List the microstructures that will form, when you continuously cool iron-carbon

Question

List the microstructures that will form, when you continuously cool iron-carbon alloy (0.76 wt% Carbon), from 750 degree C to room temperature for cooling rates of 170 degree C/s, 1 degree C/s, 20 degree C/s, and 100 degree C/s Show everything in a CCT diagram. (At the beginning of cooling, specimen is 100% Austenite) Explain different microstructures that are formed for iron-carbon alloys (fine pearlite, coarse pearlite, bainite etc..). Explain how they form and phases present. Draw a schematic of their microstructures, and describe their relative mechanical properties

Explanation / Answer

To do this need to have CCT curves for steel of this type. Typically this is a C shaped curve with the cooling curve superimposed on it.

750 is slightly above the eutectoid temperature so if austenite is given, the results would be Pearlite of different microstrucres.

The critical cooling rate is 140 /s higher than this martnesite forms at high cooling rate below 400

At 20/s pearlite, as the rate goes up, martensite occurs. After crossing 140s should get full martensite if quenched properly .

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