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

[knarfeng]

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.

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.

[Tsujigiri]

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.

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.

[Ankerson]

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.

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.

[salmonkiller]

Frank,
Thank you for the hard work an time you put into this.

[Buffalohump]

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?

[ezoption]

Thank you for the amazing information!!

[Rapt_up]

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?

[mcconnad]

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.

[arty]

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.

[Sonnydaze]

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

[JNewell]

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?

This. ^^^^^

[getridone]

Testing Files?

[Rapt_up]

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.

[knarfeng]

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.

[Rapt_up]

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.

[kestrel57]

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.