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Thread: Cryo?

  1. #61
    Thanks guys.
    The storage issue is worth taking note! I have to find a dealer in my area, but i'm sure that relying on a longer shelf life is a no brainer regarding the choice of the cooling medium (maybe the price gap also?). So maybe LN could be overkill for 14c28n and probably is, but ramping down for the short time needed for complete martensite transformation won't hurt even if the temperature is lower than necessary.

  2. #62
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    Quote Originally Posted by Kevin R. Cashen View Post
    *Nickel is so effective in stabilizing austenite that it is the element that is used to make austenitic stainless which is always completely austenitic and non-magnetic, even at room temperature.
    Now that is interesting - am I to understand it's the amount of nickel in non-magnetic stainless (like 316, 304 SS) rather than the amount of chrome?

    Checking 304, 316, 410, and 416 SS I see the amount of chrome is in the 10%-14% range for all of them, but the nickel is only 1% range for 410SS and 416SS Ni is .01%. while for 304 Ni is 8% to 10.5% and 316 Ni is 10-14%.

    I'd never really given it much thought what caused the non-magnetic property of SS. Until knife making 304 and 316SS were the primary SS I worked with and always considered magnetic SS as "low grade" SS because it was magnetic. Just goes to show how little I knew at the time.

    I just keep learning from this site due to great folks sharing knowledge. They keep telling us old folks to work crossword puzzles to exercise the brain - me, I'd rather keep learning new things.

    Ken H>

  3. #63
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    Both nickel and chrome are big tubby atoms but nickel is the winner at distorting the iron atomic lattice. The iron latticework is a nice repeating crystalline pattern of stacked atoms in straight lines, this allows those atoms to slide past each other and deform when needed (like when austenite transforms), but a big fat nickel atom in the middle of the mix skews all those straight lines around it, creating a log jam in the sliding action. Carbon does the same thing when trapped between the iron atoms when we super cool the steel to harden, like little wheel chocks keeping things from moving. put the two together and you can get the effect of trying to push an austenite truck up a chromium-nickel hill that is littered with wheel chocks so that you can get to the martensite on the other side. You then need a push from some extra cooling (sub zero) to get it over the hump. Chromium does this as well but it only takes a little nickle become problematic. I work with L6 all the time, but if L6 only had around .15% more carbon I would probably be freezing it due to its nickel content. At .75-.80% C the nickel by itself in L6 is not problematic. It is also worth noting that another Simple alloy containing nickle, 15n20, also limits its carbon content to .75%. Those eggheads making the steel kind of know what they are doing after all.

  4. #64
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    Thank you Kevin - you help keep this old brain cells active with learning new stuff.

    Ken H>

  5. #65
    I know this thread is going on 2 years old, but I am trying to find out information in regards to cryo treatment in the knife making world. My research shows me that there should be a ramp rate to follow from ambient to cryogenic temperatures. There are manufacturers of such machines that I have been contact with, but I am curious as to how you guys are pulling this off, or if you are just dipping your ambient temperature blades straight into LN2 temperatures? Or if anyone has found a good supplier of these machines, at a relatively decent price? I found one in the US that builds a machine specially designed for knife makers for around $6k USD. Anyone know if this is a good price? Sorry for all the questions.

    Thanks.

  6. #66
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    Old thread, but to add what I do..... I generally suspend blades above the liquid level in my tank for a couple of hours before submerging them. Then, after the treatment is complete they are laid on/covered with kawool so that they do not warm up too quickly. Generally for a couple of hours. Personally, I'm unaware of any knifemaker who has/uses the device you mentioned. I've heard of it the past, but never considered it, as the cost to usefulness ratio is just too high for me.


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    "Nobody cares what you know.....until they know you care."
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  7. #67
    Thanks Ed. I can see how it might not be cost effective in the short term, but it sure would take some of the hassle out of it, and turn it back into a science. I read this entire post and see that there is still debate out there, but I had a friend who was studying this in school and passed me off quite a few papers in the day, and they always seem to be some pretty impressive results. However, I read that most are only doing their blades for anywhere between just a dunk, to 10 hours, but I was told 20 hrs minimum. Have you ever heard that rule?

  8. #68
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    I have heard the "20 hour rule" before, but in most cases that was applied to cross sections of steel much larger then would ever be present in a knife blade. I can't back it up with any science, but based on testing I've done, blades require at least a 6 hour soak to show noticeable affects. I've found that in many cases whenever someone states "a rule" about something, you must ensure you're comparing apples to apples, which in many cases where "rules" are established, that often is not the case, and in the process, much confusion ensues.

    I've also found that from a knifemaking standpoint, there are steels that benefit from the cryo, and others.... not so much. I don't cryo plain carbon steels, as the benefits are very limited. Steels that contain higher alloy contents are the ones that derive the most benefit from cryo. It's certainly not any type of "magic bullet", so guys like me who do this full time have to weigh the benefits to cost ratio and make the decision whether the gains justify the cost and time involved. In the case of cryo, I do it to only those steels that I feel gain the most from it.

    www.caffreyknives.net
    Caffreyknives@Gmail.com

    "Nobody cares what you know.....until they know you care."
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  9. #69
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    Quote Originally Posted by Blade-Runner View Post
    I know this thread is going on 2 years old, but I am trying to find out information in regards to cryo treatment in the knife making world. My research shows me that there should be a ramp rate to follow from ambient to cryogenic temperatures. There are manufacturers of such machines that I have been contact with, but I am curious as to how you guys are pulling this off, or if you are just dipping your ambient temperature blades straight into LN2 temperatures? Or if anyone has found a good supplier of these machines, at a relatively decent price? I found one in the US that builds a machine specially designed for knife makers for around $6k USD. Anyone know if this is a good price? Sorry for all the questions.

    Thanks.

    Interesting about the cryo ramp rate. I've never seen anything about a cooling rate that but it seems to make sense.
    My ramp rate is to lower it slowly into the Ln so 5 to 10 seconds. Ed's method of suspending makes more sense but I always seem to be in more of a hurry than that. I always soak for at least 8 hours overnight, pull it and hang it in still air to warm up.
    Tracy Mickley
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  10. #70
    Quote Originally Posted by BossDog View Post
    Interesting about the cryo ramp rate. I've never seen anything about a cooling rate that but it seems to make sense.
    My ramp rate is to lower it slowly into the Ln so 5 to 10 seconds. Ed's method of suspending makes more sense but I always seem to be in more of a hurry than that. I always soak for at least 8 hours overnight, pull it and hang it in still air to warm up.
    Ok, so I am not sure how much background everyone has on heat treatment and more specifically, cryogenics, but I have a little. I have read a few books - I know, not the real world, but...- and a few studies on the process. If you're interested look up "Cryogenics", by William E. Bryson. He also has some great books on "Heat Treatment, Selection, and Application of Tool Steels" is a great one that I am sure anyone/everyone on here would find relevant. I have also read this from Jay Fisher:

    "What is the specific rate of cooling for most of these steels? 4-5 degrees Fahrenheit per minute. That means in order to reach -100F, it should take about 40 minutes (from room temperature), and to reach -325F should take about an hour and a half (from room temperature). This is why simply dipping blades into cryogenic baths of dry ice and alcohol or liquid nitrogen is a huge and destructive error, yet knifemakers who are uneducated in this process frequently do this, and tell others that it's the proper way to quench! Sad, truly sad for the knife client. The cryogenic process cooling rate is absolute and critical." http://www.jayfisher.com/Heat_Treati...Quenching_Rate

    Which seems in line with what the books and studies say. So I am now "fishing" all the forums to see how other knifemakers are making this a reality....but so far, I have yet to find anything.

    I am super interested in hearing any feedback you might have.
    Last edited by Blade-Runner; 03-14-2017 at 10:29 PM.

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