Comparison of CPM M4 HC, ZDP-189, M390, and S30V edge retention

Discussion in 'Knife Reviews & Testing' started by knarfeng, Nov 20, 2010.

  1. knarfeng

    knarfeng senex morosus moderator Staff Member Super Mod Moderator

    Jul 30, 2006
    Dennis Strickland has an amazing collection of cutlery. Whether it be the nicest GEC traditional or the latest hot alloy, Dennis probably has it. He also has the knowledge base to go with it, as he’s been collecting and using knives for a long time (longer than I, and I’ve been using knives for ~50 years). Dennis and I occasionally discuss blades and steel via PM. Recently, Dennis asked me if I would like to try some high-end PM steels. Now obviously, since I never met a steel alloy I didn’t like, I said, “Yes, please.”
    Without further ado, Dennis sent me 3 exotic PM steel blades to try: ZDP-189, M390, and CPM M4 HC. I added in my own S30V just for the fun of it.

    Test Method:
    If you’ve read my testing posts, you know my methods, Watson.

    If you’re you are familiar with the test method, skip down to the steel section. (You can do this anyway but if you aren’t familiar with my test method, my results will make more sense to you if you read the next couple of paragraphs.)

    There are a number of factors that enter in to blade performance, several of which have more impact on edge retention than blade alloy does.
    - Blade geometry
    - Edge Angle
    - alloy composition
    - Alloy hardness.
    I try to control as many as possible.
    - I measure the hardness of each blade. (I can’t control the hardness, but it helps me understand what I am testing and helps me reach conclusions.)
    - I modify the edge angles so that they are all the same (15° per side)
    - I do my best to put an equally sharp edge on each blade. In this set of tests I used DMT diamond stones, X-tra Coarse, Coarse, Fine, X-tra Fine.
    - I make an equal number of cuts through 3/8” manila rope with each blade. I usually mark out on the blade my intended start and stop so that I use approximately the same length of blade on each knife. In this comparison, I used ~2” of each blade.
    - I do my cutting on a simple jig that supports the rope, but has a split in it so that the blade only cuts rope. That way the blade does not hit the support. This makes the forces acting on the blade more uniform and the results much more reproducible. I try very hard to cut at 90° to the rope.
    - I then examine the edges under a 3x lens using a high intensity lamp looking for light reflected off the edge of the blade. The shiny spots equate to wear or deformation. I always check the blades before beginning the rope cutting to make sure I can see no edge at all under the lens in the light.
    - I rank the blades by the amount of deformation I observe.
    - I repeat the tests several times until I am sure of the results.

    The advantage to this method is that the blade geometry is not a factor in the results. This allows me to eliminate a major factor in cutting performance.

    The disadvantage is that it is a comparative method. It is extremely difficult to quantify the difference and say that one blade is 25% better than another. For the most part one can only rank the alloys and say that one is better than another.

    The knives:
    Blade Alloy____Measured Hardness ____Maker_______Model
    CPM M4 HC______62 _______________Spyderco ___Gayle Bradely
    ZDP-189________62 _______________Spyderco____Stretch II
    S30V___________59.6 ______________Buck_______Vantage-Pro

    Here are data sheets on the alloys, (note that the Gayle Bradley uses CPM M4 HC, which does not have exactly the same composition as melt M4).\DataSheets2010\dsM4v1 2010.pdf\DataSheets2010\dsS30Vv1 2010.pdf
    No gots for ZDP-189.

    It is probably worth noting that none of these knives was heat treated to maximize edge retention. These are all standard working blades. Each has a heat treat that will provide a measure of toughness in addition to edge retention. The Crucible data sheet says you can take CPM M4 HC to a 65.5 and the Bohler data sheet says you can get M390 to almost 63. So take that into consideration when you look at my information. The results may change somewhat if the heat treats were different.

    Results and discussion:
    In order of retension, best at the top:
    CPM M4 HC – M390

    I could not differentiate between M390 and CPM M4 HC. After some runs, I thought maybe the CPM M4 was less damaged, after others, I thought the M390 had fared better. Bottom line: a tie.

    What I really found significant in this comparison was the relative edge retentions of M390 and CPM M4 HC compared to those of other alloys I have tested. When testing 440C and VG10 by this method, I found that I saw enough damage to rank the alloys after ~20 cuts. To see that level of damage on ZDP-189 in this test, I had to go to 40 cuts. To see that level of damage with either M390 or ZDP-189 I had to go to 80 cuts. Now all those alloys were still easily cutting the rope after that many cuts, but that is about how many it took for me to be able to discern damage to the edge. Based on this, I made a graph to show relative edge retentions of theses alloys in comparison to some other, more common alloys:

    One thing that fascinates me about this comparison is that, for a long time it's been clear that edge geometry is more important than alloy. I'm not sure if that is still clear to me. I can't help wondering if a blunter blade of M390 might not outcut a blade with better geometry, but lesser alloy. A battle for another day, I think

    Thanks to Dennis for loaning the knives. I learned a lot from this comparison. I hope others find it useful, as well.

    Frank R

  2. gunmike1


    Dec 9, 2005
    Great test. My Stretch CF was 64.5 RC, and my M4 Mule was 63, so it seems those Spydercos were softer than the norm. I'll report back in a week or so on the Hardness of my 2 M4 Millies, my Gayle Bradley, and a few others like my second S90V Manix 2 (my first one came back at 58.5-59 RC). Either way I'm really impressed with M390, if it is there with M4 and is stainless to boot it sounds like a really nice steel. It also appears to take a very nice edge, if it is anywhere near M4 in sharpness it appears to be a really nice steel. I think Carpenter 20CP is similar to M390, and I am pre ordered for the Para 2 in that steel so I should get a good look at how it performs (if I don't get a Phil Wilson custom in M390 first).

    I have a Benchmade Rift in 154CM that is 61 RC, it would be interesting to see how 154CM compares to that S30V at 59.5 in your tests. I know my Rift performs really good for 154CM, taking a nice edge and holding it nicely, but ZDP, M4, and S90V have been in my pockets a lot so anything in the 154CM/VG-10/S30V class seems lacking to me in edge retention, but it is all relative. If you want to borrow some of my folders in M4 that are harder than 62, ZDP-189 at 64.5, or S90V at 59 or so I'd be glad to ship them off to you in a couple weeks after I get them back from testing. It would be interesting to see how much a couple extra points of hardness effect your tests, and S90V would be new to your testing.

  3. JNewell


    Nov 18, 2005
    Frank, thanks for the continuing time and love you put into these comparisons. This is great, real-world info. :thumbup:
  4. DennisStrickland

    DennisStrickland Banned BANNED

    Jun 24, 2009
    frank took many hours to accomplish these results. he is a working engineer so minute details are the guiding force in his profession. repeating these tests several times certainly establishes accountable values. [ although it's very tedious] there are other members hard at work also constructing tests. my graditude is enormous because i did'nt have to do all this work to obtain the interesting knowledge. knives are only objects but knowledge is forever. thanks a ton frank.
  5. Ankerson

    Ankerson Knife and Computer Geek Gold Member

    Nov 2, 2002
    Very nice testing Frank. :D

    I know you put a lot of work into you testing process. :)
  6. Kaizen1


    Jan 4, 2006
    Very cool. Thanks for all that work:thumbup:

    I wish someone would do this with all the different Spyderco Militaries and their steels or all of the Spyderco Mules.
  7. thejamppa


    Aug 20, 2009
    I didn't knew M390 was so good stuff. Spydderco's M4 is really good too. But for $50 Knife, Buck gave more expensive knives run for their money. Thank you for sharing this test.
  8. KeithAM


    Dec 15, 2003
    Knarfeng--thanks for taking all the time and trouble to perform the tests. :thumbup:
  9. dericdesmond


    Sep 10, 2007
    Thanks for the very easy to follow review :thumbup:

    I still have a lot to learn so please pardon me if this is a dumb question. Do you know if the ZDPs score would of been affected had the blade been laminated? I ask because I have some laminated zdp and it just seems out of this world, surprised it didnt score higher. Its also a very thin blade so maybe that plays a factor :confused: Thanks again.
  10. neuron

    neuron Moderator Moderator

    Apr 18, 2010
    Very nice methodology, explanation, and presentation. Thanks for taking the time to do this! :thumbup:
  11. nevermind35


    Aug 14, 2009
    Thanks for sharing your findings. This M390 sure does seem to be turning out better than I thought it would.
  12. shunsui

    shunsui Gold Member Gold Member

    Aug 12, 2008
    Thanks for the point of reference :thumbup:
  13. knarfeng

    knarfeng senex morosus moderator Staff Member Super Mod Moderator

    Jul 30, 2006
    Thanks to all for the kind comments.

    The laminated steel, in and of itself, should not affect the edge retention because the central core of ZPD-189 is what would contact the rope and show the wear.

    However, the performance could easily be affected by the hardness of the ZPD-189 core. The solid ZPD-189 blade that I tested had to be tempered to a hardness at which there is some toughness to the steel. In a laminated blade, toughness comes from the outer layers of softer steel, so the central core could be heat treated to a higher hardness and give better edge retention.

    So your laminated ZDP-189 blade might have performed better than the one I tested, though I don't think it would reach the performance level of the CPM M4 HS or the M390.
    sniper66 likes this.
  14. knarfeng

    knarfeng senex morosus moderator Staff Member Super Mod Moderator

    Jul 30, 2006
    Thanks, Jim. I especially value the complement, coming from you. You also have put much work into testing and know what it takes.
  15. Planetcat


    Jul 28, 2009
    Thank you for the great tests and time spent on them. You guys continually reinforce the decision I made to buy my most expensive folder I own, the BM 710 in M390. I'm in the middle of hunting season right now, so hopefully I'll get to break it in on some flesh and bone and publish my findings on those "materials" with the 710. Love that knife!
  16. STR

    STR Knifemaker/Moderator Moderator

    Aug 27, 2004
    Very nice Frank. I can't help but wonder how the M390 would have faired if it was just a bit harder. At 62 it may have have won out over the others and M4.

  17. michaelm466


    Mar 5, 2009
    Thanks for doing this as well as the excellent write up and explanation of methods and results.
  18. Twindog

    Twindog Gold Member Gold Member

    Apr 6, 2004
    Thanks so much for the great tests. As you know, the geometry of all these knives are different. You did control for edge angle, but even with a consistent edge angle, the shoulder-to-shoulder width of the edge will make a difference. The M4 Gayle Bradley has a narrow shoulder-to-shoulder width, making it cut better and longer.
  19. knarfeng

    knarfeng senex morosus moderator Staff Member Super Mod Moderator

    Jul 30, 2006
    Yes, I noticed that the Gayle Bradley cut a bit more easily than the 710, and I did attribute that to overall blade shape. However, the impact of blade shape difference is minimized as my measurement is not directly based on the amount of pressure used to cut, but only on the amount of edge deformation observed.

    I suppose that if the difference in pressure were extreme I might get more wear, but I feel that in these tests, the difference in pressure was not enough to overly impact the results.
  20. Ankerson

    Ankerson Knife and Computer Geek Gold Member

    Nov 2, 2002

    Your findings are good. :thumbup:

Share This Page