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Thread: Preferred RC Hardness

  1. #1

    Preferred RC Hardness

    A question to the knife makers.
    What is a preferred hardness on your knives? It seems that 60-61RC is very common and 62 not too common. What about 62-63RC for steel that have excellent edge stability like 52100? Overkill?

    Marko


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  2. #2
    Delbert Ealy's Avatar
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    I do not use 52100 as my steel of choice, and thus I cannot answer your question directly for that steel, however with all steels hardness is a compromise between hardness and toughness. Going too far in one direction may result in less than satisfactory results.
    I have often found that this question can be answered by test-to-destruction tests, it also helps give you a better undestanding of the steel properties at certian hardnesses.
    Thanks,
    Del

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  3. #3
    A risk is there if RC is pushed, that you increase the likelyhood of edge chipping, and reduced toughness. Try a grind on a few scrap pieces of the steel you want to use, do a brass rod edge flex test, and check for chipping. It will give you a level of confidence with regards to how far to push your hardness.


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  4. #4
    here is where i come on and bash the brass rod test as a test for hardness.
    one it is mostly used as a test in the heat with a torch and quench in any old oil and see how the edge holds up (i like to think that wiht working with edges as extreme as the ones we do that we have a bit better way of HTing)
    2
    i can make a blade pass the rod test at 64rc and if i want i bet i coud make one fail at 58

    the brass rod test was from what i can understand was mostly used to test razors but it was not a test of the HT it was a test of the grind and to make sure that it was ground to the proper thinness

    in that use a razor would have to be not HTed and the blade woudl take a set or not tempered and maybe it would brake (but not at the edge)
    if the brass rod test is used to see about the edge its more about if you have grossly missed the HT and even that can bee covered up by how the blade is ground (both if its too thick and unyeilding or too thin )

    i have a 63rc blade that i can bend to 90 degrees (another of those fun tests) and it comes right back to straight (and its even cpm154 SS) no chipps cracks or any other problems

  5. #5
    I don't use a brass rod test for hardness testing. It is a way to get the edge to flex past its normal line, to deform it as it were. It isn't ment to replace a Rockwell tester, or any other meathod of determining hardness, just another thing a maker can use to see what the edge will do. Your right you can beat the test, sure, To call it a test might me the wrong term, but it will allow you to flex an edge past normal, and if there is chipping, it (the test) has helped you out, wouldn't you say? At63, with that much flex, wouldn't you be fairly confident in saying the edge will be fairly chip resistant. Whether you use a rod, pair of plyers, a vice or whatever, makers sill test edge flex, to check for chipping., or deformation. Then determine if an end user would go that extreme and decide if an adjustment to the HT is warented. Otherwise why bother to flex a given edge 90* if not to "test" it? Have I used a brass rod test sure, do I still no, not much, but I will if I am trying a new steel, or adjust a HT, I'll also bend it till it breaks or chips out, tested to distruction as it were.


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  6. #6
    no worries i just see too many smiths fall back on that as proof that there HT is good

    how bout this
    make a knife and then sharpen it
    then drag it sideways across the board like some might do to "clear" the board
    does the edge chip or roll? but what if the edge is too obtuse and you dont see any problem? does this mean you nailed the HT ?
    does any of that show much about HT or blade hardness

    im not after any makers so dont think im tring to nail any one down its more about making sure we are all thinking about what we are doing after all we have seen many makers adn HTs that work great for the knives they make and many at different RCs

    steel like knife shapes are all about trade offs in strength, sharpen-ability, reactivity and many other options

  7. #7
    Thanks, guys. I can't say I understand brass rod test very well, but I will read up on it.

    I heat treated a few knives to 63RC, so I think I will grind one and put it to test. If need be, I can draw it down by a point later. I was just curios, as my last one was 62RC and I beat c*** out of it without any adverse effects, so I wanted to see if at 63RC I will be able to do the same.

    Many Japanese makers harden their blades to 63RC and Carter does it as well and as posted by a person who works for him, there is no issue with chipping. White steel has less of an edge stability of 52100, so that was another reason why I wanted to give 52100 a try at a higher hardness.

    I will grind the blade to about .007 above the edge, so at this thinness if it is brittle, I should know right away. Standard cutting includes everything vegetables, cheese, meats, etc., push, pull cutting, down-cutting and down-chopping.

    M


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  8. #8
    Quote Originally Posted by Marko Tsourkan View Post
    Thanks, guys. I can't say I understand brass rod test very well, but I will read up on it.

    I heat treated a few knives to 63RC, so I think I will grind one and put it to test. If need be, I can draw it down by a point later. I was just curios, as my last one was 62RC and I beat c*** out of it without any adverse effects, so I wanted to see if at 63RC I will be able to do the same.

    Many Japanese makers harden their blades to 63RC and Carter does it as well and as posted by a person who works for him, there is no issue with chipping. White steel has less of an edge stability of 52100, so that was another reason why I wanted to give 52100 a try at a higher hardness.

    I will grind the blade to about .007 above the edge, so at this thinness if it is brittle, I should know right away. Standard cutting includes everything vegetables, cheese, meats, etc., push, pull cutting, down-cutting and down-chopping.

    M
    thats the best testign as it will tell you if you can use that hardness it can also help you fine tune how thin you grind your blades
    if you start hard and thin you can always sharpen the blade till it stops chipping/rolling the edge (it will get slightly thicker ever time you "fix" a chip) or temper down a bit and keep your edge thickness the same

    my first big buy (over 200$) that i made in knife making was a kiln and then LN dewer
    ugly knives that are well HTed are still great knives beautiful knives that are poorly Hted are little more then letter openers

  9. #9
    That is a good way to go Butch/Marko for sure, I didn't mean to sound so hard there, the house was a zoo this morinig, and I was typing while trying to bring order back!

    At the end of the day, HT, grind, test, adjust, test again. Be sure of your meathod, test till your confident, and your work will hold up.



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  10. #10


    Bill Burke's Avatar
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    Marko 52100 will hold up fine at 63 If you have refined the grain sufficently. I do this with multiple quenches after forging then normalize three times then sperodize aneal and grind. I then tyriple quench and triple temper then finish grind and polish. I still use a torch to harden and an oven to temper. However I would be willing to change my ways if someone can show me a way that works better.

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