Could it have been a case hardened rasp? Do you have some cut-off pieces from profiling that you could quench test in water to see if they harden? Maybe try to spark test? 10 second oil should harden at least the edge of any 10 series or W steel at that thickness.
Other thoughts: can that oil be preheated for a faster quench? Or, what if you coat your blades with a very thin wash of Satanite to increase surface area, may help quench faster?
My feeling is still that this is not high-carbon. Good luck!