Hardening is a process of heating a metal above its upper critical temperature and quenched in water,oil,and salt solutions. In this material is heated because the heated materials are some of the precipitants to inside them

1. BY
JEEVAN B M
1ST SEM, AUTOMOTIVE ELECTRONICS
P151905
SJCE,MYSORE
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2. Contents
• Introduction
• Quenching
• Tempering
• Methods of hardening
• Applications of hardening
• References
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3. INTRODUCTION
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• Hardening is process in which steel is heated to a temperature
above the critical point, held at this temperature and quenched in
water, oil or molten salt bath
• In this material is heated because the heated material or steel that
allow some of precipitates or alloying elements to go into it
• Selecting the hardening temperature depends up on
o material composition
o Carbon content
o Size or part to be hardened

4. Con..
• Heating rate is maintained slower to avoid warping and cracking
• Heating is followed by
o Quenching-means cooling process
o tempering
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5. 5
QUENCHING
• Quenching is a process of rapid cooling of hot object in order to cooling it
• Quenching is used to provide
o hardness to material
o Tensile strength
o Fatigue bending strength
• The most commonly used quenching media are water, salt and alkali
solutions, mineral oil and air burst.

6. Tempering
1.Tempering is usually performed after hardening, to reduce the some
of the excess of hardness.
2.It is done by heating the metal to some temperature below the critical
point for a certain period of time.
3.Allowing it to cool in still air
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7. Methods of hardening:
1.Quenching in two media
2.Hardening with self-tempering
3.Stepped quenching
4.Isothermal quenching
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8. 1.Quenching in two media
METAL
HEATINGAT
TEMP. 300 TO
400 C
QUENCHING IN
WATER MEDIA
QUENCHING IN
OIL AND AIR
BLAST
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9. 2.Hardening with self-tempering
1. in this method is not held in the quenching medium until it is completely
cooled but is withdrawn to retain a certain amount of heat in core which accounts
for the tempering (self-tempering).
2. more heat is retained in the core than is required for tempering and when the
tempering temperature is reached.
3. this hardening method is applied for chisels sledge hammers, hard hammers,
centre punches, and other tools that require a high surface hardness in conjunction
with a tough core
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10. Stepped quenching
1. in this method after heating the metal in hardening temperature metal is quenched
in a medium having a temperature slightly above(or below) point M (usually from
150 to 300 C)
2. then it is cooled further to room temperature in air or oil.
3. Austenite is transformed into martensite during the subsequent period of cooling to
room temperature.
4. This treatment will provide a structure of martensite and retained austenite in the
hardened metal.
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11. Isothermal quenching
its performed in the same manner, principally as Stepped quenching but with a longer
holding time at hot bath temperature (above the martensite point) to ensure a
sufficiently complete austenite decomposition (usually into acicular troostite or
bainite).
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12. Applications of hardening of Material
1.Construction materials - High strength reduces the need for material thickness which
generally saves weight and cost.
2.Machine cutting tools (drill bits, taps, and lathe tools) need be much harder than the
material they are operating on in order to be effective.
3.Knife blades – a high hardness blade keeps a sharp edge.
4.Bearings – necessary to have a very hard surface that will withstand continued stresses.
5.Armor plating - High strength is extremely important both for bullet proof plates and for
heavy duty containers for mining and construction.
6.Anti-fatigue - (Martensitic) case hardening can drastically improve the service life of
mechanical components with repeated loading/unloading, such as axles and cogs.
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13. References:
 Engineering Physics Metallurgy-Y.LAKHITN
 https://en.wikipedia.org/wiki/Quenching
 Evaluation of As-Quenched Hardness- O. R. Bodede, P. O.
Ojo, O. R. Ayodele, A. F. Owa and O. B. Ajayi
 http://www.eng.uokufa.edu.iq/staff/mwahids/lic/3Hardening.
pdf
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