calorised

Calorised refers to a surface treatment applied to metals, primarily iron and steel, to enhance their resistance to high-temperature oxidation and corrosion. This process involves packing the metal part in a mixture of aluminum powder and a refractory material, such as alumina or chromite, and then heating it in a furnace to a high temperature, typically between 800 and 1000 degrees Celsius. During this heating cycle, aluminum diffuses into the surface of the base metal, forming a continuous layer of aluminum-iron alloy. This alloy layer is highly protective against scaling and other forms of high-temperature degradation.

The calorising process is particularly effective for components exposed to aggressive environments at elevated temperatures, such as in furnaces, kilns, and exhaust systems. The resulting calorised surface is hard and adheres strongly to the base metal, providing long-lasting protection. It is a diffusion coating, meaning the protective layer is an integral part of the metal's surface rather than a separate coating applied externally. This characteristic makes it more durable than some other surface treatments, as it does not peel or flake off easily. The depth of the calorised layer can be controlled by adjusting the process parameters, such as temperature, time, and the composition of the packing mixture.