COOLING CURVE TRANSFORMATION DIAGRAM

COOLING CURVE TRANSFORMATION DIAGRAM

1. CONTINUOSLY COOLING TRANFORMATION ( CCT )

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

3. Introduction 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. CCT diagram for Fe-C system 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.

5. Properties of 0.8% C steel Constituent Hardness (R c ) Tensile strength (MN / m 2 ) Coarse pearlite 16 710 Fine pearlite 30 990 Bainite 45 1470 Martensite 65 - Martensite tempered at 250 o C 55 1990 Carbon contain and its effect on mechanical properties

6. Factors Affecting CCT Diagram Grain size Carbon content Alloying elements

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

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