Decarburization
Decarburization is the process opposite to carburization, namely aimed at decreasing the content of carbon in metals (usually steel). Decarburization occurs when carbon in the metal reacts during heating with oxygen- or hydrogen-containing gases present in the atmosphere, starting at 700°C[1].
The most common reactions are
\[\mathrm{C + CO_2 \ \rightleftharpoons \ 2 \ CO \quad}\]
also called the Boudouard reaction
\[\mathrm{C + H_2O \ \rightleftharpoons \ CO + H_2}\]
\[\mathrm{C + 2 \ H_2 \ \rightleftharpoons \ CH_4}\]
Other reactions are[1]
\[\mathrm{C + \tfrac{1}{2}O_2 \ \Rightarrow \ CO}\]
\[\mathrm{C + O_2 \ \Rightarrow \ CO_2}\]
\[\mathrm{C + FeO \ \Rightarrow \ CO + Fe}\]
Electrical Steel
Electrical steel is one material that uses decarburization in its production. 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 made into carbon monoxide.[1]
Stainless Steel
Because the components (like chromium and molybdenum) of some stainless steels are very oxidizable, these steels can only be decarburized by reacting with dry hydrogen, which has no water content, unlike wet hydrogen, which is produced in a way that includes some water and can otherwise be used for decarburization.[1]
As a Secondary Effect
Incidental decarburization can be detrimental to surface properties in products where carbon content is desirable when done during heat treatment or before 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 negative pressure atmosphere, applying resistive heating for a short duration, by limiting the time that material is under high heat as 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.[1] The carburized surface material can also be removed using a grinding machine.[1]
See also
References
External links
