ANS:D - Calorising

The process of coating the surface of steel with aluminum oxide, thereby imparting increased resistance to corrosion and oxidation up to a temperature of 700°C, is called Calorising. Calorising, also known as aluminizing, is a thermochemical diffusion process where aluminum powder or vapor is diffused into the surface of steel at elevated temperatures (typically around 950-1050°C). During the process, aluminum atoms react with the surface of the steel to form a thin layer of aluminum oxide (Al2O3), which provides protection against corrosion and oxidation. This aluminum oxide layer acts as a barrier that prevents the underlying steel from coming into direct contact with corrosive agents and high-temperature environments. Calorising is commonly used to enhance the corrosion resistance and durability of steel components exposed to aggressive operating conditions, such as those encountered in industrial furnaces, automotive exhaust systems, and chemical processing plants.