Will 0-1 benifit from Cryo

"hand warm", now it makes better sense. I couldn't find any warnings prohibiting room temperatures in any of my data sheets or other literature, but the term "hand warm" does appear. Often, it is recommended that the best place to store the part is in the "basket" until tempering. With complex shapes a steel like O1 that is not martempered could suffer some awful problems by radical cooling. My only concern with it is that I have hyoung guys in the shop that hade been only colling to perhaps 50% martensite and then going straight to the temper, to each his own, but the martensite has to form sometime and tempering austenite can be fairly counter productive ;) .

With the salts, it is easy, about the time the stuff goes solid on the blade, and it is time to quit messing with it, since enough martensite has set to make any more straightening efforts difficult or disastrous. Rarely have I found much distortion after that (occasionally some odd pieces will have some stored issues that will cause it to move then or in the temper), often the distortion is present after the quench to Ms or it will show itself at around 50% martensite; in which case it is guided along in my loving hands ;). It gives one a real feeling of hand crafting to guide each blade through its birth with your own two hands;). It is one way to keep something as trying a sword straight. They like are children, in that I may end up putting them across my knee to insure they behave themselves;).
 
Kevin, I have associated hand warm with about 125 F, probably from some writing I can not point to directly at this time. I really should go back through some vendor sheets to confirm the 125 F info I have stuck in my mind. I can point to one well known publication but that particular reference is not a data sheet. Let me go through some of my vendor sheets and see if my association with hand warm and about 125 F is just a bunch of smoke in my head.

Later.

Here is one on L-6. I haven't dug deep enough into the pile to reach the O1 sheet(s) yet but as a matter of interest this Lindquist Steels, Inc. sheet on L-6 is recommending quench to 150 F and temper immediately.

Well now, here is not a data sheet for a particular steel but a publication by Timken Latrobe titled 'Heat Treating Practices' (bulletin 102). Within the short chapter titled TEMPERING (Drawing) third paragraph down reads as follows: "Tempering should be performed as soon as the part cools to about 150 - 125 F (66 - 51 C) during the quench. This temperature range is traditionally known as hand warm because it is when the part can be held in the bare hand without burning." That is the paragraph in total. It should be noticed though that it seems to me they are suggesting, actually saying, the part be held in quench until hand warm. That is not normally how I do it and certainly does not seem to qualify as an interrupted quench, does it(?).

Here is one specifically about O1: Title Tool Steel Facts AISI O1 Cold work tool steel; by UDDEHOLM. The data concerning tempering is a follows: under QUENCHING MEDIA, "oil, Martempering bath. Temperature 360 - 435 F (180 - 225 C), then cooling in air." and then this note:"Temper the tool as soon as its temperature reaches 120 - 160 F (50 - 70 C)."

I always try not to second guess vendor sheets because I am not educated enough in that subject to do so but I do believe knives usually unique compared to other tooling. So, I am open on this but default to the vendor specifications.

RL
 
Roger ,I haven't been able to find a scientific reason for tempering when the steel gets to 150-120F. However I wonder if it has become a standard practice because of dealing with tool steels with sometimes complex shapes and trying to minimize warping or cracking .Both Timken/Latrobe and Uddeholm specialize in tool steels.
 
Thanks for that Mete. I believe that is the only explaination I have yet heard or read of.

RL
 
:D I've told guys for a long time that that's the time to straighten out the blades,, before it cools right from the quench.,
some of them looked at me like I had two heads :)

you mention oils that have a higher flash point this is something I've known of for years and didn't mention that it would be an option to use,
the plant I was a tool and die maker at way back then, 28 years, used a transformer oil I believe it was called ( I might add, it's not good for you either)
with the atmosphere generating ovens we used, we took the tool steel quenched and cooled to the oil temp and removed to cool as it may, then it as in the parts, which were shoe shanks,, that could have set for days until the girls packed them in trays, then we'd temper them in a conveyor oven.

so from what I'm reading it can be done with oils. I'm not saying it's the best way just it can be done..right :)
 
Dan,

When removing the blade from quench what do you use to straighten the blade out? Bending against a hard surface?
 
Brian
it depends on how it's bent or warped (if you're getting warping I should say ;) )

you can by hand if a long sweep or by a 3 point vice for short places.
I do this with the SS's also.

edited to add I normally, if needed use a hand press (the small lever type)then you can place
wood (rounded)anywhere you want as a point of contact.
 
I would sure be interested in knowing the scientific reasons myself. I believe that in his "Heat Treatment, Selection, and Application of Tool Steels", Bill Bryson states that it is "critical" that the part be tempered as soon as it drops below the 150F range. He states this for almost every steel discussed in his book. IIRC, Bill worked for Crucible for a long time so there must be a reason. Like Roger, I have been following that procedure because a respected metallurgist stated that it should be done, but I cannot offer more reason than that.
 
Yes, that is what I remember about Bryson's book except that as I recall he more closely states "temper before falling below about 125 F". I also think I recall he then leaves us hanging as to why except that he states it is important to tool life.

Fox, that was the reference I mentioned above but did not quote from because it was not from a vendor data sheet.

RL
 
mete said:
Roger ,I haven't been able to find a scientific reason for tempering when the steel gets to 150-120F. However I wonder if it has become a standard practice because of dealing with tool steels with sometimes complex shapes and trying to minimize warping or cracking .Both Timken/Latrobe and Uddeholm specialize in tool steels.
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You can bank on what mete is saying. I have not had any problems with blade cross sections, but if you quench O1, in thickness greater than 1/2" from critical all the way to cold, I can guarantee a huge crack somewhere in the middle of that part. This is one of the few constants in my shop. However, the problem was completely absent with martempering, and an interrupted quench will not be effective in this thickness because there will just not be enough time for the core to equalize with the outer surfaces.

Your reasoning is sound Roger, and I would not hesitate to use those methods in order to play it safe. I am now relieved to understand the points better. I would just be certain to do more than one temper in order to get any new martensite, and of course if one is doing the cryo, that will be done anyhow.

This does point out a reason for the prevalence in industry of cryo benefits even in less complex steels. Leaving things “in the basket” for convenience and process simplification, or stopping at 125F. to save a complex shape from becoming complex shapes would leave work for the cryo process to do.
 
Dan Gray said:
:D I've told guys for a long time that that's the time to straighten out the blades,, before it cools right from the quench.,
some of them looked at me like I had two heads :) ...QUOTE]

I have gotten that same look from some very experienced smiths. "Oh no! Never straighten before the temper! You'll Crack it!" :eek:

Never straighten martensite before you temper it, untempered austenite can be tied in a knot and not even care ;)
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Brian all this talk of precise temperatures for heat treatments is why I gave up trying to do it with the forge. It isn't impossible (as proven by the many fine knives done this way), but I just can't do it and don't have the time to practice, practice, practice.

Even on forged forged stuff I use a digitally controlled furnace. It gives me the confidence that there isn't a 'spot' on the blade that got too hot or not hot enough. Each blade is consistent and the best I can make it. I doubt I'll go as far as salt baths.

Steve
 
Roger quoted Uddeholm (Bohler/Uddeholm North America) above where they recommend tempering when the steel gets down in the 120° to 160°F range. For all of their tool steels, they also suggest that if cryo (they call it sub-zero) treatment is done, it should follow quenching as soon as the steel gets down to room temperature.

Also WRT dry ice treatment, due to the geometry of blades and the conductivity of steel it is only necessary to sandwich the blades between two blocks. You do not need to make a liquid.
 
blgoode said:
Dan,

When removing the blade from quench what do you use to straighten the blade out? Bending against a hard surface?
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Dan gave you the info you needed, but it is also worth pointing out that before the martensite sets, that blade is austenite- the stuff at 1600F that you forge so easy because it is so soft. All I have ever needed was my hands, the stuff is like putty. In fact be very careful, there is no resilience or elasticity to the stuff. When you striaghten a blade at room temp you will have to push beyond the point you want because of the spring. Not so with an austenitic blade, it is very easy to over bend it. I have left my finger impressions on very thin ground edges before by getting too zealous with my tweaking :( . I like to have a 2x4 laying on the bench for something flat, non abrasive and softer to push against.
 
Kevin R. Cashen said:
Never straighten martensite before you temper it, untempered austenite can be tied in a knot and not even care ;)
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Actually, steel loses all brittle strength during the Martensite transition, weakening even WRT Austenite.
 
Kevin R. Cashen said:
Dan gave you the info you needed, but it is also worth pointing out that before the martensite sets, that blade is austenite- the stuff at 1600F that you forge so easy because it is so soft. All I have ever needed was my hands, the stuff is like putty. In fact be very careful, there is no resilience or elasticity to the stuff. When you striaghten a blade at room temp you will have to push beyond the point you want because of the spring. Not so with an austenitic blade, it is very easy to over bend it. I have left my finger impressions on very thin ground edges before by getting too zealous with my tweaking :( . I like to have a 2x4 laying on the bench for something flat, non abrasive and softer to push against.
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I wondering if it's confusing saying

"Not so with an austenitic blade,"
maybe
Not so with a blade in an austenitic State..(temperature related)
once martensite sets (part of the transformation) in this state you'll have problems straitening the Blade.
 
Sando said:
Brian all this talk of precise temperatures for heat treatments is why I gave up trying to do it with the forge. It isn't impossible (as proven by the many fine knives done this way), but I just can't do it and don't have the time to practice, practice, practice...
Click to expand...


I'm not too keen on many forges for heat treating myself. However, I often get really odd looks when I say that if I had my salts taken way I would prefer to heat treat in a coal forge. Gas forges heat too evenly for my tastes, in heat treating. That even heat brings the ti0p and the edge up to temp long before the spine or ricasso can catch up, and the atmosphere has to be just so or the scaling is more than I care for. Any of the remedies I have seen for this only seemed to intensify the problems, in my opinion. Perhaps the best way I have found to handle it is to have an opening, front and back and keep moving the blade in and out of these in ways to keep the smaller parts cooler until things level out.

In a coal forge I can build an enclosure over the fire and lay just the spine or riccasso in the fire and bring it up first then let the heat even out into the edge and then at the last minute get the point. The atmosphere in there is always pretty good, and I have pulled some blades out of the quench that looked as clean as if I had done them in the salts.
 
I agree that most forges are way too hot for heat treating
it would help to cool them down way closer to the end temp you're looking for.
 
Dan Gray said:
I wondering if it's confusing saying

"Not so with an austenitic blade,"
maybe
Not so with a blade in an austenitic State..(temperature related)
once martensite sets (part of the transformation) in this state you'll have problems straitening the Blade.
Click to expand...

Point taken, as shgeo pointed out, when the martensite transformation begins things get complicated and changes happen pretty fast in the steel, but it is all temperature dependant and if your interrupt is significantly above Ms you can often find some distortion while you are still working with meta-stable austenite. You will notice at around 250F and 300F that things take aon a very different feel and from there on you will feel less at ease moving the steel.
 
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