Using the Animated Figure $10\mathrm{.}40,$ the isothermal transformation diagram for a $0\mathrm{.}45wt\%C$ 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 $700$ degrees $C,$ hold for $100,000$ s$,$ then quench to room temperature.

b$)$ Rapidly cool to $625$ degrees $C,$ hold for $1$ s $,$ then quench to room temperature.