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Black oxide on stainless steel is rubbing off

adv.

Q. 1) What is the nature of the black oxide on stainless steel?

2) Is there any method, such as plasma or electrochemical methods, to increase the amount of chromium oxide - hydroxide content on the surface?

Thanks,

Diane Dang
- Menlo Park, California
2001

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Red rust through black oxide on SS part

Q. During a recent investigation concerning the use of a black oxide process on a 304 stainless steel part, our department noticed red/orange spots on the surface of the part subsequent to 72 hours of ASTM B117 salt-fog. The salt spray test was run to confirm the proper passivation of a weld on the part. However, a phenomenon that appears similar to rust was observed in areas far removed from the weld.

It is our understanding that the black oxide process does not adversely affect the chrome oxide layer of the stainless steel and as such does not affect the natural corrosion resistance of the material. If this is a true statement, what are some possible sources of the spots and what can be done to eliminate this problem? At this point, I do not have any detailed information on process used to apply the black oxide.

Any insight into this issue would be greatly appreciated.

Mark Thomas
- Oshkosh, Wisconsin
2002

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Q. Thank you Mr. Stevenson for your response. In your response, you mention that "the activation is not intended to degrade the chrome oxide layer." However, if a 304 part can now only go 96 hours in salt spray until red rust it would appear that that is exactly what happens. In my salt spray test, however, the apparent corrosion has not progressed any further despite several hundred hours of additional salt spray. Is the apparent detrimental effect of the activation somehow temporary? Does the 304 material eventually re-passivate such that corrosion is once again prevented? Once again, any insight into this phenomenon would be greatly appreciated.

Thanks,

Mark Thomas [returning]
- Oshkosh, Wisconsin
2002

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Multiple threads merged: please forgive chronology errors :-)

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Q. We are have been using a stainless steel handle w. black oxide finish on our electronics assemblies. Recently we have had batches of these handles come in with the black oxide finish rubbing off and the handle looking splotch-y. Based in what I know about black oxide finishes they should be more robust than this however I have recently heard that this problem can happen with cold-process black oxide.

Is this normal?

Thanks.

Steve Ferranti
- Dallas, Texas
2002

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A. Hi Steve. I'm not sure whether you are implying that your vendor switched to cold blackening or not, but yes, that can lead to smutty, marginally adherent coatings. Cold blackening is not true black oxiding; rather, it's the deposition of a black selenium-based compound. These are your parts, and your plater should not have carte blanche to change the process applied to your parts. I suggest that you find out what he was doing formerly, and what he is doing now ... and that you write a spec that makes him or another shop do it the old way. You also need to check that the grade of stainless steel hasn't been changed. If you are just buying standard parts from a catalog and have no control over the specs, you may have to find another supplier :-) Luck and Regards, Ted Mooney, P.E. Striving to live Aloha finishing.com - Pine Beach, New Jersey 2002 A. This is common with cold blacks. It can also happen with hot blacks for stainless, especially if the surface is not properly activated. Steve Loudermilk - Springdale, Arkansas 2002

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Q. I would like to know how to "Blacken" stainless steel chemically? It will not react to parkerizing. I heard that a Sodium Dichromate or Potassium Dichromate Dip will work. Is this the only way besides painting it. I want to keep the restoration of firearms historically correct but perhaps up to date. I am mainly involved with Zinc Phosphate and Manganese Phosphate coatings.

Thank you,

Chris Conlon
Firearm Restoration - Avon, Indiana
2004

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Need Sodium and Potassium DiChromate

RFQ: [Where to get] Sulfuric Acid H₂SO₄ Sodium DiChromate Na₂Cr₂O₇ Potassium DiChromate (to blacken stainless steel parts)

Chris Conlon [returning]
Firearm Restoration - Avon, Indiana
2004

Ed. note: Sorry, this RFQ is old & outdated, so contact info is no longer available. However, if you feel that something technical should be said in reply, please post it; no public commercial suggestions please ( huh? why?)

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Black Oxide on Stainless: Smut residue problem

2005

Q. As a small gunsmithing shop, I have recently been attempting Hot Black oxide on Stainless Steel: Barrels, Frames, small parts, etc. Mostly 416 type SS.

While my attempts have been producing a deep rich and uniform color, There is a significant amount of black residue(smut)left on the parts that must be wiped off during reassembly. The smut seems to lessen as the post treatment(water displacing oil)is wiped dry. But seems to reappear once a more suitable gun oil is applied for exterior corrosion protection.

Process being used:

Brownell's Oxynate 84 ⇦this on Brownells affil link] (similar to Heatbath's PX5) - 5 lb salts - 1 gal water boils at 245 °F
Media blast - 100 gt Al Oxide - desired matte finish
Dicropan cleaner
Water rinse
muriatic acid ⇦this on eBay or Amazon [affil links] dip - 2-5 min.(smutting occurs with or without this step)
Water rinse
Hot dip Black Oxide -
Water rinse
Blow dry
Water displacing oil

Thanks in advance for any helpful replies.

Rich Saunders
- Gardnerville , Nevada USA

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Black Oxide on stainless finish WITHOUT sulfur

Q. My company currently uses black chromium plated stainless (type 304 and 316) parts for experiments, but would like to replace this with a less expensive and more robust black oxide process. The blackening is for optical absorption, such as laser dumps, laser baffles, and spectrometer view backgrounds. The parts are in a ultra-high vacuum and often get up to 350 deg C. The problem is that tests have shown that the black oxide parts contain traces of sulfur that "outgas" in the vacuum and sulfur is extremely problematic to our experiments. It seems that the "activators" that are used prior to the blackening salts use sodium bisulphate. Is there a black oxide process for stainless steel that is sulfur free? What happens if the activator is not used prior to using the salts?

Thank you.

Doug Taussig
- San Diego, California
2006

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Can 15-5 PH Stainless H900 be Black Oxide Coated

Q. We are building a prototype for a military application, and would like the appearance of the final prototype to be black in color. Most of our exposed stainless parts are 15-5 PH age hardened to condition H900. Looking through MIL-DTL-13924 [on DLA] (Coating, Oxide, Black for Ferrous Metals), section 6.3.4 states that corrosion resistant steels of MINIMUM 17% Chromium and 7% Nickel can be black oxide coated, but does not specify if stainless steels of lesser concentration can be black oxide coated. My question is, will the black oxide treatment work successfully on 15-5 PH stainless steel?

Thank You

Philip Chu
Prototype Designer - New York, New York
April 29, 2008

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