Cryo Treatment- O1 steel?

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The only reason that I and my workmates would warm our chisels on a cold and frosty morning was to keep our hands warm! We never gave a thought to chisels getting damaged.
They can apparently shatter. Found this out on a city and guilds course i did yonks ago.
Also in that course was safe use of ladders, where we had to climb, then descend a 15' ladder. That was the sum total needed to pass that module :LOL:

So I am fully qualified in ladders :D
 
Cryo on those low alloy steels is always going to be marginal at best though

From larrin's charts, about 1/2 to 1 point on the C scale and greater differences for someone chasing high hardness and higher austenizing temps in a furnace.

I don't use a furnace, though, so don't know how often heat treat isn't that great commercially. For someone using a forge (and doing so accurately) low tail end temps and fast quench definitely improve hardness by a physically noticeable amount.

The charts suggest the higher temp issues have more dispersion with stainless and other steels, though - you're right on that.

And what I noticed about Steve's irons vs. others (and what appears to also show up in brent beach's pictures) could be any number of things. I will generally chase a point of hardness if I can get it, though - it makes a better chisel if the hardness is there without undertempering.
 
They can apparently shatter. Found this out on a city and guilds course i did yonks ago.
Also in that course was safe use of ladders, where we had to climb, then descend a 15' ladder. That was the sum total needed to pass that module :LOL:

So I am fully qualified in ladders :D

Haven't heard much talk of cold steel here in the US, but in northern canada, equipment breaks more easily in the winter (this is at temps like -30 or -40C, things begain to have strange failures). Probably a bit inconvenient to weld or braze when they do, too.
 
Here's the start of several excellent articles on cryo by larrin thomas.

https://knifesteelnerds.com/2018/12/03/cryogenic-part1/
The link to later articles is at the end. Even a2 is addressed. Increase in hardness, decrease in toughness.

Larrin does address the idea of cryo after steel stabilization and how even a short snap temper stabilizes steel and limits some of the reduction in retained austenite.

The charts showing improvement with a slight furnace overheat are drastic.

I use a fast quench oil and seem on simple steels to get hardness with freezer that is in the range for cryo, but due to the lack of a controlled furnace, I'm limited to getting optimal results only with a narrow range of steels. Even 1095 ended up at 63.1 average hardness after double tempering at 400f. 26c3 ended at 63.8, and o1 at 61.6. 1095 has too low toughness at high hardness, but the other two are excellent.

Interesting. Thanks.

While I don’t have a reference immediately available to support this, my recollection is that cycling through the cold temperature phase change observed in some alloys will convert more of the retained austenite than a single cooling cycle. It’s my recollection that A2 exhibits such behavior; going to liquid nitrogen temperatures causes it to pass through a phase change and corresponding density shift that, as I recall, not only converts some of the retained austenite but also reduces the size of the carbides (i.e. if I am remembering correctly, some of the carbon from the carbides goes into martensite formation).

Now, it’s been quite a while and I may be misremembering or conflating information here; but there might be a worthwhile experiment to test O1‘s response (if any) to cold cycling.

I don’t know if O1 exhibits such a phase change, let alone at what temperature that might be observed, but have you experimented with multiple freeze-thaw cycles prior to tempering?
 
Dry ice seems like a decent alternative to liquid nitrogen for a guy in a garage.

It is. It's almost as good for most things unless there's a major sin or from the AEB-L chart, unless you're intentionally heating lower carbon or complicated steels to then cryo treat them and get greater hardness.

I'm assuming that some element of this kind of trade off exists in routine treatment of some of the PMs that are like 20% carbide content and super high carbon levels.

It may be worth exploring at some point rather than running to the freezer, though (but L.N. may be a better compromise with a used decanter just because it'll last about a month in a decanter. Dry ice would be good for about 3 days from what I read in a sealed polystyrene container, and about 1 day if in a cheap styrofoam party cooler.
 
Price of LN is about US$2 per liter, a 10L container about US$220.

I wonder what are the hazards of using this stuff, besides blowing up... ;)
 
cracking the steel or touching it for long! I saw a knife maker using a typical bent hanger putting knives into it, though and he more or less said "when I started using this, there was nobody to learn from. I always just do it this way and have never had a knife crack" (over decades).

Any time I've had an issue with cracking (Which has been rare unless I try actually doing the top end of the quench in water with a thin cross section ...bad idea) the crack has occurred at the top end of the heat treat and not in the water.

Someone on another forum unwittingly in a spat gave me the idea of using ice water, and I was surprised to find in one of larrin's data tables that a fast quench and a finish even in room temp water is very good. Ice water is a little bit better, and on simple steels, somewhere around as good as slower quench and dry ice. Since I don't have any way to use stainless types other than fast quenching XHP (Which has huge surpluses of carbon), I don't have much to do with the top end of treatment (intentionally high temperatures). I love the idea of AEB-L for woodworking as it's fine grained like carbon steel but wear is nearing XHP/V11, but it doesn't attain high hardness with a quick cheating heat. It still has great wear resistance even when it's a little soft and will go far longer than anything like A2 or O1, but it feels like carbon steel on a sharpening stone .

At any rate, that's a future side note - it'd be interesting to use some of those matrix steels, but they don't have enough carbon in them to be forgiving in open atmosphere - despite the interesting experience that even when suboptimally done (heat really hot quickly, quench and temper), they will be long wearing in a plane.

I have never seriously looked for a decanter, but recall seeing someone say they didn't have much trouble finding a used one (getting toward $300 for a whole setup probably doesn't make sense just for screwing around - but I guess each guitar costs 2-3 times that to build, so it's not like I can make a case that making is a thrifty endeavor. )

For now, at least, the ability to quench fast and finish in ice water or the freezer is very effective (two chisels made and tested in the same test will set themselves apart somewhat).
 
You’ll want a dewar rather than a decanter if planning to store LN for any time
 
Interesting. Thanks.

While I don’t have a reference immediately available to support this, my recollection is that cycling through the cold temperature phase change observed in some alloys will convert more of the retained austenite than a single cooling cycle. It’s my recollection that A2 exhibits such behavior; going to liquid nitrogen temperatures causes it to pass through a phase change and corresponding density shift that, as I recall, not only converts some of the retained austenite but also reduces the size of the carbides (i.e. if I am remembering correctly, some of the carbon from the carbides goes into martensite formation).

Now, it’s been quite a while and I may be misremembering or conflating information here; but there might be a worthwhile experiment to test O1‘s response (if any) to cold cycling.

I don’t know if O1 exhibits such a phase change, let alone at what temperature that might be observed, but have you experimented with multiple freeze-thaw cycles prior to tempering?

I recall seeing pictures of distribution of carbides - I don't know if they were necessarily on average smaller, but for lack of a better way to put it, they were "thinner" and tied together to each other better or tied into the matrix better.

Carbides are sort of poorly understood, and the most complicated thing that I do is a quick heat with XHP, which gets things done about 80% as well as commercial could (the highest reaches of hardness aren't accessible to me). But stuff like ingot stainless and D2s, A2s, etc, I don't have a way to normalize them and re-dissolve the chromium carbides (PM you can cheat by not enlarging them from the state that they're delivered - in ingot, they're not so well distributed from the start).

At any rate, big carbides crack, then the crack propagates and they break up and then fall out of the matrix leaving an unsupported area. I thought they left the matrix whole until sometime last year when someone pointed me to pictures on the science of sharp and you could see the actual breaking carbides..

...or maybe better put, I read it on larrin's page first that cracks threatening toughness start in carbides and then propagate to the matrix, but seeing pictures of it solidified what larrin said more clearly - the cracking and leaving the matrix is drastic, and early. So, to have smaller carbides or more even distribution is a good thing.

I saw this problem with blue steel, which has odd tungsten carbides distributed unevenly. It's just not that good of a steel if you like uniformity and I haven't seen a sample in a plane of blue or super blue that doesn't do this. I get the origin of it (tungsten carbides melt during forging, but keeping them away must require something that modern processors don't do, or maybe nobody ever did - like continuing to forge until risky temps).



notice the pocks in the edge. Compare this to O1


this pocking starts right away and when you can compare the surface finish, the pocks aren't big enough to create visible large scratches, but the surface is more dull.

And for comparison, A2 - LN cryo treated irons (they are the best I've seen - in my limited testing IBC's irons wore less evenly and I didn't test LV's but beach shows that).



Having not really experimented with these, I wonder if the change in structure that's drastic in pictures is all cryo.

Regardless if it isn't, I've seen schedules for high vanadium and chromium PMs that are crazy long (like several days in total) and have several cryo treatments).

I often wonder how many commercial woodworking products in the turner's arena made of stuff like 10V actually get proper attention (and there's a whole bunch of other problems I never see in simple steels, like carbide coarsening).
 
The O1 iron is my own. I am pretty good with O1 and 26c3.
26c3 has iron carbides which aren't as hard and don't seem to exit stage right as fast:


They look like the matrix is wearing around them.

The downside is they don't do anything. 1095 and O1 actually wear longer. These carbides do seem to do something for hardness (it tempers 2 points + harder than O1 and has twice the toughness - a nice combination. Edge crispness is great, too, but wear resistance is surprisingly low - about 75-80% of O1).

If I tempered this at 325 instead of close to 400, it would be 66 hardness. my tested strikes on coupons (which I have trouble heat treating in the first place because they get hot too fast and are hard to finagle with tongs) were 63.8 at 390F.

Just making comments in random order at this point, the carbides leave the matrix in the A2 picture in the prior post, and they're kind of ugly (and when they do start leaving in quantity, the surface suffers in a way I didn't see with V11/XHP). same hardness O1 and A2 have such a difference in properties that while A2 wears 25% longer, that 25% is practically intolerable for anything other than jack planing.

There are some poor relatively comparisons for folks with different alloys, too -for example. LV's hardening target for O1 is really low. It lacks strength and O1 doesn't have a strong downside for toughness (if you keep tempering it softer, it doesn't really get tougher past about 400 or 425F). And the A2 from LN is better, so there's no great reason I can think of that LV offers A2 other than that it can be kept in stock and there may be some people who have written A2 in their underpants and just have to have it because they're used to it.

Their V11 is good, though a bit chippy in the fine edge (may be the nature of the steel -here's the carbide density in my own XHP irons - with one thing in mind for A2 above and this picture - different camera after my old one didn't work with win10 and a PC change - so the light angle may be different and some of the darkness in the LN picture may be shadows.



I don't have starrett O1 at hand right now, but the picture of the surface with wear shows pretty much nothing in visible carbides. Same goes for 1095 (which looks great, but for some reason, 1095 doesn't have very good toughness potential, just like O1 - except 1095 is even worse - it hits a higher hardness target for me but is usable in a way that's not as good as O1).
 
The O1 iron is my own. I am pretty good with O1 and 26c3.
26c3 has iron carbides which aren't as hard and don't seem to exit stage right as fast:


They look like the matrix is wearing around them.

The downside is they don't do anything. 1095 and O1 actually wear longer. These carbides do seem to do something for hardness (it tempers 2 points + harder than O1 and has twice the toughness - a nice combination. Edge crispness is great, too, but wear resistance is surprisingly low - about 75-80% of O1).

If I tempered this at 325 instead of close to 400, it would be 66 hardness. my tested strikes on coupons (which I have trouble heat treating in the first place because they get hot too fast and are hard to finagle with tongs) were 63.8 at 390F.

Just making comments in random order at this point, the carbides leave the matrix in the A2 picture in the prior post, and they're kind of ugly (and when they do start leaving in quantity, the surface suffers in a way I didn't see with V11/XHP). same hardness O1 and A2 have such a difference in properties that while A2 wears 25% longer, that 25% is practically intolerable for anything other than jack planing.

There are some poor relatively comparisons for folks with different alloys, too -for example. LV's hardening target for O1 is really low. It lacks strength and O1 doesn't have a strong downside for toughness (if you keep tempering it softer, it doesn't really get tougher past about 400 or 425F). And the A2 from LN is better, so there's no great reason I can think of that LV offers A2 other than that it can be kept in stock and there may be some people who have written A2 in their underpants and just have to have it because they're used to it.

Their V11 is good, though a bit chippy in the fine edge (may be the nature of the steel -here's the carbide density in my own XHP irons - with one thing in mind for A2 above and this picture - different camera after my old one didn't work with win10 and a PC change - so the light angle may be different and some of the darkness in the LN picture may be shadows.



I don't have starrett O1 at hand right now, but the picture of the surface with wear shows pretty much nothing in visible carbides. Same goes for 1095 (which looks great, but for some reason, 1095 doesn't have very good toughness potential, just like O1 - except 1095 is even worse - it hits a higher hardness target for me but is usable in a way that's not as good as O1).

Thanks for the detailed response.

I did find a reasonable reference that talks about home-freezer cold treatment in addition to cryogenic treatment: https://ctpcryogenics.com/wp-content/uploads/2017/12/asmcryodef.pdf

I didn’t see anything about multiple cold cycles, so I may well have been misremembering that point; it does, however, refer to a phase change in the cemented carbides and indicates crystalline defect reduction at the reduced temperatures, which makes sense as an energy driven process. Both of these should apply to most steels useful for woodworking, and the latter should provide advantages for any steel. This seems to support your observation that O1 improves upon cold treatment.
Very interesting; I wonder if the chisels sitting in my shop right now could perform better if I stick them in the freezer for a while.
 
Most freezers will be about -25F, so if it’s not in the freezer and down to temp within 0.1hours (6 minutes) of coming out of quench it’ll do nothing………
Graph shows T1 steel but won’t be wildly different for others.



02C9EAEA-4CB0-457D-8B47-A535B78C2663.jpeg
 
If you reheat them, they might. If they have unstable austenite that's converted to martensite (I doubt this actually happens much with woodworking tools as I don't think the stress is right - who knows), you could always temper them if you have an accurate way to do it to minimize the unstable bits.

Larrin's an interesting case because he's a true professional metallurgist but the high carbon steels and knife stuff isn't his day job. His dad is a professional knife maker, so he's got boatloads of practical knowledge about knives and was exposed to shysters at knife shows that in combination with the actual knife experience appears to have tipped him off in sorting out what's real and what isn't.

I can't hang on the knife forums or the guitar forums. There's too much woo and on the guitar forums, there's great players, but not that many enthusiastic oddball builders like me. the knife forums are kind of a strange set of enthusiasts who just buy gobs of knives and then take pictures of them - it's not like woodworking because the knives aren't getting used practically. It's more like "I have this rex 121 pattern, and I don't know what everyone is talking about -i didn't find it hard to sharpen" .

Reading the history on those sites, I can see what set larrin off - it's like religions. If you become part of one knife maker's faction for $400 abuse knives made with steel that's got nitrogen added to it, you may not ever say that you've seen edge damage on your knife. You'd have been shouted down. The claims border on attesting to have seen someone levitate.

I found larrin on there, actually, looking for advice about developing commercial matching heat treatment and he sort of let me know I was peeing into a breeze. Then I did match a few alloys and I think he was put off by that and it caused him to pause - If my second set of all samples had been good, too (one was a match, the other a failure and a third oddball trial at doing stainless in the open atmosphere was just ho hum - not faulty, just underhard). That pleased him. I saw the comments he has to wade through on the knife forum, so I didn't expect that he'd entertain much and testing my samples was good enough.

Theres nothing special about me doing any of this for reason 2, either - I did it by eye snapping samples and testing chisels. some of the best chisels I've ever seen (ward, etc) must've been done this way. the fact that almost nobody does it well now is just because it's not popular, not because it's difficult.

And because it's only doable with very limited alloys (and the influential folks in the knife community where there is still a lot of shop heat treating don't like open atmosphere heat treat because it's kind of linked in with the people romanticizing blacksmithing to the point that they might as well just make movies of themselves in costumes and be done with it)...at any rate, those kinds of things mean it won't be taken seriously.

But ward did it, and a lot of japanese tools were made the same way. it has to be doable on a tuesday afternoon when you're thinking about someone insulting you saturday, so we can do it, too.
 
Most freezers will be about -25F, so if it’s not in the freezer and down to temp within 0.1hours (6 minutes) of coming out of quench it’ll do nothing………
Graph shows T1 steel but won’t be wildly different for others.



View attachment 131837

I don't give it 6 minutes - it goes into the water and may sit a minute. I think its important in something like this when I don't really know (assuming that chart is ideal with fast transition forge heating where there's a little less R.A. issue than there can be with time duration in a furnace) and many of us may not, just assume the rule is right away. I take chisels to the freezer one by one and put them in the bottom if I can get them there. In the chest freezer, opening the door doesn't allow all of the cold to dump out.

I'm sure 30 seconds is better than 6 minutes. The combination quench is free to do, so when you're doing stuff like I'm doing it, which is the lazy and quick way, you take what is freely available. Do the top side of the quench in the right oil to get fast transition and no cracks, finish cooling in water and run to the freezer. The only pause being if the warping is so bad that you know it's not going to make it - then it gets a re-do on the quench after partial reheat and tapping straight. Sometimes you get away with that and sometimes you just introduce more stress and the warping is the same the second go.

My results with 1095 and 26c3 suggest that this works well. O1 tempers on average for me just under 62 at 390F (the temperature I used for my first sample set), which is also a good result. 1095 is above spec for 400 at 63.1 average for three samples. There's precious little information about doing this stuff really cheaply that has numerical info, but larrin's got a table somewhere on his site that compares R.A. in ice water to R.A. in slightly longer time duration to a lower temperature, and the ice water's immediate use is actually a little better than oil to freezer (not sure about oil to water to freezer).

All of the results that are needed for woodworking tools, though - easily gotten with nothing more than feel on stones, performance testing and then snapping samples here and there and taking a picture with a small scope.

open air heat treatment is sort of the hand tooler's version of toolmaking.
 
I was commenting more on the fact that people were starting to think they could take ready made chisels and cold treat the steel to any effect.

Continuous cooling from critical to martensite finish is the optimum, but unrealistic. As quick as possible from quench to cold is achievable, and then depending how cold you get it and how fast influences how effective it is.
 
The only reason that I and my workmates would warm our chisels on a cold and frosty morning was to keep our hands warm! We never gave a thought to chisels getting damaged.
And why, if they were so worried about their chisels and trowels becoming brittle and cracking, did they show no concern over working on steel scaffold as we did in the '60s at the Canvey Island Methane Terminal, where the storage tanks were 180 feet deep holes, dug with NO shoring, because the earth walls were frozen solid by a system of vertical tubes circulating brine at many degrees below ambient. Due to an accident where a crane fell onto the roof of the hole on which I was involved in building, a scaffold had to be built from the base of the hole up to the underside of the roof to enable repairs to be made. I found that sipping on the hoar frost was the biggest hazard.
 

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