Guindesigns
Well-Known Member
What is the set up for a cryo cycle? With liquid nitrogen? Do I just put my blades on a wire and put them in my Dewar to soak? And what about bigger blades that won't fit in the Dewar?
Cryo quenching
- Thread starter Guindesigns
- Start date
Yep, that's pretty much it for cryo. I do put the blade into freezer to cool off a few minutes while getting other stuff ready, then drop into dewar for LN treatment. You just don't make "bigger" blades {g}. You can purchase a dewar with around 3" opening which is pretty wide blade. The "normal" dewar seems to be 50mm which is about 1.94" wide blade will slide in.
Smallshop
KNIFE MAKER
LN is best. Almost all cold treatments help...some very much depending on the steel. You can buy large mouth dewars to accommodate larger blades. I borrow mine but want to get a smaller capacity dewar so I don't have to spend so much to get it deep enough to cover the blades.
Guindesigns
Well-Known Member
Ok I have been giving a Dewar that does not have a bigger mouth and can NOT afford a new one right now. But I have some nitro v chef knives I need to do. How can I do those??
J. Hoffman
Dealer - Purveyor
When putting blades in your Dewar try to keep them above the liquid. The liquid will gas off much quicker if the blades are actually submerged.
How wide is the chef knives at the widest point? I used to make my full size chef knives a full 2" wide at heel, but now I knock off about .060" to a widest width of 1.94" so they will slide into my dewar with a 50mm opening. Never know the difference in that .060" width loss.
Since I have only a 50 liter dewar the blade must go into the liquid for longer blades. Only small 3" to 5" blades can be held above the liquid once the level falls a bit.
Depending on how many knives you make/yr, and cost of LN at your location, you may find it much more cost effective to send blades to https://www.jarodtodd.com/ or other places for HT'ing with cryo. I just like doing it myself. My cost for LN is 50 cents/liter at one and $6/liter at another place.
fitzo
Well-Known Member
Build a small insulated vessel out of metal tube and welded plate bottom. Insulate the outside with thick insulating rubbery stuff. Fill with LN carefully.
Put knife in. Cover with blanket, etc. That'll last long enough. Not all LN work has to be in a Dewar, though it is nice when that happens, eh?
Put knife in. Cover with blanket, etc. That'll last long enough. Not all LN work has to be in a Dewar, though it is nice when that happens, eh?
Smallshop
KNIFE MAKER
Hi Jess....why would that matter?
Gliden07
Well-Known Member
So the Vapor is as cold as submerging the blade in the Nitrogen? Does this also help to prevent any warping associated with Cryo? Thanks??
Putting a warm (relatively speaking) blade into the liquid nitrogen will cause more to boil off, while suspending in the vapors doesn't cause as much boiling off. The vapor area above the liquid is still really cold, in the -300F range. Problem is in a normal size dewar there isn't much vapor space above the liquid until dewar gets low.
fitzo
Well-Known Member
I have a 30L Dewar. Current wisdom apparently says minimizing the delay time between plate quench and into the LN is critical with a steel like CPM154. So, rather than leave a full Dewar out in the garage and run a cooling blade out there I shall try and get a 10L fill and get it down into the basement with some help from my wife.
I will thus have to use headspace temps to do the cryo. -300F you think is achievable, @KenH ? And, then, I suppose, the question is how long it takes to achieve steady-state after closing it back up with a hot blade in there?
I will thus have to use headspace temps to do the cryo. -300F you think is achievable, @KenH ? And, then, I suppose, the question is how long it takes to achieve steady-state after closing it back up with a hot blade in there?
Mike, I'm not sure how you're planning to work that headspace in a 10 liter dewar. Do you plan to transfer a couple liters from 30 liter dewar to the 10 liter dewar so will have a good bit of headspace above liquid? If so, should work just fine - not sure how to transfer LN from the big dewar to small dewar. If you plan to get a 10 liter dewar and have it filled, then when full you wouldn't have any headspace.
By "hot blade" I'm assuming you are talking "relative" to the LN temp <-300F? I tend to move a blade from quench to a freezer to cool blade before putting in dewar. A freezer temp of -5F is still a "hot blade" relative to LN, but it seems to boil the LN less than a room temperature blade. How long before steady state is achieved in a LN vapor space? Not sure but I suspect about same time as with liquid LN. I tend to leave in a hour and up to few hours. There has been talk about 24 hrs in LN to create ETA carbides, but I've also read that is not a proven thing. Doesn't hurt, but not sure it really does much good.
My understanding is cryo treatment is a continuing part of the quench, so the blade shouldn't sit as room temp long at all. The blade should see a continual cooling from austenitizing temp to LN temps. The austenite conversion to martensite happens during quench and continues thru the cooling. If the cooling stops for any length of time it's possible for the RA (Retained Austenite) to get locked in place, hence the desire for a continual cooling.
The above is my understanding and is ALWAYS open for correction.
Ken H>
By "hot blade" I'm assuming you are talking "relative" to the LN temp <-300F? I tend to move a blade from quench to a freezer to cool blade before putting in dewar. A freezer temp of -5F is still a "hot blade" relative to LN, but it seems to boil the LN less than a room temperature blade. How long before steady state is achieved in a LN vapor space? Not sure but I suspect about same time as with liquid LN. I tend to leave in a hour and up to few hours. There has been talk about 24 hrs in LN to create ETA carbides, but I've also read that is not a proven thing. Doesn't hurt, but not sure it really does much good.
My understanding is cryo treatment is a continuing part of the quench, so the blade shouldn't sit as room temp long at all. The blade should see a continual cooling from austenitizing temp to LN temps. The austenite conversion to martensite happens during quench and continues thru the cooling. If the cooling stops for any length of time it's possible for the RA (Retained Austenite) to get locked in place, hence the desire for a continual cooling.
The above is my understanding and is ALWAYS open for correction.
Ken H>
Smallshop
KNIFE MAKER
so it's an economy thing not a quality of blade thing...as in a shock advantage?
fitzo
Well-Known Member
Thanks for the quick reply, Ken!
What I plan on doing is getting a 10L fill in the 30L Dewar so I can carry it down the stairs in the clumsy manner I do things today. (LN is only 5 minutes away. Some of the old businesses that supported industry are still here in this post-industrial wasteland.) 20L headspace should still allow me plenty of height so as not to have mixed liquid/gas immersion.
I was only wondering if you knew through prior experience in engineering if an LN headspace in a sealed system will achieve a -300F headspace? I don't think any thermocouple I happen to have on hand can measure that temp, so I can't check. Wish I could, now that I'm curious. LOL Hard to get he lab out of the boy.
I will almost certainly do that most famous of laboratory hold times - overnight - so it is more a question of scientific interest than necessity!
Doug Lester
Well-Known Member
At the risk of looking like a smart ass (my ex-wives would agree that that's one of my strong points) may I ask what steel you are treating. With something like 1075 all you are going to do is make your steel real cold with no real benefit for the molecular structure of the steel. Some of you high alloy steels need it for peak performance. Just saying that before you spend time and money on the dewar and liquid nitrogen, make sure that you need them.
Doug
Doug
I think Mike is talking about CPM154 while Guin was talking about nitro v steel.
Yes Mike, I have measured the vapor space with a TC and it was almost same temp as the liquid nitrogen. I like the idea of putting only 10 liters in the 30 liter dewar to make it easier to handle. I would need to work a 30 liter dewar the same way I work a 100 lb propane tank - with a shop crane and hand cart.
Ted, I think of it as more of a way to lessen shock, it might not make a bit of difference after all, the difference between 80F and -325F isn't all that much different than -5F and -325F, but it does "seem" to boil less and that seems like it would lessen the shock and perhaps save a bit of LN also. At 50 cents/liter cost of LN isn't much, just the trip to get dewar filled.
Yes Mike, I have measured the vapor space with a TC and it was almost same temp as the liquid nitrogen. I like the idea of putting only 10 liters in the 30 liter dewar to make it easier to handle. I would need to work a 30 liter dewar the same way I work a 100 lb propane tank - with a shop crane and hand cart.
Ted, I think of it as more of a way to lessen shock, it might not make a bit of difference after all, the difference between 80F and -325F isn't all that much different than -5F and -325F, but it does "seem" to boil less and that seems like it would lessen the shock and perhaps save a bit of LN also. At 50 cents/liter cost of LN isn't much, just the trip to get dewar filled.
fitzo
Well-Known Member
@Doug Lester Good points, thanks!
I've had the Dewar for 25 years, so that's not a problem. Thought about a smaller new one but, wow, way big bucks. I may become a denizen of my old Big Pharma company's salvage operation. They sell a lot of lab equipment. "til then I've got the 30L.
I don't know what all I've cryo'd over the years - 440C, ATS34, D2, 154CM, A2, O1, CPM154, CPM3V, S30V. That may be it.
I've never tried plainer steels, though I suspect a couple of the popular things like 52100 might well benefit, if one defines benefits as gaining a point or 2 in HRC. I don't know what current wisdom is about all this.
I do my HT in the basement. I learned years ago the stench of burnt quench oil is a no-no in a house with one of us asthmatic, one emphysemic, and both with COPD. So, I will be sticking with air quenchers (plates and forced air) and stock removal.
I've had the Dewar for 25 years, so that's not a problem. Thought about a smaller new one but, wow, way big bucks. I may become a denizen of my old Big Pharma company's salvage operation. They sell a lot of lab equipment. "til then I've got the 30L.
I don't know what all I've cryo'd over the years - 440C, ATS34, D2, 154CM, A2, O1, CPM154, CPM3V, S30V. That may be it.
I've never tried plainer steels, though I suspect a couple of the popular things like 52100 might well benefit, if one defines benefits as gaining a point or 2 in HRC. I don't know what current wisdom is about all this.
I do my HT in the basement. I learned years ago the stench of burnt quench oil is a no-no in a house with one of us asthmatic, one emphysemic, and both with COPD. So, I will be sticking with air quenchers (plates and forced air) and stock removal.
fitzo
Well-Known Member
@KenH Thanks for that verification, Ken. -300F* oughtta surely get whatever changes are there to be made without any science fiction stories attached.
Did you do that with a standard thermocouple at home? I didn't know they'd work in that range. That'd be cool and geeky if I can measure this stuff at home.
Did you do that with a standard thermocouple at home? I didn't know they'd work in that range. That'd be cool and geeky if I can measure this stuff at home.
Mike, I've got this instrument: https://www.amazon.com/dp/B018QHQSB8/ not by any means lab grade but it seems to read "somewhat" ok. The specs show with type K TC it reads -328℉ to 2501℉ which covers LN range. I don't remember exactly what the vapor read but I remember I was surprised how close it was the LN temp.
BTW, how much do you have to pay for LN/liter where you get it so close to home? The "close to home" for me is 10 mile away and they want $6/liter, but driving 30 mile away it's 50¢/liter.
BTW, how much do you have to pay for LN/liter where you get it so close to home? The "close to home" for me is 10 mile away and they want $6/liter, but driving 30 mile away it's 50¢/liter.