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Martempering 15N20/1075 damascus


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So I've completed and played with my low-temp salt tank to compliment the high one. Whee! It heats very evenly. Quenching into it is really anti-climactic. Nothing happens! I was expecting violent bubbling and boil over. :ph34r:

 

I'm having a little trouble nailing down some facts with regards to martempering 15N20/1075. The first being if it's even a good idea due to the slightly hypoeutectoid nature of those steels. I do hear that oil quenching steels will martemper, and both of these are arguably oil quenchers, at least at blade dimensions. I certainly *could* simply quench in 150F Parks #50, clean up and temper in the low temp salt... the primary function here is escaping my kitchen oven's 28.5" diagonal length limitation. However, if possible, I'd love to enjoy some warpage reduction and convenience with my new toy tool, in steel materials I have in spades.

 

For experimentation's sake, I heated a piece of the aforementioned combination up to 1455F and quenched it into 500F salt. The piece felt like it hardened a little as it cooled, but didn't seem to fully harden on reaching room temperature. I lowered the temp to 400F and tried again with somewhat better results. I tempered it for a half hour (it was midnight by this time...) at 525F or so, since Kevin Cashen in another forum suggested that martempering results might not be immediately perceptible until after tempering. I have a fairly springy piece, but I can bend it if I try, so again I think I missed something. I'll temper it some more this afternoon and see if that changes anything. It seems *different* than anything I've experienced, and it's possible this is simply what the material should be like, maybe I'll go for a more springy temper to see how the material responds.

 

Current theories for better results include raising my initial heat temperature (I have been in the habit of keeping it low due to inequalities in the high temp salt tank which I think I have resolved, thus I think temps that used to average out above my internal thermocouple's reading are now reading more accurately...) I'm also variously thinking that 500 may have been too low, as evidence suggests that the Ms for .75C should be on the higher side; or that 400 may have been too high, as evidenced by some folks who claim to quench into 350F oil/salt. (Is this really martempering anymore?)

 

I'm not finding good information on the Ms numbers for these materials. I note from searching here that Jake and Ben Potter have used 1075, going from 1500F to variously 475F and 375F, though of course, this may have changed since questions were posed in the forums. I did find a mention of a piece that Howard Clark "marquenched," online made of 15N20/1084, so I suppose anything is possible.

 

Anyway, anyone have martempering experience with this combination?

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THis may not be good advice, since it comes from experience with different steel and temperatures.

I have noticed that I get a thin layer of decarb even when using my salt pot (austenitizing). It is very thin and can be polished away quickly with a fine belt on the grinder.

Without taking the decarb away, a perfectly hardened blade feels like less than fully hard and will take a set if flexed. After the thin decarb is ground away, it will spring back eagerly and not take a set.

 

I thought perhaps this was what you experienced.

 

I am looking for numbers on Ms and Mf for 15n20.

That will tell if you get some autotempering at the higher temperatures in the quench bath.

 

I´ll get back soon as I find anything.

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Thanks, Peter.

 

I should be quite lucky if the problem turns out to be resolved with a little sanding! ;) I'll try that.

 

I'll also raise my austenitizing temperature and try another piece. Having raised the level of my high temperature salts and placed a much more efficient lid on the heating chamber seems to have really evened out my temperatures, making my internal thermocouple much more accurate. If anything, they're a little hotter towards the bottom, when they used to be hotter at the top.

 

I still haven't found a TTT or CCT for either 15N20 or 1070 / 75. :huh:

 

Though looking at 1084, which I did find, the Ms is about 430F, and 1070 / 75 can't be too different. I'm thinking 1500F into 450F will be a decent bet.

 

Maybe tomorrow afternoon. Argh, one more week of my terrible, busy schedule writ with exams at school and I'll have a lot more time to play experiment.

 

Peter, did I remember that you were curious to build something like this low-temp tank in another thread a ways back? If so, I seem to have found some nice, simple solutions I'd certainly share. I added another pic in the 10 Year Saga thread.

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Well, I got to play around a lot this afternoon. The good news is that a 450F quench seems to be the trick. In my set up at least, with 15N20 / 1070 at a 1450-1500F high temp range.

 

The bad news is I was straightening out a rather nice blade I thought wasn't hardened.

 

It was. :blink:

 

However, as a result, I had a really typical long pattern welded piece to experiment on in ways I'd not try if I thought I had a perfect blade. All systems go!

 

Peter, I think you may have been right about a thin decarb layer on that piece, which is a cool thing to know. Thanks for that insight.

 

Sigh.

 

Back to the forge!

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Well, I got to play around a lot this afternoon. The good news is that a 450F quench seems to be the trick. In my set up at least, with 15N20 / 1070 at a 1450-1500F high temp range.

 

The bad news is I was straightening out a rather nice blade I thought wasn't hardened.

 

It was. :blink:

 

However, as a result, I had a really typical long pattern welded piece to experiment on in ways I'd not try if I thought I had a perfect blade. All systems go!

 

Peter, I think you may have been right about a thin decarb layer on that piece, which is a cool thing to know. Thanks for that insight.

 

Sigh.

 

Back to the forge!

 

Ms temperature for 1065 is 525 and Ms for 1090 is 420F - so what you found empirically is about right. I have not found the Ms temperature for 15n20 but it is very high - much higher than 525F. I found the data on p 79 of "Practical Guide for Metallurgists" - very practical little booklet that is a freebie.

 

As an approximation:

 

Ms (°F) ~ 930 - 600 x C - 60 x Mn - 20 x Si - 50 x Cr - 30 x Ni - 20 x Mo - 20 x W from E. S. Rowland and S. R. Lyle, Trans. ASM, 37, 1946, p 27.

 

 

I agree that you probably have a slight decarb.

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Thanks for the condolences, Peter. :( I feel your pain.

 

Scott, thanks for the response and the resource, it's very helpful.

 

A few things I noticed and a follow up question, if I may borrow your expertise for a moment...

 

Peter's scenario seems plausible for this piece, but at the time I cracked it, it had been quenched in 400F salt. I thought it was unhardened enough to gently untwist it. The crack occurred in the edge material, which I'm 95% sure was laminated 15N20. Tiny chance it's possible it was laminated 1070.

 

In the meantime I quenched several small 15N20 / 1070 flawed blades for experiments. They were all 48 layer *tight* twists; effectively tight enough to count for higher layer counts... about 50-100. (Lucky for me I have a LOT of them. ;) )

 

At 450F they were hard but bent a bit before breaking. At 475F they snapped clean, with no indication I could ascertain with regards to layers.

 

When I requenched the big blade at 475F, it definitely seemed harder, but also kind of "tough". Though I hear this is to be expected I have no physical reference point with which to compare it. It had a little bit of give and broke along layer lines after major torquing. Crunchy-like. I could even post pictures.

 

Is it possible that the low layer counts of this Migration style pattern welding hardened the layers differently since the Ms of the 15N20 is so much higher? (This would be a cool modern echo of the fable, see, all that "hard and soft layers" made it tougher stuff...)

 

Is it possible that the 15N20 is still hardening due to the quenching effect of the 450F curve getting it below the high Ms point regardless, and that basically only the 1070 is getting the martemper effect?

 

Either way the warpage is extremely reduced, and the big blade that broke only twisted, and mildly at that, after being normalized, quenched twice and bent a bit. These salts rawk!

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Thanks for the condolences, Peter. :( I feel your pain.

 

Scott, thanks for the response and the resource, it's very helpful.

 

A few things I noticed and a follow up question, if I may borrow your expertise for a moment...

 

Peter's scenario seems plausible for this piece, but at the time I cracked it, it had been quenched in 400F salt. I thought it was unhardened enough to gently untwist it. The crack occurred in the edge material, which I'm 95% sure was laminated 15N20. Tiny chance it's possible it was laminated 1070.

 

In the meantime I quenched several small 15N20 / 1070 flawed blades for experiments. They were all 48 layer *tight* twists; effectively tight enough to count for higher layer counts... about 50-100. (Lucky for me I have a LOT of them. ;) )

 

At 450F they were hard but bent a bit before breaking. At 475F they snapped clean, with no indication I could ascertain with regards to layers.

 

When I requenched the big blade at 475F, it definitely seemed harder, but also kind of "tough". Though I hear this is to be expected I have no physical reference point with which to compare it. It had a little bit of give and broke along layer lines after major torquing. Crunchy-like. I could even post pictures.

 

Is it possible that the low layer counts of this Migration style pattern welding hardened the layers differently since the Ms of the 15N20 is so much higher? (This would be a cool modern echo of the fable, see, all that "hard and soft layers" made it tougher stuff...)

 

Is it possible that the 15N20 is still hardening due to the quenching effect of the 450F curve getting it below the high Ms point regardless, and that basically only the 1070 is getting the martemper effect?

 

Either way the warpage is extremely reduced, and the big blade that broke only twisted, and mildly at that, after being normalized, quenched twice and bent a bit. These salts rawk!

 

That certainly makes sense. What you could have also done is created bainite in the 1070 - making it nicely tough, but still had martensite in the lower hardenability stuff. For grins - try a 1070 blade with only 1070 and austemper it, i.e., hold at Bs (°F) ~ 1526 - 486 x C - 162 x Mn - 126 x Cr - 67 x Ni - 149 x Mo for a period of time - then quench. You will end up with a baiitic structure - hard and tough. Maybe not real hard - maybe 53+ HRC but it will be real tough.

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Ms temperature for 1065 is 525 and Ms for 1090 is 420F - so what you found empirically is about right. I have not found the Ms temperature for 15n20 but it is very high - much higher than 525F. I found the data on p 79 of "Practical Guide for Metallurgists" - very practical little booklet that is a freebie.

 

As an approximation:

 

Ms (°F) ~ 930 - 600 x C - 60 x Mn - 20 x Si - 50 x Cr - 30 x Ni - 20 x Mo - 20 x W from E. S. Rowland and S. R. Lyle, Trans. ASM, 37, 1946, p 27.

 

 

I agree that you probably have a slight decarb.

 

Scott,

 

On further reflection, I was trying to figure out why that Ms for 15N20 was so high and I realized that we seem to be talking about different steels.

 

My contents as listed from the source, Admiral Steel, are as follows:

 

C .75

Mn .75

Si .25

Ni 1.5

 

I realized that in another forum you had compared it to 15B22, which reads really different, (notably missing carbon,) though still not the numbers above.

 

When I calculate the figures from Admiral, (here: http://calculations.ewi.org/cgi-bin/IgorCGI.exe/ ) including for various variables, I consistently come up with 350F - 400F numbers for the 15N20, which place near, again depending on exact composition, to the 1075 (Correction on my part, the material from Admiral is listed as 1070/1080, and the carbon may run as high as .88. I don't have the exact specs they sent on hand, but will find or obtain them.)

 

This leads me to conclude that the first heat treatment indeed suffered from the stiff decarb, OR that quenching into 450F and 475F worked better because of an actual alloy content as opposed to one on paper, i.e. if I had low carbon content within the specs of both of these alloys, the Ms is raised in one case to 404F, and the 400 quench could have just missed it. The high temp tank has a range from top to bottom, but the low temp one seems very consistent throughout.

 

Another variable I am considering is time spent in the low-temp tank, up to 10 minutes on the large piece, for "equalization." Should I think of this process more as a controlled interrupted quench with these alloys and quench into oil / water as soon as possible after inspecting & adjusting for warpage?

 

Am I missing something?

 

Edited to add: I found the specs on the 1075: C .74, Si .16, Mn .65, Ni .04, Mo .008, Cr .19, V .005, Co .008, B 0.0. The calculator says 399.88F for Ms. Now. For the 15N20. Phone calls have been made...

 

Further edited to add... according to the formula above, when I calculate the alloy contents that I have (specs, not actual certificate figures,) I come to a Ms of 475F for the 15N20...

Edited by J.Arthur Loose
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Another variable I am considering is time spent in the low-temp tank, up to 10 minutes on the large piece, for "equalization." Should I think of this process more as a controlled interrupted quench with these alloys and quench into oil / water as soon as possible after inspecting & adjusting for warpage?

 

Yes, that is more time than you need. All you need to do is get the piece down to the temperature of the salt, then cool it in still air. I have used this technique on many hundreds blades made from 1086m/L-6 as well as several other alloys and combinations in pw materials. I generally use 450f with as much water as it will hold in solution at that temp for quenching. The exact temperature you use to quench is not the most critical piece of the puzzle. How much moisture is in the salt can and will radically affect the heat extraction rate of the quench, and the cross section and chemistry are a lot more important than the temperature of the quench, in my experience.

 

I know it is not the correct term to say mar-quench, and it is technically correct to say mar-temper, but that invites a great deal of confusion, since the piece still has to be tempered afterward, just like with a regular quench in some other material. So that particular convention is one that I disregard, and do not really care if anyone approves of it or not.

 

Keep playing with it and find a set of numbers and conditions that work for you, with your stuff and materials. It will all come together for you I am sure. :)

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Scott,

 

On further reflection, I was trying to figure out why that Ms for 15N20 was so high and I realized that we seem to be talking about different steels.

 

My contents as listed from the source, Admiral Steel, are as follows:

 

C .75

Mn .75

Si .25

Ni 1.5

 

I realized that in another forum you had compared it to 15B22, which reads really different, (notably missing carbon,) though still not the numbers above.

 

When I calculate the figures from Admiral, (here: http://calculations.ewi.org/cgi-bin/IgorCGI.exe/ ) including for various variables, I consistently come up with 350F - 400F numbers for the 15N20, which place near, again depending on exact composition, to the 1075 (Correction on my part, the material from Admiral is listed as 1070/1080, and the carbon may run as high as .88. I don't have the exact specs they sent on hand, but will find or obtain them.)

 

This leads me to conclude that the first heat treatment indeed suffered from the stiff decarb, OR that quenching into 450F and 475F worked better because of an actual alloy content as opposed to one on paper, i.e. if I had low carbon content within the specs of both of these alloys, the Ms is raised in one case to 404F, and the 400 quench could have just missed it. The high temp tank has a range from top to bottom, but the low temp one seems very consistent throughout.

 

Another variable I am considering is time spent in the low-temp tank, up to 10 minutes on the large piece, for "equalization." Should I think of this process more as a controlled interrupted quench with these alloys and quench into oil / water as soon as possible after inspecting & adjusting for warpage?

 

Am I missing something?

 

Edited to add: I found the specs on the 1075: C .74, Si .16, Mn .65, Ni .04, Mo .008, Cr .19, V .005, Co .008, B 0.0. The calculator says 399.88F for Ms. Now. For the 15N20. Phone calls have been made...

 

Further edited to add... according to the formula above, when I calculate the alloy contents that I have (specs, not actual certificate figures,) I come to a Ms of 475F for the 15N20...

 

No - you are not missing anything. I misread it - I was thinking that you had a laminate of low carbon steel with a high carbon steel. I goofed. Thank you for calling it to my attention. The Ms temperature that you determined empirically is about right.

 

Because the section size is small and the thermal mass of the salt is high, I would use a much shorter time at the martempering temperature.

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Yes, that is more time than you need. All you need to do is get the piece down to the temperature of the salt, then cool it in still air. I have used this technique on many hundreds blades made from 1086m/L-6 as well as several other alloys and combinations in pw materials. I generally use 450f with as much water as it will hold in solution at that temp for quenching. The exact temperature you use to quench is not the most critical piece of the puzzle. How much moisture is in the salt can and will radically affect the heat extraction rate of the quench, and the cross section and chemistry are a lot more important than the temperature of the quench, in my experience.

 

I know it is not the correct term to say mar-quench, and it is technically correct to say mar-temper, but that invites a great deal of confusion, since the piece still has to be tempered afterward, just like with a regular quench in some other material. So that particular convention is one that I disregard, and do not really care if anyone approves of it or not.

 

Keep playing with it and find a set of numbers and conditions that work for you, with your stuff and materials. It will all come together for you I am sure. :)

 

Thanks, Howard. I appreciate your feedback.

 

I'm with you on marquench as a word, by the way. I put it in quotes because everyone says it's wrong, but that is how your customer described it. So many folks get confused about "tempering swords by quenching them," that "martemper" just seems wrong. It's a quenching process, with possible tempering side effects... :huh:

 

I'm curious about this water-in-the-salt thing though. How do you determine how much is enough? I assume this speeds the quench, and seem to recall that it can create more violent bubbling. Perhaps I'm wrong there.

 

At any rate, I have a few wide-open days to experiment, so fun is to be had...

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Jol,

I have read about the water in the salt too and while what I've read makes since, I'm not sure how you test for it either.... From what I understand it is not just water added but the water combines differently than just soaking the salt? I'm assuming it combines chemically some how....? Is it the same king of thing going on like with anhydrous borax but in reverse?

 

Dick

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Water in the low temperature salt is an inevitable reality if you live here in the conrnpatch. The stuff is hygroscopic, which literally means it sponges moisture from the air if there is any. In Iowa, the only time there is not enough moisture in the air to cause a puddle on top of the non-heated low temp salt is now, in the dead of winter, when it is -5F outside. This will soon change, and it will be humid again soon (possibly in two or three days when it snows and gets back up to near freezing).

 

So then, what do you do about that ? What I finally settled on was heating it to 232C(450F) and using it at that temperature for quenching. Lower operating temperature means there is more water in solution here when it is humid, and higher temperature means less water in solution, whatever the conditions otherwise. Driving all the water off seems to occur at about 300C(575F). Or alternatively, if you leave it heated for a very long time, most any temperature will eventually drive all the moisture off. At 232C there is some boiling when you quench a blade, but it last only a second or two, and anecdotal evidence indicates to me that it speeds heat extraction. Lower temperature with more water seems to slow it down, as does being hotter and dryer. I have not ever actually conducted a proper experiment with thermocouples and recorders fast enough to provide proof of this, but I have done experiments in the hundreds with knife sections (blades) made of low hardenability steel with fine grain and can move the hamon up and down the sides of the blade by altering these conditions. Moisture content, temperature, section size, grain size, and chemistry of the alloy all have significant influence on what microstructures you get, and where they are, and how well you control that.

 

Add to that the options of control available with high temp salt to austenitize (which I also believe can result in higher heat extraction rates in the beginning of the quench as the liquid film of ht salt blows off the surface, especially in water quenches), and things can get quite complex. :)

 

So in brief, too much water is bad, and if you ramp the temp of your low temp salt up too fast with water sitting on it, it will boil over and you lose all you salt. :( If you boil all the water off it is safe, with no boiling when you quench a hot work piece in it, but the heat extraction rate is 'not quite' as fast as it 'can be'. The sweet spot for me is 232C(450F).

 

Maybe Scott can shed some light on industrial salt process for mar-tempering. I know I have seen references to moisture level monitoring and steam injection someplace.

 

On the very rare occasion that I want to add moisture, I dip out of a bucket that has some salt in it and was left open to the atmosphere. This bucket is full of salt/water, and has very beautiful crystals of KNO3 in the bottom, and the solution is mostly NaNO3 and NaNO4. It's all the pick up of solid stuff from the floor, full of dirt, after boiling it over the sides from heating it up too fast. I Always meant to filter and clean it and boil the water off to re-cycle it, but somehow just never get around to it. :rolleyes:

Edited by Howard Clark
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Exciting stuff, Howard. I am doing a boatload of reading at the moment and genuinely motivated to unlock some mysteries now that I have the technology.

 

I have been covering my salt with an airtight seal to prevent moisture from getting in, as I had thought it was a potential danger exclusively. Interesting to consider it another variable, though I think I have enough on my plate for now. ;)

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Thanks Howard,

I think have read this before in another thread ( maybe from youwink.gif). It was good to read it again... I hope I can retain more of it this time, senior moments and allcool.gif

 

Jol, I buy popcorn in 50# bags at a time ... the first year I bought it that way I kept in inside... about december of that year I noticed that is was not popping like it should and got to where half of the kernals didn't pop... I was storing it inside.... I moved the bag out on my screened in porch and within a week it was back to "normal" ... popcorns need about 6 to 10 percent water content to make it explode ... so during winter your pots being inside are probably on the dry side of the sweet spot Howard mentioned...

 

Dick

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Thanks Howard,

I think have read this before in another thread ( maybe from youwink.gif). It was good to read it again... I hope I can retain more of it this time, senior moments and allcool.gif

 

Jol, I buy popcorn in 50# bags at a time ... the first year I bought it that way I kept in inside... about december of that year I noticed that is was not popping like it should and got to where half of the kernals didn't pop... I was storing it inside.... I moved the bag out on my screened in porch and within a week it was back to "normal" ... popcorns need about 6 to 10 percent water content to make it explode ... so during winter your pots being inside are probably on the dry side of the sweet spot Howard mentioned...

 

Dick

 

Ha ha, I thought you were going to tell me that mousepoop doesn't pop in hot oil!

 

My studio is very dry in the Winter and very moist in the Summer- I have to run a dehumidifier. I'm just trying to be in the habit of covering it carefully. I think I'll skip intentional water contents for now. ;)

 

Last night I discovered that I can get a nice gold / blue on my stainless damascus material, though I had to heat them up to 850F, and there's sections that didn't get the blue. I think they're the sections I sanded right before firing... I wonder if it's is a reaction with alloying element oxides. Curious! And they say it can't be done... :ph34r:

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Last night I discovered that I can get a nice gold / blue on my stainless damascus material, though I had to heat them up to 850F, and there's sections that didn't get the blue. I think they're the sections I sanded right before firing... I wonder if it's is a reaction with alloying element oxides. Curious! And they say it can't be done... :ph34r:

 

Jol,

Who says what can't be done?

 

 

Ric

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Jol,

Who says what can't be done?

 

Ric

 

Exactly! :lol:

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According to the ASM metals hand book volume 4 the addition of water can drastically affect the quench speed of molten salts to the point that they are faster than most oils. The whole section on Martempering is fascinating but the section that describes it best starts on page 339. They have a chart detailing what percentage of water to salt works for what temperatures on the page after.

 

Oh and just for you Howard, "The term martempering is somewhat misleading and is better described as marquenching." pg 324 of the very same book. Let people disaprove it if they want, the people who literally wrote the book on this stuff seem to agree with you. ;)

 

 

I have the book in PDF form if you would like it JOL. Or its an easy find via Google.

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This is an interesting thread .

Peters comment on the decarb skin and how it makes a blade feel/ behave has really helped to solve a problem I have had with crossbow prods not returning enough power .

ones I have scraped down from larger stock post Ht are kick ass however the ones with fire finish do not perform to their optimum .

I had never correlated the two

there are jems of knowledge all over the place here .

Edited by owen bush
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Yes, Peter's comment regarding decarb on the surface is relevant to many things, Owen. It is especially important with springs. Think of the Scandi blades with hard core and soft sides. It doesn't take much depth to the soft sides to make a great deal of difference.

 

Gems are where you find them, and can be hidden in unexpected places sometimes. Like mushrooms. :)

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