Decarburization (or decarbonization) is the process of decreasing carbon content, which is the opposite of carburization.
The term is typically used in metallurgy, describing the decrease of the content of carbon in metals (usually steel).
To prevent the atmospheric gases from reacting with the metal itself, electrical steel is annealed in an atmosphere of nitrogen, hydrogen, and water vapor, where oxidation of the iron is specifically prevented by the proportions of hydrogen and water vapor so that the only reacting substance is carbon being oxidized into carbon monoxide (CO).
[1] Incidental decarburization can be detrimental to surface properties in products (where carbon content is desirable) when done during heat treatment or after rolling or forging, because the material is only affected to a certain depth according to the temperature and duration of heating.
[1] This can be prevented by using an inert or reduced-pressure atmosphere, applying resistive heating for a short duration, by limiting the time that the material is submitted to a high heat, as it is done in a walking-beam furnace, or through restorative carburization, which uses a hydrocarbon atmosphere to transfer carbon into the surface of the material during annealing.