Class 4 (4th Engineer) MEKG 📅 Aug 2023

Exam Question

(a) Describe each of the following: (8)

(i) Work hardening

(ii) Nitriding

(iii) Cold working

(iv) Normalising

(b) With reference to the component parts of shipboard machinery and equiment, state with reasons, one example of where each of the above in (a) (i), (ii), (iii), (iv) may be used (8)

Reference Answer

### (a) Description of Metallurgical Processes
#### (i) Work Hardening (Strain Hardening)
Work hardening is the process by which a metal becomes harder and stronger as it is plastically deformed. This deformation is typically carried out below the material's recrystallization temperature.
* **Mechanism:** At a microscopic level, plastic deformation occurs by the movement of dislocations through the crystal lattice of the metal. As deformation proceeds, these dislocations multiply, move, and interact with each other and with grain boundaries, becoming entangled and impeding further movement. This increased resistance to dislocation motion manifests as an increase in the metal's strength and hardness.

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