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GATE 2023 MT – Question 50

Physical Metallurgy · Heat treatment and recrystallization · 2 marks · Multiple select

For the given schematic TTT diagram of an eutectoid steel, the following statement(s) is/are true for the heat treatment schedules HT-1, HT-2, and HT-3.

Diagram for GATE 2023 MT question 50
  1. HT-3 leads to the formation of a pearlite microstructure
  2. HT-1 leads to a predominantly martensite microstructure
  3. HT-2 leads to a bainite microstructure
  4. HT-3 leads to a mixture of pearlite and bainite microstructure

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Show answer and explanation

Correct answer: (A) HT-3 leads to the formation of a pearlite microstructure; (B) HT-1 leads to a predominantly martensite microstructure; (C) HT-2 leads to a bainite microstructure

Explanation

HT-1 avoids the diffusional-transformation nose and quenches below martensite start, giving predominantly martensite. HT-2 holds in the bainite range through transformation. HT-3 holds in the pearlite range until transformation is complete before cooling.

Hence **A,B,C**; HT-3 does not produce the proposed pearlite–bainite mixture.