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I had an issue in my heat treat of a short sword and a knife I made from some Damascus I made. I did them together in my Evenheat oven at 1500°. I've HT'ed over 70 blades so it's not my first go around. The steels I used in both of these is 15N20, 1075, and 1084. Easy heat treat, right? Really, as easy as it gets. I use these steels a lot and have never had a problem HT'ing them.  They always come out hard, well, except for this time. I'm pretty sure I know what went wrong but I will tell you what I did, and you can tell me if my suspicions are correct.

First off, I put Satanite on the spine of my knife, and down the center of the sword, but not to the tip or pommel area[it's a full tang]. This is the very first time I have ever clayed a Damascus knife and only the second time I have done it on anything.

I did a 3 stage normalization on both an hour or so before HT.

I started the oven and put the blades in when it got up to around 1250°.

I also placed a piece of 1018 steel bar that is 2" x 12" x 1/4" in with them to use to preheat the oil[which was room temp around 78°].

I took the 1018 bar out at 1450°[it was plenty red] and dipped it in my knife quench tank, an ammo box about 18" long x 6" wide x 12" high for about 3-4 seconds, then I put it in my sword quench tank, a 4" diameter steel tube x 36" long, for about 3-4 seconds. It was about 2/3'rds full. 1 gallon of Canola oil. This is where I think I went wrong. I think I got the oil too hot, and I don't think I had enough of it. I touched the side of my sword quench tube and it was hot. I dipped my finger in the oil in my knife quench tank and it was hot enough to where I could not keep my finger in it, which is pretty hot since my fingers are used to hot and cold due to my job. I handle both on a regular basis. I'm guessing they were 160°-170°.

At any rate, when the oven got to 1500°, I waited about 30 seconds and quenched the knife, then I quenched the sword. The sword sat at 1500° for about a minute.

I file tested them after and they seemed like a HRC60 file skated on both, but now I'm thinking it was skating on the scale, and not the steel.

I took the blades to work and bead blasted the scale off, and cryo treated them for 24 hours.

Pull them out of the Cryo and file test them and both of them are soft as butter. An HRC40 file grabs on both.

I like to learn from my mistakes so if you have any ideas on where I went wrong, please let me know. I'm pretty sure I just overheated the quench oil, but would like to hear your thoughts about it before I HT them again. I think before I do, I will get some of that ATP641 anti-scale solution.

These are the first 2 blades I have HT'ed that did not come out hard. I don't see it being from the Satanite as it was not on the edges, but that sure is coincidental.

Any thoughts? Thanks!

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Two things come to mind:

 

1. Decarb. Try filing a bit more, electric kilns are the most oxidizing atmosphere possible and are known for causing decarburization issues. 

2. How thick was the Satanite?  If it was really thick it might could have prevented a fast enough quench?  I doubt the was too hot.

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The Satanite was about 1/16" thick I would say. No more than .100". Should it be very thin? Even thinner than 1/16"?

Thanks again Alan!

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I glass bead blasted all the scale off before I cryo treated it. Here are some pics of it. In the last pic you can see the spots where the HRC40 file dug in. Normally I grind my bevels before HT, but since I was using Satanite on it, I thought maybe I shouldn't grind the bevels first. Do you grind the bevels before or after HT? And what about if you use some sort of clay on the spine?

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If you are using clay trying for hamon, always grind the bevels before HT.  Hamon is a very shallow effect and is easily ground through.  

Speaking of, 1084 isn't great for hamon, too much manganese.  Aldo's low-Mn 1075 is of course great for it, but needs a water quench for best results. 15n20 kind of takes a sorta hamon.  I wonder...  If your ratio of 1075 to the other two is high, you may be right about the oil being too hot. Although, it would need to be way hot, like over 200 F, to not harden 1084...

Finally, cryo does nothing for any of those steels, so that's a step you can leave out.

 

I still think it's decarb.  In an electric kiln you can easily get total decarb for 1/32" or deeper, with partial decarb to 1/16". And thats from both sides. Carbon loves oxygen far more than it likes iron and will combine fast and easy at high temperatures. 

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you could heat the oil to its flash point and expect a reasonable amount of hardness once it cools to room temp (mar quenching i believe its called) did you harden the tang if you did you could test drill (hss bit) a spot it will get threw any thickness of decarb and stop if you hit the as quenched hardness on eather of the steels mentioned

 

i dont know if you have experienced it before but some patterns/combos of steel dont look as defined after etch if not fully hardened so a differential quench can be an aquerd ascetic 

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Alan, the 1075 is very little. It is very thin strips about 1/32" IIRC. You can see in the pics that there is no more decarb on it since I blasted it off, so I am file testing the steel itself. Before blasting, I believe I was getting a false hard test from the decarb.

 

Dragon, I know the pattern doesn't pop as good on unhardened Damascus, compared to hardened, which is why I have never done clay before on Damascus. I had given it a quick etch before hardening and the pattern popped so I figured I would experiment with it to see how it would come out. This was an experiment I won't conduct again.

 

They say Cryo does nothing for these steels but Cryo does far more than just convert Austenite to Martensite. It relieves any stress in the blade also[some will argue this point, but their arguments are meaningless to me because I see the stress relief benefit every time I hone a Cryo treated engine block, not to mention the fact that engine parts rarely ever break after Cryo], as well as give a better finish when I sand and polish. I have Cryo treated every blade I have made so far since it doesn't cost me anything[I own a Cryo treating business]. I have never been able to break a Cryo treated blade I've made. They'll bend 90° if I want to[and have done]. I also straightened a blade that was bent in the last inch to the tip. I used the three pin method and bent the last inch of tip over about maybe 5/32"-3/16" without it breaking off. That was on hardened 52100 steel. Never had a blade chip or crack either from Cryo. I have seen some amazing things from Cryo, so I swear by it. So everything I make gets Cryoed. Some of the results I personally saw from Cryo when I was paying to have it done is what prompted me to buy this Cryo equipment from the guy that was doing my Cryo when his health got bad enough that he couldn't do it anymore.

 

I'm starting to think that it was the clay that caused this as I have never had a problem HT'ing these steels before. Chalk this one up to a failed experiment!

 

Do you guys think it is necessary to normalize these blades again since they never really got overheated? Or just re-heat treat them?

 

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Fair enough on the cryo, I can't argue the results! B)

 

One thing I will clarify, though: scale is not decarb, scale is oxide.  Under the scale will be clean steel that has suffered carbon loss to the atmosphere.  That's what has to be filed into to hit hard steel again.  What happens is the reverse of smelting.  In an oxygen-rich atmosphere the oxygen will always be trying to bond with everything it can, which is why stuff rusts even in dry climates.  Like all chemical reactions, it happens faster at high temperatures.  This is one major reason why commercial heat treaters use gas injection in the ovens, to remove unbound oxygen.  CO2 is pretty inert, CO will steal oxygen like nobody's business, and O2 will steal carbon in preference to iron. 

 

In smelting, you heat iron oxide in a pure CO  atmosphere to remove the extra oxygen from the iron oxide.  If you want cast iron, you do it fast with an excess of CO to add carbon to the iron.  If you want to use the Bessemer process to turn cast iron into steel, you blow compressed air through the molten cast iron so the oxygen removes the extra carbon.  On a small scale, that's what happens if you heat unprotected high carbon steel in a natural atmosphere.  The oxygen in the form of O2 will combine with the iron to form iron oxide scale in the form of Fe3O4, and the excess oxygen will then steal the carbon from the surface layer of the steel to form CO and CO2.  Since carbon moves through hot steel as a pretty fast rate, like 1/16" per hour at 2100 degrees, the carbon being stolen from the surface is replaced by carbon from deeper down.  That's why I'm betting there is hard steel under a layer of soft steel. 

 

That's also why people use foil in electric kilns, and anti-scale compounds in both electric and fired ovens.  It's not just to prevent scale. If oxygen can't get to the steel, scale can't form, but more importantly for our purposes, carbon loss can't occur.   In a forge, be it gas or solid fuel, the atmosphere is always lower in oxygen than the natural atmosphere around us all the time because we are burning oxygen and producing CO and CO2.  Any excess O2 causes scale, but we can correct for that by running a neutral flame (no excess oxygen, all that goes in is combined with carbon) or even a bit reducing (excess carbon in the exhaust).  In an electric kiln, unless you run an inert gas injection you will be heating in the presence of 21% O2.  That massive amount of oxygen is going to combine with everything it can, producing lots of scale, yes, but also removing carbon from your steel.  

 

Try Brandon's drill suggestion above somewhere it won't show, I bet you'll hit hard steel under a thick-ish skin of soft stuff.  

 

In the event that shows there is no hard steel, well, I'm stumped.  I seriously doubt you were in there at heat long enough to decarb more than 0.005" under the scale.  But that's enough to allow a file to bite, about the thickness of a sheet of heavy printer paper.

 

I know a smith who was producing perfect heat-treats using a drum forge who switched to electric to get better control.  It took him a few months to figure out why the same time/temperature formulas that worked perfectly in the neutral atmosphere gas forge  were producing apparently soft blades in the electric oven.  I am passing along what he learned, here. And it wasn't me!  I still don't have mine hooked up yet...:wacko:  

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Alan, thanks a ton for that explanation! I thought scale and decarb were the same thing. So what you're saying is the steel underneath may be hard. So I will try the drill test as mentioned. Never knew this could happen. Great to know. So, maybe after the drill test(if it shows hard) I just need to grind my bevels and see if hard steel appears. I'll bet you two are 100% right about this as I just can't possibly understand why they didn't get hard. They are as easy as it gets for HT'ing.

 

Thanks again!

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Alan, Dragon, you guys are genius! I tried to drill the tang hole where I plan a lanyard hole(it was even in a spot I clayed) and I got about .050" in and it wouldn't drill anymore. So I did a rough grind on the edge(just enough to get through the surface) and retested it and it now skates a 60 file, and almost skates a 65.! Thanks again!

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Just wanted to chime in here to add a little info on cold and cryogenic treatments (-115F and -315F respectively).  The general consensus by metallurgists (and keep in mind that that is typically hard to come by; so when everyone agrees, chances are it is right) is that the primary benefit is in cold treating, which converts all retained austenite in most steels, but some steels need the cryo treatment to achieve full conversion.  Internal stresses exist between retained austenite and martensite.  Once the retained austenite is converted those stresses are gone.  The newly formed martensite is stressed on it's own, but the steel is now uniformly stressed martensite.  Uniform stresses are MUCH better to deal with than non-uniform stresses.  That is the end of the metallurgist consensus.  There are also some that theorize that there is some submicroscopic precipitation of carbides.  This would reduce the stresses in martensite.  As far as I can tell, that is just theory though, and there is no testing that has proved it.  

 

WARNING:  The above is sound scientific knowledge.  The below is 100% personal opinion.  Merely my take on things for others to consider.  

 

On a related note:  I would put forth that a blade that bends 90 is definitely a failure in HT.  There is no application of which I am aware where this is a practical use of the blade (fencing "blades" are not blades; they are springs and require different heat treat than blades).  Therefore any flexing of a blade to 90 degrees is firmly in the category of abuse.  Stresses are what make the steel hard (carbides don't make the steel hard, they are hard ceramics in a steel matrix).  Hardness is what provides edge retention.  If you are not stressed enough to break when bending to 90 degrees then you are leaving potential hardness on the table.  Yes, I am aware of the ABS bend test.  I am not a fan of that test because it makes people think it is a good thing for blades to perform like that.  At the same time I don't see anything wrong with it for a test of the smith.  If you understand HT well enough to pass that test, then you understand HT pretty well.  My proposal would be that if the smith chooses to HT all their blades to meet that criteria, then they are actually doing a disservice to their customers.  I don't feel bad for people that break their knife using it as a prybar or try punching it through a steel plate.  I feel really bad for the guy that can't skin a deer without stopping halfway through to sharpen his knife. 

Again, this is just my opinion.  Others are entitled to theirs, and if they think a 90 degree bend is important, that is fine.  I also don't really like the color purple, avocados, asparagus, and jazz, but those really aren't relevant to discuss here (not that I care to anyways).  

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On 10/6/2020 at 10:29 AM, Jerrod Miller said:

 

 

WARNING:  The above is sound scientific knowledge.  The below is 100% personal opinion.  Merely my take on things for others to consider.  

 

On a related note:  I would put forth that a blade that bends 90 is definitely a failure in HT.  There is no application of which I am aware where this is a practical use of the blade (fencing "blades" are not blades; they are springs and require different heat treat than blades).  Therefore any flexing of a blade to 90 degrees is firmly in the category of abuse.  Stresses are what make the steel hard (carbides don't make the steel hard, they are hard ceramics in a steel matrix).  Hardness is what provides edge retention.  If you are not stressed enough to break when bending to 90 degrees then you are leaving potential hardness on the table.  Yes, I am aware of the ABS bend test.  I am not a fan of that test because it makes people think it is a good thing for blades to perform like that.  At the same time I don't see anything wrong with it for a test of the smith.  If you understand HT well enough to pass that test, then you understand HT pretty well.  My proposal would be that if the smith chooses to HT all their blades to meet that criteria, then they are actually doing a disservice to their customers.  I don't feel bad for people that break their knife using it as a prybar or try punching it through a steel plate.  I feel really bad for the guy that can't skin a deer without stopping halfway through to sharpen his knife. 

Again, this is just my opinion.  Others are entitled to theirs, and if they think a 90 degree bend is important, that is fine.  I also don't really like the color purple, avocados, asparagus, and jazz, but those really aren't relevant to discuss here (not that I care to anyways).  

First off I agree with your first statement. And I value your opinions. Normally you would not want a blade that bends. Just so happens that the one blade we bent 90° was an ABA test knife for our final project in class. We had to make a knife that would cut a hanging rope, chop up a piece of wood and still shave hair off your arm afterwards, then bend 90° without breaking. I did an edge quench on it. Not even the edge cracked. Edge was unharmed after chopping wood and it shaved. I have straightened a lot of blades that tested harder than 60 that I had to bend quite a bit(beyond the point where I thought they would break) to have them spring back to straight. I just feel Cryo does more than scientists have discovered so far.

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