I do heat treatment of mostly tool steels for complex injection molds. Disclaimer... I have never heat treated a sword blade. However we noticed that we were warping our mold components a lot ( this was with s-7 steel) so I looked up the heat treat info sheet from the manufacturer and found that when hardening the components a pre-heating cycle should be used. I had previously thought that this ment that you put the parts in the oven at room temperature and then let them heat as the oven warmed... this was erroneous.. what it ment is that I needed to put the parts in at room temp and let it he