Historically, hydrogen embrittlement was thought to be confined to parts over Rockwell C 39. In my experience, small electroplated parts over Rockwell C 43 seem to populate the ranks of hydrogen-embrittlement-related cracks at a significantly higher rate than those between 39 and 42. This is a problematic statement since the Rockwell C test method accuracy is generally considered plus or minus 2. This is my experience, so I am reporting it. 

Here is the reason that I decided it would be useful to review the issue of hydrogen embrittlement. It has come to my attention that some companies are allowing electroplaters of hardened steel to wait up to four hours, or even more, before doing a hydrogen-embrittlement prevention bake. This is a mistake. In “the old days,” hydrogen embrittlement was such a problem that the federal government was considering prison time for technicians who made mistakes when testing Grade 8 fasteners used for military applications! (My technician at the independent lab at the time made me promise to bring him clam chowder, not cream of tomato, should that have been his lot.) 

The prison threat was a result of numerous hydrogen-embrittlement problems in military hardware and nuclear reactors. Adding insult to injury, SAE J429 Grade 8.8 bolts were found to have been incorrectly marked as Grade 8 bolts. Grade 8.8 do not hold up under elevated temperature conditions as well as Grade 8, which are required to be tempered at a higher temperature, and Grade 8.8 bolts may have higher residual stresses even before being placed into service. This sets the stage for hydrogen cracks to nucleate immediately after electroplating. 

Fig. 2. Optical micrograph showing uniform tempered martensite. No visible separate grain-boundary phases/constituents to indicate that the material has a heat-treating problem instead of classical hydrogen embrittlement.