One of my students worked on a similar question for his MS thesis and found that higher-strength fasteners (RC hardness > 37, achieved by more extensive case hardening through to the tapping screw center) were more susceptible to hydrogen embrittlement, (due to a zinc acid plating process), as expected, (and is geometry dependent).
Subsequent baking for 8-12 hours at 200C showed no positive effects, and in some cases worsened embrittlement (as evidenced by lower fracture loads and notch toughness).
So, this experimental work suggests that baking may not be a good idea (at least for the conditions investigated in this limited study).
If you are interested in further detail, please check the paper (attached).
Medcalf, John S., Thomas, Brian G., and Brahimi, Salim V., "Hydrogen Embrittlement Susceptibility of Case Hardened Steel Fasteners," SAE Internat., Technical Paper 2018-01-1240, WCX Conf., Detroit, MI, Apr. 10-12, 2018, pp. 1-17, 2018, DOI:10.4271/2018-01-1240.
--Brian.
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Brian Thomas FASM
Professor of Mechanical Engineering
Colorado School of Mines
Golden CO
(217) 493-9633
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Original Message:
Sent: 07-16-2020 15:08
From: Robert Gaster
Subject: Hydrogen embrittlement of fasteners
Hydrogen embrittlement of fasteners is a problem caused by improper baking that can lead to failure under static tensile loading. There is a difference of materials professional opinions on whether or not hydrogen embrittlement can be reversed. Some professionals say that hydrogen embrittled fasteners can be reclaimed by rebaking them. Others say that once the hydrogen embrittlement is in the fasteners it cannot be reversed. Which do you support, and what is your technical reasoning/data for your position?
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Robert Gaster
Retired Senior Staff Engineer
John Deere Moline Technology Innovation Center
(563) 340-8862
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