I have never heard of the term "chelation" used to describe a corrosion process nor can I find any mention of it in any of my reference materials. Perhaps you are correct that very little has been written about it! If you are having corrosion issues with cobalt-based hardfacing materials I would suggest you talk to the alloy/coating manufacturer of the material in question (for example, Stellite 6 is manufactured by Deloro Stellite). The alloy manufacturers are often the best source of information about specific alloys and should have experts that understand the detailed corrosion mechanisms for their alloys in various environments.