Ttt diagram for eutectoid steel(bainite, spherodite, martensite)

TTT diagram for eutectoid steel(bainite, spherodite, martensite)

1. TTT DIAGRAM FOR EUTECTOID STEEL(BAINITE, SPHERODITE, MARTENSITE) 4PRESENTED BY DARSHIT DESAI EMAIL: [email protected]

2. BAINITE The microstructure of bainite consists of ferrite and cementite phases, and thus diffusion processes are involved in its formation . Bainite forms as needles or plates, depending on the temperature of the transformation. T he microstructure details of bainite are fine so that their resolution is possible only using electron microscopy can not in optical microscope.

3. B ainite forms at temperatures between about 215 and 540C ( 420 and 1000F ).

4. Microstructure of B ainite

5. SPHEROIDITE If a steel alloy having either pearlitic or bainitic microstructures is heated to, and left at, a temperature below the eutectoid for a sufficiently long period of time—for example , at about 700C (1300F) for between 18 and 24h—yet another microstructure will form. It is called spheroidite

6. Microstructure of Spheroidite Cementite Ferrite

7. MARTENSITE M artensite is formed when austenitized iron–carbon alloys are rapidly cooled (or quenched) to a relatively low temperature. Martensite is a nonequilibrium single-phase structure that results from a diffusion less transformation of austenite. Martensite is a nonequilibrium single-phase structure that results from a diffusion less transformation of austenite.

8. Martensite have a body centered tetragonal (BCT) crystal structure. Martensitic transformation does not involve diffusion, it occurs almost instantaneously. The Martensite grains nucleate and grow at a very rapid rate Thus the martensitic transformation rate is time independent. Martensite grains take on a plate like or needle like microstructure.

9. Microstructure of Martensite Return austenite Martensite needle

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