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Pickling 410 Stainless to Remove Rust After Passivation

Q. I am running a lot of 410 material through a passivation line. The parts are coming out of passivation with rust spots. I have ran these parts for some time now and never have had this happen to me. I check the tanks and everything came out perfect so I know it's not the tank.

The material house that I got the material from sandblasted these parts with a tumbler prior to delivery. So they suggested to me that I "Pickle" the parts. I don't know much about it. I have tried to do some research on it. I see that there is a acetic acid ⇦ this on eBay or Amazon [affil links] and there is a Nitric Acid pickling. These parts have to be processed to ASTM A390.

What is the best way to set up the Acetic or the Nitric? Is there something wrong with the material causing the rust? Also,Is there a place that I can find a Solution Make Up ratios?

Wes Oettinger
2007
Process Manager - Chattanooga, TN, U.S.A.

A. Dear Oettinger,
Kindly scroll down to letter no.46618 posted in this forum. You will get the right answer. After reading please do post your queries.
regards

T.K. Mohan
plating process supplier - Mumbai, India
2007

Q. I read the other article. However, it still leaves me with no solution on how to stop the rust from appearing. I cannot switch to a citric bath. Also, I have ran these parts a long time without this result. Why now?

Wes Oettinger
Precision Machining Services - Chattanooga, Tennessee
2007

A. Wes:
There are a number of possibilities here. Just because it has always worked before does not mean that the steel is the same. Stainless steel is manufactured by a lot of companies, and some are quite different. If you get the steel direct from the mill and it is the same mill always, you have a fairly good control.
Are these castings?
I do not understand when you say the parts were sandblasted in a tumbler. These are two different processes. Regardless, either sandblasting or tumbling with contaminated media will be a big problem.
If the parts are manufactured and blasted or tumbled correctly you should not have to pickle the parts ever. Passivation is all that should be necessary, unless the parts are dirty.
Our customers have done millions of 410SST parts with no problem, but that does not necessarily mean that it is easy, especially if they are castings of a 410 type alloy.

Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois

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January 3, 2008

ASK for the SANDBLASTING PROCEDURES. Probably they are utilizing higher pressure, time or blasting angle. Also, the media must be evaluated: clean level, maker, properties,....
If it is possible do interfacial test of the sandblasted parts. I suspect that there are deposited media. Write back results please.

USE HOT WATER after etching, and then the rest of your procedures.

Jose Castellanos
- Minneapolis, Minnesota, USA