Answer the following questions using the phase diagram of the iron$-$carbon system.

a$)$ A plain carbon steel contains $70$ wt $\%$ ferrite and $30$ wt $\%$ pearlite. Estimate the carbon

content of the steel.

b$)$ This steel is heat treated under a CO$2-$CO$-20\%$ N$2$ gas mixture at $900$C$.$ The total pressure

in the furnace is $0\mathrm{.}9$ atm. Calculate the composition of a CO$2-$CO$-20\%$ N$2$ gas atmosphere that

will keep the carbon content of the steel unchanged throughout the heat treatment.

c$)$ Will the steel carburize or decarburize if the composition of a CO$2-$CO gas mixture used for the

heat treatment purpose consist of $80\%$ CO$-20\%$ CO$2.$ Briefly explain your reasoning.

d$)$ We would like to decrease the surface carbon content of the steel to $0\mathrm{.}2$ wt$\%$ carbon by

decarburizing it at $900$C in a CO$2-$CO gas atmosphere without changing the total pressure in

the furnace. What should be the composition of the CO$2-$CO gas mixture?

DATA:

C $+$ O$2=$ CO$2$G$=-394184-0\mathrm{.}84$ T joule$/$mole

C $+1/2$ O$2=$ CO $$G$=-111727-87\mathrm{.}66$ T joule$/$mole

R$=8\mathrm{.}314$ joule$/$mol degree.Answer the following questions using the phase diagram of the iron$-$carbon system.

a$)$ A plain carbon steel contains $70wt\%$ ferrite and $30wt\%$ pearlite. Estimate the carbon

content of the steel.

b$)$ This steel is heat treated under a $C{O}_2-CO-20\%N_2$ gas mixture at $900C.$ The total pressure

in the furnace is $0\mathrm{.}9$atm. Calculate the composition of $aC{O}_2-CO-20\%N_2$ gas atmosphere that

will keep the carbon content of the steel unchanged throughout the heat treatment.

c$)$ Will the steel carburize or decarburize if the composition of a $C{O}_2-CO$ gas mixture used for the

heat treatment purpose consist of $80\%CO-20\%C{O}_2.$ Briefly explain your reasoning.

d$)$ We would like to decrease the surface carbon content of the steel to $0\mathrm{.}2wt\%$ carbon by

decarburizing it at $900C$ in a $C{O}_2-CO$ gas atmosphere without changing the total pressure in

the furnace. What should be the composition of the $C{O}_2-CO$ gas mixture?

DATA:

$C+O_2=C{O}_2,G=-394184-0\mathrm{.}84T$ joule $\frac{?}{\text{m}\text{o}\text{l}\text{e}}$

$C+\frac{1}{2}{O}_2=CO,G=-111727-87\mathrm{.}66T$ joule $\frac{?}{\text{m}\text{o}\text{l}\text{e}}$

$R=8\mathrm{.}314$ joule $\frac{?}{\text{m}\text{o}\text{l}}$ degree.