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Black Oxide Flaking

Hello,

We are having issues with black oxide flaking. We are manufacturing a Class 1 Black Oxide per Boeing specification MS 8.17 (also see Class 1 per MIL-DTL-13924 [on DLA]) on low alloy steels. We are using Liquid Black Magic ABM from Hubbard Hall and abrasively bead-blast prior to blackening. The blackening process consists of an alkaline cleaner and the blackening bath (~285F).

Has anyone else experienced problems with flaking or poor adhesion with black oxide? We have not changed any processing parameters and we suddenly have been having this issue come up.

Any help or advice would be greatly appreciated.

Jonathan Lelah
Materials Engineer - Bedford Park, Illinois
June 24, 2011

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What you have is a bit of an enigma. Black oxide can not flake. Well not a black oxide produced by immersion in sodium nitrate ⇦ this on Amazon [affil link] and sodium hydroxide anyway. All the process does is add a couple of atoms to the existing iron atoms to create a new atom FE3O4. Well, as I understand it with my limited high school chemistry. That's why they call it a non-dimension changing coating. It is in fact not a coating at all. What seams to be happening must be one of three things. Its not a true black oxide and whatever sort of a coating it is its simply not sticking and is pealing off. Or, the undetopad material is of a nature that when the chemical process takes place the black oxide becomes so dissimilar to the original base material that they simply separate. (like rust flaking off). Or, (and this one I have seen) the object will not take a black oxide blue and the article has been PLATED with iron and then blued and the plating is pealing off. I think its time to go back to the manufacturer of your blackening and ask him what's going on and if he does not know find out exactly what's in his blackening solution. Then find out exactly what sort of material you are trying to blacken and exactly what has been done to the material prior to blackening and move from there. You can also try to blacken a control piece of 4140 or 1018 steel and subject it to the same use/misuse your regular parts get and this will point you towards the material or the blackening solution.

Rod Henrickson
gunsmith - Edmonton, Alberta, Canada
June 30, 2011

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WELL, HELL! I just looked at your post again. You say a roller is working on the area in question. I would be willing to bet the roller is work hardening the material under the bluing and as it gets brittle its cracking and flaking off. Try taking the piece about 2 to 4 points Rockwell C higher than the roller before bluing. Or change materials to something that will not work harden. Probably the best bet would be to incorporate a bearing on to the piece. I guess it might help if I read the post a couple times before opening my big mouth.

Rod Henrickson
gunsmith - Edmonton, Alberta, Canada
June 30, 2011

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Are you suggesting that we all start reading the posts carefully before responding, Rod? Are you some kind of elitist or something? I'll have to purge half of my responses :-)

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
July 1, 2011

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I should have known there would be feedback from the PEANUT GALLERY on that one.
⎝ᄽ⏝ᄿ⎠

Rod Henrickson
gunsmith - Edmonton, Alberta, Canada
July 1, 2011