Using the isothermal transformation diagram for a 0.45 wt% C steel alloy (Figure below), 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 845ï°C (1550ï°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 250ï°C (480ï°F), hold for 103 s, then quench to room temperature.
(b) Rapidly cool to 700ï°C (1290ï°F), hold for 30 s, then quench to room temperature.
(c) Rapidly cool to 400ï°C (750ï°F), hold for 500 s, then quench to room temperature.
(d) Rapidly cool to 700ï°C (1290ï°F), hold at this temperature for 105 s, then quench to room temperature.
(e) Rapidly cool to 650ï°C (1200ï°F), hold at this temperature for 3 s, rapidly cool to 400ï°C (750ï°F), hold for 10 s, then quench to room temperature.
(f) Rapidly cool to 450ï°C (840ï°F), hold for 10 s, then quench to room temperature.
(g) Rapidly cool to 625ï°C (1155ï°F), hold for 1 s, then quench to room temperature.
(h) Rapidly cool to 625ï°C (1155ï°F), hold at this temperature for 10 s, rapidly cool to 400ï°C (750ï°F), hold at this temperature for 5 s, then quench to room temperature.
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