CPM440V too hard?

hardheart

hardheart

Joined
Sep 19, 2001
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Does anyone think 440V is too hard a steel for some blade designs? I had a Kershaw 1510 random task, and the edge bevel was very uneven and extremely difficult to reprofile. I just got a Spyderco Gunting a couple of weeks ago, and there was a tiny chip in the blade OOB, maybe the steel is kind of brittle? I saw a magazine article rating 440V 1st in edge holding but last in ease of sharpening amongst something like 10 blade steels (not a recent article, don't remember which mag or when exactly). It's really not the kind of trade-off I'm looking for in a blade steel.
 
Hard??? Depending to heat treatment it might be brittle at (RHC 58+) but when done right - at lower hardness (RHC 55) it is reasonably tough (not still good for choppers) and wery wery wear resistant.

Still I find it easier to sharpen than Benchmades ats-34. I've heard that Benchmade has changed heat treat recipe. I don't have any newer ats-34 - only 154CM.
If you do have diamond stones you'll find no big difference in ease of sharpening between ats-34 and CPM 440V.
 
I know I am not voicing the most popular view, because lots of people seem to love 440V, but it is not my favorite. It does hold an edge extremely well on abrasive cutting media like rope and cardboard. But it is hard for me to put the kind of edge on it that I like to keep on my blades. It cuts well, but it just seems to be hard for me to put the same quality of edge on it that I can on my 52100 and even VG-10 blades.
 
I have not used any 440V blades, however I have used 420V, 10V and 15V as well as other high alloy steels. The problem with sharpening them is that they contain high amounts of very hard carbides, that are in fact harder than common abrasives. To sharpen them well you want SiC or Diamond abrasives. I used a large SiC waterstone for basic reshaping and DMT benchstones or SiC sandpaper for finishing depending on flat or convex bevels.

In general, for ease of sharpening, you will want a high hardness on high alloy steels as at the lower RC those steels will burr far too readily. If you just soften a high alloy steel it pretty much makes it worse to sharpen as now the carbides still won't get cut by soft abrasives and you get a big burr forming that is difficult to remove. The solution is just to use a high quality sharpening abrasive.

This is one of the reasons that stainless steels got a bad rap as being hard to sharpen. People were used to plain carbon steels like 1084 and 1095 which will readily be cut by soft abrasives. The much harder carbides in stainless steels will not be cut by softer buffing compounds and thus the edge gets formed by rounded out carbides and results in poor cutting performance.

Note as well that edge geometry plays a large part in ease of sharpening. I have a CPM-10V blade at 63 RC that is very ease to sharpen. The edge bevel is ground at about ~15 degrees per side and is only about 0.01" wide.

-Cliff
 
I find that with 440V the key is to keep the knife sharp, rather than letting it dull down and then reprofiling. I have no problem keeping shaving edges on my 440V knives by doing somewhat frequent touchups on a fine stone. I have had some chipping problems, but only on knives that were made very early in the 440V adoption period. Once the heat treats became more standardized, the knives seem to hold up fine.
 
I don't have any problems sharpening my Military. As previously stated, the key is not letting the knife get extremely dull in the first place. Over the last 6 months, I've only done two light touchups to my Military with no trouble whatsoever. It really isn't hard to sharpen at all...at least not Spyderco's CMP-440v.
 
I have been able to get a super super sharp edge on my Boa. I keep a utility edge on the back of the recurve but the front and the belly are definately RAZOR sharp. (stole this technique from another forumite. i think it was Joe Talmadge. thanks Joe) it did take a long time to get it re profiled and sharp but since then it has been easy to maintain if i touch it up once a week. it's actually my favorite steel so far because it holds the edge very well. (of course having owned 4 CRKT with AUS-6 i can really appriciate this)I haven't had any problem with it chipping but of course i haven't chopped any bricks or pipes with it. (I use my friends knife for that):D all in all if you don't let it get too dull its easy to keep a good edge
 
I have talked at great length about my experiences with CPM 440V from Spyderco and have found a number of things.

1. It is not the steel to chose if you want a hair popping edge. It can be done, but you really need to thin that edge to 15deg per side or less! It also takes a LOT of practice to do this. This is NOT a simple steel to get a hair popping edge on.
2. However, while a Spyderco Military sharpened with the Sharpmaker of my Fine DMT stone might not shave amazingly well (scrape shaves) that same knife holds and edge on heck of a long times and cuts through paper, cardboard, wood etc like crazy! I cut a lot of bark of a tree with my Starmate (which I still need to send back for a new one as the liner lock is a poor one, lazy me!) and it cut like the Devil!
3. CPM 440V even by Spyderco is not the choice for a chopper. I cut and cut and cut with the Starmate, but a few chops into moderatly hard wood at wrist swing force and the edge was showing dull spots right away. I think the edge folded or impacted slightly. It did NOT chip however.

If you want to use this steel to cut, then you will find it a very good steel, yes it is no M2 for toughness, but then few steels are! I cut a hard plastic toothpaste bottle in half a little while ago. The plastic was very hard and the knife cut it no problem at all. The edge was very very very slightly dulled, but you had to look just so under a light bulb to see the damage. No dents, chips or other nasties, a couple of passes on the 204 and great!

I would get some and try it!
 
My only experience with this steel is in a Starmate. If find it both very easy to sharpen and capable of a stunning edge. I have also experienced no chipping problems. While the edge is relatively thin out of the box, I have thinned it somewhat more by putting a tri-bevel on the edge using a Lansky (@ 17, 20, 25 degrees). I simply use a medium diamond stone for sharpening, finish up on the extra fine and strop. Takes less than 5 minutes start to finish. The knife doesn't just shave, it will take the top off free standing hair. The key is to use a diamond hone that will cut through the carbides. There are several reasons this is one of my favorite production folder, the steel is just one of them.
 
The same use as any stainless with the additional advantage of greater wear resistance via higher alloy content, and benefits of finer grain structure and low carbide segregation.

-Cliff
 
Originally posted by The General

1. It is not the steel to chose if you want a hair popping edge. It can be done, but you really need to thin that edge to 15deg per side or less! It also takes a LOT of practice to do this. This is NOT a simple steel to get a hair popping edge on.
Click to expand...

I disagree. Three of my sharpest knives are 440V, and all are sharpened at the same angle as my other knives on the sharpmaker.
 
OK...

When you say they are the sharpest how are you defining this? I am talking about hair shaving and only that as a test. I have tried a number of differing ways to sharpen this steel on different stones and always the result is the same. This steel can be made to shave but with very great difficulty.

Take AUS-8 for example at 20 degrees finished with a leather strop this steel pops hair at 100 paces. The same job the same way on a CPM 440V blade is mediocre by comparison. Yet cut paper or cardboard and the CPM 440V steed races right through the material where the 8a does a poorer job.

Sal suggests that the step three on the Sharpmaker gives the best all round performance. I find step four the best. I tried an Ultra Fine Spyderco Benchstone on this steel (three seperate blades) and the hair cuttung performance got better but not much. The Same stone on another selection of steels 6a, 8a and ATS-34/154CM gave vorpal results. I have noted how my CPM 10V (Paul Bos @ Rc-58) blade is far simpler to sharpen and holds an amazing edge that shaves! Now this steel has even more Vanadium and Carbon but far less Chromium. Possibly it is the Chromium with the other elements that makes CPM 440V harder to sharpen?

What stones do you use and what is your 'test' that says how sharp they are? If I were to test by general cutting agression my CPM 440V blades would be near enough the sharpest blades I own bar my Sebies, Moran or Custom Doug Mondt. It is only in shaving terms that this steel does less well and is harder to get that hair popping edge. Otherwise CPM 440V is not THAT much harder to sharpen if you want a general utility edge. I agree with Cliff that the Vanadium Carbides require the sue of a Diamond hone to cut. Ceramics only round them off and cutting performance drops then.

I now 'rough' up the edge with several passes on a fine DMT stone before using the step four on the sharpmaker. At 20 degrees per side the edge will shave fairly well and is an amazing cutter in other ways. Oh and I have yet to get this steel to rust or chip!

CPM 440V is a very good steel, just perhaps not the best for a beginner?
 
Well.....for the most part.....I disagree with all of the above. 440V is an EXCELLENT steel.....I believe (this is theory) that the perceived brittleness come from the way it is made, and not in fact from any brittleness inherent in the steel. All the chipping I have EVER seen on 440V is right at the edge, and very minor...and appears to be particles of the material rather than the material itself...as it is PARTICLE METALLURGY....(theory...remember) It take a MOST excellent razor sharp edge and holds it for a VERY LONG TIME> Unlike some here who are commenting about it without ever having touched the stuff.....I have made a LOT of knives out of 440V (HEAT TREAT BY PAUL BOS!!) and it has performed above ALL expectations with only a few MINOR cases of edge chipping....all under pretty severe usage. Thats my input. :)
Heat treat is ALL important to sophisticated steels.....you cant do it in your garage with a $1000 oven and some dry ice. :)
 
Originally posted by Brian_Turner
I disagree. Three of my sharpest knives are 440V, and all are sharpened at the same angle as my other knives on the sharpmaker.
Click to expand...
Yep, the angle has nothing to do with sharpness;) Same for me with 420V.
 
For me 440V just took some getting use to. When I got my 1st 440V knife (Kershaw Ricochet) and sharpened it for the 1st time I wondered what I was doing wrong. I sharpened it the same way as my other knives but just couldn't get it to shave, but it still cut awful well. After a couple more sharpening sessions I had a shaving sharp edge, and soon after I got a really nice edge that would pop hair with the best of them and cut cardboard like mad. I also have a Kershaw Boa in 440V now and have no problems putting a stupid sharp edge on it either.

I think it's just practice and getting use to it or something, maybe there's a bigger learning curve involved with sharpening 440V, I really don't know. I HAD problems with 440V before and I don't now, and I'm using the same sharpening equipment, maybe my technique has changed without me really knowing it. As far as rust is concerned I can't get anything to rust, not even M2 or O1, and I don't use any kind of oil or rust protection. I have managed to chip 440V and pretty much everything else from accidentally cutting into large metal packing staples that box makers like to hide in places where there shouldn't be staples.
 
Same test you're referring to, Wayne. My Native, Military, and Kershaw Boa will all pop a single fine hair at the touch. I don't bother with testing by "patch" shaving when I'm talking about "super-sharp", as then pressure and technique play too much into the equation.

The stones are standard Sharpmaker 204 medium and fine stones, set in the "edge" slots, although I don't let them get dull enough to use the medium stones. Touch ups consist of ten passes (5 each side) on the corners, and then ten on the flats of the stones. And I ain't no sharpenin' pro. Heaven help the blade I try reprofiling.

Truth be told, I also have less sharp (by this test) blades of 440V, and the "sharpest" blade I own is a convex edged CPM-3V blade. The AUS steels, by my experience, can also be sharpened well, but they lose the edge quickly, and to a greater extent than most others.

I have yet to find a steel that can't be made super sharp, with enough work and the right hand. That's why I try to guage my opinion more on the durability of the edge, and how quickly they move off of the ability to just touch them up and into the need for more abrasive media.
I find CPM 440V to be an excellent steel in these terms.

This is a judgement which can also be mitigated by how easily, once on the stones, a relatively durable edge returns. ATS-34, for example is great in these terms.
 
tom mayo :

All the chipping I have EVER seen on 440V is right at the edge, and very minor...and appears to be particles of the material rather than the material itself...as it is PARTICLE METALLURGY
Click to expand...

Consider what that would imply about the grain size of the steel. This is exactly one of the problems that the CPM process is supposed to prevent. If it is happening then the heat treat was blown and excessive grain growth / carbide clumping resulted.

In regard to edge polish, I have used CPM-15V, 10V and 420V, none had any problems shaving hair very finely, nor push cutting light paper, push cutting light thread at ~100 g, etc. . Due to the nature of the CPM process they should produce fine edges because of the small grain size and low carbide segregation.

I also handled a CPM-440V Military from Spyderco, while I never sharpened it (as I never used it), NIB it was as sharp as any other production blade I have seen, and would do similar tests as I mentioned in the last paragraph.

-Cliff
 
cpm is a super alloy.. they may not be hard.. some hardened to only 57 (rockwell).
the reason why its so difficult ... wait..
to sharpen a knive to its razor sharp edge... the sharpening tool have to be harder than the blade... if your blade has a hardness of 57(rock well scale) and if u think that using a sharpening tool about 70 (rockweell) on cpm.. then... kekekek. u are not going to get a good edge,,, cos.. there are lots of carbide ( vana...carbide. i forgot how to spell it). i think the vana.. carbide has a hardness up to 82(rockweell.) so when u are sharpening your blade, the tool only remove the material but not the carbide and infact the carbide is removing your tool... so try using a diamond...tool.. :D :o :mad: :barf: :confused: ;) :D :) :( :o
 
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