Using the Pots
We do mostly carbon steel and damascus, but have now done rather a few ATS-34 knives as well. Mike Alexander's pattern is as follows:
1) 15 minutes at 1950F in the high temp pot.
2) Immediately into the low pot at 400F for 15 minutes.
3) 8 hours in liquid nitrogen
4) Two draws at 400F for 1 hour each. Yields 61 Rockwell C hardness, and is supposed to be more stain resistant and tougher than an air quench and draw at 900F. This a little softer than D. Holder's blades (last 4 we had done were RC 62.1, 62.3, 61.4, and 62.3). However, knives hardened with Mike's technique are the tough that we see in blades treated by Paul Bos.
So far, users have not had any complaints with them. I asked one of my customers how he'd fared sharpening the knife ... he said he hadn't needed to. So I asked (rather suprizedly) "Haven't been using it? He responded: "Yup, field dressed five deer with it this year ... don't need to sharpen it though." (I was much relieved!)
No Scaling or Warping
We've seen no scaling or warping of blades hardened in the salt pots. Some practical pointers though:
1) Blades must be DRY when they are placed in the high temperature pot. Introduction of any moisture into a 1500F to 2000F environment gets very exciting!
2) Blades MUST be oil free when placed in the high temperature pot. Any carbon bearing material is instantly flashed off and it leaves tracks for later on ... seems to burn away a layer of surface steel.
3) Believe it or not, you have to agitate the blade upon placement in the cold pot to assure rapid enough cooling. Our first attempts at doing simple carbon steels were not successful because the rate of temperature drop was not high enough.
4) Blades can be taken to quite a high polish before they are heat treated, and clean back to that same polish in a jiffy.
Before you take on this for yourself, remember that D. Holder only charges $5 a blade to do a nice job. If you REALLY have to do it yourself ... do NOT construct these things on the "completely cheap." Use good materials for the containment vessel, good controls, and layout of the controls. Molten salts (from 350F to 2100F) are amazingly vile and dangerous materials. The introduction of water into a hot pot results in instantaneous vaporization and a resulting steam explosion that projects molten salt where ever it wants to go!
Molten salt does TERRIBLE damage to people.
Overheating of low temperature salts can cause oxidixer explosions!
Salt pots must be used will all due care and caution. As we CANNOT control the manufacture or use of this design, you're on your own and we CANNOT accept ANY liability whatever!