Depending on the operation (annealing, hardening, etc) a protective atmosphere of Nitrogen with additions of a hydrocarbon such as natural gas or propane, hydrogen or cracked methanol is used. The gas composition of the atmosphere changes based on the type of operation required. In some of these operations, high purity specialty gases or prepared specialty gas mixtures are used to improve consistency and increase product quality. For example, mixtures of several percent Hydrogen in a balance of Nitrogen are commonly referred to as “forming gas mixtures”.
High purity Helium can also be used, due to its high thermal conductivity and inert property, as an environmentally friendly alternative to oil quenching in heat treatment furnaces.