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Posted by: 15. October 2013

Chromium in Carbon, Alloy and Stainless Steels is Not Hexavalent

Miles Free

 

The valency (oxidation state) of chromium metal as an alloying constituent of steels is zero (0). The chromium atoms are present in “substitutional” lattice positions, replacing iron atoms. These atoms are held in place in the lattice by shared electrons that make up a “metallic bond.” Since there is no loss or gain of electrons, the valency state is zero (0).

The chromium in solid steels (carbon, alloy and stainless) should not be regarded as a health hazard.  That is why stainless steels, in particular, can be used for food prep and bodily contact in medical and dental applications- the chromium is not available in an ionic state.

Hexavalent Chromium Cr (VI) is an ionic state and typically encountered as a ‘chromate’ or ‘dichromate’ salt. These hexavalent compounds are typically found in plating solutions. Hexavalent chrome has been identified as a cause for health concerns and shown to be toxic.

Machining steels—carbon, alloy, and stainless—does not expose the operator to hexavalent chromium. Hexavalent chromium is an ionic form of chromium in a chemical compound. Metallic chromium is a form that is sharing electrons as part of a metallic bonding arrangement. The valence state of metallic chromium is zero (0).

We’ve written about this before:

"Chromium in Steel"

"Hexavalent Chromium Rule Finalized"

"British Stainless Steel Association Article on Chromium in Stainless"

Originally posted on PMPA Speaking of Precision blog.

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