Normalizing is heating the steel until all of the atoms are aligned. This is the first step of annealing. Then it is cooled slowly, so that the steel remains soft(er). The piece is then worked, producing new internal stresses. Normalizing again removes the stresses. Tempering (with oil) introduces a differential in hardness. Basically, cool the steel slowly to make it soft, and quickly to make it hard. Too hard and it cracks/chips, too soft and it deforms instead of bending. The process ZippoVarga described will work just fine for a generic tool steel like these old files. If you knew the exact composition of the steel, you could look up the specific temperatures and times to produce the properties you wanted, but who cares if its not perfect? Just make another one.