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Metal finishing Q&As since 1989


Can steel be anodized? If so, how?

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Q. Is there a process to anodise steel or cast iron? If not, what can be done to achieve similar results?

Josh Jones
Aftermarket Manufacturing - Flint, Michigan

Q. Ours is an Aluminium Extrusion and Finishing Company. We have the anodizing facility for aluminium profiles using sulfuric acid. We do get enquiries for anodizing steel. But our sulfuric acid process is not suitable for steel.

Can anyone give some guidelines / process (suitable electrolyte and other data) to carry out industrial anodizing of steel?



A. Hi Josh; hi Manalel. The reason that aluminum is anodized is because aluminum oxide can form a tight, tenacious, corrosion resistant coating on aluminum, such that aluminum can be beneficially anodized. But iron oxide (rust) will not to my knowledge form a tight, tenacious, corrosion resistant coating on steel, so I don't think it can be beneficially anodized.

I don't know quite what you have envision by 'similar results'. Nitriding would give a wear resistant surface, but it is conductive (unlike anodizing which is an insulator); further, it cannot absorb dye. Paint, powder coating, or electrophoretic lacquering might do what you want but would not be as hard or wear-resistant as anodizing. Certain platings might achieve what you could be looking for. Although anodizing of steel sounds like it is not the answer, if you can detail what characteristics you are looking for, people can probably direct you to finishing processes that deliver what you are looking for.

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

A. Anodizing forms an oxide protective barrier on aluminum but if you form iron oxide over steel it will not protect it adequately; for that reason a different compound has to be developed. You may want to explore blackening, galvanizing or phosphate coating of steel.

Guillermo Marrufo
Monterrey, NL, Mexico

A. Hi. Some companies claim that they know an Electrochemical Process for stainless steel wherein Chrome Oxide can be produced/enhanced and by varying the thickness it attains different color. Maybe you are talking about that? But, to the best of my knowledge, the term "Anodizing" is used only for Anodizing of Aluminum.


Keshava Prasad M
- Chennai, India

A. You do not want to make the surface of steel more anodic. To protect it, it should have a continuous cationic coating.

Fred N. Teumac
- Fort Myers, Florida, USA

? Hi Fred. I don't understand that one. Are you suggesting cataphoretic electrocoating (CED)? Please expound. Thanks!


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

A. Hi. Anodizing is used only for Aluminum, but for steel you can use metal spray (with Aluminum wire) over it.
After that you can Anodize it.
Good luck

Amir. H. Matin
- tabriz, Azerbaijan, Iran
December 16, 2008


Anodizing Steel in KOH and NaOH Solutions:

Marcus Rowland
- Columbia, Maryland, USA
July 10, 2009

thumbs up signThanks, Marcus, very interesting paper -- something new under the sun!
That link broke a while ago, but this URL works and includes links to that paper:

From a quick review it doesn't look like a process which will offer a hard and wear-resistant surface, or even a very corrosion resistant one.


But I find it intriguing as a possible alternative to phosphate pretreatment before painting -- especially for the short sighted 'environmentalists' who see an ounce of phosphate as a problem, but not the endless re-mining, re-smelting, re-rolling, re-fabricating, re-painting, re-packaging, re-shipping, re-selling, and re-landfilling operations for the ton of steel repeatedly necessitated due to products being 'protected' with inferior non-phosphate pretreatments which last 2-3 years instead of the 20-30 years they lasted with phosphate pretreatment. The present situation with outdoor furniture and tools is a scandal, and unfortunately an object lesson in the environmental pennywise-&-pound-foolishness policy of focusing pressure on the folks whose business is improving sustainability instead of those who profit from the lack of it :-)


Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey
January 28, 2013

Black Anodizing of Steel to Match a Black Anodized Aluminum Casting

Q. We are working on a project to put a cast steel threaded cover on an aluminum casting that has been black anodized. The customer wants the same finish cosmetic appearance on both parts even though they are different materials.

Been scratching my head over it and figured I would try you all for some opinions or experiences.

Joe Paterson
New Product Development Engineer - Austin, Texas

simultaneous replies

A. You may not have a lot of luck - the few times I've seen this come up, the advice I've seen has been to try to anodize the aluminum to match the steel rather than the other way around. Probably your biggest holdup isn't going to be color so much as gloss and shine...

Look at topic 37471 -- it talks about different ways to electrolytically color steel (might just be stainless - my notes don't say). Otherwise just start checking out samples from different finishing technologies - just use the search engine for blackening steel for ideas.

Color matching-wise, your best luck may be with paint or powdercoat.

Good luck!

Jim Gorsich
Compton, California, USA

A. Try black nickel or chromium, or even electrolytic or chemical colouring of steel, or forget all that and powdercoat both parts. Good luck!

Goran Budija
- Cerovski vrh Croatia

A. Black oxided steel per MIL-DTL-13924 [on DLA] can closely resemble black anodized aluminum. Depends on the micro-roughnesses of the surfaces and the rust preventative (oil or wax) used on the black oxide.

Ken Vlach [deceased]
- Goleta, California
contributor of the year honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at, continue to benefit from.

Q. Dear Sir
Can you (please) send me the relationship between Time & Voltage for steel anodizing?
I am a student to get MS.c in chemical engineering -- Anodizing of steel.
Thank you
Best regards,

Basheer Ahmed
- Baghdad-Iraq
January 28, 2013

A. Hi Basheer. There is no such commercial process. But you might wish to review the previously suggested link to for your experimentation purposes.


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

Q. Dear sir,
Our company is consistently producing case hardened kingpins (knuckle pins for trucks & bus). The final finishing of these kingpins are either grinding (only) or Hard chrome plating and grinding.

Recently, our competitor introduced a very hard black (very deep greenish) and corrosion resistant coated kingpin in the market and is dramatically establishing an upper hand. It seems their kingpins are hard-Anodized or something like it (I am confused and getting hopeless gradually). But I again learned that, only Aluminum can be anodized. Or it may be a phosphate coating over the Case hardened steel.
Any kind advice would be appreciated with gratitude.


Muhammed Hanifa
engineering works - Pabna, Rajshahi, Bangladesh
November 30, 2013

A. Hi Muhammed. Yes, it is indeed easy to get confused about whether steel can be anodized because it depends on exactly what you mean by "anodized" :-)

- If we mean "can it be immersed into a conductive liquid and be attached to the positive pole of the circuit to any beneficial purpose", the answer is a qualified yes because it seems that anodizing of steel is a development laboratory idea as a possible pretreatment option before painting, or for coloring weathering steel ... but it is not a commercial practice.

- If we mean can we get similar properties to what we get from sulfuric acid anodizing of aluminum (hard, wear-resistant, dyeable, insulating, highly corrosion resistant) the answer is a clear no.

Trying to guess what your competitor is doing from the color of the coating may not get you too far. But might it be a QPP salt-bath nitriding process? Or a solid-film lubricant process? What properties does it offer that the customers are finding attractive?


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

Q. Hello sir,
Gratitude for your kind reply.
Our competitors' kingpins (knuckle pins) are far better wear & corrosion resistant. I mean, better than hard chrome plated or carburized (case hardened & ground).
Sir, my point is, is it possible to give case hardened steel components a black corrosion resistant coating without altering its dimension (increasing obviously) and hardness?
If so, then we can somehow cope up with our competitor in the market. Maybe black oxide or manganese phosphate coating over our case hardened kingpins?


Muhammed Hanifa [returning]
engineering works - Pabna, Rajshahi, Bangladesh
December 10, 2013

A. "Our competitors' kingpins (knuckle pins) are far better wear & corrosion resistant. I mean, better than hard chrome plated or carburized (case hardened & ground)."

In that case I would think that their product is carbonitrided, or nitrocarburized, both of which mean almost the same thing. And ... it's fairly deep, maybe .010" to .025"

That's the only way I know of to beat carburized and hardened and hard chrome.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg, South Carolina

Q. Hello sir,
your assumption on "what my competitor is doing" was exactly right & helpful. Their kingpins are in fact quench:polish:quench nitrocarburized. Thanks.
I have already contacted the nearest HEF Durferrit agent. They can supply us with the required chemicals for the surface treatment process. My point is, will it be optimum, if I purchase their chemicals for our requirement?
thumbs up sign Thanks again for supporting us from your immense experience.

Muhammed Hanifa [returning]
mechanical engineering works - Pabna, Rajshahi, Bangladesh
January 1, 2014

A. Hi Muhammed. I don't know about "optimum", but yes, the point is that Q-P-Q sounds like an appropriate process for your needs, and perhaps what your competitor is doing!


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

Q. A few years ago Mr. Josh Jones asked about a process of anodizing steel to achieve "similar" results.

I write a blog about cookware of all types, most of which have been created to eliminate the drawbacks of using steel to construct bakeware and cookware.

Is there a food grade process, similar to anodizing, where steel can be made corrosion free, where the food will be easy to release and the pan or pot be easy to clean?

Tin was an attempt, vitreous enameling is an attempt, but these are applied coatings.

Thanks for your consideration.

Richard Pousson
Bakeware/Cookware Blogger - Concord, California
May 20, 2016

A. Hi. I do not believe there is any mechanical finishing process or conversion coating process which can make a steel pot into appropriate bakeware or cookware ... but as you mention, there are various coating processes that will do so.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

Q. Hi
My project is about anodized iron.
The data could not find a way to do it, someone has a better solution?

shahin zare
sharif university - Tehran, Iran
July 13, 2016

A. Hi Shahin. The previously offered pdfs from New Mexico Tech seem to explain the solutions they tested as well as their preferred embodiment. I don't understand quite what you mean about not being able to find a way:

What are you expecting from the process; what properties are you looking for; what are you doing; what are you attaining? Please try your best to keep the discussion here moving forward. Thanks :-)


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

Q. I'm trying to paint cast iron starter parts that have been anodized because the interior needs it. I'm using an oil based enamel paint and am having it not adhere. What can I do. Thanks.

randy montagno
- shandaken, New York usa
January 15, 2017

Bulldog Adhesion Promoter

(affil links)

A. Hi Randy. I don't know what finish is on your cast iron parts, but it's certainly not anodizing. If they are not plated with anything, just bare cast iron, phosphatization would be the normal pretreatment. You can't do true phosphatization yourself, but you can apply naval jelly [on eBay or Amazon affil links] which is the consumer's best imitation of a phosphatized coating. If the parts are plated with something like zinc, nickel, or chrome, you could try an adhesion promoter .
But if that doesn't work well enough (and it probably won't work great), you would probably have to remove the plating before painting, or have the parts replated instead of repainted.

Still, the most common cause of poor adhesion is simply that the parts aren't really clean :-(
Good luck and Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

Ed. note: We have other closely related threads which readers may find interesting:
Thread 13970 discusses applying aluminum to iron and steel and then anodizing that.
Thread 39602 inquires about possibility of chromate conversion coatings on iron and steel.

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