# Engineering Materials

 Question 1
Fluidity of a molten alloy during sand casting depends on its solidification range. The phase diagram of a hypothetical binary alloy of components A and B is shown in the figure with its eutectic composition and temperature. All the lines in this phase diagram, including the solidus and liquidus lines, are straight lines. If this binary alloy with 15 weight % of B is poured into a mould at a pouring temperature of $800^{\circ}C$, then the solidification range is

 A $400 \; ^{\circ}C$ B $250 \; ^{\circ}C$ C $800 \; ^{\circ}C$ D $150 \; ^{\circ}C$
GATE ME 2022 SET-2   Manufacturing Engineering
Question 1 Explanation:

Solidification range $=A'B$
$\triangle ABC \text{ and } \triangle MB'C$ is similar
\begin{aligned} \frac{MA}{MB'}&=\frac{BC}{BC'}\\ \frac{700-T_A}{700-400}&=\frac{15}{30}\\ 700-T_A&=\frac{1}{2} \times 300\\ T_A&=550^{\circ}C \end{aligned}
Solidification range $=T_A-T_B=550-400=150 ^{\circ}C$
 Question 2
In $Fe-Fe_3C$ phase diagram, the eutectoid composition is 0.8 weight % of carbon at $725 ^{\circ}C$. The maximum solubility of carbon in $\alpha$-ferrite phase is 0.025 weight % of carbon. A steel sample, having no other alloying element except 0.5 weight % of carbon, is slowly cooled from $1000 ^{\circ}C$ to room temperature. The fraction of pro-eutectoid $\alpha$-ferrite in the above steel sample at room temperature is
 A 0.387 B 0.864 C 0.475 D 0.775
GATE ME 2022 SET-1   Manufacturing Engineering
Question 2 Explanation:

Fraction of pro eutectoid $\alpha-$ Ferrite
$=\frac{0.8-0.5}{0.8-0.025}=0.387$
 Question 3
Which of the following methods can improve the fatigue strength of a circular mild steel (MS) shaft?
MSQ
 A Enhancing surface finish B Shot peening of the shaft C Increasing relative humidity D Reducing relative humidity
GATE ME 2022 SET-1   Manufacturing Engineering
Question 3 Explanation:
Surface Treatments:
During machining operations,small scratches and grooves are invariably introduced into the workpiece surface by cutting tool action. These surface markings can limit the fatigue life. It has been observed that improving the surface finish by polishing will enhance fatigue life significantly.
One of the most effective methods of increasing fatigue performance is by imposing residual compressive stresses within a thin outer surface layer. Thus, a surface tensile stress of external origin will be partially nullified and reduced in magnitude by the residual compressive stress. The net effect is that the likelihood of crack formation and therefore of fatigue failure is reduced.
Residual compressive stresses are commonly introduced into ductile metals mechanically by localized plastic deformation within the outer surface region. Commercially, this is often accomplished by a process termed shot peening. Small, hard particles (shot) having diameters within the range of 0.1 to 1.0 mm are projected at high velocities onto the surface to be treated. The resulting deformation induces compressive stresses to a depth of between one-quarter and one-half of the shot diameter.
 Question 4
Which of the following heat treatment processes is/ are used for surface hardening of steels?
MSQ
 A Carburizing B Cyaniding C Annealing D Carbonitriding
GATE ME 2022 SET-1   Manufacturing Engineering
Question 4 Explanation:
Case-hardening, also referred to as surfacehardening, commonly involves one of four different methods: carburizing, nitriding, cyaniding, or carbonitriding. Case- hardening is used on parts such as gear teeth, cutting wheels, and tools. These case-hardened pieces represent a compromise between the hard, wear-resistant brittleness of high-carbon steel and the softer, more ductile, less wear-resistant low-carbon steels.
 Question 5
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 5 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 6
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 6 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 7
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 7 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 8
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 8 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 9
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 9 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 10
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 10 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.
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