Super Hard (70 Rc) High Speed Steels – Maxamet, Rex 121, and More Explained

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

  1. Larrin

    Larrin Gold Member Gold Member

    Jan 17, 2004
    jux t, LG&M, superpog and 11 others like this.
  2. DeadboxHero

    DeadboxHero

    Mar 22, 2014
    I liked reading the thought process behind these steel designs.

    Its nice for folks to understand that the mechanism for getting that hardness is different and not like 1095.

    At knifeshows folks often scratch their heads when I show them a knife like Rex 121 at +70

    "How is that possible?"

    "Was it even tempered?"

    Yes, of course it's tempered :D

    So this article is a good read for curious folks


    [​IMG]
     
  3. patrickguignot

    patrickguignot

    196
    Sep 10, 2015
    Thank you Larrin for this article.

    I don't understand the toughness diagram displayed.
    Here the CPM M4 steel at 62RC is roughly at 30 ft/lbs :

    [​IMG]

    But in this other article from you (about Nitro-V) we also have a diagram about steel toughness. And in this case CPM M4 at 61 RC seems to be at 15 ft/lbs :

    [​IMG]
     
  4. Larrin

    Larrin Gold Member Gold Member

    Jan 17, 2004
    The top chart is Crucible numbers using full-size c-notch specimens. These are all tested in the "longitudinal" direction relative to the rolling direction. The bottom chart is Knife Steel Nerds results using subsize unnotched specimens tested in the longitudinal direction. This new article has another more complete chart with more Rex 121 numbers on it. The Hitachi chart in the article uses full-size "R-notch" specimens tested in the longitudinal direction. Uddeholm uses unnotched "Izod" specimens in the transverse direction. Bohler uses unnotched Izod specimens in the longitudinal direction. Carpenter uses both Izod and Charpy unnotched specimens in the rolling direction, sometimes they pick one or the other and sometimes do both.

    As you can see there is no standard test. All give different numbers and can't be compared. That is why we picked one simple version and started testing steels from all the different manufacturers with it.
     
  5. Larrin

    Larrin Gold Member Gold Member

    Jan 17, 2004
    I think the toughness testing with a unified test type across all the different manufacturers is one of the biggest contributions of Knife Steel Nerds so far. Could never seem to convince anyone that AEB-L had excellent toughness, for example.
     
  6. cistercian

    cistercian Gold Member Gold Member

    411
    Apr 22, 2015
    Thank you very much for posting this!!!
     
    Larrin likes this.
  7. Revolverrodger

    Revolverrodger

    Jul 23, 2007
    Very interesting
    The very low toughness is surprising
    I guess these steels should be used in small blades only
     
  8. Larrin

    Larrin Gold Member Gold Member

    Jan 17, 2004
    What about in big kitchen knives?
     
  9. DeadboxHero

    DeadboxHero

    Mar 22, 2014
    Let's do it!
     
    marrenmiller likes this.
  10. marrenmiller

    marrenmiller Basic Member Basic Member

    Apr 6, 2017
    I'd love a maxamet paring knife.
     
  11. superpog

    superpog Basic Member Basic Member

    49
    Nov 9, 2019
    Will they be ok for over night in dish washer? As they are under non-stainless category...

    I don't know if it's just me, but I find myself usually left them in dishwasher over night:(
     
  12. Larrin

    Larrin Gold Member Gold Member

    Jan 17, 2004
    Don’t under any circumstances put them in the dishwasher. They are non-stainless. But even stainless tool steels are not built for repeated trips through one.
     
  13. ScooterG

    ScooterG You mean Ireland? Yeah, it’s mine. Gold Member

    Mar 15, 2016
    A good trick is to not put your knives in the dishwasher. Go old school.
     
  14. DeadboxHero

    DeadboxHero

    Mar 22, 2014
    A good knife is NEVER washed in the dishwasher EVER.
     
  15. DeadboxHero

    DeadboxHero

    Mar 22, 2014
    People are destroying their knives in the dishwasher.

    The handles come apart, wood swells, bolts corrode, glue fails, edge bangs on the metal rack dulling it to all hell. Chemicals and heat wreak havoc on the blade, microcorrsion on the blade and edge pits and chips it. Sharpening them out to another pit which turns into another chip.


    A knife maker has two options, educate folks so they can acutually get the performance they deserve and the user changes behavior so they can acutually get performance.

    Or lower the bar and cater to the lowest common denominator.

    Bomb the edge performance out to compensate for abuse. Also it's more cost effective to make knives that solely designed to compensate for misuse.

    This is fine, can just be preference, not everyone wants or needs crazy performance nor cares. Things work good enough for most folks even when considered horribly dull by others standards. However, if you DO care, you don't ever use a dishwasher on your knives, EVER.

    Just figure out what you want is all.
     
  16. superpog

    superpog Basic Member Basic Member

    49
    Nov 9, 2019
    Thanks for good explanation and understanding!

    Totally agree with the preference. I am new to the knife world, but I found myself by default had a mindset that kitchen knives are just a different thing from the knives I am going to put in my collections... (I still don't know how that happened.) My impression is that the couple steel and ceramic knives in the kitchen work just fine. Rarely needed to sharpen, but maybe like you said they are already horribly dull by other standards... I only recently realized the potential damage issues with dishwasher, and I am surprised that our kitchen knives hold up fine (by our standard) with their trips in the dishwasher. Never noticed rusts at least... I don't even know the steel type and couldn't find it in addition to just stainless. Maybe it's not important or cared by ordinary people (like myself couple months ago), so the producer don't even care to put it on.

    Speaking of the trade off, I guess the technology hasn't been developed to the point to give knife makers the option of keeping edge performance while dishwasher safe.
    Technical innovations have freed people from many repeated tasks, dishwasher is one of them. I don't think kitchen knifes are destined to be excluded. The fact that enough people have done that destroying their knifes seems to suggest a market for dishwasher safe knives (or maybe knife safe dishwashers). I hope in the near future, the new materials can free knife makers from trading one off another.
     
  17. DeadboxHero

    DeadboxHero

    Mar 22, 2014
    If you're using the dishwasher your knives can never be this sharp. To make them hold up to the dishwasher this amount of performance MUST be reduced.
    It's not a technology thing just the limits of things. Maybe in 100 years when the make a knife out of nanobots...wait might short circuit in the Hyperwasher. Oh well.


     
    Natlek likes this.
  18. Revolverrodger

    Revolverrodger

    Jul 23, 2007
    yes they should be excellent for kitchen work! Just less ideal for stuff loke chopping, battoning and the succh
     
    Larrin likes this.
  19. Natlek

    Natlek

    Jun 9, 2015
    I found this dimension ........Subsize specimen sizes are: 10 mm × 7.5 mm × 55 mm, 10 mm × 6.7 mm × 55 mm, 10 mm × 5 mm × 55 mm, 10 mm × 3.3 mm × 55 mm, 10 mm × 2.5 mm × 55 mm.

    i think that in your test you use last one 10 x 2.5 x 55 ? I have question for you if you don t mind .IF we increase first dimension from 10 to say 30mm /the average width of a small knife / and leave thickness 2.5mm how much toughness will increase ?
    or maybe this situation is better ... if we increase only thickness from 2.5mm to 5mm would be toughness be twice as large ? Or things don t go like that ?
     
  20. Larrin

    Larrin Gold Member Gold Member

    Jan 17, 2004
    Toughness can be normalized by the width*thickness so it becomes J/cm^2. However differences in thickness change the behavior because the surface is always more ductile so the thinner it is the greater the percentage of the thickness is affected by the surface. You can read more here: https://www.nde-ed.org/EducationRes...ge/Materials/Mechanical/FractureToughness.htm
     
    Natlek likes this.

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