CPM M4 steel question....

7

72jroberts

Joined
Mar 16, 2012
Messages
277
So I picked up the BM 810 today and wanted to ask you guys what kind of qualities M4 steel has.

I searched here and got 37 pages of the key word "cpm m4" and scrolled thru but nothing popped up being specific to m4.

I don't mind you guys sending me links or whatever you do is appreciated!!

Thanks,
John
PS: Great knife, I really liked the handle first and the blade shape second, which is usually opposite of what I do. I got the black coated plain blade.
 
M4 takes a very nice edge and holds it for a long, long time. It also is very tough and can handle alot of lateral stress and can be hardened very deeply so it can also take very thin edges. I think for harder use that may involve more than just cutting but where optimum edge holding is needed its the best steel available. Its a great steel and even though its not stainless when its coated you don't really have to worry about rust. I EDC a Contego and personally think its the best big folder out there, especially when you factor in cost.
 
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I can't speak for the Benchmade, but I have a few Spydercos in CPM-M4 and it is one of my favorite steels. Takes and holds a very keen edge like KalEl mentioned above, and can be made to be pretty tough (Gayle Bradley's competition choppers use CPM-M4). A lot of people stay away from it because of its non-stainless nature, but I've found that it holds up pretty well to my use. I did have a forced patina put on my M4 Military, but my Gayle Bradley hasn't even developed anything too noticeable even after using it for over a year cutting up all kinds of stuff.
 
Seems tough, doesn't chip, easy to sharpen. I have a BM M4 knife and I use it quite a bit on all kinds of stuff.
 
Everything you've read about cpm-m4 applies, it's the same. M4 is definitely one of my favorite steels, if not the favor at the moment. It takes an extremely nice edge very easily and holds that edge for a long time. It doesn't chip, but doesn't really seem to roll much either. Sharpens easily, takes a nice polished edge, but also preforms spectacular if left a bit toothy. M4 is really a great all around steel for a folding knife. It's one downfall is obviously that it is not stainless, but with a coated blade it is a non issue. The sharpened bevel can rust if neglected though.
 
I haven't used M4 or CPM M4, but I've used M2. If you're looking for a steel to hold a very sharp edge for a relatively long time, then M4 should work. I've cut nearly 400-500 inches of cardboard with the same 1.5 inches of blade with M2, and it would still shave my arm above the skin. Heat treatment is everything though. My blades run between 64 and 66 HRc. I have no idea what range BM or Spyderco run their hardness.
 
me2 said:
I haven't used M4 or CPM M4, but I've used M2. If you're looking for a steel to hold a very sharp edge for a relatively long time, then M4 should work. I've cut nearly 400-500 inches of cardboard with the same 1.5 inches of blade with M2, and it would still shave my arm above the skin. Heat treatment is everything though. My blades run between 64 and 66 HRc. I have no idea what range BM or Spyderco run their hardness.
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Spyderco runs their m4 pretty high, around 64 I think. Benchmade runs a bit lower. I believe the more recent knives are run around 62 and the older ones 59-61.
 
Oh good. I was hoping they didn't stop at 60 or some other such nonsense. IMO, it's a waste of steel to use M series steel less than 63.
 
CPM-M4 is Crucible Particle Metallurgical process of M4. The Particle process gives even distribution of the steels composition this is later important for heat treat and the steels performance.

Molybdenum steels (M category) usually have a low toughness compared to other steels such as CPM-3V but still higher then most stainless steels.

It can be hardened between 61-66HRC given a few points on either side of course. The harder it goes the more it is suited for cutting only.

Affects of some of the elements that make M4 such a wonderful steel (source, Zknives.com):

Molybdenum (Mo): A carbide former, prevents brittleness & maintains the steel's strength at high temperatures. Improves machinability and resistance to corrosion. Present in many steels, and air-hardening steels (e.g. A2, ATS-34) always have 1% or more Molybdenum.

Tungsten (W) - Scientific Wolfram. Strongest carbide former after Nb and then V. W increases wear resistance. When combined properly with chromium or molybdenum, tungsten will make the steel to be a high-speed steel. The high-speed steel M2 has a high amount of tungsten.

So, M4 has the same amount of Vanadium as S30V, but ad Mo and W to it and one has a steel that is high wear resistant, tough, can be ground very thin, take a fine edge and reach high hardness. It is just, not stainless...

This is my opinion at least. Ps, I have a video of a custom maker Andre Thorburn and his personal folder with CPM-M4 at 67 HRC where he shows how P600 grit does nothing to the steel but remove some of the light grey patina.

It is an awesome working mans steel IMO and it gets great character with a patina.
 
Thanks Guys,
and Marthinus thanks for all that technical info, that's what I was after, the theory and use. Oh yeah, I used to live in Pretoria, what a great city!! Good Times! Baie Dankie, hoor!!

John
 
M4 is one of the best around but it is vulnerable to the elements if not cared for properly. Best if coated in DLC. I keep hoping Spyderco will do a M4 blade coated in their excellent DLC. But Benchmade seem more inclined to use M4 these days. Either way, its a great steel. Some say M390 is a close alternative in stainless.
 
marthinus said:
CPM-M4 is Crucible Particle Metallurgical process of M4. The Particle process gives even distribution of the steels composition this is later important for heat treat and the steels performance.

Molybdenum steels (M category) usually have a low toughness compared to other steels such as CPM-3V but still higher then most stainless steels.

It can be hardened between 61-66HRC given a few points on either side of course. The harder it goes the more it is suited for cutting only.

Affects of some of the elements that make M4 such a wonderful steel (source, Zknives.com):

Molybdenum (Mo): A carbide former, prevents brittleness & maintains the steel's strength at high temperatures. Improves machinability and resistance to corrosion. Present in many steels, and air-hardening steels (e.g. A2, ATS-34) always have 1% or more Molybdenum.

Tungsten (W) - Scientific Wolfram. Strongest carbide former after Nb and then V. W increases wear resistance. When combined properly with chromium or molybdenum, tungsten will make the steel to be a high-speed steel. The high-speed steel M2 has a high amount of tungsten.

So, M4 has the same amount of Vanadium as S30V, but ad Mo and W to it and one has a steel that is high wear resistant, tough, can be ground very thin, take a fine edge and reach high hardness. It is just, not stainless...

This is my opinion at least. Ps, I have a video of a custom maker Andre Thorburn and his personal folder with CPM-M4 at 67 HRC where he shows how P600 grit does nothing to the steel but remove some of the light grey patina.

It is an awesome working mans steel IMO and it gets great character with a patina.
Click to expand...

Thanks for pointing out that Thorburn video, the surface hardness of CPM M4 often goes unmentioned when people talk about its qualities. When I got my Gayle Bradley, I forced a patina on it with a lemon overnight. It came out super dark, but it doesn't look great because it's very spotty. For the life of me, I can't get this patina off; 0000 steel wool and metal polish literally do nothing. It's pretty incredible just how hard this stuff is.
 
Yep--I tried to give my GB a nice brushed finish and couldn't get the 600 grit to even scratch the blade. It's a wicked steel.
 
mkjellgren said:
Spyderco runs their m4 pretty high, around 64 I think. Benchmade runs a bit lower. I believe the more recent knives are run around 62 and the older ones 59-61.
Click to expand...

They are both around the same now. BM advertises the 810 as 62-64 hardness, and Spyderco lowered the hardness a bit after the first run of GBs.
 
KalEl said:
M4 takes a very nice edge and holds it for a long, long time. It also is very tough and can handle alot of lateral stress and can be hardened very deeply so it can also take very thin edges. I think for harder use that may involve more than just cutting but where optimum edge holding is needed its the best steel available. Its a great steel and even though its not stainless when its coated you don't really have to worry about rust. I EDC a Contego and personally think its the best big folder out there, especially when you factor in cost.
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I agree with KalEl, the M4 steel is sweet and with a little time can be razor like and maintain for a long period.....My Spyderco Gayle Bradley has held up really well under all kinds of cutting tasks. Just remember to clean it after use, cause M4 will rust or take on a pantina effect when cutting certain corrosive items.
 
Misanthropia said:
Thanks for pointing out that Thorburn video, the surface hardness of CPM M4 often goes unmentioned when people talk about its qualities. When I got my Gayle Bradley, I forced a patina on it with a lemon overnight. It came out super dark, but it doesn't look great because it's very spotty. For the life of me, I can't get this patina off; 0000 steel wool and metal polish literally do nothing. It's pretty incredible just how hard this stuff is.
Click to expand...

I had a similar experience, i had a light grey patina on my GB and I can not remove it, nor can I apply a deeper one. Seems once a greyish patina has formed it protects the blade quite well.
 
hardheart said:
They are both around the same now. BM advertises the 810 as 62-64 hardness, and Spyderco lowered the hardness a bit after the first run of GBs.
Click to expand...

I heard the same, but I could never find any confirmation about it. Either way. 62-64 in good for the steel regarding a production company. They have to concider how many people use a knife as a cutting tool vs those that use it for everything. Running it to hard can result in to many returns making it not worth while.
 
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