At 9:12 AM 3/2/5, Terry Blanton wrote: >One of the first engineering tasks I had while still in school was to find >out why a steel conveyor chain for my employer was failing. Long story, >but the short answer was hydrogen embrittlement in the electroplating >process. This was in 1975. > >Since then I keep checking to see if anyone has figured out the mechanism >for hydrogen embrittlement (they really haven't.) In the googling process >I stumbled across the chemical industry expert witness site. Check this >one out:
It looks to be fairly well covered and understood in *Topics in Physics Vol 72 - Hydrogen in Metals III*", Edited by Helmut Wipf, Springer-Verlag, ISBN 3-540-61639-X, 1997, pp 221 ff. Interestingly, one of the processes, called "hydrogen attack", is due to carbides forming methane: FeC + 2H2 --> CH4 + 3 Fe "The pressure of methane increases parabolically with the pressure of hydrogen." It does say, "The kinetics of the process is unclear." though. The bubbles of methane form on grain boundaries, and this requires diffusion of the carbon. A graph of the pressure vs temperature boundary below which the embirttlement does not occur is given. It goes on to say that hydrogen attack is not limited to carbides, but can be due to other reactions leading to bubble formation, for example hydrogen combining with oxides or oxygen bubbles to form water. It goes on to describe other mechanisms, like metal hydride formation, and physics of crack growth, etc. Regards, Horace Heffner
