Explain any two of the following processes: (i) Annealing - Leaving Cert Engineering - Question 3 - 2009

Case hardening is a process used to harden the surface of low carbon steel while leaving its core tough. This is achieved by increasing the amount of carbon at the surface through processes such as carburizing. The low carbon steel is heated to a red-hot temperature and then allowed to absorb carbon before being quenched in water, producing a hard, tough surface.

Part A of the centre punch is first hardened by heating it to a cherry red color and then cooling it rapidly in clean water. This rapid cooling transforms the structure of the metal, making it hard yet brittle. To temper the centre punch, it is polished to remove any oxidation and then heated slowly until tempering colors appear. Once these colors reach the desired state, it is cooled in air or water to achieve the right balance between hardness and toughness.

1. Always hold the component securely to prevent it from slipping or moving during the hardening and tempering process.
2. Wear protective clothing to shield against steam or oil flashbacks, which can occur during the heating and cooling stages.