METALS

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METALS

• Composition and Microstructure
• Ferrous Metals and Alloys
• Non-Ferrous Metals and Alloys
• Specifications and Proof Testing
• Corrosion

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Composition and Microstructure

• Metal element that readily loses electrons to
  form positive ions, characterized by high
  electrical conductivity and malleable
• Alloy combinations of metals in a crystalline
  structure

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Structure of Metals

• Microstructural properties determine all of the
  material properties of metals and alloys.

• Different from Covalent and Ionic Bonds

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Alloying Structure

• 3-D lattice in metalic bonds provides
• opportunity for other element to occupy some of
  the positions.
• or for small element to enter the lattice

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Interstitial Alloy

• Between atomic lattice location
• lt 60 of the size of the lattice atoms
• only a small can fit interstitially
• For Transition metals only a few fit
• H, B, C, N

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Substitutional Alloy

• Replacing elements in the lattice
• 15 radius of lattice atoms
• large percentage is possible
• Alloys may contain both interstitial and
  substitutional elements

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Forming a Crystalline Structure

• Liquid large degree of disorder
• Freezing Point order begins to form
• Grain Initiation initiation energy
• Solidification ordered lattice structures form
• Grain Boundary separate lattices collide
• FCCBCC or FCCFCC with different angle

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Forming a Crystalline Structure

• Grain Structure each grain has its own lattice
  structure (FCC, BCC, HCP).

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Introduction to Steel

• Production
• Commercial Forms
• Applications
• Microstructure
• Strengthening Mechanisms
• Corrosion

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Metal Processing

• Crushing and Calcining, or Separation
• Extraction
• Smelting
• Ore is melted and separated in solution
• Electrolytic processing
• electric furnace or process is used to separate
  metal
• Leaching (liquid processing)
• metal is recovered from leachate

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Ferrous Metals

• principle element is iron, cast iron, steel,
  wrought iron.
• Metals come from ore, "minerals" ore consists of
  metal and gangue (valueless extra)
• Mining
• open pit
• underground

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Refining the Metal

• Refining the Metal
• oxidizing impurities
• distillation
• chemical agents
• electrolysis

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Iron Production

• Blast Furnace
• Reduces iron ore to metal
• Separates metal from impurities
• Molten Iron
• Slag

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Processing of Virgin Steel

• 1) first step in reducing iron ore,
• 2) separates impurities
• 3) absorbs carbon (leaves 2.5 - 4.5 carbon)
• End product is cast in bars, "pigs".

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Ferrous Metals

• Pig Iron
• Iron ore is combined with coke, and limestone
  (fluxing agent). Blasts of hot air are forced
  through the material to ignite the coke and melt
  the iron ore. The impurities in the iron are
  absorbed by the limestone and forms blast furnace
  slag.

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Forms of Ferrous Alloys

• Cast Iron
• cast iron is pig iron is any other shape.
  Remelted and cast into desired shape.
• Malleable Cast Iron
• annealed (heating then slow cooling to encourage
  refined grains and soften mechanical properties,
  removes internal stresses, removes gases) cast
  iron that has been made more ductile and formable.

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Forms of Ferrous Alloys

• Wrought Iron
• a form of iron that contains slag, and virtually
  no carbon. making it workable when it is hot but
  hardens very rapidly when cooled rapidly.
• Ingot Iron
• low carbon steel or iron cast from a molten state.

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Forms of Ferrous Alloys

• Steel
• Iron - Carbon alloy which is cast from a molten
  mass in a form which is malleable. Carbon steel
  is steel with less than 1.5 carbon. Alloy steel
  is steel which has properties controlled by
  elements other than carbon.
• Steel has the best structural properties of these
  materials

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Carbon Steels

• Carbon steels have between .008 and 1.7 percent
  C (most are between 0.1 and 0.8)
• Carbon may be substitutional or interstitial
  depending upon the amount present
• Alloys with greater than 1.7 percent carbon
  become very brittle and hard, i.e. cast iron
  properties.

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Phase Diagrams

• Phase Diagrams relate the
• composition temperature
• to the
• crystalline structure (phase)
• Inverse Lever Law
• determines the percentage of each crystalline
  phase

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Two Component (Binary) Phase Diagram for
completely soluble elements or compounds
Melting Temperature of A
Liquid
Temperature, C
Liquid
Solid
a
Solid
a
Components
Melting Temperature of B
Percent A by weight
0
10
20
30
40
50
60
70
80
90
100
Percent B by weight
100
90
80
70
60
50
40
30
20
10
0
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Two Component (Binary) Phase Diagram Ni - Cu
1700
Nickel - Copper Alloy
1600
Liquid
Liquidus Line
1500
1455C
1400
Temperature, C
1300
Liquid
Solid
a
Solidus Line
Solid
a
1084C
Percent Ni by weight
0
10
20
30
40
50
60
70
80
90
100
Percent Cu by weight
100
90
80
70
60
50
40
30
20
10
0
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Binary Phase Diagram for insoluble elements or
compounds
Liquid A B
Temperature. C
Liquid A
Liquid B
Solid A B
Composition of A
Composition of B
Actual atomic form will depend on the composition
of formation (will discuss later for steel)
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Definitions

• Eutectic Reaction
• Eutectic Point
• Eutectic Solid

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Water - NaCl Phase Diagram
15
10
5
Liquid Brine (Water Dissolved NaCl)
0
-5
Eutectic Point
Temperature. C
-10
Salt
Ice Brine
-15
Brine
-20
-25
Ice Salt
-30
0
5
10
15
20
25
30
-21 oC (-5.8F)
23.3
Weight Percent NaCl
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Binary Phase Diagram for partially soluble
elements or compounds
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Lead-Tin Phase Diagram
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Definitions

• Eutectoid Reaction
• Eutectoid Point
• Eutectoid

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Steps to Analyzing a Phase Diagram

• Determine the phase/phases present at the point
  (composition vs. temperature)
• The mass percentage composition of each phase at
  the point can be determined by the drawing a
  horizontal through the point for the length of
  the entire region.
• The intersection of the horizontal line and a
  line on the phase diagram defines the composition
  of the solution.

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A Point with 2 Phases

• If the point is located in a region with more 2
  phases, the mass percentage of each phase within
  the region can be determined by the inverse lever
  law.

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Inverse Lever Law

• Inverse Lever Law (Derivation on pgs 56 57 of
  text)
• The mass percentage of a phase present in a two
  phase region is the length along the tie line
  portion from the state point to the other phase
  region divided by the total tie line length.
  Compositions are used as a measure of length.

State Point
x
y
Mass percentage of Phase I in the two-phase
region y/(xy) Mass percentage of Phase II In
the two-phase region x/(xy)
Phase I Region (e.g. Solid)
Phase II Region (e.g. Liquid)
Phase I Phase II Region (e.g. Solid Liquid)
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Example Ni-Cu

• For a 1000 kg block of Ni-Cu metal at a defined
  state point of 53 Nickel and 47 Copper at 1300
  oC, determine the following
• Compositions () of both the liquid and solid
  phases
• Mass percentages of the liquid and solid phases
• The mass of Nickel in the Liquid Phase

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Example Ni - Cu
1700
Nickel - Copper Alloy
1600
Liquid
1500
State Point 53 Ni, 47 Cu
1400
Temperature, C
1300
Solid
a
Percent Ni by weight
0
10
20
30
40
50
60
70
80
90
100
Percent Cu by weight
100
90
80
70
60
50
40
30
20
10
0
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Phase diagram for Fe-C

• Cementite
• above 4.35 to 6.67
• very hard and brittle alloy forms
• 6.67 Carbon 93.33 Iron "iron carbide"
• Ferrite
• iron which contains very little carbon. this is
  soft ductile material

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Phase diagram for Fe-C

• Pearlite
• combination of ferrite and cementite structures
• intermediate property structure
• Austinite
• solid state gamma phase iron-carbon combination.

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Phase Diagram for C-Fe
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Microstructure

• Phases of Steel
• Ferrite (BCC)
• Austenite (FCC)
• Cementite (Orthorhombic)
• Delta Iron (BCC)
• Grain Size

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Time-Temperature-Transition Curves

Critical Temp.
Coarse Pearlite
Fine Pearlite
Bainite
Martinsite
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Heat Treatments

• Annealing
• heated above critical temperature and
• cooled slowly
• softens structure
• Quenching
• heated above critical temperature and
• cooled rapidly in water or oil
• improves hardness and strength

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Heat Treatments

• Tempering
• heated below critical temperature,
• held and
• quenched
• improves ductility and toughness
• while retaining hardness

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Mild Steel Grades

• A992 Low Alloy Carbon Steel
• lt0.23 Carbon
• Common Structural Sections
• Replaced A36 steel
• A 572 High-Strength Low-Alloy Columbium-Vanadium
  Steel
• Grades 42, 50, 60, 65
• Structural sections and bolts.....

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Mild Steel Grades

• A 615 Billet Reinforcing Steel
• low alloy, high ductility steel
• reinforcing bars
• A588 Weathering Steel
• should not be used in Cl water environments
• Free from moisture 40 of the time avoid
  extreme humid environments

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Corrosion

• Oxidation of metal requires
• oxygen,
• water,
• two different metals connected electrically
• electrolyte

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Corrosion

• Major problem with steel
• Control Methods
• Protective Coatings
• Galvanic Protection
• Cathodic Protection
• Corrosion-resistant Steels

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S-N Curve
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Strengthening Mechanisms

• Alloying
• Heat Treating
• Cold Working

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Alloying

• Forming Solid Solution with Iron
• Carbon, Chromium, Manganese, Nickel, Copper, and
  Silicon
• Formation of Carbide
• Titanium, Vanadium, and Molybdenum
• Formation of an Undissolved, second phase
• Lead, Sulfur, and Phosphorus

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Heat Treatments

• Full Annealing
• Process Annealing
• Normalizing
• Quenching

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Cold Working

• Plastic deformation
• Done below recrystallization temperature

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Other Properties of Steel

• Impact
• resistance to dynamic loadings (toughness)
• Creep
• time dependent deformation due to sustained loads
• Ductility
• mild steels may yield at ? 0.002 and
• fracture at ? gt 0.200

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Forms of Steel

• Structural Shapes
• Wide flange sections,
• Channels,
• Tubing,
• Plate
• Reinforcing Steel
• Cold Rolled forms, pans, sheet
• Pipe

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Structural Grades

• ASTM
• A36 A 572 (being phased out)
• A992 Structural Shapes
• A325 Bolts
• AISI - SAE
• 10XX
• XX defines Carbon content
• 13XX
• 13 defines a manganese alloy steel

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Applications

• Structural Members
• Bolts, Connectors
• Reinforcement
• Tools
• Machines

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Steel Grades