Time temperature-transformation diagram
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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: [email protected] 1
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Transcript of Time temperature-transformation diagram
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MM: 304 Heat treatmentTopic: Transformation diagrams
Compiled for T.E, MetallurgybyEngr. Muhammad Ali SiddiquiLecturerDepartment of Metallurgical EngineeringNED university of Engineering and technologyEmail: [email protected]
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Isothermal Transformation (I.T) / Time Temperature Transformation (TTT)
Diagram
Today we will discuss about its Construction
What is TTT? T (Time) T (Temperature) T (Transformation) diagram is a plot
of temperature versus the logarithm of time for a steel of definite composition.
It is used to determine when transformations begin and end for an isothermal (constant temperature) heat treatment of a previously austenitized alloy.
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Step: 4 After Cooling, check sample hardness and microstructure.
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• Step 2,3 and 4 are shown in the following Figure
• If we draw a curve b/w %age of Pearlite Transformed and Time
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Step: 5 all steps are repeated at different sub-critical temperature below Ac1 in order to get sufficient points for plotting the curve.
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Composition of AISI 1080 Steel
C= 0.75-0.88, Mn= 0.60-0.90 ,
P= 0.040, S= 0.050
Fe= balance
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(TTT) curve of carbon steel AISI 1050 (Hypoeutectoid steel)
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Example: Effect of Alloying Elements
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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.
Since the coordinates of the I-T diagram are the same as those for a cooling curve,
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
