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reprofiling GEC 440C vs GEC 1095

Discussion in 'Traditional Folders and Fixed Blades' started by fatcorgi, Mar 1, 2013.

  1. fatcorgi

    fatcorgi

    655
    Nov 12, 2011
    Until now I have only had GECs with 1095 steel, and always reprofiled the blades to a 30 degree angle, this works well for this steel, now I have my first stainless 440C GEC, and was wondering if this steel can also be reprofiled to 30degrees, or whether this is too steep for this type of steel, and whether 40 degrees would work better. What are other people's experiences?
     
  2. pinnah

    pinnah

    Jul 28, 2011
    Depends on GEC's heat treat, which I understand is very good.

    If I understand things correctly (massive if), 1095 can be hardened to around 56-57Rc while 440C can be hardened up to around 60Rc. Buck's old 440C was often reported to be in the 58-60Rc range, based on what I've seen. This should allow it to be sharpened to a narrower angle than 1095.

    This is consistent with my experience with Buck's 440C and everybody's carbon steel when working with wood. I sharpen my 440C blades to 20 degrees. At 20 degrees and under hard use, I get rolled edges on my carbon steel knives but not my 440C blades. I now put a 25 micro bevel on my carbon knives and find that handles hard use better.

    Also, 440C is a big step up in terms of abrasion resistance. Conversely, it's a noticeable step up in difficulty in terms of sharpening. Takes longer when reprofiling the edge with normal stones. Definitely holds an edge longer when cutting wood but doesn't respond to a strop or steel as well.

    Basic trade offs.

    Again, my experience is based on Buck's older 440C. If GEC isn't hardening their 440C as much, results may be different.
     
  3. knarfeng

    knarfeng senex morosus moderator Staff Member Super Mod Moderator

    Jul 30, 2006
    Yes. I have reprofiled GEC 440C blades to 30° inclusive and it works just fine. Use ceramic or diamond stones as opposed to a Washita.
     
  4. richstag

    richstag

    Feb 22, 2007
    Frank,

    I have come to you for help on steel composition before and I hoped you could help me once again. My preferred stones are true hard arkansas stones. These stones, as you know, are composed of novaculite which has a mohs hardness of 6.5 and equivalent of RC 69. I realize this is constant and the specific gravity is what changes the grade of these stones.

    My question for you is with an RC hardness of 69 I know general blade hardness is never a problem, but I realize different carbides in steel can skyrocket in RC hardness. For 440C do you know the RC hardness of the carbides?

    Thank you again,

    Kevin
     
  5. knarfeng

    knarfeng senex morosus moderator Staff Member Super Mod Moderator

    Jul 30, 2006
    Hard to say. Wiki says there are three crystal structures for Chromium Carbide, each with a different hardness. I couldn't tell you which one is found in steel. The crystal structure which Wiki says is most stable has a hardness (measured on a different scale) which roughly equates to a hardness considerably above 66 Rockwell. (the conversion tables end at about 66HRC.)

    My comments on using a ceramic or diamond stone are based on my own experiences when I was a young man trying to sharpen my Buck 440C blades on natural stones. It didn't work very well. When I eventually got a Norton aluminum oxide stone, it got a whale of a lot easier to sharpen 440C.

    Edited to add:
    [​IMG]

    according to
    http://www.ppm.bc.ca/Cermet_Carbide_Nitride_Powder_Products.html
    the Knoop hardness of Chromium Carbide is 1735

    This conversion chart
    http://www.ndt-ed.org/GeneralResources/HardnessConv/HardnessConv.htm
    says that 1735 Knoop is about a 78 Rockwell C.

    However, a lot of these hardness scales don't really equate when you get out to the ends.
     
    Last edited: Mar 2, 2013
  6. richstag

    richstag

    Feb 22, 2007
    Thank you Frank and that makes sense. According to my source Norton Aluminum Oxide - India Stones rate 9.2 on mohs scale and Norton Silicon Carbide - Crystolon 9.5 on mohs hardness scale. Diamond being 10 on the scale as you know.

    The only place I have found much about carbide harness is on Devin Thomas's website. Here is a quick quote from FAQ page that I first read about this.

    Thank you again for taking the time to try and help me get a better grasp on this. I believe this means K1 carbides form in 440c at 72RC which puts it out of true hard Arkansas league, at least in edge leading honing. I just found this information again. What do you make of it, Frank?

    Kevin
     

  7. That makes perfect sense to me.

    440C (in a Buck 112) was the very first and most graphic example demonstrated to me, of the limits of Arkansas stones. Seemed to be just beyond what the stones were capable of grinding efficiently. It isn't that 440C is that difficult, compared to other more wear-resistant steels (D2, S30V, etc.), but it's just a little too much for what these stones can handle. 440C is easily sharpened on almost anything else (alumox/ceramic, SiC, diamond), but not on natural stones. I was really amazed the first time I tried it on SiC (wet/dry paper), which removed swarf from 440C like it was chalk dust. Prior to that, all my impressions were based on the tough time I had with it on natural stones, which barely scratched the stuff. There's a very distinct threshold in ease of sharpening with this steel, and Arkansas stones are unfortunately on the wrong side of it, it seems to me.


    David
     
  8. richstag

    richstag

    Feb 22, 2007
    Thank you for that additional info, David. What I find interesting is that I have actually had great results with 440C and S30V when using my translucent stone to finish and do touch up. I'm not talking about major sharpening, I'm talking about what a finishing stone is meant for. With that said I have had times when an S30v blade has actually visibally cut into the stone. Once I figured the right finess I am getting very, very impressive results. So I'm not sure how it performs so well at this task but NOT for hogging off steel?

    Thanks

    Kevin
     
    Last edited: Mar 2, 2013
  9. Yes, that's what I'm referring to, the major grinding stages. My Buck 112 (old '2-dot') in 440C had a very thick edge on it, when I first got it a long time ago. I had tried to thin it on some cheap Arkansas stones I had, which barely fazed it. Fast-forward a couple decades, after I'd just stashed that knife away and forgotten about it, and I picked up some wet/dry paper and fixed it. Seemed astoundingly easy by comparison. I'm glad I kept that knife, as I wasn't too happy with it before. :)

    I have a small black hard Arkansas pocket stone, which I've used occasionally to touch up edges on more wear-resistant blades (VG-10, D2, 440C and others). It works well to put some finishing touches on a polished bevel, and also works nicely to re-align rolled edges or clean up burrs.


    David
     
  10. richstag

    richstag

    Feb 22, 2007
    Thank you AGAIN, David :)

    So how do you think the harder carbides get cut by the softer stone when finishing. I have viewed under a microscope and it does appear to cut. I just don't understand it.

    Thanks bud :)

    Kevin
     
  11. knarfeng

    knarfeng senex morosus moderator Staff Member Super Mod Moderator

    Jul 30, 2006
    Well, AEBL has about the composition of 13C26, which, at 6.5% Carbon, doesn't have enough carbon to form the large carbides which are the basis of the superior wear resistance of 440C et. al. The fine carbides which precipitate out of alloys like 13C26 don't affect wear resistance because they are so fine.

    Lot of folks prefer to depend on high hardness instead of wear resistance for edge retention. To me it depends on what you are doing as to which works better for you.

    Anyways, at the end of the day, if the alloy contains carbides the way 440C does, I recommend a ceramic or diamond sharpening stone.
     
  12. richstag

    richstag

    Feb 22, 2007
    Thank you Frank and I agree I use DMT and blue Zirconium mainly for S30v and 440c, I just found the conversation interesting and one that I had questions about. Primary carbides with 440C being a stated issue for a lack of ease of sharpening was a good eye opener. I take that to mean the carbides are very substantial to hone vs precipitated carbides. Just trying to visualize. :)
     
  13. To be honest, I really don't even know IF the carbides are being significantly abraded by the hard Arkansas. I only use it when I know the edge is already in good shape, cutting-wise, and sometimes it adds just a little bit to the polish. May be more effect on the steel matrix itself (between the carbides), and basically skidding over the 'cobbles' of carbide otherwise. I see the most value in how it can realign a rolled edge (more bending, less abrading), and I've used it to 'flip' stubborn burrs/wires on VG-10 and 420HC. I slide the stone lengthwise down the edge, heel-to-tip, and this technique with a hard stone works well to flip the wire from side-to-side. Done the same with a ceramic, but the ceramic sometimes abrades more than I really want it to, when the edge is already very fine. That gives the hard Arkansas sort of an ironic advantage, in that I can work on the burr alone, and not detrimentally affect the good edge behind it. Ceramics re-create burrs in a heartbeat, if taken just a hair too far while trying to remove a burr.


    David
     
  14. richstag

    richstag

    Feb 22, 2007
    Thanks for the thoughts, David.

    I'm sure it cuts though on S30V, everytime I see my brother I bring back the edge on his knife with my pocket stone. I mention his knife because its never sharp.

    I think we may have exhausted this thought, at least I have :)

    Kevin
     
  15. Minor point, sure it was a typo. The carbon content in 13c26 is 0.65%, as opposed to 6.5%.

    Here's some info from Crucible, about the hardness of various carbides in (presumably their own) steels. The site is linked below, and is a gold mine in explaining how carbides affect wear-resistance:

    ( from site -->: http://www.crucibleservice.com/eselector/general/generalpart1.html )
    David
     
  16. richstag

    richstag

    Feb 22, 2007
    Wow, David thank you.

    I believe the number less than 5 and up to 20 percent of composition could answer how my translucent is cutting. Like you said it's mainly the steel matrix between the carbides? Possibly the carbides tear out as opposed to abraiding? S30v in particular with 80-84RC carbides almost seems impossible that the stone is actually abraiding the carbides?

    I'm glad I asked. Very interesting info!

    Kevin
     
  17. That's why I sort of don't expect much, in terms of natural stones' ability to abrade some of these steels. The steel matrix into which the carbides are 'embedded' is still just iron/carbon, essentially. If the stone abrades anything, it'll abrade that. May still work a tiny bit on the carbides, albeit very, very slowly. S30V is apparently known for the carbides fracturing out (tearing out) of the edge as it gets finer, which is also why it has a reputation for not holding a super-fine shaving edge for long, but tenaciously holding a real 'working edge' afterwards (exposed carbides at the edge are doing that job). Somebody described it, I think most aptly, like the exposed pebbles at the edge of an aggregate concrete slab; the finer cement binders in the mix can form & hold a crisp edge when new. But the crisp edge eventually abrades & chips away, leaving the harder and coarser pebbles exposed, which don't abrade near as quickly, but sometimes will be dislodged, leaving a coarser edge.

    At least from Crucible, their CPM process has been geared towards reducing the overall size of the carbide 'pebbles', which used to be quite large and made fine edges nearly impossible in steels with a lot of these carbides. As the size of the carbides decreases, the 'pebbles' get smaller, allowing edges to be made finer, but still afford better wear-resistance than steels without these carbides.


    David
     

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