GATE 2020 MT – Question 47

Mechanical Behaviour of Materials · Creep · 2 marks · Multiple choice

Determine [a] Low-alloy steels used for medium-temperature creep resistance often contain strong carbide-forming elements; and [r] During creep, particles with higher matrix misfit lose coherency.

Both [a] and [r] are true and [r] is the correct reason for [a].
Both [a] and [r] are true but [r] is not the correct reason for [a].
Both [a] and [r] are false.
[a] is true but [r] is false.

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Correct answer: (B) Both [a] and [r] are true but [r] is not the correct reason for [a].

Explanation

Carbide-forming additions generate stable precipitates that hinder dislocation motion and improve creep resistance, so [a] is true. Precipitates with sufficient misfit can lose coherency as they evolve, so [r] is also treated as true. However, loss of coherency is not the reason for selecting strong carbide formers; precipitate stability and resistance to deformation provide that link. Thus B.

GATE 2020 MT – Question 47

Explanation

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