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Temper Help ....?

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by Poop Fungus, Sep 23, 2012.

  1. Poop Fungus

    Poop Fungus Banned BANNED

    Sep 13, 2012
    Howdy. I was just wondering what would be the better way of these 2 ways to achieve a nice deep, even blue color when tempering.
    1. preheat the oven to 600 degrees (F) and put in the knife/tomahawk and watch closely until it gets blue/purple or all blue (20 minutes or so) and then quickly quench with water.
    2. preheat oven to 400 degrees and bake knife/tomahawk for a much longer period (2'ish hours) until a nice blue forms.
    i've tried the first one but am having trouble getting a uniform blue. i havent tried the second one but have heard that metal will eventually turn higher tempurature tempering colors if left at lower tempurature, for extended time. i've also seen videos using a pencil torch and wet rag to temper but havent tried that either.
    any other methods are welcomed also...thanks
  2. ecos


    Jul 2, 2006
    First off are you sure you want blue for a knife? Typically that is considered too soft...most makers d blades to a straw/gold color (400-450).

    Definitely leave it in for longer times. Most makers leave it in for 2+ hours, for 2-3 cycles. At 20mins there is a very good chance you are only getting the surface hot, and not all the way through (might explain your splotchy colors).

    No water quench is needed after tempering, just let it air cool. Quenching is done after hardening....did you harden the steel prior to tempering it?
  3. Poop Fungus

    Poop Fungus Banned BANNED

    Sep 13, 2012
    im just messing around now, on some blanks, before i do anything with them.. just messing around with temper colors/tecniques. probly wont ever actually do a blue knife but it looks good on functional, but more decorative, tomahawks. in the first method the quenching is more to stop the color right where it is/not keep going. you basically get it to color quick (20 min'ish) and then cool to stop it, right there. i tried another one, much more polished/smooth, it took color much much better. appreciate the info. keep em coming guys :thumbup:
  4. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    If you want a blue/dark color on a knife blade use bluing, FC, or Parkerize it. You don't want to temper much above 450° for a knife blade. A hawk could take 500°.

    Fire bluing ( heat bluing) is done for guards and pommels by heating them with a torch or oven to get the rich blue color. A knife blade would be ruined if done this way. The trick is to heat it to just the right temp and dunk it in water before the blue passes into gray.

    As to the water quench from the temper oven, Roman Landes has done some pretty extensive studies on this and recommends that a hardened knife not be cooled slowly from the temper oven, but quenched in water to drop the temperature quickly. It has to do with the structures, but the long and short is that it is beneficial, and there is no risk of cracking the blade or warping it.
  5. Shaw Blades

    Shaw Blades

    May 18, 2009
    So tempering 1095 at 500 is bad? I read in Kevin Cashen's site that would put you at around 59-60 rc.

  6. ecos


    Jul 2, 2006
    Well thats interesting...most people I know just allow it to air cool. I'm not familiar with Landes, but after a quick Google I saw Kevin Cashen talk highly about him so I am definitely interested in learning more. Most of what I am seeing from my search are people saying "Landes does it this way....anyone know why?" then others giving their best guess. Is there a repository of info straight from him or published testing? I'm curious if the fast cooling applies to simple carbon steels, higher alloys, if it refines grain structure further, etc etc.
  7. Poop Fungus

    Poop Fungus Banned BANNED

    Sep 13, 2012
    ANOTHER QUESTION: ...I'm also wondering if placing the metal in preheated oven @590 (F) for 20 min. , just to achieve a nice blue, and then quickly quenching it in water would come out as soft as something that had been fully tempered for 2 hours @400'ish (F) and left to air cool? ...i.e. would it be possible to get the blue color without making it "too soft"?
    Also, I've heard that metal left at lower tempuratures (400'ish, to get the yellow/straw color) will eventually turn the higher temper colors (blue/purple) without ever actually reaching those higher temperatures (550-600'ish)----if left for an extended period. (how long? i dont know/never tried it). Would leaving the metal for an extended period @400'ish, to get a higher temper colors make the metal any softer than normal tempering @400 for 2 hours?
    Tha, tha, tha, tha, that's all for now folks!!
  8. BenR.T.

    BenR.T. Tanto grinder & High performance blade peddler Moderator Knifemaker / Craftsman / Service Provider

    Apr 18, 2011
    Cold blue.
  9. Bo T

    Bo T

    Feb 12, 2011
  10. Poop Fungus

    Poop Fungus Banned BANNED

    Sep 13, 2012
    well, in this link=the guy got a nice blue/purple color on a KNIFE and everything checks out okay (its hard)..... interesting
  11. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    You need to do a lot more reading in order to understand the tempering and hardening process well.
    The colors on that photo link were just the oven colors from the post-quench heating. They have noting to do with temper colors. Those, and temper colors, are very thin and would rub off in assembly and clean-up. The color a blade comes out of quench, and then out of the oven can be a wide variety of colors. The golden/straw color is normal for very clean blades at temper, but any shade of the rainbow ( and often all of them at one time) are common. Getting a deep blue color requires a lot higher heat than a user blade should be at. A good rule of thumb is - If it gets hot enough to blue it - Re-do it!
    If you want the deep blue/purple color you see in many knife books, look up Niter Bluing. It is a low temp (500-600) salt pot treatment with nitrate salts. The blade does not stay in the salts long enough to greatly affect the temper....and these knives are usually safe queens. Even this is only a very thin layer.

    In a perfect world,......in a metallurgical lab,...... with an absolutely nailed hardening by water quench,...... a temper at 500F would give about Rc 59-60.
    In the real world,...on a knife heated in a forge and quenched in oil..... a 500F temper would probably give you Rc 57-58.
    450F would get about Rc59-60.

    Generally most metallurgical bladesmiths advise to stay away from tempering much above 500F. Temper embrittlement is probably an over-rated problem in knives, but avoiding it completely is surely a good idea.
  12. Broomhead


    Jan 12, 2012
    If you want the knife to have a blue color, then, as many others have said, don't try to do it with tempering. I have used Birchwood Casey's Perma Blue cold bluing and it turned out really good. Take everyone's advice and skip trying to temper to a certain color.

    BTW, that was my thread that was linked above and I can tell you that the temper color came off way too easily for me to ever consider trying to use it as a patina.
  13. Shaw Blades

    Shaw Blades

    May 18, 2009
    Thanks Stacey. I guess the concern is the oven spiking in temp to come back up to 500 when it drops below? So that would at times put the blade over 500 degrees in the temper? I try to overcome that with a slotted fire brick holding the blade and a couple of firebricks in the oven to soak up radiant heat. 450 does sound like a safer bet though.
  14. aarongb


    Nov 2, 2007
    So am I reading this correctly or out of context, that it may be a good idea to quench after temper? I usually do all my worrying at the forge and quench bucket, but after tempering, I let my blades sit in the toaster oven until cool enough to touch. I haven't noticed any problems with HT of 1084, but if I can improve it with a simple step, I'm all for it. If this step is advised, should it be water or oil?
  15. mgysgthath


    Dec 15, 2009
    Stacy said water quench.. it won't shock the steel at such a low temp.
  16. Poop Fungus

    Poop Fungus Banned BANNED

    Sep 13, 2012
    how long would it stay in the salt [email protected]?
  17. Poop Fungus

    Poop Fungus Banned BANNED

    Sep 13, 2012
    ohh. and----- tomahawk head.. differentially heat treated/tempered... edge=plain/yellow... fading to brown/purple/pink, into blue-up til about the handle whole.. and back into yellow up to the hammer pole (or hammer pole left plain?)... good idea? do'able?
  18. Cody Hofsommer

    Cody Hofsommer

    Dec 2, 2011
    I'll throw out AN answer, not sure if it's the answer. I think that lots of axes of old were edge quenched, and with heat still in the body, let the colors run to the cutting edge, and then quenched again to stop everything. So, to recap... after the edge quench, quickly file/grind the cutting edge to clean off the decarb. When the desired color is reached quench again. This leaves the body soft, and the edge hard. That and most of the axes of old had iron bodies and tool steel cutting edges forge welded into them.

    I think that hammer poll should be tempered softer then yellow, my guess would be blueish.

    Just my take on that.... Many more knowledgeable then me on here.
  19. Poop Fungus

    Poop Fungus Banned BANNED

    Sep 13, 2012
    ...not really
  20. SteelSlaver


    Feb 17, 2007
    I wouldn't want any any knife edge of mine to get over 450 for any length of time. 1/100 of a second or less. Tempering does have more effect over time, but stuff starts to happen right away and the edge is a very thin section. The reason a hatchet, ax, of hawk is usually tempered to a higher temp is the nature of its cutting with a high striking force means that it would be much more prone to chipping than a knife. The edge of an ax is also at a much wider angle than a knife and therefore it will not roll over at a softer temp. But, ax, knife or anything else will benefit much more from a long soak at the desired temp in a controlled oven than any torch type temper. You are reforming or refining the martensite formed during hardening when you temper and the process is far more complete with time. A second temper is also done because during the first temper the retained austentite from hardening is converted to martensite and it needs to be tempered, which occurs during the second temper. After those steps you can soften the body of the ax or a knife to a softer state with a torch while keeping the edge cool and hard. The smiths of old did not have even kitchen ovens with temp controls and they did not, have the means to achieve a better temper. You do. USE it.

    There are lots of people here with far more knowledge than me. Some of them are highly educated in metallurgy. They are very willing to share their knowledge and it behooves you to listen to them. I have and still do. I thank them for the knowledge they have given me. I highly suggest you read the stickys and do some seaching if you want to understand what is going on. Your questions make it obvious that you do not.

    There are several types of bluing processes and the temps necessary to achieve bluing with them vary from ambient air temps to over 600f. IF you Want to keep a carbon steel blade at an acceptable hardness you need to use one that works below 450f.

    The colors that you achieve heating in an oven vary according to the steel, what contaminants are on the steel and the atmosphere in the oven. Heat coloration is not very durable at all.

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