Ut P5 (Product Tech.)

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UT Product TechnologyUT Product Technology


Product TechnologySteel Production

Wrought Production

Extrusion

Forging

Rolling

Casting Welding

Defects Inherent

Processing

Service

Heat Treatment


2 Stage Process• Iron ore is reduced into pig iron assisted

by other materials.• Carbon content of Pig Iron is lowered by

reacting with oxygen• The molten metal is then cast into Ingots

or continuously cast• Ingots are rolled into Blooms, Billets or

Slabs

Steel Production


1st Stage • Iron ore is reduced into pig iron assisted by

other materials.

• Raw materials Hematite (Fe2O3)orMagnetite(Fe3O4) +CokeLimestone Air

Steel Production


1st Stage

Blast furnace reactions

Steel Production

• Fe2O3 + 3CO = 2Fe + 3CO2

• Fe2O3 + 3C = 2Fe + 3CO

• SiO2 + 2Cao = 2CaOSiO2

Lime from limestone combines with impurities (mainly silica) in the ore to form fluid slag


Blast Furnace

Charge• Ore 4000• Limestone 800• Coke 1800• Air

8000

14600

Steel Production

Products• Pig Iron 2000• Slag 1600• Dust 200• Furnace gas

10800

14600


Blast FurnaceSteel Production

Product of Blast Furnace - Pig iron (>3% carbon)


Steel Production

• Pig iron converted to steel by blowing molten metal with oxygen or oxygen rich gases

• Oxygen reacts with excess carbon

• C + 2 O CO2

• C + O CO

• CO + O CO2


Steel Production• Bessemer

• Open hearth process

• Basic oxygen process


Steel Production• Basic oxygen process

Solid scrap



Molten Pig Iron



Oxygen lance



Steel


Steel ProductionMolten steel poured into large molds (ingots)

Ingots are used for further processing

Hot top


Steel Production

Molten steel poured into large molds (ingots)

Ingots are used for further processing

2 types of mould - Narrow end up, Wide end up


Steel Production• Metal solidifies from outside inwards

3 types of crystal formed

• Chill or fine exui-axed• Columnar

• Large equi-axed


Smelting Defects

• Pipes

• Shrinkage

Primary pipe/sink

Secondary pipe


Smelting Defects

• Non-metallic inclusions


Smelting Defects

• Segregation of metals


Steel Production• Alternative to ingots is Continuous casting

Tundish

Mold forming slab

Water spray chamber

Rollers


Steel Production


Steel Production

Advantages of Continuous casting

• Faster : 300 tons of steel in 45 mins compared to 12 hours

• No piping problems

• Cheaper :No ingot molds, handling


Product Technology

Casting


Casting Process

• Liquid metal is caused to fill a cavity and solidify into a useful shape

• All materials used in metal manufacture cast at some time


Casting Process

• Stage 1 : A pattern of the finished item slightly over sized

• Stage 2 : Mould constructed from the pattern

• Stage 3 : Liquid metal poured through the channels to fill the mould


CastingRiserPouring

basin

Runner

Sprue

Core


Casting

Chaplets Chills


Casting• Casting involves the solidification from liquid to solid

• Solidification proceeds from outside to centre

• Solidification involves shrinkage


Grain Growth


Casting Methods• Sand casting


Sand Casting


Casting Methods

• Sand casting

• Die casting / Injection moulding


Die Casting

Injection piston

Casting cavity

Die Fixed platenMoving platen


Casting Methods

• Sand casting

• Die casting / Injection moulding

• Investment casting / Lost wax process


Investment Casting

Wax Pattern


Investment Casting

Coat with refractory slurry


Investment Casting

Reinforce with plaster backing (Investment)


Investment Casting

Oven dry to liquify or vaporise pattern and dry mould


Investment Casting

Pour metal


Investment Casting

Remove investment material


Choice of Casting Method

Dimensional Accuracy• Investment casting• Die casting• Sand casting

Cost• Sand casting• Die casting• Investment casting


Casting Defects

• Shrinkage cavities

• Sinks

Primary pipe/sink

Secondary pipe


Casting DefectsBlowholes and porosityBlowholes and porosity

Cross-sectional changes /corners


Casting Defects

• Inclusions

• Scabs

• Fins


Casting DefectsShrinkageShrinkage


Casting DefectsScabsScabs


Casting DefectsScabs- Scabs- part of mould stuck to the castingpart of mould stuck to the casting


Casting DefectsFinsFins

Gaps


Casting DefectsFins- Fins- excess metal of castingexcess metal of casting

Fin


Casting Defects

• Hot tears The larger section cools slower than the

smaller section

The grain are different between the sections

Hot Tears


Hot Tears


Chills are used for:

1. Directional grain growth

2. Uniform cooling rate


Casting Defects

• Segregation


Product Technology

Wrought Production Methods


Wrought Production

• Forging

• Extrusion

• Rolling


Wrought Production

Forging• Metal confined under

pressure to cause plastic flow

Extrusion• Metal forced through

a die under a large load

Rolling• Thickness reduction

through compression


Rolling

Two-High Reversing Mill

Ingots, slabs and billets rolled to produce long length products with uniform cross section

PRIMARY ROLLING PROCESS / COGGING


Rolling


PRIMARY ROLLING PROCESS

Secondary piping


Rolling

Three-High Reversing Mill

SECONDARY ROLLING PROCESS

Lamination


Rolling



Non-metallic inclusion


Rolling



Stringers


Rolling



Segregation of metals


Rolling



Banding


Cold Rolling• Initial rolling hot

• Finishing by cold working

Cluster mill 4 High mill


Rolling

• Bloom - Square c/s 150x150mm minimum• Slab - Rectangular c/s area greater than 14400 mm2 • Billet - Square 50x50 up to 120 x 120mm

• Primary rolling- ingot to blooms and slabs• Secondary rolling - blooms and slabs to plates ,

sheets etc


Forging

Hammer

Anvil

Blacksmith


Forging

6 basic actions

• Upsetting

• Swaging

• Bending

• Welding

• Punching

• Cutting out


Forging

Hammer

(Tup)

Anvil

Blacksmith / Open die forging


Forging• Pressure forging


Forging• Closed die


Extrusion

• Direct

• Indirect

• Impact

• High loads used to shape ferrous and non-ferrous alloys

• Items produced are of uniform cross section


Direct Extrusion

Billet Ram

Die


Indirect Extrusion

Die

Extruded item

Billet


Impact Extrusion

Die

Blank

Punch


Extrusion Defects

• Oxide films (‘Extrusion’ defect)

• Surface cracks

• Grain structure variation


Impact Extrusion


Wrought Production Defects

• Cracks

• Laps

• Seams

• Stringers

• Slugs

• Bursts

• Laminations


Wrought Production Defects• Banding• Excessive flash• Lack of fill• Mismatch• Internal cracking• Mechanical marks


Other Wrought Processes

Drawing

• Material is reduced or changed in profile by pulling through a die

Die

Wire or rod Force


Other Wrought Processes

Drawing

• Material is reduced or changed in profile by pulling through a die

Die

Tube ForceMandrel


Product Technology

Welding


A Weld : Definitions• A union between

pieces of metal at faces rendered plastic or liquid by heat,pressure or both.

BS 499

• A continuous defect surrounded by parent material

NASA


Welds• An ideal weld must give a strong bond between

materials with the interfaces disappearing

To achieve this

• Smooth,flat or matching surfaces

• Surfaces shall be free from contaminants

• Metals shall be free from impurities

• Metals shall have identical crystalline structures


Welding• A union between pieces of metal at faces rendered

plastic or liquid by heat,pressure or both.

BS 499

• Ultrasonics• Electron beam• Friction• Electric resistance• Electric arc

Possible energy sources


Electric Arc Welding

Power supply

Work piece

Electrode

Clamp(Earth)


Electric Arc Welding• Electric discharge produced between cathode and

anode by a potential difference (40 to 60 volts)

• Discharge ionises air and produces -ve electrons and +ve ions

• Electrons impact upon anode, ions upon cathode

• Impact of particles converts kinetic energy to heat (7000o C) and light

• Amperage controls number of ions and electrons, Voltage controls their velocity


Electric Arc WeldingArc Welding Processes• Manual metal arc• Tungsten Inert Gas• Metal Inert Gas• Submerged Arc

Differences between them• Methods of shielding the arc• Consumable or Non-consumable electrode• Degree of automation


Zones in Fusion Welds

• Fusion Zone



• Fusion Zone

• Heat Affected Zone



• Fusion Zone

• Heat Affected Zone

• Parent Material or Base Metal


Joint Design

Butt Weld


Joint Design

Butt Weld

Lap Joint


Joint Design

Butt Weld

Corner Joint

Lap Joint


Joint Design

Butt Weld

Corner Joint

Lap Joint

Edge Weld


Joint Design

Butt Weld

Corner Joint

Lap Joint

T JointEdge Weld


Manual Metal Arc (MMA)Consumable electrode

Flux coating

Core wire

Arc

Evolved gas shield

Parent metal

Slag

Weld metal


Manual Metal Arc Welding

• Shielding provided by decomposition of flux covering

• Electrode consumable• Manual process

Welder controls• Arc length• Angle of electrode• Speed of travel• Amperage settings


Tungsten Inert Gas (TIG)

Non-consumable tungsten electrode

Arc

Parent metal

Weld metal

Gas shield

Filler wire

Gas nozzle


Metal Inert Gas (MIG)

Consumable electrode(filler wire)

Arc

Parent metal

Weld metal

Gas shield

Gas nozzle Reel feed


Submerged Arc

Consumable electrode

Reel feed

Flux feed

Flux retrieval

Parent metal

Weld metal

Slag


Electroslag

Filler wire

Molten flux

Weld metal

Water cooled copper shoes


Welding Defects

4 Crack Types

• Solidification cracks

• Hydrogen induced cracks

• Lamellar tearing

• Reheat cracks

CracksCracks


Welding Defects

Classified by Shape

• Longitudinal

• Transverse

• Branched

• Chevron

CracksCracksClassified by Position

• HAZ

• Centreline

• Crater

• Fusion zone

• Parent metal


Welding Defects

Solidification

• Occurs during weld solidification process

• Steels with high sulphur content (low ductility at elevated temperature)

• Requires high tensile stress

• Occur longitudinally down centre of weld

• eg Crater cracking

CracksCracks


Welding Defects

Hydrogen Induced• Requires susceptible grain structure, stress and

hydrogen • Hydrogen enters via welding arc• Hydrogen source - atmosphere or contamination of

preparation or electrode• Moisture diffuses out into parent metal on cooling• Most likely in HAZ

CracksCracks


Welding Defects

Lamellar Tearing• Step like appearance • Occurs in parent material or HAZ• Only in rolled direction of the parent material• Associated with restrained joints subjected to

through thickness stresses on corners, tees and fillets

• Requires high sulphur or non-metallic inclusions

CracksCracks


Welding Defects

Re-Heat Cracking• Occurs mainly in HAZ of low alloy steels during

post weld heat treatment or service at elevated temperatures

• Occurs in areas of high stress and existing defects• Prevented by toe grinding, elimination of poor

profile material selection and controlled post weld heat treatment

CracksCracks


Welding Defects• Incomplete root penetration

Causes• Too large or small a root gap• Arc too long• Wrong polarity• Electrode too large for joint preparation• Incorrect electrode angle• Too fast a speed of travel for current


Welding Defects• Root concavity

Causes• Root gap too large• Insufficient arc energy• Excessive back purge (TIG)


Welding Defects

• Lack of fusion

Causes• Contaminated weld preparation• Amperage too low• Amperage too high (welder increases speed of travel)


Welding Defects• Undercut

Causes• Excessive welding current• Welding speed too high• Incorrect electrode angle• Excessive weave• Electrode too large


Welding Defects

• Incompletely Filled Groove

Causes• Insufficient weld metal deposited• Improper welding technique


Welding Defects• Gas pores / Porosity

Causes• Excessive moisture in flux or preparation• Contaminated preparation• Low welding current• Arc length too long • Damaged electrode flux• Removal of gas shield


Welding Defects• Inclusions - Slag

Causes• Insufficient cleaning between passes• Contaminated weld preparation• Welding over irregular profile• Incorrect welding speed• Arc length too long


Welding Defects• Inclusions - Tungsten

Causes• Contamination of weld during TIG welding

process


Welding Defects• Burn Through

Causes• Excessive amperage during welding of root• Excessive root grinding• Improper welding technique


Welding Defects• Arc Strikes

Causes• Electrode straying onto parent

metal• Electrode holder with poor

insulation• Poor contact of earth clamp

• Spatter

Causes• Excessive arc energy• Excessive arc length• Damp electrodes• Arc blow


Steel MetallurgySteel- Iron and carbon alloyed with other elements

• Carbon- Strength, hardness, toughness, ductility• Manganese- Strength, hardenability• Silicon - Toughness• Molybdenum- Creep resistance, temper embrittlement• Chromium- Hardness, wear resistance, corrosion• Nickel - Ductility, strength, toughness


Steel MetallurgySteel- Iron and carbon alloyed with other elements

BCC FCC


Steel Metallurgy

Low Stress

Increased Stress

Elastic Deformation

Plastic Deformation


Heat Treatment

• Softening• Hardening• Tempering• Stress Relief

• Post heat treatment performed to improve specific metallurgical or mechanical properties or stress relief

Controlled by• Heating rate• Temperature attained• Time at the elevated temperature• Cooling rate


Heat Treatment900

850

800

750

700

Ar3

Ac1

Ac2

Ac3

Ar1

Ar2

1 2

Minutes to raise temperature by 10 C


Iron Carbide Diagram

Ac3

Ac1

.2 .4 .6 .8 1 1.2 1.4 1.6 1.8 2

Carbon %

1000

900

800

700

600


Iron Carbide Diagram

Ac3

Ac1

.2 .4 .6 .8 1 1.2 1.4 1.6 1.8 2

Carbon %

1000

900

800

700

600

Austenite

Ferrite and Pearlite Pearlite and Cementite

Austenite and Fe3 CAustenite and Ferrite


Heat Treatment

Hardening• Produce hard but

brittle material• Heat to above

transformation range• Cool very quickly

( quench ) in oil, water or brine


Heat Treatment Stress Relief• Relax stresses without significant changes in the metallurgical structure• Heat to 550-650 degrees C• Hold for 1 hour per 25mm thickness• Cool in air


Heat Treatment Full Annealing• Produces very soft low

hardness material for machining or cold work

• Heat to above 910 degrees C

• Hold • Cool very slowly in

furnace• Once reached 680 C ,

cool in air


Heat Treatment Sub Critical Annealing• Spheroidizing produces soft low hardness material cheaper than full anneal• Heat must not rise above 700 degrees C• Hold for recrystallisation to occur• Cool in air


Heat Treatment Normalising• Maintains and improves mechanical properties and modifies grain structure• Heat to above 910 degrees C• Hold • Cool in air


Nature and Origin of Defects

• Inherent

• Processing

• In Service


Heat Induced Defects

• Heat treatment cracks

• Grinding cracks

• Friction induced cracks


In Service Cracks

• Fatigue cracks

• Stress corrosion cracks

• Hydrogen induced cracks

Hydrogen

Cyclic stress

Fatique crack

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