"Steel needs to be rested"

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by PEU, Nov 30, 2019.

  1. PEU

    PEU Gaucho Knifemaker

    808
    Aug 6, 2006
    So I was watching a video on YouTube with an interview to Vincent, the sharpener at the famous Korin store in NY when I stumbled upon the post title statement and how Mizono, a kitchen knife japanese brand, ages its steel before shipping it to customers.

    It sounded like BS, but since you never stop learning, maybe this is true, so guys, please tell me if this smells or not please...

    Skip to 7:00 for the comment about "knives needs to be rested"

    Pablo

     
    Mecha likes this.
  2. DevinT

    DevinT KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Jan 29, 2010
    It’s true, steels grow when heat treated, especially carbon steels. They will continue to move for a year. It will show up most in laminated blades because the low carbon cladding does not move as much as the core.

    This falls under “distortion in heat treating”, it’s something that tool and die makers deal with. One reason tool steels are cryogenically treated is to stabilize them against movement. Retained austenite wants to convert to fresh martensite which expands.

    Whole books are written on the subject.

    Hoss
     
  3. Joel Mercier

    Joel Mercier

    75
    Dec 3, 2017
    Can we safely assume that a cryo treatment will do as much, if not more, than letting the blade rest for a year?
     
  4. ten-six

    ten-six

    139
    Mar 11, 2017
    How much growth are we talking about here? Could it be measured with something like a mikrokator indicator or is this at the atomic level?
    I can understand that precision would be imperative to a die maker but to a knife maker this seems like overkill, big time.
     
    GABaus likes this.
  5. DevinT

    DevinT KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Jan 29, 2010
    It’s about .0015-.002 per inch for carbon and low alloy steels. On a single bevel blade with only two layers it can cause severe warping.

    Hoss

    Edit: a ten inch blade would grow .020
     
  6. DevinT

    DevinT KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Jan 29, 2010
    It will eliminate most of the movement but not all.

    Hoss
     
    Joel Mercier likes this.
  7. weo

    weo KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Sep 21, 2014
    In your opinion, Devin, when using 1080/15N20 (and/or O1), what is the minimal number of layers to make this a non-issue. Or would you recommend makers who forge their own damascus do a cryo treatment to minimize warping in future years due to this movement?
     
    GABaus likes this.
  8. DevinT

    DevinT KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Jan 29, 2010
    It’s a non-issue unless there are welding flaws.

    Hoss
     
    GABaus likes this.
  9. weo

    weo KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Sep 21, 2014
    Thanks Devin. One less thing to worry about. What do I owe you?
     
  10. PEU

    PEU Gaucho Knifemaker

    808
    Aug 6, 2006
    Thanks Devin, now I wonder, if this is a real/common issue, why I don't keep receiving calls from old customers about warpage... My knives are almost all thin, in the 2mm / 0.08" range.

    Pablo
     
  11. DevinT

    DevinT KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Jan 29, 2010
    It’s only a problem with ni-mai and san-mai laminated blades. Mono steel blades properly heat treated won’t be a problem.

    Hoss
     
    Rhinoknives1 and Storm W like this.
  12. tkroenlein

    tkroenlein

    152
    Dec 10, 2016
    So the amount of movement is relative to the % of RA?
     
  13. DevinT

    DevinT KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Jan 29, 2010
    Austenite is smaller than tempered martensite is smaller than newly formed martensite. Some steels with large amounts of retained austenite grow very little when hardened.

    Hoss
     
    tkroenlein likes this.
  14. coldsteelburns

    coldsteelburns

    Aug 2, 2010
    I remember learning about this in an older Murray Carter video, although I thought it mostly only applied to ni mai blades. Always interesting to see the methods and processes used by bladesmiths in other cultures.

    Here's the one I'm talking about, where it's discussed a little @ about 10:00 in:






    ~Paul
    My Youtube Channel
    ... (Some older vids of some of the older knives I made)
     
  15. PEU

    PEU Gaucho Knifemaker

    808
    Aug 6, 2006
    One of the steels I like the most is VG10 and one of the variants I use is a 1.5mm (1/16") sanmai from Takefu, warpage is never a problem, you can straight it cold because the sides do not harden, it only takes patience.

    Pablo
     
  16. JTknives

    JTknives Blade Heat Treating www.jarodtodd.com Knifemaker / Craftsman / Service Provider

    Jun 11, 2006
    Not sure if this holds water so to speak but I can bend an aebl blade after a cryo quench by hand. Some times I have to tweak blades by hand after cryo and befor tempering. Aebl is the only steel I will do this to.
     
    Last edited: Dec 1, 2019

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