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  #31  
Old 02-21-2017, 12:08 AM
jimmontg jimmontg is offline
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Cool Man there is a lot of knowledge on HT O1 here.

I'm trying WBE's method above and finish my blades to 100% 220 grit and pre equalize for one hour at 1200 the day before. I'm tired of finishing my blades after they get hard, so try something new. All are 3/16 and 1/8" so two HTs and as per SamuraiStuart straight into LN from quench and straighten and hope none of them crack. Since I never used LN before for cryo on O1 what should be my temper temperature? 450 2x still acceptable or should I drop to 425 two tempers both with cryos before and in-between? I'm thinking 425 2 hours each?

I figure at those thicknesses if it warps it won't be much and I'll be able to straighten them when I get them back at about RC59 per my instructions. 58 to 60 is acceptable, I've had customers complain my RC 60 blades wouldn't hold an edge when their problem was they couldn't put an edge on them. I started giving small 400 grit EZE Lap diamond hones with the blades and no more complaints. I get them on sale at USA Knifemakers for like $10. It isn't like they are dull when I sell them or I don't tell them to get a diamond hone or a system they can use.

Where do I buy ATP641 or is Brownells just as good for decarb prevention WBE?

Wish I had my old job, they had a small black oxide tank. Oh well Super Blue works well with O1.
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  #32  
Old 02-21-2017, 07:42 AM
WBE WBE is offline
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ATP-641 is for both scale and decarb prevention. I find it to work best with a second coat after the first is thoroughly dry, and I also apply a third coat along the cutting edge, to about a 1/4" or so up the bevel.
Now, I have a question. Why would you bother to cryo treat 01? Any positive results would be very minor and insignificant. If cryo makes a notable difference in your 01, it would indicate that there may be something lacking in your overall HT.
As far as the oven process, I would recommend you go with the heat application that Ray Rogers described. 01 is not subject to aus grain problems arising from a cold start, and as Ray said, most, if not all, recipes for 01 HT call for a pre-heat, usually at or about 1250. Now call me foolish or gullible, but when three or four different steel metallurgists recommend to me a stress relief heat soak for 01, I kinda figure they may know something that I don't.
Now maybe it's just me, but I feel that I should believe and follow at least most of what actual metallurgists who major in steel recommend, rather than someone who gets a little knowledge and then decides they can go maverick and do better, or do it easier. Whether or not their methods may seem to work. Often it turns out that their method may work for them, but not you.
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  #33  
Old 02-21-2017, 07:42 AM
dtec1 dtec1 is offline
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Ok so I haven't thrown my opinion because I have never worked with O1. All I have used is 1084, 440c, cpms35vn, and 154cm. I have never had a blade warp bad. Actually only 1 blade of 1084 ever had a slight warp witch was so slight I could grind it out, Maybe I have had a lot of luck maybe I shouldn't be talking about it don't want to jinx myself LOL Anyway I did just want to point out as ray said there are others than him that grind after heat treat. Well I am one of those others. All I do before HT is the profile that's it. As long as you keep dunking it in water and you will burn your hands before you blow the temper. Maybe this is one reason I haven't had blades warp on me there is more meat on the bone you know.
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  #34  
Old 02-21-2017, 05:21 PM
jimmontg jimmontg is offline
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I do a cryo on O1 because I was taught to.

By a metallurgist professor at AB Tech in Asheville and by pro HT when I worked at a Machine shop in 2004-8. I had the dry ice and was simply told that it would improve toughness and turn some retained aus to mart. Toughness is what I noticed the most. I made a few knives with dry ice, they were paying for it. Hinderliter in OKC said they had to stay under it for 3 days, same for D2. So OK. Never cryo'd O1 before, but there was a noticeable improved toughness in it even at the same RC hardness. It won't cost me anymore and LN is supposed to bring out the eta carbides so why not?

It's a hyperalloy and they benefit from cryo to one degree or another, especially LN cryo. I was just wondering if the temper temperature changes by much. I certainly wouldn't buy a dewar just for O1.
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  #35  
Old 02-21-2017, 05:48 PM
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Ray Rogers Ray Rogers is offline
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I always cryoed O1 in LN just because I had it available. Seemed to me that I got additional toughness that way although that stuff is so tough already its hard to be sure. Anyway, it surely didn't hurt it and the time in cryo allowed my oven to cool over night so I could use it for tempering the next day. The tempering temp didn't change ...


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  #36  
Old 02-21-2017, 06:53 PM
jimmontg jimmontg is offline
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Thanks Ray.

Samaraistuart told me it actually hurt to pre temper the O1 before cryo, but I did it because I had one blade crack right after placing on dry ice. In retrospect having all the heat being pulled out of it from one side was probably the cause.
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  #37  
Old 02-22-2017, 06:35 AM
WBE WBE is offline
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Dry ice is not a cryo treatment, and does even less of course . Dry ice is simply a sub-zero treatment with zero effect on 01, or simple steels. Cryo treatment is done with LN, but has near zero effect on simple steels, and such minimal effect on 01 as to be a waste of time and effort. If you have LN on hand any way, no harm, but also no real gain. Another question. How does one test for toughness when the hardness has no change? Toughness is a sacrifice in hardness done by the temper process, with the goal of reaching an ideal, or desired balance in edge retention and toughness. One more notation. With a decent HT, and no cryo involved, 01 has such little RA that it is pretty much an insignificant and moot concern. The main reason to do a cryo treatment is to convert more of the RA in those steels known to have an excess of it after just a common HT. In general, steels that have no appreciable amount of RA after hardening, will show no appreciable gains in anything of real importance. With 01, one might gain a full point of Rc hardness with a LN soak. That is not worthwhile unless you do already have a LN set up, and even then, that is a very minor gain. If 01 picked up 2 or 3 points of Rc with cryo, it would be SOP in all the 01 HT recipes. You would be wise to question test results to the contrary without having full confidence in the testing and the tester.
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  #38  
Old 02-22-2017, 09:00 AM
jimmontg jimmontg is offline
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OK, so I converted some of the 8% retained austenite to martensite from the regular HT of O1. No big deal. Do not want to argue about it. It is what I was taught in 2006 and the best O1 filet knife I ever made resulted from it with absolutely no change in the HT except 3 days under dry ice. You make a O1 filet knife (1/8") that cuts through 80 fish and is somewhat flexible with no sharpening. Not scientific, but without making the knife just plain harder than it should be it worked pretty good.
I never said dry ice was as good as LN. Just that it did improve my filet knives. 80 fish is a lot of bones. Cryo is expensive for hyper eutectic alloys, but it does improve them to a certain degree.

https://www5.kau.se/sites/default/fi..._pdf_16802.pdf
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  #39  
Old 02-22-2017, 10:27 AM
jimmontg jimmontg is offline
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Everybody, please excuse my bad mood. Have hardly slept and right now am looking at a freaking hernia operation. Sorry.
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  #40  
Old 02-22-2017, 11:49 AM
samuraistuart samuraistuart is offline
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Jim and I are talking privately in PM, and some of this is coming out here. WBE is correct about the O1 and cryo or sub zero.

For the benefits of this thread and learning, let's use the terms that have generally been settled upon. "Sub zero" is dry ice slurry temps of -100F. "Cryo" is LN2 temps of -300F.

O1 is hardened at 1475F. This is what gives the maximum RC reading, and there will indeed be some small of amount of retained austenite, which is an undesirable structure (For the most part) in a knife. Knives that see impact may benefit from some RA, sort of like a cheat for toughness, but it's a one-and-done thing from my understanding. I mean by that...a knife with RA may experience less failure with an impact, however, don't impact that spot again...because the RA has now been shocked into untempered martensite (at the location of the impact). I have not verified that claim with metallurgists. Take it how you will.

Back to O1. There is so little RA in O1 HT, that if you are seeing HRC gains by employing "sub zero" dry ice, then you need to rethink your HT. Your target aus temp is wrong. The martensite finish temperature of O1 is above (or around) room temp. Going below that Mf temp does not give you added hardness or anything other than a cold blade. D2 has an Mf temp of just below sub zero temps of dry ice...lies around -150F. So even employing dry ice for D2 will convert most of the RA, but not all. LN2 would be needed for D2 full martensite conversion. However, cryo (LN2) does one added thing sub zero does not.....eta carbide precipitation (which happens when tempered). These super small carbides give added "cohesion" between the carbides in the steel and the martensite matrix. This does not directly translate to added "wear resistance" as I understand the term, but it does give added "apex stability", which is "edge retention" as we call it. Wear resistance is good, for some applications, but most knife applications do not need wear resistance. If wear resistance was paramount, and needed in let's say a kitchen knife, our teeth would be worn over by the food we are eating (and cutting), but this is not the case. Most knife apex damage comes from rolling and or chipping (bone contact, ceramic plates, glass cutting boards...whoever invented glass/ceramic cutting boards should be shot). Wear resistance does not play a roll here. Toughness absolutely does play a roll. LN2 can and will add "toughness" and thus "edge retention".

Apologies to the OP with slight thread derail.
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  #41  
Old 02-22-2017, 01:47 PM
WNC Goater WNC Goater is offline
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Quote:
Originally Posted by samuraistuart View Post
... glass cutting boards...whoever invented glass/ceramic cutting boards should be shot).
I have not weighed in here as I certainly don't have any metallurgical expertise with which to add anything to the conversation. However, the quote above I can agree with.

Several years back my wife brought one of these home. I said what the #$@% IS THIS?

yeah, shoot 'em.


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  #42  
Old 02-22-2017, 01:54 PM
samuraistuart samuraistuart is offline
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WNC Goater, you're input is always valued here! Just a disclaimer...I am not a metallurgist by any stretch of the imagination. But I have spent WAY too much time reading the stuff that is available online, research papers, metallurgists like Cashen and Landes, posts from guys who may not be metallurgists or scientists, but really know their stuff like Nathan Carothers.
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  #43  
Old 02-22-2017, 01:55 PM
jimmontg jimmontg is offline
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Thanks Stuart.
I guess all I was saying is the toughness got better and the best, Best O1 knives I ever made were cryo'd spent 3 days under dry ice. There is some science behind it, but I first encountered dry ice for HT 4140 parts. The results were remarkable, but I spent days trying to find out how to do it.
Do AEB-L steel with dry ice. It is called for and the steel won't work right without it.

HT to this day has some fuzzy edges. Some are solid, but some are fuzzy like O1 cryo. What I read a long time ago is that any steel with chrome will cryo. Why the article focused on chrome is not something I know, but there was a time after reading that article I thought that all steels with minute amounts of chrome needed cryo and cryo for knives just barely came out.
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  #44  
Old 02-23-2017, 11:07 AM
samuraistuart samuraistuart is offline
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Yes...the toughness got better with cryo...not wear resistance. There are charts, most of us have seen them, that claim something like 400% increase in WEAR RESISTANCE with O1 that has been cryoed, over O1 that was not. Now think about that for a minute. If it was wear resistance....then you would spend 4 times the amount of time/effort in hand sanding an O1 blade that was cryoed over one that wasn't. That most certainly is not the case. It isn't wear resistance that is changed...it is overall toughness (due to the cohesion gained between matrix and carbides).

Yes, AEBL is a good candidate for sub zero dry ice. Why? Because of the retained austenite after an AEBL quench. How do we know without X ray diffraction examination? Because the hardness goes up after the sub zero quench! That is RA being converted over to martensite (technically...untempered martensite).

HT is fuzzy, no doubt. Some if it's straightforward. Some isn't. Like re-heat treating SS. It's been said not to do it. But you CAN, depending on the alloy.

Cryo with any steel that has alloying, whether it is Cr, V, Mo, W, whatever.....can benefit because of the carbide precipitation that happens during upon tempering. If those alloys were not in the steel, then cryo would be of less benefit, other than converting the RA over. And especially a eutectoid steel like 1075 or 1084. Cryo isn't going to do much at all with these steels. There isn't hardly any RA (there is a little minute amount), nor are there alloys to allow the carbide precip.

Last edited by samuraistuart; 02-23-2017 at 11:09 AM.
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  #45  
Old 02-23-2017, 02:53 PM
Doug Lester Doug Lester is offline
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My understanding of why alloys with chromium, and possibly other elements, it that not only can the chromium help form carbides in the steel but atoms of chromium can be substituted for iron atoms in the iron matrix. That helps prevent the austenite formation from slipping into a body centered tetrahedron. In short, to form retained austenite. The cold treatment with a dry ice and acetone bath or true cryotreatment with liquid nitrogen forces the retained austenite to shear into untempered martensite.

Doug


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