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topic 4674

Carbon Smut Problems in Plating; Pretreatment for Adhesion

Current question and answers:

December 20, 2020

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
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December 2020

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,

pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey




Previous closely related Q&A's starting in:

2000

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
^- Reply to this post -^


2000

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, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - 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


2000

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, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


2000

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
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Steel Smut Composition

2006

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
^- Reply to this post -^


2006

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


Alternate for sulphuric acid for pickling process

2007

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
^- Reply to this post -^


2007

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, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


2007

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.
Shane

SHANE HO CHENG CHYE
- SINGAPORE
^- Reply to this post -^


2007

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, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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