Heat treatment process(TTT, CCT &CCR) For material technology subject

1. SEMINAR ON
HEAT TREATMENT PROCESS
(TTT,CCT & CCR)
NAME- KISHOR T.
GHEGAD
ROLL NO-2663
CLASS-S.E.(MECH.)
WEL-COME

2. INTRODUCTION
The heat treatment is a very broad term and
includes any heating and cooling operations or
any sequence of heat of two or more such
operation applied to any material in order to
modify its internal structure or to alter its physical,
mechanical or chemical properties. Heat treatment
is carried out by heating the material to some
specific temperature, holding at that temperature
for a define period and cooling to room
temperature or below room temperature with a
definite rate.

3. HEAT TREATMENT OF STEEL:-
The heat treatment is a very
broad term and includes
any heating and cooling
operation or any sequence
of two or more such
operation.

4. OBJECTIVE OF HEAT TREATMENT OF STEEL:-
1) To increase hardness, wear and abrasion resistance.
2) To remove internal stresses.
3) To increase machinability.
4) To refine grain structure.
5) To change the composition of steel.

5. TTT DIAGRAMS
TTT diagram stands for “time-temperature-
transformation” diagram. It is also called isothermal
transformation diagram
Definition: TTT diagrams give the kinetics of
isothermal transformations.

6. TIME TEMPERATURE TRASFORMATION (TTT) DIAGRAM:-
The iron-iron carbide equilibrium diagram is having
little value in the study of the steels cooled under non
equilibrium conditions. It has been found in the study of
steel that, Austenite is unstable below the lower critical
temperature A1.Below A1 temperature austenite may
transform to pearlite, bainite or martensite, It is
necessary to know that, How these transformation
occurred. To study the transformation of austenite,
eutectoid composition of 0.8% carbon steel bar is cut
into large number of specimens

7. Fig. TTT diagram for eutectoid steel

8. CONTINUOUS COOLING TRANSFORMATION (CCT) DIAGRAM:-
A cooling curve is determine experimentally
by placing a thermocouple at a definite
location in steel sample and then measuring
the variation of temperature with time. Since
the coordinates of the TTT and CCT diagram
are same those for a cooling curve. It is
possible to superimpose variation cooling
curve on them.

9. Fig. Continuous cooling transformation (CCT)

10. CRITICAL COOLING RATE (CCR)
When cooling curve tangent to the nose of TTT
curve, it is called as critical cooling rate(CCR).
CCR can be defined by two ways ‘The slowest
cooling rate at which unstable austenite can be
transformed into martensite.’
or
‘The faster cooling rate or within minimum time at
which unstable austenite can be transformed into
perlite.’

12. FACTOR AFFECTING ON COOLING RATE:-
(1) Carbon content.
(2) Austenite temperature.
(1) Carbon content:-
With higher carbon content or alloying element,
decrease critical cooling rate and shift TTT curve towards
right. It rated the transformation of austenite to perlite or
bainite.
(2) Austenite temperature:-
Higher the austenitic temperature, it will coarsen
the structure and make it softer. Higher austenitic
temperature gives lower critical cooling time and increase
CCR.

13. REFERENCE:-
1) Material technology textbook by S.B.
BARVE
2) http://www.slideshare.net
3)http://www.chegg.com
4)http://en.wikipedia.org/wiki/Isothermal_tran
sformation_diagram

14. Thank you