Question $3$

$($a$)$ You have been given samples of the following materials:

$($i$)$ Pure iron

$($ii$)0\mathrm{.}3wt\%$ carbon steel

$($iii$)1\mathrm{.}2wt\%$ carbon steel.

Sketch the structures $(20-25mm$ circular field$)$ that you would expect to see at room temperature if you looked at polished sections of the samples under a reflecting light microscope. Label the phases, and any other features of interest. You may assume that each specimen has been cooled moderately slowly from a temperature of $1100C.$

$(9$ marks$)$

$($b$)$ Consider $10$ kg of austenite containing $0\mathrm{.}65wt\%C$ cooled slowly. Using the diagram in in Figure $3$:

$($i$)$ What is the pro$-$eutectoid phase, and what is its mass at the eutectoid temperature?

$($ii$)$ How many kg each of pearlite and the pro$-$eutectoid phase form just below the eutectoid temperature?

$($iii$)$ How many kg each of ferrite and cementite form at room temperature?

$($iv$)$ What is the mass of the pearlite at room temperature? If the answer is different from $($ii$),$ why?

$($v$)$ Calculate the fraction of ferrite in pearlite at room temperature.

$(11$ marks$)$

Figure $3$