The GATE Grind

GATE 2022 MT – Question 28

Physical Metallurgy · Heat treatment and recrystallization · 1 mark · Multiple choice

With increase in carbon content (up to 2 mass%) in Fe-C alloy, which one of the following statements is correct with respect to the lattice parameters (c and a) of BCT martensite?

  1. Both c and a increase
  2. c increases but a decreases
  3. c decreases but a increases
  4. Both c and a decrease

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Correct answer: (B) c increases but a decreases

Explanation

Interstitial carbon preferentially occupies sites that elongate the tetragonal c direction. Increasing carbon raises c while the a parameter decreases slightly, increasing tetragonality c/a.

Therefore **B**.