Cryo Treatment- O1 steel?

[D_W]

Can anyone think (given what you've seen from various woodworking manufacturers) of a reason that someone would have O1 steel cryo treated.

We know it's popular in A2. if V11 is at the top of its hardness spec, it's probably also cryo treated.

but O1 and carbon steels? I don't see it often in O1 but I've seen it once in a while. I've got some thoughts (actually, I know the conclusion now but I though it might be interesting to see what some folks are guessing).

At the end of this, I'll tell you what cryo actually does vs. what publication in ad copy claims.

(cryo treatment in this case specifically having to do with putting a blade in liquid nitrogen).

 

[Phill05]

Is is hardening and less wear resistance?

 

[TRITON]

I've no idea really in exactly how or what happens. Interested to know all the same.
So I'll add this to the 'pop back in later' list.

Personally we understand that low temps when it comes to metal make it more brittle, which is why brickies and people using cold chisels, engineers and the like were always recommended to heat their chisels and hammers on cold frosty mornings.
I would think that this is to do with the grain(to look at it from a layman's terminology) or structure of the molecules/atoms.
So if it rearranges the grain or structure of it, being subjected to extremely low temperatures must also have an effect on it. So I reckon thats the key. It 'tightens' it in some way, making it less easy to come apart in use or when struck, or driven into hard surfaces.

This would have been a question for my Father, but sadly he's no longer around. But interested to hear the exact reasons.

 

[D_W]

For our purposes, the change in properties only really matter for one reason. There may be reasons that ultra complex materials get some cryo treatment mid cycle (between tempering, etc), but for us, that's not solving anything.

For woodworkers, the value of the cryo treatment is after the quench. I don't think I've ever actually seen an honest(and probably not intentionally) advert talking about cryo treatment.

https://www.leevalley.com/en-us/sho...sels/bench/69847-veritas-pm-v11-bench-chisels
I don't see a mention of it for V11 (LV doesn't use cryo on A2, or at least didn't in the past) - but I couldn't resist posting the link here for this because the first comments are humorous. V11 is wear resistant and the suggestion that it's somehow more impact resistant than an inexpensive silver steel rod chisel or a 1% cv steel driven to high hardness is kind of funny as it's much more coarsely grained and the toughness is just OK).

so as not to just copy stuff from LV's site, this is the amazon ad copy for the narex richter (I haven't used one - they're simple steel and relatively high hardness, so they're probably very good). However, the bolded statement from the ad is maybe 1/3rd true and 2/3rds woo. If what's going on was actually explained honestly without being tin plated and glossed up, it should be plenty). Someone somewhere along the way has to go for the gold though and add extra.

https://www.amazon.com/Narex-853600-Cryogenic-Ergonomic-Stainless/dp/B082FPB1Q5
Following initial hardening, cryogenic treatment is performed which cools the steel down to −190° C (-310o F) using liquid nitrogen. This alters the mechanical properties of the steel at the molecular level greatly increasing its strength, toughness and wear resistance.

 

[D_W]

(the 1/3rd, 2/3rd is at the end). As far as altering mechanical properties, you can literally do that just by changing the heat before quench or what you're quenching in. It's kind of a meaningless statement).

 

[D_W]

some background re: why I posed this. I do a fair amount of hardening and tempering and have done testing to see if I can improve it. However, I don't have L.N. and am not going to buy a decanter and keep it around as it's something that needs to be replenished often and only makes sense if you have a constant flow of tools to go into it. But it's got some value for pretty much everything and not just complex steels.

I learned of it and a bit of a "half way" technique reading a metallurgist's discussions and actual data (outcomes from tests vs. just hypothesizing), but it's less forgiving than L.N.

And I recalled something...

.....years ago, steve knight was making planes. this sort of happened in stages so don't take any of what i"m going to say as a reason to track down something he made and pay a bunch for it. The last stage was him focusing on kits coming from his CNC and the irons that came with the kits weren't as good as the earlier irons, but they were the same shape (they were warpy and would've been a bear).

But - he used O1. on top of that, it was exceptionally hard O1 and it wasn't chippy at the hardness. It was at least as hard as hock's irons, but fared a little better planing. At the time, the woodworking world touted it for A2 and showed pictures of distributed carbides. I don't know how much of that was due to A2 and how much was due to other HT processes and temp controls, but what cryo does is definitely useful for A2 to improve terminal hardness before tempering.

So steve was harrassed a little bit about the pointless cryo treatment for O1 and I thought the same thing. However, his response was "i don't know what it does, but it makes the irons better" or something of that sort. He may have changed that statement over time if a metallurgist talked to him more, but no doubt, the O1 irons he had were as good as any I've ever seen at high hardness (they were at least 63 hardness).

Unfortunately, they're fat little 2" blocks of plane iron (1/4th inch thick) which means their application is going to be limited.

But a flashback to that after developing an HT process this year with ice water or water to freezer brought back solving why steve's irons were improved. They were good enough to say conclusively that they were better than the custom chinese laminated irons that he had made and sold for an upcharge. I got a pair of those (extra charge) only to find out they were poor in comparison to the O1 if you paid attention to the results (I don't think the upcharge that he applied amounted to much for him, it was just the cost to get the laminated irons - which abruptly disappeared since then).

 

[clogs]

I thought and seem to remember that it was a good way to charge more for the tools.....
Wasn't there a US supplier of turning tools hardened this way for exorbident amounts of money......
Not knocking the US in anyway....
I would have thought that a few extra turning tools Carbide tipped would be better and longer lasting.....
I will be turning root balls this winter all being well and only Carbide will do/last.....

 

[D_W]

OK, I won't remember to come back later and am on hold over lunch so here's what cryo does:
* when you heat steel to quench it (the steels we use for woodworking), you convert it to a structure that's not magnetic (austenite)
* when you quench steel, the objective is to turn as much of that as possible into martensite (the final state that we like to temper and make for a nice working tool)
* the lower the final temperature after quench, the lower the amount of austenite left in a tool (austenite is tough, soft and not stable compared to martensite). If we're going to get a good result, we want it gone and if something needs to be softer, it's better to get there by tempering further

A2 is a steel that sucks wind a little bit to get to 62 hardness without undertempering. If there's a way to get steel colder after quenching than liquid nitrogen (cryo treatment), then I don't know what it is. There are additional complicating factors in commercial process such as increasing austenite (and thus the amount retained after quenching) if steel is overheated somewhat. If you drop a tool in liquid nitrogen, the margin for error on the top side is higher and in some cases a slight overheat results in even harder steel).

How much difference can it make? Without errors, up to 2 points of hardness. it depends on the steel and circumstances. 2 points is a huge margin when you start tempering, and if you had two chisels - one 62 and one 60, you'd instantly determine that the 62 hardness chisel is better.

if you had two at 62 and one was comfortably tempered after L.N. and the other was undertempered to try to hit a high hardness target, the second would be chippy and obnoxious.

So, long story short, liquid nitrogen cryo treatment is valuable if you're chasing high hardness, because high hardness leads to high strength after appropriate temper (higher strength means more force needed for deformation to occur). the lower terminal quench temperature from liquid nitrogen leads to more converted structure to the final material that we want (martensite) and less retaining of stuff that's not very hard.

We don't actually do that much with toughness in woodworking - toughness is a separate thing - how much force it takes to break a sample, and not just to deform it. A really tough steel with compromised strength is valueless (think something like a crow bar - it'd be hard to break, very high toughness, but probably wouldn't hold a very good edge).

if you did two samples and tempered both to 400F (kind of a sweet spot temperature for most woodworking steels that aren't HSS) and cryo treated one and not the other, the lower hardness non-cryo sample would actually be tougher. We wouldn't notice because unless something is so lacking in toughness that it's brittle (like untempered steel) we only really care about strength (avoiding deformation in the first place).

 

[D_W]

I thought and seem to remember that it was a good way to charge more for the tools.....
Wasn't there a US supplier of turning tools hardened this way for exorbident amounts of money......
Not knocking the US in anyway....
I would have thought that a few extra turning tools Carbide tipped would be better and longer lasting.....
I will be turning root balls this winter all being well and only Carbide will do/last.....

there are some complex alloys that retain a lot of austenite and don't really finish without cryo treatment. Cryo treatment isn't expensive, but the alloys that need it probably are (especially very high carbon powder steels that have a bunch of other stuff in them).

 

[D_W]

if you remember nothing from this, it's that cryo treatment allows steel to have a terminal hardness at a given temperature that's a little higher. We give up some toughness in tools to get the higher hardness, but we don't really care that much about toughness.

Wear resistance for any acceptable hardness range isn't much different with or without cryo, so ad copy talking about how much longer wearing steel is is pretty meaningless. If there are tests showing great increases in wear resistance, it's probably because the test is challenging the strength of a tool (for plane irons, we don't really do that above 60 hardness or so). to get better wear resistance, we have to change alloys, often with another trade off (fine edge holding corresponds to a combination of hardness and grain size - and greatly increasing wear always makes grain coarser)

 

[D_W]

So the mystery of Steve's irons even though people said O1 was a waste of time on O1 tool steel is that they could get fully quenched and properly tempered and remain harder. After using one of his irons and noticing how much harder it was on the stones, I thought for sure it would chip. The one that I had didn't.

And then I later found brent beach's old page.

https://brentbeach.ca/Sharpen/Knighttest.html
https://brentbeach.ca/Sharpen/Hocktest.html
compare hock's. Hock's irons are probably about the same hardness but subjectively a little bit undertempered to hit a high target. I don't know if the O1 irons are cryo from hock, but I can duplicate them with a 350F temper after a water/freezer quench.

Which is the poor man's half way - either finish the quench in icewater as soon as possible, or finish in water (after doing the front end of the quench in quench oil) and dump the tool in the freezer.

Writings from Larrin Thomas helped me understand this an enormous amount making it possible for me to get commercial level, and in one case slightly better, on three different relatively simple steels. To finish in quench oil and then temper right away vs. ice water or water to freezer actually makes a discernible difference in chisels.

Larrin's actually qualified to talk about what he talks about, but above and beyond that, he also experiments constantly to get actual outcomes. I can tell you from experience he thinks heat treating in open air is dippy, but he also tested my samples and I matched his results (bettered with one) with three alloys and fell short with two (fortunately, two I don't use in the first place). he was pretty pleased to see that I wasn't able to match the furnace results with all five!!

 

[D_W]

(steve's iron was slightly better than my "hock imitation" temper, and I would guess that's because cryo bumped the terminal hardness higher and he could temper at a higher temp - or his heat treater could - and get the same terminal hardness).

It's also interesting to note that clifton's irons didn't far as well as hock or knights, but I would guess that's due to how difficult it is to actually forge an iron and then shrink the grain back to the same level that it would come from the factory when bar stock is rolled. The pictures seem to show slightly coarser grain for clifton - and I don't do heavy forging with chisels - just light shaping at hot but not heavy forging hot temperatures. Two other people who have forged knives and sent larrin samples in the past sent junk (hard but coarse grain and brittle), so my first two samples seem to have shocked him a little.

Cryo for me remains the freezer just to try to get an extra point and then temper back. Liquid nitrogen has another dimension of forgiveness in this chasing "converting austenite" - you can delay for a while and then put the steel in L.N. whereas if the terminal destination isn't as low, it won't do anything. so when I finish something, I can't cycle and harden five things and wait to put them in the freezer - they need to go in right away, one or two at a time within a minute or two.

 

[D_W]

one more bottom line - if you have a chance to get two similar items for the same price, and they're the same spec and one is cryo treated and the other is not....

...you get the cryo treated item every time. It's beneficial.

My thoughts in posting this aside from recalling Knight's O1 (thus the original question) come from reading the richter ad copy a couple of weeks ago. You could literally write the ad copy to state that cryo treating increases the steel's strength and improves terminal hardness after tempering and it'd be 100% accurate and it should sell tools.

Why have to include the "yeah, and when I won the bike race, my tire was flat, too" type stuff?

 

[TRITON]

So,without having to go through all the above, can we treat something by simply dipping it in liquid nitrogen ?.
IE take a chisel, iron or cutter, dip it in the liquid and get a better tool as a result ?

 

[D_W]

heat to nonmagnetic, heat a little more, dip in oil until fully cool, then tie on wire and hang in liquid nitrogen overnight.

that's the basic process. then temper after that.

Poor man's way as I described is instead of letting the tool finish in oil that's gradually heating from, say 70F to about 150 or 200F, quench in oil and then once mostly cool, change over to ice water and finish cooling as fast as possible...or...

finish in water (which isn't heating because it's not taking the initial quench heat - the oil is absorbing that) and then toss in a chest freezer immediately.

The drawback? In carbon steels, faster transition and lower terminal temperature are both associated with increased warping. If you're a toolmaker, you will have some warping to deal with - a little more is no big deal.

-----------------

For your purposes as a buyer, though, if someone is telling you the truth (that they went to L.N. at the end of a quench), the steel will be improved with additional hardness at the expense of a little bit of toughness. The misdirection for us here is people want to talk about how tough a tool is all the time, but toughness is for machetes and crowbars.

 

[--Tom--]

@TRITON Ideally it’s a constant cooling rate from critical temp down to cryo temp, so need to move fast from quench to cold treatment. This means cryo won’t do anything for anything you have already. It has to be done at heat treat stage and before tempering.

By dropping the retained austenite through cryo, you then have more martensite that can be tempered. Tempered martensite is what you want. Retained austenite can be converted to untempered martensite through stress of use which is then brittle and liable to chippiness. So cryo does more than just increase hardness.

Heat treat is fun until you get consistent results that differ from what they should be. I run a PID controlled HT oven and have a hardness tester. Some stuff comes out spot on where it’s supposed to time after time. Some steels just won’t play ball for me. I need to experiment more but each time it costs time and money.
If I could find a LN supplier that would supply hobbyist amounts I’d get some, to try.

 

[dannyr]

@TRITON Ideally it’s a constant cooling rate from critical temp down to cryo temp, so need to move fast from quench to cold treatment. This means cryo won’t do anything for anything you have already. It has to be done at heat treat stage and before tempering.

By dropping the retained austenite through cryo, you then have more martensite that can be tempered. Tempered martensite is what you want. Retained austenite can be converted to untempered martensite through stress of use which is then brittle and liable to chippiness. So cryo does more than just increase hardness.

Heat treat is fun until you get consistent results that differ from what they should be. I run a PID controlled HT oven and have a hardness tester. Some stuff comes out spot on where it’s supposed to time after time. Some steels just won’t play ball for me. I need to experiment more but each time it costs time and money.
If I could find a LN supplier that would supply hobbyist amounts I’d get some, to try.

Yes.

I never got why cryo treatment should give results, as many suggested, AFTER usual quench, which fixes a crystal structure and then temper which modifies that in a controlled way. What would the further cool some time later do?

Though I can see perfectly well that for some alloys room temp may not be enough of a quench to fix the structure in which case rapidly carrying on down to a much lower temp may help.

There's a lot of 'puff' out there, but, last time I looked seriously, (a few years ago), very little hard evidence for property improvement outside a few special (mostly non-tooling) alloys, especially for any effect if done after the usual heat treat.

 

[Limey Lurker]

I've no idea really in exactly how or what happens. Interested to know all the same.
So I'll add this to the 'pop back in later' list.

Personally we understand that low temps when it comes to metal make it more brittle, which is why brickies and people using cold chisels, engineers and the like were always recommended to heat their chisels and hammers on cold frosty mornings.
I would think that this is to do with the grain(to look at it from a layman's terminology) or structure of the molecules/atoms.
So if it rearranges the grain or structure of it, being subjected to extremely low temperatures must also have an effect on it. So I reckon thats the key. It 'tightens' it in some way, making it less easy to come apart in use or when struck, or driven into hard surfaces.

This would have been a question for my Father, but sadly he's no longer around. But interested to hear the exact reasons.

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.

 

[D_W]

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.

 

[--Tom--]

Cryo on those low alloy steels is always going to be marginal at best though