Carbon Smut Problems in Electroplating

A. Hi Thomas. Is it possible that some of the components are leaded steel? HCl won't work with that.

If the parts are not leaded, it sounds like a typical case of 'overcleaning' high carbon steel parts.

Although it's hard to over-clean plain, mild, low carbon steel parts, if the parts are high carbon it's very easy to do do. 30% HCl for 7 minutes sounds excessive and quite possibly problematic for the high carbon steel parts. The HCl is for removing rust and oxides on the surface, but 1 minute is probably enough, and 2 minutes is surely enough.

Luck & Regards,

A. Try
1. Soak cleaner 10-20 min ( alkaline)
2. Electro cleaner 1-2 min
3. Rinse x2
4. Water break minimum 20seconds
If pass the WB continue if not repeat cleaning cycle.
5. Acid salts or HCl 30% 1-2 minutes
6. Rinse x2

A. Conventional alkaline cleaning, electrocleaning, and muriatic acid dip should do it for low carbon steel. Baking is not necessary to good adhesion, but it can be a useful test of adhesion (if it blisters, the adhesion isn't good).

A. Hi Veronica ,

High carbon steels when treated conventionally often leave a "smut" on the surface which seems resistant to everything except wiping with a rag or a brush, if this occurs then the best recommended cycle is as follows

• Soak Clean
• Electroclean
• Rinses
• Hydrochloric Acid Pickle (or warm Sulfuric)
• Rinses
• Anodic Electroclean in a "chelated" cleaner
• Rinses
• Nickel Plate

You could put a 5% Sulfuric Dip just prior to Nickel Plate to prevent drag - in of too much caustic if your rinsing was not up to scratch

Best regards

Thanks John. To me, 'carbon steel' meant 'plain old vanilla low carbon steel, so I thought Ms. Dewis' question was about just basic pretreatment. But you may be right that she is dealing with high carbon steel.

A. Dear Mr. Tenison-Woods,

I'd string along with your recommended process cycle if it were not for the fact that Veronica Dewis is talking about Carbon steel and I wonder if the electrocleaner before the pickle isn't a little more elaborate than what may suit the function. A double anodic cleaning may embrittle the parts further and if the soak cleaner is doing its job right, then I would probably skip the anodic cleaner before the pickle, or double dip in the soak cleaner.

Veronica, the post nickel plating baking may be required to remove hydrogen from your parts, but will also help to identify parts with bad adhesion, on which the peel off becomes obvious after 3 hours of hydrogen de-embrittlement.

All the best,

A. Veronica,

Low carbon steel plating cycle:
Soak, Ultrasound, two electroclean, rinses, HCl, RINSE, HCl again, then cyanide copper strike, cyanide copper plate, and nickel.

A. You won't get much oxidation in hydrochloric acid!

Do you get the smut when you apply the same treatment to lower carbon rods? You might test some rods with around, say, 0.4%C, and some with around, say, 0.1%C or less. If there is a difference, you might then look for a correlation between the severity of the smut and the amount of various metallurgical constituents in the different steels.

You are a student: Do the experiment, observe the results, try and explain the observations.

Clue: Think cementite (Fe3C)

ou might collect the smut, wash and dry it, then briquette it for chemical analysis by one of the X-ray fluorescence techniques (maybe using an XRF spectrometer, or maybe a facility built into an electron microscope).

If XRF can't determine elements with an atomic number as low as carbon, you might use a combustion instrument to find how much, if any, carbon is in the smut. It will be determined as elemental carbon, but you should not assume that is in elemental form in the smut.

A. Hi Sunil. An alternative to sulfuric acid is "dry acid salts", sometimes called "tri-acid salts". But acid will not selectively remove the carbon from carbon steel; in fact, it may do the opposite, surface enriching it with carbon.

Another "dry chemical" you could consider is sand :-)
-- blasting may be a good alternative to chemical pickling. Good luck.

A. Hi Sanjeev. Please be clear on exactly what the substrate is (photos e-mailed to mooney@finishing.com for posting here would be helpful as well).

I don't think you are talking about plating onto a carbide substrate, but the appearance of a carbon smut on your steel parts? We appended your inquiry to one thread where that issue is discussed, and you can search the site for many other threads on the subject, but two quick points:
1. You may find as Milt Stevenson suggests in topic 45748, that the key is Less anodic cleaning and Less acid treatment, not more.
2. You may find that what you are trying to do, cleaning hardened high carbon steel parts chemically without blasting, is not possible; but Yehuda Blau suggests in topic 3708 that alkaline permanganate may solve the problem

Luck & Regards,