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Plating Problems with Tool Steels

My company manufactures machined components that use 4140 heat treated & stress relieved. A hard face weld material such as Colmonoy-56 is then applied to a protion of the component. The part is then hard chrome plated and subsequently finish ground. The problem is two-fold: 1) often the plating flakes in small areas, especially sharp corners. 2)there often pinholes in the plating. Neither of these conditions is acceptable and causes us to have to strip and replate the part.

We are open for suggestions!

Tom Hoffman
- Atlanta, Georgia, USA

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Hi Tom:

The cause of your problem seems to be the following: hard chromium platers prepare the steels by means of a reverse cycle (most often done in the same bath) and then forward plate it. This works fine with most alloy steels, but Colmonoy, stainless or any other special alloy containing high percentages of nickel, chromium, cobalt or the like, will become passivated by this reverse. This interferes with adhesion of the chrome plate. About the pits or pores, it could be the same reason, or contamination in the chrome bath.

Guillermo Marrufo
Monterrey, NL, Mexico

What is your current process for cleaning, activating, and plating?

Michael Brewington
- Salisbury, Maryland, USA

I am experiencing the same pit hole problems with cold work tool steel components that are chromium plated. The electroplaters are at a loss as to why it happens. The surfaces of the components appear to be defect free before they are plated.

Lucy Davies
- UK

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Personally go into your shop, talk to every operator, and find and throw away every old scrap of emery cloth and give them new. It will cost you about $20 and I'll give you 50-50 odds your problem will be gone.

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