Using the isothermal transformation diagram for a 0.45 wt% C steel alloy (Figure), determine the final microstructure (in terms of just the microconstituents present) of a small specimen that has been subjected to the following time-temperature treatments. In each case assume that the specimen begins at 845(C (1550(F), and that it has been held at this temperature long enough to have achieved a complete and homogeneous austenitic structure.

(a)? ? ? ?Rapidly cool to 250?C (480?F), hold for 10³ s, then quench to room temperature.

(b)? ? ? ?Rapidly cool to 700?C (1290?F), hold for 30 s, then quench to room temperature.

(c)? ? ? ?Rapidly cool to 400?C (750?F), hold for 500 s, then quench to room temperature.

(d)? ? ? ?Rapidly cool to 700?C (1290?F), hold at this temperature for 10⁵ s, then quench to room temperature

(e)? ? ? ?Rapidly cool to 650?C (1200?F), hold at this temperature for 3 s, rapidly cool to 400?C (750?F), hold for 10 s, then quench to room temperature.

(f) ? ? ? ?Rapidly cool to 450?C (840?F), hold for 10 s, then quench to room temperature.

(g)? ? ? ?Rapidly cool to 625?C (1155?F), hold for 1 s, then quench to room temperature.?

(h)? ? ?Rapidly cool to 625?C (1155?F), hold at this temperature for 10 s, rapidly cool to 400?C (750?F), hold at this temperature for 5 s, then quench to room temperature.

900 1600 A. 800 A +C 1400 700 1200 A+ P 600 1000 A +B 500 800 400 A 600 300 50 % M(start) 400 200 M(50%) 100 200 M(90%) 102 10 104 105 106 10 Time (s) Temper ature C) Temperature ('F)