MATERIAL SCIENCE PRACTICE QUESTIONS

 Question 1;

Which of the following process is used for producing bainite?

SOLUTION; 

                   Austempering is the process of formation of bainite.The advantages of austempering are improved ductility, decreased distortion.The microstructure of bainite consists of ferrite and cementite phases

Question 2;

While operating quenching process, the cracks are developed due to

SOLUTION;  

                    Cracks in quenching is due to density difference and not due to thermal stresses.These quenching cracks can be avoided by martempering.

QUESTIONS 3;

The lattice structure of zinc is __________.

SOLUTION;                                                                                                                                                    The lattice structure of zinc is hexagonal cubic packing.It has repeated stacking of two types of layers offset one from the other in an "ABABAB.........." pattern

QUESTIONS 4;

Engineering material is mostly ductile in nature. The decreasing order of ductility of basic crystalline structure of engineering material FCC, HCP and BCC

SOLUTION;                                                                                                                                                    BCC material is almost brittle in nature and FCC has the highest ductility.The correct order is FCC>HCP>BCC.

QUESTIONS 5; 

Match List-I (Quenching media) with List-II (Structure produced) and select the correct answer using the codes given below the lists:

SOLUTION ;

                    Water:

The martensitic reaction begins during cooling when the austenite reaches the martensite start temperature (M_s) and the parent austenite becomes mechanically unstable. As the sample is quenched, an increasingly large percentage of the austenite transforms to martensite until the lower transformation temperature M_f is reached, at which time the transformation is completed.

Oil:

Oil quenching leads to a formation of relatively fine ferrite and pearlite grains in comparison to normal air and forced air cooling. Relatively fine ferrite, pearlite increase strength but decrease ductility. The cooling rate has a remarkable effect on the microstructure and mechanical properties at room temperature.

Air:

The eutectoid composition of austenite is approximately 0.76% carbon; steel with less carbon content (hypoeutectoid steel) will contain a corresponding proportion of relatively pure ferrite crystallites that do not participate in the eutectoid reaction and cannot transform into pearlite. Likewise steels with higher carbon content (hypereutectoid steels) will form cementite before reaching the eutectoid point.

Furnace coal:

The formation of pearlite also indicates that the transformation occurs sooner at low temperatures, which is an indication that it is controlled by the rate of nucleation. At low temperatures, nucleation occurs fast and grain growth is reduced (since it occurs by diffusion, which is hindered at low temperatures). This reduced grain growth leads to fine-grained microstructure (fine pearlite). At higher temperatures, diffusion allows for larger grain growth, thus leading to coarse pearlite.

QUESTION 6;

Jominy end-quench test is carried out to determine

SOLUTION;

                  The Jominy end quench test is used to measure the hardenability of a steel.

                Hardenability The Jominy end quench test measures the hardenability of steel. This is the ability of the steel to partially or to completely transform from austenite to some fraction of martensite at a given depth below the surface, when cooled under a given condition from high temperature. The quench and temper heat treatment uses this phase transformation to harden steels. After tempering, the martensite microstructure gives the steel a good combination of strength and toughness. Without tempering, martensite is hard, but brittle. To select steels for a heat treated component, it is important to know their hardenability. Alloying and microstructure both affect the hardenability, allowing the correct steel and quenching rate to be selected.

QUESTION 7;

Match List-I with List-II and select the correct answer using the codes given below the lists:
List-I
[A]. Elasticity
[B]. Malleability
[C]. Ductility
[D]. Plasticity
List-II
[1]. Deform non elastically without fracture
[2]. Undergo plastic deformation under tensile load
[3]. Undergo plastic deformation under compressive load
[4]. Return to its original shape on unloading

SOLUTION;

                  Elasticity: is the property by virtue of which material is able to return to its original shape on unloading.

                Malleability: is the property by virtue of which material is able to undergoes plastic deformation under compressive stress.
            Ductility: is the property by virtue of which material is able to undergoes plastic deformation under tensile load.
                Plasticity: is the property by virtue of which material is able to deform nonelastically without fracture.

QUESTION 8;

Match the List 1 and List 2

List 1 (Name of material)

P) Hypo-eutectoid steel

Q) Hyper-eutectoid steel

R) Hypo – eutectic cast iron

S) Hyper - eutectic cast iron

List 2 (% of carbon range)

1) 4 .3 – 6 .67

2) 2 .0 – 4 .3

3) 0 .8 – 2.0

4) 0 .008 – 0 .8

Correct match is?

SOLUTION;

                  Hypo-Eutectoid steel → 0.008 – 0.8

                     Hyper-Eutectoid steel → 0.8 – 2.0

                     Hypo – Eutectic cast iron → 2.0 – 4.3

                     Hyper - Eutectic cast iron → 4.3 – 6.67

QUESTION 9;

The structure of Fe₃C in iron carbon diagram is

SOLUTION ;

                    Cementite or iron carbide, is very hard, brittle intermetallic compound of iron & carbon, as Fe3C, contains 6.67 % C.It is the hardest structure that appears on the diagram, exact melting point unknown.Its crystal structure is orthorhombic.

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