Metallurgy questions on triple quench

Hey Dakota,"Alan", this is ole some guy down in TX. Nobody can pay your dues for you, so set up your own tests and check them according to your methods. We can point you in the right direction, but the rest is up to you.

Ken Beatty:D
 
If knife maker Joe learns how to make a better knife with his use of "X" heat-treatments,,,and then tells me how to do his, "X" heat-treatment,,,, I should be able to copy his work point-by-point and get the same results correct?

If your answer is "Yes", then there is value in testing and passing on knowlege of what has been learned..

If your answer is "No", then there is no point to test anything, for the results are meaningless and un-repeatable...

I dont believe that when I fire-up my new Low Boy Forge*, (*She works like a dream by the way, thanks Ragnoor!) and forge a blade out of a Load Shaft that I have to dive into Magic.

I believe that there is real science at work in the fire/steel/ and hammer, and that everything I may do has an effect that is understood by someone someplace, or is writen down in a book somewhere.

I do many heat-treatments on my bblades based on what I have read by knife makers I trust 100%...But I also know that even if I dont understand much about the reasons for a triple-quench, that there really "ARE' reasons to do it...

I would just like to know what changes between the 1st and 3rd quench?
 
Bang out 3 pieces of flatware, all same thickness and length. Heat one to critical and quench, take it to the vise and break it, look at the grain. Next piece do a dble quench, brake it and compare with #1. Etc with piece #3. Theres the test and results. The smaller the grain structure the stronger the steel, the better the edge holding.


Ken Beatty:D
 
I did have a friend of mine use his digitized heat treat oven that is very precise do a little experiment for me once.
He put 3 pieces of 3/4" x .140" that were 5", 6" and 7" long in the oven at 1500 degrees for up to 23 hours. The first piece of 5" was removed and quenched at 1 hour, the 6" piece was removed in 6 hours and quenched, and the third piece was removed in 23 hours and quenched. All three pieces were broke and all three pieces had the same grain stucture. The outside of the 23 hour one was scaled a lot more than the others and that was the only difference. The grain was very small on all of them. These were normalized and annealed pieces of the same lot with the only difference in them being the length and the length of time in the oven at 1500 degrees.
I don't know what that would have to do with the triple quench but I thought it might save some one some time on that part of testing. :)
 
23 hours ??? After 23 hours at 1500F you would have VERY large grain size and substantial decarburization, it would have been good only for the scrap pile.
 
The grain did not grow. There were no difference in the grain size.
Try it, it should be the same for all the carbon steels, but that is a guess as I only used the 52100.
 
Visually, but I had my glasses on. :)
They all looked exactly the same, as it did to several others that looked at them. I have seen the grain enlarged from too high a heat but I don't think that 1500 deg is high enough to cause grain growth. I had always wondered about it because of what you read of the thoughts of others so I decided to find out for myself. According to the temperature chart, it doens't start to enlarge till you reach about 1750 deg.
As I said, try it for yourself and see what happens. Using a heat treat oven will keep it from overheating so you can eliminate the eye factor. If you use something besides the 52100, and it turns out the same, then it may be the same for all the high carbon steels.
 
raker...

While that is an interesting test on one time quenched steels,,,,I still seek information about the merits of a triple quench.
 
Thats a cool test Ray, it would be interesting to know if the percentage of retained austenite changed in each piece and if so how much.

Bill
 
I don't know, Bill.
I thought the retained austenite would be after the tempering,if any.

On the triple quench, if it looked the same, and if the triple quench was needed so that the steel wouldn't be at the critical temperature so long that it would promote grain growth, then the time of 23 hours at 1500 degrees shows that the grain doesn't grow. If you wanted to hold it 20 minutes, which I have read on the forums is about right for the steel to do what it needs to, and then quench it, that would give you the projected time at critical for the 3 times with a torch quenching. I wish we had done a test of one, five, and 30 minutes at 1500 before the quench, to see if there would be any difference in grain structure. I don't see how there would be but then there are still some things that I don't understand. :)

DaQo'Tah
I use the single quench in transmission fluid at a temperature of 300 degrees. This gives me a longer time for the steel to stay in the martinsite transformation zone. It will only form martinsite when the temperature is falling and I figure that the slower the transformation, the more thorough the transformation will be. I do know that it takes a tempering temperature of 475 deg to keep the edge from forming micro chips when cutting the aluminum cans and it Rc's at about 57/58. I have tried other methods of heat treat and this is the one that gives "me" the best results. What I see when forging and heat treating is impossible to explain, you would have to experience the event to understand. Without the ability to have measuring equipment and some one to log the times and duration at temp., it is not possible to convey the exact meanings of my explanation. That is one reason that it is best to visit and watch to see for yourself. You know that red is red but no one can tell you how bright the red is without a visual. You might find some one close by that will help. If you get the chance, go to a hammer in and take notes and ask questions, that is what has helped me the most and the friends that I have made there, continue to help.
 
I don't know Ray, every time I think I'm getting a handle on whats happening somebody tells me something else. I beginning to think no one really knows, :D .
I had a good discussion of this at Ron Clarborne's hammer in, we got an old metalurgy book out and started reading, this is what we came up with, the austenite transformation into martinsite is complete after the steel is taken from critical heat to below the nose of the curve (approx 900). then the martinsite transformation is complete when the steel hits room temp. So after quenching any retained austenite is left unchanged. Thats why we were wondering that maybe with multible quenchs, the already attained martinsite from the previous quench didn't have time to transform back into austenite, but a percenage of the remaining austenite then tranformed into the martinsite,therefore reducing the total amount of retained austenite, but after 3 quenchs any additional transformation is so minimal that it wasn't worth persueing. Don't send me any nasty letters, this is just my opinion and I have no idea if its correct.:D
 
Bill and All,

Interesting thread here. Bill, what you describe seems to apply more to the tempering process. A triple temper, as opposed to a triple quench, will do much to convert retained austenite into martensite. As I understand it, the first tempering cycle tempers new martensite while also converting retained austenite into new, untempered martensite. The second cycle tempers the fresh martensite and largely finalizes the conversion of retained austenite to new, untempered martensite. The third and final cycle is mainly to temper this new martensite as, in theory, little if any retained austenite is left to convert. You also mentioned room temp as Mf, but anything from a home freezer to liquid nitrogen may more completely convert retained austenite to martensite as well.

Fun stuff,

John
 
John, thats where its confusing to me. according to the book we had the transformation of austenite to marsinite stops when steel gets below the nose curve. No more transformation is made to the austinite after that, no mater what, unless you deep freeze it or after a long, long period of time. Therefore after the quench your not doing anything to tranform austenite when tempering, all your doing is releaving the stress build up in the martinsite. Like I said above this is just my opinion, I don't even want to memtion the others that I had the discussion with, because this is just theroy.

Bill
 
Originally posted by B . Buxton
I don't know Ray, every time I think I'm getting a handle on whats happening somebody tells me something else. I beginning to think no one really knows, :D .
Click to expand...

That may very well be true. The problem with interpreting the results of "backyard" heat treating methods is that the process is rarely precise or controlled. That, coupled with subjective interpretation of the results can lead to nothing but confusion. The place to look for real information are the refereed scientific journals. Surely there is a graduate student somewhere who has done most of these things we have questions about and published the results...it's probably just a matter of wading through the appropriate journals search engines to find the papers.

I'm not nearly the knifemaker that you are Bill, or Ray, but I did do a little science in my day. I'm still kicking myself for not having gotten into this craft sooner, as I had free run of one of the countries highest resolution SEMs with EDX attachment at one time in the not too distant past (as well as just about every other microscopy technique one can imagine...oak ridge national lab is a cool playground!) There are so many experiments I'd love to do that would quickly prove some techniques useful as well as put to rest other nonsense beliefs. But, unfortunately, those days are gone.

If enough people got together and chipped in $, experiments could be done and the results sent off to labs for analysis. Len Landrum is one of the only people I know in the knifemaking community who has done this, but even his experiment wasn't completely "controlled" in that he didn't do a comparison with single and double quench...only sent the triple quench samples in, whose results were impressive, but somewhat meaningless (in regards to a triple quench merit study) since there wasn't a basis for comparison. But, then again, I don't think Len was trying to study the merits of the triple quench method either, so please don't take those comments the wrong way...Len's a good friend of mine.

Anyway, I generally stay away from discussions involving metallurgical topics so I'm going to retreat from this one now. I remember when I was teaching physics at UT, and I'd have a student who went out and bought one of those popular science type books dealing with subjects of wormholes, or general relativity or some other advanced esoteric topic. That student would come up to me at the end of class and want to discuss at length this or that topic that they had just read a very general book on and want to speculate about things they would extrapolate from the book....it was always hopeless, they really didn't understand the fundamentals enough to be able to really get the more advanced stuff....the popular science type book would leave out too much detail and overgeneralize too many things. I'd have to tell them that they needed to go back and fill in all of the gaps in their knowledge to fully understand the implications of what they were talking about...which was generally 4 - 5 years of full time study! :) The student didn't always like that answer, they didn't want to hear that they needed 4 - 5 years of full time study to be able to really understand what they were talking about that was in some book they just spent good money on! So I adopted the policy of just not getting involved in those types of discussions. And while discussion of metallurgy may not be the same, I've stepped on some toes in the past firmly standing behind the scientific method, and I want to keep you guys as good friends so I bow out of these types of discussions...


:)

-Darren
 
Most of all of my experience has been using the 52100. I didn't know it was supposed to be a bear to forge and heat treat when I started so it didn't make any difference in the learning process. :)

Bill,
The temperature range that forms martinsite for 52100 is about 475 down to 175. After the temperature falls below the 900 degrees, the time you have to straighten or tweak the blade while it is still soft, could be up to a minute or until the temperature drops to 475. There is no martinsite conversion above the 475 degree line. At about 500 degrees, you could hold it for a certain period of time and would have banite form. At about 1550, only about 50% of the available carbon will go into solution so that there should be no need to sub zero quench it and all the martinsite should be converted after the 3 tempers. Two tempers is what I use and what small percentage of untempered martinsite is left, will just make it a little better as it gets older. Maybe :)
 
The point of the "nose of the curve" is to avoid forming pearlite. That is why a differentially hardened blade has the desired pearlite band on the spine. It cools too slow to form martensite.


Darren, does that mean if I read an academic text and I wasn't in college then I can't understand??? :D ;) :D
Just joshing, we've had this discussion before, eh?? hehe

What you boys down there close to Oak Ridge have to do is keep yer eyes open for an old metallograph in their salvage heap! Even one of the old puppies that used a carbon arc lamp would work for what we need! Perhaps a bunch of us could go together and kick in on it. And josh knows, most all of us know how to polish and etch a test piece!
Just a thought that occurred. Of course, an SEM or xray diffraction unit would help, too.... :)

Cool thread. Someone mention Verhoven is writing a "metallurgy for knifemakers" book. Anxious to see that.
 
Until Verhoeven's book comes out ,read my tutorial on Dan Gray's website. John has it about right. Temper #1 - tempers existing martensite and converts some of the retained austenite to martensite. Temper #2 - tempers newly formed martensite and stabilizes any remaining austenite. Temper #3 doesn't do much. I would like someone to explain what is there about the number 3 that is so sacred to bladesmiths. Is it that bladesmiths have three gods and each has to be satisfied ? Three elements , fire steel and water ? 33333?????
 
Mete,
Twice on the temper is what I have done and it was explained to me that way when I first started in 89. The explaination was that each tempering cycle would temper 95% of the martinsite the first time and then 95% of the remaing 5% the second time, after it was returned to room temperature between tempering cycles.
What was left would be insignificant to the strength of the material as .025% of the untempered martinsite would be surrounded by the rest and "may even help in the cutting ability". These thoughts are mine and I don't know if it would make any difference in the overall performance of the blade or not.
 
Originally posted by fitzo

Darren, does that mean if I read an academic text and I wasn't in college then I can't understand??? :D ;) :D
Just joshing, we've had this discussion before, eh?? hehe
Click to expand...

Hey Mike, I'll bite for just a moment! :) I hope my previous post didn't come across the wrong way, it wasn't meant to by any means.

You can read an academic text and understand, just be careful about what you understand and infer. Also, be careful about what others "tell" you about things, there are a lot of opinions and beliefs I've heard from knifemakers that were pretty "out there" in regards to scientific reality. You and I have had this discussion before a few times :D, and I've also had it with Batson. :) Batson's pretty smart with the politics though, I've heard him say things like "why tempt fate" when pinned down with a question he knew there'd be differing opinions on...very good response, and I should learn from Jim more. :D

It's not good enough for me to have someone say "by triple quenching, my knives cut better and have a smaller grain structure by eye", I want to see the unbiased tests and data...I guess it's just a product of where I came from before getting into this wonderful craft of knifemaking. I think what would be more useful than seeing you guys discuss theory, would be to see discussions on experiment design. Then follow through with the controlled experiments and have the data analyzed! Then definitive conclusions could be made. I love this craft of knifemaking, I'm a relative new guy in the craftsmanship area compared to a lot of you on this forum, I learn from you daily by reading your posts and working with people like James Gibson and Len Landrum here locally...and I sincerely appreciate the friendships I've made both online and in person, but its good to be critical, especially when it comes to the most important aspect of knifemaking..the heat treat of the steel...so please don't take any comments I make out of context, when I was working in science, we'd gather weekly to tear apart each others work and analyze results, it was a way to keep on track as our work would eventually be published in referred journals for the rest of the community to see...you wanted to make sure it was correct. Ok, I'm out of here, no more controversial discussions for me for a while! :D :D

:)

-Darren
 
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