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What is carbon migration?

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by David Loukides, Jul 4, 2007.

  1. David Loukides

    David Loukides

    Mar 17, 2006
    Hi Guys,
    What is carbon migration? Are the small dots on the last 1/2" of my knife point a sign of it?
    This question is because I think the point of my knife made out of 1070 got to hot in the forge during the heat tratment phase.
    I am TRYING to learn new things.
    Thanks for your Posts
  2. J.McDonald Knives

    J.McDonald Knives Basic Member Basic Member

    Jan 28, 2007
    Carbon Migration is where the carbon flies down once a year from the north to the south for the winter and back north for the summer. :D Actually I don't know the full definition of it but I thought that was funny. :D
  3. Jared Stenoien

    Jared Stenoien

    Dec 4, 2005
    What you're talking about is referred to as decarburization. It's basically the same thing but usually when someone talks about carbon migration they're talking about steel to steel. Are you using any sort of shielding?
  4. David Loukides

    David Loukides

    Mar 17, 2006
    Hi Jared,
    What I did was to put the blade into the forge un protected untill it got to none magnetic. The point was brighter than the rest of the blade and that is what I based my question on. It hardened to RC 62 pryer to tempering. As far as the term carbon migration, it is a term that I heard and I wanted learn what it ment and if it applied to the small spots on the knife tip.
  5. Kiwi303


    Feb 13, 2005
    from reading here, carbon migration is what happens during damascusing, when hammering say a 1% carbon and a .5% carbon steel together, after a while the steel becomes a homgenous .75% carbon less decarburisation losses as carbon migrates from the high carbon steel to the low carbon steel.

    how many welds/layers, and how thick a layer i have no idea about, just that it happens.

    Case Carburisation uses the same principle, heated high carbon stuff migrates some of it's carbon into the skin of the lower carbon steel being carburised. Which is why case carburised bearigns are crap for knives and everyone asks Scott Ickes to ID their mystery bearings.
  6. Jared Stenoien

    Jared Stenoien

    Dec 4, 2005
    Are you using a pipe to help equalize the temperature?
  7. jdm61

    jdm61 itinerant metal pounder Knifemaker / Craftsman / Service Provider

    Aug 12, 2005
    Little dots on the tip in my experience indicate massive grain growth out where it got too hot.
  8. mete

    mete Gold Member Gold Member

    Jun 10, 2003
    Caribou migrate , carbon diffuses !! How hot ?? Some overheating will give you grain growth which will result in brittle steel and broken tips. Longer time and higher temperatures mean diffusion of elements ,including bad ones, into the grain boundaries >>> brittle steel .Even higher temperature results in burned steel which is oxidation of the grain boundaries but these temperatures are only reached when forging.A little bit of overheating can be fixed by HT ,normalizing and rehardening.
  9. David Loukides

    David Loukides

    Mar 17, 2006
    Ok Guys,
    The Pipe Sounds like a Great Idea Jared. I'll try it.:thumbup:
    Grain growth Jmd61 fits what was going on during the heat treatment. :thumbup: :(
    I usually have been heat treating in my heat treating oven with foil rap.
    Since I have set up my forge I am starting at the base of the learning curve again.
    This is :cool:
  10. David Loukides

    David Loukides

    Mar 17, 2006
    Just Saw your Post Mete,
    I guess the term I heard was a " Junk" term.
    I have to get a new battery for my Pyrometer:eek:
  11. Karl B. Andersen

    Karl B. Andersen

    Jul 27, 2003
    When you're bringing that blade up to heat, keep an eye on that tip!! It will want to come up to heat FAST!
    If you have a back door on your forge, pass the tip through, bringing the heavy metal up to heat first, and then heat the tip up last.
    Or, as the tip starts to get red/orange, pull the blade out and dip the tip in your oil to cool it off a fw times while the heavy metal comes up to heat. You DON'T want that tip getting yellow and staying that way for the emtire treatment.
    You'll end up with what Mete described.
  12. Kevin R. Cashen

    Kevin R. Cashen

    Sep 9, 2003
    decarburization is almost always a bad thing that you want to avoid. Here is what it look likes inside the steel under magnification:


    High temperature + Oxygen = decarb, except there are often circumstances where other variables (like moisture) can cause a greater rate of oxidizing of the iron than bonding with the carbon and then you can actually get a concentration of carbon on the surface in an oxidixing atmosphere. (see -"Tool Steel Simplified" by Palmer and Luerssen for more details).

    The pipe idea can add to the problem, if you defeat the effects of the gas forge atmosphere for controlling decarb and add nothing into the tube to burn out the extra oxygen. I support the idea better when I hear folks mention that they toss a couple pieces of wood or charcoal into the tube.

    As mete pointed out "Carbon migration" is just a nonsensical term that bladesmiths use to describe carbon diffusion. It seems that every smith that has written about it has described it as something that is bad or to be avoided, and this is the really unfortunate nonsense. All these years that smiths have been dumping mild steel into their damascus the only thing that has been saving their butts from the embarrassment of having huger chunks blow out their weakened edges is "carbon migration". Unless one goes to great lengths to overcome it, carbon diffusion is something that is unavoidable at welding temperature and we should embrace it. Real contrasts in the etch is very very weakly affected by carbon anyhow and one of the reasons that the whole folding and welding thing was done in ages past it to evenly distribute things like carbon, only modern smiths seem to want to do the opposite.
  13. Arthur Washburn

    Arthur Washburn

    Jul 15, 2000

    Very well stated!


    Dec 17, 2005
    Make sure you use a piece of pipe that isn't galvanized. The zink vapors and zink oxide are not a a list of approved additives for you body!

    Old exhaust pipe works but doesn't last long.

    Jim Arbuckle

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