METALS

Composition and MicrostructureFerrous Metals and AlloysNon-Ferrous Metals and AlloysSpecifications and Proof TestingCorrosion

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

Structure of Metals

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

Different from Covalent and Ionic Bonds

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

Interstitial Alloy

Between atomic lattice location < 60% of the size of the lattice atomsonly a small % can fit interstitiallyFor Transition metals only a few fitH, B, C, N

Substitutional Alloy

Replacing elements in the lattice+ 15% radius of lattice atomslarge percentage is possible

Alloys may contain both interstitial and substitutional elements

Forming a Crystalline Structure

Liquid: large degree of disorderFreezing Point: order begins to formGrain Initiation: initiation energySolidification: ordered lattice structures formGrain Boundary: separate lattices collide FCC:BCC or FCC:FCC with different angle

Forming a Crystalline Structure

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

Introduction to Steel

ProductionCommercial Forms ApplicationsMicrostructureStrengthening MechanismsCorrosion

Metal Processing

Crushing and Calcining, or SeparationExtraction 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

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

Refining the Metal

Refining the Metal oxidizing impurities distillation chemical agents electrolysis

Iron Production

Blast Furnace Reduces iron

ore to metal Separates

metal from impurities

Molten Iron Slag

Processing of Virgin Steel

1) first step in reducing iron ore,2) separates impurities3) absorbs carbon (leaves 2.5 - 4.5

% carbon)

End product is cast in bars, "pigs".

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.

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.

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.

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

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 presentAlloys with greater than 1.7 percent carbon become very brittle and hard, i.e. cast iron properties.

Phase Diagrams

Phase Diagrams relate the composition & temperature to the crystalline structure (“phase”)

Inverse Lever Law determines the percentage of each

crystalline phase

Two Component (Binary) Phase Diagram for completely soluble elements or compounds

0 10 20 30 40 50 60 70 80 90 100Percent A by weight

Tem

pera

ture

, °C Melting

Temperature of ALiquid

Solid

Liquid + Solid

100 90 80 70 60 50 40 30 20 10 0Percent B by weight

Components Melting Temperature of B

Two Component (Binary) Phase Diagram: Ni - Cu

1000

1100

1200

1300

1400

1500

1600

1700

0 10 20 30 40 50 60 70 80 90 100Percent Ni by weight

Te

mp

era

ture

, °C 1455°C

Liquid

1084°CSolid

Liquid + Solid

Liquidus Line

Solidus Line

Nickel - Copper Alloy

100 90 80 70 60 50 40 30 20 10 0Percent Cu by weight

Binary Phase Diagram for insoluble elements or compounds

Tem

pera

ture

. °C

Liquid + A

Liquid A + B

Solid A + B

Composition of A Composition of

B

Liquid + B

Actual atomic form will dependon the composition of formation(will discuss later for steel)

DefinitionsEutectic Reaction –

Eutectic Point –

Eutectic Solid –

Water - NaCl Phase Diagram

-30

-25

-20

-15

-10

-5

0

5

10

15

0 5 10 15 20 25 30

Weight Percent NaCl

Tem

pera

ture

. °C

Ice + Brine

Liquid – Brine (Water + Dissolved NaCl)

Ice + Salt

Salt + Brine

23.3%-21 oC (-5.8°F)

Eutectic Point

Binary Phase Diagram for partially soluble elements or compounds

Tem

pera

ture

. °C

Liquid

Solid

Eutectic Point

Composition of A Composition of

B

Liquid + Liquid

Lead-Tin Phase Diagram

0

50

100

150

200

250

300

350

0 10 20 30 40 50 60 70 80 90 100

Percent Tin

Tem

pera

ture

, °C

61.9%19.2% 97.5%

183°C

327°C

232°CLiquid

Liquid + Liquid

Definitions

Eutectoid Reaction –

Eutectoid Point –

Eutectoid –

Steps to Analyzing a Phase Diagram1. Determine the phase/phases present at the point

(composition vs. temperature)

2. 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.

3. The intersection of the horizontal line and a line on the phase diagram defines the composition of the solution.

A Point with 2 Phases

4. 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.

Inverse Lever LawInverse 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.

Ph

ase

I R

eg

ion

(e

.g.

Solid

)

Ph

ase

II R

eg

ion

(e.g

. Li

qu

id)

State Point

Phase I + Phase II Region(e.g. Solid + Liquid)

x yMass percentage of Phase I in the two-phase region:y/(x+y)

Mass percentage of Phase IIIn the two-phase region:x/(x+y)

Example: Ni-CuFor 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

Example: Ni - Cu

1000

1100

1200

1300

1400

1500

1600

1700

0 10 20 30 40 50 60 70 80 90 100Percent Ni by weight

Te

mp

era

ture

, °C

Liquid

Solid

Liquid + Solid

Nickel - Copper Alloy

100 90 80 70 60 50 40 30 20 10 0Percent Cu by weight

State Point 53% Ni, 47 % Cu

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

Phase diagram for Fe-C

Pearlite: combination of ferrite and cementite

structures intermediate property structure

Austinite: solid state gamma phase iron-carbon

combination.

Phase Diagram for C-Fe

Microstructure

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

Grain Size

Time-Temperature-Transition Curves

Critical Temp.

Coarse Pearlite

Fine Pearlite

Bainite

Martinsite

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

Heat Treatments

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

Mild Steel Grades

A992 “Low Alloy” Carbon Steel <0.23% 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.....

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

Corrosion

Oxidation of metal requires oxygen, water, two different metals connected

electrically electrolyte

Corrosion

Major problem with steelControl Methods Protective Coatings Galvanic Protection Cathodic Protection Corrosion-resistant Steels

S-N Curve

00.10.20.30.40.50.60.70.80.9

1

%Fy

10 1000 100000

Number of Cycles to Failure

Strengthening Mechanisms

AlloyingHeat TreatingCold Working

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

Heat Treatments

Full AnnealingProcess AnnealingNormalizingQuenching

Cold Working

Plastic deformation Done below recrystallization temperature

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 > 0.200

Forms of Steel

Structural Shapes Wide flange sections, Channels, Tubing, Plate

Reinforcing SteelCold Rolled forms, pans, sheetPipe

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

Applications

Structural MembersBolts, ConnectorsReinforcementToolsMachines

Steel Grades ASTM Physical Reqmnts Chemical Reqmnts Comments Grade A36 Low Carbon Structural Steel 36

8”=20% Fu=58-80 <.26C <.40Si Mn, P, S, Cu General purpose A 500 Cold Form Tubing w/ maximum perifery of 1.6 m; t <16mm 50

2”=21% Fu>60 <.30C (Mn, P, S, Cu) General Purpose A 572 High-Strength Low-Alloy Columbium (Nb)-Vanadium (V )Steel 42

8”=20% Fu=60 <.21C <1.35Mn Si,P,S,V,Nb Rivet, Bolt, Weld Building&Bridge

50 8”=18% Fu=65 <.23C <1.35Mn,Si Rivet, Bolt, Weld

Building&Bridge 60

8”=16% Fu=75 <.26C <1.35Mn,Si Rivet, Bolt Bridge; Weld Building

65 8”=15% Fu=80 <.26C <1.35Mn,Si Rivet, Bolt Bridge;

Weld Building; A 588 High-Strength Low-Alloy Structural Steel (Weathering Steel) 50 A 615 Billet Reinforcing Steel 60

8”=8% Fu=90 A 616 Rail Reinforceing Steel 60

8”=4.5%

Fu=90 <.C