of
grains of ferritic and austenitic stainless steel
 When duplex stainless steel is melted it solidifies from the liquid
phase to a completely ferritic structure.
 It is a combination of ferritic and austenitic steels in equal amounts.
 This enables the duplex steel to be stronger than both the
components.
 It is resistant to corrosion, moderately weldable, and is weakly
magnetic.

48. Precipitation Hardening Stainless Steel
 This is a hardened variety of steel, that results from addition
of 17% chromium and 4% nickel.
 In addition to these, copper, niobium, and aluminum are
also added in variable quantities.
 It is moderately resistant to corrosion, and can be molded
to intricate shapes

49. Tool steel
 It is high carbon steel 0.7-1.5%
 It is very hard
 Strength is very high
 Wear resistance
 it is used for the formation of following things
 Chisel
 Drawing dies
 Cutting tools

50. Hardenability
 The hardenability of a metal alloy is the depth to which a
material is hardened after putting it through a heat
treatment process
 Hardness of Martensite is Related to Carbon Content of
Steel
 It Refers to Depth Of Hardening That Obtained

51. Hardenebility
 Hardenibility is important Property of Steel
 A steel with high hardenbility will harden to greater depth
below the surface that one of lesser hardenbility for same
rate of cooling
 Martenstic Structure will be achieved
 Lessen the risk of cracking and distortion occur in heat
treated components

52. Tempering
 Tempering is a process of heat treating, which is used to
increase the toughness of STEEL
 Martensite is Hard and Brittle, it required a further heat
treatement know as tempering
 Carbon diffuse from lattice in the form of iron carbides particles
 An increase in temperature increase the diffusion, increase in the
Extent of Softening and increase toughness

53.  The tempering done at temperature of 700°C of Martensite
result in SOFT but incredibly TOUGH Material
The various colors produced during TEMPERING indicate the
temperature to which the steel was heated. Light-straw indicates 204 °C
and light blue indicates 337 °C

54. Tempering Temperatures
Temperature °C Suitable for
220 Hacksaw Blades
240 Milling Cutters, Drills
260 Drills for wood
280 Plane blades, Chisels
450-700 Great Toughness, Springs,
Wood Saws

55. Effects of Alloying Elements in Steels
An alloying element entering in the Solid Solution
will Increase the strength of STEEL.
Increase in Carbon will Increase the Strength
Alloying Elements reduce critical cooling
velocities and increase the Hardenebility of Steel

56. Alloying Element
 If the excess amount of ALLOYING ELEMENT PRESENT it will effect
the ALPHA to GAMMA transformation
 CHROMIUM and SILICON raise the transformation temperature
 NICKEL and MANGANESE lower that Temperature
 If Chromium present in Excess amount (12%) it will make STEEL
STAINLESS
 Cause breakdown of Cementite result in formation of Graphite in
Steel

57. Composition of Steel based on Carbon
Carbon% Name Applications
0.05 Dead Mild Steel Car bodies, wire
0.15 Mild Steel Screws, reinforcement
Bars
0.25-0.4 Medium Carbon Steel Shafts, High Tensile Tubing
0.4-0.5 Medium Carbon Steel Railway tires, Gears
0.65-0.75 High Carbon Steel Hammers, Railway rails
0.85-0.95 High Carbon Steel Punches, high tensile wire
1.1-1.4 High Carbon Steel Ball bearings, drills
Metal cutting Tools
Knives, Axes