Chapter 9.
Phase Diagrams_ Equilibrium
Microstructure Development
•
•
•
•
Phase Rule
Phase Diagram
Lever Rule
Microstructural Development During Slow
Cooling
1
Copyright Joseph Greene 2002 All Rights Reserved
Phase Rule
• Phase rule
– Identifies the number of microscopic phases associated with a given state
condition, a set of values for temperature, pressure and other variables that
describe the nature of the material.
• Phase
– Chemically and structurally homogeneous portion of the microstructure.
• Single phase can be polycrystalline (Fig 9-1), but each crystal grain differs only in
crystalline orientation or chemical composition.
• Component
– Distinct chemical substance from which a phase is formed.
• Example, Copper and nickel are so similar in nature that they are completely soluble
in each other in any alloy proportions.
– There exists a single phase (solid solution) with two components.
• Example, Compounds can be components
– MgO and NiO form solid solutions similar to Cu Ni with one phase.
• Example, Two components can form distinct phases each richer in a different
component.
– Perlite structure forms from alternating structures of ferrite and cementite
– Fig 9-2. Ferrite is -Fe with a small amount of cementite in solid solution.
2
Cementite is nearly pure Fe3C. Components are Fe and Fe3C.
Copyright Joseph Greene 2002 All Rights Reserved
Phase Rule
• Degrees of freedom
– Number of independent variables available to the system
• Example, pure metal at its melting point has zero degrees of freedom.
– At this condition, or state, the metal exists only in two phases in
equilibrium, that is solid and liquid phases simultaneously.
– Any change in temperature will change the state of the microstructure
» If temperature is raised, all of the solid phase will melt and become
the liquid state.
» If temperature is lowered, all of the liquid phase will solidify and
become the solid state.
– State (processing) variables to control microstructure
• Temperature, pressure, and composition
– Relationship between microstructure and state variables
• Pressure is very small relationship at most processing conditions
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• Gibbs Phase Rule
Phase Rule
– Relationship between microstructure and state variables
– F = C – P + 1 (Most common equation for most processes)
• F = degrees of freedom, C = number of components, P = number of phases, 1 = state
variable is temperature
– Example, Pure metal at its melting temperature
• C = 1 component, P = 2 phases (solid and liquid),
• F = 1 – 2 + 1 = 0 Degrees of freedom is zero. This means we can change the two
phases (solid and liquid) by varying the temperature.
– Example, metal with a single impurity at its melting point, solid and liquid
phases can usually coexist over a range of temperatures.
• C = 2 components, P = 2 phases; F = 2 –2 + 1 = 1, Have One independent variable.
• Single degree of freedom means we can maintain the 2 phase microstructure while
we vary the temperature of the material. By changing the temperature, we indirectly
vary the composition of the individual phases. Composition is a dependent variable
• Josiah Gibbs (1839-1903)
– American Professor of mathematical physics at Yale University
– Known as quiet individual who is the biggest pioneer in thermodynamics.
• Phase rule is the cornerstone of thermodynamics (relationship between matter and
4
energy) Thermodynamics is the basis for air conditioning, pumps, heaters, anything
that has liquid and
gas combinations.
Copyright
Joseph Greene 2002 All Rights Reserved
• Phase diagram
Phase Rule
– A map that helps explain the microstructure that exists at a certain temperature
and pressure and composition.
– Example, Water phase diagram. Fig 9-3
Gas
Temp
• The one component diagram summarizes
• The phases present for water as a function of T and P
– F=1–2–1=0
» If change temperature, then can get solid or liquid
• For a fixed pressure of 1 atm (14.69 psi),
– Water at room temperature 25C is liquid,
» at T= 100C is gas and at 0C is solid.
100 C
Liquid
0C
Solid
1 atm Press
– Example, Pure iron Fig 9-4
•
•
•
•
Can be in a different crystalline structure (phase)
Temp
Liquid

1538 C Gas
 - iron
 austenite
 - iron is austenite
910 C
 ferrite
- iron is ferrite
– F=1–2–1=0
Solid
» If change temperature, then can get solid or liquid
1 atm
Press
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Phase Diagram
• Phase diagram is any graphical representation of the state variables
associated with microstructures through Gibbs phase rule.
– Phase diagrams are used for binary (2 Component; C= 2) and ternary diagrams
(3 component systems; C=3)
– Phase diagrams are maps of the equilibrium phases associated with the various
combinations of temperature and composition.
• Concern is to change phases and associated microstructure that follow changes in
temperature and composition.
• Complete Solid solution
– Simple binary solution is two species that are completely soluble in each other in
both liquid and solid states.
• Cu and Ni are completely soluble;
Temp
Liquidus
• MgO and NiO are completely soluble;
L + SS
• Fig 9-5 Phase diagram
Melting
– Melting points of A and B
Point
B Rich
A Rich Solidus
– For high T of any composition will give a liquid of A
A
B
– A and B are completely soluble in liquid phase field, L
0 20 40 60 80 100
– A and B are completely soluble is solid solution (SS)
100 80 60 406 20 0
– Intermediate temperature has liquid plus solid solution
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Composition
Phase Diagram
• Complete Solid solution
– Compositions of A and B are read of x- axis
– Compositions of liquid and solid solution are
Temp
Melting
Point
of A
Overall composition
of A and B
SS
Liquid
L
x
L + SS
SS
Solidus
A
B
0 20 40 60 80 100
100 80 60 40 20 0
• Are read from x-axis by
– Overall composition of SS and liquid, X
– Composition of SS is SS
Composition
– Composition of Liquid is L
Liquidus
Temp
• Horizontal line connection the two phase compositions is
F = 2 –1 + 1 =2
F=0
termed tie line.
Melting F = 2 –2 + 1 =1
• Relative amounts of each phase with lever rule
F=0
Point
F = 2 –1 + 1 =2
– Gibbs phase rule: F = C – P +1
of A
Solidus
• For melting points of pure material, F = 0
A
B
– Invariant point. Change T, changes to liquid or solid 0 20 40 60 80 100
100 80 60 40 20 0
• For 2 phase region (L+SS), F = 1,
– Change in T results in composition changes by lever
rule
• For Liquidus and solidus areas the F = 2,
– Change in T or composition does not change basic
nature of microstructure
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Composition
7
Phase Diagram
Overall composition
Temp,
of A and B
C Liquid
SS
1500
• Inorganic material use Phase diagrams1100
• Materials that are soluble
– Metals and ceramics systems
L
x
L + alpha
SS
Alpha phase
Cu
Ni
0 20 40 60 80 100
100 80 60 40 20 0
Composition
• Fig 9-9 Cu –Ni complete solid solution
• Variety of Cu-Ni alloys fall within system, Temp, Liquidus
C
Monel
2800
L + SS
• NiO-MgO system is a ceramic system
Solid Solution
2000
– Structure has similar cations in solid
NiO
MgO
0 20 40 60 80 100
solution
Composition
– Note: composition axis for NiO-MgO
Mole% MgO
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Copyright Joseph Greene 2002 All Rights Reserved
Phase Diagram
• Inorganic materials that are insoluble
Temp,
Liquid, L
C
B+L
A+ L
– Metals and ceramics systems
Solidus
• Fig 9-1. Binary systems that the components are not soluble
A A+B
B
– At low temperatures there is two-phase field for pure
0 20 40 60 80 100
solids A + B.
Composition
– Solidus (solid solution) is the horizontal line that
Fig 9-1
corresponds to eutectic Temp
» Temperature at which liquid cools to solid at the
composition.
» There are no solids is liquid state and no liquids in
solid state at the composition
Temp,
Liquid, L
C
» This is the only composition that the liquid
Crystallites of
material cools to a solid without any other phases Crystallites of
B in matrix L2
A in matrix L1
present
• Fig 9-12 Relative microstructures for binary eutectic
Eutectic Layered
diagram.
AA+B
B
– Liquid + solid microstructures
0 20 40 60 80 100
– Layered structure of A & B in eutectic
Composition
10
Fig 9-12
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Phase Diagram
• Eutectic diagram with limited Solid Solution
– For many binary systems, two components are partially
soluble
Temp,
Liquid, L
C
B+L
A+ L
Solidus
A A+B
B
0 20 40 60 80 100
• Fig 9-14 shows eutectic diagram with limited solid solution
• Two solid-solution phases,  and , are distinguishable
Composition
• Each component will have a crystal structure
Fig 9-11
– Each component serves as a solvent for the other
impurity component
» Example,  consists of B atoms in solution in
crystal lattice of A.
Temp,
» The use of tie lines determines the composition of C Liquid, L
 and 
Crystallites of
Crystallites of
B in matrix L2
A in matrix L1
– Fig 9-16 Pb-Sn System
» Common solder alloys for binary eutectic
Eutectic Layered
» Solder (< 5% tin) used for sealing, 120C
AA+B
B
» Solder (20% tin) used for radiators
0 20 40 60 80 100
» Solder (50% tin) used general purpose
Composition
Fig 9-1411
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Eutectoid Diagram
Temp,
C
• Transformation of eutectic liquid to a
relatively fine-grained microstructure of two
solid phases upon cooling can be described
as special type of chemical reaction
• Liquid  (eutectic)
+
– Notation corresponds to Fig 9-14
– Fig 9-17
– Fig 9-18 representative microstructures
Liquid, L


+
+L
L+ 
+

Solidus
+
A
B
0 20 40 60 80 100
Eutectic Composition
– Eutectoid reaction play important role in steel
Eutectic
industry
Temps
Fig 9-17
Liquid, L

+
• Fe-Fe3C system Fig 9-19 is basis for commercial steel
+
• Chapter 11. Irons and steels boundary is with 2%
A
B
carbon, which is the carbon solubility of austenite 
structure fine of
• Diagram represents the microstructure development Eutectoid micro
Composition
• Important areas are eutectic and eutectoid reactions
Fig 9-1812
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Iron-Carbon Phase Diagram
• Iron and Carbon are two main elements in steels.
– Ferrite- alpha iron. BCC and magnetic. Alpha/delta = pure iron
• Room temp dissolve only 0.008% C.
• Delta iron if T is between 2552F and 2802F
• Small amount of carbon dissolves interstitially (imperfection in the lattice)
– Carbon steel of 0.77% carbon (eutectoid- lowest T a single phase can exist
before becoming 2). All carbon dissolved into austenite.
– Austenite- gamma iron. FCC and non-magnetic.
– Steel must be taken into austenite region for all hardening and softening. When
solution cools slowly steel separates into 2 distinct phases, ferrite and cementite.
– Cementite- very hard and brittle compound, not alloy.
– Iron is allotropic- can exist in more than one phase.
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Eutectoid Diagram
• Fe-Fe3C diagram is not true equilibrium.
– Fe-C system represents true equilibrium Fig 9-20
• Graphite C is more stable precipitate that Fe3C, the rate of graphite
precipitation is enormously slower than that of Fe3C.
• Result is that in common steel the Fe3C is metastable (stable at common T,
P, and time) and follows Gibbs phase rule
– Fe-C is more stable but less common than Fe3C because of slow
kinetics (Chap 10)
• Extremely slow cooling rates can produce the results indicated on Fe-C
diagram. (Fig 9-20)
• More practical method is to promote graphite precipitation is to add
silicon (2 to 3%) stabilizes the graphite precipitation
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Iron-Carbon Phase Diagram
• Iron is ferromagnetic- magnetism is dependent upon which crystalline
structure is present due to Carbon content and temperature.
• Curie Temperature- temperature at which magnetism changes
• Ferrite holds between 0.006% Carbon at 392F and up to 0.04% at 1333F.
• Austenite holds 0.77% at 1333F and up to 1.7% at 2066F
• Pearlite is an eutectoid mixture of ferrite and cementite which form a
lamellar structure.
• Hypoeutectoid -less carbon and Hypereutectoid- more carbon than eutectoid
composition for the steel.
• Martensite- very hard and very brittle steel and forms when steel is rapidly
cooled from the austenite state. Ferrite with highly saturated Carbon trapped
in BC tetragonal structure.
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Phase Diagram
• Peritectic Diagram
– In some systems, components form stable compounds
that may not form stable compounds that have a
distinct melting point.
• Example, Fig 9-21
• A and B form a stable solid compound AB, which does not
melt at a single temperature as do A and B.
• A and B undergo congruent melting (liquid forms upon
melting has the same composition as the solid from which it
was formed.
• AB (50% A and 50% B) undergoes incongruent melting
(liquid formed after melting has composition other than AB.
AB
L+B
• Peritectic comes from Greek “To melt nearby”
• Fig 9-21 and Fig 9-22 shows microstructures for peritectic
• Fig 9-23. Al2O3-SiO2 is an example of peritectic diagram
– Very important to ceramic industry
– Others are refractory silica bricks (SiO2) with 1% Al2O3
» Need to keep Al2O3 content as low as possible
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Phase Diagram
• General Binary Diagrams
– Intermediate compounds are formed in peritectic diagram.
• Chemical compound formed between two components in binary system
• Fig 9-24
– AB melts congruently
– It is equivalent to adjacent binary eutectic diagrams (Fig 9-11)
– A-AB binary does not exist for overall composition Fig 9-24b.
– Nowhere in the development of microstructure for that composition will
crystals of A be found in a liquid or will crystals of A and AB exist
simultaneously.
• Fig 9-25 demonstrates this for complex binary system
– Diagram with 4 intermediate compounds (A2B, AB, AB2, and AB4) and several
individual binary diagrams.
– For overall compositions only AB2 – AB4 binary is relevant
• Fig 9-26
– MgO-Al2O3 is similar to 9-24 but with limited solid solubility.
– Includes important intermediate compound (spinel- magnetic materials)
– Figures 9-27 to 9-29 good examples of general binary diagrams
» Age hardenable Al in  area.
» Complex diagram can be analyzed as simple binary eutectic in high
Al
17
region
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Phase Diagram
• General Binary Diagrams
– Fig 9-28 Al-Mg phase diagram
• Several Al alloys and Mg alloys can be described by phase diagram
– Fig 9-29 Cu-Zn phase diagram
• Complex diagram that can be used for single phase region ( region)
– Fig 9-30 CaO-ZrO2 phase diagram
• Example of general diagram for a ceramic system.
• ZrO2 is an important refractory material through the use of stabilizing
additions, such as CaO.
• Pure ZrO2 has a phase transformation at 1000C in which the crystal structure
changes from monoclinic to tetragonal upon heating.
– Transformation involves a substantial volume change that is structurally
catastrophic to the brittle ceramic.
– Cycling pure material through the transformation temperature will
reduce it to a powder.
– Addition of 10wt% CaO produces a solid solution-phase with a cubic
crystal structure from room temperature to the melting point (2500C)
– Stabilized zirconia is a practical, refractory, structural material 18
Copyright Joseph Greene 2002 All Rights Reserved
Lever Rule
• Previously, phase diagrams were used to determine present
at equilibrium that corresponds to a microstructure.
• Tie line (Fig 9-6) gives the composition of each phase in the
two-phase region.
– Tie line can determine the amount of each phase in the 2-phase
– Note: for single-phase region, microstructure is 100% single phase
– For 2-phase systems the amount of each is found per mass balance
• Example, Fig 9-31(Fig 9-6 with values)
– Tie line gives composition of 2 phases with point, L +SS region, and the
composition of each phase and of overall composition of system.
– Overall mass balance requires sum of two phases equal total system.
» Step 1. Assume 100 g for system, then
» Step 2. Mass balance on one of the components.
» Step 3. Solve two equations with two unknowns
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Lever Rule
• For 2-phase: the amount of each is found per mass balance
– Example, Fig 9-31(Fig 9-6 with values)
• Tie line gives composition of 2 phases with point, L +SS region, and the
composition of each phase and of overall composition of system.
• Overall mass balance requires sum of two phases equal total system.
– Step 1. Assume 100 g for system, then Equation 1 is
» mL + mSS = 100g
– Step 2. Mass balance on one of the components, then Equation 2 is
» Amount of B in liquid (L) phase plus that in Solid Solution (SS)
must equal the total amount of B in overall composition.
» Fig 9-31, 0.3 mL + 0.8 mSS = 0.5 (100g) = 50g
– Step 3. Step 3. Solve two equations (1 and 2) with 2 unknowns mL,mSS
» Write equation 1 into mL = 100g - mSS
» Substitute 100g - mSS for mL in Equation 2
» 0.3(100g – mSS )+ 0.8mSS = 50g
» Solve for 0.5 mSS = 20g or mSS = 40g
20
» Then from Equation 1; mL + 40g = 100g; mL = 60g
Copyright Joseph Greene 2002 All Rights Reserved
Lever Rule
• Lever Rule method
– Lever rule
• Material balance method is convenient, but a streamlined method is:
• Mass balance in general terms.
– xm + xm = x (m + m )
– xx are the compositions of the two phases and x is the overall
composition. Expression can be rearranged as
x  x
m

m  m 
x   x
m
m  m 

x  x
x   x
– These equations are the lever rule
» Fig 9-32. Mechanical analogy is to a lever balance on a fulcrum
» Mass of each phase is suspended from the end of the lever
corresponding to its composition
» Relative amount of  phase is directly proportional to the length of
the opposite lever arm (=x  – x)
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» Sample Problem 9.3
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Microstructural Development
• Development of various binary systems
– Assume: microstructure is developed during solidification
– Only consider slow cooling- equilibrium is achieved at all points
– Simple binary systems
• Complete solubility in both liquid and solid phases
• Fig 9-33. Slow solidification of 50% A 50% B treated earlier
• Microstructures corresponds with relative position of overall system
composition along the line.
– High Temp, overall composition is near L-solid boundary and
microstructure is liquid.
– Low temperature, microstructure is mostly solid.
• Composition of binary at Eutectic is aided by lever rule
– Fig 9-34. Only differences from T1 microstructure are the phase
compositions and the relative amount of b will be proportional to
xeutectic  x
x   x
Copyright Joseph Greene 2002 All Rights Reserved
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Microstructural Development
• Development of various binary systems
– Microstuctural development, noneutectic composition is complex
• Fig 9-35 for hypereutectic composition (composition greater than eutectic)
– Gradual growth of crystals above eutectic Temp is a similar to Fig 9-33, except
that the crystals stop growing at eutectic temp with only 67% of the
microstructure solidified. Final solidification occurs when the remaining liquid
transforms to eutectic microstructure upon cooling.
» 33% of microstructure undergoes eutectic reaction in Fig 9-34
» Lever rule calculates that microstructure is 17%  and 83%  (In two
forms- large grains during slow cooling (proeutectic) and finer lamellar
eutectic structure .
• Fig 9-36 similar situation for hypoeutectic (Less than eutectic composition)
– Analogous to hypereutectic composition
» Development of large grains of proeutectic  along with the eutectic
microstrucre of  and 
• Fig 9-37 Two other types of microstructural development
– Overall composition of 10% , similar to that of complete solid solution
» Leads to single phase solid solution that remains stable upon cooling to
low Temp
– Overall 20% solution leads to precipitation of small amounts of  phase along
grain boundaries.
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Copyright Joseph Greene 2002 All Rights Reserved
Microstructural Development
• Fig 9-38. Cooling path of white cast iron
– Microstructure produces eutectoid reaction to produce pearlite
– Hypereutectoid composition
– Proeutectoid composition
• Fig 9-39 Microstructural development for eutectoid steel (C
< 0.77%
• Fig 9-40. Fe-C diagram for gray cast iron
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Copyright Joseph Greene 2002 All Rights Reserved
Carbon Content in Steels
•
•
•
•
Carbon is the most important alloying element in steel.
Most steels contain less than 1% carbon.
Plain carbon steel- carbon is the only significant alloying element
Mild steel, or low carbon steel, are produced in the greatest quantity
because it is cheap, soft, ductile, and readily welded. Caution: it can
not be heat-treated
• Mild steels are used for car bodies, appliances, bridges, tanks, and
pipe.
Name
Low carbon (mild)
Medium carbon
High carbon
Cast iron
Carbon Content
0.05% - 0.32%
0.35% - 0.55%
0.60% - 1.50%
>2.00%
Examples
Sheet, structural
Machinery
Machine tools
Castings
Copyright Joseph Greene 2002 All Rights Reserved
25
Carbon Content Cold Working in Steels
• Medium carbon steel - used for reinforcing bars in concrete, farm
implements, tool gears and shafts, as well as uses in the automobile
and aircraft industries.
• High carbon steels - used for knives, files, machine tooling,
hammers, chisels, axes, etc.
• A small increase in carbon has significant impact on properties of the
steel. As Carbon increases the steel:
– becomes more expensive to produce and less ductile, i.e., more brittle
– becomes harder and less machinable and harder to weld
– has higher tensile strength and a lower melting point
• Cold working is used to enhance the properties of steel
– Reducing thickness by 4% raises the tensile strength by 50%
– Cold working is plastic deformation at room temperature.
– Cold working produces dislocations in the metal’s structure which block
dislocations as they slide along the slip planes
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Copyright Joseph Greene 2002 All Rights Reserved
Other Elements in Steels
• Alloying elements are added to nullify undesirable elements
– Carbon
– Manganese
• increases strength, malleability, hardenability, and hardness
• Sulfur reacts with the Mn which reduces the hot short effect of the iron sulfide
accumulating at the grain boundaries and reducing strength at Temp
– Aluminum• reacts with Oxygen versus iron (no sparks). Killed steel
• promotes smaller grain size which adds toughness
–
–
–
–
–
Silicon- reduces Oxygen negative effects
Boron- increases the hardenability of steel (only with Al added)
Copper- increases corrosion resistance
Chromium- increases corrosion resistance and hardenability
Nickel, Niobium, titanium, tungsten carbide, vanadium
• increase toughness and strength and impact resistance
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Nomenclature in Steels
• SAE and AISI developed method of cataloging steel based on
– carbon content- % carbon with implied decimal
– alloying elements
– AISI 8620 steel is the same as SAE 8620 steel
• Steels are usually 4 digit designations
– 1018 steel = 10 is plain carbon steel; 18 represents 0.18% carbon
– 4030 steel = 40 is molybdenum steel of .15% to 0.30% Molybdenum and 0.30%
carbon
– 2 - - - = nickel steel with % nickel, 22-- is nickel with 2% nickel
– 10100 = five digits indicated 1% carbon more
– B in the middle of the number, 81B40 indicates min of 0.0005% boron
• Various common steels
– 1010: Steel tuning;
1040: Connecting rods for automobiles
– 4140: Sockets and socket wrenches;
52100: Ball and roller bearings
– 8620: Shafts, gears, and machinery parts.
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Copyright Joseph Greene 2002 All Rights Reserved
•
Cast
Iron
Other ferrous metals include
– cast iron (gray-3.5% carbon and >1% silicone and white- 2.5 - 3.5% carbon and
0.5 - 1.5% silicon. )
– ductile cast iron, malleable cast iron, wrought iron
• Steel with >2% iron is cast iron because of the lack of ductility.
• Carbon in form of graphite (gray) or iron carbide (white)
• Gray cast iron has no ductility and will crack if heated or cooled too quickly.
– Gray cast iron has good compression strength, machinability, vibration damping
characteristics and used for furnace doors, machine bases, and crackshafts.
• White cast iron has good wear resistance and is used in rolling and
crunching equipment
• Ductile cast iron contains 4% Carbon and 2.5% Silicon
• Ductile iron is used for engine blocks, machine parts, etc.
• Maleable cast irons are heat treated versions of white cast iron.
– Cast iron with 2 to 3% Carbon is heated to 1750F, where iron carbide or
cementite is allowed to form spherulites. Similar to ductile cast iron
– Pearlitic malleable iron- heated to 1770F and quenched cooled
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– Ferritic malleable iron- heated to 1770F and air cooled
Copyright Joseph Greene 2002 All Rights Reserved
Stainless Steel
• Definition and Applications
– Alloys that posses unusual resistance to attack by
corrosive media
– Applications include aircraft, railway cars, trucks, trailers,...
• AISI developed a 3digit numbering system for stainless steels
– 200 series: Austenitic- Iron-Cr-Ni-Mn
• Hardenable only by cold working and nonmagnetic
– 300 series: Austenitic- Iron-Cr-Ni
• Hardenable only by cold working and nonmagnetic
• General purpose alloy is type 304 (S30400)
– 400 series:
• Ferritic- Iron-Cr alloy are not hardenable by heat treatment or cold working
– Type 430 (S43000) is a general purpose alloy
• Martensitic- Iron-Cr alloys are hardenable by heat treatment and magnetic
– Type 410 (S41000) is a general purpose alloy
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Stainless Steel
• Corrosion of steels can be slowed with addition of Cr and Ni.
• Stainless steels have chromium (up to 12%) and Ni (optional)
– ferritic stainless: 12% to 25% Cr and 0.1% to 0.35% Carbon
• ferritic up to melting temp and thus can not form the hard martensitic steel.
• can be strengthened by work hardening
• very formable makes it good for jewelry, decorations, utensils, trim
– austenitic stainless: 16% to 26% Cr, 6% to 23% Ni, <0.15% Carbon
• nonmagnetic and low strength % to 25% Cr and 0.1% to 0.35% Carbon
• machinable and weldable, but not heat-treatable
• used for chemical processing equipment, food utensils, architectural items
– martensitic stainless: 6% to 18% Cr, up to 2% Ni, and 0.1% to 1.5% C
• hardened by rapid cooling (quenching) from austenitic range.
• Corrosion resistance, low machinability/weldability used for knives, cutlery.
– Marging (high strength) steels: 18% to 25% Ni, 7% Co, with others
• heated and air cooled cycle with cold rolled
• Machinable used for large structures, e.g., buildings, bridges, aircraft
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Copyright Joseph Greene 2002 All Rights Reserved
•
•
•
•
Corrosion
Ferrous metals rust because the iron reacts with oxygen to form iron oxide or rust.
Process is corrosion
Corrosion occurs as well when metal is in contact with water and metal ions
dissolved in water.
Galvanic corrosion: electrochemical process which erodes the anode.
Metals in galvanic series: the further apart the worse the corrosion
–
–
–
–
–
–
–
–
–
–
–
–
–
Magnesium- most positive or anodic. Gives up electrons easily and corrodes
Aluminum
Zinc
Iron
Steel
Cast Iron
Lead Brass
Copper
Bronze
Nickel
Stainless steel
Silver
Graphite
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Copyright Joseph Greene 2002 All Rights Reserved
Wrought Aluminum Numbering System
• Wrought Numbering System
– Aluminum Association developed system for cast and wrought Al
– Wrought aluminum- 4 digit system, e.g. 2011
• first digit represents alloying elements in the alloy
• second digit represents alloy modifications or degree of control of impurities
• third digit represents arbitrary numbers that indicate a specific alloy or indicate the purity
of the alloy over 90%
• fourth digit represents same as third digit
Number
1----
Major Alloying Element
None
2----
Copper
3----
Manganese
4----
Silicon
5----
Magnesium
6----
Magnesium and Silicon
7----
Zinc
8----
Other
9----
Unused
Copyright Joseph Greene 2002 All Rights Reserved
33
Wrought Aluminum Numbering System
• Common aluminum alloys
–
–
–
–
–
–
Silicon alloys used for castings
Copper alloys used for machining
Magnesium alloys used for welding
Pure aluminum used for forming
Magnesium and silicon alloys used for extrusion
Copper alloys used for strength
• Examples
– 2011 with 5% to 6% copper is a free machining alloy
– 2024 contains between 3.8% and 4.9% copper with 1.5% magnesium. This alloy is
heat treatable aluminum alloy that is commonly used for aircraft parts.
– 3003 has 1% to 1.5% manganese which provides additional strength
– 4043 contains 4.5% to 6% silicon and is used in welding wire
– 5154 contains 3.1% to 3.9% magnesium and is weldable and available in sheets,
plates, and many structural shapes.
– 6063 contains approximately 0.5% magnesium and silicon and is used in windows,
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doors, and trim
Copyright Joseph Greene 2002 All Rights Reserved
Casting Aluminum Numbering System
• Casting Numbering System
– Cast aluminum- 3 digit system that is not generally standardized
– Aluminum Association developed system for cast
•
•
•
•
silicon casting alloys up to 99
silicon copper from 100 to 199
magnesium from 200 to 299
silicon manganese from 300 to 399
– Applications
• Good conductor for electrical and electronics applications
• Light weight good for structural applications that require medium strength and light
weight.
• High reflectivity for infrared and visible radiation make it desirable for headlights, light
fixtures, and insulations
• Flake form is used for pigment
• Cast Al engine blocks and pistons
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Copyright Joseph Greene 2002 All Rights Reserved