S3 Tool & Die Engineering diploma Material Testing & Heat Treatment

1. Material Technology and
Heat Treatment
Diploma in Tool & Die Engineering
S4

2. Module 1

3. Engineering Materials
• Material is nothing but a matter of substance used to create a certain
thing.
• Engineering materials are the materials used to for the application of
engineering works.
• Materials that are used as raw material for any sort of construction or
manufacturing in an organized way of engineering application are
known as Engineering Materials

5. Material selection criteria
• Here is a list of the categories of the requirements to consider when
selecting a material for a component or a joint between components:
• Performance requirements
• Reliability requirements
• Size, shape, and mass requirements
• Cost requirements
• Manufacturing requirements
• Industry standards
• Government regulations
• Intellectual property requirements
• Sustainability requirements

6. Mechanical properties
• The mechanical properties of a material affect how it behaves as it is
loaded

8. Tensile strength
• Tensile strength refers to the amount of load or stress that a material
can handle until it stretches and breaks.
• A material testing laboratory usually conducts the test using
a universal testing machine (UTM), which holds a specimen material
in place and applies the tension stress needed to check the breaking
point.
• The equipment is connected to an extensometer, which measures
changes in the specimen’s length

13. Ductility
• Ductility is the ability of a solid material to deform under tensile
stress.
• Practically, a ductile material is a material that can easily be stretched
into a wire when pulled

15. • Ductility is expressed in percentage elongation or percentage reduction in area

16. Malleability
• A malleable material is one in which a thin sheet can be easily formed by
hammering or rolling. In other words, the material has the ability to deform
under compressive stress

17. • A metal's malleability can be measured by how much pressure (compressive
stress) it can withstand without breaking.
• When a large amount of stress is put on a malleable metal, the atoms roll over
each other and permanently stay in their new position.
• Examples of malleable metals are:
• Gold
• Silver
• Iron
• Aluminum

18. Hardness
• A material’s ability to withstand friction, essentially abrasion resistance, is known
as hardness.
• Hardness is defined as a material’s ability to resist permanent indentation (that is
plastic deformation).
• Typically, the harder the material, the better it resists wear or deformation.
• The term hardness, thus, also refers to local surface stiffness of a material or its
resistance to scratching, abrasion, or cutting.

19. • Some materials are naturally hard. For example, tungsten is an incredibly hard
metal that finds use as an alloying element in tool steels
• Hardness is measured by employing such methods as Brinell, Rockwell, and
Vickers, which measure the depth and area of a depression by a harder material,
including a steel ball, diamond, or other indenter.
• The commonly used units for hardness measurement are:
• Brinell Hardness Number (HB)
• Vickers hardness number (HV)
• Rockwell hardness number (HRA, HRB, HRC, etc)

20. Elasticity
• When a material has a load applied to it, the load causes the material to deform.
Elasticity is the ability of a material to return to its original shape after the load is
removed.
• Theoretically, the elastic limit of a material is the limit to which a material can be
loaded and still recover its original shape after the load is removed.
• The physical reasons for elastic behavior can be quite different for different
materials. In metals, the atomic lattice changes size and shape when forces are
applied (energy is added to the system).
• When forces are removed, the lattice goes back to the original lower energy
state. For rubbers and other polymers, elasticity is caused by the stretching of
polymer chains when forces are applied

24. Plasticity
• Plasticity is a mechanical property of materials that shows the ability to deform
under stress without breaking, while retaining the deformed shape after the load
is lifted.
• Metals with higher plasticity are better for forming.
• For example, a solid piece of metal being bent or pounded into a new shape
displays plasticity as permanent changes occur within the material itself.
• In engineering, the transition from elastic behavior to plastic behavior is known
as yielding.

27. Impact strength and Toughness
• Impact strength is the capability of the material to withstand a suddenly applied
load and is expressed in terms of energy.
• Often measured with the Izod impact strength test or Charpy impact test, both of
which measure the impact energy required to fracture a sample.
• Toughness is the ability of a material to absorb energy and plastically deform
without fracturing.
• One definition of material toughness is the amount of energy per unit volume
that a material can absorb before rupturing.

30. Stiffness
• Stiffness is the extent to which an object resists deformation in response to an
applied force
• The stiffness, k, of a body is a measure of the resistance offered by an elastic
body to deformation.
• For an elastic body with a single degree of freedom (DOF) (for example, stretching
or compression of a rod), the stiffness is defined as
• F is the force on the body
• δ is the displacement produced by the force along the same degree of freedom
(for instance, the change in length of a stretched spring)

33. • Fatigue can be determined by SN curve plotted by carrying out fatigue test.
• The test demonstrates the number of cycles that the material will survive in
service with a given cyclic stress ie the fatigue life of a material
• Fatigue is the weakening of a material caused by cyclic loading that results in
progressive and localized structural damage and the growth of cracks

37. Creep

39. Primary Creep: starts at a rapid rate and slows with
time.
• Secondary Creep: has a relatively uniform rate
. • Tertiary Creep: has an accelerated creep rate and
terminates when the material breaks or ruptures.
It is associated with both necking and formation of
grain boundary voids.

40. • Creep test: consist of subjecting a specimen to a constant load or specimen while
maintaining constant temperature
• Typically, applications that have high heat and high stress can be susceptible to
creep. Examples include nuclear power generation, industrial engine
components, heated metal filaments, jet engine components, and pressurized
high-temperature piping.

41. Space lattice
• A crystalline materials or crystal structures can be considered to have formed
when atoms arrange themselves in an orderly three dimensional pattern, in
which rows can be identified running in various directions along which the atoms
are regularly placed.
• If the atoms are considered as points in space, then the array of infinite, perfectly
periodic array of points in a space is a LATTICE
• Hence crystal lattice or space lattice can be defined as a three dimensional
network of lines, the intersection of which generates a 3 dimensional array of
points which are occupied by atoms or about which a group of atoms are cluster,
forming the crystalline material.

43. Unit Cell
• A unit cell is the basic building block of the crystal, because the crystal can be
thought of as being built up of a series of parallel repetitions of the unit cell
• The crystal consist of unit cells stacked together tightly, each identical in size,
shape and orientation with all others.
• Unit cell is the smallest unit which when repeated in space indefinitely will
generate the space lattice

44. • In a lattice there can be a number of unit cells.
• These unit cells fall into seven categories, which differ in the three unit
cell edge lengths (a, b, and c) and three internal angles

46. Crystal structure
• A crystal structure is defined when a lattice is specified along with a
basis.
• The basis represents a group of one or more atoms associated with
each lattice points.

47. • Crystal structure and Amorphous structure
• Crystalline structure
• Atomic arrangements which have a regular repetitive pattern in all 3 dimension are
called crystal structure.
• They are having long range order (the repetitive pattern exist over many atomic
distances)
• They have a characteristic geometrical shape.
• They have sharp melting point.
• Properties of solids are different in different direction. Phenomenon is called Anisotropy.
• They are symmetrical

48. • Amorphous structure
• Atomic arrangement is not based on a regular repetitive pattern.
• Short range order ( regular arrangement may exist in localized regions, but the pattern
breaks up at different places, exist over a few atomic distances)
• They don’t have a definite geometrical shape
• They don't have particular melting point. They melt over a wide range of temperature.
• Properties of amorphous solids are same in different direction, i.e. amorphous solids
are isotropic
• Amorphous solids are unsymmetrical

49. Body Centered Cubic Structure (BCC)
• This type of unit cell has a full atom positioned at the body centre in addition to
the 8 atoms at the corners.
Each atom at the corners are shared by 8 other unit cells, while the atoms at the
body center is fully inside the cell.
• Number of atoms in the unit cell is 2.

51. Face centered cubic structure (FCC)
• In this type of cubic cells, the lattice points are at the center
of each face, as well as at each corner,
• The atoms are positioned such that the empty space between them is minimized.
• The 8 corner atoms together becomes effectively 1 atom and the 6 atoms at the
faces (shared by 2 unit cells) contributes 3 atoms.
• The effective number of atoms in FCC unit cell is 4 atoms.

53. Hexagonal closed packed structure
Effective no of atoms is 2+1+3=6

54. • The top and bottom faces of the unit cell consist of six atoms that form regular
hexagons and surround a single atom in the center.
• Another plane that provides three additional atoms to the unit cell is situated
between the top and bottom planes.
• The atoms in this mid plane have as nearest neighbors atoms in both of the
adjacent two planes.
• The equivalent of six atoms is contained in each unit cell; one-sixth of each of the
12 top and bottom face corner atoms, one-half of each of the 2 center face
atoms, and all the 3 mid plane interior atoms.

56. Atomic packing factor
• Atomic packing factor (APF), packing efficiency or packing
fraction is the fraction of volume in a crystal structure that is occupied by constituent
atoms.
• It is dimensionless and always less than unity.
• In atomic systems, by convention, the APF is determined by assuming that atoms are ri
gid spheres.
• The radius of the spheres is taken to be the maximal value such that the atoms do not
overlap.

62. • Crystallization or crystallisation is the process by which a solid forms, where
the atoms or molecules are highly organized into a structure known as a crystal.
• Some of the ways by which crystals form are precipitating from
a solution, freezing, or more rarely deposition directly from a gas.

63. Grains
• A crystallite is a small or even microscopic crystal which forms, for example,
during the cooling of many materials.
• Crystallites are also referred to as grains. The areas where crystallites meet are
known as grain boundaries.
• Polycrystalline materials, or polycrystals, are solids that are composed of many
crystallites of varying size and orientation.

65. • While the structure of a (single) crystal is highly ordered and its lattice is
continuous and unbroken, amorphous materials, such as glass and many
polymers, are non-crystalline and do not display any structures, as their
constituents are not arranged in an ordered manner

67. Deformation of metals
• When a sufficient load is applied to a metal or other structural
material, it will cause the material to change shape. This change in
shape is called deformation

68. ➢Various metal forming operations are based on deformation of
metals.
➢Two types of deformation
➢Elastic deformation
➢Plastic deformation

70. Mechanism of plastic deformation
• Plastic deformation occur in metals mainly by 2 mechanism
❑ slip
❑ twinning

84. Module 2

85. Ferrous metals and alloys
• Ferrous metals are those metals which contain iron as the main constituents with
small amounts of carbon and other materials to get desirable properties
• Ferrous metals have distinctive properties that include tensile strength, ductility,
magnetic, toughness, durability etc.
• Used in many applications like shipping containers, industrial piping, automobiles,
railroad tracks, and many commercial and domestic tools

87. Pig iron
• It is an intermediate form of iron produced from iron ore and is subsequently
worked into steel or wrought iron.
• It is an intermediate product of smelting iron ore with a high carbon fuel such as
coke with limestone as flux in a blast furnace
• Pig iron has a very high carbon content, typically 3.5-4.5% and contain other
elements in small amount like manganese, sulpher etc.

88. • To remove impurities from iron ore, smelting process is done
• Smelting- it is process of heating the iron ore with carbon and flux (limestone).
• It is carried out in a blast furnace
• The iron thus produced is in the crudest form and settles in the bottom of the
furnace in molten form which is tapped out

90. • Properties and uses of pig iron
❖It is hard and brittle as such it is neither ductile nor malleable
❖It is difficult to bend, high compressive strength but weak in tension.
❖It melts easily, the fusion temperature is 1200o C
❖It can be moulded to various shapes such as pipes, storage tanks, bath tubes etc.
❖Sheets and wires cannot be made
❖As it is comparatively weak form it is subsequently used as a raw material for
producing other components like steel.

92. Wrought iron

96. • Applications: bolts, nuts, crane hooks, railway couplings, sheets,
boiler tubes etc

97. Cast iron

109. Phase diagram
• Phase diagram is a graphical representation of the physical states of a substance
under different conditions of temperature and pressure.
• A typical phase diagram has pressure on the y-axis and temperature on the x-
axis.
• As we cross the lines or curves on the phase diagram, a phase change occurs

110. Water phase diagram

111. Steel
• Alloy of iron and carbon (with carbon content upto 1.5%)
• The carbon is in compound form with iron.
• Besides carbon, there are other elements present in steel like silicon, sulphur,
manganese, phosphorous
• Carbon in steel influence on the internal structural changes and properties
• Steel is used in many application like construction, automobile, machine tools etc.

112. • Steel making process
• Bessemer process
• L-D process
• Open-hearth process
• Electric process
• Duplex process

113. Bessemer process
• Consist in blowing air through molten pig iron contained in a special furnace
known as converter shaped like a huge concrete mixer
• Converter-lined with refractory material of type depends on process-Acid process
and basic process
• Acid process- refractory material-silica bricks- does not eliminate phosphorous or
sulpher from the metal
• Basic process- refractory material-dolomite-removes phosphorous

114. • 3 stages
• First stage- blowing period- blast is turned on after charging- vessel turned
upright- oxygen oxidises iron to ferrous oxide-silicon and manganese impurities
are burned and goes to slag- high temp process
• Second stage-metal reached high temp-intensive burning of carbon from the
molten bath-gas produced is carbon monoxide- white flame
• Third stage- after white flame drops-converter is turned horizontal to tap–
deoxidisers like ferromanganese or ferrosilicon added to eliminate oxygen

116. L-D process
• It is known as Linz and Donawitz process.
• Consist of blowing a jet of almost pure oxygen at high pressure and speed
through a water cooled lance on to the molten iron held in a converter lined with
basic refractories (dolomite).
• High speed oxygen produces intense heat (2500 to 3000oC) and reduce blowing
time that increases the production rate.

118. Open hearth process
• Here pig iron, iron oxide and steel scrap are melted in a Siemens- martin open
hearth furnace-molten metal lies in a shallow pool on the furnace bottom or
hearth
• Hearth surrounded by a roof and wall of refractory bricks
• Charge fed through charging door and heated to 1600 to 1650oC mainly by the
heat from the burning of gaseous fuel above it.
• Also called duplex process as it has 2 stages: 1) blowing molten pig iron in the
Bessemer converter 2) further purification of blown metal in open hearth furnace

119. • When the impurities brought down to required level, metal is taped off.
• Acid open hearth process- lined with silica bricks- acid slag high in silica is
produced- cannot remove phosphorous-better quality steel
• Basic open hearth process- lined with magnesite and limestone added to the
charge-basic slag high in lime

121. Electric furnace process
• Here electricity is used solely for the production of heat
• Advantages- produce high temperature, clean process, facilitate the removal of
harmful impurities, temperature regulated, any variety of steel can be used.
• Disadvantage-more expensive in operation, low production rate
• Two types of electric furnace- direct arc furnace and high frequency induction
furnace

122. • Direct arc furnace- consist of steel shell lined with refractory bricks and a
removable roof through which carbon or graphite electrodes pass.
• electrode are lowered in to the furnace and current switched on
• Heat generated by the powerful spark between the electrodes and metallic
charge on the hearth melt the charge
• Charge- steel scrap and iron oxide-pig iron not directly treated in electric furnace-
partly purified in an open hearth furnace and finally treated in electric furnace
• A definite distance must be maintained between electrode and charge by raising
and lowering them by automatic controls

124. • High frequency induction arc furnace
• Principle of an induction furnace-
• primary coil-alternating current passed through it set up alternating magnetic
field with magnetic lines of force of definite density.
• Magnetic field induces alternating eddy currents in the secondary circuit which
comprises a crucible containing the metal charge

125. • Induction crucible furnace
oRefractory crucible- metal charged and melted by heavy secondary currents- can
be tilted horizontal to tap the molten metal
oCoil or inductor- copper
oCooling water
oInsulating lining
oMostly employed for making high alloy steel and special purpose alloys.

127. Alloy steel
• Alloying : changing chemical composition of steel by adding elements
with purpose to improve its properties as compared to plain carbon
steels.
• Alloy steels are materials where other elements (besides carbon) are
added to iron to improve
• Mechanical property: increase strength, hardness, toughness, creep
and high temp resistance
• Increase wear resistance
• Environmental property (eg: corrosion)

135. •Tool steel

136. Stainless steel

137. Austenitic stainless steel
• Possess austenitic structure
• Highest corrosion resistance of all stainless steels
• Non magnetic
• Possess greatest strength at highest temperature
• Chromium-16-26%, Ni-3.5-22%, Mn-2%-10%
• Applications- aircraft industry, chemical processing and food, dairy industry

138. Ferritic stainless steel
• Ferritic microstructure
• Magnetic and good ductility
• More corrosion resistance than martensitic steels
• Chromium 11-12%, Mn-1-1.5%, C-0.08-0.20%

139. Martensitic stainless steel
• Martensitic microstructure
• Highest carbon-chromium ratio, hardenable by heat treatment
• Magnetic, best thermal conductivity
• Hardness is more and ductility is less
• Cr-11.5-18%

140. Hss tool steel
• High speed steel is a highly alloyed steel capable of maintaining hardness even at
elevated temperatures.
• High speed steel are so named because of their ability to machine materials at
higher cutting speeds.
• High speed steel has unusually high resistance to softening at temperatures upto
600o c , it is called red hardness
• They are complex iron base alloys of carbon, chromium , vanadium, molybdenum
or tungsten and some amount of cobalt.

141. • Especially suited to applications involving complicated tool shapes such as drills,
taps, milling cutters and broaches
• Two basic types of HSS
• Tungsten type, designated as T-grade
• Molybdenum type, designated as M-grade

142. Nickel steel
• Nickel steels are having nickel composition of about 3.5%
• Can be readily welded, formed, machined and cast
• Properties
✓More elastic
✓Higher tensile strength
✓Less brittle than mild steel
✓Improved hardness and ductility

143. • Limitations:
• It corrodes easily as compared to steel
• Effect of alloying nickel to steel
❑Increases toughness
❑Strength increases
❑Abrasive resistance increases
❑Elastic limit increases

144. Application

146. CODING OF STEEL
• According to IS: 1962-1974, steel can be classified on
• The basis of mechanical properties
• Basis of chemical composition

147. On the basis of mechanical properties
• These steels are carbon and low alloy steels where the main criteria for selection
is tensile or yield stress.
• Code designation consist of
1. Symbol Fe or FeE depending on whether the steel has been specified on the
basis of minimum tensile strength or yield strength
2. Figure indicating the minimum tensile strength or yield strength in N/mm2
3. Chemical symbols for elements the presence of which characterizes the steel
4. Symbols indicating special characteristics covering method of deoxidation, steel
quality, surface condition, weldability etc.
5. Eg: Fe 410 Cu K- killed steel (K) containing copper as alloying element with a
minimum tensile strength of 410 N/mm2

148. On the basis of chemical composition
• Unalloyed steel
• Code designation shall consist of the following in the order given
• Letter C
• Figures indicating 10 times the average percentage of manganese content. The
result shall be rounded off to the nearest integer
• Symbol indicating special characteristics
• Eg: 45 C 10 G, steel with average 0.45 per cent carbon. 1 per cent manganese and
guaranteed hardenability

149. • Other coding includes
• Unalloyed tool steels
• low and medium alloy steels (total alloying elements not exceeding 10%)
• High alloy steels (total alloying elements more than 10%)
• Alloy tool steels

150. Iron carbide phase diagram

151. Module 3

152. Aluminium

155. Processing of aluminum
• Rolling
• Casting
• Extrusion

158. Aluminium alloys
• Aluminium finds its widest use when alloyed with small amounts of
other metals
• The addition of small quantities of other alloying elemtents converts
this soft, weak metal into hard and strong metal while still retaining
its light weight
• Alloys are classified into cast and wrought alloys

159. Duralumin
• Wrought alloy with 3.5 to 4.5% copper, 0.4 to 0.7 % manganese, , 0.4 to 0.7 %
magnesium and remainder aluminium
• Widely used for forging, stamping, bars, sheets etc.
• It has an age hardening property- after working, the metal allowed to age for 3-4
days, it will be hardened
• Used in aircraft industries

160. Y alloy
• 3.5 to 4.5 % copper, 1.8 to 2.3% nickel and 1.2 to 1.7% magnesium
• Has the characteristics of retaining good strength at high temperature
• Useful for piston and other components of aero-engines
• Largely used in the form of sheets and strips

161. Hindalium
• It is an alloy of aluminium and magnesium with small quantities of chromium
• Trade name is derived from Hindustan Aluminium corporation as it is produced
by it.
• Mainly used for anodized utensil manufacture

162. Copper

163. Properties of copper

164. Copper alloys
• Copper alloys are classified in to mainly 2 types
• Brass
• Bronze

165. Brass
• Alloy of copper and zinc
• It’s often preferred over other metal alloys for its colour
• The properties of brass can also be changed with relative ease.
• This is done by changing the ratio of copper to zinc.
• Adding more copper and less zinc makes it harder, while adding more zinc and
less copper makes it softer
• Brass is used in many other applications as well, such as bearings, gears, locks,
valves, fittings, musical instruments and more.

166. Properties of brass
• Higher malleability
• Relatively low melting point (850-900oC)
• Easy to cast
• Density of brass-8.4-8.73 kg/m3
• 90% of brass is recycled
• Corrosion resistance
• Excellent machinability
• Good strength

167. Types of brass
• Catridge brass
• Admirality brass
• Muntz metal
• Naval brass

168. Cartridge brass
• Cartridge brass, a copper alloy containing about 30% zinc by weight, is easy to
produce and is often cost effective because zinc generally costs less than copper.
• A wrought brass containing usually about 70 percent copper and 30 percent zinc
and having sufficient ductility and other properties to stand the severe
mechanical treatment necessary in making cartridge cases
• This most popular brass has attractive properties for terminals, springs, switches,
contacts, and other connector components
• Cartridge brass, as its name implies, was and still is used for ammunition
cartridges.

169. Admirality brass
• Admiralty Brass is a Copper-Zinc Alloy, and has a small amount of tin
and arsenic as well.
• a corrosion-resistant alloy containing about 69-71 percent copper, 28-
30 percent zinc, and 1 percent tin
• Used for condenser tubes and heat exchanger in steam power plants

170. Naval brass
• Naval brass is the classic marine, high-strength and corrosion-resistant alloy
containing 60 percent copper, .75 percent tin and 39.2 percent zinc.
• It is widely used in marine construction where strong, corrosive-resistant and
hard material is required and is suitable for both salt and fresh water
applications.
• Naval brass is used in propeller shafts, marine hardware, decorative fittings,
shafting, propeller shafts and turn buckles.
• There are also many industrial applications, such as welding rods, condenser
plates, structural uses, valve stems, balls, heat exchanger tubes, aircraft
turnbuckle barrels, dies, and many more.

171. Muntz metal
• Muntz metal is an alloy of copper (60%) and zinc (40%).
• Apart from its shiny, metallic appearance, muntz metal is having good
strength
• It is used to make machine parts that require resistance to corrosion.
• It is used in valve stem, brazing rods and architectural works

172. Aluminum bronze
• Copper alloys with aluminum gives aluminium bronze
• 6-10% aluminium and copper respectively
• Aluminium gives alloy lightness while the addition of copper to pure aluminium
increases its strength
• 6% aluminium alloy has a fine gold colour, used for imitation jewellery and
decorative purposes

173. Bearing metals
• Classified into four types
• Copper base bearing metals- copper, tin and lead
• Tin base-tin, antimony and copper
• Lead base- lead, tin and antimony
• Cadmium base- cadmium and nickel

174. White metal bearing alloys (White metal)
• Tin, lead and cadmium predominating elements
• High plasticity combined with low hardness and low melting point
• Facilitates the formation of bearings by casting the metal directly

175. • Copper based alloy harder and stronger than white metal
• Used for heavier pressure resisting bearing
• Tin base white metal- used where bearing are subjected to high pressure and
load
• Cadmium base alloy used for bearing at elevated temperatures and greater
compressive strength
• Lead base alloy- 80% lead and 20% antimony

176. Destructive testing
• Destructive testing (often abbreviated as DT) is a test method conducted to find
the exact point of failure of materials, components, or machines.
• During the process, the tested item undergoes stress that eventually deforms or
destroys the material.
• Naturally, tested parts and materials cannot be reused in regular operation after
undergoing destructive testing procedures.

188. Hardness
• A material’s ability to withstand friction, essentially abrasion resistance, is
known as hardness.
• The term hardness, thus, also refers to local surface stiffness of a material
or its resistance to scratching, abrasion, or cutting.
• Hardness is measured by employing such methods as Brinell, Rockwell, and
Vickers, which measure the depth and area of a depression by a harder
material, including a steel ball, diamond, or other indenter.
• The commonly used units for hardness measurement are:
• Brinell Hardness Number (HB)
• Vickers hardness number (HV)
• Rockwell hardness number (HRA, HRB, HRC, etc)

190. • In Brinell test, a steel ball of 10 mm diameter is used as an indenter to create an
impression on the test piece to calculate its Brinell hardness number.
• The ball is held in place for a predetermined time, usually 30 seconds, and a force
is applied on the ball. This force will vary depending on the test metal being
measured.
• On removal of the indenter, the dent is observed with a low-power microscope
and the size is calculated by taking the average of the measurements at right
angles.

191. • Rockwell hardness test is the most commonly used method for indentation
hardness measurements. The value of Rockwell hardness is accompanied by the
scale used.
• Depending on the material being tested, an appropriate scale must be selected.
This hardness scale gives information on the type of indenter-load combination
used
• The most commonly used scales are “B” and ”C”.

223. Non destructive testing methods
Non destructive testing (NDT) is an important testing method used in the quality
control of the material.
A material is subjected to these testing methods to check for any flaws or defects
and to ensure that the product conforms to the best quality
In this method the testing of component is done without damaging it so that it can
be used in future.

224. Advantages
• The equipments are easy to handle
• Defects are detected without damaging the components
• Methods are quick and accurate
• Non expensive
• Less skill required

226. Basic principle
❖Application of testing medium to the product to be tested
❖The changes in the testing medium due to the defects in the structure of the
product
❖A means by which it detect these changes
❖Interpretation of these changes to obtain information about the flaws in the
structure of the product

227. Methods of NDT
• Dye/ fluorescent penetrant test
• Radiographic test-X-ray test, r-ray test
• Magnetic particle test
• Ultrasonic test
• Crystallographic test

228. Dye/ fluorescent penetrant test

229. Introduction
✓One of the most widely used ndt method
✓Used to detect surface or subsurface cracks and defects
✓Used to inspect almost any material provided that its surface is not extremely
rough
✓It is used for surface detection of forging, casting and weld elements

230. Process
• Cleaning and drying of surface (applying cleaner)
• Application of penetrate (dye)
• Removal of excess of penetrate
• Application of developer

233. Advantages
• High sensitivity to very small cracks
• Large areas and large volumes of parts inspected very rapidly and at low cost
• Indications are produced directly on the surface of the part (visual representation
of flaw)
• Relatively inexpensive
• Portable

234. Limitation
• Only surface defects can be detected
• Inspector must have direct access to the surface being inspected
• Surface finish and roughness can affect inspection sensitivity
• Post cleaning is required
• Chemical handling and proper disposal is required

235. Radiographic test
• It is method of finding defects or flaws in a material by using the ability of short
wavelength electromagnetic radiation (high energy photons) to penetrate various
materials
• It is nothing but to take the shadow picture of an object onto a film by the
passage of X-ray or Gamma ray through it

240. • The part to be inspected (Test material) is placed between the radiation source
and a sensitive film.
• If the material is sound or flawless, entire rays (either X-rays or Gamma rays) pass
through the material very evenly.
• But if the material contains any flaw (or flaws), then some of the rays which will
pass through the flaws will get absorbed to some extent due to the change in the
density.
• The rays which will not encounter any flaw will remain intact and will pass
through the material evenly. These rays are finally made to fall on a light-sensitive
film placed on the backside of the material being inspected.

241. • The defects possess lesser density than the sound parent metal, hence they
transmit radiation (either X-rays or Gamma rays) much better than the sound
metal does.
• Hence the film appears to be darker at the area exposed by the defects

242. X-ray radiography

243. • X-rays are produced by an X-ray tube, which is an evacuated tube (usually made
of glass) and it contains an electrically heated filament and a tungsten anode.
• The electrically heated filament releases electrons which are made to hit on the
tungsten anode. Due to the collision of high-velocity electrons with the tungsten
anode, X-rays are emitted.

244. Gamma ray radiography

245. • Gamma rays are produced by radioactive isotopes. The nucleus of a radioactive
isotope remains unstable. Commonly used isotopes for industrial radiography
are:
• Cobalt 60 (Co 60)
• Iridium 192 (Ir192)
• Caesium-137 (Cs137)
• A lead or tungsten alloy container of sufficient thickness is used containing the
gamma-ray source (300 mg). Such containers are used to provide the necessary
protection.

246. limitations
• Possible health hazard
• Need to direct the beam accurately
• Film processing and viewing facilities are necessary
• Not suitable for surface defects

247. Applications
• Detection of internal defects
• Detection of porosity, casting, lack of fusion in welding, cracks
• For measurement of geometric variation and thickness of
components

248. Magnetic particle test
• This method is suitable for detection of surface and near surface discontinuities
in magnetic material mainly ferrite steel and iron.

249. Principle of MPT

251. Steps in MPT
• Component precleaning
• Introduction of magnetic field ((using permanent magnet/electro magnet or
flowing electricity through specimen)
• Application of magnetic media (dry particles or particles suspended in liquid)
• Intrepretation of magnetic particle indications

255. Ultrasonic testing
• Ultrasonic testing (UT) comprises a range of non-destructive testing
(NDT) techniques that send ultrasonic waves through an object or material.
• These high frequency sound waves are transmitted into materials to characterize
the material or for flaw detecting.
• Most UT inspection applications use short pulse waves with frequencies ranging
from 0.1-15 MHz, although frequencies up to 50 MHz can be used.

256. Principle of ultrasonic testing
• Ultrasonic waves are introduced in to a material where they travel in a straight
line and at a constant speed until they encounter a surface
• At surface interfaces is some of the wave energy is reflected and some is
transmitted.
• The amount of reflected or transmitted energy can be detected and provides
information about the size of the reflector
• The travel time of the sound can be measured and this provides information on
the distance that the sound has travelled

259. Through-transmission testing uses an emitter to send the ultrasound waves from one
surface and a separate receiver to receive the sound energy that has reached the opposite
side of the object.
Imperfections in the material reduce the amount of sound that is received, allowing the
location of flaws to be detected.

261. Limitations
• Requires experienced technicians for inspection and for data interpretation
• Objects that are rough, irregularly shaped, very small or thin, or not
homogeneous are difficult to inspect
• Loose scale or paint will need to be removed before testing can commence,
although clean, properly bonded paint can be left in place

262. Applications
• Aerospace
• Construction
• Automotive
• Rail
• Medical
• Oil and gas industries

263. Crystallographic test
• Crystallography is the experimental science of determining the arrangement of
atoms in crystalline solids
• Crystallographic methods now depend on analysis of the diffraction patterns of a
sample targeted by a beam of some type. X-rays are most commonly used; other
beams used include electrons or neutrons.
• X-ray crystallography (XRC) is the experimental science determining the atomic
and molecular structure of a crystal, in which the crystalline structure causes a
beam of incident X-rays to diffract into many specific directions

264. X-ray diffraction
• X-rays were discovered by William Roentgen, who called them X-rays because it
was unknown at that time.
• They are short wavelength electromagnetic radiations produced by the
decleration of high energy electrons in the inner orbital of atoms
• X-rays are produced by cathode ray tubes which are filtered to monochromatic
light and concentrated on a sample
• The interaction of incident ray with sample produce constructive intereference
when condition satisfy Bragg’s law.

265. The path difference between ray 1 and ray 2 = 2d sin θ
For constructive intereference nλ = 2d sin θ

266. • The variable distance d is the distance between atomic layers in the crystal
• λ is wavelength
• n is integer
• θ is angle of incidence
• This Bragg’s law is the basis of X-ray diffraction that is used to study the structure
of solids
• This can provide information on unit cell dimension

268. • To get the diffraction pattern from all parts of crystal, the primary beam must
strike the crystal form many different direction
• This is achieved by rotating the crystal in the beam during the experiment
• The diffracted spots are recorded either on a film or by an electronic detector
feed the signals directly in a digitized form into a computer. Several diffraction
spots are collected
• All diffraction methods are based on generation of X-rays in a X-ray tube. These X-
rays are directed at the sample and diffracted rays are collected.

270. Powder method

273. Scanning electron microscopy
• Scanning electron microscope are scientific instruments that uses a
beam of energetic electrons to examine object on a very small scale.
• It was developed due to the limitation of light microscope
• It was developed for seeing the internal structures of cells (10000X
magnification)
• The first instrument was developed in 1938, the technology involve
scanning the beam of electrons across the sample.

274. • Scanning electron microscope is a type of electron microscope that images a
sample by scanning it with high energy beam of electrons in a raster scan pattern
• The electrons interact with the atoms that make up the sample producing signals
that contain information about the sample’s surface topography, composition and
other properties such as electrical conductivity.

276. • When the specimen is bombarded with electron beam, electrons are ejected
from the atoms of the specimen surface
• Inelastic scattering, place the atoms in excited state and excited atoms want to
returns to ground state giving off excess energy
• Resulting electron vacancy is filled by an electron from a higher shell

283. • Application
• In addition to topographical, morphological and compositional information, a
Scanning Electron Microscope can detect and analyze surface fractures, provide
information in microstructures, examine surface contaminations, reveal spatial
variations in chemical compositions, provide qualitative chemical analyses and
identify crystalline structures.
• SEMs can be as essential research tool in fields such as life science, biology,
gemology, medical and forensic science, metallurgy.

284. Advantages
• Advantages of a Scanning Electron Microscope include its wide-array of
applications, the detailed three-dimensional and topographical imaging and the
versatile information garnered from different detectors.
• SEMs are also easy to operate with the proper training and advances in computer
technology and associated software make operation user-friendly.
• This instrument works fast, often completing SEI, BSE and EDS analyses in less
than five minutes. In addition, the technological advances in modern SEMs allow
for the generation of data in digital form

285. limitation
• The disadvantages of a Scanning Electron Microscope start with the size and cost.
• SEMs are expensive, large and must be housed in an area free of any possible
electric, magnetic or vibration interference.
• Maintenance involves keeping a steady voltage, currents to electromagnetic coils
and circulation of cool water.
• Special training is required to operate an SEM as well as prepare samples.

286. Module 4

287. Heat treatment
• Heat treatment is the process of series of operations involving heating and
cooling of metals in solid state
• Its purpose is to change a mechanical property or combination of mechanical
properties so that the metal will be more useful, serviceable and safe for definite
purpose
• By heat treating, a metal can be harder, stronger and more resistant to impact
• Heat treatment can also make a metal stronger and more ductile

288. • Defined as the controlled heating and cooling of metals for the primary purpose
of altering their properties (strength, hardness, machinability, toughness)

289. Objectives of heat treatment

294. • It refers to a heat treatment in which material is exposed to an elevated
temperature for an extended time period and then slowly cooled .
• When the part is allowed to cool in the furnace , it is called an annealed heat
treatment
Annealing

302. Process annealing

305. • Isothermal annealing is used to achieve a more homogeneous microstructure
within the steel and is faster and less expensive than full annealing. It is typically
performed on hypoeutectoid steels and it is usually not performed on
hypereutectoid steels
• When isothermal annealing is used in continuous production lines for small parts
or for parts with thin cross-sections, it is called ‘cycle annealing’.

312. Quenching process
• Quenching is a type of metal heat treatment process. Quenching involves the
rapid cooling of a metal to adjust the mechanical properties of its original state.
• To perform the quenching process, a metal is heated to a temperature greater
than that of normal conditions, typically somewhere above its recrystallization
temperature but below its melting temperature.
• The metal may be held at this temperature for a set time in order for the heat to
“soak” the material. Once the metal has been held at the desired temperature, it
is quenched in a medium until it returns to room temperature.

313. Quenching media
It is the medium with which the cooling is done
It affects the rate of cooling and influence the properties of the material
There are a variety of quenching media available that can perform the quenching
process.
Each media has its own unique quenching properties

314. • The important quenching media are
• Air- slow rate
• Oil-more uniform, less internal stress
• Water- inexpensive, convenient to use, rapid cooling
• Brine-5-10% salt added in water, slightly faster than water

315. Tempering

316. Surface hardening

330. Induction hardening
• Induction hardening is a process where material is hardened by means of
induction heating and subsequent quenching in water.
• Induction hardening is a process used for the surface hardening of steel and other
alloy components
• Applications include hardening bearing races, gears, pinion shafts etc.

331. Principle

333. TTT diagram
• Also known as isothermal transformation diagram
• They are plots of temperature vs time
• It is different from Fe-C diagram that it provides details of influence of cooling
rate on the formation of different structures
• It graphically describes the cooling rate required for the transformation of
austenite into different structures

336. Pearlite

337. Bainite

340. Martensite

342. • Austempering

344. Martempering
• Martempering is also known as stepped quenching or interrupted quenching.
• In this process, steel is heated above the upper critical point (above the transformation
range) and then quenched in a salt, oil, or lead bath kept at a temperature of 150-300 °C.
• The workpiece is held at this temperature above martensite start (Ms) point until the
temperature becomes uniform throughout the cross-section of workpiece.
• After that it is cooled in air or oil to room temperature. The steel is then tempered.
• In this process, Austenite is transformed to martensite by step quenching, at a rate fast
enough to avoid the formation of ferrite, pearlite or bainite

349. Heat treating furnace
• Furnaces which are used for heat treating metals may be classified into
1. Hearth furnace
2. Bath furnace
Heat treatment involves raising the metal to a correct temperature in a furnace
heated by various methods
The fuel may be coke, coal, gas, electricity etc.
Electric furnace are simple, economic, precision of temperature control and highly
efficient

350. Hearth furnace
• Heating may be gas, oil or electricity
• Two type of hearth furnace
• Stationary hearth
• Movable hearth

351. Stationary hearth furnace
• Consist of rectangular structure of steel lined with fire bricks.
• One end is provided with a movable door also lined with fire bricks
• Also known as box type or batch type furnace
• Classified into 4
1. Direct fuel fired: used in all temp range. Metal is heated in direct contact with
products of combustion of fuel. Used in annealing steel castings and heating
steel for forging
2. Indirect fuel fired: used in temp range upto 1100oC. Separate heating and
combustion chamber for work piece. Reduced scaling and contamination

352. • Muffle furnace: muffle made from suitable refractory is a permanent part of the
furnace and contains all the work space. The hot gas surround the heating
chamber but do not enter it. Used in tool rooms for heat treatment of dies and
special tools to avoid scaling, decarburization and other compositional changes

353. • Recirculation furnace: used for tempering, toughening and stress relieving in the
temperature ranges below 723oC.
• In this furnace, the fuel, gas or oil is burned in a chamber and products of
combustion are circulated through work space by a suitable arranged centrifugal
fan and baffling

354. Movable-hearth furnace
• 2 types
• Car bottom furnace: in the car bottom furnace, excluding the bottom, the
furnace is similar in shape to a fixed hearth furnace. The charging and discharging
of a large heat treating furnace is done most conveniently by mounting the
hearth on a car which can be moved from the furnace for loading and unloading.
• Rotary hearth furnace: used for hardening, tempering and carburising process.
The furnace structure is a refractory-lined shell that encloses a rotating hearth.
The materials are charged as individual pieces or as small pieces in trays through
the door. Do not require much floor space

356. • Car Bottom Furnace is one of the most versatile and widely used industrial
furnaces because:
• They can be easily loaded or unloaded from either side
• Work is loaded in baskets, or in stacks of various sizes and items
• They can handle very high load weight and large work piece sizes
• They can accomplish multiple processes such as stress relief, quench and
normalize

357. Bath furnace
• Liquid bath often used for heating steel in the heat treatment processes.
• They are cylindrical and consist of sheet steel casing lined with insulating bricks
faced with refractory material. This forms the heating chamber
• The material which serves as heating media are usually salt, lead and oil
• Heating may be gas, oil or electricity

358. • Externally heated bath furnaces are used for quenching and tempering upto
700oC.
• The immersed electrodes salt bath furnace are used for preheating, carburizing
and hardening between 700oC to 1000oC electrodes immersed in liquid bath
decompose the liquid salt on passing alternating current.
• Salt Bath: filled with salt or mixture of different salts which melt when heated
and so form a liquid heating medium.
• The workpiece is inserted into the liquid and heat of the liquid raises the
temperature to the required point
• Salt used should be non corrosive

359. • Common salts are sodium and potassium chloride, nitrates and cyanides
• Mixed in various proportion in temp range from 180 to 1000oC
• Lead bath: here a pot made of cast steel filled with lead, here lead used is pig
lead
• Low melting point 327oC it is raised to temp upto 1285oC and used effectively in
that temp range. Used for hardening of files, broaches, reamers, drill etc.
• Major advantage is that uniform temp can be obtained

362. NATURAL POLYMERS
SEMI SYNTHETIC POLYMERS
SYNTHETIC POLYMERS

363. LINEAR POLYMERS
BRANCHED CHAIN POLYMERS
CROSS LINKED CHAIN POLYMERS

364. Mechanism of polymerisation
• The process of linking together of monomers is called polymerization. The need
to start with the process of polymerization lies on the necessity of breaking the
double bond (C=C) of the monomer.
• Polymerization mechanism are of two types
• Addition polymerization
• Condensation polymerization

365. Addition polymerisation
• This polymerization is of simple form.
• When a large number of single molecule are chemically added together to
increase the average molecule size without wastage, process of addition
polymerization takes place.
• It takes place by 3 steps
• Initiation
• Chain propagation
• Termination

368. Condensation polymerisation
• It is defined as the process of linking together of unlike monomers accompanied
by splitting of a small molecule.
• This process usually requires a catalyst
• In comparison to addition reaction in which a simple molecular summation
occurs, condensation reactions result in splitting out of simple nonpolymerizable
molecules eg water which are considered to be by-product of the process.
• Thus when phenol and formaldehyde monomers are polymerised, water is
released and the resulting product is polymerised phenol formaldehyde, more
commonly known as Bakelite

385. Thank you