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Using the Animated Figure 10.40 , the isothermal transformation diagram for a 0.45wt% C steel alloy, specify the nature of the final microstructure (in terms of the microconstituents present) of a small specimen that has been subjected to the following temperature treatments. In each case assume that the specimen begins at 845C 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 degrees C, hold for 1000s, then quench to room temperature. b) Rapidly cool to 450 degrees C, hold for 10s, then quench to room temperature. proeutectoid ferrite + pearlite proeutectoid ferrite + martensite proeutectoid ferrite + pearlite + martensite proeutectoid ferrite + pearlite + bainite + martensite all spheroidite all bainite all martensite bainite + martensite