Chemical polishing of stainless steel

A. Hi Jamal. Electropolishing (properly done) will smooth stainless steel. However, I am not confident that it will increase the wettability ... I believe that is a function of cleanliness primarily, and of exposing raw metal rather than oxides secondarily.

Luck & Regards,

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A. Hi Jamal,

This article uses a product named "DS-9-314" - consists of 10-30% phosphoric acid, 1-10% hydrochloric acid, 1-10% nitric acid, and 1-10% proprietary surfactants - to chemically polish 316.

The article also determined that electropolishing made the surface more hydrophilic compared to sand blasting and chemical polishing.

Link to article:
"Reducing surface roughness by chemical polishing of additively manufactured 3D printed 316 stainless steel components"
eds.p.ebscohost.com/eds/pdfviewer/pdfviewer?vid=1&sid=00b823a1-4a1d-47c5-a607-91321cf98df3%40redis

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Ed. note: Thank you Jules. The article was available to us by going to www.ebsco.com and signing into our public library's system first, then searching for the article by its title. We don't think readers will find the direct link workable as it apparently contains session info, but the article is useful :-)

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A. Hi folks. ASM Metals Handbook, Vol. 5 mentions that proprietary products for chemical polishing are available and that generally "they are based on combinations of phosphoric acid, nitric acid, sulfuric acid, hydrochloric acid, organic acids, and special stabilizers and surfactants to promote a high degree of brightness and long bath life."

Regards,

A. You should also investigate electropolishing. This process simultaneously brightens, cleans, deburrs, smoothes, and passivates most stainless steels. The process is electrochemical, much like a plating or anodizing operation.

Regards,

A. You can use next solution:
10% phosphoric acid
10% hydrochloric acid
5% nitric acid
75% water
(80 °C temp., add 10 gm soot, 5 minutes immersion)
Good luck!

A. Hi, Dan. Can your waveguide be made of copper, nickel, or gold instead of stainless steel? If so, you could electroform it on a .03" diameter wire mandrel and the ID would be every bit as smooth as the OD of the mandrel.

Q. Nope. It's intended to be a thermally-isolating section of waveguide. WR-3 rectangular waveguide (0.034" x 0.17") is commercially available in coin silver, but not steel. So I am using the round stainless tube as a substitute, which is already a compromise. That's why I'd like to limit the loss as much as possible in the tubing I have. We have extensive electroforming capabilities in-house, but it's not an option.

I've sent a sample off to a stainless micropolishing company in California, and they claim to have an electroless steel polishing technique. I have not gotten the samples back yet, but I understand their dip solution is proprietary. Anyone have any idea what they use?

Thanks.

Dan

Ed. note: the internet, and this no-registration site, are too anonymous for us to post info about the formulations of proprietary products, Daniel. There's no way to know it's not coming from, for example, a disgruntled former employee wishing to blow their trade secrets. But if anyone can point us to a book or published article, that would be excellent.

Q. Was there a solution to this problem yet? I actually have a very similar problem trying to get a mirror finish on a 1 mm ID in Hastelloy. I'm not even sure a chemical polish will work because of the corrosion resistance of the material but am willing to try.

Thank you for any info you might have.

A. Hi, Michael.

An obvious problem here is that a shorthand term like "chemical polishing" can mean one thing to one person and quite another thing to someone else. In the discussions on this page prior to yours, people seemed to be referring to chemicals that will polish stainless steel by dissolving metal without any mechanical abrasion; whereas to you, the "chemical polishing compound" seems to mean something added to a buffing compound in addition to the abrasives.

What actually happens in mechanical polishing and buffing is that particles of abrasive rip away metal. If the abrasive particles are large, they rip away large chunks of metal, leaving a rough surface. If the abrasive particles are small, the chunks that they rip away are small, leaving a smoother surface -- but polishing a rough item to a smooth finish with a fine compound can take forever -- it's like trying to excavate the foundation for a building with a teaspoon.

So, what usually needs to be done is multiple courses of polishing/buffing, starting with aggressive compounds with large abrasive particles and ending with very fine compounds. To my knowledge there is no chemical added to a buffing compound to help get a smooth surface from a coarse abrasive, or to help get super rapid cutting from a fine abrasive.

Regarding imbedding, a mechanically polished surface always looks like a plowed field -- it's just a question of what magnification you need to see the furrows. Chemical polishing or electropolishing attempts to dissolve away some metal from the surface, attempting to offer more of an "ocean swells" finish than a "plowed field" finish. For this reason, electropolishing is often specified for critical surfaces like in pharmaceutical packaging equipment and dairy equipment. Good luck.

A. Hi Bikash. I don't think you are looking for a chemical polishing dip, but for a polishing or buffing compound that you can use with mechanical scouring. Stainless steel is designed to robustly resist attack from common non-hazardous and non-toxic products, so you probably won't find any innocuous chemical that you can simply dip stainless steel into to shine it ... and scouring seems more practical for a bakery than installing an electropolishing line or an automated polishing and buffing line. Good luck.

Hi, Abhishek. We usually find it difficult to offer help in response to abstract questions. If you can tell us your situation, we can probably offer some specific advice, but the "general" proposition of polishing stainless utensils fills whole books and indeed whole library shelves. About all we can say in summary is that both mechanical polishing & buffing, and electropolishing are generally viable approaches to a mirror finish, but chemical treatment is not.

Regards,

A. Muthu,
Please refer also to the previous discussion on this page, but in general chemicals on their own don't polish, they etch.

It's certainly possible to pickle/etch a stainless surface to a uniform finish, but it wouldn't be a "polished" surface per the usual definition of polished meaning "more smooth that it was before".