lecture 1 - part ii - engineering materials

ME 140 - WORKSHOP TECHNOLOGY

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Introduction

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ME – 140 WORKSHOP TECHNOLOGYFALL 2009

Instructor

Asst. Prof. Ejaz YaqubAsst. Prof. Rizwan Arshad

Part II – Engineering Materials

echanical & Aerospace Engineering

utics (IAA)

AIR University, E-9 Islamabad

Lecture 1 –

Department of M

Institute of Avionics & Aerona


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• Engineering materials are used to manufacture products

• Type of material decides the kind of manufacturing process that will be used to get the desired shape

• It is important to know what kind of materials are available

• Material Properties - physical, chemical, mechanical, thermal, optical, electrical etc

• A design engineer must have knowledge of engineering materials, their properties and applications to meet the functional requirements of the design product

• Additionally, one must understand the effects of manufacturingprocesses and heat treatment on the properties of the engineering materials

Introduction

Introduction


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Examples of products in different Engg. Materials

[Stainless steel rods, Salem Steel Trading Co, India]

Introduction

[Malleable cast iron pipe fittings, SDH China]

[Pure Aluminum Pellets, EPSI Metals, Oregon, USA]

[Pure Copper wire]


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Examples of products in different Engg. Materials

[Plastic bottles]

Introduction

[A section of yew branch of wood]

[Glass] [Ceramic tiles]


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Materials Classification

Classification


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• Ferrous materials have iron as their main constituent

• Pure Iron is a soft metal having crystalline structure

• Microstructure of pure iron looks like a map having fieldsseparated by hedges

Shape looking like fields - CrystalsLine like hedges - Where crystals join

• Average size of crystal – depends upon the metal treatment

Iron (Fe)

[Schematic diagram. Microstructure of pure iron]

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Crystal

Crystal boundary


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• Iron is found naturally in the form of ores

• Iron ores chiefly exist in the form of oxides and carbonates

• Iron ores are cleaned from earthly impurities before processed for getting iron

Occurrence

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[Main types of Iron Ore]


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Iron Ores

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[Hematite (blood ore) from the US state of Michigan]

[Magnetite from the Kola Peninsula, Russia] [Siderite from Poland]

[Limonite]


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Production of Ferrous Materials

[Diagram showing production of the materials in the iron and steel group]

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Ore

Cupola

Blast Furnace

Reverberatory Furnace

Wrought Iron

CrucibleSteel

ShearSteel

Tool Steel

Cast IronBlister Steel

Pig Iron

BessemerConverter

Open Hearth Electric

Steel for general use

Arc Furnace

High FrequencyFurnace

Smelting, Reduction

Puddling

ForgeRemelt

Remelt


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Main Types of Iron

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Pig Iron

Cast Iron Wrought Iron

Plain Carbon Steels Alloy Steels

Grey cast iron

White cast iron

Ductile cast iron

Malleable cast iron

High speed

Stainless

Dead Carbon steels

Low Carbon steels

Medium Carbon steels

High Carbon steels


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Pig Iron (Carbon Content 3.5% – 4.5%)

• Smelting and reduction of iron ore is carried out to produce pig iron in a tall structure call Blast furnace

• Blast furnace is charged with ore, small quantities of coke and lime stone

• Coke provide fuel – provides heat necessary to reduce iron oxide to iron

• Limestone serves as flux – combines with nonmetallic part to produce slag

• Hot air is blown into lower portion via the tuyeres

• Slag over molten iron is tapped of from the hole and molten iron from hearth

[Blast Furnace]

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• Molten pig iron can be further used in following waysCast in pig bedsCast in pig casting machineTransferred in hot metal ladles direct to an adjacent steelmaking process

• Pig iron acts as the raw material for production of all kinds of cast iron and steel products

Pig Iron (Carbon Content 3.5% – 4.5%)

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[Foundry pig iron. Courtesy: HuiCheng, China]

[Double Strand Pig Casting Machine at Maryland Pig Co..]


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• Grey pig iron (Grades 1, 2 & 3) - soft type of pig iron

Approx. 3% carbon in free form (i.e., graphite form) Approx. 1% carbon in combined form

• White pig iron (Grades 4) - hard and strong

Contains almost all of the carbon in the combined form

• Mottled pig iron (Grade 5) - average hardness and mottled appearance

Between the grey and white pig iron The free and combined forms of carbon are in almost equal proportion in mottled pig iron

Types of Pig Iron (on the basis of combined and free form of carbon)

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• Cast iron is basically an alloy of iron and carbon

• Obtained by re-melting pig iron with coke, limestone andsteel scrap in a furnace known as Cupola

• Carbon content in cast iron varies from 2% – 4.5%

• Impurities of silicon, manganese, phosphorusand sulphur elements are present

• PropertiesVery brittle and weak in tensionLow cost, good casting characteristics,High compressive strength, high wear resistanceExcellent machinability

Cast Iron

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• Obtained by re-melting pig iron with coke, limestone andsteel scrap in a furnace known as cupola

• Coke fire is lit first at the bottom.

• Cupola is charged by adding alternate layers of coke and pig iron along with limestone

• Pig iron is mixed with a set proportion of iron and steel scrap

• Proportion depends upon the desired quality of melt

• When charge has burnt up, the blast is gradually increased and the cupola is closed

• Iron melts and sinks to the bottom of the furnace

Producing Cast Iron

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[A cupola furnace in operation at Wayne State University, in Detroit, Michigan]

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• Grey cast iron is grey in colour due to the carbon being in the form of graphite (C in free form in iron)

• Produced in cupola furnace by refining pig iron

• CompositionC = 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

Grey Cast Iron

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[Typical structure of grey cast iron]


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• Properties

1. When fractured it gives grey color.2. Easily casted3. Easily machined 4. Lowest melting of ferrous alloys.5. High vibration damping capacity.6. High resistance to wear.7. High fluidity and hence can be casted into complex

shapes and thin sections.8. High compressive strength.9. Low tensile strength.10. Low ductility and low impact strength as compared

with steel

Grey Cast Iron

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• Applications1. Machine tool structures such as bed, frames, column2. Household appliances etc3. Gas or water pipes for under ground purposes.4. Man holes covers5. Piston rings6. Rolling mill and general machinery parts7. Cylinder blocks and heads for I.C. engines8. Frames of electric motor9. Ingot mold10. General machinery parts11. Sanitary wares12. Tunnel segment

Grey Cast Iron

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• White color - carbon in combined form as iron carbide • Hardest constituent of iron • Produced by casting against metal chills or by regulating

analysis• The chills are used when a hard and wear resistance surface

is desired for products such as for wheels, rolls crushing jaw,crusher plates

• CompositionC = 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

White Cast Iron

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• Properties1. Freshly broken surface shows a bright white fracture2. Very hard due to carbon chemically bonded with iron

as iron carbide (Fe3C)1. Brittle 2. Excellent abrasive wear resistance3. Extremely hard, therefore it is very difficult to machine4. Solidification range is 2650-2065°F5. Shrinkage is 1/8 inch per foot6. High tensile strength 7. Low compressive strength

White Cast Iron

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• Applications

1. For producing malleable iron castings

2. For manufacturing those component or parts which require a hard, and abrasion resistant surface such asrim of car

3. Railway brake blocks

White Cast Iron

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• Small quantities of magnesium or cerium added to cast iron • Graphite content is converted into spheroidal or nodular

form • It is well dispersed throughout the material

• CompositionCarbon = 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

Ductile Cast Iron

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• Properties1. High fluidity2. Excellent castability, strength, 3. High toughness, excellent wear resistance4. Pressure tightness, 5. Weldability and higher machinability in comparison to

grey cast iron.

Ductile Cast Iron

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[Ductile cast iron (Ferritic matrix), Courtesy: Toa Koki Ko Ltd. Japan]


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[(a) Schematic diagram of spheriodal cast iron (b) Ductile iron microstructure at 100x. Note carbon islanding effect around nodules,

Courtesy: Apex Metal Co Ltd.]

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[Comparison among Grey, White and Spherodidal Cast Iron]

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• A malleable metal is one easily spread or flatten under pressure or hammering

• Produced by White heart and Black heart process

• Name given due to colour of fracture given by castingsproduced by each method

Malleable Cast Iron

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• White heart - Castings consisting of all carbon in combined form

are packed in iron or steel boxes

- These boxes are surrounded with a mixture of new and used haematite ore

- Boxes heated from 900 to 950 deg. C

- Temperature maintained for several days

- During this time part of carbon is oxidised and remainder is dispersed in small specks through out the structure

- Heating period is followed by very slow cooling for severaldays

- Resulting casting is tough and can withstand hard treatmentwithout fracture

Malleable Cast Iron

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• Produced in a reverberatory furnace

• Wrought iron is produced by Puddling process

• Puddling leads to the oxidation of nearly all carbon and otherelements from pig iron

• Furnace hearth is lined with iron oxide, grey pig iron, andand millscale (oxide) are fed into it

• Slag is formed when melting is complete

• Slag is stirred into the melt and more millscale is added

• This leads to the oxidation of carbon and other elements

• After oxidation the iron becomes stiffer and pasty in form

Wrought Iron

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• Assumed approximately as purest iron - 99.5% iron. • Contains a large number of minute threads of slag lying

parallel to each other giving the metal a fibrous appearance when broken.

• Said as a mechanical mixture of very pure iron and a silicate slag.

• Also be said as a ferrous material, aggregated from asolidifying mass of pasty particles of highly refined metalliciron with which a minutely and uniformly distributed quantityof slag is incorporated without subsequent fusion.

• CompositionC = 0.02 – 0.03% P = 0.05 – 0.25% Si = 0.02 – 0.10%S = 0.008 – 0.02% Mn = 0.0 – 0.02% Slag = 0.05 – 1.5%Fe = remainder

Producing Wrought Iron

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[Reverberatory Furnace for producing wrought iron]

Producing Wrought Iron

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The microstructure of wrought iron, showing dark slag inclusions in ferrite (iron)

Wrought Iron

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• Properties1. Easily shaped by hammering, pressing, forging, etc. 2. It is never cast and it can be easily bent when cold. 3. It is tough and it has high ductility and plasticity4. Forged and welded easily. High resistance towards

corrosion.1. It can accommodate sudden and excessive shocks loads 2. High resistance towards fatigue 3. Ultimate tensile strength - 2,500 kg/cm2 - 5,000 kg/cm24. Ultimate compressive strength - 3,000 kg/cm2. 5. Can be elongated considerably by cold working. 6. High electrical conductivity. 7. Melting point - 1530°C. 8. It has elongation 20% in 200 mm in longitudinal direction

and 2–5 % in transverse direction. 1. Its poison’s ratio is 0.30.2. It can be easily formed when cold, without the outer side

cracking at the formed portion.

Wrought Iron

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• Applications

1. Making chains, crane hooks, railway couplings, 2. Water and steam pipes.3. Plates, sheets, bars, structural works etc.

Wrought Iron

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• Alloy of iron and carbon - carbon content max. upto 1.5%

• Upto 1.5 %Carbon occurs in the form of iron carbide having the ability to increase hardness and strength of the steel

• Steels are classified as,• Plain Carbon Steel • Alloy Steels

Steel

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• Dead Mild steel• Carbon content – 0.1 -0.125 %• Applications: wire rod, thin sheets, solid drawn tubes etc.

• Mild Steel• Carbon content – 0.15 – 0.3 % • Applications: boiler plates bridge work, structural sections

• Medium Carbon Steel• Carbon content – 0.3 – 0.5 % • Applications: axles, drop forgings, high tensile tubes

• Carbon content – 0.5 – 0.7 % • Applications: springs, locomotive tyres, , hammers etc

• Carbon content – 0.7 – 0.9 % • Applications: shear blades, wood chisels etc.

Plain Steels

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• High Carbon Steel (Cast Steel, Carbon Tool Steels)

• Carbon content – 0.9 – 1.1 %• Applications: cold chisels, press dies, punches,

screwing dies, wood working tools

• Carbon content – 1.1 – 1.4 %• Applications: razors, hand files, drills, gauges,

metal cutting tools

Plain Steels

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• High Speed Steel (HSS)

• 18% tungsten, 4% chromium and 1 % vanadium, 0.8 carbon and remaining iron.

• Name given since these steels can be operated as cuttingtools at high speeds

• Cutting tool speed is 2 to 3 times higher than HCS cuttingtool

• Steels have the property of retaining their hardness even when heated to red heat

• Generally used for making lathe cutting tools, planner cutting tools, shaper cutting tools, slotting cutting tools,

drills, reamers, broaches, milling cutter and punches.

Alloy Steels

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• Stainless Steel

• Contains chromium together with nickel as alloy and rest is iron

• Minimum chromium content of 12% for film formation

• 18% is sufficient to resist the most severe atmospheric corrosive conditions

Alloy Steels

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lecture 1 - part ii - engineering materials

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