Selective hardening processes allow for hardening of only specific areas of large or complex parts. This improves dimensional accuracy and reduces costs compared to fully hardening the entire part. Common selective hardening methods include flame, induction, laser, and electron beam hardening. Flame hardening uses an oxy-acetylene torch to heat treat small areas, while induction hardening uses induction coils to rapidly harden surfaces like gears or camshafts. Laser and electron beam hardening offer precise control over case depth and produce clean, self-quenched parts without quenching media. Selective hardening improves properties in localized areas while minimizing distortion of the overall part.

1. Selective Hardening
Processes
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2. Why Selective Hardening
 1. Parts to be heat-treated are so large
 2. Only a small segment, section, or area of the
part needs to be heattreated
 3. Better dimensional accuracy of a heat-treated
part
 4. Overall cost savings
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3. Methods of selective hardening
 Flame Hardening
 Induction Hardening
 Laser Hardening
 Electron Beam Hardening
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4. Flame hardening
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5. Features of Flame Hardening
1. Oxy acetylene torch is used
2. Torch is adjusted so that temp. is above critical range but
below 850°C
3. Torch is moved so that part is heated uniformly followed
by quenching
4. Tempering is done to reveal stresses
5. For good results carbon content should be between 0.3-
0.6%
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6. Advantages
Very rapid n provide
deep cases upto
6mm
Zone Hardening is
possible
Disadvantages
Depth of heat
penetration into metal
is difficult to control
Only certain steel can
be hardened
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7. Induction Hardening
 Process involves induction heating with Induction coil.
 Heating Effect is produced on the surface by Induction.
 Temperature produced is about 750-800°C
 Hardness to a Depth of 0.8mm is achieved in 1 to 5 secs.
 Suitable for heat treatment for camshafts, crankshafts,
gears etc..
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8. Advantages
 It is faster. Effect is produced in 1
to 5 secs.
 Irregular shapes can be handled
easily
 Depth of case can be controlled by
varying freq. and time
 Accuracy is possible and entire
process is cleaner
Disadvantages
 Steel required is more expensive
 Hardness depends on C content.
Therefore higher hardness is
obtained only if expensive alloy
steel is used.
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9. Applications
 Hardening of Irregular shaped surfaces such cams chain links, piston rods…
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10. Laser Hardening
 Phosphate coating is applied over surface to absorb laser
energy.
 Temp. of 900-1400°C is obtained
 Depth of heat absorption can be controlled by varying
power of laser
 Materials self quenched heat transfer to cooler mass
inside
 As no quenching media is involved work pieces are clean
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11. Electron Beam Hardening
 In this heat source is a beam of high energy electrons
 Beam is manipulated using electromagnetic coils
 Process is self quenched
 Depth of case varies from 0.1 to 1.5mm
 It is a conventional option due to less energy consumption
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