double qeunching

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franklin

franklin

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does anyone out there double qeunch? is there a advantage to this do you get better edge retention or tougher blade? or do you think i should just stick with a single qeunch? i am not going into what oil to use just the double qeunch part thanks
 
Double or triple quenching is used to reduce the grain size in the steel. The quicker the steel goes from one phase to another, from ferrite to austinite and back, the smaller the grain size. The down side to this, and the reason that I have stopped doing it, is that it gives more opportunity for quenching cracks to develope. The higher the carbon content of the steel the more it is prone to it due to plate martensite and any steel that is used for knife making will form at least some plate martensite with 100% plate martensite occuring at around 100 points carbon or higher. Grain refinement can be done by multiple normalizations except, of course, in air quenching steels.

Doug
 
doug i have 1095 annealed steel from jantz,so would normaliztion even be needed? and would it then just not be advisable on 1095 with the carbon count being higher?
 
What Doug said. You will also hear an awful lot about the quite sensational benefits in performance from quenching many times, but you need to remember the difference between generating attention for magazines and how things work in the real world. Grain size reduction can be a good thing, except when working with shallow hardening steels that you want to fully harden, and then only in moderation. But the best time to accomplish this is in the normalizing so that you and the blade only have to deal with the stress of hardening once. One other note on the distortion or cracking thing, you will notice that the greatest proponents of this practice often only edge quench and thus only have to deal with perhaps 1/3 of the issues those of us who prefer fully hardened blades have to.

What gave rise to this modern bit of folklore is bladesmiths using complex steels that were a bit beyond their tools and methods. Let’s take 52100 for example, this is not a beginner’ steel, it is highly prone to retained austenite, intergranular carbide precipitation and is very easily overheated. It really needs a precise soak at a specific lower temperature to avoid many of these issues, but if all you have is a forge or a torch you will encounter some issues. So without the precise means to heat it, the hardening temperature is best kept much lower than recommended to avoid some problems, but this will result in incomplete carbide dissolution. What to do? Heat it quick and low and put a fraction of the carbon into solution and then quench and trap it there. Now reheat again but this time there is an amount of carbon already taken care of so you can take another bite out of the undissolved stuff, by the third heat you will have approximately the same amount of austenite in solution that you would have if you had the means to soak it properly.

Now if one has a penchant for using their own previous blades as their control you can see the direction that the narrative gets skewed in. Suddenly, using this approach, the blades started to perform many times better. There will be an increase in toughness from less carbide in solution by using lower temperatures, edge retention will rise significantly by the reduction of retained austenite, and decreased grain size. But these are all things that could have also been accomplished by a single, controlled, hardening preceded by proper normalizing, or simply choosing a steel that matches your equipment and methods. The problem arises when folks are too quick to shout eureka and focus exclusively on their last blade being 10 times better than their first, instead of taking time to ask why their first was 10 times worse, and the blade they are treating as the Holy Grail is the one they finally got up to par. Create a problem and then fix it, it is a very old and effective approach to getting peoples attention.

All the thermal treatments leading up hardening are equally important to the outcome as they set up everything inside the blade for the one successful hardening. Proper normalizing, this can be done in multiple cycles, matched with the anneal best suited for your steel is the key. Is one learns to work with sub critical (spheroidal) annealing as industry does you can set up your carbides and grain size with normalizing and not effect them at all during the anneal so that everything will be ready to go for the hardening.
 
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wow you must be getting through my thick skull just had that eureka moment were i understood everything you just said Kevin. don't give up on me yet i got a ton more to learn thanks for this it cleared up a ton of misconceptions I've been led to believe. that's one reason i got my oven was after reading your posts and wondering if what i was doing couldn't be better.
 
Franklin, I take it that you are forging your blades. Even though you are starting out with annealled steel, which is acturally not important to this discussion, with probably a good grain size that doesn't mean that you will gave good grain size after you have finished forging the blade. Those of us, which is the vast majority of us, who don't have the means to measure the grain size of the blade that they've just forged out just go ahead and normalize X3 to make sure that it's small. It's like cryoquenching some of the simpler tool steels, as opposed to stainless, to drive the steel through the true Mf point. Most ITT diagrams only list M90% and not the true Mf point so you can do a cryoquench not knowing if it is going to help but you know that it won't hurt either. Same as extending the austempering cycle because the data at the temperature that you're forced to use is a little nebulus. It may be overkill but it won't damage anything.

One caveat concerning multiple normalizations, or quenchings. It can be overdone and the grain made too small, with some steels, to allow hardening. Or you could cause the steel to be so shallow hardening that you could grind away the hardened edge of the blade during the finishing grind.

Doug
 
i do forge some blades doug but most are stock removel. but i still like to now the forging side to. for now i want to work on heat treating my stock rem. blades well then move on to the forging side of things. im going to the library mon to find heat treat books can anyone give me some books to look for?
 
Books on heat treating may be a little on the thin side at the public library. Look for books on metallurgy, that will probably be your most likely bet, and read what they have to say on iron and steel. The best book for the beginner is probably going to be Steel Metallurgy for the Non-Metallurgist by John Verhoeven. It's a good one to have on hands.

I have that one and two others that I got from a used book seller. One was a old text book that was plenty marked up but it was complete and cost me $4.95, shipping included. A second used text I don't recall the price on but it was probably at least half price, these things are real pricey new, and if it was for two underlined words it could have passed for brand new.

Books on metallurgy are going to be something that you are going to want to have on hand and go over repeatedly. I've picked up a lot from the three that I have but I still find something each time I go through them. I've also needed help from Kevin and others to understand what appeared to be contradictions. One draw back that I have found in all the books is that the authors don't necessarily mention all the conditions that take place like specific temperatures and steels used. One thing that I had to have Kevin explain to me is when I was confused by one book stating that retained austinite converts to untempered martensite and another states that it converts to ferrite and cementite. I found out that it can change to both or either depending on the conditions and the steel composition. My advice: only read the black parts; no reading between the lines; no assumtions.

Doug
 
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Doug, your "no assumptions" advice is some of the best I have seen when it comes to understanding the texts, that is why I have to slightly disagree with Verhoeven's book being the best for beginners. John dumbed it down quite a bit for a guy like him but it is still far enough above the heads of the average bladesmith that I have seen more confusion and misinterpretation from that text than from other metallurgy texts. For beginners I always recommend "Metallurgy Fundamentals" by Daniel Brandt, it is the clearest and easiest to understand text written on the topic and I use it for my textbook in advanced classes that I teach. If folks were to read the Brandt book before moving onto Verhoeven many of the bad conclusions that folks are making could be avoided.
 
Franklin - thanks for asking the question!
Kevin & Doug - I bet I speak for many when I thank you for your clear answers - especially making it understandable to a rube like me! And thanks for the book suggestions - they've been added to my look-for-list.
 
GREAT QUESTION!!! I've been meaning to bring this subject up, I've seen where some makers act like it's a selling point because the blade was "Triple Quenched"! Not saying it isn't a selling point, but in my mind the grain can be reifned only so much and with proper thermal cycles, before HT, shouldn't that be enough? I have to say it sounded a little like snake oil to me. BUT, I honestly don't know if it is a benefit. How sharp is sharp enough, how long does the egde have to retain it's sharpeness? I agree that we should always be striving to improve every aspect of our craft. All steel has limits, and it seems to me at some point your just adding more processes to a blade that can't be improved more. I sure hope Kevin chimes in on this one, and I hope he has done some real world testing, to see if there is any difference in the grain structure. I know there are well know and successful bladesmiths that swear by triple quenching a blade, I think some of Kevins Microscopic pics would be a better way to decide, no offense to anyone that feels that double or triple quenching works, besides if it works for you and you get the results and performance you're looking for, and it makes yo happy, by all means stay happy! For me I would like to know if it is worth the extra expense, that does make a difference when you're maing the transition from a beginner/hobbyist to a maker trying to build a carreer! Looking forward to hearing from a lot of folks on this one, Rex

Well there I go again, I saw the topic and didn't look to see who ot if anyone had posted on it, sorry for jumping the gun yet again, and THANK YOU KEVIN! That is about how I felt about triple quenching, but didn't know for sure, I did know what I was doing worked well, thought about giving it a try, but thankfully didn't waste my time and resources!
And Thanks to Doug as well, you have a great understanding of this stuff and an ability to put it in understandable termonology. Kevin, I'm not saying that you don't, it's just sometimes you are so far over my head I can't conceive what you're saying! I do get it, it just takes me a little longer and a bit more work to get it in my noodle!
And ALWAYS WORTH IT! Thanks Guys for a great thread! Rex
 
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One thing that one has to ask one's self when they read that such and such a process is the latest, greatest is: how do they know. Kevin, Ed Caffrey, and others have the ability to do the microscopic and other mechanical testing themselves or can afford to pay others to do the testing for them. Most of us, me included, are only able to do performance testing. At most they might only have a hardness tester. When reading statements about superior results of certain methods, a little skepticism is a very good thing.

Doug
 
you bet , performance is a great indicator . You can compare it to audio equipment . the human ear usually can only hear up to 20,000 cps . and yet you see stereos that advertize all kinds of technical data that is beyond our ability to hear , whats the purpose ? All I have is a 250. dollar rc tester. not saying all data about knives isnt important to some folks . I try and keep it simple .Unless you are writing a technical journal , most knife data is really not that important , as long as it is properly HT and tempered correctly and will keep and hold an edge . man has been making blades for several thousand years with out any specialised equipment . I know I will get blasted for this but, I dont care . I will put my carbon steel blades against any ones blades as far as performance . I am quite sure during the early shinto period in fuedal japan when a samurai cut off his opponents head he did not jump up and ask, was that steel sperodised and what was RC ? respectfully Bubba
 
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i now i shouldnt say ask this but if one only has say tranny fluid and there new to heat treating would it be then better for them to at least double qeunch to get a little better performance from what they have on hand? did you see me cringe as i typed that? i just got asked that and i really did not want to say anything i told him i would ask someone that knew more then i did before i would answer that. and to both doug and kevin thanks for your time and help / books i just ordered both.
 
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Great thread; very informative.

Thank you for the recommended literary references; I just now ordered two of them.
 
I have used this for quenching handforged hammers , 20 weight non detergent motor oil ( new) has almost exactly the same viscosity as parks 50 # try it if you can find it , lot cheaper does good job on hamons or any steel that need fast quench simple, uncomplicated and available . Bubba
 
Franklin, that's a deffinant maybe. You say that you are using 1095. Depending on the manganese level, not to mention the "trace" elements that tend to show up in recycled steel-which is probably what we are dealing with here, trany oil may be too slow to convert the austinite to martensite completely, if at all. If that's the case then, yes, you are transforming the face centered iron crystal found in austinite to a body centered crystal of ferrite but not the modified body centered crystal known as martinsite so you will really just be spinning your wheels and the crystal refinement will be immaterial, as far as knife making is concerned. So you may refine the grain but that won't bring you anywhere near the steel's greatest potential.

Your first priority is to check to see if the steel has hardened by forming adequate martensite. The best way would probably test it with a hardness tester, but most of us don't have one of those on hand. The next best is to try to file the spine. Take the blade out of the quenchant after the color has gone away and cooled down to hot. Try to file the spine. It the file bites in then you do not formed martensite to any degree and you're back to square one. If the file skates across the spine then you have formed enough martinsite to harden the steel.

Now you can attempt to refine the grain with either multiple normalizations, if possible, and 1095 can be normalized or multiple quenches which even air hardening steels can do. Be aware that each time that you quench a steel with enough carbon in it to make a knife blade with you run the risk of forming microscopic cracks where plates of martinsite meet. Something like 1095 form all of it's martensite in plate form as opposed to lath form and will form more of these microscopic cracks that, lets say, 1060 which will form partially lath martensite and have fewer opportunities to develope these cracks. Whatever the potential for developing these microscopic cracks is, doubling the quenches that will form martensite doubles the risk and possibly the amount of these cracks. Enough of these cracks may cause a broken blade at some time in it's existance from heat treating to the stresses of use.

Using multiple normalizations to refine grain size eliminates this martensite cracking because no martensite is formed in this process. Multiple quenching may be better at forming smaller grain but, if done correctly, multiple normalizations will just or about as well with a lot less risk. Personally, I have chosen not to accept the risk of martensite fractures (cracking) for the purpose of refining the grain.

You will notice that I worked hard to make my statements condition specific, and I hope accurate. This is the world of metallurgy.

Doug
 
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franklin said:
i now i shouldnt say ask this but if one only has say tranny fluid and there new to heat treating would it be then better for them to at least double qeunch to get a little better performance from what they have on hand? did you see me cringe as i typed that? i just got asked that and i really did not want to say anything i told him i would ask someone that knew more then i did before i would answer that. and to both doug and kevin thanks for your time and help / books i just ordered both.
Click to expand...

That is something that I am wondering as well

The main difference I have with Franklins post (besides I look much better in a dress:shush:) is I has the fast and medium quench oil but none of the ability to properly soak the steel (coal forge Lively style)

so with the proper quench oils, is a double or triple quench the way to go until we can get a temp controlled forge or a HT oven and hit it with a 5 minute soak??

and of course

since we has discussed it, can one of you list the actual recipe you use for thermal cycling?

Kevin, Doug and Bubba tanks for your help guys... Mucho respect
 
One can avoid the need for many of these bizarre bladesmithing rituals if they just choose a steel suited for what they are doing and how they do it. For around 2,000 years the tools of the blacksmith or bladesmith worked fine for the available steels, they were perfectly matched with the simple iron-carbon alloys, but then something huge changed everything- alloying. If you want to emulate or use the tools of the smiths of old you better get a steel close to those they used. Add just a pinch of chromium and we're not even talking the same animal anymore, and even Masamune would be screwed without changing his ways. Indeed none of those old timers needed to know the Rockwell of a sword, but then a copper or bronze sword is more than capable of doing the job quite well. I always pause to think what the world would be like if folks took the same philosophy toward medicine that they do with other technologies; after all a barber didn't need fancy test equipment to see that all you needed was a good bleeding! Materials change, technology develops and knowledge increases, it is how the world works.

So the trouble is not in the quench medium, or even the type of oven but in how well you match you steel to them. Quench 1095 in Parks #50 and you can expect 65-66 HRC, quench it in Parks AAA and you should be happy with 56 HRC. Heat O-1 up to some temp after the magnet stops sticking and then quench you shouldn't expect your moneys worth, but do the same with 1084 and you will be quite pleased. Choose your steel wisely and all the hocus pocus doesn't matter so much any more and you can quench once and get on with life.
 
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