Sub Zero, huh?

[DaveL]

I am interested in the ways to sub zero quench in a small shop. I have one friend that has a small unit that looks like a cabin type machine that goes far below zero and he does a raally good job of heat treat with it. What are the best methods to do a quench and who has links to the small units like I mentioned?

[DaveL]

Okay, maybe it is the time of year but since no one has posted a response I will talk a little more. I know some heat treaters that do not sub-zero quench and think it is overblown. I know some makers that use liquid nitrogen and love it. Others use dry ice but I think a unit that goes down low and the knives could be placed inside would be nice. I have one suggestion by a very good heat treater who uses cryogenic quench but told me another way. More on that later if we get some feedback.

[Chris Daigle]

Hey Dave. I don't want this thread to die out either. I've heard where putting a blade into a standard freezer will even see improved results, but I'd like to hear from some HT veterans.

Best of the holidays to all!
Chris

[cactusforge]

I have also heard of small freezers that will go a very long way down below 0 far enough to do sub zero quenches but never could find them or prove thy exist. Any refrigeration people here? any one about these things? Gib

[Shakudo]

many of us could just stick the blade on the picnic table in the backyard tonight. - 15 may be the median temperature tonight.

[luc]

Hey Guys!
From what I understand You have to take the steel to at least -100 to get any effect
and I've heard that at -100 you get 90% effectivness if you take it -300 you get a 100%
I have been looking for plans for some type of small bench freezer that could be flooded with some type of gas C02 or nitrogen maybe, but haven't found anything yet!
Or a small cryo oven, but I haven't found one of those either. I have seen larger cryogenic ovens, but they've always been obscenely expensive, ($25,000 range)
I have been using dry ice and acetone (the Acetone transfers the temp without freezing)
I can't remember right now but I think dry ice is -110.
Dave is there any chance you can find out what type of unit your friend has?
Also I would like to hear the other method you spoke of!
Hopefully someone more experienced than myself will chime in! RJ.... QuenchCrack...
Happy holidays!
Lucas

[tmickley]

Hey Dan, the whole state is a cryo treatment.

I have a 30liter used liquid nitrogen dewar. You can find them on eBay all the time. I get it half filled for around $40 at the local welding supply. They put in around 20liters for me. It will last around 6 weeks in the summer, more in the winter stored outside where I live.

I just hang the blank from a piece of wire over night. I had a very healthy skeptisism about cryo treatment and did quite a bit of reading and research. I am satisfied it is for real in making a knife edge last longer. You will need to get to at least 90 below zero for the cryo to have an effect -- or at least that is what professional research has proven. Ed Fowler, I think has been the most vocal about throwing a blade in the freeze for a day or two and seeing an improvement in performance.

[cactusforge]

One thing to remember is this TEMPERATURE and TIME, when talking about heat treating you have to conceder both. There has been threads about this on this Forum That explain what we are talking about. There are also people who know about this stuff, maybe thy will help us out. Gib

[DaveL]

Tracy, tell us to look for on Ebay. I am not sure how to search for what you were talking about. Dave

[luc]

Hey dave!
Not Tracy but.
Look for, Nitrogen dewars, and semen tanks.
Some welding supply places will fill a thermos for you as well, not ideal but it works!

[tmickley]

Here is a search on eBay you can use and it will bring up several dewars:
eBay dewars

and here is a very typical example of one I've seen most makers use, including me:
30 liter dewar on eBay
Mine didn't come with a cap so I made one by rolling up a piece of (sleeping bag camping) foam into a 'cork' shape and stick it in the top. When I put a blade in and cork it, 'steam' shoots out of the top while it bubbles for a minute until the blade cools down. Very cool.

You are looking for some thing from at least 15 liters to 30 or 40 liters. Ignore any gauges or dials, they don't matter at all. Most of the designs I've seen have narrow openings. Make sure if you are bidding on one, that the opening is large enough to fit your knife blank through.

[mete]

Since transformation to martensite is not a diffusion process it doesn't take all that much time to transform in cryo. Dry ice and acetone will do most of the job.Also remember that the more complex the steel the more the benefit. So with 5160 - no benefit , S30V - about 2 points difference in hardness.

[rhrocker]

Mete, are you saying (I hope) that one could get by with not cryoing? I'd like to do some SS bladework, but haven't because of the cryo issue.

[tmickley]

Robert, you do everything else, you might as well start heat treating. The cyro process is simple, hang a blade in the LN for 8 hours, done. You can do cryo as simple as a foam cooler lined with plastic, a gallon of kerosine and a block of dry ice. I know some use acetone and I think that is too volatile for my taste. The conversion from austinite to martinsite only requires around -90 so dry ice and kerosine will work fine.

I get at least 1 point higher RC and have gotten as much as 2.5 extra RC points after a cryo soak. The variance in increased RC, I think, was due to different (air) quench methods. I went to the junk yard and bought a couple scraps of aluminum plate and now plate quench. There was such a debate on plate quenching that I had to try it. Now I think it's the way to go after trying it and testing hardness. I believe I will get more consistant results going forward this way so the variance in increased hardness from RC should narrow.

[mete]

Robert, you don't have to cryo but it doesn't make sense to me to use the best steels such as S30V and not get the best properties . On that point remember some of the variables ,as tmickley found ,quench speed is important . In addition for those that snap temper before cryo - a snap temper of 400F will stabilize the austenite preventing the cryo from transforming it !! Snap temper at 300-350F.