CPM 440V...

F

Fung

Joined
Mar 19, 2000
Messages
13
I've been reading some posts about CPM 440 being a brittle steel, is this true ?
I ask because I am going to be getting a Spydie Native soon and plan to use it for simple camping chores (i.e. it may involve some wood whitling) would this chip the blade easily ?
 
I think that CPM 440V is now called CPM S60V. It is a very hard steel because of the Vanadium that is used. That makes it hard to sharpen. I do not find it a brittle steel, but one that is actually very tough. If not properly heat treated I imagine that it would be brittle, as would any steel. You should also be careful not to grind the blade to thin. So far I have had absolutely no problems with chipping.

Keith.
 
As Keith implied, the brittleness is related to the heat treat. Any knife left at full hardness would be quite a lot like glass. So, the knife is tempered down to a lower hardness. If S60V isn't tempered down far enough, it is brittle. If it is at the right hardness, it should do fine.

--JB

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e_utopia@hotmail.com
 
I believe Spyderco's 440V is 56RC. If I'm not mistaken, 440V becomes brittle at 60RC. I've had no problems with my Native.

Paul
 
i recently purchased a native. i used it to remove bung seals/covers from a 55 gallon barrell of lube oil at work. the seals are plastic with an aluminum band holding them on. i've done this for years with other knives and no problems, (specifacally gerber ez outs the latest in ats 34) i used the non serated tip to jab, cut and pop off the seal only to see about 3 chips in my blade. i was disapointed but the chips were easilly removed with an ez-lap diamond rod. Did i abuse the blade? perhaps but thats what i do with work knives....kirk
 
So, what about CPM440V in Kershaw Avalanche. I don't use it too often (I carry MT UDT daily) but I'm sure I will soon (spring comes after all)... So, is 440V tough enough for an all purpose camp folder?

Piter
 
My understanding is that when CPM440V and the new designation CPMS60V for the same steel, manufacturers did have it treated in the 59 60 range which caused brittleness problems. They learned to heat treat to a lower range and alleviated the problem.
In CPM 440V, I have a Spyderco Native, Starmate, Military and Chinook and have had no chipping or other related brittleness problems. I'm sure Kershaw is competent at heat treating too.
John Row
colobbfan

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A day without Spydies is like a day without ... WELL, Spydies!!!

[This message has been edited by colobbfan (edited 02-21-2001).]
 
CPM-440V (S60V) is a very brittle steel. For reference it has half the impact toughness of D2 when both are at 59 RC. And D2 is hardly a high reference point, it is not even one of the tougher steels. It is also very brittle. For reference D2 at 58/60 RC has less than half the impact toughness of A2 at 60 RC.

Now you can adjust the impact toughness by varying the heat treat, so you can get CPM-440V with a decent level of toughness. However you will end up with a much softer steel and you will be giving up a lot of wear resistance and a significant amount of strength to gain the necessary impact toughness.

It is easily possible that you would be better served by a steel that has less wear resistance but a greater toughness and thus can function at a higher RC and thus resist impaction and rolling much better than the softer 440V while having the same level of impact toughness (and an overall higher level of durability given the greater strength).

-Cliff
 
Ciff, as I understand it, the wear resistance is the result of the vanadium in the mix, not the heat treat, so a lower RC resulting from the heat treat would not necessarily mean a lower resistance to wear. As I understand it, the vanadium forms with the excess carbon (over 2%, remember) to make vanadium carbides in tiny crystals held in the matrix of the steel, and these vanadium carbide crystals are what make the edge. That is one of the reasons why it has been my experience that over-honing the blade to too fine an edge can interfere with its cutting ability, because, as I understand it, the over-honing smooths out the crystals, when what you want is somewhat of an aggresive, toothy edge. In any case, I have a StarMate, a BF Native, a Military, and a new Gunting, all with 440V blades. I certainly would not have bought more if I didn't like the ones that I had. I have used and used the StarMate and the BF Native extensively and cut many things with them and never had a problem with them chipping or denting on staples or whatever. I have pried with the StarMate, but I gave that up, not for fear of the blade, but for fear of the pivot and of the G-10 scales.

BTW, it is called CPM S60V now and there is an excellent article in, I believe, the latest "Blade" magazine on the hot new(?) blade materials such as CPM S60V, CPM S3V, BG 42(!), and Talonite.

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Walk in the Light,
Hugh Fuller

[This message has been edited by FullerH (edited 02-21-2001).]
 
FullerH:

<font face="Verdana, Arial" size="2">a lower RC resulting from the heat treat would not necessarily mean a lower resistance to wear.</font>
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In general for a given steel you lose wear resistance as you drop RC points, there are contradictions to this for example in D2 you can get grain refinement at 58/60 RC that you can't get at 62 RC which gives the lower RC more wear resistance. However I would seriously doubt that ~55 RC 440V has the wear resistance of 59-61 RC 440V.

In any case as noted in the last paragraph, this isn't the main problem. I would still assume that even with the drop in wear resistance from 59-61 RC to 54-56 RC, CPM-440V (S60V), is still going to have better wear resistance than most if not all of the current stainless steels, due obviously to the insane C and V percentages. The point however is that it will not be as strong nor as resistant to impact as the harder steels that can functional at such RC's due to the inherent greater relative toughness.

<font face="Verdana, Arial" size="2">That is one of the reasons why it has been my experience that over-honing the blade to too fine an edge can interfere with its cutting ability, because, as I understand it, the over-honing smooths out the crystals, when what you want is somewhat of an aggresive, toothy edge. </font>
Click to expand...

This is a general statement not something that is particular to S90V. Highly polished blades do not have the same slicing ability of blades left at a coarse finish, the loss of cutting ability is a simple matter, it is the same performace difference that you will see if you go from a very fine tooth pattern on a saw to a much larger coarser one. The cutting is proportional to the bite of the "teeth" or basically the depth that they will sink into the material.

In regards to polishing, you will only round out the carbides if you use an abrasive that cannot cut them and thus the cutting action goes the other way. To preserve an aggressive finish at a high polish you want to finish with a diamond abrasive, there are stones up to 1000 grit and belts that are finer still. There are also sandpaper and industry quality stones of higher grits but they are much more expensive than the normal (DMT grade) diamond abrasives.

This "fact" is often used to hype certain materials when the claim is "XXX is a really aggressive material for slicing *but* to really get the most out of it finish at a medium grit hone". The hype part is that any steel with experience a huge gain in slicing ability when you go from a high polish to a coarse finish. If a material is really to be promoted as being an aggressive cutter in regards to slicing, it should retain a significant amount of bite *at* high a high polish. Something which most materials fail at horribly.

-Cliff
 
Thanks for all your responses, I think I will check out that article on Super Steels.
 
Cliff, I am really sold on the steel. I have used it extensively for day to day chores and have had no problems. Now I have admittedly never tried to cut a brass or other metal rod with it as one tester did. This caused, not a chip, but a dent in the matrix that was easily corrected with a hone, if I remember. But I have chopped small branches with my StarMate, about what you would expect with a 3+" bladed folder. I doubt that I would consider 440V for a large camp knife or a Bowie, let alone a sword, but as a steel for a smallis folder in the sub-5" category, or a similar sized fixed blade, I would have no problems with it and would probably prefer it. Well, maybe not as a skinner, cutting into bones with 440V may not be such a good idea. But, then, you always pick your blades for your uses.

I agree with you on the question of sharpening and oversharpening. It was a bit of enlightenment that took me some time to gain.

BTW, do you live in Saint Johns? I have an acquaintance who moved up there some years back to teach in a college. His name is Ted Houckmann (I think that that is the spelling, it may be Heuckmann), and he came from Arlington, Virginia, down in the Lower 48. If you run into him, say that Hugh Fuller sends his best.

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Walk in the Light,
Hugh Fuller
 
FullerH, to clarify, I don't think that CPM-440V (S60V), is a poor blade steel. I just think there are better ones, what I mean by better being detailed in the above.

<font face="Verdana, Arial" size="2">do you live in Saint Johns?</font>
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I live in Flatrock, about a half hour drive away.

-Cliff
 
My 440V Starmate takes an eternity to reprofile on Spyderco's sharpener(many hours), and chipped easily when I accidentaly brought it down on top of one of the ceramic rods. Edge retention seems to be good. It is good steel, just not my favorite.

-IPR
 
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