[M.D. Holloway]

Something I came across:

Hydrogen embrittlement is a major cause of fastener failure. Prevailing thought is
that steels with Rockwell hardness above C30 are vulnerable. The phenomenon
is well-known although the precise mechanism has eluded extensive research. A
number of proposed mechanisms have been proposed, and most have at least
some merit. Current thinking is that the susceptibility to hydrogen embrittlement is
related directly to the trap population. Generally, hydrogen embrittlement can be
described as absorption and adsorption of hydrogen promoting enhanced
decohesion of the steel, primarily as an intergranular phenomenon.
Electroplating is a major cause of hydrogen embrittlement. Some hydrogen is
generated during the cleaning and pickling cycles, but by far the most significant
source is cathodic inefficiency, which is followed by sealing the hydrogen in the
parts. Baking is often performed on high strength parts to reduce this risk, and the
ASTM, in 1994, issued a specification for baking cycles, as shown below. For the
production plater, having to remove the parts from the production line to
bake - followed by a separate chromating process - is a laborious process.

For Nearly fifty years mechanical Plating has been accepted as a means of
eliminating hydrogen embrittlement. Today, many specifications reflect industry's
confidence in this unique process. While it is true that mechanical plating uses
inhibited acids which generate less hydrogen, PS&T believes that mechanical
platinng as a process is inherently free from hydrogen embrittlement because the
deposit is porous (as are phosphate coatings), allowing hydrogen to escape through
the coating; in electroplating, by way of contrast, hydrogen is sealed in the part.