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.
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
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
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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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
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
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
48.
49.
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.