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Black Oxide grey color on Sae J2340 High Strength Steel

2007

Black Oxide grey color on SAE J2340 High Strength Steel

We are a job shop and we have a very important prospect requiring Black Oxide on Sae J2340 High Strength Steel (dent resistant steel) per GM 4347M without supplementary oil or wax.

The thing is that the client needs a black uniform color and our Hot Alkaline Black Oxide solution produces a grey to dark grey color. If we apply wax, oil, lacquers, etc we obtain this dark black color, but without it, we can only get a grey-ish color. When the part is wet it looks black, but as soon as it dries it looses its color, and we can't apply any after treatment.

We have tried at lower temperatures (125°C) and higher temps (140°) and nothing works. If we go to hot then we get a greenish color.
Time also has been modified from 15 to 30 minutes.
Pickling with hydrochloric acid and with sulfuric acid doesn't seem to make a difference, also we've tried electrolytic cleaners and immersion cleaners, and no difference in color is obtained.

Cleaning cycle is alkaline immersion cleaner, rinse, pickling, rinse, activation, rinse, black oxide, rinse, dry.

Any suggestions?

Thanks in advance

Enrique Segovia
Plating Job Shop - Guadalajara, Jalisco, Mexico

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It may prove too expensive for production parts, but just to see what you are up against, maybe you could try to high polish a sample part before black oxiding. I think it will come out much blacker.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007