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Kyle Johnson

Tempering questions

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its discussions like these that make me keep a properties list of various alloys, its in a binder with complete step by step guides on how to do what :P

i even have most of your website tutorial printed out in there Don :D

 

anyways it even tells you what temperature to normalize, temper, etc

good thing to keep around i found it browsing the ol' web figured it was a must print!

now combining alloys into dimascus adds a whole new ballgame that i will have to figure out, but thats a lil down the road

:;):

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Guest Kevin R. Cashen

I found the link that Quenchcrack (Mr. Nichols) left over at the Knife Networks, and followed it here to see that my input was desired.  Well I am sorry to say that I can add more confusion to the issue and perhaps complicate it even more, but that seems to be the nature of this whole metallurgy gig.

 

 In addition to the previous references I have these to offer.  In Grossmans “Principles of Heat Treatment†lower Bainite is the only microstructure given as the result of tempering retained austenite in the 450F-700F range.  In Bain and Grossmans “Principles of Heat Treatment†not surprisingly, the same (lower bainite) is given. In “Physical Metallurgy†by Bruce Chalmers, the products are given simply as “the final phases of ferrite and cementiteâ€. However in “Metallurgy†By B.J. Moniz the products are said to be cementite, Bainite or martensite!   John Verhoeven mentions it in “Fundamentals of Physical Metallurgy†as a formation of Bainite from retained austenite in Fe-C alloys above  .4% carbon, which is a good point since the products and their amount will be heavily influenced by the chemistry present.  Most metallurgy texts have an annoying habit of just assuming that you know that they often use hypoeutectoids in their examples, charts and texts.  

 

 Now here is my slant on things.  First I have my doubts about pearlite being one of the products at all.  Pearlite has a range in which it forms and it is a whole lot higher than any tempering temperatures.  Diffusion at temps below Ar1 is assumed to create Spheroidal carbides, not lamellar, even in the ultra fine epsilon or eta variety (at least in theory, since we don’t have the luxury of seeing them with a light microscope).  Cementite and ferrite are often given as the products, and pearlite is certainly made of cementite and ferrite, but to me serious diffusion at higher temps seems necessary to go lamellar. So it may be splitting hairs but I would prefer to say ferrite and cementite.

 

 All the more recent books seem to attribute tempered martensite embrittlement to precipitation of intergranular cementite from retained austenite in the second stage of tempering (450F-700F) .  this would suggest that retained austenite will go to cementite if the carbon is sufficient, but the problem is how often do we as knifemakers go over 450F.  for tempering?  This is a really good possible reason as to why most knifemakers have never experienced the TME phenomenon.

 

 This does leave Bainite as a possibility, but perhaps we need to remember the time required for diffusion to Bainite at the temperatures we are talking about.  Much of our tempering occurs in a range at or below temperatures of Ms (depending on the alloy).  Lower Bainite takes many hours at these temperatures, how would this affect its formation in the 2 hour tempering cycle?  

 

 But then what would be the driving force to initiate further shear transformation of martensite?  It is athermal so time is completely eliminated.  Strain on the metastable austenite (a.k.a- the “Bain strainâ€) would be necessary. Could simple thermal expansion and contraction provide the trigger to create the new martensite? If so, could quenching from the tempering temperature help the process? It is a tough question.    

 

 Almost every time I have the salt baths running, I like to do little experiments with hardenability or heat treating effects, so I often have a dozen or so 1†samples that I run through at the end of the day.  Coincidentally, just yesterday I did another series with the effects of varying amounts of tempering.  One thing that I always notice in my endless series of hardness tests (I do way too many, but use them to get averages), is the equalization effect the subsequent tempering has on the consistency of hardness.  After the first temper I will get a wider array of readings than the second and by the third things are very consistent and just a few tests are necessary to judge the overall hardness of the piece.  Here is the nasty part- I often will get spikes in the hardness reading after the second temper, that will abate by the third.  Could a newly precipitated microstructure that is harder than the surrounding tempered structures be responsible for this?  This is not a huge spike, and one needs to take a lot of readings to get a big enough picture to notice it, but it is intriguing.  

 

Sorry I know this will probably just muddy the water more, but it is the best I have right now.

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Actually it's great.

It gives an answer to the question of whether multiple tempering are useful or necessary. Experimentation shows yes for consistency. There may be a benefit to do 2 instead of three (at least from a hardness point of view) but it needs confirmation on the whole spectrum of mechanical properties.

There seem to be no question that Martensite formation is not depending on time. So age hardening comes only from carbide formation? What about blade cracking when left alone (is it only after quenching or does it occur also after proper tempering? For after quenching it would be just mechanical constraints related I presume, but after tempering there may be a physico-chemical cause to it (ultimately it's always mechanical constraints))

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Michael,age hardening is more properly called precipitation hardening where precipitates strain the lattice thereby strengthening it.Smaller carbides do more for strengthening the matrix and larger carbides do more for wear resistance. On  quenching  the martensite formed has very high stresses , enough to fracture if not relieved by tempering.Blade fracture is exacerbated by uneven structure ,uneven heating and quenching, and decarburization.

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Don, I just saw a question you asked of me back on Jan 22 that I did not respond to.  By quench temperature, I meant the temperature of the quenchant.  Assuming you do not remove the part from the quench until it has cooled to the same temperature of the quenchant, that is the temperature you must go below to initiate more transformation to martensite.  Again, this presumes the Mf temperature is BELOW the quenchant temperature.  Although I am barely more than a guest here myself, I would like to welcome Kevin Cashen and Mete to this forum.  I have seen Kevin's incredible work and respect his input.  He speaks from both technical and bladesmithing experience.  I don't know if mete is a blademaker or not, perhaps he can fill us in.

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I am not a blademaker ,just a metallurgist with an interest in blades. I,ve joined a number of the forums to teach blademakers about metallurgy so they can make better blades.

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So we've been speaking primarily from the perspective of theory here...  I find all the theory really interesting, but I have to admit I was happy when Kevin Cashen moved from the theoretical to the emperical and started to talk about testing he's done on actual blades.

 

I'd be curious to know if anybody else has done any emperical testing of multiple versus single tempering cycles and what their results have been with respect to wear resistance, shock resistance, hardness, etc.

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Walter, the VAST majority of metallurgical knowlege is EMPERICAL.  It is based upon countless dreary experiments that taught us what is the basis of "theory".  We do have theories about atomic shape and behaviour that are not easily subjected to laboratory experimentation.  However, cooling curves, phase diagrams, isothermal transformation diagrams, tempering curves, etc are all based upon the emperical work of our founding fathers.  From the emperical, we can deduce certain behaviors and create "laws" and "rules of thumb" and other shortcuts.  However, I would expect Kevin would acknowlege that his formal education provides insight and understanding that helps him explain the behavior of metals during heating and cooling beyond what is readily observable.

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Guest Kevin R. Cashen

Absolutely, I would say that without the work done by those who developed the field of metallurgy, I would be blindly fumbling with this stuff, repeating the same errors over and over again simply because of variable too numerous for me to comprehend.  One of the major downfalls of knifemakers is our bullheaded insistence on reinventing the wheel.  There are whole lifetimes worth of experiments and testing that I don't need to do because guys like Austen, Martens, Bain, Grossman, Shepherd etc... have done them for me, and were kind enough to record and publish the results.  "If [we] see farther, it is because [we] stand upon the shoulders of giants."  

 

 I can't count the number of times I have solved problems in my shop by correcting a mechanism that I had no way of seeing, or even proving to an observer that it existed, simply because I had the luxury of having read the results of folks who did have the means to observe it and prove it.  

 

 I test to find answers to my questions.  I wouldn’t even know what questions to ask if I didn’t have the principles provided by the books on my shelves.

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Definitely!  I take it as a given that metallurgy is based upon emperical research.  And that metallurgical theory can help us refine our processes and pose useful practical questions for us as smiths.  I can't begin to tell you how much I appreciate hearing from you guys who have serious metallurigical knowledge on this forum.

 

Hope I wasn't being unclear.  In my earlier post, I was not trying to knock theory, but rather was hoping to hear from some people who have done reasonably methodical tests regarding, say, (and I'm just picking a random example here) the impact of multiple tempering cycles on the wear resistance of their blades.

 

I'm constantly telling myself that I'm going to test this or that shop practice in a rigorous fashion...only to end up making another knife instead!  Sure, we all do tests like the brass rod test and whatnot to make sure our blades meet certain minimum standards.  And we all gradually improve our practices based on observation.  That said, I know that I tend to base my shop practice on data (if that's even the right word!) that's mushy and anecdotal.  I make a knife that seems to exceed previous performance and I go: "Hey, I'll keep doing that."  But because there might have been three or four variables (several of them unknown to me) that distinguished that blade from my earlier efforts, I'm not really sure what made that blade better and I might end up perpetuating some technique that's of no value.

 

Bottom line, I'm just chummin' for data!

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Guest Kevin R. Cashen
...I'm constantly telling myself that I'm going to test this or that shop practice in a rigorous fashion...only to end up making another knife instead!...

That is a real problem, and if you want to stay financially healthy- keep making the knives!  I just finished a new section on my shop that I like to call my "lab", I will soon have a year thrown into building it and filling it with testing equipment and microscopes.  The strain it has put on my finances are much more than I imagined, but the amount of your life that worrying, about every little diffusional process in that blade, can eat up is astronomical.  I don' get paid to look at structures under the microscope, I get paid for making knives, and my wife will not hesitate to remind me of that.     :(   For years the world has been more than happy with knives that have retained austenite in them, how much of our lives do we want to devote to getting that 1% or 2% more out of our knives?  Ignorance is bliss and I will readily admit that I was much happier before I starting looking so far inside of the blades  :(

 

Also, about formal education; I have often described myself as an idiot savant. On the one or two topics that interest me I can immerse myself and absorb information over time, but with anything that doesn’t hold my absolute attention I have the intellect of a tree stump.  In an attempt to counterbalance so much of the bad information out there in bladesmithing, I have immersed myself at every opportunity in ferrous metallurgy, but lure me into stainless, non ferrous alloys or anything with heavy mathematics and you could have no end of fun watching my brain melt down and flow out my ears.   :o

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I just finished a new section on my shop that I like to call my "lab", I will soon have a year thrown into building it and filling it with testing equipment and microscopes.  The strain it has put on my finances are much more than I imagined, but the amount of your life that worrying, about every little diffusional process in that blade, can eat up is astronomical.  I don' get paid to look at structures under the microscope, I get paid for making knives, and my wife will not hesitate to remind me of that.

Hi Kevin.

 

Good to see you here!

 

A quick aside, if I may.  Have you considered offering the services of the lab to other bladesmiths?  It might help bridge that gap at bit.  I can see potential for stuff like that being a little dicey, though.

 

josh

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Walter, then what you are doing in a less formal and rigorous way is exactly what the founding fathers did.  Sir Arthur Conan Doyle said: "The beginning of all science is simple observation".  I was once chastened on a blacksmithing site which has now been shut down, for offering metallurgical insights into blacksmithing processes.  The person, who is a well educated man, said "Blacksmithing is not metallurgy; metallurgy is not blacksmithing".  If there is a definitive line between them, where do you draw the line?  How does understanding the process in any way degrade the the skill of the smith or the beauty of the object?  Blacksmiths are regarded as the fathers of metallurgy.  The statue outside the American Society for Metals and Materials building is A BLACKSMITH!  All metallurgists and metallurgical engineers (there is a difference) owe our blacksmithing forebearers an enormous debt of gratitude for being curious and observant! Not Worthy

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So, I observed, as a blacksmith, that three draw cycles at the same temp had a different effect than two, and a different effect than one, and I was quickly informed that the books said this didn't work.

 

I'm all for science, I'm all for learning.

I'm also for a lot more doing than talking, and personally, I still have this feeling that folks without the letters after thier names are looked down on by those who do, here as well as in other places.

 

 

The answers are not all in the books.

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"if there is one thing you learn at university, is to think critically, then your education is a success! "....  this was a quote from my chem prof that has alway stuck with me...

- alway ask "why" ....  alway test the accepted rules and laws

 

- I'm not sure which books to believe...  but I have also noticed that 2 temper cycles (or 3) does make a blade with better characteristics

 

Thanks to RK, I now am being critical of what I thought was the rule.

 

Greg

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Of course not all of the answers are in the books!  That would imply that we already know everything that can be known.  Take what is in the books and see how it applies to your reality.  If something does not agree, either the books are all wrong, or your observations are flawed.  It is up to you to determine which.    I consider myself as a volunteer consultant on the metallurgical considerations of bladesmithing.  And yes, I could be in error on some issues and if anyone should prove me to be in error, I am man enough to admit it publicly.   I believe in more than talking, too.  I also believe in utilizing the appropriate scientific methods to dispel errors and promote understanding.  Anyone who reads what I say is free to disregard any or all of it for such is the nature of a free society.

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I'm always amazed to hear about the technical/scientific reasons of why things happen. Especially when they are contrary to the things I have observed by testing and observation.

 

A lot of the technical aspects of why things work the way they do is lost on me...and this comes from a guy who began his heat treat experiements with austempering/marquenching low alloy steels instead of with simple water hardening/oil hardening steels. I only just recently began playing with the simple aspects of heat it up hot, quench it in water, and temper it til it "ain't chippy" anymore.

 

I love hear about the chemistry and physics of it all. But I'm always a little curious as to why so mush of it is sometimes contrary to what I have observed or seen happen in practice. Maybe it's a lot like Ju-Ju or Voodoo. It only works that way if you believe that it works that way. And if you don't know how it works (or why) sometimes it's a little easier to get to the crux of the biscuit. :cool:

 

Brian

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Perhaps someone could be a bit more explicit and give us some examples of the things that have been observed to be contrary to what the book says.  I am NOT defending everything in the books.  I once had a young man working for me who graduated from the same school I did and used the same text for Physical Metallurgy as I did.  Only his was the next edition.  He and I got into a debate about the formation of martensite and we both went to the book to prove it.  My book proved my point and his proved his point.  In the intervening years between editions, more had been learned and the concepts had been modified.  Another point is that what appear to be exceptions to the theory is really the result of a small difference in the conditions under which the exception was noticed.  Remember that these experiments are made in laboratories under controlled conditions with precisely calibrated measuring equipment.  As I said, if you find an exception to what is accepted theory, you can either prove the exception or prove your observations were flawed.  To condemn what is the prevailing wisdom without demonstrable proof is nothing more than presenting another theory with even less data.  C'mon guys, lets move from the general to the specific and see if we can figure out what is going on.  There are three metallurgists posting here, one of whom is a respected Master Bladesmith.  Surely we can come to some mutually acceptable explanations.

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Guest Kevin R. Cashen

I see where leaving out specifics can be an issue.  My original post left out a very critical point; my series of tempers in that most recent experiment were not all the same temperature, I start low and bump the temp up as I zero in on my desired HRC.  

 

Mr. Nichols, I for one am tickled to death that any of you serious academics will even give bladesmiths the time of day.  With so much of the information that represents bladesmithing including everything from packing metal molecules to magic energies, I don’t see how we have earned much reason for you to take us very seriously.  It took a very long time to break myself from the mode of thought that had me heating steel with a torch until it looked good, dumping it in the nearest cool liquid, and after testing it by putting it in a vise and yanking, proclaiming that the books were all wrong. I started to doubt that in one afternoon, behind my garage with a torch and a scrap of steel, I had proven Edgar Bain competely wrong.

 

I find the taste of crow so repugnant that now when my results contradict well established metallurgical concepts, I first look for the error in my data.  Most of the time if I give the benefit of the doubt to the eggheads, who did the work under far more control than I have, I will be able to adjust the variables and locate the one that was causing my results to contradict common sense.  There are still some exceptions due to the unique conditions of our craft, but I will never get to the bottom of them if I don't trust a foundation to start from.

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Guest RKNichols
Kevin, you're the first to accuse me of being a serious academic!  :P   I am just a working metallurgical engineer and I use these "theories" to make money for my company and put a few bucks in my own pocket.  My company doesn't make swords, however.  We make pipe for the oil and gas industry; casing, tubing and line pipe.  We heat treat about 40% of the 23,000 TONS per month we put through the plant where I work.  I don't presume to believe that there are not special and unusually situations in heat treating a sword blade especially if you are claying the spine and creating a hamon.  The complexity of the desired microstructure is far beyond what we do to a piece of pipe where we are trying to achieve a uniform tempered martensite.  However complex the structure, it obeys the laws of physics in forming even if we can't understand everything that happens.  If we can begin to understand what is happening, we can predict it and if we can predict it we can control it and use it to serve our purposes.  Heck, you knew that, though......... Super

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Those were specific observations that I quoted before, based on observations involving, oh, I dunno, 400 blades or so, three draw cycles on simple steel, all the same temp, every time they've been  drawn three times there were better results in practical testing as opposed to two draws, or one draw.

 

You said that this wouldn't happen unless differing temps were utilized.

You also said the same thing with normallization, after I said I had good results using the same basic temp.

 

So, seems to me the testing and observation that needs to be done is on your end, since you were the one that pointed out the deficiencies on what I had observed.

 

I'm specifically using the Victor melt of W-1, 1086M from Howard clark, I can send you some if you like, and pretty standard 1095.

I have used decending temperature routines , as well as differing temps during multiple draws and singles... my observations say single temp points work as good, and multiple draws work better.

I've tried other methods in my shop, over years and years.

Just wondering if you have.

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Guest Kevin H

What the heck - I've been off over the weekend doing work & this has gotten more interesting. Actually even got to heat and beat some steel. RH - one question to consider - I'm assuming your temperature controls say you were at the same temperature. Were you really at the same temperature? With commercial heat treat equipment (in good repair), the only way I've been sure that temperatures are relatively the same is to take a digital recorder calibrated and traceable to NIST, stud the furnace with calibrated thermocouples traceable to NIST, (NIST= the National Institute of Science & Technology) and then run a survey. On the electrically heated lab furnaces where I needed to be at +/- 15 degrees F  at 925 degree F for aging of PH stainless steels I wasn't throughout the furnace volume (small volume furnace - approximately 12" x 12" x 24" ). We had to restrict furnace usage to "the sweet spot" that was within the allowable temperature range until I could specify and purcahse a funace with assisted convection to assure temperature unifromity.

 

With electric heat at low temperatures, heat transfer is lousy, unless it's boosted by something like a convective current generated by a fan - even then it's not great. Think about putting your hand in a 500 degree oven - no problem for a fair amount of time. Think about doing the same thing in a pot of boiling water - over 300 degrees cooler than the oven, but instant burn.

 

This isn't meant to be a knock - I'm tremendously impressed by the knives you guys make and post, and the work you've done to learn the metallurgy behind the work you do.  It's meant rhetorically to promote thinking and discussion. As RK said, most of the metallurgical work was based on laboratory experiments with actual steel.

 

One reason I can think of for some changes between what was said then and now, is that in the 70's and before a lot of the simpler steels were made by the BOF process. Now, almost every US alloy shop is running an EAF - residual element content, for elements such as Cr, Mo, V, Ni, & Cu even on a plain carbon steel are all creeping up from what they were in a BOF steel produced with hot metal from a blast furnace.

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Kevin H, yes one of the bladesmith's problems is assumptions.I did some experiments years ago measuring  temperatures visually on an every day basis and checking it with instruments.No you can't hold it very close !! Assumptions of composition too I have explained to blademakers how everything is melted to a range and they may keep to the high side or low side with any element and some of the tool steels have optional elements .So two mills may make the same steel with very different properties.We are now at a time where two other conditions occur .As more and more scrap is used ,some of dubious composition residuals are increasing .Also since China is buying 25% of the steel supply there is a great shortage and some mills make poor steel and say take it or leave it !!

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My low temp salt rigs have run +/- 2 degrees F since I first started building that stuff 10 years ago.

My high temp will run +/- 5 degrees F.

All verified with optical pyrometer when I had access, now verified with an infrared pyro.

IF I need to be more accurate than that then good luck, industrial ht stuff hasn't shown the ability to be anywhere close as controllable as the small "home-built" units that are out there.

I know because I've built some large industrial-weight heat-treating equiptment.

I'm not just a blacksmith, I'm a fabricator/weldor. HAve been since I was 16 in the family business... I've worked in shipyards, steel-mills, rail mills, coal mines, oilfield welding all that tempered martensite crap pipe in -45c canadian winters... so yeah, I'm cracked, but I ain't totally stupid either.

 

+/- 15 degrees is not very tight controll dude, if one of the rigs I build for other folks only held that swing It would get scrapped and re-built.

I can hold that by eye in my forge... anad you are welcome to come with a pyro anytime ya'll want to verify that....bring beer money... :P

 

Here's what I'm trying to point out.

On a number of occasions I've reported things observed over the course of a lot of blades, based on observation. THe reaction by some is fairly immediate... "you can't do that. or it doesn't work that way"

Then ya'll come back and say big fluffy fuzzy things about blacksmiths and thier role in the start of metttalurgy, about observation, blah blah blah...

And from my point of view it doesn't add up very well when I sit back and have a look at was being said.

 

It seems on a large part it's assumed that some folks that are bladesmiths have no education in the field, or no grasp on mettalurgy or have done any reasearch on the subject. I have some books, I have access to any of them I want, I have access to other smiths who have books and the knowledge, I have accesss to mettalurgists as well, and a lab.

 

So, when i said that i found no advantage to using decending temp regimens with normallizing simple steels, it wasn't based on a guess.

But no one stopped to ask me what it WAS based on either before I was corrected.

 

Anyway, I'm not particularly concerned or upset about it one way or the other, I test my stuff more than most people, I know what it's going to do, and I get consistant results for my customers.

I don't have to know big words to know if my HT is working or not.

What does kinda bug me is when I'm trying to help people out a little there is always somebody jumping on and saying "that won't work"...anad talking about something geneally they've never done.

Whatever...

 

This always happens when I get into discussions with mettalurgists, and it's likely my sensitivity to the subject, for sure, so continue on guys, I gotta bow out of thses conversations, it does nothing but get me in a state where I piss everybody off.

 

In any case, if ANYBODY wants to come check out my gear, my temp controlls, and my HT routines, you are more than welcome.

Bring a pyro, some beer money, and some dirty cloths, cause you don't get to be in my shop and just talk... be prepared to pony up...

 

:D

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I'll have to agree with Randal on the +/- 15 degree holding temp.  If my drum forge, which I've been using for over ten years, was that sloppy, I'd scrap it and start over.  

 

Sheesh!

 

Old man Fikes

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