7. Using the isothermal transformation diagram for an iron-carbon alloy of eutectoid composition below, specify the nature of the final microstructure (in terms of microconstituents 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. (10pts) 800 p Temperature (°C) 700 600 500 400 A -Eutectoid temperature B T 1400 1200 1000 L 00 600 T 800 L Temperature (°F) A 300- M(start) 50% 400 200 M+A M(50%) M(90%) 100 200 0 10-1 1 10 102 103 104 105 Time (s) A Austenite, P= Pearlite, B = Bainite, M = Martensite (a) Cool rapidly to 370°C, hold for 102 s, then quench to room temperature. (b) Rapidly cool to 580°C, hold for 10 s, then quench to room temperature. 5