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Stainless Steels and PFAS Chemicals

At BSSA a question that we are being asked more often in recent years is – “Do Stainless Steels contain PFAS chemicals?”

 

The simple answer is that no steels, stainless steels included, contain the organic PFAS chemicals in their internal structure.

 

Steels consist of a metallic bond matrix, typically with either a Body Centred Cubic, BCC, or  Face Centred Cubic, FCC, crystal arrangement. Those steels hardened by heat treatment, typically have a metastable, Martensitic, Body Centred Tetragonal, BCT matrix structure. Within these Iron/Fe matrices the other elements present can be in solid solution, either on  the lattice sites, forming substitutional solid solutions,  or in the interstices between the lattice atoms/sites, forming an interstitial solid solution . There is usually a limit on the levels of elements that can occupy these two sites, known as the solubility limit. Levels of any alloying elements in excess of this limit leads to the formation/precipitation  of second phase particles, such as carbides, nitrides, and intermetallic phases such as Sigma, Chi etc. etc., or indeed the precipitation of unbonded elemental particles. Hume-Rothery established the rules for this behaviour a long time ago, see https://en.wikipedia.org/wiki/Hume-Rothery_rules, and https://www.phase-trans.msm.cam.ac.uk/2004/titanium/hume.rothery.html during his research work at Oxford University.

But basically during the steel production route, where very high temperatures are involved, no organic chemicals survive, or are incorporated into the steel matrix.

 

However, steels post their primary production can be coated or packaged with organic products which may contain PFAS, so if there is a concern this would need to be checked with the secondary processors/fabricators of the steel/steel products.

Most of the work published on PFSA’s, the so called ‘forever’ chemicals, currently is from the USA. In 2023 the US Environment Protection Agency proposed a list of PFSA’s 6 PFSA’s with very strict limits on the contamination levels allowable in drinking water. See the following list: https://www.epa.gov/sdwa/and-polyfluoroalkyl-substances-pfas#:~:text=On%20March%2014%2C%202023%20%2C%20EPA,known%20as%20GenX%20Chemicals)%2C%20perfluorohexane.

 

See also https://www.niehs.nih.gov/health/topics/agents/pfc for further information on the chemicals themselves and studies on their effects.

The compounds listed by the US EPA are thus not part of the stainless steel metallurgical structure, and are not used in the primary production processes, as noted above.

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