Ok I know I have heard of it as being a real good thing and have even heard it mentioned here in passing but what IS cryo treating, what dose it do, how and why? Can you do it just with dry ice or do you have to have something more like liquid nitrogen?
A very short and a bit incomplete answer is that cryo treating is stress relief done at cryogenic temperatures. No, dry ice is not cold enough, it is commonly done at liquid nitrogen temperatures, tho' other gases will do, they are just more expensive. The metallurgical activity that cold makes possible is a mystery to me, but it works. Stress relief, in general, is a good thing in that it increases strength of the metal by releasing the internal stresses that are caused by any sort of cold working or partially treated (such as blade edges) steels. I don't know, and would not try it with one of Valkman's blades, simply because I don't know that it would not be ruined by the process. When cold soaking, the time at temperature and rate of cooling and warming is critical, the experts have tables to consult for any given alloy vs. thickness of the part. #1 son was looking into it a couple years ago, the setup to start was 80K and he had to rent a place for it, then buy the gas. He passed.
When heat treating stainless steels cryo treatment "completes" the process. This is why I won't HT stainless myself - Paul Bos uses sweet ovens and vacuums and at $70 for 20 knives it's a good deal. If you only have one knife though it's different, and he charges like $14. I will have a batch going in in a few weeks so if you want yours to go with it let me know. It won't be fast but it will be cheap and done right!
Here ya go: Cryogenics, or deep freezing is done to make sure there is no retained Austenite during quenching. When steel is at the hardening temperature, there is a solid solution of Carbon and Iron, known as Austenite. The amount of Martensite formed at quenching is a function of the lowest temperature encountered. At any given temperature of quenching there is a certain amount of Martensite and the balance is untransformed Austenite. This untransformed austenite is very brittle and can cause loss of strength or hardness, dimensional instability, or cracking. Quenches are usually done to room temperature. Most medium carbon steels and low alloy steels undergo transformation to 100 % Martensite at room temperature. However, high carbon and high alloy steels have retained Austenite at room temperature. To eliminate retained Austenite, the temperature has to be lowered. In Cryogenic treatment the material is subject to deep freeze temperatures of as low as -185°C (-301°F), but usually -75°C (-103°F) is sufficient. The Austenite is unstable at this temperature, and the whole structures becomes Martensite. This is the reason to use Cryogenic treatment.
Cryogenics is also what is keeping Ted Williams head cold! Or more specifically the liquid nitrogen. My dad owned a Cryogenics company at the time of his passing in 04'. While in high school and college I delivered liquid N2 to ABS breeders all over the state, and helped my pop with the repairs and building of cryogenic systems, vessels and the like. Back in the late 80's he had the only mobile leak detection service in the U.S. It is incredible equipment that you use to find leaks that produce one bubble every two to three thousand years. They are big enough though that you lose vacuum in a heartbeat. Sorry to hijack the thread, but it brought back lots of good memories. I miss my pop.
So would leaf spring metal (5130 I think) fall into this catigory? What is the temp of dry ice? Also would just doing the heat treatment 2-3 times do the same thing? With leaf spring how much benifit would this realy be? Thanks for the info given so far. I just started cutting out the blank for it today so it will be at least a couple of weeks before it is even close to being done and ready for HT and handles and so on, probably a little longer since will also be haveing to shape out the hilt and get it fitted and pinned in place and such. Think I woll most likely heat treat the hilt right along with the blade since it will be the same material and figure it couldnt hurt for bonding them togeather. BTW; This is for the blade was asking some of the knife makers here about that I wanted to make.
No, leaf spring steel would not need cryo treatment. I use O1 all the time and it doesn't need it either as it does not benefit from it. My stainless steel gets the treatment from Bos. Heat your stuff to non-magnetic and quench in oil. Temper and you're done! I made one knife from hacksaw and files, and I won't do it again!
Well I do have a bench grinder (the type with the stone wheels) thats real light duty but helps and a belt sander that I put upside down in the vise and use in adition to the file, but this is the third one this way and the 4th is in planning. I was kind of looking at a deal atthe new Lowes in town today thats a bench top grinderthat runs a 4"x36" (or was it 32"...whatever) belt and also has a disc with the sand paper on the side, has a 1/3 HP motor and runs $100, kind of thinking I may pick one of those up some time as long as the finer belts can also be had for them for the finish work. Finest belts I saw for them was I think 180 grit.
Finer belts for 4x36 can be hard to find but Tru-Grit has 'em up to 600 grit if I remember right. I use 'em on my 4x36 to do the sides of blanks before I grind 'em - the more scratches I get out before heat treat the less I have to fix after heat treat! http://www.trugrit.com/
