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Black oxide layer wear off during ECD process

Helllo,
We have hot black oxide process in our plant.
We use caustic soda [affil links] and sodium nitride under strict control. We use same condition for heat treated and non heat treated parts also. We have one type of part which we should blacken after machining process (material is not heat treated ) and then we have an electrochemical deburring process. During the ECD process the blackening layer wears off from the surface.
Do you know why the blackening layer wears off?
Thanks in advance.
Kind regards, Eszter

Eszter Pongraicz
plating shop employee - Hungary
February 10, 2011

Just a guess but there is probably some type of acid being used in you chemical deburring that is eating away the black oxide? Your question is a bit vague.

Rod Henrickson
gunsmith - Edmonton, Alberta, Canada
February 15, 2011

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