Metallurgy Background

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Metallurgy Background
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Metallurgy Background

• Learning Activities
• Read Handbook pp 90-102
• Look up Keywords
• View Slides
• Read Notes,
• Listen to lecture
• View Demos
• Do on-line workbook

• Lesson Objectives
• When you finish this lesson you will understand
• Phases of mater
• Crystal Structure Crystal Defects
• Phase changes and resulting properties
• Iron Carbon Alloy System

Keywords Phase, Component, Constituent,
Solidification, Cooling Curve, Crystal Structure,
Vacancies,Substitutional Alloy, Interstitial
Alloy, Dislocations, Grain Boundaries, Allotropic
Transformation, phase diagram, ferrite, pearlite,
austenite, cementite
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Structure of Materials

• Phases of Mater
• Crystal Structure
• Phases Changes
• Iron - Carbon Alloy System

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Liquid
Gas
Solid
Solid
Evaporation
Sublimation
Melting
Condensation
Solidification
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AWS Welding Handbook, 8th Ed Vol 1
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Demonstration
Take a moment tonight to observe the
Time-Temperature Curve During Casting
Demonstration found on the Demonstration Page of
the WE300 Website.
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AWS Welding Handbook, 8th Ed Vol 1
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(No Transcript)
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AWS Welding Handbook, 8th Ed Vol 1
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Questions?

• Turn to the person sitting next to you and
  discuss (1 min.)
• Often metallurgist want to know how many atoms
  are shared in any unit cell (e.g. face centered
  cubic unit cell).
• The atoms located on the face share ½ with one
  cell and ½ with the other
• How much of a corner atom is shared in each
  cell?
• Adding up all the partial atoms how many atoms
  are there per unit cell in a face centered cubic
  structure?
• In a BCC structure?

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Imperfections in Crystals

• Point - Vacancies Alloys
• Line - Dislocations
• Surface - Grain Boundaries

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Edge Dislocation
Force
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Screw Dislocation
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Demonstration
Also take some time tonight to link to the
Dislocation-Atom interaction during deformation
Demonstration found on the Demonstration Page of
the WE300 Website
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Grain Boundaries
Metals How to Weld Them, Lincoln Foundation,
1954
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Questions?

• Turn to the person sitting next to you and
  discuss (1 min.)
• A grain boundary is the place where a crystal
  with atoms all aligned in one direction meets
  another crystal with atoms aligned in some other
  direction with a real mismatch at the boundary.
  This boundary can be thought of as a tangled mess
  of dislocations. What happens when a dislocation
  within one of the grains has a force applied and
  it moves into the boundary tangle?

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Equilibrium Arrangement of Iron Atoms in Pure Iron
1534 C 2795 F
(Body Centered Cubic)
Delta ferrite
1390 C 2550 F
(Face Centered Cubic)
Austenite
910 C 1670 F
Ferrite
(Body Centered Cubic)
RT
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Cooling Curve for Pure Iron
Magnetic Transformation
Metals How to Weld Them, Lincoln Foundation,
1954
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Alloying Elements Added to Pure Materials
Substitutional Alloy
Interstitial Alloy
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Phase Diagram When Interstitial Carbon Alloys
with Iron
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Metallurgical Systems

• COMPONENT
• Unit of the Composition Variable of the System

• CONSTITUENT
• Association of Phases in a Recognizably Distinct
  Fashion

PHASE Homogeneous, Physically Distinct, Portion
of a System
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Questions?

• Turn to the person sitting next to you and
  discuss (1 min.)
• If we take a glass of warm water and start to
  dissolve sugar in it, and keep adding sugar until
  no more dissolves, what happens? If we heat it a
  little more what happens?
• If we take warm steel in the austenite phase
  (say at 1700F) and dissolve carbon in it, and
  keep adding carbon until no more dissolves, what
  happens? If we heat it to 2200F what happens?

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EUTECTOID STEEL
Slow Cooling (Equilibrium) From Austenite to Just
Below the Eutectoid Temperature
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Pearlite Growth
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0.02C
0.8C
6.67C
X
X
X
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Garbarz et al, The effect of microalloying on
microstructure and properties of medium and high
carbon ferrite-pearlite steels, Microalloying
95 Conf. Proc., 1995
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Demonstration
Please click on the Pearlite Growth
Demonstration on the Demonstration Page of the
WE300 Website
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Questions?

• Turn to the person sitting next to you and
  discuss (1 min.)
• As the pearlite forms from the very slow cooling
  from the austenite, carbon atoms must diffuse to
  make the lathes. What happens if we cool a
  little faster thus not giving enough time for the
  carbon to diffuse the complete width of the
  lathes?

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Cooling Eutectoid Steel Rapidly To Lower
Temperatures
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Fine Pearlite
Shorter Time Lower Temp
Bainite
Martensite
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Questions?

• Turn to the person sitting next to you and
  discuss (1 min.)
• In the hot water in which we added the maximum
  amoount of sugar in the earlier question, we now
  let it cool, what happens?
• In austenite steel where we cooled it fast and
  the carbon did not have a chance to get out but
  rather formed a supersaturated solution, what
  happens if we just let it set at room
  temperature? What happens if we heat it up just
  a little.