Freaky A2 ???

Discussion in 'Heat Treating Forum on KnifeDogs' started by AkWildman, Feb 12, 2017.

  1. AkWildman

    AkWildman Well-Known Member

    So I just heat treated a A2 blade,did my normal heat treat,sealed stainless foil pouch,I brought my temp up to 1450 and held for 10 mi then ramped up to 1800 for 40 minutes.Plate quenched,some of the foil stuck to the blade and I never had this happen before.The blade hardened as expected and I tempered giving it 3 one hour cycles.Using my hardness files it come in under 65 and obove 60.Now here's the freaky thing,I've never had foil stick to the blade so this was the first time I did this procedure with A2 .I went over to my large belt grinder with the intention of using the flat deck to get rid of the foil,I have a large powerful magnet that I hold blades with and it barely sticks to the blade .I've never that I can remember stuck a magnet to heat treated A2.The magnet sticks but not like I expected.What gives ????
  2. Smallshop

    Smallshop KNIFE MAKER

    Perhaps send Kevin C or Ed C a pm?
  3. AkWildman

    AkWildman Well-Known Member

    Just sent Kevin a pm.
  4. Kevin R. Cashen

    Kevin R. Cashen Super Moderator

    A2 has never been my cup of tea but I will give it a shot.

    The majority of any steel is iron. Iron is ferromagnetic at room temperature when the electron motion that coincides with the BCC (Body Centered Cubic) atomic stacking allows for that magnetic condition. Iron, when heated to 1414F becomes paramagnetic according to the new electron dynamics of FCC (Face Centered Cubic) atomic stacking, this FCC iron is also known as gamma iron, and a hand held magnet will no longer be attracted to it. Gamma iron’s FCC stacking has a very high solubility rate for carbon so when carbon is present and goes into solution we get the solid solution known as austenite. In something like A2 the carbon would normally be bound up in bonds with the Cr to make carbides, but we break some of those bonds when we make austenite solution for heat treating.

    When there are enough substitutional atoms from alloying present (chrome, nickel, etc…) they reinforce the austenite and make it resistant to transformation back to BCC at room temperatures. This is what we refer to as “retained austenite.” Carbon bound in carbide does not contribute as much to this reinforcing action, but when it is put into solution it does, and the more that is put into solution the greater this effect. This is why there are strict upper temperature recommendations to be followed on high carbon steels and why cold treatments are so often necessary to full harden stainless alloys.

    With alloys that have large amounts of chrome and nickel (one of the best austenite stabilizers there is) you get austenitic stainless that does not harden at all and will not attract a magnet at room temperature. These are the mechanisms that affect a steels magnetism. I give this long explanation because without being present to observe and analyze things first hand anything I have to offer is only guessing, but I do have these principles to work with.

    What type of stainless is your foil? Is it contributing to the low magnetism? Are your temperatures accurate so that you know you didn’t overheat to cause some sort of critical level of retained austenite? Does the blade get a little harder and attract the magnet a little better over time? Do these properties improve with cold treatments? Anytime you get an increase in HRC from cold treatments, you can bet there were issues with retained austenite.
  5. John Wilson

    John Wilson Well-Known Member

    ^ yeah, I was just about to say that.

    holy cow, I'm still on Google looking up the terms
  6. AkWildman

    AkWildman Well-Known Member

    309 high temp SS foil,monitored temps the entire duration,I went ahead and finished grinding the blade and without putting a handle on put a edge on it,it took a fine edge and will do some cutting and see how it holds up,I havnt noticed any change in the amount of hold with a magnet.And I probably wouldn't have noticed this had some of the foil not stuck to the blade.Freaky I tell Ya !
  7. springer82

    springer82 Well-Known Member

    Wow,,, sounds like I'm back in school. A little different topic but still. Kevin,,, what do you read for fun. Tech info?? lol,,,
  8. Kevin R. Cashen

    Kevin R. Cashen Super Moderator

    The most recent one, that my wife rolled her eyes at when she saw me curled up next to the fire reading, was "Metallographic Polishing by Mechanical Methods" by L.E. Samuels, it is a great companion text for "Optical Microscopy of Carbon Steels" which is one of my favorites and by the same author. The last non-tech book I read for fun was a Terry Pratchet Discworld novel, but since his death, no other entertainment books seem worth the bother in comparison. Pratchet was thoroughly entertaining, and before Alzheimer's claimed his mind, and eventually his life, he got together with a smith, smelted his own steel to make a sword, a man after my own heart. I have read all of his Discworld novels except the very first, which I am saving until just the right time since it will be the last.
  9. springer82

    springer82 Well-Known Member

    Meteorite and Excalibur,,
    clay, hay and sheep $hit,,, lol
    The 65 million copies sold could not match the honor of being Knighted with a sword like that.
    Thank you for sharing. I did enjoy reading about Sir Terry!!!

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