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Match the items in List-I with the corresponding items in the List-II.

  List-I
(Heat treatment)
  List-II
(Effect on properties)
A. Annealing 1. Grain refinement
B. Nitriding 2. Improves hardness of the whole mass
C. Martempering 3. Improves surface hardness
D. Normalizing 4. Reduce ductility

Choose the correct option from the following:
1. A - 3, B - 1, C - 4, D - 2
2. A - 1, B - 3, C - 2, D - 4
3. A - 3, B - 1, C - 2, D - 4
4. A - 1, B - 3, C - 4, D - 2

1 Answer

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Best answer
Correct Answer - Option 2 : A - 1, B - 3, C - 2, D - 4

Explanation:

Annealing:

  • Annealing is heating of steel to austenite temperature and then cooling slowly in the furnace.
  • Annealing results in the formation of ferrite, spheroidal cementite and coarse pearlite.
  • All the phase constituents are relatively soft and therefore this is known as softening treatment and produces relatively lower hardness values while ductility increases.
  • Purpose of annealing:
    • to reduce hardness, relieve internal stress
    • improves machinability
    • it refines grain size.

Nitriding:

  • Nitriding is a case of the hardening process in which nitrogen (Ammonia) instead of carbon is added to the surface of the steel. 
  • Nitriding heats the steel part to 482-621°C (900 -1,150°F) in an atmosphere of ammonia gas and dissociated ammonia.
  • The time the part spends in this environment dictates the depth of the case. 
  • No quenching is done after nitriding.

Normalizing: 

  • Heat the steel from 30°C to 50°C above its upper critical temp, hold about fifteen minutes, and then allow to cool down in still air. 
  • The homogeneous structure provides a higher yield point, ultimate tensile strength, and impact strength with lower ductility to steel.
  • The main purpose of normalizing is to refine grain size.
  • Main objective:
    1. Refine grain size in metal, improve strength and hardness, reduce ductility
    2. Remove cold work stress.
    3. Remove dislocations due to hot working.

Martempering:

  • In this martensite is formed and quenching is done in two medium
  • First quenched in water to a temperature of 300 - 400°C and then quickly transferred to a less intensive medium like oil or air where they are held until they are completely cooled.
  • The purpose of the second medium is to reduce internal stress associated with the austenite to martensite transformation.
  • Used for the heat treatment of C-steel tools like taps, disc, milling cutters, etc. to improve hardness of the whole mass

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