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The affects of hydrogen embrittlement on cold headed threaded studs.

1999

I have a supplier that cold heads studs for an insert molding operation. These studs have a one inch long, 5/16 - 18 NC-2A thread on one end, a 1/8 thick by .600 inch diameter flange in the middle, and a 3/8 long by .400 inch long diameter shank on the other end that is sheared open into a tripod shape that holds the stud in place after the stud is insert molded in place using a phenolic material. This stud is made out of 1022 cold rolled steel and is zinc plated through the electrodeposit process. No heat treating is involved.

My question is hoe would hydrogen embrittlement affect the shear strength of the threaded stud as it is torqued to failure? If you had a suspect lot of parts that may have been subjected to this phenomenon, would you see a large difference in torque to failure values across the board or would you see a wide varience of torque values?

We have a situation where the majority (over 99%) of these studs are torque tested and will hold torque in excess 200 inch pounds. One failed at 120. Would this be a case of hydrogen embrittlement or should I be looking in a different direction?

I'm looking forward to seeing what other peoples thoughts are on this scenario.

Joe Ufheil
- Chicago, Illinois, USA

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I suspect a defect in the fastener, rather that H embrittlement. I'd mount the failed (along with a passed specimen) fastener and cross section, polish, etch, and inspect at 50 -200 X.

To what specification are you supplying these fasteners? With the major scandal about fasteners of 10 years ago, I believe that even the U.S. Congress got involved. And the platers of fasteners and the aerospace industry was sure running around for a while.

  
Tom Pullizzi
Falls Township, Pennsylvania
1999