Classification

of

Engineering Materials

WINTER :2021

SEM-3^RD

PREPARED BY : ER.B.S. MOHANTA

INTRODUCTION

• Materials are an important aspect of engineering design and analysis.

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• The importance of materials science and engineering can be noted from the fact that historical ages have been named after materials

• There is a wide variety of materials available which have shown their potential in various engineering fields ranging from aerospace to house hold applications.

• The materials are usually selected after considering their characteristics, specific application areas, advantages and limitations.

Classification of Engineering Materials

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METALS & ALLOYS

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Metals

polycrystalline consisting of a great number of fine crystals

Possess low strength

Do not have the required properties

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Alloys

are produced by melting or sintering two or more metals or metals

and a non-metal together.

Faceted glass objects are sometimes called crystals!

Classification of Materials

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• Materials used in the design and manufacture of products

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• Plastics
• Wood
• Composites
• Ceramics
• Metals
• Fabrics

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Acrylic lens

Balsa wood model

Layers of polycarbonate, aluminium & acrylic

Tungsten carbide tool bit

Steel, aluminium

Linen, cotton, nylon, Kevlar

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Classification of Engineering Materials –

Classification of Metallic Materials -

Classification of Steels

Ferrous Material - Steels

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– Low Carbon (<0.25 wt% C)

– Medium Carbon (0.25 to 0.60 wt% C)

– High Carbon (0.6 to 1.4 wt% C)

• Steels - alloys of iron-carbon.

- May contain other alloying elements.

• Low Alloy

(< 10 wt%)

– Stainless Steel (>11 wt% Cr)

- Tool Steel

•High Alloy

Low Carbon Steel

 Plain carbon steels - very low content of alloying elements and small amounts of Mn.

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 Most abundant grade of steel is low carbon steel – greatest quantity produced; least expensive.

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 Not responsive to heat treatment; cold working needed to improve the strength.

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 Good Weldability and machinability

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 High Strength, Low Alloy (HSLA) steels - alloying elements (like Cu, V, Ni and Mo) up to 10 wt %; have higher strengths and may be heat treated.

Medium Carbon Steel

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 Carbon content in the range of 0.3 – 0.6%.

 Can be heat treated - austenitizing, quenching and then tempering.

 Most often used in tempered condition – tempered martensite

 Medium carbon steels have low hardenability

 Addition of Cr, Ni, Mo improves the heat treating capacity

 Heat treated alloys are stronger but have lower ductility

 Typical applications – Railway wheels and tracks, gears, crankshafts.

High Carbon Steel

Stainless Steels

Main Types of Iron�

1. Pig iron

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• Cast iron

(A) White cast iron

(B) Gray cast iron

(C) Malleable cast iron

(D) Ductile cast iron

(E) Meehanite cast iron

(F) Alloy cast iron

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3. Wrought iron

PIG IRON

- Pig iron acts as the raw material for production

of all kinds of cast iron and steel products.

- It is obtained by smelting (chemical reduction of

iron ore in the blast furnace.

- It is of great importance in the foundry and in steel making processes.

- The charge in the blast furnace for manufacturing pig iron is :-

(a) Ore - Consisting of iron oxide or carbonate associated with earth impurities.

(b) Coke - A fuel

(c) Limestone - A flux

Approximate composition of PIG IRON

Carbon — 4 to 4.5%

Phosphorus — 0.1 to 2.0%

Silicon — 0.4 to 2.0%

Sulphur — 0.4 to 1.0%

Manganese — 0.2 to 1.5 %

Iron — Remainder

Classification of Cast Iron -

Cast Iron

• alloy of iron and carbon
• obtained by re-melting pig iron with coke, limestone and steel scrap in a furnace known as cupola.
• The carbon content in cast iron varies from 1.7% to 6.67%.

Grey cast iron

grey in color

It contains:

C = 2.5 to 3.8%.

Si = 1.1 to 2.8 %

Mn = 0.4 to 1.0%

P = less than 0.15%

S = less than 0.1%

Fe = Remaining

White cast iron

White in color

C = 3.2 to 3.6%

Si = 0.4 to 1.1 %

Mg = 0.1 to 0.4%

P = less than 0.3%

S = less than 0.2%

Fe = Remaining

Ductile cast iron

Carbon = 3.2 to 4.2%

Silicon = 1.0 to 4.0 %

Magnesium = 0.1 to 0.8%

Nickel = 0.0 to 3.5%

Manganese = 0.5 to 0.1%

Iron = Remaining

Cast Iron

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• Wide range of applications (including pipes, machine and car parts, such as cylinder heads, blocks and gearbox cases) due to:
• low melting point,
• good fluidity,
• relatively easy to cast,
• excellent machinability,
• resistance to deformation
• wear resistance
• Cast iron tends to be brittle, except for malleable cast irons, so shaping these by deformation is very difficult.

Cast iron coated with durable porcelain enamel distributes heat slowly and evenly.

Grey Cast Iron

Grey cast iron is named after its grey fractured surface that occurs when the graphitic flakes deflect a passing crack and initiate many new cracks as the material breaks.

• graphite flakes surrounded by α-ferrite or pearlite matrix
• weak & brittle in tension (the graphite flake tips are sharp; act as stress raisers)
• stronger in compression
• excellent vibrational dampening
• wear resistant

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Applications of Grey Cast Iron :-

(i) Machine tool structures such as bed, frames, column etc.

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(ii) Household appliances etc.

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(iii) Gas or water pipes for under ground purposes.

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(iv) Rolling mill and general machinery parts.

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(v) Cylinder blocks and heads for I.C. engines.

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(vi) Frames of electric motor.

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(x) General machinery parts.

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