CPM M4 vs K390

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Chumango
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Re: CPM M4 vs K390

Postby Chumango » Tue Nov 21, 2017 5:18 pm

Gayle Bradley. I should note that I think the finish on the GB is finer than the finish on other M4 knives, like my M4 PM2, which may influence results. I have had some corrosion issues with mine (sweaty, humid TN also plays a role) while he has had no issues cutting a variety of things with a GB (central valley of CA).

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Re: CPM M4 vs K390

Postby Eee » Tue Nov 21, 2017 5:29 pm

I’d agree that in my use, M4 (GB1) was more corrosion resistant than K390 (Pingo).

I have noticed different levels of patination from what might be slightly different heat treatment. I recall someone (maybe Xavierdoc) saying the M4 Manix sprint took a patina far more easily than the GB. I’ve also noticed the CPMD2 Millie Sprint runs seem to patinate darker than the PM1 sprint (mine has taken a hazy light grey). My point is that one person’s experience of M4 or K390 could be quite different depending on the heat treatment.

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Re: CPM M4 vs K390

Postby Chumango » Tue Nov 21, 2017 6:58 pm

And the surface finish.

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Re: CPM M4 vs K390

Postby hambone56rx » Thu Mar 14, 2019 1:14 pm

Fellas,

I'm bumping up this old thread to heat up the discussion on K390 v M4. I have some knife purchases on the wish list and trying to think them out rather than buy them all (although that's what I want to do :D )! Future wants:

1. Parata - For the first Stop Lock on the market!
2. Shaman Cruwear & Micarta Sprint- Want the model, love Cruwear and always have wanted micarta scales!
3. Police lightweight in FRN & K390 - After hearing all the love for K390 makes me excited to try out this lightweight version of a 4.4" monster blade.

However now the Shaman M4 sprint makes me reconsider #2 and potentially #3! I don't have the steel and the model, which makes me want to jump the gun!

Some have said on this thread that K390 is more corrosion resistant and some have said M4. Can I get more feedback on this? I live in East TN where heat, humidity and sweat are prevalent. So the one that is more corrosion resistant has huge advantages for me.

Thanks!

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ferider
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Re: CPM M4 vs K390

Postby ferider » Thu Mar 14, 2019 1:54 pm

hambone56rx wrote:
Thu Mar 14, 2019 1:14 pm
Some have said on this thread that K390 is more corrosion resistant and some have said M4. Can I get more feedback on this? I live in East TN where heat, humidity and sweat are prevalent. So the one that is more corrosion resistant has huge advantages for me.

Thanks!
My practical experience with M4 and K390 corrosion resistance is similar to Larry's prediction below. M4 is better, I had K390 pitting over night in the kitchen just by having a couple of drops of water on an otherwise clean blade.

Also, the current P4 liners are definitely not stainless. I'm wondering if the FRN version's liners will be ?

Image

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Deadboxhero
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Re: CPM M4 vs K390

Postby Deadboxhero » Thu Mar 14, 2019 3:50 pm

Like Doc Dan says

"K390, M4 Killer"

K390 is plenty tough for a folder and has superior strength and wear resistance to M4 especially with the HT on the Spydercos.

So if K390 was more available I'd see no reason to own a knife in M4 in 2019.

I think M4 was impressive for it's time, but it's 2019 now and those of us in the know now see there are superior steels available now that unfortunately have yet to make there way to being widly available
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Re: CPM M4 vs K390

Postby TomAiello » Thu Mar 14, 2019 4:26 pm

Like the ZDP thread, this one is making me want to carry k390.

I already do that pretty regularly though.

For me, Maxamet is more of the M4 killer. I like v4e and k390 in bigger blades, and tend to carry them in my fixed blades a lot.

On the other hand, today I'm carrying a fixed blade that is Rex 121, so I guess I'm in the "none of the above" category again. Sigh.

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Re: CPM M4 vs K390

Postby hambone56rx » Thu Mar 14, 2019 4:26 pm

ferider wrote:
Thu Mar 14, 2019 1:54 pm

My practical experience with M4 and K390 corrosion resistance is similar to Larry's prediction below. M4 is better, I had K390 pitting over night in the kitchen just by having a couple of drops of water on an otherwise clean blade.

Also, the current P4 liners are definitely not stainless. I'm wondering if the FRN version's liners will be ?

Image
Thanks for the feedback!

Incredible to see! That's interesting to see that M4 is right up there with S30V regarding pitting. Can you elaborate on what the Cr-Eq Acetic testing is? I tried to google it and turned up nothing.

Hamilton

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Re: CPM M4 vs K390

Postby hambone56rx » Thu Mar 14, 2019 4:30 pm

Deadboxhero wrote:
Thu Mar 14, 2019 3:50 pm
Like Doc Dan says

"K390, M4 Killer"

K390 is plenty tough for a folder and has superior strength and wear resistance to M4 especially with the HT on the Spydercos.

So if K390 was more available I'd see no reason to own a knife in M4 in 2019.

I think M4 was impressive for it's time, but it's 2019 now and those of us in the know now see there are superior steels available now that unfortunately have yet to make there way to being widly available
Deadboxhero,

Thanks for the feedback. This makes me really wany M4 hearing this! I'd love to have a knife patina, but I don't want it to rust. Going to David's comments on taking care of the blade, I certainly plan on doing that, but do you have any experience with K390 or M4 pitting/rusting? Is one more prone to the other? That's what I'm really curious about.

Because to be honest, either one will far outdo my needs & capabilities for my light EDC. The thought of having a great quality steel like either of these would be amazing, but either will do. So if they are both great, but one's better in corrosion resistance, that would peak my interests and potentially sway me.

I know, I know... BUY BOTH! :D

Hamilton

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ferider
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Re: CPM M4 vs K390

Postby ferider » Thu Mar 14, 2019 4:36 pm

hambone56rx wrote:
Thu Mar 14, 2019 4:26 pm
Thanks for the feedback!

Incredible to see! That's interesting to see that M4 is right up there with S30V regarding pitting. Can you elaborate on what the Cr-Eq Acetic testing is? I tried to google it and turned up nothing.

Hamilton
The data are from our Larrin, Hamilton, this thread has more information: viewtopic.php?f=2&t=82616. Cr-Eq Acetic is basically an index based on the steel composition, predicting corrosion when the steel is exposed to Acid, like when you cut a lemon.
Deadboxhero wrote:
Thu Mar 14, 2019 3:50 pm
I think M4 was impressive for it's time, but it's 2019 now and those of us in the know now see there are superior steels available now that unfortunately have yet to make there way to being widly available
Well, M4 did get an upgrade via CPM, BBB. That only impacts toughness, but still :)

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Re: CPM M4 vs K390

Postby Deadboxhero » Thu Mar 14, 2019 4:39 pm

Realistically man,you don't pick One or the other based on reactivity. They are both reactive. Any differences between them in real world use is marginal in that aspect.
My M4 Millie has more patina then my k390 but I've just had that knife longer.

You just buy the k390 cause you want the top dawg edge performance without going too extreme.

hambone56rx wrote:
Thu Mar 14, 2019 4:30 pm
Deadboxhero wrote:
Thu Mar 14, 2019 3:50 pm
Like Doc Dan says

"K390, M4 Killer"

K390 is plenty tough for a folder and has superior strength and wear resistance to M4 especially with the HT on the Spydercos.

So if K390 was more available I'd see no reason to own a knife in M4 in 2019.

I think M4 was impressive for it's time, but it's 2019 now and those of us in the know now see there are superior steels available now that unfortunately have yet to make there way to being widly available
Deadboxhero,

Thanks for the feedback. This makes me really wany M4 hearing this! I'd love to have a knife patina, but I don't want it to rust. Going to David's comments on taking care of the blade, I certainly plan on doing that, but do you have any experience with K390 or M4 pitting/rusting? Is one more prone to the other? That's what I'm really curious about.

Because to be honest, either one will far outdo my needs & capabilities for my light EDC. The thought of having a great quality steel like either of these would be amazing, but either will do. So if they are both great, but one's better in corrosion resistance, that would peak my interests and potentially sway me.

I know, I know... BUY BOTH! :D

Hamilton
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Deadboxhero
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Re: CPM M4 vs K390

Postby Deadboxhero » Thu Mar 14, 2019 4:42 pm

Whenever I say M4 I'm always implying CPM M4.

I feel it's safe to say that all "M4" is PM now. I don't think they make the non PM M4 really anymore just like how Cruwear is now all PM except the old stock floating around.

ferider wrote:
Thu Mar 14, 2019 4:36 pm
hambone56rx wrote:
Thu Mar 14, 2019 4:26 pm
Thanks for the feedback!

Incredible to see! That's interesting to see that M4 is right up there with S30V regarding pitting. Can you elaborate on what the Cr-Eq Acetic testing is? I tried to google it and turned up nothing.

Hamilton
The data are from our Larrin, Hamilton, this thread has more information: viewtopic.php?f=2&t=82616. Cr-Eq Acetic is basically an index based on the steel composition, predicting corrosion when the steel is exposed to Acid, like when you cut a lemon.
Deadboxhero wrote:
Thu Mar 14, 2019 3:50 pm
I think M4 was impressive for it's time, but it's 2019 now and those of us in the know now see there are superior steels available now that unfortunately have yet to make there way to being widly available
Well, M4 did get an upgrade via CPM, BBB. That only impacts toughness, but still :)
Big Brown Bear
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Re: CPM M4 vs K390

Postby AccountDeletedUserRequest » Thu Mar 14, 2019 5:06 pm

I haven't seen my K390 Police rust due to cutting different types of foods or moisture in general. Just a very, very mild patina. Almost let down with how little patina it shows.....I was hoping to develop a strong natural patina by the time it warmed up.

My sweat makes it get small orange rust spots, but nothing else has caused it to rust for me. That's pretty normal for any blade steel for me, even stainless.

If corrosion resistance isn't a big concern, I haven't seen a better steel for folding knives than K390. I'm generally a fan of simple steels that are quick to sharpen, and don't place muchvvalue on edge retention....but K390 is very impressive stuff.

I've never seen a steel cut so much cardboard and still have a shaving sharp edge. I touch my knives up when they stop scraping arm hair, so I don't care about how long a steel holds a working edge. Most high edge retention steels seem to lose shaving sharpness pretty quick, but not K390. I'm glad I gave it a shot.

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Re: CPM M4 vs K390

Postby Deadboxhero » Thu Mar 14, 2019 5:25 pm

Agreed, highest wear resistance and edge stability in a Spyder currently.

Really a better comparison is the Rex 45 vs K390.
Not M4.

I still put K390 a tier above Rex45.

Just has more aggression.

Top dawg for me is still definitely Maxamet but K390 seems more friendly in the sharpening and durability department.


Vivi wrote:
Thu Mar 14, 2019 5:06 pm
I haven't seen my K390 Police rust due to cutting different types of foods or moisture in general. Just a very, very mild patina. Almost let down with how little patina it shows.....I was hoping to develop a strong natural patina by the time it warmed up.

My sweat makes it get small orange rust spots, but nothing else has caused it to rust for me. That's pretty normal for any blade steel for me, even stainless.

If corrosion resistance isn't a big concern, I haven't seen a better steel for folding knives than K390. I'm generally a fan of simple steels that are quick to sharpen, and don't place muchvvalue on edge retention....but K390 is very impressive stuff.

I've never seen a steel cut so much cardboard and still have a shaving sharp edge. I touch my knives up when they stop scraping arm hair, so I don't care about how long a steel holds a working edge. Most high edge retention steels seem to lose shaving sharpness pretty quick, but not K390. I'm glad I gave it a shot.
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Re: CPM M4 vs K390

Postby elena86 » Thu Mar 14, 2019 5:26 pm

My K390 Urban is a little beast. We need more K390 ...
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Re: CPM M4 vs K390

Postby Deadboxhero » Thu Mar 14, 2019 5:39 pm

elena86 wrote:
Thu Mar 14, 2019 5:26 pm
My K390 Urban is a little beast. We need more K390 ...
Word on the street is the k390 Urban is a little softer then the K390 Police 4.

That P4 is an edge junkies dream.

Needs an edge before use. The seki factory edge should not be the judge of the steel.
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Re: CPM M4 vs K390

Postby p_atrick » Thu Mar 14, 2019 5:46 pm

Deadboxhero wrote:
Thu Mar 14, 2019 5:25 pm
... but K390 seems more friendly in the sharpening and durability department.
K390 still needs CBN or diamonds for sharpening, right?

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Deadboxhero
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Re: CPM M4 vs K390

Postby Deadboxhero » Thu Mar 14, 2019 6:00 pm

Short answer from my experience, Yes.
I just wouldn't be able to get the edges as crisp at 1000 grit without a type of bonded diamond/cbn.
The diamond/CBN compounds on leather are a nice touch as well after the edge is very very sharp on the stones, the strop gives it a boost in the finesse.

Coated diamond/ CBN is too coarse if you want more push cutting. Too deep a cut, the abrasive grains are fully exposed and penetrate the bevel making a very ragged cut. (Great for draw cutting, like a microscopic serration)

I've seen people get by with a SiC "Norton Fine" 325 grit if one likes that type of toothy edge.

I like 1000 grit (800-1500) 20-10um, I like the blend of polish and toothy.

That works best for the variety of uses I like, a little blend of push cutting precision and draw cutting aggression but best at neither.

p_atrick wrote:
Thu Mar 14, 2019 5:46 pm
Deadboxhero wrote:
Thu Mar 14, 2019 5:25 pm
... but K390 seems more friendly in the sharpening and durability department.
K390 still needs CBN or diamonds for sharpening, right?
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Re: CPM M4 vs K390

Postby AccountDeletedUserRequest » Thu Mar 14, 2019 7:14 pm

Deadboxhero wrote:
Thu Mar 14, 2019 5:25 pm
Agreed, highest wear resistance and edge stability in a Spyder currently.

Really a better comparison is the Rex 45 vs K390.
Not M4.

I still put K390 a tier above Rex45.

Just has more aggression.

Top dawg for me is still definitely Maxamet but K390 seems more friendly in the sharpening and durability department.


Vivi wrote:
Thu Mar 14, 2019 5:06 pm
I haven't seen my K390 Police rust due to cutting different types of foods or moisture in general. Just a very, very mild patina. Almost let down with how little patina it shows.....I was hoping to develop a strong natural patina by the time it warmed up.

My sweat makes it get small orange rust spots, but nothing else has caused it to rust for me. That's pretty normal for any blade steel for me, even stainless.

If corrosion resistance isn't a big concern, I haven't seen a better steel for folding knives than K390. I'm generally a fan of simple steels that are quick to sharpen, and don't place muchvvalue on edge retention....but K390 is very impressive stuff.

I've never seen a steel cut so much cardboard and still have a shaving sharp edge. I touch my knives up when they stop scraping arm hair, so I don't care about how long a steel holds a working edge. Most high edge retention steels seem to lose shaving sharpness pretty quick, but not K390. I'm glad I gave it a shot.
K390 and CTS204P both impress me with their combination of edge holding and ease of sharpening. I feel like both are easier to sharpen and quicker to reprofile than S90V, S110V and Maxamet (Though I've only tried those steels briefly, one knife each). I hope to see Spyderco using more of each.

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Re: CPM M4 vs K390

Postby AccountDeletedUserRequest » Thu Mar 14, 2019 7:16 pm

p_atrick wrote:
Thu Mar 14, 2019 5:46 pm
Deadboxhero wrote:
Thu Mar 14, 2019 5:25 pm
... but K390 seems more friendly in the sharpening and durability department.
K390 still needs CBN or diamonds for sharpening, right?
For sharpening, no. Reprofiling, yes in a practical sense.

I've been using my medium ceramic bench stone to finish mine. I set the bevel with an extra course DMT, then microbevel on the medium stone and that's it. No stropping or polishing besides that. Sharp enough to send hairs flying without touching the skin.


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