Red-short carbon steel
Red-short, hot-short refers to brittleness of steels at red-hot temperatures. It is often caused by high sulfur levels, in which case it is also known as sulfur embrittlement.
Iron or steel, when heated to above 460 °C (900 °F), glows with a red color. The color of heated iron changes predictably (due to black-body radiation) from dull red through orange and yellow to white, and can be a useful indicator of its temperature. Good quality iron or steel at and above this temperature becomes increasingly malleable and plastic. Red-short iron or steel, on the other hand, becomes crumbly and brittle.
Sulfur hot-shortness
[edit]In steel contaminated by sulfur this embrittlement happens due to the sulfur forming iron sulfide/iron mixtures in the grain boundaries of the metal which have a lower melting point than the steel.[1]
When the steel is heated up and worked, the mechanical energy added to the workpiece increases the temperature further. The iron sulfide (FeS) or iron/iron sulfide alloy (which has an even lower melting point)[2] begins to melt, and the steel starts to separate at the grain boundaries. Steelmakers add manganese (Mn) to the steel when it is produced, to form manganese sulfide (MnS). Manganese sulfide inclusions have a higher melting point and do not concentrate at the grain boundaries. Thus, when the steel is later heated up and worked, the melting at the grain boundaries does not occur.
Copper hot-shortness
[edit]When steel has elevated levels of copper, which may happen due to ore specifics but is more often cased by contamination of steel scrap, also exhibits hot-shortness.[3] This is caused by selective oxidation of iron at the grain boundaries, where more noble and softer copper is enriched.[4]
References
[edit]- ^ Deev et al. (May–June 1982). "Role of iron sulfide in the formation of cracks in weld joints". Materials Science, Vol. 18, No. 3, pp. 109–112.
- ^ Sachinath Mitra. High-pressure geochemistry and mineral physics. p. 1028.
- ^ Daehn, Katrin E.; Cabrera Serrenho, André; Allwood, Julian M. (2017-06-06). "How Will Copper Contamination Constrain Future Global Steel Recycling?". Environmental Science & Technology. 51 (11): 6599–6606. doi:10.1021/acs.est.7b00997. ISSN 0013-936X.
- ^ Jiang, Yinghua; Xie, Chunqian (June 2017). "Evaluation model of susceptibility to Cu hot shortness of Cu-containing LC steel". IOP Conference Series: Materials Science and Engineering. 207: 012098. doi:10.1088/1757-899x/207/1/012098. ISSN 1757-8981.
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