Rory Carter

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 heat to 1400 deg F then let them soak for 1 hour per inch of thickness and then boost the temp to the critical temp for hardening which is 1750 deg F then let the temp heat the part evenly and then soak for another hour per inch of thickness. this solved all of our warping issues with this steel.. So to sum up this is not a totally similar case but I think the principles may apply. Look up the manufacturer's data and see if it recommends a preheat cycle. This cycle will be significantly lower temp than critical temp for hardening. What it does is it causes less stress in the metal when it goes through its phase changes. This should not cause any decarburization either. Obviously the times of heating the blade will not be the same as mold parts but again I think this would be worth pursuing.

I am a toolmaker and we use d2 for making progressive dies. Normally we are talking cross sections of no more than 2 inches. We just put in in a stainless bag (to prevent scale) and put it in the furnace when the furnace is cold and have it heat it to 1850 F and then hold it at 1 hour per inch of the thinnest cross section. We then remove it from the oven and let it air cool and temper it at 400 F. This usually achieves 55-60 rockwell. I have never had any problems with this steel.