CPM-M4 vs CPM-20CV

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DracoKrys

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Jan 17, 2018
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How do they compare to each other in terms of toughness, edge retention, ease of sharpening etc? Which one do you prefer and why? Are they designed for different purposes? They both seem to be very popular and premium steels.
 
I would think M4 is tougher, have slightly less edge retention, is easier to sharpen, and is less corrosion resistant compared to CPM-20CV.

I prefer M4, as I would guess the majority of people on BF would. Everybody just seems to love M4 and M390 for stainless because they're in a sweet spot for all the attributes. I enjoy the upper-end of the sharpness spectrum and I believe M4 is better at getting that type of edge and maintaining it
 
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Very different steel. Both have exceptional edge retention, though I'd say m390/20cv/204p out lasts it from what I've seen in all the independent tests.
At lower Rockwell's 20cv can be tough but not really at 60-62hrc. That's where m4 shines. The only m4 I generally see tested is from Benchmade or spyderco, some custom makers take it to a higher Rockwell. In that case I'm not certain of the results.

M4 will rust and patina. M390 is stainless so it's going to take alot to make it rust.
It's been a while since I've sharpened m4... But I want to say m390 is way easier to reprofile and touch up.

I enjoy both very much. I oil my m4 with fluid film and it has not taken a patina and I've used it a fair bit even in the rain. But always dry it off and re oil.
 
DracoKrys said:
How do they compare to each other in terms of toughness, edge retention, ease of sharpening etc? Which one do you prefer and why? Are they designed for different purposes? They both seem to be very popular and premium steels.
Click to expand...

20CV is way more corrosion resistant

M4 has much higher toughness

Edge rentention is a different discussion alltogether. Both are very high on edge retention, but M4 can take more abuse(cutting more abrasive media) and still slice cleanly. At one point m390/20cv/204p was seen as a stainless M4. Not so sure of that anymore.

To give more of an idea.....

Edge retention
20CV M4 S30V

Stainless
20CV S30V M4

Toughness (all are very tough)
M4 S30V 20CV

As an example, benchmade has 20CV toughness listed lower than S30V, but stainless and edge retention both similar.

I love both M4 and 20CV, but these days 20CV gets the nod due to stainless
 
I was very reluctant in the past but I have to admit that carbon steel have more to say in order of edge finesse and sharpening plus they usually can withstand more edge abuse than stainless.
Of course you need to take care more of your tools made by carbon steel.
 
In addition to what everyone else has said, 20CV is becoming a fairly common steel IMO. You still don’t find M4 in too many production blades, making it feel a little more exclusive.

My preference depends on the application, but for a pocket knife I generally will prefer M4. I would argue that differences in pure edge retention will be pretty negligible in real use. I think toughness and edge degradation due to corrosion will play in more than pure edge retention. I don’t have corrosion issues with M4 so I will generally prefer it for a folder mostly because of the edge that it take (for me at least) and additional toughness.

I think some makers (or atleast Benchmade) might run their 20CV harder than M390 so the difference in toughness between M4 and 20CV is probably something worth noting depending on application.
 
Popsickle said:
20CV is way more corrosion resistant

M4 has much higher toughness

Edge rentention is a different discussion alltogether. Both are very high on edge retention, but M4 can take more abuse(cutting more abrasive media) and still slice cleanly. At one point m390/20cv/204p was seen as a stainless M4. Not so sure of that anymore.

To give more of an idea.....

Edge retention
20CV M4 S30V

Stainless
20CV S30V M4

Toughness (all are very tough)
M4 S30V 20CV

As an example, benchmade has 20CV toughness listed lower than S30V, but stainless and edge retention both similar.

I love both M4 and 20CV, but these days 20CV gets the nod due to stainless
Click to expand...


Maybe that’s why competition blades are predominately made with M4
 
M4 is my current favorite. It’s very tough, takes a toothy edge really well and can support pretty fine edge angles. M390 is a great steel too. I don’t have any experience with 20cv but they are essentially the same as others have pointed out.

I think M390 sharpens easier, but it doesn’t seem to like to take as aggressive of an edge. Like it’s sharp enough to cut paper or shave, but it doesn’t have the same crisp bite that m4 gets. I’m sure if you were better at sharpening it would be a moot point.

The corrosion resistance of m4 isn’t great. But I’ve not had any rust, just some discoloration and that’s without ooling it.
 
My first question is: Where are you seeing so much M4? I feel like I could name all the regular production models using M4 without running out of fingers to count on.

Anyway, adding to the discussion:
Toughness depends on how high the hardness is set from the heat treatment - most production 20CV / M390 / 204P blades aren't going to be run at such a high hardness that you're going to run into chipping issues from general use.

Tool steels like M4 are well-suited for situations that would be abusive or highly damaging to typical, generally stainless steels. If you are looking for a knife that will handle terrible situations* well, go for M4. If you're looking for a general EDC knife, the M390 family of steels is an excellent choice - if not superior, when one considers corrosion and sharpening issues that often come with tool steels.

Armchair sociology time: I'd bet the reason you see M4 as often as you do* is that people want it, and companies like to make things that people want to buy. Competition cutters like tool steel, and, as much as we might not like to think so, people are influenced by the choices of those who excel in their field of interest.

* Not actually very common, honestly
 
^^^ I agree, and I think an added component for buying folders with tool steels might actually be BECAUSE they require more maintenance rather than in spite of it. People that buy them will likely be knife nuts like us who like to use, handle, sharpen, and take care of their blades, and for me at least, that can be relaxing and fun.
 
^Informative discussion.
I'm currently looking at the M4, 20cv and the S90v for a hunting knife to be used for skinning and boning out animals in the field. I like the S30V models I'm using now....but it seems one of these steels at the same or higher Rockwell would be an improvement.

Does anyone have a negative opinion or experience with leaving blood or moisture on one of the above blades? It sounds like putting an M4 blade away bloody is a really bad idea?
 
M4 is not stainless, but I don't find that it stains very easily. Not like 52100 or superblue, which takes a dark patina if you look at it wrong. I've left fruit and vegetable juices on my M4 blade without wiping off and it didn't really patina as bad as something like 1095 would. I wouldn't worry about corrosion too much, just keep your knife dry when you put it away. I like M4, because I can take the edge down pretty thin and it's still stable enough for slicing abrasive material. Not sure about 20cv taken down to 15 degrees per side though. I'd imagine it would chip out easily.
 
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This is my M4 blade after a year and a half (or so) of nearly daily use. Not stain proof, but pretty stain resistant.
 
M4 is tougher, edge retention is close, 20CV is VERY stainless in comparison, but the M4 does oxidize gracefully when a patina is formed.

They are a good argument for buying both.
 
^ what they said. Do you want extra corrosion resistance or extra toughness? That is basically what it comes down to. You will not be disappointed with either, they are both amazing steels!
 
I don't have any issues with corrosion on M4 either. My Benchmade contego has a DLT coating. But I don't see much, if any corrosion on the edge. If I did see a stain, it would be surface only (asthetic) and would rub off easy. Much different than my super blue spyderco - which patinas easy, but no orange rust. My M4 blade is incredible with edge retention. I'm probably a little weird, but I don't mind a little patina - it turns my expensive purchase into a usable tool - kind of like the fable of the farmer who hits his new truck with a hammer a few times to turn it into a work truck.
 
Popsickle said:
As an example, benchmade has 20CV toughness listed lower than S30V, but stainless and edge retention both similar.
Click to expand...

Benchmade's steel chart is questionable, at best. For example, it shows M390 and 20CV as having very different properties, when the two are chemically identical, and you'd be hard pressed to tell them apart in any real world use. I wouldn't trust in. In particular, I have no idea how they came up with S30V being tougher than 20CV. Generally speaking S30V has a reputation for chipping, while the 20CV family is amongst the tougher stainless steels.

Back to the topic on hand, CPM's data sheet on 20CV shows a comparison to CPM-M4:
http://www.crucible.com/PDFs\DataSheets2010\Datasheet CPM 20CV.pdf
 
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