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Thread: Tojiro Powder Steel

  1. #11
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    Marek, I'm definitely no sharpening guru and although I have an interest in steel metallurgy, I'm not an expert in that either. My understanding is that carbide pull-out is microchipping caused by carbides being pulled out during use. It's more likely in highly alloyed steels with large carbides (I'm guessing tool steels including PM steels and many alloyed SS are in this category). It's more likely if the angle at the very edge is greater than that particular alloy can support. For example, I have been told that 14dps is far too acute for SG2 (which is hardly the most alloyed PM steel). Carbon steels and fine-grained SS with fine carbides (such as AEB-L) don't tend to have this problem, even with very acute edges. Microvbevelling is often suggested to counteract this problem.
    I'm not sure the extent to which this is based in theory vs empirical evidence, but some guys who seem to have a lot of sharpening experience place a lot of store in it, so I guess that it's based in their experience, at least.
    I'd very much welcome the input and perspective of those who know more.
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  2. #12
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    Tojiro Powder Steel

    afaik tojiro never disclose specific details about what exactly the PM steel is. R2 first emerged from Chinese websites a couple of years ago which I don't believe it is accurate and I don't believe a rakuten seller knows more.

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  3. #13
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    Quote Originally Posted by pkjames View Post
    afaik tojiro never disclose specific details about what exactly the PM steel is. R2 first emerged from Chinese websites a couple of years ago which I don't believe it is accurate and I don't believe a rakuten seller knows more.
    So it could even be a steel that we aren't really familiar with? I guess I'll give it an edge and see how it goes and adjust from there (which is kinda what I already do I suppose).
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  4. #14
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    Quote Originally Posted by Nemo View Post
    Marek, I'm definitely no sharpening guru and although I have an interest in steel metallurgy, I'm not an expert in that either. My understanding is that carbide pull-out is microchipping caused by carbides being pulled out during use. It's more likely in highly alloyed steels with large carbides (I'm guessing tool steels including PM steels and many alloyed SS are in this category). It's more likely if the angle at the very edge is greater than that particular alloy can support. For example, I have been told that 14dps is far too acute for SG2 (which is hardly the most alloyed PM steel). Carbon steels and fine-grained SS with fine carbides (such as AEB-L) don't tend to have this problem, even with very acute edges. Microvbevelling is often suggested to counteract this problem.
    I'm not sure the extent to which this is based in theory vs empirical evidence, but some guys who seem to have a lot of sharpening experience place a lot of store in it, so I guess that it's based in their experience, at least.
    I'd very much welcome the input and perspective of those who know more.
    Thanks Phil.
    I think I got most of that - not too technical for my little brain and an insight into the carbide issue from a knife/sharpening perspective.
    The only PM steels I have are a couple of Takamura and a Takayuki Shibata Kotetsu - both in R2. I've only sharpened one of the Takamuras so far and they are thin knives with quite a fine edge. Perhaps even around the 14dps limit you spoke of, but I don't really know - still sharpened OK (by my standards).
    If you or any one else would care to comment about the angles on PM steels or Takamuras specifically, I'm all ears.

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    Quote Originally Posted by Marek07 View Post
    Thanks Phil.
    I think I got most of that - not too technical for my little brain and an insight into the carbide issue from a knife/sharpening perspective.
    The only PM steels I have are a couple of Takamura and a Takayuki Shibata Kotetsu - both in R2. I've only sharpened one of the Takamuras so far and they are thin knives with quite a fine edge. Perhaps even around the 14dps limit you spoke of, but I don't really know - still sharpened OK (by my standards).
    If you or any one else would care to comment about the angles on PM steels or Takamuras specifically, I'm all ears.
    I think that a lot of PM steels can get quite fine-grained (I think because of the PM process) so will shapen to quite an acute angle and quite a refined edge. The carbide pull-out in my (limited) understsnding is more to do with edge retention. That is, highly alloyed steels (especially if the carbides are large) microchip rapidly at acute edge angles but retain their edge for ages at less acute angles. I don't know if its a threshold effect or a gradual transition.

    I have more knives than I can use every day (more just seem to keep showing up! What's with that?&#128518, so I guess that estimating edge retention is difficult except in a pro environment. I've only just started microbevelling tool steels so I can't comment on whether the edge retention is any better yet. Having said that, I hadn't noticed rapid edge failure on Sg2 or SRS15 or SKD-12 knives at 14 dps (back whe I used to use Edgepro). But it may have been due to intermittent use.

    Maybe we should start a new thread on this topic in the sharpening station?
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    "a couple of Takamura and a Takayuki Shibata Kotetsu - both in R2"

    At least the first comes OOTB with a far steeper edge than 14dps

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    Quote Originally Posted by LifeByA1000Cuts View Post
    "a couple of Takamura and a Takayuki Shibata Kotetsu - both in R2"

    At least the first comes OOTB with a far steeper edge than 14dps
    Yep. I had a Ryusen Blazen in SG2 that came with ~12dps, as did my Akifusa.

    As I said, I don't really know if this phenomenon is based in theory or on experience.
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  9. #19
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    Quote Originally Posted by Nemo View Post
    Yep. I had a Ryusen Blazen in SG2 that came with ~12dps, as did my Akifusa.

    As I said, I don't really know if this phenomenon is based in theory or on experience.
    It will depend on the steel, its composition and its HT, but from my experience R2 can take a very fine edge. There are some great threads floating around on here about controlling carbides etc etc. but for the life of me I can't remember where they were.

  10. #20
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    @Nemo the red handled Takamuras are usually specified as delivered with 9dps.

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