MECHANICAL WORKING

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MECHANICAL WORKING
ZUBAIR AHMAD UNITED GULF STEEL
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• Rolling (Hot/Cold)

Mechanical Working
Permanent Deformation


Mechanical Working Is a permanent deformation to
which metal is subjected to change its shape
and/or properties.
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Steel Mechanical Properties
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Microstructure
Steel Mechanical Properties
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Basic Metallurgy
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Basic Metallurgy
Iron is so important that primitive societies are
measured by the point at which they learn how to
refine iron and enter the iron age!
Gold is for the mistress . silver for the maid
Copper for the craftsman cunning at his
trade. "But Iron Cold Iron is master of them
all ! Rudyard Kipling, 1910
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Basic Metallurgy
Iron

• Strong material
• Easy to shape
• Conduct heat and electricity
• Unique magnetic properties
• Iron is plentiful (5 of the Earth's crust)
• Relatively easy to refine

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Basic Metallurgy
Iron ores are rocks that contain a high
concentration of iron

• Hematite - Fe2O3 - 70 iron
• Magnetite - Fe3O4 - 72 iron
• Limonite - Fe2O3 H2O - 50 to 66 iron
• Siderite - FeCO3 - 48 iron

Hematite
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Basic Metallurgy
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Basic Metallurgy
Crystal Structure(Atomic Arrangement)
Space Lattice A collection of points that
divided space into smaller sized segments.
Unit Cell A subdivision of the lattice that
still retains the overall characteristics of the
entire lattice.
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Basic Metallurgy
Formation of Polycrystalline Material
Solid (Unit Cell)
Liquid
a
b
Grain Boundaries
c
d
Grain Boundary The zone of crystalline mismatch
between adjacent grains. The lattice has
different orientation on either side of the grain
boundary
a) Small crystalline nuclei
b) Growth of Crystals
c) Irregular grain shapes formed upon completion
of solidification
d) Final grain structure
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Grain Boundary
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Basic Metallurgy
Atomic Packing in Iron (Allotropic)
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Basic Metallurgy
Body Centered Cubic (BCC)
Squared Packed Layer
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Basic Metallurgy
Face Centered Cubic (FCC)
Close Packed Layer
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Basic Metallurgy
Effect of the Atomic Packing in Deformation
Behavior
Displacement
High Dense Atomic Packing
Displacement
Low Dense Atomic Packing
Slip occurs easily on closest packed plane (high
atomic packing density) along the closest packed
direction where the slip distance is minimum.
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Basic Metallurgy
Effect of the Atomic Packing in Deformation
Behavior
Smooth Surface
Easy to slip with minimum power
Example of closed Packed planes
Uneven Surface
Relatively high energy is required for limited
slip
Example of squared packed plans
Rough Surface
Extremely hard to slip
Example of squared packed plans with high
inter-atom spaces
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Basic Metallurgy
STEEL IRON Alloying Elements ( C Mn, Si,
Ni, )
What is the difference between STEEL and CAST
IRON ?
IRON lt 2 Carbon STEEL
IRON gt 2 Carbon CAST IRON
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Basic Metallurgy
Solid Solution

• Solid Homogenous Mixture of Elements with at
  least One Metal
• Solute Dissolves in Base Metal
• No Visible Signs of Presence
• Structure Metallic Characteristics as those of
  Base Metal
• Hardness Increases with Solution
• Distortion of Lattice Structure

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Basic Metallurgy
Solid Solution Hardening
Interstitial Atoms
Small solute atoms (e.g. Carbon in Iron) that sit
in the space between parent atoms.
Substitutional Atoms
Large solute atoms (e.g. Tin in Iron) that occupy
the same sit as the parent atoms.
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Iron Carbon Phase Diagram
0.5
Peritectic
Eutectic
Eutectoid
Cementite (Fe3C) Pearlite
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Basic Metallurgy
Atomic Packing in Iron (Allotropic)
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Basic Metallurgy
0. 8 C
0. 5 C
0 C
0.2 C
0. 7 C
0.35 C
1.2 C
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Basic Metallurgy
Fundamental Mechanical Properties

• Strength
• Ability to withstand loads (Tensile
  Compressive Strength)
• Ductility
• Ability to deform under tensile loads without
  rupture
• Bending Ability
• Ability to bend without Fracture
• Toughness
• Ability to absorb energy in shock loading
  (Impact Strength)
• Hardness
• Resistance to penetration
• Weldability
• Ability to be welded without cracking

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Basic Metallurgy
Effect of Alloying Elements
Carbon (C)
? Strength Hardness ? Ductility,
Malleability Weldability
Silicon (Si)
De-oxidizer, ? Strength, Hardenability Impact
Strength
Manganese (Mn)
De-oxidizer, ? Strength Toughness ?
Hardenability
Strong De-oxidizer, ? Grain Refinement ? ?
Strength Toughness
Aluminum (Al)
Sulfur (S)
Harmful ? Ductility, Weldability Strength
Impact Strength
? Grain Refinement ? ? Strength,
Hardenability Toughness
MAE (V, Ti Nb)
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Stress Vs - Strain
Basic Metallurgy
Stress Force per unit area Measuring the
internal resistance of the body.
s F/Ao
Strain Unit deformation Measuring the change in
dimensions of the body
e (L1 Lo)/Lo
Force (F)
F
L1
Lo
L1
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Stress Vs - Strain
Basic Metallurgy
P Elastic Limit Y Yield Point S Max. Load
Value B Breaking Point
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Elastic Plastic Deformation
Basic Metallurgy
Elastic Deformation Deformation of a material
that recovered when the applied load is removed.
This type of deformation involves stretching of
the bonds without permanent atomic displacement.
Plastic Deformation Permanent deformation of a
material that is not recovered when the applied
load is removed. This Type of deformation
involves breaking of a limited number of atomic
bonds.
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Basic Metallurgy
Microstructural Defects
Theoretical yield strength predicted for perfect
crystals is much greater than the measured
strength. The existence of defects explains the
difference.
Which is easier to cut?
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Basic Metallurgy
Braking all atomic bonds at once requires grater
energy in perfect crystal
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Basic Metallurgy
Microstructural Defects

• 1) Point defects a) vacancies, b) interstitial
  atoms, c) small substitional atoms, d) large
  substitional atoms, etc.

2) Surface defects Imperfections, such as grain
boundaries, that form a two-dimensional plane
within the crystal.
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Basic Metallurgy
Microstructural Defects

• 3) Line defects dislocations (edge, screw,
  mixed)

Dislocation A line imperfection in the lattice
or crystalline material
They are typically introduced into the lattice
during solidification of the material or when the
material is deformed.
Movement of dislocations helps to explain how
materials deform. Interface with movement of
dislocations helps explain how materials are
strengthened.
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Basic Metallurgy
Motion of Dislocation
When a shear stress is applied to the dislocation
in (a), the atoms displaced, causing the
dislocation to move one step (Burgers vector) in
the slip (b). Continued movement of the
dislocation eventually creates a step
(deformation) direction (C)
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Thank You