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Current Affairs January 2024

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4

Secondary hardening in steels arises out of the

A. Precipitation of fine alloy carbides at high temperatures

B. Refinement of ferrite grain size by working

C. Decomposition of retained austenite upon heat treatment

D. Precipitation of complex inter-metallic upon heat treatment

Correct Answer :

C. Decomposition of retained austenite upon heat treatment


Related Questions

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4

Unit of surface tension in S.I. unit is

A. Watt/m

B. Joule/

C. Newton/

D. Joule/m

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4

In a furnace with heating element temperature at 1700°C, the dominant mechanism of heat transfer will be

A. Conduction

B. Radiation

C. Natural convection

D. Forced convection

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4

Thermistors are used in __________ devices.

A. Voltage measuring

B. Temperature measuring

C. Temperature compensating

D. Both (B) & (C)

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4

Carbide tipped cutting tools are manufactured by powder metallurgy techniques and have a composition of

A. 90% tungsten carbide and 10% cobalt

B. 70% aluminium oxide & 30% silica

C. 30% nickel, 15% chromium & 55% tungsten

D. 65% tungsten & 35% zirconium

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4

Resistance of an electrical conductor is proportional to its (where, l = length and A = cross-sectional area of the conductor)

A. A

B. l

C. A2

D. Both 'a' & 'b'

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4

A 2 kg object weighs 1.8 kgf on a spring balance. The value of 'g' at that location in m/sec2 is

A. 8.82

B. 9.81

C. 10.88

D. 0.95

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4

Cold cracking in the heat affected zone of a high strength steel weld can take place because of the

A. Retained austenite

B. Martensite formation

C. Relatively high sulphur content in the base metal

D. Sufficient hydrogen present in the welding arc

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4

High endurance limit of carburised machine parts is because of the fact that carburisation

A. Suppresses any stress concentration produced in the parts

B. Enhances the yield point of the material

C. Introduces a compressive layer on the surface

D. Produces a better surface finish

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4

Fibrous fracture is normally encountered in the __________ materials.

A. Hard

B. Elastic

C. Ductile

D. Brittle

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4

The most important consideration, while designing the refrigeration system of an aircraft is that the refrigeration system

A. Is as light as possible

B. Has very high C.O.P.

C. Employs minimum quantity of refrigerant

D. Consumer minimum horse power

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4

Nusselt number is related to the Reynolds number (Re) in turbulent & laminar flow respectively as

A. Re0.5, Re0.8

B. Re0.8, Re-0.5

C. Re0.8, Re0.5

D. Re-0.8, Re0.5

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4

An alloy of Fe - 0.4 % C is

A. Cast iron

B. Hypo-eutectoid steel

C. Hyper-eutectoid steel

D. Eutectoid steel

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4

The same volume of all gases is representative of their

A. Specific gravities

B. Densities

C. Gas characteristic constants

D. Molecular weights

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4

An oxidation process is accompanied with decrease in the

A. Number of electrons

B. Oxidation number

C. Number of ions

D. All (A), (B) & (C)

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4

__________ is not used as the control rod material in a nuclear reactor.

A. Cobalt

B. Hafnium

C. Cadmium

D. Boron

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4

Fibre glass is a composite material of

A. Glass fibre in a polymer matrix

B. Glass fibre in a metallic matrix

C. Polymer fibre in a glassy matrix

D. Both 'b' & 'c'

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4

Neutrons are present in all atoms except that of

A. He

B. C

C. H

D. Ar

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4

Cassiterite is an ore of

A. Tin

B. Lead

C. Molybdenum

D. Chromium

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4

Pick out the wrong statement.

A. A ferromagnetic material becomes paramagnetic above the 'Curie temperature'

B. Permanent magnets are made of hard materials, whereas electromagnets require soft magnetic materials

C. Soft magnetic materials (e.g., pure iron) have higher permeability and low hysterisis loss and coercive forces

D. Tungsten steel and alnico are not hard magnetic materials

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4

The most economical channel section for the fluid flow is the one for which the discharge is maximum for a given cross-sectional area. Vertical velocity distribution in an open channel for laminar flow can be assumed to be

A. Parabolic

B. Hyperbolic

C. Straight line

D. None of these

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4

Coating provided on the electrodes used in the arc welding is not expected to

A. Add alloying elements

B. Prevent electrode from contamination

C. Stabilise the arc

D. Provide protective atmosphere to weld

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4

For efficient performance of a blast furnace, the extent of reduction of Wustite (FeO) should be

A. 100% indirect reduction

B. 100% direct reduction

C. 50-60% indirect reduction

D. 30-40% indirect reduction

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4

Air/fuel ratio by weight for combustion of methane with theoretical quantity of air will be about

A. 9 : 1

B. 17 : 1

C. 23 : 1

D. 29 : 1

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4

Principal alloying elements of cast tool alloys which have very high wear resistance & high temperature strength are

A. Cobalt, chromium & tungsten

B. Cobalt, chromium & nickel

C. Molybdenum, tungsten & chromium

D. Cobalt, zirconium & molybdenum

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4

Ceramic compounds as compared to metallic compounds

A. Crystallise faster

B. Resist greater tensile stress at room temperature

C. Have higher melting temperature

D. Are better conductor of electricity at higher temperature

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4

Secondary hardening in steels arises out of the

A. Precipitation of fine alloy carbides at high temperatures

B. Refinement of ferrite grain size by working

C. Decomposition of retained austenite upon heat treatment

D. Precipitation of complex inter-metallic upon heat treatment

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4

If Reynolds number is greater than 1, then the

A. Viscous force is larger than the inertia force

B. Inertia force is larger than the viscous force

C. Inertia force is larger than the surface tension force

D. Inertia force is larger than the gravitational force

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4

When the wet steam is throttled but still remains wet at the exit of the throttle valve, then its temperature & dryness fraction respectively

A. Decreases & increases

B. Increases & increases

C. Increases & decreases

D. Decreases & decreases

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4

Plastics as a material of construction suffer from the drawback of low

A. Machinability

B. Density

C. Strength

D. Plastic deformation

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4

Circular cross section machine parts which are symmetrical about the axis of rotation are made by hot

A. Piercing

B. Spinning

C. Drawing

D. Extrusion