Letter 18037

Green patches on hard chrome [India] 

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I have done hard chrome on a stainless cylinder for marine application, now I can see green patches on the chrome after a few days, can any of you tell me why could this happen.

Sandeep Ramakrishnan
HYTEC INTERNATIONAL LLC - Dubai

I am interested in the discoloring effect you have. Does the defect always occur? Are the spots local to certain geometric features (tight corners?) I am seeking ways to intentionally colorize chromed steel. What materials, process are you using?

Joe Martone
- New Britain, Connecticut, USA

Sandeep,

Probably the hard chrome layer has been affected somehow by HCl.

Christos Sigalas
Metalchrom S.A. - Athens, Greece

An interesting problem! Ideally we should know more details such as how thick is the chromium and what is the substrate. It could well be a chromium (III) salt being produced on the part, but it could also be a nickel salt being produced from a sublayer if the chromium coating is too thin and/or porous. I would suggest you get an independent analysis of the parts carried out.

Trevor Crichton R&D practical scientist - UK

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