Dry Ice for Cryo treatment

[Philip Lee]

Seasons Greetings to everyone and family on CKD,

I have managed to buy some dry ice locally - temperature -79 below zero.

I have never done serious cryo treatments before , could someone kindly run me through on using dry ice on my blades.

At present, i do one temper cycle, into the deep freezer - temp - 5 below. Then i do the second temper after leaving the blade their for 1 week.

Thanks in advance.


Philip Lee

[RPatton]

Philip,
The Crucible handbook recommends one heat draw before freezing for stress relief to reduce the risk of cracking. I subscribe to this myself. I've talked to several makers who practice 'continuous quench' where the as-quenched blade is gradually cooled and then frozen before any tempering is done. I've tried that too. Then I cracked a nice 1095 blade and decided that I'd stick to one temper and then freeze.

As for leaving them in the ice for a week....I'm not so sure that time at temperature is as important as the fact that the steel is going through the extreme range of temp...the trip is more important than the destination so to speak. Your blades are as cold as they're going to get in say 4-6 hours. Maybe more, maybe less. I don't think you need to keep them there for a week.

Follow with two more heat draws and you should be in good
shape. And like so many other issues in knifemaking...if you ask five makers for an answer....you may get five different answers.



Happy Holidays
Rob

[shgeo]

I use a dry ice treatment in a continuous quench on tool steels. For S30V, I snap temper like Crucible recommends.
For the tool steels, I use an interrupted oil quench. Only leave in the oil until the blade gets black, then air cool to room temp, then into the cooler on dry ice overnight. Triple temper the next morning. Mostly, I am doing D2 this way. I got the procedure from Bohler/Uddeholm's data sheets on heat treating tool steel and for D2.

http://www.bucorp.com/pdfs/UddeholmH...fToolSteel.pdf

http://www.bucorp.com/Products/ColdW...ts/aisi_d2.pdf

They recommend cold treatment at dry ice temperatures after quenching.