Electropolishing 420 SS Stainless

A. Hello, Gary_, Ashok. Most of the "must have" metal finishing books include good chapters on electropolishing of stainless steel, including the Metal Finishing Guidebook, ASM's Metals Handbook, Vol. 5., but especially the Electroplating Engineering Handbook [on AbeBooks or eBay or Amazon affil links] , which has a great chapter on the subject. Take a look at it and formulate some questions. Good luck!

Good luck.

A. Proprietary electropolishing processes for SS400 series are available in India.

A. Hi, Bob. There are many different recipes, most based on sulfuric acid or a mix of phosphoric and sulfuric acid. The Electroplating Engineering Handbook [on AbeBooks or eBay or Amazon affil links] has an excellent chapter on electropolishing, and includes some recipes you could try. But as implied by Ramesh's reply, you best strategy at this point might well be to contact a vendor of proprietary electropolishing solutions who can offer experience and testing to get you running again. It often requires not just a recipe but hand-holding as well :-)

Good luck.

Regards,

A. From your university library or a local library, try to get a copy of the Electroplating Engineering Handbook [on AbeBooks or eBay or Amazon affil links] , Mahesh. It has a chapter of electropolishing of stainless steel which will tell you what you need to know. If that book is for any reason unavailable, other treatments of the subject (although not quite as good) can be found in the ASM Metals Handbook Vol. 5 or the Metal Finishing Guidebook. Good luck.

A. Hi, Steve. Etching is sometimes the result of insufficient current density or excess water in the electropolishing solution.
But it isn't clear to me whether you are doing this electropolishing in-house vs. contracting it out; nor whether this is a problem which has just recently developed in your long-established proven process vs. whether you haven't yet successfully electropolished anything. But if you can flesh out your situation I am confident that the readers will have good next steps for you.

Regards,

A. Steve, 420 stainless steel is not the easiest of stainlesses to electropolish - in fact all 400 series are quite a problem! The basic formulations for stainless steels are based on sulfuric acid and orthophosphoric acid, but these are generally not very successful with 400 series, so extra additives such as hydroacetic acid ⇦this on eBay or Amazon [affil links] and/or aryl sulphonic acids are used. You may get best results if you talk to your supply house, as they may well have a suitable solution.

adv.
Stainless steel 420 and other 400-series steels can easily be polished in Universal electrolyte. We have installed such 1000 gal tank in March in one American shop. They have not replaced electrolyte yet and use it mostly for 420 series, although aluminum, copper, nickel and other metals can be polished in this tank also.

A.  Apologies Anna, I am aware of your non-acid saline based electrolytes for stainless steel, but unfortunately I have no first hand experience of them. My response was based on the conventional phosphoric acid-sulfuric acid mixes, where 400 series steels do present major problems. I believe that your systems may well be the answer to many prayers.

 We outsource the electropolishing service. Many thanks for the feedback received.

A. 420 is not the best for electropolishing. Use the same conditions as for 304, make sure specific gravity is high enough, no excess water, shorten polishing time, keep bath temp 120-130 °F, current density at least 150 ASF. The best you can hope for is semi-bright and smooth.

A. It may be a case of bath composition. If you are using a phosphoric/sulfuric based mix, the phosphoric acid may be too high. 300 series will work over a wide range of ratios. But, 400 series work best with a ratio of about 50:50. If you are operating at around 60 °C (140 °F) then you may have to raise the temperature to around 85 °C (185 °F) to get the brightest results.
One of the disadvantages of such a bath is that the minimum current density to obtain polishing (rather that etching) will have to be increased. Also, 400 series may start to dissolve chemically. Unless the chemical attack is only slight, it may be necessary to raise to initial current density to start the polishing action.

A. I agree with Harry Parkes suggestions and would like to suggest that to avoid low current density areas during the electropolishing process, multiple connections are made and special focus made on "difficult areas" where you may get lower current densities.

 Sorry for the delay!!

I was running samples.

Thanks, it worked fine, I obtained a satin finish, a very good shine, and sometimes not the same but acceptable.

The delay was because I did not want to write that I was not able to do it, or to say that I surrendered.

Thanks to Mr. Trevor, Mr. Parkes and Mr. Jeffrey!!

At the beginning it did not work --

I raised the temperature but changed the solution on a small bath, but the result was grey dull appearance. So I added an alcohol and lowered the temperature.
I suspect the problem was that the bath was very small so the bath got a very high temperature just before starting to work and the metal got etched by the solution.

A. Hi Matineh. We appended your inquiry to a thread where Trevor has offered a general answer regarding the additives. If that is not sufficient a search of the technical literature at surfacequery.com, or possibly even scholar.google.com might possibly find some published results. Good luck.

Regards,