250+ TOP MCQs on Iron-Carbon Systems and Answers

Materials Science Question Bank on “Iron-Carbon Systems”.

1. What is maximum solubility % of carbon and temperature range that α-ferrite exist?

a) 0.05% and 273°c to 910°c
b) 0.025% and 273°c to 910°c
c) 2.1% and 910°c to 1394°c
d) 0.05% and 910°c to 1124°c
Answer: b
Clarification: Interstitial solid solution of C in BCC iron. Max solubility of C is 0.025% and it exists from 273°C to 910°C.

2. What is maximum solubility % of carbon and temperature range that Austenite (Ɣ) exist?

a) 0.05% and 273°c to 910°c
b) 0.025% and 273°c to 910°c
c) 2.1% and 910°c to 1394°c
d) 0.09% and 1394°c to 1539°c
Answer: c
Clarification: Interstitial solid solution of C in FCC iron has a 2.1% max solubility of C and exists from 910°C – 1394°C.

3. What is maximum solubility % of carbon and temperature range that δ-ferrite exist?

a) 0.05% and 273°c to 910°c
b) 0.025% and 273°c to 910°c
c) 2.1% and 910°c to 1394°c
d) 0.09% and 1394°c to 1539°c
Answer: d
Clarification: δ-ferrite (BCC) exists over the temperature range of 1394°C to 1539°C and the maximum solubility of C is 0.09%.

4. What is the % C content in Cementite (Fe₃C)?

a) 6.67%
b) 0.025%
c) 2.1%
d) 0.09%
Answer: a
Clarification: It is an intermetallic compound. C content in Fe₃C is 6.67%.

5. What is the hardest phase of Fe-C system?

a) Graphite
b) Bainite
c) Martensite
d) Cementite
Answer: d
Clarification: Cementite is the hardest phase in the Iron-Carbon system whereas martensite is not a phase because it is metastable in nature.

6. What is eutectoid temperature?

a) 727°c
b) 768°c
c) 1146°c
d) 1495°c
Answer: a
Clarification: The eutectoid temperature (727°C) during heating and cooling is Ac1 and Ar1 respectively. Eutectoid reaction is a reaction that transforms one solid into two different solids on cooling.

7. At what temperature Fe turns paramagnetic while heating?

a) 727°c
b) 768°c
c) 1146°c
d) 1495°c
Answer: b
Clarification: At 768°C. Iron converts from ferromagnetic to paramagnetic and this temperature is known as curie temperature. It is also called as A₁ isotherm in iron carbon phase diagram.

8. What is the value of eutectic temperature?

a) 727°c
b) 768°c
c) 1146°c
d) 1495°c
Answer: c
Clarification: The eutectic temperature for Fe-C system is 1146°C. The eutectic reaction is a reaction that transforms one liquid phase into two solid phases on cooling.

9. What is the value of peritectic temperature?

a) 727°c
b) 768°c
c) 1146°c
d) 1495°c
Answer: d
Clarification: The peritectic temperature is at 1495°C for the Fe-C system. The peritectic reaction is a reaction that transforms one liquid and solid to another solid on cooling.

10. Carbon steel containing 9,1% ferrite is cooled from the region of austenitic (727 °c). What is the percentage C content in the steel?
a) 0.05% C
b) 0.1% C
c) 0.2% C
d) 0.3% C
Answer: b
Clarification: Let c be Carbon content. Applying the lever rule
0.091 = (6.67 – c)/(6.67 – 0.025)
c = 0.1% C.