screwy idea for tempering

Kevin, realy love to read your answers. Please do elaborate whenever you get the chance. Everytime I read your stuff, I go away with more questions than I started with. The more I learn, the more I realize how little I know. Feel free to share your views as some inquiring minds DO want to know!!
 
Lets try to keep Kevin from hijacking this thread and go for what the people want, and what Kevin is much better at than poetry apparently – tech talk.

Lets first completely separate some concepts and terms here- tempering and martempering, two entirely different things. Any hot oil that can handle up to 450F should work great for tempering, I use salts for this process as well and love it much more than kilns or ovens. Tempering is the process of heating a hardened blade up in order to reduce brittleness and impart varying degrees of toughness.

Although it is not used by industry I prefer to use the term “marquench” instead of martemper because of the confusion that “martempering” causes because industry just named this one wrong. It is a quenching, and thus a hardening, technique and not a method of tempering at all, and indeed one must follow it up with a proper tempering just like any other quench. In a traditional quench the part is supercooled in a medium, let’s go with a liquid for this discussion, fast enough to avoid other transformation products that form at higher temperatures. If this is done successfully one will have meta-stable austenite until the Ms point (around 400F) is reached, when the austenite will then give way and allow the formation of martensite. So from 400F to ambient (or Mf, whichever comes first) is the temperature where steel actually hardens, it is also the part of the process where the steel is subjected to the greatest stresses, both by the cooling medium and the hardening process. Parts with varying cross sections will go through the torture of having the thinner sections complete the transformation first and greatly expand against the thicker sections that cannot keep up. This is where much distortion comes from and is the leading cause of the dreaded “ping” of death.

Marquenching (or martempering, if you must), is a technique where the quench medium is a substance with just the right properties to handle all of the extra heat while being able to cool fast enough to avoid those high temperature transformations (some steels need to get below 1000F in less than 3/4 of a second to avoid pearlite) , and is heated to around Ms. The part is quenched into this and is super cooled to around 400F and held there long enough to equalize the temperature and then removed to air cool to from martensite and harden. This results in a more even rate of hardening throughout and much less shock to steel that is already going through unimaginable stress as iron atoms are forced around trapped carbon atoms in ways nature never intended. This allows you the luxury of watching the blade slowly harden and being able to gently guide it back straight if you should see any warps beginning. I cannot make super miracle blades but many who have used the technique have found the blades to be a little tougher in the absence of slamming it into Mf.

Some steels are just not suited for true martempering, and something like 1095 would be a good example. 400F. liquids just are not typically fast enough to cool a steel that must be quenched that fast. The greatest enemy of a quench is the vapor jacket, and any liquid that readily forms a vapor must be considered carefully before using as a quenchant. Water quickly forms all kinds of vapor at 212F and that is the real reason for all the distortion when using it, if it cooled everything evenly at that rate it would not be a problem. Obviously the hotter you heat a liquid the closer it will be to its vapor point and the worse will be the problem.

Salts are so often used for martempering because they have very good conductivity and a boiling point so high that one can heat them very hot without any hassles from a vapor jacket, so they are the preferred method, although there are oils designed to go this high made specifically for martempering as well.

So you don’t want to go all NASA about things just to make knives but you want to avoid the shock of traditional quenching, or you would like to get the effect with something like 1095, what can you do? What you don’t do is try to build a Saturn V rocket out of yarn and popsicle sticks, if you don’t want to be an astronaut then leave the Apollo missions to NASA. Instead truly find a better way to accomplish you goals and leave total martempering to the guys who have martempering equipment- go with an interrupted or timed quench instead

An interrupted quench accomplishes a lot the same things but requires a little more human interaction and can be done with any medium, thus allowing one to do it even with 1095. How it works is you simply interrupt the quench by removing the blade from the 130-150F oil when it has cooled to around 400F, then allow it to cool to room temp. Your numbers won’t be dead on and things will not be as even as in martempering but you won’t get any more pearlite than you would from a traditional quench, since at the point where pearlite forms it is a traditional quench.

Once again simple for simple, complex for complex; match simple steels with simple tools, but also if all you have is simpler tools then simplify your techniques to maximize them. Simple logic dictates that overreaching the capabilities of your tools or materials necessitates compromises somewhere.
 
Deweyknives said:
... The more I learn, the more I realize how little I know...
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If you are doing it right that will never end. Believe me I am 10 times as ignorant about this stuff as I was 10 years ago. Knowledge should have that humbling effect.

Also there is always so much talk about testing among knifemakers, the best testing, I have found, provides much less in the form of answers than it tells us about what question we should be asking.
 
Thank you, Kevin. Now that was a response I can print out and add to my little binder of wisdom. :thumbup::D

If that was painful, tell me and I will send you a flagon of your favorite poetry juice and you can attend the cold Michigan moon and quell the burn with a soliloquy appropriate for the rapt attention of the trees. ;)

Joking, joking, lest any take umbrage.....

Edited to add...not joking about the Scotch! I figure I owe you a bottle by now. Knowledge has value, no?
 
Thank you Kevin, and Fitzo!!! It is like a breath of fresh air. I'm surprised that Keven hasn't been drug out and strung up as a traitor. Well done Kevin! Evey thing, even Knife Making, has rules. Too many not only don't follow the rules, but are sadly ignorant of the fact that they even exist, or why. You guy's keep right on doing what you are doing. Mike Lovett
 
As always, one good answer, five new questions....................

I've been doing interupted quenches for some time and now have a better understanding of cause and effect. Determining temperature has been an issue but I have a few more ideas to better control that also. Would there be any advantage to being able to hang at martempering [marquench] temperature for a period of time, or a slow, controlled descent to ambient temperature?
 
MY thread, Kevin........hijack all you want, although I am a bit leary about John Hughes quotes, even those I was smitten by Mary Stuart Masterson in that particular flick.....lol. Let me clarify what I am looking for, other than more info to pack into my pointy little cranium:D I am going to attempt to make some combat knives to give.....or eventually sell to soldiers IF I can manage to produce a suitable product. So yeah, it would be nice if they were tough:thumbup: The better, more consistent quality steels that I have on hand are W2 and 5160 round bar. What technique is going to get the best results with those? Next set of silly question......when you do the interrupted quench, how do you know when the blade gets to 400F? Do you "edge quench" or do you harden the entire blade in the processes you have described?
 
fitzo said:
Thank you, Kevin. Now that was a response I can print out and add to my little binder of wisdom. :thumbup::D

If that was painful, tell me and I will send you a flagon of your favorite poetry juice and you can attend the cold Michigan moon and quell the burn with a soliloquy appropriate for the rapt attention of the trees. ;)

Joking, joking, lest any take umbrage.....

Edited to add...not joking about the Scotch! I figure I owe you a bottle by now. Knowledge has value, no?
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single malt poetry juice, eh? Sounds like a more sophisticated version of what we in the south refer to as "liquid courage" otherwise known as Jack Daniels
:D
 
Kevin R. Cashen said:
What you don’t do is try to build a Saturn V rocket out of yarn and popsicle sticks, if you don’t want to be an astronaut then leave the Apollo missions to NASA.
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Rats. You mean that won't work?:D


Interesting that you chose 1095, of all things, for your example in this... I'm kind of wondering why that steel over others -- purposeful, or accidental?


Maybe because I got into this arena 'late' (as in the last few years), but I'll admit that it really surprises me at how many are unwilling to accept what educated observation can explain over folklore or tradition. My guess is that it doesn't hurt for me to be quite the iconoclast that I am.;)

I agree that there's nothing wrong, per se, with the idea of 'it works for me' being accepted, but in many cases it isn't a function of acceptance, it's a function of the ideals of a zealot -- not 'it works for me', but 'this is how it's done'. THAT is what disturbs me!
 
I went to the Ashokan event this year and watched as Kevin demo'd his interrupted quench routine. It made complete sense to me.
Rather than leave the blade in the oil until it was completely cool, he removed the blade after about a 5 second delay. After the blade cooled while he was talking, he "accidentally" dropped the blade while holding it from the tang. It hit the concrete point down and made a hole in the slab.
He then passed around the blade - which I beliece was 1084? - and the point was perfect.
Note also, that the blade was ground to just a hair short of full finish.
The point was unharmed. That puppy was hard!
Anyway, I have a rather large supply of 1" square 5160 -3000 feet -that is on the high end of carbon content normally found in 5160.
I have been quenching at a long soak in my oven, and holding in the oil until it cooled off. What I didn't know was that by cooling off completely, I was halting martensite transformation before it had the chance to complete! As I understand it, the blade needs to remain up at, or near, the 400 degree mark for this to happen.
Anyway, I started interrupting my quenches. I still do basically the same tempering recipe.
After cleaning up my quench scale and going to do finishing hand sanding, I couldn't sand the scratches out!!
My 5160 is now harder than I ever dreamed. Much harder than I was accustomed to.
If I hadn't learned some hand-sanding techniques from Don Fogg, I'd be screwed!
This is the result of one of those blades. I'll mention here that I sent a knife to be Field tested by one of the gentlemen who own one of the Hunting Programs on The Outdoor Channel. The name of the program is Backland Outdoors and the guy says he dresses out over 100 animals a year. Deer, hogs, elk, pronghorn, caribou, etc.
I sent him a knife to use on one of his hunts where I live here in Illinois. He had been accustomed to factory stuff up until now, and was very sceptical of the "hand-made" stuff.
Here is the email he sent me when he returned home in Minnesota:

"Dear Karl,

Just back in town and wanted to touch base with you about your knife. OK, I must admit this is one meat cutting "mo fo." What an edge! Love it, can’t wait to rip into my next animal! That almost sounds sick doesn’t it? I quartered out a buck yesterday in Illinois in about three minutes and had him in bags for donation to the feed the hungry program. A great knife "takes the work out of work" is how I look at it. I just wanted to say thank you and I now can say that I can't wait to show your knife on the air. In fact I had many at the last camp ask me about who made this knife that I was hooting and hollering about. Now my staff is asking about their knives! Why do I get all the cool toys?
Give me a call when you get a chance.

Sincerely,
Scott Anderson
BackLand Outdoors"


So there is the result of the interrupted quench in the "real world"!
 
kbaknife said:
... What I didn't know was that by cooling off completely, I was halting martensite transformation before it had the chance to complete! As I understand it, the blade needs to remain up at, or near, the 400 degree mark for this to happen....
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I am on my way out the dorr for some bussiness, I will touch on many of the questions and things that I have read this morning tonight, but I feel the need to get to this one now and elaborate later. In order for martensite to form completely you MUST reach Mf. IT is a function solely of temperature and not time. Holding at higher heats will only arrest the martensite development. There was another question here about the effects of even slower cooling or even holding- the idea behind the marquench is not to retard martesnite formation but to equalize it, if you monkey around too much above Mf you can stabalize austenite and end up with retained austente that needs to be LN dipped in order to get rid of.

What I propose in my demos is that cooling way too fast, or more importantly unevenly, results in more than neccesarry stored energy in the steel that will increase the chance of distortion, or failure when more stress is applied in use. Martempering doesn't make more martensite, it just doe it more evenly and produces what Tim Z. likes to call "happier martensite".
 
Karl.....did Kevin quench the edge for 5 seconds or the entire blade?
 
O.K., if I've got this right,you need proper heat treat temperature, proper soak time, snap cool [quench] to 400 deg.[marquench range] and then slow descent to ambient temperature. Is this the correct scenaroi?

This is great stuff, perhaps we can get into detail of desired grain structure and affects of variations to this prociedure.[if & when you have time]
 
" Martempering doesn't make more martensite, it just doe it more evenly and produces what Tim Z. likes to call "happier martensite".[/QUOTE]

Do you mean "marquenching"? (interrupted quench?)
 
I love reading stuff that Kevin, Mete and Fitzo write. I am not a knife maker "Yet". I am a Mechanical engineer with a background in Thermo and material processing. The stuff that they write is like Crack for a nerd like me. Can't wait to try some of this out on a real knife. Just need space and time. Steven
 
I agree Steven, this is good stuff! I've been making knives for about five years, seriously for three.I've learned more here in two weeks than I have in the last year of stumbeling around! It's a long road when you use the read,do,learn method but I've loved every bit of it. Hats off to all these guys who share their knowledge!!!!!!!!!!!!
 
John Frankl said:
Never seen Kevin quench and edge, nor recommend doing so. :)

John
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Except for your JS and MS test performance knives cuz that is what is expected? lol I read something that Kevin posted a number of months ago wherein he said that he had no use for a knife that bent like silly putty and that the martensite make the blade tough so not having a "very soft spine", etc, is not an issue. Any comments?
 
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