# Decarburization

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Decrease of the carbon content in metals (usually steel)

For the corrosion caused by exposure to hydrogen, see [Hydrogen embrittlement](/source/Hydrogen_embrittlement).

**Decarburization** (or **decarbonization**) is the process of decreasing [carbon](/source/Carbon) content, which is the opposite of [carburization](/source/Carburization).

The term is typically used in metallurgy, describing the decrease of the content of [carbon](/source/Carbon) in [metals](/source/Metal) (usually [steel](/source/Steel)). Decarburization occurs when the metal is heated to temperatures of 700 °C or above when carbon in the metal reacts with gases containing [oxygen](/source/Oxygen) or [hydrogen](/source/Hydrogen).[1] The removal of carbon removes hard [carbide](/source/Carbide) phases resulting in a softening of the metal, primarily at the surfaces which are in contact with the decarburizing gas.

Decarburization can be either advantageous or detrimental, depending on the application for which the metal will be used. It is thus both something that can be done intentionally as a step in a manufacturing process, or something that happens as a side effect of a process (such as [rolling](/source/Rolling_(metalworking))) and must be either prevented or later reversed (such as via a carburization step).

The decarburization mechanism can be described as three distinct events: the reaction at the steel surface, the interstitial diffusion of carbon atoms and the dissolution of carbides within the steel.[2]

## Chemical reactions

The most common reactions are:

- C + CO 2 ↽ − − ⇀ 2 CO {\displaystyle {\ce {C + CO2 <=> 2CO}}}

also called the [Boudouard reaction](/source/Boudouard_reaction)

- C + H 2 O ↽ − − ⇀ CO + H 2 {\displaystyle {\ce {C + H2O <=> CO + H2}}}

- C + 2 H 2 ↽ − − ⇀ CH 4 {\displaystyle {\ce {C + 2H2 <=> CH4}}}

Other reactions are[1]

- C + 1 2 O 2 ⟶ CO {\displaystyle {\ce {C + 1/2O2 -> CO}}}

- C + O 2 ⟶ CO 2 {\displaystyle {\ce {C + O2 -> CO2}}}

- C + FeO ⟶ CO + Fe {\displaystyle {\ce {C + FeO -> CO + Fe}}}

## Electrical steel

[Electrical steel](/source/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](/source/Annealing_(metallurgy)) in an atmosphere of [nitrogen](/source/Nitrogen), [hydrogen](/source/Hydrogen), and [water vapor](/source/Water_vapor), where oxidation of the [iron](/source/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](/source/Carbon_monoxide) (CO).[1]

## Stainless steel

[Stainless steel](/source/Stainless_steel) contains additives which are highly oxidizable, such as [chromium](/source/Chromium) and [molybdenum](/source/Molybdenum). Such 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](/source/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](/source/Vacuum) atmosphere, applying [resistive heating](/source/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](/source/Hydrocarbon) atmosphere to transfer carbon into the surface of the material during annealing.[1] The decarburized surface of the material can also be removed by [grinding](/source/Grinding_machine).[1]

## See also

- [History of ferrous metallurgy](/source/History_of_ferrous_metallurgy)

- [Steelmaking](/source/Steelmaking)

## References

1. ^ [***a***](#cite_ref-TSB_1-0) [***b***](#cite_ref-TSB_1-1) [***c***](#cite_ref-TSB_1-2) [***d***](#cite_ref-TSB_1-3) [***e***](#cite_ref-TSB_1-4) [***f***](#cite_ref-TSB_1-5) [***g***](#cite_ref-TSB_1-6) Shvartsman, L.A. (1973). "Decarburization". [*The Great Soviet Encyclopedia*](/source/The_Great_Soviet_Encyclopedia) (Print) (3rd ed.). New York: Macmillan. *Available in English [**here**](http://encyclopedia2.thefreedictionary.com/Decarburization) and in the original Russian [**here**.](https://archive.today/20130504140431/http://slovari.yandex.ru/%D0%BE%D0%B1%D0%B5%D0%B7%D1%83%D0%B3%D0%BB%D0%B5%D1%80%D0%BE%D0%B6%D0%B8%D0%B2%D0%B0%D0%BD%D0%B8%D1%8F/%D0%91%D0%A1%D0%AD/%D0%9E%D0%B1%D0%B5%D0%B7%D1%83%D0%B3%D0%BB%D0%B5%D1%80%D0%BE%D0%B6%D0%B8%D0%B2%D0%B0%D0%BD%D0%B8%D0%B5)*

1. **[^](#cite_ref-Alvarenga_2-0)** Alvarenga H.D.; Van de Putte T.; Van Steenberge N.; Sietsma J.; Terryn H. (Apr 2009). "Influence of carbide morphology and microstructure on the kinetics of superficial decarburization of C-Mn Steels". *Metall. Mater. Trans. A*. **46**: 123–133. [doi](/source/Doi_(identifier)):[10.1007/s11661-014-2600-y](https://doi.org/10.1007%2Fs11661-014-2600-y). [S2CID](/source/S2CID_(identifier)) [136871961](https://api.semanticscholar.org/CorpusID:136871961).

## External links

- [Protecting Against Decarburization with Cress Furnaces](http://www.epsovens.com/heat-treat-headlines/protecting-against-decarburization-with-cress-furnaces/19) [Archived](https://web.archive.org/web/20190702190650/https://epsovens.com/heat-treat-headlines/protecting-against-decarburization-with-cress-furnaces/19/) 2019-07-02 at the [Wayback Machine](/source/Wayback_Machine)

v t e Iron and steel production History of ferrous metallurgy List of steel producers Iron production (Ironworks) Smelting Bloomery (produces sponge iron) Blast furnace (produces pig iron) Cold blast Hot blast Anthracite iron Direct reduced iron Secondary Wrought iron (via Finery forge or Reverberatory Puddling Furnace) Cast iron (via Cupola furnace or Induction furnace) Steelmaking (Steel mill) Primary (Pre-1850) Pattern welding Crucible steel (Damascus steel, Wootz steel) Tatara furnace Cementation process Primary (Post-1850) Bessemer process Open hearth furnace Electric arc furnace Basic oxygen process Secondary Electro-slag remelting Vacuum arc remelting Argon oxygen decarburization Heat treatment methods Annealing Low hydrogen Short circuit Hardening / Case-hardening Ausforming Boriding Carbonitriding Carburizing Cryogenic Ferritic nitrocarburizing Induction Nitriding Precipitation Quench polish quench Tempering Austempering Martempering Cryogenic treatment (Deburring Deflashing Hardening) Differential heat treatment Decarburization Forming gas Post weld heat treatment Quenching Superplastic forming Production by country Bangladesh China India Italy Luxembourg Nigeria Taiwan United Kingdom United States

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Adapted from the Wikipedia article [Decarburization](https://en.wikipedia.org/wiki/Decarburization) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Decarburization?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.