Calorizing

in Europe, aliting, the saturation of the surface of steel or other metal parts with aluminum for the purpose of increasing resistance against scaling at temperatures up to 1100°C and of increasing resistance to atmospheric corrosion. Most frequently parts of low carbon austenitic steels and refractory alloys are calorized. Calorizing is performed in powder mixtures (50 percent Al or fer-roaluminum, 49 percent Al₂O₃ and 1 percent NH₄Cl or 99 percent ferroaluminum and 1 percent NH₄Cl). At 1000°C with a soaking of eight hours, a layer of 0.4–0.5 mm saturated with aluminum is formed. Calorizing is also done by metallizing (a layer of aluminum powder is deposited on the surface of the parts, and after the deposition of an insulating coating the part is subjected to diffusion heat treatment), by painting the parts with aluminum paint (with subsequent heat treatment in a protective atmosphere), by an aluminum melt (with 6–8 percent iron) at 700–800°C followed by soaking, and by other methods. Calorizing is used in the production of valves for automotive engines, blades and nozzles of gas turbines, oil and gas cracking equipment parts, steam superheater pipes, furnace parts, and so on. Calorizing in molten aluminum is widely used instead of hot zinc plating (sheet, wire, pipes, construction parts).