Super Hard (70 Rc) High Speed Steels Explained

Discussion in 'The Kitchen Knife' started by Larrin, Dec 2, 2019.

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  1. Dec 2, 2019 #1

    Larrin

    Larrin

    Larrin

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  2. Dec 2, 2019 #2
    After a long time I managed to sit down and read one of your articles. I found it very interesting - and surprising. I would have naively expect that these crazy high speed steels would offer larger advantage over 440C that just about factor 2 - 3. I am wondering whether the advantage when using them what they were designed for - as tools to shape metals would be larger.
     
  3. Dec 2, 2019 #3

    Larrin

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    In the case of use as a high speed tool 440C would have very poor hot hardness so it wouldn't be very good at all.
     
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  4. Dec 2, 2019 #4
    These steels are 100 times harder to finish than 440C but only 2-3 fold increase in edge holding.

    Still want to try some maxamet.

    Hoss
     
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  5. Dec 2, 2019 #5

    Eloh

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    Practical testing does seem to suggest that these steels do profit overproportionally from finer finished edges in terms of edge holding compared to lower alloyed steels though.

    I'm using a S290 blade atm to do some testing.

    Thanks larrin for the article.
     
  6. Dec 2, 2019 #6

    kayman67

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    I have an XHP pocket knife and there is a good difference in edge retention based on the way it was sharpen. As fine as possible was much better. I saw others getting similar results. This is what I find most important for people to understand. Even when everything would be perfect (HT, geometry and so on) they should be aware if they sharpen usually to the best of what that alloy can provide or if they can sharpen it at all. I have sharpened many REX 121, most likely more than most and, while if done right has an amazing edge retention, I reckon very few can do it. It's very attractive to get such knives, but there are some serious drawbacks. When I read about just how hard is to sharpen M390, I feel like it's kinda butter in comparison to REX 121.

    As far as "only" 2-3x goes, in real life, if one could maximise what the alloy had to offer, I would say it's much more than that in some scenarios. Imagine doing a big boar after hunting. With 121 you finish it with that edge, no problem. With 440 you would struggle a lot and would do more sharpening than cutting. Regular "meat" knives were a joke.
     
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  7. Dec 2, 2019 #7

    Larrin

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    The best sharpening depends on what the knife is used for. Slicing rope likes a very coarse edge, for example.
     
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  8. Dec 2, 2019 #8

    kayman67

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    True. REX 121 is not one for fine polished edges anyway. Just doesn't do very well like that from my experience.
    But for any given regular usage (that involves sometimes a good amount of rope cutting, but normal stuff), still XHP with a finer edge outperforms the coarser edge.
     
  9. Dec 2, 2019 #9

    Eloh

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    True, but as a cook in a kitchen knife forum i dont care too much about cutting ropes ;)

    If you finish a simple carbon steel to a perfect 30k edge it almost loses all vegetable skin cutting ability after the first time hitting the board, a high alloyed steel will keep cutting tomatoes for a long time with the same edge.
     
  10. Dec 2, 2019 #10

    captaincaed

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    I get the sense that knife makers often co-opt/ experiment with steels designed for other industries. Which industries are the biggest buyers of these specialty high speed steels? Is this for milling car and airplane parts?
     
  11. Dec 2, 2019 #11

    captaincaed

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    What stones do you like for sharpening and finishing these steels?
     
  12. Dec 2, 2019 #12

    kayman67

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    I think CTS made XHP pretty much for blades and, to some degree, the same goes for 204P, both including knives. Unfortunately is not easy to find knives with these alloys.
     
  13. Dec 2, 2019 #13

    Larrin

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    These super hard high speed steels were designed for the same purpose as other high speed tooling. It’s too big of an industry for me to talk about not being a machinist.

    XHP was not designed for knives according to the lead developer I talked to. 204P is a copy of M390 and I don’t know if the patent mentions knives at all. Bohler never sold M390 in significant quantities for knives until after Latrobe started producing their version, 20CV, and selling it to knifemakers.
     
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  14. Dec 2, 2019 #14

    captaincaed

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    Thanks Larrin. I don't have a great mental image, but my buddy is a MechE so he likely has some insight.

    Thanks for clarifying the design background too.

    This was a cool article for sure.
     
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  15. Dec 3, 2019 #15

    kayman67

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    Not knives specifically, but blades. I assumed knives would be included into. Were they made for something entirely different?

    It would be interesting to know what exactly made them go after 204P in a similar way and not trying something else, like XHP or if they did, what went wrong. Because I imagine any maker would want something more than being similar to, some plus I could not live without (sort of) so I would desire that. Or is this a problem with the manufacturers? Some 204P pocket knives moved seamlessly to 20CV due to supposedly supply problems and maybe manufacturers would not use something hard to replace? I worked with people at high levels (not knife related, but similar goods) and most of the time was all about numbers and supply.
    Just guessing with knives. Some more inside info would be nice. I always had questions about how some alloys made it and others did not.
     
  16. Dec 3, 2019 #16

    kayman67

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    Any extra info is always nice.
     
  17. Dec 3, 2019 #17

    Larrin

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    Carpenter doesn’t care about supplying steel to knifemakers so supply is usually a major problem. You simply can’t buy the steel.
     
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  18. Dec 3, 2019 #18

    Larrin

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    M390 was primarily produced as a mold steel for the plastics industry.
     
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  19. Dec 3, 2019 #19

    kayman67

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    I understand. That makes sense. I've heard about supply problems in this regard.
    I'll die with the one I have. And this might hold true for a few others.
     
  20. Dec 3, 2019 #20

    Eloh

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    @captaincaed
    No idea who their biggest buyers are, but this is what boehler says about S290 applications, in case you're interested

    Automotive Racing
    Broaches and Reamers
    Cold Forming / Coining
    Fine Blanking / Blanking / Stamping
    Gear Cutting, Shaving and Shaping Tools
    Powder Pressing
    Shearing / Machine Knives
    Special Cutting Tools
    Wear parts

    I'm no expert, i just built upon guys with more experience with these steels, i use DMD 3K-12k, Shapton Pro 12K and also tried some diamond lapping film so far.
     
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  21. Dec 3, 2019 #21

    captaincaed

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    @Eloh thats perfect. I've been stuck in Thanksgiving travel limbo without the will to do a deep dive. Thank you for finding that.

    I have a feeling Sharpton is in my future and I've just been fighting it.
     

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