Q1: Pick the odd man out of the following.

ANS:A - Calorising

Calorising is a surface treatment process used primarily on steel components to enhance their resistance to high-temperature oxidation and corrosion. It involves the diffusion of aluminum into the surface of steel parts. The process forms a thin, adherent layer of aluminum-rich compounds on the surface, which provides improved protection against oxidation and corrosion at elevated temperatures. The calorising process typically involves the following steps:

1. Surface Preparation: The steel components to be treated are cleaned thoroughly to remove any contaminants, oils, or surface oxides. This ensures proper adhesion of the calorised layer to the steel surface.
2. Application of Aluminum: Aluminum powder or a mixture of aluminum and aluminum fluoride is applied to the surface of the steel components. The components are then heated in a controlled atmosphere, such as in a furnace or a vacuum chamber, to high temperatures typically ranging from 850°C to 1050°C (1562°F to 1922°F).
3. Diffusion of Aluminum: During heating, aluminum atoms diffuse into the surface of the steel, forming intermetallic compounds such as FeAl2 and Fe2Al5. These compounds create a protective layer on the surface, which significantly enhances the resistance of the steel to oxidation and corrosion, particularly at high temperatures.
4. Cooling and Finishing: After the diffusion process is complete, the components are cooled gradually to ambient temperature to prevent thermal stresses and distortion. They may undergo additional finishing processes such as grinding or polishing to achieve the desired surface finish.

Calorising is commonly used in applications where steel components are exposed to high-temperature environments, such as in industrial furnaces, heat exchangers, exhaust systems, and automotive components. The process helps to extend the service life of these components by providing effective protection against oxidation and corrosion, thereby reducing maintenance costs and downtime.