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Jerrod Miller

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Everything posted by Jerrod Miller

  1. I'm thinking this is getting a bit off topic for this thread so if we really want to go further on this topic we should start a new thread. But to put it bluntly: Yes I have seen temper embrittlement and have broken the test bars (tensile, Charpy, and bend, as well as some actual broken parts) that failed with poor results due to it. Dozens of them. And only dozens because it is well understood by every metallurgist that it happens and we try to avoid it. It only occurs when something went wrong in the process. Could be the wrong HT program was used, bad weld procedure, or any number of
  2. Your proof of concept/proof of process picture doesn't show anything to prove that it was good, let alone better than differentially hardening. Also, you skipped out on quoting the very next sentence from my post:
  3. The book I was referencing it the ASM Heat Treater's Guide. I do not have Larrin Thomas' book. And yes...In theory shorter times at hotter temps can yield the same hardness as longer times at lower temps. This is a fairly dangerous game to play (but to be fair, this is done a lot in industry). Especially with steep curves it is best to avoid that practice. But when you are looking much later in the curve (note that the one you pictured is a log scale on the time axis) then you don't get nearly as much hardness loss for the same amount of hold time. (e.g. The first minute of
  4. This is not normalizing. Normalizing requires a phase change. Keeping it below critical will help with stress relief, but won't do much for grain size reduction. This gets you a little bit of blue brittle martensite, which is bad. If you don't harden it you get a phase change gradient, which isn't too bad at all. Metallurgically speaking, your way is worse. Practically speaking though, I would doubt that it is significantly, or even measurably different. Unless of course you need a harder tang, then you have to do what you have to do. This is very import
  5. This is a pinned thread, so I don't feel bad adding to it so long after the last post. I recently had the "opportunity" (it was necessary) to run a couple chunks of RR track on the spectrometer for work. They both came out as 1060. C~0.62 | Mn~0.73 | Si~0.11 | P~0.026 | S~0.030 | Cr~0.02 | Ni~0.06 | Cu~0.26 | Mo,V,Al, all else<0.01
  6. One can want no Cr, but tolerate a certain level. But generally speaking you want a shallow hardening alloy, and there are many viable chemistry options that will achieve this goal. It is just that a little carbon goes a long way for depth of hardening.
  7. Ii should also add that the aggressiveness of the acid used plays into things a bit, too. Generally speaking, a less aggressive acid is desired because it will be better able to show the differences for its preferred attack (you'll really see it eat at the martensite more than ferrite). If you get too aggressive of an acid then you won't really see the difference as much because it attacks everything quickly. Best analogy I can come up with is this: Imagine sitting next to a road. When you see a car go by at 90 miles per hour, then an hour later the same car passes at 100 mph. Could you
  8. When you use acid to etch steel there are a couple things that come into play: Chemistry and energy. When we etch pattern welded steels, the chemistry difference is the big obvious difference. When you are etching things like a hamon (or other such hardening line, thin or wispy), you are looking at the energy difference. Martensite is a stressed lattice, and therefore is attacked first by the etchant, all other things being equal. So as others have mention with the different microstructures: your fully hardened (100% martensite) edge was readily attacked by the acid, the semi-hardened (mi
  9. I went to show someone these and they are both currently out of stock/unavailable. Not sure if that means they sold out and will be back eventually, or if completely gone forever.
  10. That is because you like to drink the tea afterwards, isn't it? Be honest.
  11. Could be uneven cooling, too. The heating up to austenitic should have relieved all the stresses. Then again, if the grains weren't completely even (say from excessive growth in a single direction due to rolling), that could cause warping with even heating and cooling. So many variables! Isn't this fun?
  12. Or something when wrong at some point after annealing and the bar got bent and re-straightened. At any rate, the bar should have been stress free after annealing, but something could have happened to introduce new stresses.
  13. Have you tried normalizing it? The piece may well have stresses in it that you are causing to be imbalanced as you remove material. Normalize to remove stresses and see how it goes.
  14. Have you checked out FABA yet?
  15. The ASM Heat Treaters' Guide doesn't have 4621, but it does have 4620. I'd say it is safe to consider them the same thing. This alloy is pretty much used only when it is going to be carburized, so keep in mind that the parts you have probably are. Normalizing: Heat to 1695F and still air cool Annealing: Heat to 1425F and rapidly cool to 1200F, hold for 6 hours. Hardening: None listed explicitly, as this alloy is to generally only be hardened after case hardening, so the hardening step falls under that process. In general, it looks like quenching right from the carburizi
  16. I can't imagine them going bad, but possibly picking up moisture, thus the first time heating them should definitely be slow. I would consider that to be a standard procedure from the day you received them anyway. Never used them before though, so I could be wrong.
  17. Check out this thread on M2. Then keep in mind that M42 would be even worse. There is a lot of alloy content in there, and that makes forging a nightmare. The M series is not really for the non-automated sort of work.
  18. In addition to the obvious carbon changes, I would imagine your Mn and Si would vary a bit. Those tend to react with air first (when we are talking about a liquid steel). Your Cr would be next. For more insights on oxidization, check out the Ellingham Diagram. I have never run an Aristotle Furnace before, so the changes may be pretty minimal or extreme and I wouldn't be able to tell you for sure. It is on my "someday" list though. I wonder if this could be a solution for those that want to smelt but only have an hour here or there. The efficiency would go down dramatical
  19. That right there is exactly what I was talking about Alan! You're a bad, bad man. Brian - Stay strong. Explain to the Mrs. that it is a one time thing. Maybe a half dozen, tops. It is educational. You'll "never" build a full on smelting stack. You can make it through this.
  20. Trying to push people to the realm of the Bloomers and Buttons sub-forum. You are like a drug dealer, trying to get people hooked. I'm not sure if you should be ashamed of yourself or not, though.
  21. Can you post a picture of the cracks? It would be interesting to see if it is intergranular or transgranular. My best guess is that the mild steel is just not that good of a material. This is mostly likely to happen with inconsistent chemistries (even in the same bar sometimes) combined with inappropriate heat treat (which could be exacerbated by the bad chemistry). In a nutshell, I would guess the grains grew too much, but even more so the grain boundaries got too much stuff caught in them. Very hard to fix too much junk at the grain boundaries, unlike fixing enlarged grains. Just my be
  22. I've had steel sitting in a vice for a couple days crack on me out of nowhere. I was sitting a few feet away when it cracked and it scared the crap out of me (luckily just figuratively). I was in the process of doing a 3 point bend to straighten out a bend, got interrupted and I guess I didn't back off the vice as much as I thought I did. There is always a chance of stresses being too much. We can just do our best to minimize the chances, or at the very least understand the risks. It drives me nuts at the foundry that there is a lot of air hardening stuff we do that can go a day or more b
  23. Another option is to keep some very hot oil, or possibly boiling water handy. Go straight from the quench to that. Either it will keep the blade from fully finishing the transformation (if you put it in after Ms but before Mf) or it will do a fairly light temper and reduce the harshest stresses. Then just let the blades get to room temp between the hot liquid and the temper and you're good to go.
  24. The purpose of martempering is to rapidly cool the material rapidly to beat the nose of the TTT curve (page 6 here) without actually forming martensite yet. This reduces un-needed stresses and distortions due to the phase change happening along with thermal contraction. I am not entirely sure why they are calling out the 2 different ranges for martempering, other than that the hotter one is probably to make it easy to not get bainite, while the second one is easier to get bainite. Notice that in the TTT it looks like you have over five minutes to cool below the nose of the curve, but watch
  25. Those are both usable, O1 easier than D2. Check out the Heat Treating by Alloy sub-forum for more info on individual alloys.
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