The GATE Grind

GATE 2024 MT – Question 23

Physical Metallurgy · Heat treatment and recrystallization · 1 mark · MTA

Which crystal-structure change occurs when mild steel transforms from austenite to martensite?

  1. Face centered cubic to body centered cubic
  2. Face centered cubic to body centered tetragonal
  3. Body centered cubic to body centered tetragonal
  4. Body centered tetragonal to face centered cubic

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Correct answer: MTA

Explanation

Austenite is FCC.

Carbon trapped by diffusionless transformation generally makes martensite body-centred tetragonal; at very low carbon content tetragonality becomes small and a BCC description may be used.

Because the mild-steel wording leaves this distinction problematic, the official final key awards **marks to all**, which is preserved here.