Question

5 Three steels with a composition of Fe-0.2 wt.% C, Fe-0.76 wt.% C and Fe-1.1 wt.% Care produced by melting and slowly cooling down to room temperature. By referring the phase diagram provided in figure 3, what would you expect in terms of phase changes (solidification sequence) in all three alloys as the temperature of the alloys reduces from melting temperature to room temperature? What will be the approximate weight fraction of each of those micro constituents at room temperature for the three steels?

5 Three steels with a composition of Fe-0.2 wt.% C, Fe-0.76 wt.% C and Fe-1.1 wt.% Care produced by melting and slowly cooling down to room temperature. By referring the phase diagram provided in figure 3, what would you expect in terms of phase changes (solidification sequence) in all three alloys as the temperature of the alloys reduces from melting temperature to room temperature? What will be the approximate weight fraction of each of those micro constituents at room temperature for the three steels?

Answer 1

1600 1538°C 1493c L 1400 1394 Y+L 1200 1147°C 2.14 4.30 y, Aystenite Temperature (°C) 1000 912°C y + Fe3C 800 9 727°C 0.76 600 0.522 'a, Ferrite a + Fezc Cementite (Fe3C). 400 0 0.2 0.161 (Fe) 11 2 6 6.7 0 3 4 Composition (wt% C)

Steel 1: Fe-0.2 wt % C

Cooling of steel 1 is shown by green line in the above diagram. From above diagram steel 1 starts melting from 1500⁰C (approximate).

From liquid it is first changed to a phase of "$\delta$- ferrite + Liquid" .

Then it turns to "$\gamma$- Austenite" at 1493⁰C.

Then at 727⁰C it will change its phase to "$\alpha$+ Pearlite"

Therefore at room temperature its microstructure is "$\alpha$+ Pearlite"

Steel 2: Fe-0.76 wt% C

Cooling of steel 2 is shown by blue line in the above diagram. From above diagram steel 2 starts melting from 1480⁰C (approximate).

From liquid it is first changed to a phase of "$\gamma$- Austenite + Liquid" .

Then it turns to "$\gamma$- Austenite" at 1400⁰C.

Then at 727⁰C it will change its phase to "Pearlite"

Therefore at room temperature its microstructure is "Pearlite".

Steel 3: Fe-1.1 wt% C

Cooling of steel 3 is shown by blue line in the above diagram. From above diagram steel 3 starts melting from 1450⁰C (approximate).

From liquid it is first changed to a phase of "$\gamma$- Austenite + Liquid" .

Then it turns to "$\gamma$- Austenite" at 1320⁰C.

Then at 727⁰C it will change its phase to "Pearlite+Fe₃C"

Therefore at room temperature its microstructure is "Pearlite+Fe₃C".

b a & b les respectives. Cach are the concentration of at 'i' is The mass fraction of a G-Co Ma = (b-Ca. 'b' at 6 is Similarly fraction of mb Co-Ca C6 - Ca. mass -

3. Weight fraction of pearlite and Cementite (Fes() in Toto steel-3 (Fe- lil wt. () at all 0.76 6.7 Р fezc. weight fraction of peoslite, mp. 6.7-11 6.7 -0.76 mp=0.9428 Weight fraction of fest, fic pode Mrezc 1-1- 8.76 -0.0572 6.7 -0.76 waardoor fazl 0.0572
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