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115crv3?


Aiden CC

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Metallurgy as we know it didn't really become a thing until the 1850s.  "Natural philosophy" was the name in the 1760s when actual science became a thing, and that evolved into chemistry and physics by 1790. Metallurgy was a subset of chemistry at first.  They didn't figure out that carbon was what made steel hardenable until around 1770. They had theories about "purifying" iron by forging really hot in a reducing atmosphere after baking it in a sealed container of bone charcoal starting in the medieval period, but didn't figure out why that worked until  the late 18th century.  Once they figured out how to isolate elements things really took off, especially after the Bessemer process came in around 1856.  That said, toolmakers preferred cast steel to Bessemer ( and the later technologies) well into the first part of the 1900s.  Because it just worked.  They may not have even known about grain, they just knew how to make it work.  

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I don't know if they knew about grain in the sense of what it actually was, but I understand that they would snap steel and then sort it by quality. that's what got me into snapping steel and heat treating by hand and eye. I have no reason to believe for sure that they did anything that resembles that to make butcher plane irons, though. They may have had a furnace that was very consistent and timed the soak. 

 

I never read further about the snapping grain, but understood from whatever I read that razors were at the top of the food chain when steel was sorted, and then files and then further on downward from there. I gather that a whole lot of knowing what made for good results was there, but why and how to manipulate it would not have been seen as valuable vs. having a skilled reliable group doing the work. 

 

I live in Pittsburgh, and each time I see a Bessemer converter (there's one still standing outside of Station Square here, as well as a refractory brick press), it reminds me that making good steel became a lot less expensive, but it drives me up a wall a little bit to match the best of what Butcher and others made very early. there's a whole lot more resolution to this that's not worthwhile here because it relates to tools and sharpening media and supposition about why things were they way they were, but the steel part is attractive. 

 

I've never, as it occurs to me now, looked at knives from that period because I've never seen anything from it. To get a plane iron made in the early 1800s is not difficult. To get one made in the late 1700s is a different story. 

 

Thanks for the timeline on when more calculated moves in metallurgy started.  As many samples as I've snapped, and as many tools as I've, I should know more about it, and I just don't other than hands on with the older tools. 

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1 hour ago, Alan Longmire said:

 what made steel hardenable 

 

By the way, I see that you mentioned elsewhere on here that you heat treat 52100 without a soak. I so much appreciate finding someone else who does this, as I've been working in isolation trying to push 52100 (and others) and in most cases, if I bring it up, the answer is "you'll never get much hardness out of it if you don't have a furnace". 

 

My workflow doesn't fit it, but I also make pencils sometimes and would like to make and fire leads, which will probably be what tips the scales. It's far lower on the priority list than making good woodworking tools, though, and the workflow involves a bunch of thermal cycles and a no-hold strategy for the heat that I think is beneficial. With an induction forge, the process is about ten minutes after forging, and not hours. 

 

 

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The 52100 I have is in either ball bearing or annealed round bar form, and after forging either into a blade-shaped object I figure it's had enough thermal cycles to obviate the need for a soak.  O-1 is another story, but I have Kevin Cashen's micro shots to blame for that.  

 

I do appreciate the value of the snap test. It won't tell you much about carbides, but it does tell you your grain size. The old folks knew if it looked like glass it was excellently heat treated steel, just through centuries of practice. 

 

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Curious about the O1 - what's different? I also don't soak that, but in tools, we don't really use it where toughness is important. It's tough enough for plane irons and chisels not intended for levering and bending. 

 

I found getting target hardness (and later, luckily, better than expected) out of 52100 a little harder to solve. 

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By the way, not trying to pry anything out of you that you wouldn't like to share. My background with this is the first plane iron I ever got, I followed a video that showed to just overheat O1 a little bit. That's not how the video described it (it was a DVD on how to make moulding planes in a style of about 200 years ago). The method works well as long as the quality of the O1 stock is good. I never really considered going back and thinking about how good it is vs. more, and this year, I got a hardness tester and tested a whole bunch of older stuff I made. Needless to say, I learned pretty quickly that I was undershot a little bit on things where you need to get carbon in solution - some of those things I'd solved, and then some I solved later using the hardness tester and snapping samples. My very first O1 iron was just heated, quenched (starrett, and I later found that is spheroidized, but knew nothing about any of that back then). 

 

I proceeded to make a fair number of plane irons, and one of them matched an iron of french make, but labeled in the US when i tested plane irons later, and it was also just heated pretty quickly past nonmagnetic and then tempered. Almost all of them where I had enough heat for the quick overshot were 61-62 hardness, and I wondered what all of the hullaballoo was about heat treatment. Getting introduced to more steels was kind of like going from point and shoot black and white camera to color 35mm manual, and now I really like the process a lot more and was encouraged on what to do learning about thermal cycles because I couldn't live with the idea that you need expensive equipment to match old tools. I think that's still true, though I usually use an induction forge both for forging and for normalizing and cycling, maybe out of laziness. 

 

Being introduced to knife folks and the whole concept of toughness beyond "enough to not have to think about it" was new. it's been a lot of fun and had I bought a furnace early, I'd have missed out on a lot. maybe a lot of things that have no commercial value to me in the end, but it's my hobby. 

 

(the very first iron i made is in a small plane and works well - it tempered at 400F to 61.5. For woodworking, there's not a whole lot that needs to be done better, but if you're pushing yourself in a hobby, then it's different than what has to be done just to be successful making a usable woodworking tool). 

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4 hours ago, David Weaver said:

Curious about the O1 - what's different?

 

No secrets here, that's part of the spirit of the forum!  I never used to soak O-1 either, and sometimes I still don't if it's the steel I have handy in the right dimension for a quick tool.  At the 2015 Ashokan hammer-in, Kevin Cashen did a talk with slides about how he does O-1.  Kevin is a great guy, a true steel nerd.  He is so into it he set up his own metallography lab.  He has two Vickers metallurgical microscopes (one is a parts machine) designed to produce images like those Jerrod has posted.  He has the lapping machines to produce the micron polish needed to really see the microstructure.  On top of all that, he's the only bladesmith I know who is so into steel that he bought an electron microscope :blink:.  He got it cheap because it needed some hard-to-find part, but still, he has an electron microscope in his shop.  

 

Anyway, in his talk he showed some slides that explain what happens to O-1 with no soak, with short soaks, and with longer soaks up to 30 minutes.  The basic takeaway is you can certainly do O-1 by eye and seat-of-pants. Heat to bright cherry red, quench, and it's hard.  Thing is, you're not getting the utmost performance possible that way.  It's fine for 99% of end users who wouldn't notice much difference, but now that I have seen the evidence of what can be done, I hate to do it quick and sloppy.  IIf you treat it just like 1095, it's going to act like 1095, and get the job done.  But if you treat it like O-1 and use multiple thermal cycles (normalizations) to get the grain refined (assuming a forged piece, if stock removal from spheroidized that's fine, but not strictly necessary), then soak at 1525 F for up to half an hour, you get the fine carbide distribution combined with fine grain, which equals much increased edge holding and toughness for a given end hardness.  He did these tests on round bar, not blade sections, so there is room for tweaking the soak times.  The simile he used was "Not taking advantage of the full potential of O-1 is like having a car with dual quad carbs and a supercharger, but blocking off one carb and disconnecting the supercharger.  It'll get you from A to B, but not nearly with as much performance as if you used the whole thing."  And as long as you control for decarb, you still have that lovely long window to quench in.  With 1095 you have less than a second to get from 1425 to below about 900F or it won't harden fully.  With 5160 you have something closer to ten seconds to go from 1525F to under 900F. With O-1, you have close to a minute to beat that curve.  Total relaxation in the quench, in other words.  Just don't try it with water or brine!   

 

I only have the oven because I wanted to use stainless steels for my pocketknives, and you can't easily do those long holds at 1925+ degrees in most forges.  I have a little two-brick propane forge that, once it's warmed up, can be tuned to hold at 1525F all day long.  I use that for my O-1 chisels and pocketknife blades just because the atmosphere is better suited to control decarb and there's no foil to mess with in the quench.  That said, I snapped the tips on two of my O-1 die-sinkers chisels I use to do silver inlay into steel on the last hawk head I made.  I think I'll use the oven on those to get the highest performance I can out of them after I anneal and regrind them.  They're used just like carving gouges, but on mild steel or wrought iron.

 

That's the thing with high-alloy steels and soaks:  Carbon moves fast, like 1/16" per minute, at 2000F.  Tungsten, chromium, and vanadium do not.  They take their sweet time.  As long as you know the temperature at which grain growth begins for a given alloy, you can ride that fine line for a long time to ensure you get the maximum distribution of the non-carbon parts of the alloy.  Thus for forged O-1, I consider all the time at heat while forging as part of the overall soak time.  For pocketknives that are stock removal only on stock that is spheroidized, I try to work in thermal cycles and a decent soak.  

 

The stainless I use for pocketknives is AEB-L or 13c26. It's the finest-grained stainless I know of, and takes a finer edge than the supersteels.  Doesn't hold it as long, but it's easy to sharpen.  Behaves much like 1095 in that regard.  But O-1 makes a better blade, performance-wise.  It just rusts. 

 

O-1 is really good about slow grain growth as well.  A friend who was getting into repousse asked if I could make her some matting punches.  The time-honored way to make a fine textured matting punch is to use W1 or 1095 rod forged to the desired profile, file or saw a notch all around, and bring that end to a white heat and soak for a few minutes.  Let that cool to black, reheat to nonmagnetic, quench and snap at the line, and boom! Perfect matting punch texture on the broken end.  Well, I had no 1095 or W1 on hand, but I did have some O-1.  Even after ten minutes at yellow-white the grain, while noticeably larger than it should be, was still too fine to be a good matting punch.  I ended up going to the old bolt and screw shop to buy some W1.  

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Thanks for the explanation - I am in the boat of at this point trying to find a steel that's got relatively fine carbides, or forging O1 (but not commonly) for plane irons. 

 

I always thermal cycle it now after a stiff pair or three heats if not forging it, but I don't soak it and where I lose out is just what you say. If the carbides in bar stock aren't to my liking (large spheroid, especially), there's only so much I can do without soaking. 

 

It (mine) definitely lacks toughness if it's just heated quickly and quenched - early on, I didn't know anything about thermal cycles and was only forced to learn about them two years ago when trying to push 26c3 to better a couple of old ward chisels. The only way it would separate itself from those tools is with a dose of thermal cycles, and once I learned that by snapping samples, I was off to the races. 

 

I'll look around to see if I can find more. 

 

i'm a woodworker on top of being an amateur toolmaker, and mostly by hand. Stability of the edge is more important to me by a long shot, so I am far from abandoning steels like O1, unlike the wider woodworking community. O1 is a wonderful woodworking steel, and I'm hesitant of it only in thinner chisels - especially seaton chest types. 

 

And for that same reason, I love AEB-L. I do the unholy practice of heating it really hot in a narrow tube with high heat, quenching it fast and then double tempering it. I don't know what I'm giving up, I'm sure there's something, but I end up with knives that test 60-61 at the spine, and one of them inadvertently flew last year (the one in the middle here) when I left it on a belt sander before it had the handle, but after it was ground, and then turned the sander on. it went several feet, nailed a tool cabinet, stitched a rasp tooth like thing in the side of the cabinet and fell to the ground. No damage!

 

My reasoning for using it as a cheat until I finally break down and get a furnace at some point is that there really isn't much to it. It's got a zillion tiny carbides and not enough carbon to really do unholy things. XHP has been OK, too - same idea - but it has gobs of carbides. I get it almost to yellow heat quickly, quench the top end of the quench in oil, throw it in plates for about five seconds and then finish it in water and throw it in the freezer. I'm no bladesmith and don't sell knives, only end up making them for people who I've made tools for. But I would like to get further into forging and forge some knives - that's down the road. 

 

fiKz34w.jpg

 

Much appreciate the conversation. It's lacking online, the "I can do it and figure it out and then do something else if it doesn't work" rather than dogmatic "only this schedule works". 

 

Nobody has broken one of my chisels or knives yet, which is somewhat of a surprise, but there are maybe only 100 knives and chisels that I've made floating around. I hope to go pro or semi pro in retirement (tools, not knives) making things that are harder to make if not working freehand. working with propane (sometimes Mapp for the stainless steels) and induction forge had really accelerated the amount of experimenting - one can normalize and thermal cycle and quench something in 10 minutes and see what the results are, and that's just so valuable when getting a new alloy or material from a different supplier. Even the O1 varies enormously, as you know. Both in what the snapped samples and carbide patterning may look like, but also in woodworking tools. Some is just better than others for a stable edge on a smoothing plane.  

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The only person I have fought with regarding methods of heat treating was because he was quite dogmatic about things that were just demonstrably nuts.  

 

I suspect your use of the induction forge is very helpful with the AEB-L, too.  Heating steel.uniformly from the inside out is fairly magical.  One of these days...  and yep, those tiny carbides and relatively low carbon are the greatest thing about AEB-L. I figure if they use it almost exclusively in razor blades it has something going on for it.

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  • 4 weeks later...

I cannot thank you enough for all this info. I recently got some silver steel and was looking for some decent info on HT seeing as the min/max terraces on both chrome and manganese seemed pretty wide.

 

This is my first post, been lurking for quite a while.

 

@David Weaver I have to say I'm surprised that there would be graphitization, I would have expected you'd need a lot more silica for that to happen. My knowledge on it isn't enough to say though, and what you said about being intentional for self lubricating properties makes sense, surely it could be managed if was the purpose of the exercise. 

 

@Alan Longmire I've had some experience with carbon migration, and know it's supposed to be very quick (if memory serves Verhoeven also mentions it in his book on HT) but I have found it to be notably less in practical terms. 

 

I expect the rate mentioned is for moving randomly, being if you had one carbon atom how much would it move around (potentially back and forth), not what distance would it cover. And that a hellova lot of movement can be done without much actual diffusion taking place (for instance from a high carbon to low carbon area).

 

The reason I say this is because I case hardened a wrought iron blade, putting it in a canister with calcium carbonate and fine charcoal, and shoved it into the forge when I was welding up some billets. It spent about 2 hours at more than 1000 celcius in there. Following the carbon diffusion diagrams it should have been pretty uniform carbon distribution.

 

Unfortunately the blade cracked in the quench (full water quench, and outsude couple of micron would have been close to cast iron I expect. Live and learn). 

 

I took the opportunity to polish and etch to see how deep my carbon penetration was,  and is was notably shallower than I expected. Calipers said 1.6mm for the dark parts (extremely thick blade. Spine was around 5.2mm).

 

I figured it may have just been the fact that its a very shallow hardening steel (being from wrought iron and all) and that what I was seeing was martensite, with the core still having carbon, just not showing on the etch since it hadn't hardened, but grinding past the black layer showed a drastic reduction in sparking on the grinder.

 

I'm sure that the diffusion rate is scientifically correct, but I believe translating it into practical terms of how much diffusion took place to be less predictable.

 

20191207_121659.jpg

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@Jerrod Miller nope, ill give it a look right now, thanks!

 

*edited* ok, I've read through it. Thanks a bunch, that makes sense. I had it at welding heat which would be around 1100 celcius for almost two hours, so 1.6mm sounds in the right area.

 

I have to admit the error function math is a bit beyond me, but I will tackle it and attempt to understand to the point where I can run my own equations. Thanks very much again for that.

 

I have a couple of questions regarding the calculation if you don't mind.

 

I expect the purpose of the calculation is to predict the carbon percentage at a specific point, meaning that in the example the area at 1.5mm depth would have 0.8%C, as opposed to an average carbon content and a penetration depth, meaning that there would be an average of 0.8 in the carburized area and the area would extend up to 1.5mm.

 

Is this correct?

Edited by Rean Lubbe
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8 hours ago, Rean Lubbe said:

I expect the purpose of the calculation is to predict the carbon percentage at a specific point, meaning that in the example the area at 1.5mm depth would have 0.8%C, as opposed to an average carbon content and a penetration depth, meaning that there would be an average of 0.8 in the carburized area and the area would extend up to 1.5mm.

 

Is this correct?

Yes, that is correct.  

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On 10/17/2023 at 1:01 PM, Rean Lubbe said:

I cannot thank you enough for all this info. I recently got some silver steel and was looking for some decent info on HT seeing as the min/max terraces on both chrome and manganese seemed pretty wide.

 

This is my first post, been lurking for quite a while.

 

@David Weaver I have to say I'm surprised that there would be graphitization, I would have expected you'd need a lot more silica for that to happen. My knowledge on it isn't enough to say though, and what you said about being intentional for self lubricating properties makes sense, surely it could be managed if was the purpose of the exercise. 

 

I have to admit that when reading about intentional graphitization, it was for much higher carbon steels if I can recall - plain steels that are 1.5-2% carbon. I think. But I could be wrong. I did see that silver steel and those really higher carbon steels can be used with precipitation hardening. I'm just a guy in a garage but I've got relatively good skill hardening and tempering and am not afraid to push quench speed. 

 

Are you in europe?

 

I think my personal issue mentioned in this thread is batch related, and would bet that if I were in europe and could just go to another supplier, the next 115crv3 rod would've been just what I wanted. 

 

In the states, i'm in limbo using W1 and 52100, but I have experimented enough with 52100 to push the hardness to high levels (68/69 out of the quench and 63/64 after a long double temper at 400F, or I guess that's about 205C if you're most other places in the world. ) That's quenching in brine, though - brine could not get my rods of 115crv3 to harden to spec or survive even tempering. 

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This is interesting. From what I read, it's best to case harden mild steel, is it not? that makes the core tough and malleable, the outside tough because of the carbon. Won't you harden a carbon steel core at the high temperature and pressure, then if you quench, the core will be brittle and break? Is it necessary to quench a case hardened knife to heat treat? Didn't the case hardening harden it?

 

Rean I like the look of your case hardened knife a lot. That would look gorgeous with a nice sashikomi polish. I'll have to experiment with case hardening now! I'll probably just put a mild steel blank in a crucible with a bunch of charcoal in my melting furnace for an hour or so and see what it does!

 

Do you guys know of any case hardened knives for sale? On a google search, all I found were knife skins for a video game!

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I read a bit more and it answered some of my questions! From what I've seen elsewhere online, it's usually mild steel and wrought iron that are carburized, but I suppose you could do it on any steel, provided you let it cool before heat treating. If you just carburize without heat treating, you leave the surface brittle, with many different forms of iron, so it does need heat treating. Carburizing is just a type of case hardening, as is through hardening and differential hardening. It sounds like I can just wrap a mild steel forged blank with charcoal, flour and salt, then clay, heat it in the forge and leave it at critical for 45 minutes, then let cool, then heat treat as usual. Saves a crucible, and looks like a worthy experiment!

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@David Weaver I'm in South Africa, so our selection isn't nearly as good as either the states or Europe. The only big thing we have going for us is that the country isn't that big and it's pretty centralized in the middle (and smallest) province, so things are relatively close by. Bohler's south african branch is about 60 miles from where I live.

 

There's about 3 sources for silver steel here, but all buy from the same importer, and thus have the same batches, so if mine is dodgy I expect ill just go back to my standard of 52100.

 

I'm a bit surprised you get such good results with W1, we don't get an equivalent here so I can only go on hearsay and reading, but doesn't it have massive fluctuation in carbon content? 

 

IMO, you can't go wrong with 52100 for cost vs performance and reliability.

 

I have to ask, what do you do to get those results? I also push the boundaries of "best practice" a little, but use a thermostat controlled kiln.

 

Personally I soak at the high end of recommended temp, then just before I take it out to quench I push an extra 15 degrees celcius (takes around 20 seconds for the kiln to get to it).

 

The reasoning behind it being that it takes a bit of time for grain to grow, which I want to avoid, and the time-frame is short enough that i don't see any grain growth, but the little extra heat makes a noticeable difference.

 

Please note I don't do this for anything above 0.8 carbon, as I've learned the hard way that brittle plate martensite is indeed a thing. Thus the asking how you get those

Edited by Rean Lubbe
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10 hours ago, Carlos Lara said:

it's usually mild steel and wrought iron that are carburized

 

There are some alloys made specifically for case hardening, but the reason people don't make case-hardened knives is that you eventually sharpen through the hard layer.  It's handy for bearings, wear points, and cheap files, though.

 

That's also why pre-Bessemer steels (shear steel, anyway) in the west were always refined by stacking and welding thin bars of carburized iron. It tends to even out the carbon, reducing the chance of soft spots. It was never a perfect process, though, which is why Huntsman came up with cast steel for clock springs vie melting shear steel in a sealed crucible.  Separates out the slag and evens out the carbon at the same time.  

 

More to the point with the Japanese style stuff you like to play with, a shallow-hardening steel like tamahagane (or W1!) will indeed have a hard outer layer over a tough core.  Thin profiles like blades will through-harden, but not thicker ones like, oh, a katana spine.  ;) That's what hamon is, using clay and selective polishing to reveal the difference between where it hardened and where it didn't.    

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14 hours ago, Carlos Lara said:

it's best to case harden mild steel, is it not?

It depends on the application, often it is not best.  

14 hours ago, Carlos Lara said:

that makes the core tough and malleable, the outside tough because of the carbon.

Carbon generally reduces toughness.  

14 hours ago, Carlos Lara said:

Won't you harden a carbon steel core at the high temperature and pressure, then if you quench, the core will be brittle and break? Is it necessary to quench a case hardened knife to heat treat? Didn't the case hardening harden it?

A case hardened piece will have been quenched.  You can carburize the surface without quenching, too.  The point of case hardening is to change the outer layer (case) to have a chemistry that will harden readily while the inner chemistry remains less hardenable.  If one only heats/quenches the surface and not the center, that is surface hardening, which is also useful.  Surface hardening can be done with flame or induction pretty readily.  I suppose it could be done well with molten salt baths and other fun things, too.  

13 hours ago, Carlos Lara said:

If you just carburize without heat treating, you leave the surface brittle

No.  It will be brittle if you quench it without tempering, but if you carburize and slow cool it will be as soft as it is ever going to be.  

13 hours ago, Carlos Lara said:

with many different forms of iron

It will just have pearlite (and possibly ferrite, depending on chemistry) if slow cooled, just martensite if quenched.  

13 hours ago, Carlos Lara said:

Carburizing is just a type of case hardening, as is through hardening and differential hardening.

No.  Carburizing is one step in case hardening.  It is just the adding of carbon to the surface layer.  You still have to quench from appropriate temperature (either straight from the carburizing cycle or a secondary heat treat cycle).  Through hardening is not done with case hardening, and is in fact counter to the goals of case hardening.  Differential hardening can be achieved via chemistry, like case hardening, or by temperature control, like surface hardening.  

 

3 hours ago, Alan Longmire said:

the reason people don't make case-hardened knives is that you eventually sharpen through the hard layer.

This is also something to think about with differentially hardened blades.  Hamons may look cool (beauty is in the eye of the beholder for things like this), but they definitely mean there is less hardened steel than a through hardened piece and you will eventually use up all the hardened steel before you would on a through hardened piece.  This is why I personally do not like to see hamons anywhere near the edge.  That is too much of a sacrifice of functionality for my tastes, but it isn't a big deal for others.  

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12 hours ago, Rean Lubbe said:

@David Weaver

 

I'm a bit surprised you get such good results with W1, we don't get an equivalent here so I can only go on hearsay and reading, but doesn't it have massive fluctuation in carbon content? 

 

IMO, you can't go wrong with 52100 for cost vs performance and reliability.

 

I have to ask, what do you do to get those results? I also push the boundaries of "best practice" a little, but use a thermostat controlled kiln.

 

so, for both W1 and 52100, I use an induction forge for heat treatment. There's no hold time, but rather normalization by cycling. 

* Forge

* Two strong normalization cycles (like temperature around where you'd get scaling) and cool to nonmagnetic plus some for all but the quench, but not a complete cool and not down close to tempering temperature. Two minimum, but sometimes three or four. 

* quench in brine just as the last of the normalization cycle group is going to go to nonmagnetic. this is underheated for 52100 and will result in perhaps something like 64 out of a brine quench, but the point is that I so far see less distortion on the final quench if doing this. there can be some distortion here - I heat the steel and remove it in the next steps. 

* heat to the point of transitioning to magnetic multiple times. As low as I can get that point to be. It can be anywhere from three to six, and cools are to about black heat or at least when sensing there is no lack of magnetism. it's nice to have several pieces going at once for this so that you aren't standing staring at one piece. 

    - the first one of these is where any significant distortion is removed by light tapping on the anvil - as straight as I can get things by eye

* heat to nonmagnetic, then heat past. This is not well defined, I guess. You have to get a feel for how much a steel allows. 1084 will bloat almost instantly with higher heat. 26c3 is slower to do it, same with 80crv2, O1 is slower than 26c3, and 52100 seems to be at least as slow as O1 or slower. It also benefits the most from a push. 

 

I have not bought etch yet to polish and etch a sample and measure grain size, but 52100 is a fraction of the grains you'd find in a commercial nicholson file, at least by look - which is what one would expect, and it's still finer than just getting a sample out and heating it moderately and quenching. 

 

With W1, the brine is almost mandatory unless something is very thin. if something is very thin, I use parks 50 instead. 52100 in chisels has tolerated it fine - here is a mortise chisel I made yesterday. It's 52100, surprisingly 69 out of the quench (67 an hour out of the quench, 69 the next morning average of multiple strikes). 

 

64 after a strong 400F double temper and I did knock the tip off to look at it -the grain is as fine as I've had with any other method, but the behavior is definitely changed by what is what.....lack of retained austenite or reduction in it? I don't know. I like the change for chisels. 

 

I would not know how to use an electric furnace without a bunch of experimenting as I've heat treated several hundred items and gotten to this over time testing hardness and snapping samples to look at grain size ,and then evaluating chisel performance (stronger/harder and tough enough is better in a woodworking chisel than toughest possible and then hardness secondary - well, at least for performance. Making consumer chisels that are hard to break without bending for proof of abuse might be different). 

 

I see on larrin's article that he was able to DET anneal 52100 and get over 67 hardness out of a sample. I think if he pushes heat up a little and uses a brine quench, he'll be at 69, so I don't think there is any rule breaking doing this other than that the last heat takes experience to learn, and this obviously isn't going to work for anything that really needs a long high temp normalization soak. I have samples that larrin tested when I was let's say 85% as good at this as I am now and they are good - O1 matches larrin's graphs, 26c3 is about twice as tough on average as larrin's charts - but i don't know if the high tail of those charts is real testing or software estimated. But I think 26c3 is not a great candidate for a furnace due to the potential for plate martensite, and the ability to shoot temp high with an induction forge or a high heat forge for a very short period of time may have some merit. 

 

By the way, the skill part of this is a little harder with 52100 because of how much range it has. W1 is easy because it doesn't really gain anything by pushing more than just a little past nonmagnetic for a short period of time. hardness is about the same either way, so no reason to risk bloating. it's important doing this to actually count time and note color and bloat grain, which I typically do. but I haven't for W1 because I already kind of handled that with 1095 and I have a hardness tester now. I'll do as little overshot as possible without sacrificing hardness. In a short heat overshot (like 15 seconds), there is more room than most people think....except 1084, which bloats almost instantly. 

 

..... Which brings me to my last comment here...

 

....W1 is a really wide spec on internet charts. At least one supplier here in the US (precision industries) offers it in a much tighter spec - it's min 0.95% and max 1.05% carbon, so as long as you're getting the same thing from the same supplier and it's branded like their W1 is, you're safe. I have not bought any other W1 because it's too uncommon to find a melt sheet or something specifying what it is. if it's .75% carbon, I have no use for it. If it's 1.3%, I may not either, but I doubt much ever sells with much over 1%. 

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precision's spec - 

 

https://www.precisionbrand.com/wp-content/uploads/2021/07/certs-drill-rod-water-hardened.pdf

 

This doesn't say W1 that I could see, but it's what mcmaster carr's spec for their W1 is on their site, and a couple of the cut offs still had a "watercrat" (the brand name they use for this steel) was listed on the tag. 

 

EDIT - I see W1 in the footer at the bottom. My broken samples show carbides just bigger than 1095 and with slightly more disparity in size.  

Edited by David Weaver
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Thanks everyone for the feedback! Haha, I clearly still have much to learn!

 

So if I want to carburetize a Japanese style tanto, so it's nice and dark grey/black like Rean's, and grey deep enough I don't polish it off with a proper sashikomi, but the carbon doesn't migrate too far in and make it brittle in the quench, how should I go about it?

 

My thoughts are to use a thin layer of charcoal and calcium carbonate in a clay casing, then leave it to heat in the forge for two hours while I'm working on other stuff. Maybe take it out once or twice for a short while to make sure it's not too hot for too long. Then, try differential hardening once it's totally cooled off, but use mineral oil to try and reduce the chance of breaking. Is it like Japanese forging that you just assume half of them will break in the quench? Can you assume that if it's black, it must have a particular carbon concentration, or is colour separate from concentration? Should I forge the tanto really stout, or can I reduce the migration by limiting how much carbon is available around the blade?

 

I suppose I could just use a treatment to make a more ordinary blade black, but the trouble is you'll take the patinated layer off with a polish! I suppose I could also polish the blade, patinate it, then polish it again, but you'll have to at a minimum polish off the patinated layer at the edge to make it sharp, and I'd like that deep grey/black right to the edge. The trouble too is that Rean's carburized blade has lots of depth to the grey, which is ideal for sashikomi, whereas a patinated black usually looks pretty superficial.

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Hey @Carlos Lara

 

There's a fair bit here, so here goes. I'll try to explain the whole concept a bit more - thanks for the interrest.

 

You probably know most of this allready, but it's easy to get some misconceptions about things that bite you in the butt later when you know enough about something that there's just one part that was missed and it completely throws the thing off. Long story short im not trying to be condenscending by going into basics, just running through the whole thing from the ground up.

 

8 hours ago, Carlos Lara said:

So if I want to carburetize a Japanese style tanto, so it's nice and dark grey/black like Rean's, and grey deep enough I don't polish it off with a proper sashikomi

 

When the blade broke, I polished it and etched it with ferric chloride (its an acid that leaves a black patina, but discolours steel more or less depending on what state it's in, if it has carbon in it and has been hardened it leaves a deep black colour - martensite, has carbon but isn't hardened often leaves a fuzzy grey - pearlite, and if it doesn't have much carbon in it tends not to do much - ferrite).

 

So my steel isn't actually that colour, it just had a patina applied so I could see where I had carbon and where it had hardened. People usually do this to make a hamon in a blade more visible as well.

 

Onto the carburizing part, it doesn't make it harder or anything else and isn't a heat treatment like case hardening, it just adds more carbon. That's it, the end.

 

It's just something you would do to turn a very low carbon steel (or iron in my case - the definition of steel is just iron with enough carbon in it, when people talk about iron in this context they just mean it doesn't have enough carbon to be called steel) into steel that can be hardened.

 

Onto case hardening as a heat treatment: it literally just means hardening the outer part of something (its case).

 

You could do this in the way I did it by adding carbon to the outer part through cementation (the technique of having your low carbon stuff in a very carbon monoxide rich environment at high heat for a good while, the carbon gets absorbed and forms "cementite" which is just a fancy word for iron carbide) and then heat treating it the normal way: heat it up, quench it, temper it.

 

When you do it this way only the outer shell gets hardened because only the outer shell has carbon.

 

Another way is to take a shallow hardening steel like 1095 and just heat treat it normally, it needs to go from hot to cold *really* fast to harden. So what happens is that the outer bit cools down fast enough to harden, but because the inner part cooled more slowly, being way on the inside, it didn't harden.

 

That way you also get something that only has the outer part hardened.

 

The third way is the one you'd usually find in a kobuse katana, where you wrap some high carbon steel around a core of lower carbon stuff and weld them together. Then only the outer part would harden since only the outer part has enough carbon.

 

So "case hardening" is the heat treatment, and we can make it happen a couple of different ways, while "carburizing" is only adding the carbon, and in this case was done specifically with cementation.

 

More to come, but I gotta take my daughter to extra math class

Edited by Rean Lubbe
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