M2 vs M4

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kdnolin

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Jan 16, 2017
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For thin kitchen knives, will there be noticeable difference in edge retention? Also is M2 much easier to grind when hardened, at the same RC?

I have used some M4 and like it, but Not only is M4 steel pricy, but it’s also eats a lot of belts.
 
There will be a difference, but it is hard to quantify. M4 has a higher carbide %, so it is more wear resistant. This generally means better edge retention, but that's not always the case. In the kitchen we aren't cutting wear resistant materials, but rather the edge retention is affected by impact upon cutting boards, plates, bones, and hard/tough fruits/vegetables, frozen foods, etc. This requires toughness, which M2 is slightly tougher than M4 (just going by the numbers). Because M2 has a lower carbide %, it also should be easier to grind than M4 at an equal hardness, but not by much. I don't have experience with M2, but I do have quite a bit of experience with CPM M4 64HRC in the kitchen. Edge retention is simply excellent with M4, but M2 should be right there with it.
 
PEO_M4_Carbine_RAS_M68_CCO.jpg


Vs.

M2_Browning%2C_Musée_de_l%27Armée.jpg


Ma Duce all day everyday.
Unless I have to carry it...
 
I'm working on sorting this out myself. I can tell you that the M2 makes a monster of a chef knife and cut super aggressively. I will have a M4 chef to compare it to soon but have had other stuff get in the way. You wont be disappointed with either.
 
I think changes in belt life will be incremental, not drastic, between M2 and M4. We can drop M4 hardness from Rc65/66 to Rc64 too. Those knives have great profiles, and your edge geometry is getting nice and thin.
 
samuraistuart said:
There will be a difference, but it is hard to quantify. M4 has a higher carbide %, so it is more wear resistant. This generally means better edge retention, but that's not always the case. In the kitchen we aren't cutting wear resistant materials, but rather the edge retention is affected by impact upon cutting boards, plates, bones, and hard/tough fruits/vegetables, frozen foods, etc. This requires toughness, which M2 is slightly tougher than M4 (just going by the numbers). Because M2 has a lower carbide %, it also should be easier to grind than M4 at an equal hardness, but not by much. I don't have experience with M2, but I do have quite a bit of experience with CPM M4 64HRC in the kitchen. Edge retention is simply excellent with M4, but M2 should be right there with it.
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CPM M4 seems significantly tougher than M2 at the same hardness. Ingot M4 is a different matter. So CPM M4 is both tougher and more wear resistant.
 
I agree Warren, trying M4 at RC64 should make it somewhat more manageable. We will try it on the next batch.

When looking at AKS prices, I just noticed the difference in price is likely because His M2 is not PM.
Willie71 said:
I think changes in belt life will be incremental, not drastic, between M2 and M4. We can drop M4 hardness from Rc65/66 to Rc64 too. Those knives have great profiles, and your edge geometry is getting nice and thin.
Click to expand...
 
I think the CPM version of M4 is easier to grind. I would try CPM M4 rather than M2. M2 isn't very tough according to Larrin's tests
 
I tried CPM M4, and I like the performance, but the post HT grinding is tough. I built a 2x72 that sits on my table saw, so not a premium grinder and I am a hobbies.

I still have a few bars of CPM M4, just tossing some options around before my next order.
 
I have only done the one M2 chef but the result was so good I bought a lot more. I ran it at the top of what AKS recommends with quench plates and cryo, 400 temper. That should be around 66Rc and it was about .003 at the edge. I wanted to see how much abuse it could take so I left it covered with lemon and onion and swimming in the sink over night. I had family over and I cooked 3 meals a day and used it constantly. I had zero chips. It also took 2 weeks before it began to have a visible patina.Its tough enough for kitchen use at least. I have another utility/test knife that I like a lot as well with the high temper. I wonder if it's like D2 and the large carbides make it a aggressive cutter.
 
M2 is an interesting steel. Crucible made it in cpm early on but found out that there wasn’t much benefit over the cast/wrought material. With only ~.82% carbon, most of the carbides are very small. Similar European grade M2 has higher carbon so euro M2 might be offered in a PM version.

M2 will be cheaper than PM M4 and easy to get. It is an excellent cutlery steel.

Hoss
 
Weird , I have maybe more then 20 knives from M2 steel and they rust even if they look in water ?
@StormW , 0.003 at the edge ? Is it typo or ? Because 0.003 is 0.076mm . ?????
 
A2 is half the price of M2 though. It is easy to grind and can also get very hard if using cryo.
 
Natlek said:
Weird , I have maybe more then 20 knives from M2 steel and they rust even if they look in water ?
@StormW , 0.003 at the edge ? Is it typo or ? Because 0.003 is 0.076mm . ?????
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Yes 0.003 approximately. It's a bit thicker than some of my carbon steel or AEB-L knives. I take the blade down to 0.007 because that's the last notch on my feeler gauge. Then I switch to finish grinding and eye it up at about 50% of the notch. On knives that I was trying for a zero edge I have used a micrometer to verify that they were in the 0.0015 to 0.001 range. I'm not sure what that is in millimeters. Is there something wrong with that? What thickness do you do for a chef knife?

I bought my steel from AKS and it didn't come with certs but I'm pretty sure its M2. The rust resistance is similar to the M4 blades that I have carried every day for the last 10 years. Are you sure that what you had was M2? When its hard I burned up several 120 grit ceramic belts just trying for a nice surface.
 
Of course that I m sure that I have M2 steel and that thing rust easy. If I cut apple with it I can smell it and taste it and that s why I call it ....stinkin ' :) And my personal experience says that M2 can t hold that kind of thin edge without chipping ......no way !
All my blade are in range of 63-64 hrc ....
 
Natlek said:
Of course that I m sure that I have M2 steel and that thing rust easy. If I cut apple with it I can smell it and taste it and that s why I call it ....stinkin ' :) And my personal experience says that M2 can t hold that kind of thin edge without chipping ......no way !
All my blade are in range of 63-64 hrc ....
Click to expand...

You have sulfurized high speed steel, it’s added to make it easier to machine and grind. It also is prone to chipping and stinks when you cut acidic foods.

Hoss
 
kdnolin said:
For thin kitchen knives, will there be noticeable difference in edge retention? Also is M2 much easier to grind when hardened, at the same RC?

I have used some M4 and like it, but Not only is M4 steel pricy, but it’s also eats a lot of belts.
Click to expand...

It sounds like we might be doing some of the same projects. I would be down for swapping some info. I have a small stack that I bought for testing and a few knives. I have 2 M2 pieces and I really like both of them both high and low temper. Willie71 Willie71 found that for M2 he got better toughness out of the high temper. I believe it was a bit of a outlier. I have been dealing with some health problems and have a major remodel in progress so I'm a bit sidetracked but hope to get my test pieces finished soon. I wish I could power test like Willie71 Willie71 but I'm a bit more human.
My number is 360.305.6225 if you ever want to brainstorm about the stuff. I started with this being a alternative to M4 but now I'm really interested in the steel.
 
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