The document provides an overview of heat treatment processes for metals, which involve heating and cooling to alter mechanical properties for improved usability and safety. It describes various types of heat treatments, such as annealing, normalizing, hardening, tempering, and spheroidizing, with a focus on the annealing process, which softens steel and enhances its properties. Specific annealing methods are detailed, including full annealing, process annealing, spheroidizing annealing, and isothermal annealing, along with their purposes and processes.

1. HEAT TREATMENT
PROCESSES
PRESENTED BY: B.SRINIVAS
23RS5A0312

2. INTRODUCTION
•HEAT TREATMENT
• Heat treatment of metals may be defined as an operation or a
combination of operations involving the heating and cooling
of metals or alloys in the solid state to produce certain
desired properties.
• Its purpose is to change a mechanical property or
combination of mechanical properties so that the metal will
be more useful,serviceable,and safe for definite purpose .
• By heat treating, a metal can be made harder, stronger,and
more resistant to impact, heat treatment can also make a
metal softer and more ductile.

3. TYPES OF HEAT TREATMENT
1. ANNEALING
2. NORMALIZING
3. HARDENING
4. TEMPERING
5. SPHEROIDISING

4. ANNEALING
• Annealing may be defined as the softening process, in which
steels are heated to above the transformation range and
holding the steel at this temperature for certain time,then
allowed the steel to cool slowly in the furnance.
(OR)
• Annealing is the process for softening materials or to bring
about required changes in properties ,such as machinability,
mechanical or electrical properties,or dimensional stability.

5. PURPOSE OF ANNEALING
1. To soften the steel
2. To improve machinability
3. To refine grain size
4. To remove internal stresses
5. To increase ductility and toughness
6. To imrove mechanical properties

6. CLASSIFICATION OF ANNEALING PROCESSES
1. FULL ANNEALING
2. PROCESS ANNEALING
3. SPHEROIDISE ANNEALING
4. ISOTHERMAL ANNEALING

7. 1. FULL ANNEALING
• In the full annealing process , it
consists of heating the steel to
austenite phase, holding there for a
proper time and allowing it to cool
slowly in the “furnace” itself.
PROCESS : Full annealing consists of
1.Heating the hypo eutectoid steel to
a temperature of 30º to 50º C above
upper critical point 910º C(A3) and 30º
to 50º C above the lower critical point
723º C (A1,3) in the case of hyper

8. 2.Holding at this temperature for sufficient time so as to attain
internal structural changes.
3.Slow cooling on the furnace.

9. 2.PROCESS ANNEALING
• Process annealing is a subcritical
annealing operation. A subcritical
operation takes below the lower critical
temperature (A1)
• PROCESS :
1. Heating the steel to a temperature of
600-700º C
2. Holding at this temperature for a
prolonged time
3. “Slow cooling”

10. • PURPOSE OF PROCESS ANNEALING:
1. To reduce crystal distortions resulting from cold working.
2. To remove strain hardening.
3. To relieve internal stresses.
4. To get homogenous fine grained structure.

11. 3.SPHEROIDISE ANNEALING
In spheroidise annealing,lamellar
pearlite will be transformed into
granules or spheroids.
PROCESS:
1. Heting the steel above the lower
critical temperature (730-770º C).
2. Holding at this temperature for a
prolonged time.
3. Slow cooling in furnace upto 600º C
followed by air cooling

12. • PURPOSE OF SPHEROIDISE ANNEALING:
1. To improve machinability of medium and high carbon steels.
2. To improve ductility and toughness.
3. To reduce strength sand hardness.

13. 4.ISOTHERMAL ANNEALING
• “In isothermal annealing the process is
same as the full annealing except the
cooling rate(rapid cooling)”.
PROCESS:
1. Heating the hypo eutectoid steel to a
temperature of 30º to 50º C above
upper critical point 910º C(A3) and
30º to 50º C above the lower critical
point 723º C (A1,3) in the case of
hyper eutectoid steel.
2. Holding at this temperature for
certain time to form austenite.
3. Then steel is suddenly cooled to a

14. PURPOSE OF ISOTHERMAL ANNEALING:
1. To reduce the hardness of the alloy steels.
2. To reduce internal stresses.
3. To improve machinability.
4. To improve ductility and toughness.

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