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Steel fractures on utility blade – toughness vs hardness

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    I was messing around with some different grit progressions and testing some new emulsion formulas (very promising!) and I decided that I wanted to make a permanent mark on the blade so I could be sure I was continuing to look at the same spot under the scope. The field of view is so small at high magnification that it’s easy to get lost along the bevel and never make your way back to a feature you were studying.  I took my EDC and set the edge on the edge of the utility blade I was working on and gave the EDC a little tap on the spine with a diamond stone block. It definitely made a mark:

    The above image is at 200x

    Here it is at 2000x

    Again at 2000x. You can clearly see fracturing of the steel above the area where the large chip is removed.

    Another look at some fracturing.

    My sense about the utility blades is that they are not overly hard, but rather designed to be tough, which is why the fracturing was a little surprising. You can’t see the fractures with the naked eye, or even a good loupe. It makes me wonder how often blades do have micro-fractures like this that go undetected and lose their edge in that area.


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    I’ve wondered about hidden fractures myself.

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    I just can’t see why some people do not finding taking the time to stop and observe is important.  I have been studying Todds blog at lately and I am all screwed up now.   Their is a little world going on at the micro level that we are just now starting to understand.  Not only am I convinced that micro fractures are causing some of our problems but that these problems are variables found in each step of the blade forging processes.  When we start looking you start seeing these issues everywhere.

    I have started rethinking the way I see a metal blade.  We perceive it as this “indestructible thing” used to carve other things when in reality it is more like a gelatin fluid at the microscopic level.  As we are sharpening and then looking under a microscope we are only seeing the pattern left behind in a moment of time, however, after each pass of the stone, the metal is moving.

    Sorry to go esoteric on you but I share your intrigue Clay.   These blades are much more fragile than we once thought.  I am starting to believe that more is not better, after all, especially at the microscopic level.  Todds SEM photos and your careful observation are telling us this.

    I have also studied Murray Carters work as well and the Japanese where onto something.  I keep hearing him saying that they made blades by forcing “Just a little more” out of it at each step of the forging process with reverse succession of temperature and force.  They must have been doing this for a reason.  They new something that has been lost over time.

    Both of these observations seem to contradict what we are observing or do they? I think we are just missing something somewhere.

    Keep up the good work if I can help I will.

    Eddie Kinlen
    M1rror Edge Sharpening Service, LLC

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