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

Tsujigiri said:
Great post, thank you for sharing this information. On a side note, do you know how CPM-M4 and M390 compare in toughness? I know that M4 is very tough, but I haven't heard anything about M390.
Click to expand...

I'm sorry. I do not know how the two alloys compare in toughness. But I do know that the CPM M4 has been used as blade steel for competition chopping knives. I would imagine that this would testify as to the toughness of the CPM M4 at least.
 
knarfeng said:
I'm sorry. I do not know how the two alloys compare in toughness. But I do know that the CPM M4 has been used as blade steel for competition chopping knives. I would imagine that this would testify as to the toughness of the CPM M4 at least.
Click to expand...

Thanks for responding. Maybe it's too new; I haven't heard any mention of M390's toughness. For now, I guess I'll assume that it's an issue of whether you want toughness or stainlessness for those two steels.
 
Tsujigiri said:
Thanks for responding. Maybe it's too new; I haven't heard any mention of M390's toughness. For now, I guess I'll assume that it's an issue of whether you want toughness or stainlessness for those two steels.
Click to expand...

I have pushed the edge on M390 very hard on my Custom and it's .010 behind the edge and 62 HRC with no issues.
 
Good stuff! M390 is a mother of a steel for sure. I prefer stainless so I'd choose it every time over CPM-M4. It would also appear to be more readily available than the other giant killer, S90V, given the number of knives that are appearing in it. So that's also a bonus. I have a custom coming in M390 and one next year in S90V. I plan to carry and use them both as much as possible. Why settle for less?
 
I'm curious as to how the hardness of the blades are tested.

I have access to a calibrated digital Rc tester and it leaves a dimple in the steel, are people doing this to their knives in the interest of knowing their hardness, or are they using some other method?
 
I just realized that this is an old thread, but it is very interesting information. I wonder if anyone has compared the edge holding ability and toughness of these steels with cpm 3v.
 
This sort of testing is very helpful to all of us. Thanks.
I wonder if you might be using a low power magnification to discriminate fine differences between edges. Clearly 3X will show you pretty large differences in the edges of blades. If performance seems similar, (like with M4 and M390) a higher magnification, say an 8X loupe, might pick up some differences that aren't visible under 3X.
I realize that all of this is costly in terms of time and money, but it is possible to get some inexpensive loupes that are pretty good for this sort of purpose.
Leonard Lee's book on sharpening shows illustrations of the edges of blades under high magnification, using microscopes. You don't need a microscope to look at edges of blades, but a higher magnification than 3X could be helpful.
 
knarfeng: Thanks for your labor of love. Good data; material that I have already saved for future reference. I'm a bit of a steel junkie, but perhaps more of a collector than a user.
Sonnydaze
 
Rapt_up said:
I'm curious as to how the hardness of the blades are tested.

I have access to a calibrated digital Rc tester and it leaves a dimple in the steel, are people doing this to their knives in the interest of knowing their hardness, or are they using some other method?
Click to expand...

This. ^^^^^
 
Testing done with a Rc test machine, leaves dimples but they are relatively minor if you're talking about a "user" knife. Its far more precise than test files.
 
Howdy,
Sorry. I didn't see the activity in the thread. These days I spend most of my BF time modding the Traditional Forum. I don't have time to come over here very much. Thanks for the warm comments.

I use Rockwell testing. All my knives are users. The dimple is so small as to be unnoticeable unless you are really closely examining the knife. The Rockwell test has to be made on a section which is flat and has front and back sides which are parallel to one another. For many knives that means the test has to be run on the tang. A tiny dimple on the tang is especially hard to see.
 
:) Thanks for the update and commentary on here and on the thread I started on tested hardness values. Its great you contribute to the forums by being a mod. :thumbup:
 
Tx. I need to give up my MBA in Finance and become an a Metallurgy Engineer (or something higher up!). Truly fascinating!!!

Incredibly well done work, too!!!

Some really bright minds here.
 
knarfeng said:
Howdy

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
ZDP-189
S30V.

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:

bladesteel50Kview-1.jpg

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
Click to expand...
Awesome work, very informative.
Thank you!
Just wondering about the y axis of the bar chart which sadly doesn't show any number. Does it start at 0 or did you shift it up a bit to enhance the difference between the bars?
What do I mean? When I take 2 rods one is 3 yards and 1 inch the other is 3 yard and 2 inches long. So in real numbers they are very close. But what if I zoom in so much that only the last two inch are visible? Then one rod will look twice as big as the other one.
:)

Just came home and read it again on my computer. Seems like the bars are not cut off! Seriously impressive to have such a big difference.
Thanks again.
 
Last edited:
No. This is the correct thread and the correct forum in which to ask questions about the technique.

NJBillK said:
Linked thread edited for brevity.


Ok, so in short, the horizontal lines are 10 cuts per. Which works, but only if there is a standard at which the cut count is based off of (such as Ankerson using a predetermined force applied to effectually cut the medium). Just stating that you saw "enough damage" doesn't give me any frame of reference.
Was "enough damage" one small roll that was under 1/16" in length, or the whole 2" cutting section showed a continuous roll, but maintained a "working edge" due to carbide, which would account for the drop in ZDP on the scale.

On top of that, regarding your test, do you think it is skewed in the favor of the hardest steel? One would think that a Rockstead in ZDP @ hrc66+ would have outperformed the m4 in terms of visable damage since there wasn't much of a chance at impact damage, just edge wear.
-----------
Click to expand...

Damage was comparative. As I said in the original post, all blades were capable of continuing to cut when I stopped each slicing section. This technique does not show an absolute "number of cuts". It only shows relative performance.

The method is not skewed to favor hardness. Since the cuts were slicing cuts, damage can be either due to rolling or to edge wear. Carbide content, carbide hardness, and steel hardness all contribute to a higher ranking. That is why 440C, which was measured using a blade with a hardness of 58 outperformed AUS8 which was measured using a blade with a hardness of 59. 440C has carbides, AUS8 has some, but they are not large and they do not impart wear resistance.

Impact resistance is not part of the measurement.
 
You must log in or register to reply here.
Back
Top