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Carbon steel chisels destroy corrosion resistance of stainless

Workers are using carbon steel tools to clean welds and carbon blocks as temporary spacers on Stainless Steel components although they do use Stainless Steel approved wheels and brushes. The blocks are not welded to the Stainless Steel and the product is cleaned with an approved chemical prior to shipping (low hydrocarbons).
Is it possible that the SS could still be contaminated by using the carbon tools and spacer blocks as the Free Irons are usually a surface condition?

Larry Morey
Inspector - Ottawa, Illinois, USA
April 9, 2009

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April 27, 2009

If your standard is "perfect" you are not going to sell many parts. What is acceptable (with a pad for boo-boo's) probably is what you are looking for.
Any metal saw cutting, high speed cutting tools, clamps/positioners are going to contribute to the problem also.
Having done salt spray testing on 316L stainless that was wire brushed with "stainless brushes" absolutely would not pass as many of the tips of the bristles (410 SS)were embedded in the part.
You might be better off with chisels made of hardened 17-4PH, or D-2 or S-7 materials. ScotchBrite is a bit more expensive than brushes, but causes far less problems with follow on rusting.

James Watts
- Navarre, Florida

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First of two simultaneous responses --

I definitely would be wary of any carbon steel interaction with a stainless product. The prudent thing would be to test possibly affected areas with something like copper sulphate, and if you see evidence of iron surface contamination, start passivating your parts and/or eliminate the use of carbon steel tools.

What James said is also our experience, many stainless wire brushes are 400 series grades and can introduce problems when used on 300 series grades. 304/316 wire brushes are harder to come by but do exist.

Ray Kremer
Stellar Solutions, Inc.

McHenry, Illinois

April 29, 2009

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Second of two simultaneous responses --

Larry, you are right - carbon steel tools contaminate stainless steel surface. That is why you need nitric acid passivation, which will remove free iron from stainless steel surface.

Anna Berkovich
Russamer Lab

Pittsburgh, Pennsylvania

April 30, 2009

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Hey Larry,
Yes the carbon steel contact contaminating the stainless. And is indeed causing the rusting.
As a suggestion you could do away with manually/mechanically cleaning up the weld scale and discoloration by simply just passivating. This will remove the discoloration and if left in the passivation vat long enough will produce a matte grey uniform finish over the entire part.
One step further would be to electropolish the parts which would increase the corrosion resistance a lot more than passivation only and the remaining surface would be polished bright and extremely clean.

As an example that contact contamination does occur. We had a job come in that was a brushed finished 304 s/s square tubing handrail. After manufacturing the sections of rail were loaded onto the carbon steel deck plate of the shippers truck with inadequate insulation. The weight of the rail rubbed through the plastic wrap, contacted the deck plate and began rusting.

Cliff Kusch
electropolishing shop - North Vancouver, British Columbia, Canada
September 20, 2009