# Engineering Materials

 Question 1
The Cast Iron which possesses all the carbon in the combined form as cementite is known as
 A Grey Cast Iron B Spheroidal Cast Iron C Malleable Cast Iron D White Cast Iron
GATE ME 2021 SET-2   Manufacturing Engineering
Question 1 Explanation:
On the basis of nature of carbon present in cast iron, it may be divided into white cast iron and gray cast iron.
In the gray cast iron, carbon is present in free form as graphite. Under very slow rate of cooling during solidification, carbon atoms get sufficient time to separate out in pure form as graphite. In addition, certain elements promote decomposition of cementite. Silicon and nickel are two commonly used graphitizing elements.
In white cast iron, carbon is present in the form of combined form as cementite. In normal conditions, carbon has a tendency to combine with iron to form cementite.
 Question 2
Which one of the following statements about a phase diagram is INCORRECT?
 A It indicates the temperature at which different phases start to melt B Relative amount of different phases can be found under given equilibrium conditions C It gives information on transformation rates D Solid solubility limits are depicted by it
GATE ME 2020 SET-2   Manufacturing Engineering
Question 2 Explanation:
Phase diagram - Useful information:
Important information, useful in materials development and selection, obtainable from a phase diagram:
It shows phases present at different compositions and temperatures under slow cooling (equilibrium) conditions.
It indicates equilibrium solid solubility of one element/compound in another.
It suggests temperature at which an alloy starts to solidify and the range of solidifcation.
It signals the temperature at which different phases start to melt.
Amount of each phase in a two-phase mixture can be obtained.
 Question 3
Match The Following
 A P-2, Q-3, R-4, S-1 B P-1, Q-1, R-3, S-2 C P-3, Q-3, R-1, S-3 D P-4, Q-3, R-2, S-1
GATE ME 2020 SET-1   Manufacturing Engineering
Question 3 Explanation:
Tempering is a process of heat treating, which is used to increase the toughness of iron-based alloys.
Quench hardening is a mechanical process in which steel and cast iron alloys are strengthened and hardened.
Annealing is a process involving heating and cooling, usually applied to produce softening of the metal to facilitate machining or forming operations.
Normalising is used to improve the mechanical properties of, mainly, unalloyed and low-alloy structural steel and cast steel.
 Question 4
The crystal structure of $\gamma$ iron (austenite phase) is
 A BCC B FCC C HCP D BCT
GATE ME 2020 SET-1   Manufacturing Engineering
Question 4 Explanation:
Austenite has a cubic-close packed crystal structure, also referred to as a face-centred cubic structure with an atom at each corner and in the centre of each face of the unit cell.
 Question 5
The binary phase diagram of metals P and Q is shown in the figure. An alloy X containing 60% P and 40% Q (by weight) is cooled from liquid to solid state. The fractions of solid and liquid (in weight percent) at $1250^{\circ}C$, respectively, will be
 A 77.8% and 22.2% B 22.2% and 77.8% C 68.0% and 32.0% D 32.0% and 68.0%
GATE ME 2019 SET-2   Manufacturing Engineering
Question 5 Explanation:
Lever line :

\begin{aligned} \text{Mass friction of solid }&=\frac{c_{o}-c_{L}}{c_{s}-c_{L}} \\ &=\frac{40-32}{68-32} \\ \mathrm{m}_{\mathrm{s}}&=\frac{8}{36}=0.2222 \approx 22.2 \% \end{aligned}
\begin{aligned} \text{Mass friction of liquid }&=\frac{c_{s}-c_{o}}{c_{s}-c_{L}} \\ &=\frac{68-40}{68-32} \\ \left(\mathrm{m}_{\ell}\right)&=\frac{28}{36}=0.777 \approx 77.8 \% \end{aligned}
 Question 6
Hardenability of steel is a measure of
 A the ability to harden when it is cold worked B the maximum hardness that can be obtained when it is austenitized and then quenched C the depth to which required hardening is obtained when it isaustenitized and then quenched D the ability to retain its hardness when it is heated to elevated temperatures
GATE ME 2019 SET-2   Manufacturing Engineering
Question 6 Explanation:
It is the depth to which required hardening is obtained when it is austenitized and then quenched. Hardenability is the ability of steel to form marteniste. The greater the hardenability the more martensite.
 Question 7
During solidification of a pure molten metal, the grains in the casting near the mould wall are
 A coarse and randomly oriented B fine and randomly oriented C fine and ordered D coarse and ordered
GATE ME 2018 SET-2   Manufacturing Engineering
Question 7 Explanation:
During solidifiction of pure metal at the surface of the mould due to fast rate of solidification randomly oriented fine grains are produced.
 Question 8
Denoting L as liquid and M as solid in a phase-diagram with the subscripts representing different phases, a eutectoid reaction is described by
 A $M_{1}\rightarrow M_{2}+M_{3}$ B $L_{1}\rightarrow M_{1}+M_{2}$ C $L_{1}+M_{1}\rightarrow M_{2}$ D $M_{1}+M_{2}\rightarrow M_{3}$
GATE ME 2018 SET-2   Manufacturing Engineering
Question 8 Explanation:
$\begin{matrix} M_{1} &\rightarrow & M_{2} &+ M_{3} \\ \gamma-\text { iron }& &\alpha-\text { ferrite } &\text { cementite }\left(F e_{3} C\right) \end{matrix}$
 Question 9
The number of atoms per unit cell and the number of slip systems, respectively, for a face-centered cubic (FCC) crystal are
 A 3, 3 B 3, 12 C 4, 12 D $4,48$
GATE ME 2018 SET-1   Manufacturing Engineering
Question 9 Explanation:
$\begin{array}{|c|c|c|c|c|} \hline \text {Unit cell} & N & C N & \text {a/R} & \text {APF} \\ \hline \text {Simple cubic} & 1 & 6 & 2 & 0.52 \\ \hline \text {Body centered cubic} & 2 & 8 & \frac{4}{\sqrt{3}} & 0.68 \\ \hline \text {Face centered cubic} & 4 & 12 & \frac{4}{\sqrt{2}} & 0.74 \\ \hline \text { Hexagonal close packed } & 6 & 12 & \begin{array}{l} a / \mathrm{R}=2 \\ \mathrm{c} / \mathrm{a}=1.633 \end{array} & 0.74 \\ \hline \end{array}$
 Question 10
Given the atomic weight of Fe is 56 and that of C is 12, the weight percentage of carbon in cementite $(\textrm{Fe}_{3}C)$ is ________
 A 1.25 B 3.25 C 6.67 D 9.12
GATE ME 2017 SET-2   Manufacturing Engineering
Question 10 Explanation:
$\frac{12}{56 \times 3+12 \times 1} \times 100 \%=6.67 \%$
There are 10 questions to complete.

### 4 thoughts on “Engineering Materials”

1. For q8, answers should be given as follows :
1. A&B
2.A&C
3. B&C
4. ONLY B