HOw would you all compare M4 with M2?

I am familiar with M2, and have(had) a couple of different knives with M2, but have no experience with M4. Are M2 and M4 comparable in edge retention and sharpening characteristics, or is there a noticable difference between the two in other ways?

Neat chart, I've never seen it before. Note though that BM doesn't harden its blades to 64-65 HRC.

I also notice there's a powder metallurgy M4 but no equivalent entry for PM M2. If the M2 benefits in the same way that M4 does, one would imagine that PM M2 would be even tougher. Of course, that's just a wild guess.

probably not a bad guess.

The graphs seem to follow typical wisedom, as hardness and wear resistance go up, toughness (ductility, the ability to bend without breaking) goes down.

Bsaed on your supposition, M2 PM would have greatly increased wear resistance with the equally decreased toughness (at the listed hardness levels).

For plain M4 goes, that would be a huge concern for me - the marked reduction in toughness of M4 compared to M2 would lead me to believe that M4 would be much more suseptible to chips and broken tips (given improper usage).

The PM steels, both the included M4 PM and the extrapolated M2 PM would have much greater wear resistance but would have greatly increased brittleness.

Of course, since BM does not harden their blades to that extent, we are just guessing based on this chart. tempering the steels down to the typical ~58 RC levels could/would dramatically change the results shown here.



So, the question still remains, how do the production M2 and M4 blades compare in real world usage?

This message has been edited. Last edited by: Lightning,

quote:

Originally posted by Lightning:

Bsaed on your supposition, M2 PM would have greatly increased wear resistance with the equally decreased toughness (at the listed hardness levels).

I think you're reading the graph wrong. The only significant difference between M4 and PM M4 on this chart is increased toughness in PM M4.

Anyway, there are no units on the chart, no references, an incomplete sampling of steels used by BM, and the hardness levels are all higher than those used by BM anyway. I mean no disrespect to michaelm, but it'll take a lot more than what's given on that chart to convince me of specific differences.

EDIT: Source http://www.hudson-metals.com/p...ical/cpmM4/pmM4.html

This message has been edited. Last edited by: kirbysdl,

I was primarily comparing the M2 to the M4, with the odd reference to the PM, and suspect i did a poor job of differentiating to which comparison I was refering to at the time - sorry.

And I do agree, this particular chart leaves much to be desired. without knowing the scales the attributes are being measured against, we are just guessing if the bars are even valid for comparison purposes.

Besides, there is no mechanical measure for 'toughness', in my experience, different people consider different mechanical properties to be toughness.

Is it elastisity (how far can you bend it before it won't return to it's original shape)?

or maybe yield strength (the point at which a bent material is permanently deformed)?

or perhaps its impact strength (how hard can you hit it before it breaks)?

something else entirely?


To me, toughness all of the above and not something that can be scientifically measured and put on a chart anyway.


regardless, it is the heat treatment that is of more importance than the steel used. I am sure a 440A knife blade properly heat treated will out perform and out last one made from S35V, M4, ZDP-189, or whatever that has received a really bad heat treatment...

I have no experience with M2, however I will say, the first run of Gayle Bradleys from Spyderco were treated with this high hardness (64-65) and I've never read anything about chipping problems (current production is around 63 I think), it's unfortunate there isn't a good stainless in the chart to compare the toughness too, like S30V, because CPM-M4 has a very good toughness even at high hardness levels compared to just about any other premium stainless. I have 4 knives in CPM-M4, 3 from spyderco and 1 Ritter. I have never had any chipping problems even when used on harder materials, and with the exception of the Ritter, they are all probably at least run at 62 hrc. most likely a point or two higher.

quote:

Originally posted by michaelm466:
I have no experience with M2, however I will say, the first run of Gayle Bradleys from Spyderco were treated with this high hardness (64-65) and I've never read anything about chipping problems (current production is around 63 I think), it's unfortunate there isn't a good stainless in the chart to compare the toughness too, like S30V, because CPM-M4 has a very good toughness even at high hardness levels compared to just about any other premium stainless. I have 4 knives in CPM-M4, 3 from spyderco and 1 Ritter. I have never had any chipping problems even when used on harder materials, and with the exception of the Ritter, they are all probably at least run at 62 hrc. most likely a point or two higher.

you also have to keep in mind that spyderco has a better heat treatment than BM and have higher rockwell than BM for same given steels. 1 point on the rockwell scale can be very dramatic in comparisons.

I do not have any experience with M2, but I do know M4 if very much desired

I've got 4 Ritters a large & mini of both M2 & M4 models. I have used the M2's for quite a while now and absolutely love the steel. I believe that the M2 Ritters were the last run of M2 BM will do. The M2's inspired me to try the M4. All in all I find them to be very similar. Any differences there maybe are so slight it's almost not worth mentioning. I am partial to my M2's but that could be all in my head. I've had the M2's longer and have more experience sharpening them, so it's easier.
I don't have a problem with the M4 it's just slightly different.

quote:

Originally posted by Keyman:
I've got 4 Ritters a large & mini of both M2 & M4 models. I have used the M2's for quite a while now and absolutely love the steel. I believe that the M2 Ritters were the last run of M2 BM will do. The M2's inspired me to try the M4. All in all I find them to be very similar. Any differences there maybe are so slight it's almost not worth mentioning. I am partial to my M2's but that could be all in my head. I've had the M2's longer and have more experience sharpening them, so it's easier.
I don't have a problem with the M4 it's just slightly different.

Thanks Keyman; this is great info. I think what you have said applies to a variety of steels as well, but it sure is fun to try and collect them!