What is gained by Triple quench?

[DiamondG Knives]

Ive been doing some reading, and find refrences to triple quenching. I understand that with 52100 muli quench is the norm. My question is will 5160, 1095 and 1084 benifit from doing multiple edge quenches? Also are multiple tempering cycles needed?? And while Im at it, will these steels benifit from Cryo treatment? And if so, at what stage do you do it?

Thanks And God Bless
Mike

[Quenchcrack]

Mike, triple quenching is used to reduce the grain size of the austenite from which the martensite forms, thus improving toughness. It also dissolves more of the carbides, putting more carbon into solution, thus improving hardness. You must use progressively lower tempertures to austenitize so it takes some degree of instrumented control to really do it right. If your target austenitizing temperature is 1500F, quench first from 1600F, then from 1550F, then from 1500F. However, you can eyeball it and do some good. Tempering between quenches is not really necessary but re-heat gently to prevent thermal shock.

Cryo treatment is used to transform any retained austenite to martensite so it is a continuation of your quench. High carbon (.95% and over) responds best to cryo treatment as the retained austenite is caused by high carbon content. 5160 would probably not show any improvement.

[MixonKnives]

So a cryo treatment could also be benificial for 1095? I was under the impression that it was meant for stainless steels. Or at least all the talk I've ever heard about it was on the topic of 440c or 154-cm.

[Ed Caffrey]

As quench said, cryo is just another contiuation of the hardening process. Any time you can convert retained austinite to martensite, you doing a good thing. The average knife user often would not be able to tell the increased performance with simple carbon steels, but when there is a small amount of chormium present, as with 5160 or 52100 the results could almost be called dramatic by comparison to a blade of the same material that has not been cryo-treated. Generally I can achieve about 10-15% increase in cutting ability with 5160, and as much as 20% with 52100 blades that are cryo-treated versus blades of the same material(s) that were not cryo-treated. Pretty significant when you think about it.

[MixonKnives]

Sorry for having to ask so many questions on this topic but I feel it'll aid me quite a bit. So here it goes. Well talk about 5160 in this post, keeping in mind the other steels mentioned, but I'm mostly concerned with 5160 right now, as i have alot of it on hand.

Your saying a cryo would increase edge holding ability? Would this at all affect over all toughness?

I'm mostly concerned about this because my favorite knives are large camp knives and bowies. And this 5160 is great for these knives as far as toughness and shock resistance goes. But if theres a way to increase edge holding also, that's always a plus.

Now I'd like to know if its possible to do the cryo quench without being setup with liquid Nitrogen and anything like that. I do most of my forging and quench type work outside under my carport, and also have a small (12x25) shop that i do my finish work in. Is it possible to do the cryo in these work areas??

Thanx for all the help,
Michael

[AwP]

Now I'd like to know if its possible to do the cryo quench without being setup with liquid Nitrogen and anything like that.

You can cryo with acetone and dry ice, but that's probably more expensive in the long run then LN.

[Ed Caffrey]

My short answer to doing cryo without liquid nitrogen is no. Dry Ice and Acetone can be a hazardous mixture to use. The other drawback is that it will only achieve about -70F, which would take an extraorinary amount of time to achieve any conversion. There are several schools of thought concerning this, and this is just mine, but I have experiemented with the process and found little benifit from trying to cryo with dry ice/acetone.

Cryo treatment will often times cause an Rc hardeness test to read a couple of points higher but you have to remember that your converting austinite to martensite. If you worried about the extra hardness, my suggestion is to temper the blade after the cryo treatment at 25F higher than the previous temper cycle(s).

[K Juedes]

Wouldn't a cyro treatment warp or crack the blade because it would cool it too fast?

Maybe i'm just confused. :confused:

KJ

[rlinger]

The book (figurative) says yes it can cause micro cracking and advises when doing with liquid nitrogen to introduce it slowly to the steel (some form of heat exchange that can vary from simply entering drops of LN into the cavity to more elaborate methods). I have read posts of real experience where bringing the steel very slowly down to cryogenic temperature is more beneficial. We ol'knife makers normally can not afford such equipment expense. I certainly can not. I have toiled over two schools of thought on how to hand lower a blade into a LN dewar. Some think it best to go very slowly. I prefer to put her in there as quickly as possible so that all the surface gets the shock at pretty much the same time. To my knowing, I have yet had one crack or warp. I think it much more likey to crack than warp and the cracking may be so small as not to notice before the knife is delivered.

It is important to remember that cryogenic treatment is not a seperate procedure outside the heat treat but instead is a component of it. A heat treat can be done without it but if it is incorporated it is part of it and not something that is done in addition to it.

Complete martensite obsorbtion (not the correct term, I am sure) is about 0.80 percent carbon. I believe any steel containing enough carbon content can benefit from cryogenic treatment regardless of how well the initial part of heat treat went, up to and including quench. I say this because it is so difficult to achieve a perfect heat treat. As stated above, some lower carbon steels, such as 5160 as an example, most probably will not benefit at all. I have tried it with such steels with no noticable difference. Even though they are specified as high carbon they are low by comparison.

Triple quenching appears to refine grain and therefore popularly refered to as giving credit to the quench. Actually, the grain is refined during soak - not the quench. I am still at school here reading you guy's stuff about triple quench however, I think multiple soaks followed by quench may better refine grain if each and every set are done correctly. In other words: I'll stick with a proper single soak but will not close any doors behind me concerning this.

RL

[VSMBlades]

Correct me if I am wrong but dont the professional Cryo places have a system where the part is actually never in contact with the LN. I seem to remember reading in The Wonder of Knifemaking that there were some less than desireable effects from the blade surface coming in contact with the liquid. Has this theory been debunked?

[Quenchcrack]

Joe, I think you are correct. The folks at 300Below let the vapor from the LN do the chilling and never actually immerse the part into the liquid. The more gentle cooling and heating are said to minimize distortion. Remember that since the part is now below the Martensite Start temperature, the speed at which it is cooled is no longer critical. Only the temperature to which it is cooled affects the amount of martensite formed.

Now I have a question: has anyone ever heard of a maker using multiple austenitizing, quenching and cryo treatments? Multiple normalizing and multiple hardening treatments are common but I wonder if there is anything to be gained from cryo treating after each heating and quenching cycle. :confused:

[mdagley]

Quench,

There is/was a knife maker in Rochester, Wa that does (or at least did) cryo after each heating step of the treating process. The last time I talked to him was about 4-5 years ago and he was claiming that he cryo'd after the quench and then after each of three tempers (useing ATS 34) and felt he got 2-3 points higher Rc and a much tougher blade that held it's edge far better than any other process he had used at that time.

Don't know if he still does things this way or if he really got the claimed benefits. Might be wroth trying if I can ever get the time.

Mike

[mdagley]

Whoops-------meant to say that he used a double heating/quenching, triple temper heat treat. Cryo after each step.

[Quenchcrack]

Hmmmm....well I can see where cryo after every quench might help but if he was cryo treating after tempering he probably didn't get much benefit from it. Tempering will cause retained austenite to transform to bainite or martensite, depending on the temperature. I can't see that there would be much retained austenite to work with the cryo after tempering. But then, this wouldn't be the first time that someone tried something that wasn't supposed to work and it did!

[mdagley]

Quench,

I tend to agree with you on this. My guess is that if he really was going through all these heat/cryo steps that that all he really achieved was perhaps a very slight gain from the double austenize/quench/cryo process and a big waste of time on the post temper cryo.

It is my understanding that a post cryo temper is needed to relieve the stresses from the deep freeze. If this is correct, then his post temper cryo would yield a weaker blade--not the tougher blade he was claiming. :confused: