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Time temperature-transformation diagram
1. MM: 304 Heat treatment
Topic: Transformation diagrams
Compiled for T.E, Metallurgy
by
Engr. Muhammad Ali Siddiqui
Lecturer
Department of Metallurgical Engineering
NED university of Engineering and technology
Email: muetali@yahoo.com
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2. Isothermal Transformation (I.T) /
Time Temperature Transformation (TTT)
Diagram
Today we will discuss about its Construction
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What is TTT?
๏ผ T (Time) T (Temperature) T (Transformation) diagram is a plot
of temperature versus the logarithm of time for a steel of
definite composition.
๏ผ It is used to determine when transformations begin and end for
an isothermal (constant temperature) heat treatment of a
previously austenitized alloy.
13. 13
๏ผ A cooling curve is
determined experimentally
by placing a thermocouple
at a definite location in a
steel sample and then
measuring the variation of
temperature with time.
๏ผ Since the coordinates of
the I-T diagram are the
same as those for a
cooling curve,
๏ผ it is possible to
superimpose various
cooling curves on the I-T
diagram. This is shown in
the figure given below.
Cooling Curves and the I-T Diagram