Fluid bed

This method is particularly suited to the treatment of small components and those whose geometry would be prone to masking and attendant uneven hardening, were the sealed quench method to be used. Cyanide salt bath treatments have now largely been superseded by fluid bed treatments which do not have the health and safety and environmental risks associated with the operational and disposal aspects of cyanide salt baths.

The use of gas activated (hence ‘fluidised’) and heated powder, such as alumina or silica, as a means to transfer heat to components being heat treated is increasingly used instead of molten salts. Its benefits include rapid heat transfer, the ability to add process gases to alter surface chemistry, and hence case harden or nitride components, in an environmentally friendly manner.