Metal finishing Q&As since 1989

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Hydrogen Embrittlement

Q. In an effort to eliminate or lower the possibility of hydrogen embrittlement of our screws after Zinc plating I ran across your site. I am in search of technical data that will assist my decision making as to whether we should require Black oxide or Black Phosphate finish.

Thank you,

Tracy Harper
ANKO Products, Inc. - Bradenton, Florida
2003

Unless these are hard screws, you very probably do not have a hydrogen embrittlement problem. Also, all of the theoretical data is of little value. What your screws actually have is the important part. There are companies that can test your parts for you. Notch bar testing is far more common. Simple torque testing to failure with a comparison to unplated values will give you an immediate clue as to whether there is a problem or not. I further doubt if any two batches had identical values. So much depends on the processing-how long it was in the acid- and how soon it got into the bake oven after plate. From that point, time and temperature are factors, but considerably less important unless you are doing 5H bolts or something like that.

James Watts
- Navarre, Florida
2003

After the torque test carry out a fracture exam I mean fractography to find out if fracture was brittle & not yielding fracture. In case of embrittlement the fracture would be brittle without indications of yielding. Secondly the embrittlement can be ensured by adhering to baking at a temp. empirically determined, within a short period after plating.

R.R.KASHYAP
System Engineering Consultants - Bangalore, Karnataka, INDIA
2003

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