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Carbon Smut Problems in Electroplating

Q. I notice some steel doesn't fare well in my acid.
2 soak 2 electro 2 rinse 2 HCl 2 rinse plating bath (acid chloride zinc)
Some parts I run are notorious for blistering.
If I skip the HCl this seems to mitigate this "crispy-ness" -- what's happening here? Embrittlement?
Maybe worth noting a barrel is typically in the HCl 7 minutes at 30%.

Thomas Zink
- Cleveland ohio
September 14, 2021

September 2021

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,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

October 30, 2021

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

Eduardo Lorona
plater - San Diego, California

⇩ Closely related postings, oldest first ⇩

Q. What is the best way to nickel plate carbon steel and have a good adhesion ? What pretreatment is necessary and is heating after the plating necessary to have a good adhesion?

veronica Dewis
- Miami, Florida USA

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).

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

16 March 2000

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

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

John Tenison-Woods
John Tenison - Woods
- Victoria Australia

thumbs up sign 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.

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey


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,

Khozem Vahaanwala
Khozem Vahaanwala
Saify Ind
supporting advertiser
Bengaluru, Karnataka, India
saify logo

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.

popat patel
Popatbhai B. Patel
electroplating consultant - Roseville, Michigan
October 6, 2021

Steel Smut Composition

Q. Extended pickling of high carbon steel rods in hydrochloric acid has resulted in smut formation on the surface. I assume that it is the result of an accumulation of insoluble oxidation products, but not aware of what compounds these are. Is the composition (specific or classes of compounds) of smut known?

Nathan Collett
Engineering Student - Newcastle, New South Wales, Australia


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)

You 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.

Bill Reynolds
Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.

Alternate for sulfuric acid for pickling process

Q. What alternate dry chemical can I use for pickling of mild steel wire, instead of sulfuric acid to remove carbon from the surface of wire?

Sunil Gandhi
manufacturer of shoe nails - Amravati, Maharashtra, India

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.

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey


Q. Hi Ted,
I like to understand more on your comment "But acid will not selectively remove the carbon from carbon steel; in fact, it may do the opposite, surface enriching it with carbon".
As a job shop operator,I recently faced an issue of "lumps"during acid pickling with HCl BEFORE EN PLATING.These lumps in turn gets soft after plating, giving rise to blisters.
Does HCl have any connection to the way it reacts with carbon steel vis a vis your comment above?
Appreciate all the help I can get.


What I was saying is that mineral acids will not remove carbon, Shane. If Sunil or yourself is suffering from a carbon smut on the parts after acid dipping, extending the acid dipping time only makes the situation worse, not better. It is possible that you are "over cleaning" those parts; once they start becoming pitted from HCl, you won't be able to fix them.

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

Q. Anyone can tell me carbide cleaning process for nickel plating? I need it urgently.
I face an issue in carbide cleaning where a black film occurs in anodic cleaning that is not cleared in sulfuric or HCl acid dip on the other side. It gets more black in acid by this black film, no nickel deposit on it. Give me some proper process for carbide cleaning.
Thanks in advance.

Sanjeev sharMa
- Baddi Himachal, India
December 20, 2020

A. Hi Sanjeev. Please be clear on exactly what the substrate is (photos e-mailed to 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,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey
December 2020

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