Using the isothermal transformation diagram for an iron?carbon alloy of eutectoid composition (Figure), specify the nature of the final microstructure (in terms of micro constituents present and approximate percentages of each) of a small specimen that has been subjected to the following time?temperature treatments. In each case assume that the specimen begins at 760?C (1400?F) and that it has been held at this temperature long enough to have achieved a complete and homogeneous austenitic structure.

(a)?? ? ??Cool rapidly to 700?C (1290?F), hold for 10⁴ s, then quench to room temperature

(b)?? ? ??Reheat the specimen in part (a) to 700?C (1290?F) for 20 h.

(c)?? ? ??Rapidly cool to 600?C (1110?F), hold for 4 s, rapidly cool to 450?C (840?F), hold for 10 s, then quench to room temperature

(d)?? ? ??Cool rapidly to 400?C (750?F), hold for 2 s, then quench to room temperature.

(e)?? ? ??Cool rapidly to 400?C (750?F), hold for 20 s, then quench to room temperature.

(f)?? ? ? ?Cool rapidly to 400?C (750?F), hold for 200 s, then quench to room temperature

(g) ? ? ??Rapidly cool to 575?C (1065?F), hold for 20 s, rapidly cool to 350?C (660?F), hold for 100 s, then quench to room temperature.

(h)?? ? ??Rapidly cool to 250?C (480?F), hold for 100 s, then quench to room temperature in water. Reheat to 315?C (600?F) for 1 h and slowly cool to room temperature.

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800 1400 Eutectoid temperature 700 1200 P. 600 1000 500 800 400 600 300 Mistart) 50%. 200 400 M{50%) M190%) 100 200 102 104 103 105 10 Time (s) Temperature "C) A, Temperature (°F)