Cryogenic treatment for Knife steel
For this tutorial, I don't have any photos, but then they would be rather anticlimactic any way.
I recently read: Heat Treatment, Selection, and Application of Tool Steels [Paperback] by Bill Bryson (Author). This is an excellent easy to understand and follow source. In it MR Bryson describes why we would want to cryogenically treat tool steel (knife steel). I was sucked in and had to try it. I have to say, it was easy to do as it seemed when I read it.
The knives should already be hardened and drawn (tempered).
Materials: cheap Styrofoam cooler, K1 kerosene and Dry ice. Bill describes laying the steel in the bottom of the cooler and I wondered how it would circulate the cold properly so I cut 2 pieces of round stock to lay down first.
Then I laid my knives down on the rods, poured about 3 inches of kerosene in the bottom and then slit the plastic bag (holding the dry ice) open a little bit (as described by MR. Bryson) and placed the dry ice in the kerosene. I placed the lid on, punched a couple of holes in the top and walked away. I checked back on it every few hours to make sure the dry ice hadn't evaporated away to early (you want about 6-7 hours of cold).
The next day all the ice was gone and the kerosene was room temperature. Watch out, if you stick your fingers in the kerosene when there's dry ice in there, the temperature is reported to be minus (-)120 degrees F. The frozen flesh (burn) you will get will leave a lasting impression, scars and possibly amputation. As for the holes in the top, the dry ice evaporates and causes CO2 to build up in the chamber. We don't want a tight seal and or any unwanted releases on the floor. Personally, I placed the cooler in my "heat room" on the gravel floor.
Once you've retrieved your blades re-draw them (temper) them (again) about 25 deg below the original draw temperature. If D2 draws at 960 deg F, then draw them again at 935 deg F.
For those of you who have liquid Nitrogen, MR Bryson also has a process for that. As for me, this is simple and my customers/family/friends love the story of their fired and then frozen blades .
Theodore Roosevelt: No man is worth his salt who is not ready at all times to risk his well-being to risk his body to risk his life in a great cause.