UNIT IV HEAT TREATMENT

1. CONTINUOSLY
COOLING
TRANFORMATION (CCT)

2.  Introduction
 CCT Diagram for Fe – C
 Carbon Contain and Its Effect On Mechanical
Properties
 Factors Affecting CCT Curve
 Reference

3. There are two types of CCT diagrams
 Plot of (for each type of transformation)
transformation start, specific fraction of transformation
and transformation finish temperature against
transformation time on each cooling curve
 Plot of (for each type of transformation)
transformation start, specific fraction of transformation
and transformation finish temperature against cooling
rate or bar diameter for each type of cooling medium

4.  It measure the extent of transformation as a function
of time for a continuously decreasing temperature.
 Usually materials are cooled continuously, thus
Continuous Cooling Transformation diagrams are
appropriate.
 For continuous cooling, the time required for a reaction
to begin and end is delayed, thus the isothermal curves are
shifted to longer times and lower temperatures
 Main difference between TTT and CCT diagrams: no space
for bainite in CCT diagram as continuous cooling always results in
formation of pearlite.

6. Properties of 0.8% C steel
Constituent Hardness
(Rc)
Tensile strength (MN /
m2)
Coarse pearlite 16 710
Fine pearlite 30 990
Bainite 45 1470
Martensite 65 -
Martensite tempered at
250 oC
55 1990

8.  Grain size
 Carbon content
 Alloying elements

12.  www.msm.cam.ac.uk/phase-
trans/2012/Manna/Part3.ppt
 www.dss.nitc.ac.in/.../32%20TTT%20AND%20
CCT%20DIAGRAMS.ppt
 nptel.ac.in/courses/Webcourse-
contents/IISc.../PPTs/MTS_07_m.pdf
 www.csun.edu/~bavarian/Courses/.../Lectur
es.../ch11_Phase_Transf.ppt