Letter 12064

Avoiding Hydrogen Embrittlement 

I am trying to nickel/cobalt plate the mild steel suspension pieces of a racecar to eliminate corrosion and to provide a hard long lasting finish impervious to the blasting effect of other cars on the track. I am concerned about Hydrogen embrittlement in the plating process. The suppliers of the plating supplies have not been very helpful and I'm tuning to this forum. I'll be removing the remnants of an original zinc plate on the parts in a Hydrogen or Sulfuric acid pickle. Based upon my own devices, I assume that I should bake the parts (275 F for 3 hours) after pickling and prior to degreasing, electro-cleansing and plating. The suspension parts manufacture also suggests post-plating bake out (275 F for 4 hours). Any suggestions?

Jack Wilson
- Pittsburgh, PA, USA

If the parts manufacturer specifies 275 deg. F., I wouldn't go any hotter than that. It probably wouldn't hurt to stay in the ovens a few hours longer though. But I don't think I agree that nickel-cobalt plating would be an improvement over zinc for this application. Did you perhaps mean zinc-nickel or zinc-cobalt?

 
Ted Mooney, P.E.
finishing.com Inc. - Brick, NJ

Hello Jack!

The temperature used for baking, and for that matter the necessity of baking at all, strongly depends on the hardness of your mild steel parts. Any idea what it is? Generally one doesn't need to worry when under Rockwell C 30 to 35, and the most common temperature of baking is about 375F- you use 275F, or lower, if the temperature is too much to maintain the hardness of your part.

In the conservative Aerospace industry, we also tend to use 23 hour bakes- it's usually easy for a commercial plater, since it's a little less than a day.

Hope this helps!

Lee Gearhart
- East Aurora, NY

Thanks for the responses.

A couple of clarifications: I misspoke in my original post. The bake temperature recommended by the suspension parts manufacturer is 375 F. I'll use this temp for pre and post plate bake out. I talked with the manufacturer of the parts and there is no Rockwell harness spec. They use mild 1020 steel, zinc plate and then bake at 375F for 4 hours. I chose the nickel cobalt because zinc plate always eventually oxidizes (at least on my stuff). I also plan to plate some miscellaneous brackets, so I tried to make a single investment in one set of plating supplies for all of my applications.

Fundamentally, my question is whether a pre-plating bake out is required. I understand the post plate process (and will extend the time based upon your suggestion). But, does the acid/electostripping process prior to plating induce Hydrogen impregnation that may be 'sealed in' the parts after plating? If so, is 375F for 3 hours sufficient to bake of the Hydrogen prior to plating? Or, is this not a concern at all?

Thanks again for your help.

Jack Wilson
- Pittsburgh, PA

The answer to one of your questions is that pre-plate bakeout is specified for some critical parts because plating can indeed "seal-in" hydrogen. (But if the parts are soft, no baking was needed at all anyway).

Baking times are usually specified to be on the safe side, based on some guesses, rather than actually determined to be necessary. So 3 or 4 hours might actually be adequate; and I've also heard of 6 hours, 12 hours, and 24 hours.

The problem may be that if you pre-plate bake, and then have to electroclean again anyway, what do you do, bake again? Ad infinitum? One thing you might do is blast clean the parts instead of pickling and electrocleaning.

Ted Mooney, P.E.
finishing.com Inc. - Brick, NJ

Thanks very much for your help!

Jack Wilson
- Pittsburgh, PA, USA

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