d$)$

Figure $3$: Temperature$-$Time$-$Transformation curve of $4140$ steel.

$4140$ steel was heat treated under different conditions. Giving a detailed deseription, use the TTT curves above to predict the final microstructure of the steels shown in the table below.

$\backslash$table$[[$Condition $1,$Heat to $800C,$ cool in brine to $500C,$ soak$],[,$at $500C$ for $17$ mins, cool to room$],[$Condition $2,$temperature.$],[$Condition $3,$Heat to $800C,$ cool in furnace$],[,$Heat to $800C,$ cool in water to $250C,$ soak$],[$Condition $4,$for $1\mathrm{.}5$ mins, cool to room temperature$],[,$Heat to $800C,$ cool in water to $100C,$ heat$],[,$to $400C,50$ ak for $20$ mins, cool to room$],[,$temperature$]]$

$[12$ Marks$]$