over view of the metal alloys thermal treatment and how does it behave with it.

1. Heat Treatment of metal alloysHeat Treatment of metal alloys
Mohamed KablMohamed Kabl
12/11/201512/11/2015

2. 22
ContentContent
IntroductionIntroduction
CategoriesCategories
Heat treatment methodsHeat treatment methods
ReferencesReferences

3. 33
IntroductionIntroduction
What is metal alloys heat treatment ?What is metal alloys heat treatment ?
 Heat treatmentHeat treatment is a method used to alter the physical,is a method used to alter the physical,
and sometimes chemical properties of a material. Theand sometimes chemical properties of a material. The
most common application is metallurgicalmost common application is metallurgical
 It involves the use of heating or chilling, normally toIt involves the use of heating or chilling, normally to
extreme temperatures, to achieve a desired result suchextreme temperatures, to achieve a desired result such
asas hardeninghardening oror softeningsoftening of a materialof a material
 It applies only to processes where the heating andIt applies only to processes where the heating and
cooling are done for the specific purpose of alteringcooling are done for the specific purpose of altering
properties intentionallyproperties intentionally

4. 44
Reasons for using heatReasons for using heat
treatmentstreatments
Improves properties of metal alloysImproves properties of metal alloys
Modifies the microstructureModifies the microstructure
Improves formabilityImproves formability
Improves machinabilityImproves machinability
Increases strength & hardnessIncreases strength & hardness
Service performance improved suchService performance improved such
as in gearsas in gears

5. Cross section of gear teeth showing induction-hardened surfaces.Cross section of gear teeth showing induction-hardened surfaces. Source:Source: TOCCO Div.,TOCCO Div.,
Park-Ohio Industries, IncPark-Ohio Industries, Inc..

6. 66
The properties and behavior of metals (and alloys) dependThe properties and behavior of metals (and alloys) depend
on their:on their:

StructureStructure

Processing historyProcessing history

CompositionComposition

7. How to Strengthen MetalsHow to Strengthen Metals
 Increase dislocation density via Cold working (strainIncrease dislocation density via Cold working (strain
hardening)hardening)
 Add alloying elements to give – SOLID SOLUTIONAdd alloying elements to give – SOLID SOLUTION
HARDENING.HARDENING.
 DISPERSION HARDENING – fine particles (carbon)DISPERSION HARDENING – fine particles (carbon)
impede dislocation movement. (Heat treatment)impede dislocation movement. (Heat treatment)
 Key: prevent dislocations from moving through crystal structure!!!Key: prevent dislocations from moving through crystal structure!!!

8. Metals
 Valence electrons of 1,2 or 3
 Primary bonding between electrons called metallic bonding
Valence electrons not
“bonded” to particular
atom but shared and
free to drift through
the entire metal
 Properties include: good conductors of electricity and heat, not
transparent, quite strong yet deformable!

9. Crystalline structures (i.e. metals) atoms are arranged in unit
cells – 4 common cells shown above

10. How do Metal
Crystals Fail??

11. 1111
Pure MetalsPure Metals
InIn PURE METALSPURE METALS, atoms are all the same, atoms are all the same
type, except for rare impurity atomstype, except for rare impurity atoms
Pure Metals & AlloysPure Metals & Alloys
lead copper

12. 1212
AlloysAlloys
ALLOYSALLOYS are composed of 2 or more chemicalare composed of 2 or more chemical
elements, at least one of which is a metalelements, at least one of which is a metal
Tungsten copper Bronze

13. 1313
Classification of alloysClassification of alloys
Classification of alloysClassification of alloys

FerrousFerrous: containing iron, second most abundant: containing iron, second most abundant
element (5% earth's crust).element (5% earth's crust).

Non-ferrousNon-ferrous: no iron, usually more expensive than: no iron, usually more expensive than
ferrous metals.ferrous metals.

14. 1414
Solid SolutionsSolid Solutions
 Solute: the minor element that is added to theSolute: the minor element that is added to the
solventsolvent
 Solvent: the major elementSolvent: the major element
 Substitutional solid solutions: the size of the soluteSubstitutional solid solutions: the size of the solute
atom is similar to the solvent atom (example: brassatom is similar to the solvent atom (example: brass
alloy of zinc & copper)alloy of zinc & copper)
 Interstitial solid solutions: the size of the solute atomInterstitial solid solutions: the size of the solute atom
is much smaller than that of the solvent (example:is much smaller than that of the solvent (example:
steel alloy iron & carbon)steel alloy iron & carbon)

15. 1515
Substitutional Solid SolutionsSubstitutional Solid Solutions
Must have similar crystal structures (e.g.Must have similar crystal structures (e.g.
FCC with FCC).FCC with FCC).
Difference between atomic radii less thanDifference between atomic radii less than
15% (same size atoms).15% (same size atoms).
Brass (zinc + copper).Brass (zinc + copper).
Copper Grains

16. 1616
Interstitial Solid SolutionsInterstitial Solid Solutions

Interstitial Solid Solution - solvent atom hasInterstitial Solid Solution - solvent atom has
more than one valence electron (easier tomore than one valence electron (easier to
control solute).control solute).

Atomic radius of solute atom is less than 59%Atomic radius of solute atom is less than 59%
of solvent (atom sizes differ greatly).of solvent (atom sizes differ greatly).

Example = Steel (iron + carbon)Example = Steel (iron + carbon)

17. 1717
Intermetallic CompoundsIntermetallic Compounds

Complex structuresComplex structures

Solute atoms present among solvent atoms =Solute atoms present among solvent atoms =
atomic bonding.atomic bonding.

Strong, hard, and brittleStrong, hard, and brittle
 TiTi33Al, NiAl, Ni33Al, FeAl, Fe33Al.Al.
Aluminum Grains

18. 1818
Two-phase SystemsTwo-phase Systems
Most alloysMost alloys consist ofconsist of twotwo or more solid phases (alloy containsor more solid phases (alloy contains
particles of single elementparticles of single element OROR grains are differentgrains are different).).

Limited solubility (just as with sugar in waterLimited solubility (just as with sugar in water  MechanicalMechanical
mixture).mixture).

Clear boundaries, mixture - each with its own properties.Clear boundaries, mixture - each with its own properties.

Stronger and less ductile than solid solutions.Stronger and less ductile than solid solutions.

19. 1919
Phase DiagramsPhase Diagrams
 Pure metals have clearly defined melting or freezing points,Pure metals have clearly defined melting or freezing points,
and solidification takes place at a constant temperature.and solidification takes place at a constant temperature.
 Tool for understanding the relationship amongTool for understanding the relationship among temperaturetemperature,,
compositioncomposition, and, and phasesphases present in a particular alloypresent in a particular alloy
system.system.
 Alloys solidify over aAlloys solidify over a range of temperaturesrange of temperatures, based on the, based on the
composition of the mixture.composition of the mixture.
 As the alloy cools the mixture begins to freeze, changingAs the alloy cools the mixture begins to freeze, changing
gradually to a solid (liquid/solid phases).gradually to a solid (liquid/solid phases).

20. (a) Cooling curve for the solidification of pure metals. Note that freezing takes(a) Cooling curve for the solidification of pure metals. Note that freezing takes
place at a constant temperature; during freezing, the latent heat of solidificationplace at a constant temperature; during freezing, the latent heat of solidification
is given off. (b) Change in density during cooling of pure metals.is given off. (b) Change in density during cooling of pure metals.

21. 2121
Binary Phase DiagramsBinary Phase Diagrams
Composition
Temperature
L
S
L+S
Temperature
0% B
100% A
100% B
0% A
A
B
 Complete Solid Solubility
Solid Solution - Single Phase
Two Phases

22. Phase DiagramsPhase Diagrams
 Alloys solidify over a range of temperaturesAlloys solidify over a range of temperatures
 LiquidusLiquidus - solidification occurs when the- solidification occurs when the
temperature drops belowtemperature drops below
 SolidusSolidus - solidification is complete- solidification is complete
 Between liquidus and solidus the alloy is in aBetween liquidus and solidus the alloy is in a
mushy or pasty statemushy or pasty state

23. 2323
Nickel-Copper DiagramNickel-Copper Diagram
(Black & Kohser, 2008, p. 75)

25. Lever RuleLever Rule
• Used to determine the composition of various phases inUsed to determine the composition of various phases in
the phase diagramthe phase diagram
• Example: Copper NickelExample: Copper Nickel
–
At 1288 degrees C, a mixture of solid/liquidAt 1288 degrees C, a mixture of solid/liquid
–
Solid is 42% Cu, 58% NiSolid is 42% Cu, 58% Ni
–
Liquid is 58% Cu, 42 % NiLiquid is 58% Cu, 42 % Ni
•
The completely solidified alloy is aThe completely solidified alloy is a solidsolid
solutionsolution because Cu completely dissolvesbecause Cu completely dissolves
in Ni and each grain has the samein Ni and each grain has the same
compositioncomposition

26. 2626
A + Liquid
B + Liquid
A + B
A
B
0% B
100% A
Eutectic point
100% B
0% A
A
B
Two-Phase DiagramsTwo-Phase Diagrams
Limited solubilityLimited solubility
Two Phases
Solid Solution - Single Phase

27. 2727
Two-Phase Lead-Tin DiagramTwo-Phase Lead-Tin Diagram
(Black & Kohser, 2008, p. 75)

28. 2828
Two-Phase Iron-Carbon DiagramTwo-Phase Iron-Carbon Diagram
Most important phase diagram in manufacturing applications, sinceMost important phase diagram in manufacturing applications, since
steels, cast irons, and cast steels are the most common engineeringsteels, cast irons, and cast steels are the most common engineering
materials (versatile properties and relative low cost).materials (versatile properties and relative low cost).

29. 2929
Iron-Carbon DiagramIron-Carbon Diagram
 Solid Phases of the Iron-Carbon DiagramSolid Phases of the Iron-Carbon Diagram

Ferrite (Ferrite (αα-iron)-iron)

Austenite (Austenite (γγ-iron)-iron)

Cementite (iron-carbide)Cementite (iron-carbide)

30. 3030
FerriteFerrite

((αα-iron-iron))

Soft, ductile, magnetic.Soft, ductile, magnetic.

BCCBCC

Solid solution (0.022% carbon) almost pure iron.Solid solution (0.022% carbon) almost pure iron.

31. 3131
AusteniteAustenite

((γγ-iron)-iron)

FCC - higher density than BCC, ductile at elevatedFCC - higher density than BCC, ductile at elevated
temperatures (good formability)temperatures (good formability)

Interstitial SolidInterstitial Solid

Solution (2.11% carbon)Solution (2.11% carbon)

Non-magneticNon-magnetic
AUSTENITIC MANGANESE STEEL

32. 3232
CementiteCementite

Iron carbide (Fe3C) 6.67% carbonIron carbide (Fe3C) 6.67% carbon

Hard & brittle Intermetallic Compound.Hard & brittle Intermetallic Compound.

33. Fe3C CategoriesFe3C Categories
3333

34. 3434Engr 241Engr 241

35. Schematic illustration of the microstructures for an iron–carbon alloy ofSchematic illustration of the microstructures for an iron–carbon alloy of
eutectoid composition (0.77% carbon), above and below the eutectoideutectoid composition (0.77% carbon), above and below the eutectoid
temperature of 727°C (1341°F).temperature of 727°C (1341°F).
Eutectoid System

36. 3636Engr 241Engr 241

37. Hardenability and Weldability are influencedHardenability and Weldability are influenced
by four factorsby four factors
3737
Carbon content –Carbon content –
WeldableWeldable  .35% C.35% C HardenableHardenable
Heating Cycle – maximum temperatureHeating Cycle – maximum temperature
Cooling Cycle – minimum temperatureCooling Cycle – minimum temperature
Speed of coolingSpeed of cooling

38. 3838
Heat TreatmentHeat Treatment ProcessesProcesses

AnnealingAnnealing: general term used to refer to the restoration: general term used to refer to the restoration
of properties after cold work or heat treatment.of properties after cold work or heat treatment.

Full annealingFull annealing
austenitizing and furnace cool.austenitizing and furnace cool. It is used in low- and medium carbonIt is used in low- and medium carbon
steels that need extensive machining or plastic deformationsteels that need extensive machining or plastic deformation

NormalizingNormalizing: cooling cycle done in still air to avoid: cooling cycle done in still air to avoid
excessive softness in the annealing of steels.excessive softness in the annealing of steels.

SpheroidizingSpheroidizing: improve properties of high-carbon steels.: improve properties of high-carbon steels.

39. 3939
Heat TreatmentHeat Treatment ProcessesProcesses

Stress RelievingStress Relieving: reduce or eliminate residual stresses.: reduce or eliminate residual stresses.

TemperingTempering: reduce brittleness and residual stress, and: reduce brittleness and residual stress, and
increase ductility and toughness of previously hardenedincrease ductility and toughness of previously hardened
steels.steels.

HardeningHardening: heating and cooling rapidly (quenching): heating and cooling rapidly (quenching)

Case HardeningCase Hardening: complete alteration of the: complete alteration of the
microstructure and properties of just the surface of themicrostructure and properties of just the surface of the
material by heating within a particular atmospherematerial by heating within a particular atmosphere

40. Heat treatment rangesHeat treatment ranges
4040Engr 241Engr 241

41. MartensiteMartensite
 Named after the German metallurgist AdolfNamed after the German metallurgist Adolf
Martens (1850–1914)Martens (1850–1914)
 very hard form of steel crystalline structurevery hard form of steel crystalline structure
 formed in carbon steels by the rapid cooling (quenching)formed in carbon steels by the rapid cooling (quenching)
of austenite at such a high rate that carbon atoms do notof austenite at such a high rate that carbon atoms do not
have time to diffuse out of the crystal structure in largehave time to diffuse out of the crystal structure in large
enough quantities to form cementite (Feenough quantities to form cementite (Fe33C)C)
4141

42. TTT DiagramTTT Diagram
4242Engr 241Engr 241
Ability of an alloy steel to be hardened by the formation of martensite.

43. 4343
Steel MicrostructuresSteel Microstructures
Perlite (eutectoid steel) - alternating layers of Ferrite and CementitePerlite (eutectoid steel) - alternating layers of Ferrite and Cementite

fine or coarse perlitefine or coarse perlite
Spheroidite (spherical cementite) - tougher and harder than perliteSpheroidite (spherical cementite) - tougher and harder than perlite
Bainite (very fine ferrite-cementite) - stronger and more ductile thanBainite (very fine ferrite-cementite) - stronger and more ductile than
perlite, same hardnessperlite, same hardness

44. Austempring and MartemperingAustempring and Martempering
4444

45. ReferencesReferences
 George E. Totten,1997, “George E. Totten,1997, “Steel Heat Treatment Handbook” ,Steel Heat Treatment Handbook” , NewNew
York: McGraw-HillYork: McGraw-Hill,1997.,1997. ISBNISBN 0-07-042366-00-07-042366-0
 Colin J. Smithell, 1990, “Colin J. Smithell, 1990, “Metals Reference Book”,Metals Reference Book”, London :London :
Prentice-Hall International,Prentice-Hall International,19911991.. 634 p634 p. ISBN 0- 13-014502-5. ISBN 0- 13-014502-5
 AZO Materials, 2015, “AZO Materials, 2015, “Steels - An Introduction to Heat TreatmentSteels - An Introduction to Heat Treatment””
““http://www.azom.com/article.aspx?ArticleID=313”http://www.azom.com/article.aspx?ArticleID=313”

4545