Been giving some thought on adding a cryo cycle to my zone hardened 01 blades. I have already found a 35 liter dewer that a place is selling for a song. I have also checked into some tech info on the subject.

I also understand that the steps are
Grind, normalize, heat treat, temper, cryo, temper.

Now my questions are -

1) In the info I have found they say that the steel needs to be cooled slowly to avoid shock fracturing. Is this true? It has been my understanding that the blade can just be lowered into the nitrogen. I tend to doubt that everyone doing their own cryo has a $20,000 computor controlled cryo chamber.

2) How long should the blade be left in?

3) How will this affect the temperline on my blades?

Ron, you may be visiting some new ground with differentially tempered blades. They often have some stresses along the temper line, and I'm just not certain what you might experience. I suppose you could go into dry ice/alcohol for a -110 quench before the liquid nitrogen, but I'm really not sure that would help. I agree though, not many knifemakers have programmable cryo chambers.

Paul Bos uses a minimum of 8 hours (overnight) as I recall, but that's on high alloy steels. He does a "snap temper" before the cryo. You might want to call him and ask what exactly that means. Also, he does at least two tempers after the cryo. Since Paul also has a bunch of years experience with tool steels as well as high alloy steel he probably has some thoughts he's share. He's very open about his technology.

BTW, as 35 liter dewar for a song is a great score. Congratulations!

Thanks Jerry. New ground huh....This should be fun. Any guesses on how many blades I will break in the first day:D . I do plan on giving Paul a call and see what he has to say.

Missed out on the 35Liter but just picked up a 30Liter for $124.

Ebay guys, its a great thing!