Engineering Questions with Answers - Multiple Choice Questions

# Materials Science MCQ’s – Phase Transformations in Iron-Carbon Systems

1 - Question

What is the Peritectic reaction at 1495°C?
a) L (0.53% C) + δ(0.09% C) → γ(0.17% C)
b) L (4.3% C) → γ(2.1 % C) + Fe3C (6.67% C)
c) γ (0.8 % C) → α (0.025% C) + Fe3C (6.67% C)
d) L (0.53% C) + δ(0.09% C) → γ (0.8 % C)
Explanation: Peritectic reaction at 1495°C is L (0.53% C) + δ(0.09% C) → γ(0.17% C).

2 - Question

What is the Eutectic reaction at 1146°C?
a) L (0.53% C) + δ(0.09% C) → γ(0.17% C)
b) L (4.3% C) → γ(2.1 % C) + Fe3C (6.67% C)
c) γ (0.8 % C) → α (0.025% C) + Fe3C (6.67% C)
d) L (0.53% C) + δ(0.09% C) → γ (0.8 % C)
Explanation: Eutectic reaction at 1146°C is L (4.3% C) → γ(2.1 % C) + Fe3C (6.67% C).

3 - Question

What is Eutectoid reaction at 727°C?
a) L (0.53% C) + δ(0.09% C) → γ(0.17% C)
b) L (4.3% C) → γ(2.1 % C) + Fe3C (6.67% C)
c) γ (0.8 % C) → α (0.025% C) + Fe3C (6.67% C)
d) L (0.53% C) + δ(0.09% C) → γ (0.8 % C)
Explanation: Eutectoid reaction at 727°C is
γ (0.8 % C) → α (0.025% C) + Fe3C (6.67% C).

4 - Question

The eutectic mixture of austenite (γ) and cementite (Fe3C) is called __________
a) Ledeburite
b) Pearlite
c) Hyper and hypo eutectoid steel
d) Cast iron
Explanation: Eutectic reaction at 1146°C is
L (4.3% C) → γ(2.1 % C) + Fe3C (6.67% C).
The eutectic mixture of austenite (γ) and cementite (Fe3C) is called Ledeburite.

5 - Question

The eutectoid mixture of ferrite (α) and cementite (Fe3C) is called __________
a) Ledeburite
b) Pearlite
c) Hyper and hypo eutectoid steel
d) Cast iron
Explanation: The pearlite is formed under equilibrium
Conditions which consists of alternate lamellas or layers of ferrite and Fe3C.

6 - Question

Compositions right and left of 0.8% C of Pearlite are called __________
a) Ledeburite
b) Ferrite
c) Hyper and Hypoeutectoid steel
d) Cast iron
Explanation: Hypoeutectoid steels – α+ p; hypereutectoid – Fe3C + p.

7 - Question

Compositions above 2.1% C is called as _______
a) Ledeburite
b) Ferrite
c) Hyper and Hypoeutectoid steel
d) Cast iron
Explanation: Compositions up to 2.1% of Carbon are considered steels and beyond this it is considered as cast iron.

8 - Question

From the following figure if Diffusion rates below Ms is so low that γ → M transformation is a diffusionless process then what is change in crystal structure

a) FCC → BCT
b) FCC → BCC
c) BCC → BCT
d) BCT → BCC

Explanation: Diffusion rates below Ms is so low that γ → M transformationis a diffusion less process (the C content remains same). However, the crystal structure changes from FCC (γ) to body centered tetragonal (BCT).

9 - Question

.Finer size pearlite is called _______
a) Troostite
b) Ledeburite
c) Ferrite
d) Sorbite
Explanation: Finer size pearlite is called sorbite and very fine size pearlite is called troostite.

10 - Question

A eutectoid steel is slowly cooled from a temperature of 750°C to a temperature just below 727°C. Calculate the percentage of ferrite and cementite.
a) 88.3% and 11.7%
b) 70% and 30 %
c) 85.4% and 14.6%
d) 20% and 20%