Using the Animated Figure $11\mathrm{.}50,$ the isothermal transformation diagram for a $\backslash (1\mathrm{.}13\backslash$mathrm$\{$wt$\}\backslash \%\backslash$mathrm$\{$C$\}\backslash )$ steel alloy, determine 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 $\backslash (920^\{\backslash$circ$\}\backslash$mathrm$\{$C$\}\backslash )$ 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 $1000$ s $,$ then quench to room temperature.

b$)$ Rapidly cool to $675$ degrees C $,$ hold for $7$ s $,$ then quench to room temperature.