Dr. H. K. Khaira
Professor in MSME
• Lifting devices in their various forms are
constructed from a range of materials that
have specific properties for the function they
• The inherent structure that provides these
necessary properties may not be capable of
meeting a range of “working demands”.
• It is then necessary to enhance these
properties by some means.
• Alloying, cold working processes and heat
treatment are ways of altering the structure of a
material to improve its properties.
• These structure-altering procedures are often
employed in combination to achieve the desired
• For example, iron alloyed with carbon produces
steel that is further enhanced with other metals
such as molybdenum, chromium and vanadium.
• The forging process will again change the
properties, as will heat treatment.
Tools for Controlling Properties of
• 1. Alloying
• 2. Cold Working
• 3. Heat treatment
• Heat treatment is defined as heating a metal
to a specified temperature, keeping it at that
temperature for some time followed by
cooling at a specified rate.
• It is a tool to get required microstructure and
properties in the metal.
Heat treatment - controlled heating and cooling basically
The basic steps of heat treatment are:
Heating → Soaking → Cooling
Important Parameters in Heat treatment
Time of soaking
Rate of cooling
Medium of cooling
-Different combinations of the above parameters
Give rise to different heat treatments
• Annealing is a heat treatment in which the metal is heated
to a temperature above its recrystallisation
temperature, kept at that temperature some time for
homogenization of temperature followed by very slow
cooling to develop equilibrium structure in the metal or
• The steel is heated 30 to 50oC above Ae3 temperature in
case of hypo-eutectoid steels and 30 to 50oC above A1
temperature in case of hyper-eutectoid temperature
• The cooling is done in the furnace itself.
• The aim of annealing is to increase the ductility.
• Normalizing consists of heating a suitable steel
to a temperature 50-1000 C above Ae3
temperature in case of hypoeutectoid steels
and above Acm temperature in case of hypereutectoid steel, soaking for sufficient time and
then cooling in still air.
• The aim of normalizing is to increase the
• In hardening heat treatment, the steel is heated
30 to 50oC above Ae3 temperature in case of
hypo-eutectoid steels and 30 to 50oC above A1
temperature in case of hyper-eutectoid
temperature, held at that temperature for some
time followed by cooling at a rate faster than the
critical cooling rate to produce martensite which
is a hard phase.
• The aim of hardening is to increase the hardness
and strength of the steel.
• Tempering consists of heating a hardened
steel to a temperature below eutectoid
temperature and keeping it at that
temperature for a specified time to reduce
brittleness followed by air cooling.
• The aim of tempering is to decrease
brittleness of hardened steel.
• Precipitation Hardening (or Age Hardening) is
a heat treatment in which the strength
increases due to precipitation of second phase
particles in the parent phase.
• The aim of precipitation hardening is to
increase the hardness and strength .
Heat Treatment Temperature
ranges to which the
steel has to be
heated for different