Metal finishing Q&As since 1989

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Stainless gassing in HCl

I am trying to put EN onto Stainless steel. Some Stainless gasses in the HCl and in the woods nickel strike causing it to turn black. Yet other Stainless Steels don't gas at all in the HCl and work fine in the woods nickel strike

How do I correct this problem?

Steve Johnson
employee of plating shop - Johnson City, TN
May 17, 2009

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Stainless steel should not normally be put into HCl at all because of the chloride attack in the intergranular boundaries. Certainly most ferritic and martensitic grades of CRS will etch and turn black in HCl. We advise that you use some other acid to replace the HCl.

Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois

June 23, 2009

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First of two simultaneous responses --

One place that I worked, we used electrolytic sulfuric acid on 410M SS. In other places we used 15% HCl on several SS's with no problem.
I think that your problem is that you are 1. using a much higher % HCl, and 2. you have iron dissolved in your acid which is giving you a ferric chloride [on eBay or Amazon] etch which at even low concentrations will vigorously attack several SS's.
Also, try going into the Woods Strike hot, with about 30% of your plating voltage. This probably will help to prevent the smut.
Also, rinse a whole lot better after each step. With clean water, not an over used single rinse tank. Spray does not use much water after a dunk rinse and gives you a significantly cleaner of chemicals part.

James Watts
- Navarre, Florida
June 24, 2009

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Second of two simultaneous responses -- June 24, 2009

A short dip in HCl will not hurt anything, but afterwards, make contact outside the tank and enter the nickel chloride strike "hot".Use 2 pounds per gallon nickel chloride plus 1 quart per gallon HCl. Do not use S-rounds, use Rolled Depolarized (bagged) anodes and take them out when not in use. Again, enter the strike tank "hot".

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina