This document summarizes induction hardening and flame hardening surface hardening techniques. It explains that surface hardening increases the hardness of a component's outer surface while leaving the core soft. Induction hardening uses an induction coil to heat a component's surface above the critical temperature, then quenches it to form martensite for hardness. Flame hardening uses an oxy-acetylene flame to selectively harden specific surface areas, then quenches. Both provide wear resistance and control over hardness depth. Induction hardening offers more control and less distortion while flame hardening is economical for large or complex parts.
2. SURFACE HARDENING
It is process of heat treatment in order to increase the hardness
of the outer surface while the core remains relatively soft.
It increases wear resistance , resistance to high contact stresses ,
improve fatigue resistance and corrosion resistance.
CAM, RING GEAR, BEARINGS, etc. requires Surface Hardening.
3. SOME COMMON SURFACE HARDENING TECHNIQUES
• INDUCTION HARDENING
• FLAME HARDENING
• LASER BEAM HARDENING
• ELECTRON BEAM HARDENING
4.
5. PRINCIPLE
When the metallic workpiece
(usually steel) is placed in a coil
and current is flown
In the coil then current is
induced on the surface of the
metallic workpiece
and it is heated upto above its
critical temperature.
6. WHY CHOOSE INDUCTION HARDENING ?
• Has much faster heating rate than other methods.
• Provides for more control over outcome
- Less distortion of workpiece
- Easy control of hardness depth
• Heating can be localized for surface hardening
- Allows the core metal to be unaffected
7. TYPICAL HEAT TREATMENT PROCEDURES
• An induction heater consists of
an electromagnet
- Creates a high frequency Alternating
Current (AC).
• Heats the component(0.3%-0.7% of carbon
content) to the
Austenitizing temperature.
• Holds it at temperature long
enough to complete the formation
of Austenite.
8. QUENCHING STAGE OF HEAT CYCLE
• Rapidly cools the metal
until Martensitic transformation
occurs.
• Changes structure from
FCC to BCC.
• Causes a transformation
of the initial structure of the steel
into Martensite.
9. VARIATION OF DEPTH VS FREQUENCY
Where,
d=depth of hardening
p=resistivity
f = frequency
For Deep Hardening a prolonged low frequency
Heating should be employed and vice-versa.
10. ADVANTAGES
• Fast process
• No Scaling or Decarburisation
• Minimum chances of distortion
• Selectively Hardening
• Ease control of hardness depth
• High wear and fatigue resistance
DISADVANTAGES
• Equipment is more costly
11. FLAME HARDENING
• It is a rapid high intensity heating, economical
method for selectively hardening specific areas
on the surface of a part followed by an
appropriate quenching method.
• Uses direct impingement of an oxy-acetylene
gas flame onto a defined surface area.
• Used to treat components such as gears,
shafts, cams, crankshafts, camshafts, etc.
12. TYPES OF FLAME HARDENING
• STATIONARY FLAME HARDENING:- requires specified area to be heated
• PROGRESSIVE FLAME HARDENING:- integrated quench capability
• SPIN FLAME HARDENING:- requires specified area to spin in front of flame head
• COMBINATION FLAME HARDENING:- couples the progressive and spinning methods
13. HEAT TREATMENT PROCEDURES
• It may be a single torch with a
specially designed head that
automatically indexes and heats the
work material.
• Large parts such as gears or machine
toolways with sizes or shapes that
would make furnace heat treatment
impractical, are easily flame hardened.
14. QUENCHING STAGE
• After heating is
completed, the
parts are
quenched by
water spray or
by complete
immersion in
water.
15. DEPTH OF HARDENED LAYER DEPENDS ON FOLLOWING
PARAMETERS
• Distance between gas flames and the component surface.
• Gas pressure and ratio.
• Rate of travel of flame head or component.
• Type, volume and application of quench.
16. ADVANTAGES
• Fast process
• Less distortion surface
• Selectively hardening
• Faster localized cooling rates
DISADVANTAGES
• Some oxidation or decarburization may occur as compared to induction hardening.
• Explosive fuel gases have to be used cautiously.
