Welcome toPresentation on

Mechanics of Materials

By:

BALAJI Y S Assistant Professor,

Department of Mechanical Engineering,Nagarjuna College of Engineering and

Technology.

Module – IFerrous and non ferrous materials:

Properties, Composition and uses of

• Grey cast iron

• White cast iron

• Malleable iron,

• SG iron and

• Steel,

• Copper alloys-Brasses and Bronze

•Aluminium and its alloys

•Al-Si,

•Al-Zn alloys.

Classification of SteelsSteels are classified in several ways, some of them are

i) Carbon Content:

1)Low , Medium and High carbon Steels

2) Hypo eutectoid steels(< 0.8% C)

3) Hyper eutectoid steels (>0.8% C)

ii) Method of Manufacture

1) Bessemer steel 2) Open-hearth Steel

3) Electric furnace steel 3) Crucible Steel

iii) Applications of Steel

1) Machine steel 2) Spring steel

3) Boiler steel 4) Structural steel

4) Tool steel

iv) Chemical Composition1) Plain Carbon steels 2) Alloy steels

v) Standard Institutes

1) AISI-American iron and steel institute

2) BIS- Bureau of indian standards

3) SAE- Society of Automotive engineers.

4) ASTM- American Society for Testing & Materials

Plain Carbon SteelsLow Carbon Steel Among all steels low carbon steel is largely produced.

The characteristics of low carbon steels are

i) Composition: upto 0.25%C

i)Microstructure: Predominantly alpha-ferrite and small quantities of pearlite.

ii) Properties: Relatively soft and weak but outstanding ductility and

toughness.

They posses very good machinability and weldability eg. Mildsteel

iv) Advantages: Least expensive to produce

v) Disadvantages: Unresponsive to hardening heat treatment because

martensite is difficult to form owing to very low carbon content. Strengthening

can be accomplished only by cold working, very low hardenability.

vi) Applications: Automobile body parts, Structural shapes,

buildings,bridgesand small cans.

Medium Carbon Steel

The characteristics of Medium carbon steels are

i) Composition: 0.25% to 0.55%C

i)Microstructure: alpha-ferrite and Pearlite.

ii) Properties: Stronger than low carbon steel and less tougher than it.

iv) Advantages: Best range for adding alloying elements.

Good mix of strength and ductility.

vi) Applications: Railway wheels and tracks, gears, crankshafts and other machine

parts.

High Carbon Steel

The characteristics of High carbon steels are

i) Composition: from 0.55%C upto 2.1%C

i) Microstructure: Cementite and Pearlite when (>0.8% C), alpha-ferrite and Pearlite

when(< 0.8% C)

ii) Properties: Hardest, strongest and least ductile when compared with low and

medium carbon steels

iv) Advantages: Best range to make tool steels.

v) Disadvantages: Cannot be used for operations where ductility and malleability are

required.

vi) Applications: Knives, razors, hacksaw blades, high strength wire etc.

Alloy Steels:Steels which acquire some characteristic properties due to addition of alloying

elements other than carbon, are known as alloy steels.

Some of the reasons for adding alloying elements to steels are

1) Increase hardenability

2) Improve strength at ordinary temperature

3) Improve wear and corrosion resistance

4) Improve mechanical properties at either high or low temperatures

5) Improve toughness without greatly sacrificing strength

Types of Alloy Steels:

Alloy steels may be divided into four classes

1) Structural Steels

2) Tool and Die Steels

3) Magnetic steels

4) Stainless and Heat-resisting steels

Effect of alloying elements on steelsAlloying elements that are added to steel may be classified according to the way they

affect the principal phases of steel i.e., α-ferrite, iron carbide and austenite.

i) Elements which tends to form carbides: These elements combine with carbon to form carbides

just like iron forms iron carbide. These carbides tremendously increase the hardness

and wear resistance of the steels but at the same time render them brittle.

Eg.; Chromium, tungsten, titanium, vanadium, molybdenum, manganese etc.

ii) Elements which tend to graphitize carbon: These elements when added to steels oppose the

formation of carbides where carbon is in the combined form but instead stabilizes

carbon to occur in its free form as graphite.

Eg.: Silicon, cobalt, aluminium, nickel etc.

iii) Elements which tend to stabilize austenite: These elements when added lowers A ₃

temperatures and raises the peritectic point, thereby increasing the range in which

austenite is stable.

Eg.: Manganese, nickel, cobalt, copper etc.

iv) Elements which tend to stabilize ferrite: These elements are most soluble in α-iron than in γ-

iron. Hence they are ferrite stabilizers.

Eg.: Chromium, tungsten, molybdenum, silicon etc.

Some of the elements are present in more than one group and it means that they have more than

one effect.

Stainless steels or Chromium Steels:

Excellent corrosion resistance, heat resistance and aesthetic properties have made

stainless steel an outstanding material for both industrial and domestic purposes.

Corrosion resistance is majorly due to presence of chromium in them. Corrosion

resistance may be enhanced by using nickel and molybdenum as well.

stainless steels are divided into three classes on the basis of the predominant phase

present in there microstructure

i) Ferritic stainless steel

Microstructure: Predominantly α-ferrite

Composition: 11.5%-27% Chromium, 0.08 - 0.2% Carbon, 1% manganese, 1%

nickel, rest iron

Properties- Magnetic, heat and corrosion resistant, can be hardened and

strengthened only by strain hardening because they are not heat treatable.

Applications: Valves(Automotive), automotive exhaust components, combustion

chambers etc.

ii) Austenitic stainless steel

Microstructure: Predominantly austenitic(even at room temperature)

Composition: 16%-26% Chromium, 6%-22% nickel, 0.05 - 0.25% Carbon, 2-

4% molybdenum, rest iron

Properties: Non-Magnetic, heat and corrosion resistant, can be hardened and

strengthened only by strain hardening because of low carbon

Applications: Chemical and food processing equipment, cryogenic vessels,

welding construction, kitchen utensils.

iii) Martensitic stainless steel

Microstructure: Predominantly Martensitic

Composition: 11.5%-18% Chromium, 0.05 - 0.25% carbon, 1.25%-2.25%

nickel,0.75-1% molybdenum, rest iron.

Properties: Magnetic, heat and corrosion resistant, Heat-treatable, high strength

and hardness, wear resistant.

Applications: Cutlery, rifle barrels, jet engine parts, bearings, surgical tools etc.

Cast IronCast irons are the alloys of iron and carbon where the carbon content varies from

2.1% to 6.67%. High carbon content makes cast iron brittle. Most commercially

available cast iron contains carbon varying from 2.1 to 4%.

Characteristics of Cast Iron are

1) Lower melting point(About 300°C lower than pure iron)

2) Low Shrinkage and Good fluidity

3) Ease of casting

4) Cast irons are low in ductility therefore they cant be rolled, drawn or worked.

5) Cast irons are brittle and have low strength compared to steels.

According to iron carbon equilibrium diagram, the phases that are observed in the

microstructure of cast iron at room temperature are α-ferrite and cementite, which

occur at equilibrium conditions. But cementite being a metastable compound,

under certain circumstances, decomposes to form α-ferrite and graphite.

Types of Cast Iron:Cast Irons are classified according to their microstructure. Other words cast

irons are classified according to the shape of the free carbon(graphite) present in their

microstructure or absence of carbon itself.

1) Grey cast iron

2) White cast iron

3) Malleable cast iron

4) Nodular or S.G. iron or Ductile iron

Cast irons are also classified according to carbon content-

1) Hypo eutectic cast iron (between 2.1 and 4.3%C)

2) Hyper eutectic cast iron (between 4.3 and 6.67%C)

In all cast irons apart from carbon , silicon is also a principal alloying element.

Gray Cast Iron:Gray cast irons are most widely used types of cast irons. They are distinguished by the presence

of graphite in the from of flakes(like fibers). Gray cast irons can be divided into different types

based on the average length of flakes in them. The general characteristics of gray irons are:

Composition : 2.5% - 4% carbon, 1% - 3% silicon, rest iron

Microstructure: α-ferrite and flake graphites

Properties: High fluidity, very high compressive strength, very effective in damping

vibrations, low cost.

Fracture Surface: Greyish, blackish surface when fractured.

Applications: Pressure vessels, cylinder heads, pistons, clutch plates, base structure for

machines and heavy equipment that are exposed to vibrations, valves,

fittings, levers.

White Cast Iron:White cast irons are those alloys which are hypo eutectic in composition and an exception

among cast irons. This is because all the carbon present in them are in the combined form as

cementite and pearlite as against the free carbon (graphite) form present in other cast irons.

White cast iron is also an intermediate stage for producing malleable iron.

Composition : 1.8% - 3.2% carbon, 0.3% - 1.8% silicon, rest iron

Microstructure: iron carbide(light phase), pearlite(dark phase)

Properties: very hard and brittle, highly wear resistant, no ductility and malleability, not

machinable

Fracture Surface: Whitish surface.

Applications: Liners for cement mixers, ball mill, certain types of drawing dies, extrusion

nozzels etc.

Malleable Cast Iron:Malleable cast irons are those alloys where almost all the carbon is in free form in the shape of

irregular particles known as temper carbon. As the name suggests they are extremely malleable,

and are produced by heat treatment of white cast iron.

Composition : 1.8% - 3.2% carbon, 0.3% - 1.8% silicon, rest iron

Microstructure: α-ferrite matrix + dark graphite rosettes.

Properties: Highly malleable, very good machinability, good magnetic properties, wear

resisitance

Applications: Connecting rods, transmission gears, flanges, pipe fittings, differential cases

for automotive industry, valves, parts for rail roads and marine works.

Malleable cast iron is obtained by heat treating white iron for a prolonged period that causes

decomposition of cementite into graphite.

Heat treatment : two satges- isothermal holding at 950° C and then holding at 720° C.

Graphite forms in the form of rosettes in a ferrrite or pearlite matrix

Reasonable strength and improved ductility(Malleable)

Spheroidal Graphite (SG)Iron:S G iron is characterized by the presence of free carbon in the shape of compact spheroids or

nodules. S G iron is also very well known for its ductility. Hence it is also called as nodular iron

or ductile iron.

Composition : 3% - 4% carbon, 1.6% - 2.8% silicon, rest iron, very low percentage of

phosphorous and sulphur

Microstructure: α-ferrite matrix + dark graphite nodules.

Properties: Highly ductile, very good machinability, good creep properties at elevated

temperatures, high corrosion resistance.

Applications: Flywheels, furnace doors, wrenches, lathe chucks, motor frames and pump

bodies etc.

Non-Ferrous AlloysSteels and cast irons are consumed in exceedingly large quantities due to

1) Wide range of mechanical properties

2) Ease of fabrication

3) Very economical to produce.

Some of the limitations of steels and cast iron are

1) A relatively high density

2) A comparatively low electrical conductivity

3) Susceptibility to corrosion in some common environments.

Therefore, for many applications it is advantageous or even necessary to use non

ferrous alloys rather than ferrous alloys in order to have more suitable property

combinations and overcome the limitations.

Among non ferrous materials, the bulk of them are made up of alloys of copper,

aluminium, magnesium, nickel, tin, lead and zinc. Other non ferrous metals and

alloys that are used to a lesser extent include cadmium, molybdenum, cobalt,

zirconium, berylium, titanium, tantalum and the precious metals like gold, silver

and the platinum.

CopperCopper is one of the earliest metals discovered by man.

The boilers on early steamboats were made from copper.

The copper tubing used in water plumbing in Pyramids was found in

serviceable condition after more than 5,000 years.

The Properties of copper that are most important are

1) Cu is a ductile metal. Pure Cu is soft and malleable, difficult to machine.

2) Very high electrical conductivity — second only to silver.

3) Copper is refined to high purity for many electrical applications.

4) Excellent thermal conductivity — Copper cookware most highly regarded

— fast and uniform heating.

5) It is non magnetic, has a pleasing color, can be welded, brazed and

soldered and easily finished.

Electrical and construction industries are the largest users of Cu.

MODULE-1Question Bank

1) Classify the different types of steels.

2) Compare plain carbon steels with respect to composition,

microstructure, properties and applications.

3) Explain the effect of alloying elements on properties of steel

4) Classify stainless steels and compare them with respect to

composition, microstructure, properties and applications.

5) Compare Grey cast iron, white cast iron, malleable cast iron and

S. G. Iron, with respect to composition, microstructure, properties

and applications.

6) Write the short notes on aluminium and its alloys.

7) Write the important properties of copper.

8) Write a note on i) Brass ii) Bronze

9) Classify cast iron and write the properties of cast iron.

10)Explain the composition, properties and uses of any four non

ferrous alloys.