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?
From my recollection there are 3 ways to reduce hydrogen intake during zinc electroplating:
Perhaps some one from the plating industry can better explain these.
Patrick Mizik, P.E.
Principal Metallurgical Engineer Haldex Brake Systems
Haldex AB - The information contained in this communication may be confidential, is intended only for the use of the recipient named above or if improperly named, the intended recipient, and may be legally privileged. If the reader of this message is not the intended recipient, you are hereby notified that any dissemination, distribution, or copying of this communication, or any of its contents, is strictly prohibited. If you have received this communication in error, please re-send this communication to the sender and delete the original message and any copy of it from your computer system
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.
ASM International is the world's largest association of materials-centric engineers and scientists. We are dedicated to informing, educating, and connecting the materials community to solve problems and stimulate innovation around the world.
ASM World Headquarters9639 Kinsman RoadMaterials Park, OH 44073-0002
+1 440.462.0292 (International)