Knife in freezer?

nozh2002

nozh2002

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Dum question:

If I will keep knife in freezer will it help to turn austenit into martensit?

I have bulat knife which has a lot of austenit - I am wondering may I make it even better this way?

Thanks, Vassili.
 
Nope. It has to be done during the process of hardening. Ice hardening helps but not as much as a complete cycle, if possible including cryo treatment.
 
"keeping" a knife in a freezer would be a fruitless endeavuer, putting it in there long enough to drop its temperature significantly below Mf (martensite finish, where the austenite should be gone), may yield a tiny fraction of a difference, if it is right after heat treatment before conditions in the blade have stabalized. The transformation of austenite to martensite is not like the other transformations that are time dependant, it is almost instantaneous once the required temperture is reached, I cannot say what it is that makers who "soak" their blades next to their ice cream are experiencing but I am doubtful it is any austenite conversion beyond what may have happened as soon as the entire blade reached popsicle temperature.

Vassili, what makes you believe the blade has retained austenite? If it is an old bulat blade it probably has lots of pearlite.
 
If one accidentally over-temps austenitization by 100F because of an inaccurate (unknowingly, failing) thermocouple and oil quenches ATS34 the resultant HRC as hardened can be as low as 56-57. Over the span of a week or so, the hardness of the blade can be seen to slowly increase as it is removed daily from the "popsicle environment", stabilized to RT for testing, then returned to its place of honor next to the butter pecan. Eventually, HRC's of 60-61 can result.

Fit the theory? Perhaps not. Observable in several successive instances from the same barstock (that led me to realize temp control was incorrect)? Absolutely. Decent blade? Absolutely not. A couple of them still hang over my bench. The grind lines are washed out from repeated polishing/refinishing cycles because I couldn't get a mirror that didn't look like a Dalmatian. It didn't take much intuition to realize the blade was bad.

I don't know what went on with the steel, Kevin, but I am still certain that my observation of the slow increase of the hardness was correct. I say this not to enter a debate, but to give you anecdotal information that under certain circumstances the phenomenon can occur. I would willingly provide numerical data, but my old recordbook took a soak in a basement sink many years ago and I lost all my records of that time. Sorry.

Have a good day, folks.
 
As I understand austenit unsable and tend to desintegrate?

I have bulat from Ivan Kirpichev it has more then 1.5% C and a lot of austenit. Ivan did not cooling it in loquid nitrogen and I am already made knife out of it, so i try to improve it if possible keeping it in freezer (I put it week or so ago and fogot, now after searcin all over my place I accidently forund it in freezer :) ).

I experienced that some bulat blades gain hardness in time too.

Thanks, Vassili.
 
Vassili, the problem with this is that the converted austenite now needs tempering or brittleness can occur. At least this is the case in a homogeneous steel. I do not know if this is the case with heterogeneous bulat, but I suspect it will still apply.
 
Ok, I'm about the least scientific person around (I know that may drive some folks nutz) and should probably keep my mouth shut but...I put my blades in the freezer overnight after HTing. The reason being two-fold. Many old time smiths I know who forged blade claimed that the blades they forged in the winter always seemed to hold an edge better. Remember these guys were all working in open-air shops. The second part is...though this may not actually be true but, it couldn't hurt. So I do it.
 
J, I think that what you state is consistent with what Kevin said....under usual circumstances austenite would be expected to convert relatively quickly once a lower temp is reached. The higher the alloy the lower the martensite finish temp (Mf). There's no doubt that cooling some steels beyond where one would normally stop in "quench" helps, even if it isn't full cryo.

My point is only that I observed circumstances under which hardness increased over a period of several days in a high alloy stainless as measured with a hardness tester. I observed this multiple times. Not being well read in metallurgy, I can't propose an explanation. Spending my working life in science, though, I do trust my powers of observation. Something was going on in those botched up hardenings.

I hope someone may be able to explain...it has long been an interesting question to me. I have mentioned it before.
 
fitzo said:
J, I think that what you state is consistent with what Kevin said....under usual circumstances austenite would be expected to convert relatively quickly once a lower temp is reached. The higher the alloy the lower the martensite finish temp (Mf). There's no doubt that cooling some steels beyond where one would normally stop in "quench" helps, even if it isn't full cryo.

My point is only that I observed circumstances under which hardness increased over a period of several days in a high alloy stainless as measured with a hardness tester. I observed this multiple times. Not being well read in metallurgy, I can't propose an explanation. Spending my working life in science, though, I do trust my powers of observation. Something was going on in those botched up hardenings.

I hope someone may be able to explain...it has long been an interesting question to me. I have mentioned it before.
Click to expand...
mike I think it's the time period that helps not the small amount of cold.
I say this because
right after a quench you can bend the steel and it's at hand holding temperature ( before the temper)so it's still hardening so I still believe this is happening for some time afterwards, how long I don't know but I'm sure after a few days or weeks it's slowing down..Hardening..
so if I am correct this I would think would give a false impression that the home freezer is doing it.. but then a again I'm not sure if anyone has tested this out with a twin
of the same color at the same time..for testing proposes

J I agree to the point that in the winter time you have a whole new ball game.
not one thing is the same other than posably the fouge heat it would be like an other smith is doing the work as far as the steel is concerned Just My thoughts on it.:)

you can always run an air conditioner inside in the summer right :)
 
Dan, the reason I would disagree is because SS gets harder much faster as one lowers the temp. I used the freezer at first. Dry ice/acetone baths speeded it up to overnight. LN2 is much faster. In some stainless that's not cold or cryo treated and not tempered enough, unconverted, unstabilized austenite can still be detected a long time afterwards. I have zero idea what the minimum at each temp would be.

In "molecular" terms in chemistry, what I'm describing is what's considered a "time-temperature" phenomenon. Reactions happen at different rates at different temperatures, but they are not truly instantaneous at any temperature, however impossibly fast to measure.

I honestly don't know how or if this correlates at all to transiting crystalline states in ferrous metallurgy.

This is my least understood topic in my layman's comprehension of the heat treat cycle, and one I wish I could understand. All I intended to do was mention to Kevin that I have experienced the slow rise in hardness with cooling time.

That doesn't sound quite right, does it? LOL :D Perhaps I should just keep this to myself..... ;)
 
Mike I do not doubt your results, I get the same from multiple temperings, I believe my initial statements were misunderstood. Cycling up and down out of the freezer could have its effects, just as cycling up and down out of the temper can. My inital point was based on the basic metallurgical fact that the martensitic transformation is not time dependant like a diffusional process (tempering, austenitizing etc...) once the "shock" of the lower temp has been induced martensite will form rapidly, soaking at temp has no effect on the shear dependant martensitic transformation, only the shift in temperature does. As knifemakers we must be careful of our interpretation of our observations because a lot of "interesting" concepts have entered our field by hasty extrapolation of cause and effect.

here is how I view the two interpretations:

1. Fact- Martensite formation is shear type and dependant upon temperature alone (holding at any point short of Mf only arrests the transformation).

2. Observations- Both in tempering and in supercooling below room temperature, a notable change in properties is observed after each exposure to the temperature treatment, with an eventual leveling off after enough treatments.

Knifemaker "A" interprets the observations in #2 as the accumulative effect of time at temperature after testing between freezings.

Knifemaker "B" interprets the observations in #2 as the effect of repeated drops in temperature, irregardless of the time spent after reaching that temperature.

Which (A or B) interpretation works best with #1?

I think you are correct that you found changes after many times in the freezer, but I am suggesting that it is due to the cycling up and down in temp between freezing and testing, with the time it spent next to the Breyer's being irrelevent.;)
 
Well, now, thank you, sir! I am glad I mentioned it, then, grateful for clarification. A cycling effect being the determining factor is not something that had occurred to me, despite knowing why it's better to temper more than once. This is why it's dangerous to do "science" alone, as you point out most correctly. Sort of like the blind men and the elephant. Chemistry of molecules and metals is very different, and it's hazardous to make correlations.

I've learned a couple things today. That makes it a good day, neh?

Thanks, Kevin!:)
 
Just to jump into the middle of things, I've had a friends tests w/ 1095 show an increase of 2 points just by putting the piece in the freezer overnight. This was before tempering however.
 
I stayed out of this to start with,But since it has come around to being a reasonable debate,I'll add my thoughts.
Conversion of unstable Austenite is a result of cycling.That is the reason you temper two or three times for 1 hour,not one time for three hours.It is not a factor of time ,nor a factor of temperature,but a factor of the cycling from one temperature to another over a period of time. Cycling to room temperature vs cycling to 0 F will make only a very small difference (perhaps undetectable),but the repeated cycling will make a noticeable change in hardness.The necessity to bring it all the way up to tempering point is not to be missed either.If not cycled back to the tempering point ,the converted Austenite will be untempered Martensite,which is brittle.
Stacy
 
Austenit was found in Ivan's blades here in some well known metallurgy company. So it was there much more then few days - it take more to came from Tver Russia to US then few days. But micro structure of wootz is more complicated. Well I still keep it in frezer... just in case.

Thanks, Vassili.
 
bladsmth said:
I stayed out of this to start with,But since it has come around to being a reasonable debate,I'll add my thoughts.
Click to expand...


It was unreasonable at some point? Or a debate? :confused:

Here I thought it was a discussion, trading different understandings, not necessarily all correct in my case, for the edification of all. I am quite willing to acknowledge when I'm wrong, and appreciate the correction if it furthers my knowledge.

Don't imply it was something it wasn't, Stacy. It's sort of chickensh*t to wait to see which way the wind blows before you play.

Adios, amigos.....................
 
Mike was you're point,
being or thinking , if cooled it would speed up the eventual hardening time wise?
the colder the faster this would happen?
interesting..
Kevin
if so does this mean we should Cry'o more than once?
or did I misinterpret you? that could have happened un-doubtfully :)
 
fitzo said:
Here I thought it was a discussion, trading different understandings,.....
Click to expand...
I agree
I'm looking to understand Differant views and move to testing it out rather than looking for something set in stone,, which won't happen :)
 
fitzo said:
It was unreasonable at some point? Or a debate? :confused:

Here I thought it was a discussion, trading different understandings, ...
Click to expand...

Mike it is odd how that works with this internet thing, since we know each other and have a better understanding of where we may be on any given topic, we have the luxory of dissagreeing and having it not be an argument or debate, just conversation:) . I never so much as broke sweat from your questions, but often if I have to take the opposite stance as others on these forums I am quite uncomfortable not knowing if the other guy sees it as an argument.

To be honest I may be a chiken&$#@ for always sticking with facts, instead of really making enemies by voicing my multitude of incredibly strong opinions;). Facts aren't good or bad, they just are, but then on the other hand I have enjoyed some discussions that were based on personal taste because it is possible for neither side to be wrong- just different strokes for different folks;)
 
Dan Gray said:
... Kevin
if so does this mean we should Cry'o more than once?
or did I misinterpret you? that could have happened un-doubtfully :)
Click to expand...

Well, as has been pointed out on this forum, there are a couple hundred degrees difference from cryo and the kitchen freezer. Extremes of that magnitude should be well enough below Mf to beat the snot out of any retained austenite. But that is all I will say about the cryo since there seems to be an organized P.R. push by the guys selling it these days and the slightest touching of the topic can start another sales pitch... oops:foot: I guess I am capable of letting some of those opinions slip out occasionally;) .
 
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