Chapter 2 Mechanical Engineering Materials (22343)

Program: Diploma(Mechanical)
Class: SYME
Course: Mechanical Engineering Materials(22343)
Unit 02: Steel and its Alloys
Lecture 04: Concept of phase, pure metal, alloy and solid
solutions ,Iron Carbon Equilibrium diagram

1. Name of the Trainer :- Prof. S. B. Deshmukh
2. Years of Experience :- 8 Years
3. Domain Expertise :- Mechanical Engineering
www.sandipuniversity.edu.in
Presented By 02
https://www.sandipfoundation.org/
Department Of Mechanical Engineering,Sandip Polytechnic,Nashik

Unit – 2 Steel and its Alloys 03
Topic to be covered
2.1 Concept of phase, pure metal, alloy and solid solutions.
2.2 i Iron Carbon Equilibrium diagram various phases Critical temperatures and
significance ii. Reactions on Iron carbon equilibrium diagram
2.3 Broad Classification of steels
i. Plain carbon steels: Definition, Types and Properties, Compositions and applications
of low, medium and high carbon steels
ii. Alloy Steels: Definition and Effects of alloying elements on properties of alloy steels.iii.
Tool steels: Cold work tool steels, Hot work tool steels, High speed steels(HSS) iv.
Stainless Steels: Types and Applications v. Spring Steels: Composition and Applications
vi. Specifications of steels and their equivalents
2.4 Steels for following: Shafts, axles, Nuts, bolts, Levers, crank shafts, camshafts, Shear
blades, agricultural equipments, house hold utensils, machine tool beds, car bodies,
Antifriction bearings and gears.

Phase, pure metal, alloy and solid solutions. 04
Phase
It is a form of material having characteristics
structure and properties
It is a form of material which has identifiable
composition, structure, and boundaries separating it
from other phase in material volume
Phase equilibrium diagrams assist in the
interpretation of microstructure of metals
Equilibrium diagrams are presented in the form of
temperature versus composition and represent the
interrelationship between phases, temperature and
composition only under equilibrium conditions

Phase, pure metal, alloy and solid solutions. 05
Pure metal
It is a substance that contains atoms of only one type of metallic element, such as
aluminum, gold, copper, Iron, zinc, mercury, lead and zinc
. It is made into an alloy to improve the properties of a pure metal.
Most metals very rarely, if ever, appear in their pure form in nature and instead must
be extracted from a metal ore

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Pure metal

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Alloy
An alloy is a mixture of two or more elements in which the main component is a metal.
The first alloy made by humans was bronze.
Most pure metals are either too soft, brittle or chemically reactive for practical use.
Combining different ratios of metals as alloys modifies the properties of pure metals to
produce desirable characteristics.
The aim of making alloys is generally to make them less brittle, harder, resistant
to corrosion, or have a more desirable color and luster.
Of all the metallic alloys in use today, the alloys of iron (steel, stainless steel, cast iron,
tool steel, alloy steel) make up the largest proportion both by quantity and commercial
value.
Iron alloyed with various proportions of carbon gives low, mid and high carbon steels,
with increasing carbon levels reducing ductility and toughness.

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Alloy
The addition of silicon will produce cast irons, while the addition of chromium, nickel
and molybdenum to carbon steels (more than 10%) results in stainless steels. Examples o
alloys are 22 Carat gold, brass

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Solid solution
A uniform mixture of substances in solid form.
Solid solutions often consist of two or more types of atoms or molecules that share a
crystal lattice, as in certain metal alloys.
Solid solutions are of two types. They are (a) Substitution solid solutions. (b)
Interstitial solid solutions. Steel used in construction, for example, is actually a solid
solution of iron and carbon.

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Iron Carbon Equilibrium diagram various phases
Phase equilibrium diagrams assist in the interpretation of microstructure of metals.
Equilibrium diagrams are presented in the form of temperature versus composition and
represent the interrelationship between phases, temperature and composition only
under equilibrium conditions.
Iron-carbon phase diagram describes the iron-carbon system of alloys containing up to
6.67% of carbon, discloses the phases compositions and their transformations occurring
with the alloys during their cooling or heating.
Carbon content 6.67% corresponds to the fixed composition of the iron carbide Fe3C. It
shows the changes in phase due to change in composition.
Iron in Iron-Carbon equilibrium diagram is soft and ductile & also it is allotropic in
nature. The Lever rule is used to determine composition of various phases in a phase
diagram. In Eutectic reaction in iron carbon diagram no mushy zone is obtained.

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The following phases are involved
in the transformation, occurring
with iron-carbon alloys:
L - Liquid solution of carbon in iron;
δ - Ferrite: Solid solution of carbon
in iron.
Maximum concentration of carbon
in δ-ferrite is 0.09% at 2719 °F
(1493°C) – temperature of the
peritectic transformation. The
crystal structure of δ-ferrite is BCC
(cubic body centered).

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13

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Austenite
Interstitial solid solution of carbon in γ-iron.
Austenite has FCC (cubic face centered)
crystal structure, permitting high solubility of
carbon up to 2.06% at 2097 °F (1147°C).
Austenite does not exist below 1333 °F
(723°C) and maximum carbon concentration at
this temperature is 1.7%.
Martempering & Marquenching permit the
transformation of austenite to martensite,
throughout the cross-section of a component
without cracking or distortion

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α-ferrite
It is the solid solution of carbon in α-
iron.
α-ferrite has BCC crystal structure.
Ferrite is steels is softest and least
strong
It has low solubility of carbon, up to
0.025% at 1333 °F (723°C).
α-ferrite exists at room temperature.

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Cementite
It is the iron carbide,
intermetallic compound, having
fixed composition Fe3C.
Cementite is a hard and brittle
substance, influencing on the
properties of steels and cast irons.
In Iron-Carbon equilibrium
diagram, at 210oCtemperature
cementite is changes from
ferromagnetic to paramagnetic
character.
This phase has a complex
orthorhombic crystal structure

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Pearlite
It is the last phase obtained
after completing heat treatment
cycle in patenting process.
The mixture of α-ferrite and
cementite is called as Pearlite
Bainite
This phase is obtained as the
end product, after complete heat
treatment cycle in austempering
process

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Phase Transformations The following phase transformations occur with iron-carbon
alloys:
As iron starts cooling from it molten state it undergoes changes in phases .At 2912
°F it is in molten state. When it cools it forms delta ferrite, then austenite and finally
alpha ferrite.
Hypoeutectoid steels (carbon content from 0 to 0.83%) consist of primary
(proeutectoid) ferrite and pearlite.
Eutectoid steel (carbon content 0.83%) entirely consists of pearlite.
Hypereutectoid steels (carbon content from 0.83 to 2.06%) consist of primary
(proeutectoid) cementite (according to the curve ACM) and pearlite.
Iron-Carbon alloys, containing up to 2.06% of carbon, are called Steels.
In practice only hypoeutectic alloys are used.
These alloys (carbon content from 2.06% to 4.3%) are called Cast Irons.

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Critical temperatures
Upper critical temperature (point) A3 is the
temperature, below which ferrite starts to form as a result of
ejection from austenite in the hypoeutectoid alloys.
Upper critical temperature (point) ACM is the temperature,
below which cementite starts to form as a result of ejection
from austenite in the hypereutectoid alloys.
Lower critical temperature (point) A1 is the temperature of
the austenite-to-pearlite eutectoid transformation. Below this
temperature austenite does not exist.
Magnetic transformation temperature A2 is the temperature
below which α-ferrite is ferromagnetic.

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Summary
In this lesson, We have learned
Concept of phase, pure metal, alloy and solid solutions ,
Iron Carbon Equilibrium diagram

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Class: SYME
Lecture 05: Broad Classification of steels

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Broad Classification of steels
Steel
An iron base alloy, malleable under proper conditions, containing up to 2% carbon.
Alloys with high proportion of other elements and a relatively small amount of iron,
are also called as steel if the iron and carbon are important influencing elements.
Iron is a major component and primary element in steel. Carbon is the major alloying
element. 90% of the steels produced throughout the world are referred to as carbon
steel.
Pure iron is soft, malleable, and ductile and has very useful property of being
magnetic.
Small amounts of some elements such as manganese, sulphur, silicon, chromium,
molybdenum, phosphorus are also added to steel to improve its properties.

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Steel
Hardness of steel depends on the shape and distribution of the car-bides in iron.
Copper does not impart hardness to steel.
Steel made from phosphatic iron is brittle

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Types of Steel
Steels can be classified by a variety of different systems depending
The composition, such as carbon, low-alloy or stainless steel.
The manufacturing methods, such as open hearth, basic oxygen process, or electric
furnace methods.
The finishing method, such as hot rolling or cold rolling
The product form, such as bar plate, sheet, strip, tubing or structural shape
The de-oxidation practice, such as killed, semi-killed, capped or rimmed steel
The microstructure, such as ferritic, pearlitic and martensitic
The heat treatment, such as annealing, quenching and tempering, and thermo
mechanical processing
Main types are
1.Carbon Steels 2.Alloy Steels 3.Tool Steels 4.Stainless Steels

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I ) Plain carbon steels:
.
The American Iron and Steel Institute (AISI) define carbon steel as follows:
Steel is carbon steel when it is doesn't contain Aluminum, Boron, Chromium, Cobalt,
Columbium, Molybdenum, Nickel, Titanium, Tungsten, Vanadium or Zirconium. Copper
does not exceed 0.40% or when the maximum content specified does not exceed the
percentage noted -Manganese 1.65%,Silicon 0.6%,Copper 0.6%
Carbon steels are different from cast iron as regards the percentage of carbon.
Carbon contains 0.10 to 1.5% carbon whereas cast iron possesses from 1.8 to 4.2%
carbon

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Classification of carbon steels
Carbon steels contain up to 2% total alloying elements and can be subdivided into
according to their carbon content.
1. Low-carbon steels.
2. Medium-carbon steels.
3. High-carbon steels.
Carbon steel can be classified, according to various de-oxidation practices, as rimmed,
capped, semi-killed, or killed steel.
De-oxidation practice and the steelmaking process will have an effect on the
properties of the steel.
Variations in carbon have the greatest effect on mechanical properties.
As carbon percent increased, it increases the hardness and strength of steel.

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a) Low Carbon Steels or mild steel
Characteristics of Low Carbon Steels
It contains up to 0.30% carbon.
Low carbon steels are not hardened appreciably by hardening process of heat
treatment.
A decrease in carbon content improves ductility.
Low carbon steels are not hardened appreciably by hardening process of heat
treatment.
The ultimate tensile strength of low carbon steel by working at a high strain rate will
increase.
Mild steel belongs to the Low carbon steel.
Advantages of Low Carbon Steels
It has good tensile strength.
It has good magnetizing properties.
It can be easily machined, welded or forged.

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Advantages of Low Carbon Steels
It is soft, ductile and malleable.
It has good toughness.
It is cheaper.
It has wide variety available with different properties
It has high stiffness.
Disadvantages of Low Carbon Steels
The corrosion resistance is poor.
So they should not be used in a corrosive environment unless some form of
protective coating is used.
Uses of Low Carbon Steels
Its typical uses are in automobile body panels, tin plate, and wire products
These materials may be used for stampings, forgings, seamless tubes, and
Boiler plate

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Uses of Low Carbon Steels
It is used for rods, steel joints, channels and angles, structural sections, drop forgings.
It is used in motors and electrical appliances

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b) Medium carbon steels
Characteristics of Medium carbon steels
It contains 0.30 to 0.60% carbon.
It is used for machine components requiring high strength and good fatigue
resistance.
Medium steels are stronger than low carbon steels and can be further strengthened
by heat treatment.
It contains manganese from 0.60 to 1.65%.
Advantages of Medium Carbon Steels
It has better ductility.
It has better strength.
It has good wear resistance.
It can be easily machined and forged.
It possesses good formability.

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b) Medium carbon steels
Disadvantages of Medium Carbon Steels
More costly than mild steel.
Uses of Medium Carbon Steels
It is used for making shafts, axles, gears, crankshafts, couplings and forgings.
It is used for railway wheels and rail axles.
It is also used for making Drop forging dies, Die blocks, Set screws, Clutch discs, Plates
punches, Valve Springs, Cushion rings, Thrust washers.

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c) High carbon steels
Characteristics of High carbon steels
It contains 0.7% to 1.5% carbon.
These steels have high hardness and low toughness.
The combination of these properties makes it ideal for bearing applications where wear
resistance is important and compressive loading minimize brittle fracture that might
develop on tensile loading.
Strength to hardness increase with increase in carbon contents.
As the carbon is increased hardness increases and strength starts decreasing.
Advantages of High carbon steels
It has high hardness.
It has high wear resistance.
Compressive strength is highest.
It has fair formability.
It can be magnetized easily.
It can be hardened and tempered easily.

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c) High carbon steels
Disadvantages of High Carbon Steels
It has low impact strength.
These cannot weld easily.
Usually joined by brazing with low temperature silver alloy making it possible to repair
or fabricate tool-steel parts without affecting their heat treated condition.
Uses of High Carbon Steels
It is used for hardness and high tensile strength, springs, cutting tools,
Press tools, and striking dies.
It is used for drills, taps, milling cutters, knives.
It is used for cold cutting dies, wood working tools.
It is used for reamers, tools for cutting wood and brass.
It is used where a keen cutting edge is necessary, razors, saws, and where wear
resistance is important.
High carbon steel is used in transmission lines and microwave towers

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ii) Alloy steels
Steel is a metal alloy consisting mostly of iron, in addition to small amounts of carbon,
depending on the grade and quality of the steel.
Alloy steel is any type of steel to which one or more elements besides carbon have
been intentionally added, to produce a desired physical property or characteristic.
Common elements that are added to make alloy steel are molybdenum, manganese,
nickel, silicon, boron, chromium, and vanadium.
Alloy steel is steel alloyed with a variety of elements in total amounts of between
1.0% and 50% by weight to improve its mechanical properties.
Alloy steel may be classified according to their chemical compositions, structural class
and purpose.

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Purpose of alloying:
Steels are alloyed for-
Strengthening of the ferrite.
Improved corrosion resistance.
Better hardenability
Grain size control
Greater strength
Improved machinability
Improved ductility
Improved toughness
Better wear resistance
Improved cutting ability
Improved case hardening properties etc.
Improved high or low temperature stability.

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Alloy Steel
Advantages of Alloy Steel
It has greater hardenability
It has less distortion and cracking
It has greater ductility at high strength
It has greater high temperature strength
It has greater stress relief at given hardness
It has better machinability at high hardness
It has high elastic ratio and endurance strength.
Disadvantages of Alloy Steel
It has higher cost
It needs special handling
Effect of elements in Alloy steels
Alloying elements are added to achieve certain properties in the material
Alloying elements are added in lower percentages (less than 5%) to increase
strength or hardenability,

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Effect of Various Alloying Elements on Steel
Alloying elements are added in larger percentages (over 5%) to achieve special
properties, such as corrosion resistance or extreme temperature stability
Following are some common alloying elements
Chromium :-
It provides corrosion resistance.
It increases hardenability or the depth to which steel can be hardened.
It adds hardness, toughness and resistance to wear.
Prevent formation of austenite
Nickel
It increases strength and toughness.
It helps to resist corrosion.
Cobalt
Improves cutting ability
Reduce hardenability
Chromium
Nickel
Cobalt

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Nickel
It improves shock resistance.
It increases strength of steels.
Manganese
It is used in steel to produce a clean metal. If manganese exceeds 1.65 -2.10%, the
product is classed as alloy steel.
It increases hardenability and strength.
It also adds to the strength of the metal and helps in heat treating.
It counteracts brittleness from sulphur
It lowers both ductility and weldability if present in high percentage with high carbon
content in steel.
Molybdenum
It adds toughness and higher strengths to steel.
It promotes hardenability of steel.
Manganese
Molybdenum

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Molybdenum
It makes steel fine grained.
It increases toughness.
It increases tensile and creep strength at high temperatures.
It enhances corrosion resistance in stainless steels.
It forms abrasion resisting particles.
They have good creep resistance.
It is used for making high speed steels. It forms stable carbides resulting in fine grain
size.
Tungsten
It is added in the form of tungsten carbide
It gives steel high hardness even at red heats.
It promotes fine grains
It increases heat resistance.
Tungsten

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Tungsten
It increases strength at elevated temperatures.
It is used with chromium, vanadium, molybdenum, or manganese to produce high
speed steel used in cutting tools.
Tungsten steel is said to be "red-hard" or hard enough to cut after it becomes red-
hot.
Vanadium:
It gives steel a fine-grained structure.
It increases toughness.
It is often used in tool steels because of its increased resistance to impact.
It increases hardenability
It increases imparts strength and toughness to heat-treated steel.
It increases shock resistance.
Vanadium:

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Titanium
It is a very strong, very lightweight metal that can be used
alone or alloyed with steels.
It is added to steel to give them high strength at high temperatures.
It prevents formation of austenite in high chromium steels.
It reduces martensitic hardness and hardenability in medium chromium steels.
It is used in modern jet engines used titanium steels.
Phosphorus and Lead
They are added to steel to increase its machinability.
They increase hardness, strength and corrosion resistance.
They improve resistance to atmospheric corrosion.
Sulphur
Lowers the toughness and transverse ductility
Titanium
:
Phosphorus Lead
:
Sulphur

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Silicon
It is often used to increase the resiliency of steel for making springs.
It increases the strength properties especially elastic limit
without loss of ductility.
Increasing silicon increases resiliency of steel for spring applications.
It is used for magnetic circuits in electrical equipments.
It is the principal deoxidizing used in steel making.
It improves oxidation resistance
It strengthens low alloy steels
Niobium
Greatly increases tensile strength of steel.
Only 40 lb of niobium per ton of steel will increase
the tensile strength by 10,000 to 15000 lb/in2.
Silicon
Niobium

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iii) Tool steels
Tool steel refers to a variety of carbon and alloy steels that are particularly well-suited
to be made into tools.
Their suitability comes from their distinctive hardness, resistance to abrasion, their
ability to hold a cutting edge, and/or their resistance to deformation at elevated
temperatures (red-hardness).
Tool steel is generally used in a heat-treated state.
Tool steels are steels that are primarily
used to make tools used in manufacturing
processes as well as for machining metals, woods, and plastics.
Cemented carbide tools are not found to
be suitable for cutting non-ferrous alloys.

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iii) Tool steels
Characteristics Tool steels
It is generally used in a heat-treated state.
It has carbon content between 0.7% and 1.5%.
Tool steels are manufactured under carefully controlled conditions to produce the
required quality.
The manganese content is often kept low to minimize the possibility of cracking
during water quenching.
Advantages of Tool steels
It has good abrasion resistance.
It has good machinability.
It has ability to hold a cutting edge at elevated temperatures.

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iii) Tool steels
Disadvantages of Tool steels
They are brittle, especially at their higher hardness.
It has high cost.
Uses of Tool steels
It is used for stamping dies.
It is used for metal cutting tools.
It is used for injection molding moulds.
Types of Tool steels
1. High speed steel (HSS or HS) :-
The first alloy that was formally classified as high speed steel was introduced in
1910.
Tungsten-type High speed steel grades contains 0.65–0.80% carbon, 3.75–4.00%
chromium, 17.25–18.75% tungsten and 0.9–1.3% vanadium.

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Summary
Carbon Steels
1. Low-carbon steels.
2. Medium-carbon steels.
3. High-carbon steels.
Alloy Steels
Introduction to Tool steels

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Class: SYME
Lecture 06: Types ,Specification & application of steel

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1. High speed steel (HSS or HS)
1.High speed steel (HSS or HS) :-
Characteristics High speed steel (HSS or HS) :-
It is a subset of tool steels.
It includes all molybdenum and tungsten class alloys.
It is usually used in tool bits and cutting tools.
It is often used in power saw blades and drill bits.
It is superior to the older high carbon
steel tools used extensively through the
1940s in that it can withstand higher
temperatures without losing its temper (hardness).
This property allows HSS to cut
faster than high carbon steel, hence the
name high speed steel

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Advantages of High speed steel:-
It has excellent red hardness.
It can be hardened to 62-67 HRC.
It retains cutting ability up to 540°c.
It has good compressive strength.
Disadvantages of High speed steel
It has poor resistance to decarburization.
They are not easy for machining.
It is brittle, snaps before it will bend.

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Uses of High speed steel :-
It is mainly used for manufacture of various cutting tools: drills, taps, milling cutters, too
bits, gear cutters, saw blades, etc.
It is used for punches and dies manufacturing.
It is used making files, chisels, hand plane blades, and high quality kitchen and pocket
knives.
Types of HSS
a)18:4:1 High Speed Steel
It is one of the best known High speed tools steel.
It contains 18% tungsten, 4% chromium and 1% vanadium.
It has excellent red hardness.
It has good compressive strength.
It is used for milling cutters, punches, dies.
It is also used for reamers, broaches, and drills.

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Types of HSS
Types of HSS
b) Tungsten High speed steel.
c) Molybdenum High speed steel.
d) Moly Tungsten High speed steel.
e) Chrome Moly Vanadium High speed steel.
f) Chrome Moly Tungsten High speed steel.
g) Chrome Moly High Vanadium High speed steel.

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Effect of alloying elements on the properties of HSS
Alloying element Effect of alloying elements on the properties of HSS
Carbon
It forms carbides, increases wear resistance, is responsible for
the basic matrix hardness.
Tungsten and
molybdenum
It improves red hardness, retention of hardness and high
temperature strength of the matrix, form special carbides of
great hardness.
Vanadium
It forms special carbides of supreme hardness, increases high
temperature wear resistance, retention of hardness and high
temperature strength of the matrix.
Chromium It promotes depth hardening, produces readily soluble carbides.
Cobalt
It improves red hardness and retention of hardness of the
matrix.

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Types of Tool steels
2. Hot-work Tool Steels :-
Hot-work tool steels include all chromium, tungsten, and molybdenum alloys.
They are typically used for forging, die casting, heading, piercing, trim, extrusion,
and hot-shear and punching blades.
3. Cold-work Tool Steels
Cold-work tool steels include all high-chromium, medium-alloy air-hardening,
water hardening, and oil hardening alloys.
Typical applications include cold working operations such as stamping dies, draw
dies, burnishing tools, coining tools, Pipes for bicycle and shear blades.
Cold rolled steel sheets contain 0.1% carbon

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iv) Stainless Steels
Characteristics of Stainless Steels :-
Stainless steel does not stain, corrode, or rust as easily as ordinary steel, but it is
not stain-proof so called as “Stain-less”.
It is also called corrosion-resistant steel or CRES.
Stainless steel is a generic term for a family of corrosion resistant alloy steels
containing 10.5% or more chromium.
All stainless steels have a high resistance to corrosion.
This resistance to attack is due to the naturally occurring chromium-rich oxide film
formed on the surface of the steel.
Although extremely thin, this invisible, inert film is tightly adherent to the metal
and extremely protective in a wide range of corrosive media.
The film is rapidly self repairing in the presence of oxygen, and damage by
abrasion, cutting or machining is quickly repaired.

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Advantages of Stainless Steels :-
All stainless steels have a high resistance to corrosion.
It resists scaling and maintains high strength at very high temperatures.
It shows exceptional toughness.
The majority of stainless steels can be cut, welded, formed, machined and
fabricated readily.
It is available in many surface finishes.
It is easily and simply maintained resulting in a high quality, pleasing appearance.
The cleanability of stainless steel makes it the first choice in hospitals, kitchens,
food and pharmaceutical processing facilities.
Stainless steel is a durable.
It is low maintenance material.
It has good thermal conductivity.

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Types of Stainless Steels :-
In addition to chromium, nickel, molybdenum, titanium, niobium and other
elements may also be added to stainless steels in varying quantities to produce a
range of stainless steel grades, each with different properties. There are a number
of grades to choose from, but all stainless steels can be divided into following basic
categories:
1. Austenitic Stainless Steels
2. Ferritic Stainless Steels
3. Martensitic Stainless Steels

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Types of Stainless Steels
Types of Stainless Steels :-
1.Austenitic Stainless Steels :-
Characteristics of Austenitic Stainless Steels :-
When nickel is added to stainless steel in sufficient amounts the crystal structure changes to
"austenite".
The basic composition of austenitic stainless steels is 18% chromium and 8% nickel.
Chromium carbide precipitates at the grain boundaries, when austenitic stainless steel is
heated at 900 oC.
Advantages of Austenitic Stainless Steels
It has excellent corrosion resistance in organic acid, industrial and marine environments.
It has excellent weldability (all processes)
It has excellent formability, fabricability and ductility
It has excellent cleanability, and hygiene characteristics
It is non-magnetic (if annealed)

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Disadvantages of Austenitic Stainless Steels :-
These alloys are not hardenable by heat treatment.
Uses of Austenitic Austenitic Stainless Steels
It is used for computer floppy disk shutters.
It is used for computer keyboard key springs.
It is used for kitchen sinks.
It is used for food processing equipment
It is used for architectural applications
It is used for chemical plant and equipment

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2. Ferritic Stainless Steels
Characteristics Ferritic Stainless Steels :-
This group of alloys generally containing only chromium, with the balance mostly iron.
These are plain chromium stainless steels with varying chromium content between 12
and 18%, but with low carbon content.
Advantages of Ferritic Stainless Steels
It has good corrosion resistance.
They are magnetic.
It has good ductility.
They can be welded or fabricated without difficulty.

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Disadvantages of Ferritic Stainless Steels :-
These are not hardenable by heat treatment.
It has poor weldability.
Formability not as good as the Austenitic Stainless Steels.
Uses of Ferritic Stainless Steels
It is used for computer floppy disk hubs.
It is used for automotive trim.
It is used for automotive exhausts.
It is used for colliery equipment.

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3. Martensitic Stainless Steels :-
Characteristics of Martensitic Stainless Steels :-
Martensitic stainless steels were the first stainless steels commercially developed (as
cutlery) and have relatively high carbon content (0.1 - 1.2%) compared to other stainless
steels.
They are plain chromium steels containing between 12 and 18% chromium. Hardness of
lower Bainite (tempered martensite) is about RC 57 & Hardness of martensite is about RC
65.
Hardness of upper Bainite (acicular structure) is about RC48.
Disadvantages of Martensitic Stainless Steels
It has poor weldability.

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Advantages of Martensitic Stainless Steels
It has moderate corrosion resistance
It can be hardened by heat treatment.
Therefore high strength and hardness levels can be achieved.
It is magnetic in nature.
Uses of Martensitic Stainless Steels
It is used for Knife blades
It is used for surgical instruments
It is used for shafts and spindles.
It is used for pins

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v) Spring Steels:
These steels are generally low-alloy Manganese, medium-carbon steel or high-carbon
steel with a very high yield strength.
EN45 is a manganese spring steel.
It is a steel with a high carbon content, traces of manganese that effect the metal’s
properties, and that it is generally used for springs (such as the suspension springs on
old cars).
It is suitable for oil hardening and tempering.
When used in the oil hardened and tempered condition EN45 offers excellent spring
characteristics.
EN45 is commonly used in the automotive industries for the manufacture and repair
of leaf springs.
Untempered EN45 is harder than mild steel, and will not suffer as much from burs or
require as much repair and therefore have a longer life.

67
v) Spring Steels:
Composition:
Carbon, C 0.50 - 0.60 Manganese, Mn 0.70 1.10 Silicon, Si 1.5 2.0 Nickel, Ni
EN45 is used widely in the motor vehicle industry and many general engineering
applications. Typical applications include leaf springs, truncated conical springs, helical
springs and spring plates
Applications of spring steel:
Applications include piano wire (also known as[11] music wire) such as ASTM
A228 (0.80–0.95% carbon), spring clamps, antennas, springs, and vehicle coil springs,
leaf springs, and s-tines.
Spring steel is also commonly used in the manufacture of metal swords for stage
combat due to its resistance to bending, snapping or shattering.
Spring steel is one of the most popular materials used in the fabrication
of lockpicks due to its pliability and resilience.

68
v) Spring Steels:
Applications of spring steel:
Tubular spring steel is used in the landing gear of some small aircraft due to its ability
to absorb the impact of landing.
It is also commonly used in the making of knives, especially for the Nepalese kukri.
It is used in binder clips.

69
vi) Specifications of steels and their equivalents
They are differing in their chemical composition, structure and applications.
Designation: identification of each material class by a number, letter, symbol, name or a
combination,Normally based on chemical composition or mechanical properties
These are classified and designated according to following standards.
AISI- American Iron and Steel Institute
SAE- Society of Automotive Engineers
IS- Indian Standards
Designation of steel on the basis of mechanical properties
These are designated by Tensile or Yield strength. First character “Fe” indicates –Steel.
“E” indicates minimum yield strength.
The examples are:1) Fe 350 - Steel with minimum tensile strength 350 MPa.
2) Fe 410 K - Killed Steel with minimum tensile strength 410 MPa.
3) Fe E 380 - Steel with minimum yield strength 380 MPa.

70
Applications of Steels
Application Steel used
Shafts Mild steel, alloy steel
Axles Chrome-molybdenum steel, carbon steel
Nuts, bolts Carbon steel
Levers, crank shafts, Medium-carbon steel alloys ) 0.55 to 1.0%
Camshafts Carbon steel- en8/en9, alloyed steels
Shear blades High speed tool steel W6Mo5Cr4V2
Agricultural equipments Stainless steel
House hold utensils Stainless steel
Machine tool beds Cast iron
Car bodies Alloy steel
Antifriction bearings Alloy Steel

71
Alloy

72
Alloy

73
Alloy

74
Alloy

75
Summary
Tool steels
Stainless Steels
Spring Steels
Specifications of steels
Applications of Steels

76

Chapter 2 Mechanical Engineering Materials (22343)

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