Heat treatment involves controlled heating and cooling of metals to alter their properties and is used to improve machining, reduce forming forces, and restore ductility. Key heat treatments include annealing to reduce hardness and residual stresses, normalizing to obtain a uniform structure, and precipitation hardening using a solution treatment, quench, and aging steps. Heat treatment processes are aided by phase diagrams which show temperature effects. Proper design and material selection are important to avoid issues from nonuniform sections or residual stresses during heat treatment.

1. Heat Treatment

2. Heat Treatment
The controlled heating &
cooling of metals for the
purpose of altering their
properties

3. Heat Treatment
It is used in manufacturing,
providing simple and low-cost
means of obtaining
desired properties

4. Processing Heat Treatments
thermal processes designed to
increase strength-preparing
materials for fabrication

5. which includes:
improving machining
characteristics
 reducing forming forces and
energy consumption
 restoring ductility for further
deformation

6. Equilibrium Diagram as Aid
to Heat Treatment
 It indicates the temperatures
that must be attained to achieve
a desired product and change
that will occur upon subsequent
cooling

7. Simplified Iron-carbon diagram

8. Processing
Heat Treatments
for Steel

9. Annealing
 a number of process
heating operations

10. Annealing
reducing hardness
 removing residual stresses
 improving toughness
 restoring ductility
 altering mechanical , physical
magnetic properties

11. Full Annealing
Hypoeutectoid steels are heated to
30-60 °C above the A3 to convert to
homogeneous single-phase
austenite of uniform composition
and temperature then slowly cooled
to below A1 temperature

12. Full Annealing
it is time consuming
require considerable energy to
maintain the elevated temperature
Gen. Rule: 1hr at temperature/inch
of thickness of largest section

13. Normalizing
metal is heated to 60°C (100°F)
above the A3 or Acm, soaked
to obtain uniform austenite,
then removed and cooled
in still air

14. Process Anneal
metal is heated below A1,
held long enough
to achieve softening,
then cooled in air

15. Advantages of Process Anneal
cheaper
more rapid
tends to produce less scaling

16. Stress-Relief Anneal
employed to remove residual
stresses in large steel castings
and welded structures

17. Stress-Relief Anneal
 parts are heated below A1
(550-660°C;1000-1200°F),
held for period of time,
then slowly cooled

18. Spheroidization
employed when high-carbon
steels must be prepared for
machining and forming
required for above 0.6% carbon

19. Graphical Summary

20. Heat Treatments
for
Nonferrous Metals

21. Purpose for Nonferrous Metals
to be heat-treated:
obtaining uniform structure
providing stress relief
bringing about recrystallization

22. 6 Major Mechanisms:
Solid Solution Hardening
Strain Hardening
Grain Size Refinement
Precipitation Hardening
Dispersion Hardening
Phase Transformation
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23. Solid Solution Hardening
a base metal dissolves other atoms
in solid solution either as
substantial solutions
or as interstitial solutions
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24. Strain Hardening
increases strength by plastic
deformation under
cold-working conditions
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25. Grain Size Refinement
 used to increase strength,
except at elevated temperatures
where failure is by grain-boundary
diffusion-controlled creep
mechanism
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26. Precipitation/Age Hardening
is a method whereby strength
is obtained from a nonequilibrium
structure produced by a three step
( solution treat-quench and age)
heat treatment
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27. Dispersion Hardening
strength is obtained from
distinct second-phase particles
in a base matrix
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28. Phase Transformations
strengthening involves alloys
w/c can be heated to form a
single high-temperature phase,
transformed to one or more
low-temperature phase upon
cooling
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29. Strengthening Heat Treatments
for Nonferrous Metals
Aging - a continuous process
which begins by the clustering
of solute atoms on distinct
planes of the parent lattice

30. Precipitation-hardening materials
can be classified:
Naturally Aging - the req. diffusion
at unstable to the stable 2-phase
structure at room temperature
Artificially Aging - require elevated
temperature

31. Silver- Copper Equilibrium Diagram

32. Enlargement of Copper

33. Aids to understanding the
nonequilibrium processes
Isothermal transformation (IT) or
time-temperature-transformation
(T-T-T) diagram

34. Bainite
Electron microscopy maybe
required for to resolve the carbides
in the resulting structure
Martensite
Exceptionally strong, hard & brittle

35. Martensite

36. Tempering
Subsequent cooling required to
restore some desired degree of
toughness at the expense of a
decrease in strength & hardness

37. Continuous Cooling Transformation
(C-C-T) Diagram
These diagrams are used to
represent which types of phase
changes will occur in a material
as it is cooled at different rates.

38. Jominy Test for Hardenability
Used to assist understanding of
nonequilibrium heat treatment

39. Hardness - a mechanical
property related to strength
and is strong function of the
carbon content of a metal

40. Hardenability - a measure of the
depth to which full hardness can
be attained under a normal
hardening cycle and is related
primarily to amounts and types
of alloying elements.

41. Adding alloy to steel
The primary reason for adding
alloy elements to commercial
steel is to increase the
hardenability , not to improve
the strength properties

42. Quench Media
Stages of quenching
First Stage (Vapor Jacket Stage)
Second Stage of Quenching
Third Stage

43. Water
is fairly good quenching
medium because of its high
heat of vaporization.
 is cheap, but the bubbles may
cause soft spots in metal

44. Brine (Salt)
 more severe quenching
medium than water because
salt creates bubbles , forcing a
more rapid transition through
the vapor jacket stage

45. The Role of Design
in the Heat Treatment
of Steel

46. Design Details &
Material Selection
Proper consideration of it leads:
 more simple,
 more economical
 more reliable products

47. Undesirable Design Features
Nonuniform sections or
thickness
Sharp Interior Corners
Sharp Exterior Corners

50. Residual Stresses
are often-complex results of
the various dimensional
changes that occur during
heat treatment

51. Austempering
The process called if the piece
is held at this temperature
long enough, the austenite will
transform to bainite.

52. Martempering/Marquenching
The process called if the piece is
stabilized and then slowly
cooled through the martensite
transformation

53. Ausforming
 a treatment used to strengthen
metals and improve its wear
properties

54. Surface Steel Hardening
Selective Heating of the Surface
Altered Surface Chemistry
Deposition of Additional Layer

55. Selective Heating Techniques
Selective Heating
Flame Hardening
Induction Heating
Laser beam hardening
Electron beam hardening

56. Altered Surface Chemistry
Pack Carburizing
Gas Carburizing
Liquid Carburizing/Cyaniding
Nitriding
Ionitriding

57. Heat Treatment Equipment
Batch Furnaces
Continuous Furnaces

58. Box-Type Furnace

59. Car-Bottom Box-Type Furnace

60. Vertical Pit Furnace

61. Bell-Type Pit Furnace

62. Elevator-Type Furnace

63. Continuous Furnace

64. Thank You!
Sario , Pamela May
Reporter