That's likely referring to grinding with wheels, which generate more heat than belts do. In my case I know the steel hasn't over heated and softened because it hasn't changed colour. If no oxides have appeared on the surface of the steel, then it cannot have got above about 190C (unless I were grinding in an oxygen free environment, but I like breathing air). Also, if you are grinding freehand as I do, my fingers soon tell me when the blade is getting warm! The kilns don't overheat or burn the edge, but they will happily decarburise it, which is just as bad for the steel p.s Stew, sorry for the derailment!