Tag: Hexavalent Chromium

Chromium in Carbon, Alloy and Stainless Steels is NOT Hexavalent

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Chromium in Carbon, Alloy and Stainless Steels is NOT Hexavalent!

It looks really, really cool. And in metallic form it is NOT Hexavalent.
It looks really, really cool. And in metallic form it is NOT Hexavalent.

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 electons which 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 formof 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

5 Contributions of Chromium to Steels

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And it looks really, really cool.

Chromium is added to steel to

  • Increase resistance to corrosion;
  • Increase resistance to oxidation;
  • Increase hardenability;
  • Improve high temperature strength;
  • Improve abrasion resistance in higher carbon grades.

Chromium forms complex chromium-iron carbides. These carbides go into solution into austenite very slowly, so assuring a long enough heating (soak) time before quenching is very important.
In stainless steels, ~18 % chromium is typical, (303, 304 austenitics), while analyses as low as ~12 % (403, 420), and as high as 26-28% grades are available.
In non-stainless steels, chromium is essentially a hardening element. It is often used in combination with nickel (a toughening element) to produce improved mechanical properties. In combination with molybdenum, chromium contributes to higher strength at elevated temperatures.
Chromium’s principal use is in stainless steels, where its resistance to oxidation provides the protection from oxidation and corrosion.
Chromium’s decorative properties made it a favorite among automotive and motorcycle enthusiasts. Its resistance to oxidation and staining and ability to take a high polish make it an easy choice for decorative yet functional parts. Chromium’s hardness and chemical resistance makes it ideal for protecting our tools.
Chromium has several oxidation states, Hexavalent chromium (CRVI) is of concern as an industrial environmental issue. Metallic chromium is not hexavalent, but flame cutting or welding of chromium materials may release haxavalent chromium. Chromic acid used for some chrome plating applications is hexavalent. Newer environmentally acceptable chromium finishes are trivalent. (CRIII) Link.
Chromium is named for the Greek word chroma, meaning color, as its salts are brightly colored. Chromium is a constituent of rubies, and is why ruby lasers give off their characteristic red light.
Final chromium fact: your body requires chromium. Chromium in your body  ranges from 6-100 ppb in blood, up to 800 ppb in various tissues. Depending on your mass, you might contain as much as 12 milligrams of chromium in your body.
Reference.
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Hexavalent Chromium Rule Finalized

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But give OSHA the Booby Prize for “most ambiguous” News Release on their website announcing the rule.

Here's your prize...

In its Trade News Release, May 21, 2010:  “Occupational exposures to hexavalent chromium can occur among workers handling pigments, spray paints and coatings containing chromates, operating chrome plating baths, and welding or cutting metals containing chromium, such as stainless steel.”
Link.
Cutting metals  containing chromium, such as stainless steel!
Our industry cuts stainless steel in our machines at ambient temperatures every day.  Not to worry, no hex chrome involved. Our  machine cutting processes are not “oxidative.”  They don’t make the chromium in stainless steel “hexavalent.”
Here’s what  another place on the OSHA website says about forming hexavalent chromium from stainless steel :
“Hexavalent chromium can also be formed when performing “hot work” such as welding on stainless steel or melting chromium metal. In these situations the chromium is not originally hexavalent, but the high temperatures involved in the process result in oxidation that converts the chromium to a hexavalent state.”   Link.
What the OSHA Trade Release should have said was “HOT WORK TORCH CUTTING” that can generate a metal fume.
In the mean time, even if OSHA can’t speak with precision, we just want to let you know that if you happen to do HOT WORK welding or torch cutting on stainless steels, decorative or hard chrome electroplating or any other process involving – say-  chromic acid, that June 15th, 2010 is the effective date for the direct final rule requiring employers to notify their workers of all hexavalent chromium exposures. 
Everybody else- just relax. 

 

Made in USA. Stainless Steel. Cooks Food.

 It’s still safe to use stainless steel to eat your food. To make your cookstove and kitchen appliances. Your pots and pans. And to machine precision parts on your cam type automatic or cnc precision machining lathe or mill.  Photo: Sur la Table
Its still okay to use this too,  just don’t take it on a plane.
Chrome-vanadium steel . Fine knife by Case. Not hexavalent.

 Case Knife
Blue- footed Booby
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