Time temperature-transformation diagram

Education

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: [email protected] 1

2. Isothermal Transformation (I.T) / Time Temperature Transformation (TTT) Diagram Today we will discuss about its Construction 2 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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4. Step: 4 After Cooling, check sample hardness and microstructure. 4

5. 5 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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7. 7 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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10. 10 Composition of AISI 1080 Steel C= 0.75-0.88, Mn= 0.60-0.90 , P= 0.040, S= 0.050 Fe= balance

11. 11 (TTT) curve of carbon steel AISI 1050 ( H ypoeutectoid steel)

12. 12 Example: Effect of Alloying Elements

13. 13 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