Using the isothermal transformation diagram for an iron$-$carbon ally of eutectoid composition $($as given above$),$ determine the final microstructure $($in terms of phase name and its percentage$)$ of a small specimen that has been subjected to the following time$-$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.

Cool rapidly to $350C,$ hold for ${10}^{4}s,$ then quench to room temperature:

Cool rapidly to $150C,$ hold for ${10}^{5}S,$ then quench to room temperature:

Cool rapidly to $450C,$ hold for $10s,$ then quench to room temperature:

Cool rapidly to $625C,$ hold for $10s,$ then quench to room temperature:

$100\%$ martensite

x

$100\%$ austenite

$50\%$ bainite and $50\%$ martensite

$100\%$ bainite

x