low tech HT friendly steels?

Discussion in 'Shop Talk' started by inferno, Aug 6, 2019.

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  1. Aug 6, 2019 #1

    inferno

    inferno

    inferno

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    I'm planning on making a knife from scratch. my tools at hand will be:
    belt grinder, angle grinder, stones, paper etc

    and for HT i will have a 150kw handheld propane burner, acetylene torch (very big and beefy), and then i'm investing in a thermocouple and an instrument to plug it into. for tempering i will get one of these cheap tabletop mini ovens.

    I was planning on putting the blade in a steel tube and crank up the heat until i get them temps i want.
    This is not really a serious/pro or very repeatable way of HT-ing steel and i know that :)

    So now i would like to hear from you guys which steels you think is appropriate for this way of HT-ing. Obviously SS and tool steels are out of the question.
    I know 1095 and similar will work pretty well. But in reality i want to do O1, but i'm not really sure my low tech approach will be able to keep a constant temp for the longer soak times it requires to get good.

    so i found these the most interesting:
    UHB 20C (1095)
    UHB 15N20 - C-0,75 Si-0,3 MN-0,4 Ni-2,0
    80CrV2 - C=0,85 Cr=0,6 V=0,15 Mn=0,35
    UHB 26C3 - C-1,25 Si-0,25 MN-0,4 Cr-0,3
    Uddeholm Arne (O1)
    100Cr6 (only round stock) approx C 1,0 Si 0,25 Mn 0,3 Cr 1,5 Ni ≤ 0,4
    90MnCrV8 (O2) - C 0.85-0.95% Si-0.1-0.4% Mn-1.8-2.2% Cr-0.2-0.5% V-0.05-0.2%
    Böhler K510, 115CrV3 (only round stock) C 1,18% Si 0,25% Mn 0,30% Cr 0,70% V 0,10%.

    Which one of these is most friendly for low tech HH-ing would you guys guess (except for the 1095 of course)?
    I'm guessing the lower they are alloyed the more optimal (well) i will be able to get the HT. I wonder what i can get away with here. should i forget O1 completely?
     
  2. Aug 6, 2019 #2

    Caleb Cox

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    I suggest "fail fast and fail cheap" with standard 1095 bar stock very close to the final tang/spine thickness you desire. Make a few dogs while you build skills and tweak your HT setup. Another benefit besides cost is the massive amount of data on this steel, which will help your research and troubleshooting efforts. When you then try other steels you will probably find one that you like the working properties of, and your comfort/skill level is more important than steel chemistry.
     
  3. Aug 6, 2019 #3

    RDalman

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    Yea, go for 80crv2 or 15n20. try to hit 850 no soak time, right to oil quench in 60c warmed canola (willys eldorado rapsolja prima billig lösning)
    temper low and long, maybe in the 150-170c 2x2h. That should make a impressive blade even with those simpler steels. Have fun, use some dustmask.
     
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  4. Aug 7, 2019 #4

    milkbaby

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    Agree with Robin, 15N20 or 80CRV2. You can get away with a shorter soak on those whereas 1095 will do better with longer soak due to the extra carbon, as well as 1095 needs a very fast quenchant (water, brine, or fast engineered quenchant) something not practical by backyard heat treat. 15N20 and 80CrV2 should be very close to eutectoid without a lot of alloying elements to distribute and do okay without a longer soak, they also do not need as fast a quenchant, therefore warm canola oil works well. You can normalize then thermal cycle down the steel to refine the grain before the hardening step, and supposedly the V in 80CRV2 will help pin the grain boundaries to keep the grain from growing large quickly upon overheating which can easily happen near the tip in backyard heating situations. 1080/1084 is also amenable to backyard HT, though I'm not sure how easy to find where you live.

    Google it, but basically I cycle like this: Normalize ~1600F (a shade or two above non-magnetic), air cool to black. Thermal cycle: ~1500F (half a shade or so above non-magnetic), air cool to black, ~1400F just below non-magnetic, air cool to black. Then you can go through your hardening heat treat.

    You may want to invest in some soft refractory firebrick or other type of refractory insulation instead of trying to HT directly in a steel tube by itself. Don't use hard firebrick as it's not refractory and will just be a heat sink.

    Some people are happy with their backyard HT of O1, but I doubt they get the performance out of it that very good HT can get. In that case, you just waste money by paying more for O1 over the cost of 15N20 or 80CRV2.
     
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  5. Aug 7, 2019 #5

    inferno

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    cool. 80crv2 and 15n20 it is then.
    we have motor oil and hydraulic oils at work. will these work too?
     
    Last edited: Aug 7, 2019
  6. Aug 7, 2019 #6

    inferno

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    are these steps necessary?
    are these for grain refinement or similar? what is the goal with these steps?

    I'm thinking that after rough grinding i will have to do some type of stress relief (i'm guessing there will be some soak time here) and then cool to room temp.
    then straight to austenitizing, or?

    I read that one can do a double quench for grain refinement if needed. basically harden it twice in a row. But will this be needed?
     
  7. Aug 7, 2019 #7

    milkbaby

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    The normalizing will result in stress relief. Basically, it helps get everything (carbon, alloying elements) into solution and redistributed which. A further issue is that the normalizing heat can be high enough heat to grow the grain size, so then you thermal cycle with descending heats to refine the grain.

    I believe if you have steel that is supplied in coarse spheroidal state and you simply cut and grind, then you can just go directly to hardening HT (austenitizing). Robin or Kippington can chime in and correct me if wrong. Very fine spheroidal will have issues with lower hardenability, so if supplied in that state, you'll probably want to normalize to bring it back to a state that has higher hardenability.

    Yes, you can double or triple quench and there is some advantage to that tho TBH I'm not sure if refining the grain is one of them. It should be on Larrin Thomas' website knifesteelnerds.com and he may have wrote about it here on KKF or Bladeforums bladesmith/shop talk subforum. I just do: normalization, thermal cycling with descending heats, austenitization, quench (just once on the austenization/quench). Technically each time the steel is heated above the austenitizing temp you're austenitizing it, but you get the jist...
     
  8. Aug 7, 2019 #8

    RDalman

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    Yea go right for hardening with your setup. The motor oil will make a LOT of really nasty (cancerogen) smoke, but probably work. For a chef knife you want a big amount, up towards 10 l. Be wary of the risk for oil setting on fire, so have a lid handy. A electric grill lighter if you have one is practical for preheatingthe oil. Clamp the blade between a couple of flat thicker pieces during tempering for straightening if you need.
     
  9. Aug 7, 2019 #9

    RDalman

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    Also on steel, since you mentioned arne as O1. You also have groundflatstock in the uk, they have really wide selection of steel, for only a pretty small premium being flat ground.
     
  10. Aug 7, 2019 #10

    inferno

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    Allright I ordered some Thyssenkrupp 80crv2, 15n20 and then some Böhler O1. Should be arriving tomorrow i think.

    Today I have been looking at thermocouples. Been reading a bit on BF. And it appears many think 3mm is a good diameter.
    I have also noticed that you should not put the probe in the flame. Because then the TC will not last very long.

    So I was thinking about drilling a hole in my 150mm dia pipe and then welding in a stainless tube that reaches in to the center of the pipe. The end inside the pipe will be closed.
    Then the TC will not be subjected to the open flame. Will this work? Is there any reason for this not to work?
     
  11. Aug 8, 2019 #11

    inferno

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    I recieved my steel today. :)

    started working a little on the pipe "forge". basically i cut up a pipe we had laying around and then selected a few other parts i will need to make a stand for it. tomorrow i will weld it up.

    also ordered a temp meter (amprobe) and 3 thermocouples. 1 fluke with 220mm probe tip and 2 longer ones (no plastic handles on these) from another company since i think i might actually melt the handle on the fluke depending on how toasty this actually gets. but it will be useful for other things.
     
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  12. Aug 8, 2019 #12

    Caleb Cox

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    Awesome! Keep us posted and work safe!
     
  13. Aug 8, 2019 #13

    inferno

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    safety is my middle name :)
     
  14. Aug 9, 2019 #14

    milkbaby

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    Have fun! It seems like your Tc plan is okay, but worse comes to worse you just kill the probe /shrug
     
  15. Aug 9, 2019 #15

    inferno

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    I almost finished the forge today. took me about 4,5h and 1h, at least, was simply testing if it would work at all.
    all material was scrap material i found at work. you can see the donor pipe there in the corner of forge1.jpg :)

    i'm basically commenting on the pics, and they are labelled forge1-8.

    so first i had to find out if this would work at all. and it looked like it would. i'm just blasting the burner right through the pipe at full blast. the part inside got very light bright orange, almost yellow/white but not pure white. But i only ran it for about 5 minutes the first time.

    after that test run of the pipe the actual pipe was 650C lol. measured this with an IR thermometer. but since i dont know the emissivity of that pipe it could be 100C higher or lower i guess. if i positioned my hand about 10cm away from it i could only hold it there for about 5-6 seconds before it got too hot for me. but i'm very used to hot stuff. since i work with the burner almost daily. ymmv i guess.

    burner has a 60 or 65mm cup, all titanium.

    i welded a long flat bar under the pipe since i had a feeling i would need to attach some accessories when i start using it. i just dont know what yet. but i know there will be something.

    finished product can be either axial or radial fed. when i welded on the radial pipe i noticed it was snug with the cup, the exact same diameter. it made sense to build it like this. but if i pushed the cup in there so there was no gap between cup and radial feed pipe then the forge would not work. then it was just a regular flame coming out of the ends. but if i had the burner outside the radial pipe it would work. i think i starved it for oxygen. so then i had to weld on a bigger radial pipe on the first one so there would be some kind of air mix going in. then i got some juice out of it!
    you live and learn.

    welded in some SS tubes that i welded shut. thats where the thermocouple will reside.

    welded a stand for it. the plate was not "safe" enough for me so i welded some extra long flats on the under the plate. also if you weld something onto a plate in the middle it will warp. this took care of both those problems.
    it takes quite a lot for this thing to fall over now i can tell you that. not gonna happen.

    another angle of the whole forge, you can see some welding marks on there. the crap esab electrodes simply did not want to start on the pipe/SS tubes interface. I prefer elga electrodes like 1000 times more than esabs crap i can tell you that.

    yeah thats pretty much it. forge1.JPG forge2.JPG forge3.JPG forge4.JPG forge5.JPG forge6.JPG forge7.JPG forge8.JPG
     
    Last edited: Aug 9, 2019
  16. Aug 9, 2019 #16

    ian

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    Sweet! Nice setup for an inferno.

    I’ll be watching this thread—seeing people with bare bones setups is inspiring.
     
  17. Aug 10, 2019 #17

    inferno

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    it sure was an inferno around that pipe today :)

    funny thing was this: i think it heated the part inside the pipe better if i ran on half blast kinda.

    if i run the burner open air. the yellow part (the hottest part) of the flame is about 70-80cm (30 inch) from the cup and the flame is about 10cm (4 inch) diameter. and up to that distance its a blue flame. and the blue flame is colder.
    so basically when i tested the pipe the actual yellow part of the flame was outside the pipe on the other side. unless i turned it down to half blast.

    this burner can heat about 3-400kg of steel to over 100C in about 1,5-2 minutes. and thats what i usually use it for. many things i work with is press fit when cold so you have to cool one part and heat one and then you can assemble them. and have time to adjust angles/depths and such. not a lot of time, but usually 10-20 seconds at least.
     
  18. Aug 16, 2019 #18

    inferno

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    hey guys i thought i'd update the thread to let you know how its going.

    I did some more testing with the mighty hell pipe of propane power and it pretty much gets too hot during use to actally use it. the ir radiation during use is really really powerful and i have to use it outside. And on top of that it kinda shoots a flame 1,5m long out of the front :) so its kinda hard to see whats going on inside the pipe since you can't really stand in front of it.

    Also the big burner don't really do low power very good. below 50% or so the flame is not really suited to what i want to do with it.

    So i caved in and bought some fire bricks. the hard variety. which i have read you shouldn't use since they dont isolate. they still have only 1W/m*K thermal conductivity instead of the steel pipes 30-80W/m*K or whatever it now might have. the soft fire bricks are 0,1 but i could not find those here. i also bought some chamotte clay bricks.

    -------------------

    i hardened my first blade today!! :)
    i used 15n20. its a 180mm santoku. a beefy one. dont know if i will change the profile or keep it as it is.
    i decieded to just grind out the tang and leave the rest of the blade like a nakiri, no bevels no nothing, i figured it would be easier for me to get an even heat if i left it this way during HT.

    i was intending to do this yesterday but we had no discarded oil since it goes into an external underground tank usually. but today i got 60l of "compressor oil" with motor oil in it from a machine someone serviced. compressor oil is a hydraulic oil that has a much higher flame point. so this is now "infernos hardening oil" :)

    I heated this up to 90deg C but apparently it cooled down to 60C before i got my blade inside it.

    I built a little house of the bricks and put the burner in sideways. and 2 thermocouples (these were only of limited use i noticed).
    set the burner to maybe 40% or so. and immediately i noticed there would be some hot spots in the forge because the bricks started glowing orange there pretty quickly. after a few minutes i decieded to put my blade there to get some action out the steel.

    got the blade to dull orange, trying to get the whole blade to this color and then checked it with a magnet. maybe 50% was non magnetic. then i put in the flame for a bit longer to a brighter color and checked again. all non magnetic. but it very quickly turned magnetic out of the forge. so i decieded i needed to go hotter still for this to work. then i quenched it in the oil. tested with a bahco file and it skidded, it worked!! but i became unsure if i managed to get the whole blade up to correct temp, so i put the blade inside again and went even hotter maybe 1-1,5 shades and made 100% sure it was the same color all over. now this only took 1 minute to get up to temp from room temp. now when i knew how to do it. quenched it once again. and now the files skidded even better i thought. so it was a double quench.

    after getting to room temp i put the blade in my preheated tabletop oven. 160-165 degC for 1,5h. then i quenched it in water and ground the profile of the blade with an angle grinder and cooling it with compressed air to not over heat things. then on to the belt grinder to finsih the profile. and after the 1,5h 160deg temper the files still skidded on the surface. i even tested a red plastic mora to make sure i wasn't dreaming and the files bit in quite good on the 1095-ish steel (carbon moras are 59hrc or so). so i figured i did something right.

    then inside the tempering over again for 30 minutes when i made ready to leave work.

    and now the blade is inside my home freezer. trying to dial in 160-165 on my home oven before i put it in.

    did some fracture testing to judge the grain size and to be honest i cant really see any grains at all. its just a matte platinum gray surface. and i have inspected maybe 100 cracked parts to judge if its warranty or a manufacturing defect, and none were this fine grained.

    gonna do another 2h of 160-165deg C temper as soon as my oven stabilizes around there.

    ok some pics. a rough approximation of the blade profile

    and then some 100% pixel per pixel shots of the grain of the steel. it was very hard to crack it even though i cut it sligthly with an angle grinder. the grain4 pic has the best sharpness when going down to 100% since it was at the correct angle towards the lens (limited depth of field when doing "macro") and the lens image stabilization worked slightly better (i'm shooting this hand held).
    and then the grain4b pic is just resized down so you can get a perspective of how small the pieces of steel is. its 3mm thick. i'm propping it up on a small hand held IR thermometer.
    its my closest focus distance, mag is about 1/3 (this is quite good)

    i would like some input from the pros about the grain size. looks very good to me at least. what do you think? but i dont usually examine knife steels.

    15n20 blade.JPG




    grain1.JPG

    grain2.JPG

    grain3.JPG

    grain4.JPG

    grain4b.JPG
     
  19. Aug 16, 2019 #19

    inferno

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    trying to get a higher rez version of the grain4 pic in here. it may or may not work. (edit: it did not work) the pic is about 2k wide on my screen at home (offline) but now its like half or smaller even, go figure... i hope someone can still judge the grain size with it.

    grain4.JPG
     
  20. Aug 17, 2019 #20

    Caleb Cox

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    Awesome! Thanks for the update, it's not visibly warped or cracked so I would be very pleased if that was my first!!
     
  21. Aug 17, 2019 #21

    inferno

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    the tang warped maybe 2mm (because i welded an L iron on there to manipulate it in the forge i guess) but i simply banged it straight taking it out of the tempering oven. i usually bang stuff straight without heating them at all (much much thicker parts up to 25mm or so), so it was no real problem straightening this.

    no cracks!!
     
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  22. Aug 17, 2019 #22

    Kippington

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    The grain is fine, good stuff! I do find it strange that you (and many others) get breaks that look ragged compared to the smooth clean breaks that I get, but it probably has more to do with method of fracture than anything else.
    [​IMG]
    Yep, quenching twice can help grain size.
    "[Tempered martensite] produces the smallest and most evenly distributed carbides pinning the grain boundaries during hardening. The finest grain is attained austenitizing and quenching from this condition." - DevinT
    https://www.kitchenknifeforums.com/threads/triple-quench-worth-it.35683/#post-532695

    This sounds a little off to me. Super-fine grain size will lower hardenability, but fine spheroidal carbides shouldn't made the same difference. The main issue with coarse carbides is that they take a lot of time and heat to dissolve into solution - in other words, you need a longer soak time to get the same job done for large carbides over the fine ones.
    Triple quenching reportedly has a similar effect as longer soak times, as you essentially spend three times longer at the soaking temperature... all while giving the alloying elements very little time to precipitate before getting frozen in place every time you quench.
     
    Last edited: Aug 17, 2019
  23. Aug 17, 2019 #23

    inferno

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    hey kip i simply bent mine off. i did not bang them off with a hammer thats why you see those ragged edges i guess.
    yours looks beautiful.

    i think i have encountered a problem with my tempering.
    i put in pieces of steel in my ovens and heat them up to act as heatsinks. i measured their temp with the ir thermometer inside the oven.
    however if i quickly removed the blade from the oven and measured it outside, it would read 130ish instead of 165.

    so i put in 3 pieces of charcoal to simulate something that would be of a known emissivity of about 0,95. and if i measure those charcoal pieces inside the oven i also get values ranging from 120 to 130C. I have a feeling the actual real temp in my oven is around 130C and not 165 as indicated on the steel.

    so what should i trust? the charcoal or the steel measurements?

    And my thermocouples are at work so i can't really measure this with anything else to confirm.

    I guess its not really a problem since i can just temper the blade once again at real 165 right?
     
  24. Aug 17, 2019 #24

    Kippington

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    I would trust the charcoal. Steel often has an inaccurate reading due to fluctuating emissivity and reflectivity. Honestly the low to medium cost IR style thermometer guns are no good for this kind of job. I bought a decent IR gun for a couple of hundred dollars, but rarely use it now. Instead I use the thermocouple extension that can be plugged into the side of it.

    It's not a bad idea to go back to basics and use tempering colours. Grind a bit off some carbon steel so it's nice and shiney and stick it in the oven. The colour will give a decent indication of whether you're over-tempering, but won't let you know if the temp is too low.
    [​IMG]

    Also, conventional ovens have hot-spots, even if they're fan forced. It really gets hot where the elements/flames are, plus the top of the oven is generally hotter than the bottom. There's a lot going on, but I guess you'll get the hang of it in due time. Just try not to over-temper. You can always go higher later, but never lower without a re-quenching. :(
     
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  25. Aug 17, 2019 #25

    inferno

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    I went to work and picked up my meter and a few probes. dialing it in now.
     
  26. Aug 17, 2019 #26

    inferno

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    btw anyone ground out a blade on stones??

    At my job we only have this industrial belt grinder and its doing about 7,3 million m/s belt speed or so. the alternative is a flapdisc on an anglegrinder.
     
  27. Aug 17, 2019 #27

    RDalman

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    You can be the first moahaha. I think you will find there's some reason to folks doing some grinding before heat treatment. You can use the industrial belt grinder if you spend some fresh belts - they don't heatup your blade as quickly. But be careful obviously.
     
  28. Aug 17, 2019 #28

    RDalman

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    And grain looks good, seems your HT went well, grats
     
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  29. Aug 17, 2019 #29

    inferno

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    Yeah i guessed it would take an enormous amount of time doing on the stones.

    btw my blade is now in the oven at 165. 2h. and before that i have done 120-130 2x2h.

    would i make the blade overly soft by doing 2x2h at 165 now when i have already tempered it at 120-130 for 4h? or doesn't it really matter at all since i'm using a higher temp now?
     
  30. Aug 17, 2019 #30

    inferno

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    thank you. it appears i did something right for once :)
     

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