Yes, over heating can do a couple of things. One is that it can cause problems with warping. I over heated one of the first blades that I made and it came out of the bath looking like a potato chip. The worst thing is that temperatures in that range can promote grain growth which can cause brittleness in the blade. Steels above 77 points of carbon suffer from overheating the worse but that's too high for just about all steels. Maybe there are some high alloy steels that need that kind of temperature to disolve the carbides but most blade steels won't. You can go back and correct for any grain growth by heating the steel to a little above non-magnetic and then letting it air cool for three cycles, unless it is an air quenching steel. For air quenching steels that would be triple quenching.
Doug