Using the isothermal transformation diagram for a $1\mathrm{.}13wt\%C$ steel alloy $($Figure $10\mathrm{.}39),$ 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 $920C(1690F)$ and that it has been held at this temperature long enough to have achieved a complete and homogeneous austenitic structure.

$($a$)$ Rapidly cool to $250C(480F),$ hold for $103$ s $,$ then quench to room temperature.

$($b$)$ Rapidly cool to $775C(1430F),$ hold for $500$ s $,$ then quench to room temperature.

$($c$)$ Rapidly cool to $400C(750F),$ hold for $500$ s $,$ then quench to room temperature.

$($d$)$ Rapidly cool to $700C(1290F),$ hold at this temperature for $105$ s $,$ then quench to room temperature.

$($e$)$ Rapidly cool to $650C(1200F),$ hold at this temperature for $3$ s $,$ rapidly cool to $400C(750F),$ hold for $25$ s $,$ then quench to room temperature.

$($f$)$ Rapidly cool to $350C(660F),$ hold for $300$ s $,$ then quench to room temperature.

$($g$)$ Rapidly cool to $675C(1250F),$ hold for $7$ s $,$ then quench to room temperature.

$($h$)$ Rapidly cool to $600C(1110F),$ hold at this temperature for $7$ s $,$ rapidly cool to $450C(840F),$ hold at this temperature for $4$ s $,$ then quench to room temperature.

Figure $10\mathrm{.}39$ Isothermal transformation diagram for a $1\mathrm{.}13wt\%C$ iron$-$carbon alloy: A $,$ austenite; $B,$ bainite; C$,$ proeutectoid cementite; $M,$ martensite; $P,$ pearlite.

$[$Adapted from H$.$ Boyer $($Editor$),$ Atlas of Isothermal Transformation and Cooling Transformation Diagrams, $1977.$ Reproduced by permission of ASM International, Materials Park, OH$.]$