Sorry. Hypereutectic is a steel with more than .77 /.8 % carbon. Iron will only absorb that amount into a homogenous solution. Hypoeutectic steel has less than .8% carbon. Any extra carbon is in the form of carbides and will be distributed about as sort of free agents. When steel is slow annealed as in a common anneal, a lamellar structure is created. Basically layers of iron/ferrite, with layers of cementite/carbon. These layers in steel with less than .8% carbon will easily allow tooling to cut the steel. In steels with more than .8% carbon, the cementite/carbon layers will be thicker and more resistant to tool cutting. To be softer, hypereutectic steel needs a spheroidized anneal, in which the carbon forms into spheres rather than layers. This done by heating to above 1333° and somewhere under 1414° which is the temp that steel loses it's magnetic attraction. Say around 1375° and hold there at least a few minutes, then cool at about 50° per hour until under 900°, then let air cool to ambient. If you have no way of controlling temp, just give the steel multiple heats that are just under non-magnetic and let air cool. You can slowly bring a piece of scrap steel to non-magnetic and take note of the heat color, then do the annealing heats at less than that. This is not a perfect explanation of it all, but close enough I think. As I mentioned though, a few red heats on the file, with air cooling, always got me by. Not the best way, but made the files reasonably workable.