MattBower

Yeah, no real harm in overtempering a tool like this a bit.

i Water quenching wasn't your only problem, and I'm not certain it was the cause of your break, although it might have been. But your grain was a bit large -- which causes brittleness -- and I still think you undertempered. Excessive hardness will indeed cause a struck tool to crack. Fatigue is one possible problem here. But again the grain looks larger than ideal, and the fact that this piece was oil quenched doesn't mean it wasn't too hard. If it's an oil hardening steel -- which I'm guessing -- it probably through hardened. And again it was tempered to straw (although we don't know how it was tempered). I guess what I'm saying is that I don't blame bad steel unless I'm positive I had the heat treat dialed in to start with. Every broken tool provides an opportunity to learn something about how well it was heat treated. If nothing else, I always look at the grain. If it isn't satiny to the point of individual grains being almost invisible, I know that I could have done better.

Please read the "That does it, I don't like junkyard steel" thread from a couple days ago. Almost identical circumstances, and my comments there apply here as well. Your grain doesn't look ideal, and I would guess you undertempered. Straw is likely to be quite hard, especially if you got that color by letting the colors run from an unquenched part of the tool (which makes for a very short tempering cycle). I'd suggest you add at least one more normalizing cycle, and temper significantly hotter - particularly if you don't have the time or inclination to do multiple oven tempers.

Well, he did mention that he's in "Vegas." I only know one place commonly referred to as Vegas. I suggest you get in touch with JPH (Dr. Jim Hrisoulas) on this forum. Dr. Hrisoulas is in Las Vegas. If it's possible to buy blade steels locally, I bet he'll know where.

Flower pots were never intended to take the kind of thermal shock that crucibles endure. They also melt at much lower temperatures than refractory ceramics, and they're not intended to retain strength at high temperatures. Flower pot furnaces are typically lined with some kind of refractory mixture; if they're not, then, as oof said, they won't last long. So no, NO, A THOUSAND TIMES NO. Glad you asked. And no, oven bake "clays" are not going to do the trick, either. (I put "clays" in quotes because I'm not sure they contain actual clay. Even if they do, what's holding them together is not sintering of the ceramic particles, as in any normally fired ceramic.) Small commercial crucibles can be had for decent prices. http://www.lmine.com...budget_graphite Note that there is a curing or "tempering" process for clay-graphite crucibles, which you should follow before each melt to gently drive off any absorbed moisture before taking the crucible to metal melting temperatures.

@dperk: It's definitely a good idea to make flares replaceable, although the SS ones seem to last a good long time for some guys -- I assume keeping the flare tucked back into the insulation is a big part of it. But yes, they are more or less consumable. @mudbgone: That's pretty much my reasoning, too. Some of the commercial venturi kiln burners operate on very low pressure natural gas. ("Very low pressure" compared to the pressures most blacksmiths use with shop-built propane burners.) The fact that they're able to induce enough air flow to sustain good combustion and achieve high temperatures, at such low gas pressures, suggests to me that they must be very efficient. In fact, my natural gas furnace is fired by a row of little burners with the same basic shape. Obviously, if the commercial makers could achieve the same results using a piece of straight pipe, that'd cut their costs -- which would be a competitive advantage. There must be a good reason they don't go that route, and I can't help believe it's because they know they couldn't achieve the same results that way. So yeah, I'm pretty sure there's an advantage to a traditional venturi shape in making burners. @KenH: I've also given a little thought to how to make the internal taper. The mandrel idea is one I've considered (and have not rejected, although I haven't tried it). Another idea that I had was to take a piece of pipe and form the taper in just two dimensions -- in other words, use something like a guillotine fuller to make a constriction at the throat, then, forward of that constriction, forge a couple of flats opposite one another -- just two sides -- and let them gradually merge back to the original round shape. I have no idea how well this'd work, but it might be simpler than trying to form a round taper for most of the length of the tube. I also wonder if there's a real advantage to having the tube round. It might be easier to form the desired shape with square tubing, for those of us who don't have access to lathes.

The machined flares that I have seen are fairly close fits to the tube, but flares seem to work reasonably well even with larger gaps. Threading the flare on can work, too. If you have the means to give the entire tube an internal taper -- or to get your hands on tapered tubing -- yes, I think that makes for a better performing burner. I don't entirely understand why, yet. But based on what Frosty said, and some other things I've read, and the way commercial venturi burners are made, I'm pretty sure there's an advantage to doing it that way: http://www.wardburne...uriburners.html http://www.axner.com...turiburner.aspx

Good point.

Sure, Tim, I understand that sometimes you need the tool right away. I admit that I may occasionally get a little carried away , but I did try to compensate for that by offering the quicker and dirtier alternative: if he wants to temper by letting the colors run, he should aim for a higher temp than he'd use if he were oven tempering. In other words, I agree that the purple or blue that you suggested is probably about right. (Even if the tool turns out slightly overtempered that way, a little too soft and tough is usually better than a little too hard and brittle, when it comes to smithing tools.) I do think at least one normalizing heat before the quench is almost always a good idea, though. It only takes a couple minutes on most hand-held tools.

I agree with Tim. They were both under-tempered, and the chisel on the right was also overheated. (It may not have been during the heat-and-quench cycle; it could've happened during forging.) Like many other things in metallurgy, tempering is a function of temperature and time. Letting the colors run gives the hardened steel minimal time at temp. I prefer at least a couple one-hour cycles in the oven at the desired temperature. If you're going to try letting the colors run from an unquenched part of the tool, you might want to try tempering higher than you would in the oven. (In other words, if you're going to skimp on time, try a somewhat higher temp.) The solution to the grain size problem is normalizing.

Frosty, I don't think you were around when I asked about flaring the entire length of the burner tube about four months ago. That post is here: http://www.iforgeiron.com/topic/24229-venturi-burners/page__st__20 What you're saying jibes exactly with what I was guessing at in that post: However, I admit that I am having a hard time believing that if you stick a little tiny flare on the front end of 8" or 10" of otherwise straight pipe, it's going to have a significant effect on induction at the back end.

Hadn't considered that.That's a thought.

I missed the part where you specifically asked about veggie oils. The thing about vegetable oils is that they oxidize over time ("rancid" is another word for "oxidized"), and that changes their cooling characteristics, among other things. Some folks, like Thomas, don't seem to have much trouble with that, but it seems like many do. I'm sure environment and storage make a big difference. Mineral oils oxidize too, but not enough to matter at room temperatures -- and commercial quench oils have antioxidants added to help extend quenchant life. So they'll last a lot longer. I have quenched in used motor oil. Aside from the fact that it's a slow quench with unpredictable characteristics, I'm really not convinced that's such a good idea from a health perspective. Thomas, for some time now I've been thinking about some kind of immersion heater for my oil. I have used the "quench a big piece of red hot metal" method many times, but I have a feeling that that's much harder on the oil than bringing it up to temp more gently, over 15 or 20 minutes.

For the steels you mention, in not-too-large cross-sections, a medium speed oil would probably be a good choice. The McMaster-Carr 11 second oil or Brownells Tough Quench (Houghto Quench G) both come to mind as options that are readily available. (The 11 second stuff is a little toward the fast end, actually. McMaster also has a 28 second oil, which very well might be fast enough for 4140 and 5160. I'm not sure.) Brownells charges a serious premium on Tough Quench, but the McMaster stuff is about $80 (plus shipping) for 5 gallons. That's not cheap, but it'll last a long time if it's not abused.

It's also worth mentioning that if you want to add to the charge while the crucible is in the furnace, it's probably easier to do that from the top. My oil forge -- which I no longer have -- was designed to be used horizontal as a forge or vertical as a casting furnace. It wasn't a very elegant design, though, and I ended up leaving it vertical more or less permanently. :)

For small charges and pouring with tongs rather than a pouring shank, that could certainly work. But the switch to a pouring shank isn't a bug, it's a safety feature: pouring shanks typically don't have jaws that open, which reduces the chance that you'll drop the crucible. And at a certain charge size you want to be doing a two-man lift, or even using a hoist, both of which would be harder or impossible with a horizontal orientation. I suspect that's why large crucible furnaces are typically vertical, and most of the small furnaces are just scaled-down versions of their larger cousins. Those are my theories, anyway.

Yeah, I'm not sure how the traditional chip forge design would work with oil. Even extremely finely atomised oil is still a liquid, so it's not going to behave like a gas and rise up through the chips. One idea -- realize that I am just thinking off the top of my head here, and I've never seen anything like this -- would be to fire your oil burner into a very well-insulated firebox with the exhaust port on top, covered by some kind of ceramic mesh, or a ceramic (/castable refractory) plate with lots of holes in it. Put your firepot on top of that opening, and fill it with ceramic chips, so that the exhaust from the firebox passes through and heats the chips on its way to the atmosphere. You'd need a very good blower to make this work, if it could work at all.

I really don't think you have anything to worry about in terms of hardness, from the sound of it. Your blade got really hard. It's supposed to do that! Now it's just a few points softer than a file, so your file is cutting slowly. Again -- sounds about right. Just increase the tempering temp a bit until you get the hardness you want.

I didn't answer your question. I don't know if it's possible to fill a hollow metal form with molten metal of another sort. (I mean, I'm sure it's possible; the question is whether it would be practical for your purposes.) I can foresee some problems, but I've never tried it.

In my experience, properly seasoned cast iron cleans up pretty easily. That aside, it seems to me that ceramic coated cast iron cookware already has this problem -- if there is really a problem -- pretty much licked.

OK, I didn't realize he was also selling regular 1084. Do you use a magnet to help check your hardening temperature? The magnet method is far from perfect in general, but for a very simple eutectoid steel like 1084 it's actually a pretty good solution.

I second ONR's question: why? The first idea that springs to mind is to get a bunch of stainless electrodes and weld over the CI with them. One of the more accomplished welders here can tell us if that's even possible, and whether you'd need an extra layer (nickel, maybe?) between the CI and SS. Sounds very expensive if it's even possible. I wouldn't try it. I'm very happy with my CI cookware just as it is , now that I've trained my better half not to put it in the dishwasher.

The 1084 Tracy Mickley sells through USAKnifemaker also has vanadium added; that's why he calls it 1084fg (for "fine grain"). Same deal. You probably don't need more than two normalizing cycles with that stuff unless you badly overheated it during forging. One cycle might do fine. (Crucible's Cru Forge V steel has a healthy dose of vanadium in it, and I'm sure part of the rationale is that the V makes it a little harder to screw up the steel during forging and heat treating.) With regard to the soaks, let me add that the time concerns me less than temperature. (I'm always a little suspicious of propane forges when it comes to dialing them back to moderate temps and getting them to hold those temps reasonably accurately.) If you're confident that you can tune your forge down to around 1500 F, and hold it there, then soaking for a little extra time probably won't do any harm.

By the way, is this Aldo's 1084? If so, the vanadium tends to pin the grains, so triple normalizing may indeed be too much.

The ten minute soaks are longer than 1084 needs for hardening, and for normalizing. For normalizing, all you need to do is kiss the target temperature -- no soak -- remove the blade from the heat and air cool it well into the black. Target temps should be -- roughly, here, since you're eyeballing it -- a shade above non-magnetic, then a half-shade, then just non-magnetic. For hardening, a very short soak (1-2 minutes) is enough with 1084. I'd be a little concerned that with ten minute soaks and spotty temperature control, you may have grown the grain some. Full hard 1084 will be about RC 65. Tempering at 400 will get you down to around 60-61 or so. That's still darned hard. (And kitchen ovens are notoriously inaccurate when it comes to temperature, so if that's what you used I wouldn't count on having hit the desired temperature exactly.) That's likely why your file is barely cutting. (Is it a sharp file? Good quality?) If you want it softer, temper higher. 1084 shouldn't form many carbides, if any, so I doubt that's your problem.