$(10$pts total$)$ Using the isothermal

transformation diagram $($TTT diagram, right$)$

for a eutectoid steel alloy, answer the following

questions. In each case, assume that the

specimen begins at $760^($@$)$C and that it has been

held at this temperature long enough to have

achieved a complete and homogeneous

austenite structure. $($A: austenite, P: pearlite, B:

bainite, M: martensite$)$

$($a$)(3$ pts$)$ Determine the final microstructure

$($in terms of the percentages of the

microconstituents present$)$ when the

specimen is rapidly cooled to $700^($@$)$C$,$ held

for $10^(5)$sec$,$ then slowly cooled to room

temperature.

$($b$)(3$ pts$)$ Determine the final microstructure $($in terms of the percentages of the

microconstituents present$)$ when the specimen is rapidly cooled to $400^($@$)$C$,$ held at this

temperature for $2$ sec $,$ then quenched to room temperature.

$($c$)(4$ pts$)$ Sketch and label a time$-$

temperature path $($on the TTT diagram, left$)$

to produce the microstructure containing

$50\%$ pearlite, $25\%$ bainite, and $25\%$

martensite.

please solve and explain each part.