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Thread: Relative toughness of blade steels???

  1. #1
    Senior Member Chefdog's Avatar
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    Relative toughness of blade steels???

    Hello everyone,
    I feel like I have a solid understanding of kitchen steel characteristics and how they relate to real world use. But this one question has been bugging me lately because I see some contradictory information and wanted to try and get a definitive answer.

    So here it is: Is there an absolute relationship between the toughness (ability to resist chipping and deformation of the edge) and the addition of chromium (or other alloying elements) to carbon steel? In other words, is carbon steel (assuming for the sake of argument they have the same hardness, grain structure, heat treatment etc.) always tougher than stainless?
    OR
    Do the other variables have too much of an impact to make any such blanket statement?

  2. #2

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    Quote Originally Posted by Chefdog View Post
    Do the other variables have too much of an impact to make any such blanket statement?
    This.

    If the blade is hewed from a solid chunk of steel and heat treated, the toughness/durability of the blade can be estimated to a certain degree.

    Once you take that chunk of steel and manipulate it into a blade, all bets are off.

    Plus, adding certain other elements to the steel alter the properties of it and even the way the steel is made can make some drastic changes to how it behaves with regards to toughness. All this before the blade maker gets their mitts on it, and what they do has an effect.

    I know that's not going to make it any easier for you, but that's the way it is. At one time I thought I could fully understand it all, and realized that there were missing pieces to the puzzle that I could not find answers for.

    That is until I talked to people who make blades...

    An no, I won't even begin to explain it all. The facts of the matter sound so very much like magic and mystery that even I don't fully believe all of it, even though I've got first hand knowledge of what's what and can make a call to find out more info if I need to.

    Believe me, you knife folks have got it easy when it comes to steels.

    (Try explaining what blue steel #1.5 actually is to someone who's barely got the difference between white and blue steel sorted out. Start telling them and they go all cross eyed and call you a heretic.)

    Stu.

  3. #3
    Senior Member Chefdog's Avatar
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    Stu,
    Thanks, I had a feeling it wasn't so be black and white. So there can be highly alloyed and hardened stainless steels that shouldn't, but do exhibit superior toughness and edge stability compared to a "clean" carbon steel that wasn't forged/heat treated well.
    I knew it wouldn't be too simple, Thanks for the input.

  4. #4
    Quote Originally Posted by Chefdog View Post
    Hello everyone,
    I feel like I have a solid understanding of kitchen steel characteristics and how they relate to real world use. But this one question has been bugging me lately because I see some contradictory information and wanted to try and get a definitive answer.

    So here it is: Is there an absolute relationship between the toughness (ability to resist chipping and deformation of the edge) and the addition of chromium (or other alloying elements) to carbon steel? In other words, is carbon steel (assuming for the sake of argument they have the same hardness, grain structure, heat treatment etc.) always tougher than stainless?
    OR
    Do the other variables have too much of an impact to make any such blanket statement?
    The addition of large amounts of chromium generally increases the carbide volume (because of all the chromium carbides) which leads to many martensitic stainless steels having a high carbide volume and therefore high wear resistance and low toughness. There are, however, stainless steels with a low carbide volume and therefore characteristics similar to those generally attributed to carbon steels, and there are carbon steels with a high volume of carbides that have characteristics similar to those generally attributed to stainless steels.

    As far as testing results go, toughness information is often not available, and when it is, different companies have their own tests that make it difficult to compare except with general trends.

  5. #5
    Senior Member Chefdog's Avatar
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    Thanks Larrin,
    I went back and re-read your thread on "what steels and why" and it helped a lot. It really Judy comes down to the general properties of the steel, but more so how the heat treatment was performed, right?

  6. #6
    Quote Originally Posted by Chefdog View Post
    Thanks Larrin,
    I went back and re-read your thread on "what steels and why" and it helped a lot. It really Judy comes down to the general properties of the steel, but more so how the heat treatment was performed, right?
    Heat treatment is very important. Of course knives with good steels but poor heat treatment will perform poorly. However, steels are limited to certain ranges of performance based on their composition and prior processing. Low carbon simple steel will never have high wear resistance and S125V will never have high toughness regardless of how it is heat treated. Furthermore, to be in the range of strength required for a good kitchen knife with a thin edge puts you into the hardness range of 58-66+ Rc (58 would be pretty low) which further limits the range of properties achievable. Once you are looking at knives where the maker has used an "acceptable" heat treatment we can compare steels based on their achievable performance in various categories. Again, there are some ranges, you can go for lower hardness for higher toughness, or heat treat at higher temperatures for more chromium in solution for greater corrosion resistance, for two examples. However, I feel perfectly comfortable comparing steels based on the properties it can have based on obtainable hardness, carbide volume after austenitization, chromium in solution, testing results from the steel manufacturers, etc. Steel companies have no problems with comparing the general properties of their steels even though there is some range in properties based on heat treatment.

    Extra information: An "acceptable" heat treatment would be described as one where nothing was overheated, sufficient strength was obtained, sufficient soak time was used for carbide dissolution, heating was even, and carbon loss is minimal. I'm sure there are other possible mistakes but can't think of them now.

  7. #7
    Senior Member Chefdog's Avatar
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    Thank you. Always like to know more.

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