CPM440c?

[Blop]

What does "easy breakage" refer to, prying or impacts. I am not sure what "over holds the best edge to takes no" means?



What else have you used, S30V, VG-10, BG-42?

-Cliff

It means, that you will read anything about it from good things to bad things.

Some like it much some don´t.

Prying was done on some blades and those, who done it, might have been expected more.

Used? 440C, 154CM, S30V, 440A and some stainless low carbons.

 

[LHD]

Perhaps I've missed the boat here. What is CPM?

 

[Cliff Stamp]

Used? 440C, 154CM, S30V, 440A and some stainless low carbons.

Did you find S30V chipped vs RWL34 or that the edge bent or just wore more giving RWL34 better edge retention?

Are they not popular or just not for cutlery use?

Not well known in North America and the forums are massively dominated by north american culture, the states in particular.

Perhaps I've missed the boat here. What is CPM?

Crucible Particle Metallurgy. In conventional steel making a liquid metal is poured into a mold making a chunk of steel. Particle or powder metallurgy takes the liquid metal and makes a bunch of *really* small ingots of steel and then smashes them all together to make one large ingot.

-Cliff

 

[Blop]

A better edge quality vs. S30V, that´s what i would expect from CPM154.

I´ve had nice times with S30V and less nice times. I remember the edge chipping once all of a sudden. I was just getting the knife out of pocket, opened it, looked at the edge and found it, reflecting light. I was not cutting any hard before.

Usually the S30V took a nice edge and turned remarkable into a more hair zipping edge after two or three days of my normal use, which contains food preparation, paper and light cardboard cutting and once in a while it cuts soft wood.

I once managed to hold the edge under my normal use for over six weeks with moderate stropping on leather once or twice a week until it wont cut any single hair from my arm. I found that was a long period.

The RWL34 never showed that surprising chip. I didn´t remember any chips under normal use and would give in, that maybe after cardboard cutting there must have been a deformation, that didn´t went away with steeling (that is how i notice a chip: Feel the edge with your thumpnail. If something isn´t alined, try steeling it smooth, if it remains, it will be a chip). But it was very small, so small that you feel yourself a stupid knifeknut to care about this.

I didn´t found the pacience to use it over six weeks again, but the edge holding bored me over time, because there was not much to care about. I never had that hair zipping feeling even after some days of usage. It is not like the SR101 push cutting edge, which should be 52100 + fantasy.

Pressed it into a small nail until the wooden underlay deformed (so i couldn´t cut it) on around 40° included edge angle, no damage and under 30° small destruction at the edge, which was repaired with steeling and resharpening.

Damasteel promotes RWL34 achieve high hardness and that is, what i would recommend for CPM154 too. Mine has HRC 60, don´t know exactly about the S30V inbetween 58 - 60, maybe 59.

From papers and technology i guess CPM154 is the right step forth, because that steel is not that much crowded with carbid formers like S30V and if the production is that good, the carbides must be better distributed than in 154CM.

Guess, that is what i don´t like on S30V. It is crowded. If it doesn´t chip, the edge turns into a microserrated edge. But i can turn any edge into a microsaw if i want to, without that instability of carbide clusters.

I guess, i will get bored about the coming praise of how tough CPM154 will be. I expect an advantage in taking the better edge and holding it without that strong turn into microserration. Maybe a good middle way between push cutting ability and being a micro-microsaw. It surely is the right idea, considering high alloys in blade steel (good technology and not to much put in) and therefor has my sympathy. But it surely will be as tough as most stainless steel grades are.

Damasteel promotes its RWL34 to be much more resistant against breakage even than HS steel. Maybe that counts for thick bars, but on edges?

 

[Cliff Stamp]

154CM actually has a higher primary carbide volume than S30V, and the chromium carbide volume in particular which are the large ones are almost double the amount in 154CM vs S30V. Based on the materials data a CPM version of 154CM should have a more coarse carbide structure than S30V not less. It is interesting because on paper S30V should be more of a fine edge holder. I have seen similar issues as you have noted though and many others have reported the same. If you want ultimate fine edges then you want to go with steels with very little primary carbides so steels like AEB-L which can also achieve very high hardness.

-Cliff

 

[Larrin]

Damasteel did some testing with RWl-34 where they found that it holds a fine edge better than other high-carbide volume steels. They found that those high carbide steels would quickly lose its fine edge and then cut for a long time afterwords. S30V wasn't around at the time, though. It could just be hype as well, but take from it what you want.

 

[Cliff Stamp]

Which steels, and how did they measure the fine edge loss and the cutting ability?

-Cliff

 

[DGG]

I still think 440C is great stuff. I imagine it would only get better as CPM440C

How about a D2, 440C,154CM/ATS34, s30-60-90v, and ZDP combined damascus steel blade? That's the one I'd like to see!

Oh I forgot to add some "Spyderco steel" into the mix. We need some "Cobalt" and they are the only ones making knives with steel that has Cobalt in it.

VG-10 I think it is called.

 

[RJ Martin]

One of the first CPM alloys that Crucible made was a spin-off of 440C. It was ultimately called CPMS60V. It was an improvement over 440C, but the S30V is notches above it.

 

[DGG]

Perhaps I've missed the boat here. What is CPM?

http://www.crucibleservice.com/products/CPM/index.cfm

 

[Larrin]

One of the first CPM alloys that Crucible made was a spin-off of 440C. It was ultimately called CPMS60V. It was an improvement over 440C, but the S30V is notches above it.

They called it a modification of 440C, but part of the reason why they dropped the 420V and 440V names was because they no longer resembled 420 or 440C whatsoever. If you look at the compositions, they don't even look vaguely similar.

 

[Larrin]

Which steels, and how did they measure the fine edge loss and the cutting ability?

-Cliff

I don't remember if they named the steels, though they did have a list of common CPM steels at the time, both from European steel companies as well as crucible. Included on the list was Elmax and S90V that I remember, there may have been a couple others. They measured it by carving wood (there was a picture of little bowls and spoons that they carved), and they didn't exactly have a system for putting out concrete results, i.e. a table with numbers. Damasteel may still put out the book that the results are in. It was called the Damasteel Handbook or something like that. There was all kinds of interesting stuff in it.

 

[M Wadel]

iv read the damasteel handbook, a very useful and interesting book i think its from the mid 90ies

 

[Blop]

154CM actually has a higher primary carbide volume than S30V, and the chromium carbide volume in particular which are the large ones are almost double the amount in 154CM vs S30V. Based on the materials data a CPM version of 154CM should have a more coarse carbide structure than S30V not less. It is interesting because on paper S30V should be more of a fine edge holder. I have seen similar issues as you have noted though and many others have reported the same. If you want ultimate fine edges then you want to go with steels with very little primary carbides so steels like AEB-L which can also achieve very high hardness.

-Cliff

Once there was 154CM and D2 and that kind of steel with ´primary carbides inside. Large and bad for any use.

PM is the step forth out of that problem.

To me it seems, that Crucible has used the PM to get more stuff inside instead of making the same stuff better.

Damasteel for example has just added a small amount of vanadium to the ATS34 mixture. Now, CM does the same. (Is CPM154 a rip off of RWL34, or not, because it is american? )

Gilettes razor blades are PM made low alloyed steel.

Actually Vanadis 4E is the hype at german customs, similar to S30V with just the half of chromium inside (8% instead of 14%) some ppl. who are real carbonistics praise it for its edge holding capability.

So, Roman Landes checked S60V under magnifition and concluded, that the large amount of carbides (many tooth but to little flesh) caused the edge to fail like you were noticing on the small seb. Even though i found that kind of damage, you were describing, pretty large.

 

[Cliff Stamp]

So, Roman Landes checked S60V under magnifition and concluded, that the large amount of carbides (many tooth but to little flesh) caused the edge to fail like you were noticing on the small seb. Even though i found that kind of damage, you were describing, pretty large.

S60V though is very different from S30V. S60V has about 50% more carbon and a lot more chromum and vanadium, the primary carbide volume is going to be much higher than S30V. In regards to the Sebenza, the carbide issue is usually raised and it may be the case, however as I noted in that thread the scale of the damage seems high for that. I need to redo it with other S30V blades to see if this is the behavior of the steel or just that steel.

They measured it by carving wood ...

I have seen this arguement several times, that the lack of primary carbides allow the steel to hold a finer edge longer, but the other steels like D2 will still "cut a long time". To clearify what is actually being said, that steels like AEB-L have been shown to retain push cutting sharpness longer and steels like 440C have better slicing edge retention? Or that edge retention in general is higher with AEB-L until a certain point of blunting is induced and then the other steels will stay at that lower level a lot longer? Does anyone have any actual data to support this with tests of sharpness after extended cutting?

-Cliff

 

[Blop]

QCliff,

S60V has more vanadium but the result is the same: Parts of the edge break away.

How does an edge dull? Is there a difference in push cutting or pulled cuts?

I guess there are tests about this but i just can remember discussions in the german speaking forum about this.

In general it was said that dulling means, that parts of the edge break away. No matter if it was push cutting or pulled cuts.

I guess anybody agrees, that in pushed cuts a weaker part of the edge may break because of the pressure.

I had the imagination that in pulled cuts, the edge would be somehow rounded by the cutting media.

But if you round something you put away material and pressure is needed either. The structure of this material will determine how the rounding will go on.

Anyway, an edge dulls by partial breakouts, that cause further breakouts in the edge behind. The part of the edge behind that breakout is more stressed and so will deform after that and so on.

A homog. grain structure may lead to a homogeneous (less partial noticable)dulling all over the edge but a grain mixture to a more partial (more partial noticable) deformation.

In fact: An edge with a noticable chip is bad and right for maintance.

 

[Cliff Stamp]

How an edge dulls depends on what medium is being cut and how (speed of cuts, impacts and push vs slice). Edges can fracture, deform, wear or corrode. The resulting effect on sharpness is rarely the same in both push cutting and slicing.

It also depends on the angle of the edge. Two steels can have different relative performance at 15 / 10 / 5 degrees, because one of them has a higher resistance to fracture or greater strength. Lee notes this in his book on sharpening, the really brittle chisels for example have a higher final bevel to prevent chipping and let deformation/wear be the method of failure.

You can compare two knives cutting and note a similar decrease in push cutting but a massive difference in loss of slicing ability. "Edge retention" in general is too vague, it needs to be made specific to push/slice as well as media, and if you want to be really complete, include different speeds/impacts, corrosion, etc..

Which cuts better, one of Phil Wilson's fillet knives of one of Ray Kirk's large competition bowies? The answer is obvious, it depends on what you want to cut and how. Phil's knife would slice hemp rope easily, Ray's bowie would chop it much better (and of course massive other differences). The same is true of edge retention.

VG-10 and S30V for example at the same hardness have similar push cutting edge retention on cardboard but S30V is significantly better at slicing aggression. It cuts better for longer. The reason many people have problems with the high carbide steels isn't that the steels are inherently bad, just that they are often used in knives for which they have the wrong optimal set of properties.

To clearify, I think there are issues with over use of primary carbides volumes promoted as the totality of edge retention, Crucible does this for example and it is misleading. However I think the other extreme side of the arguement that they are a simple detriment is also problematic. There are benefits to both high and low primary carbide volumes, it just depends on the type of cutting.

Note that Boye uses steels which have dendretic carbides in their *AS CAST* state, these are huge and aggregated, yet he gets high praise for the cutting ability and edge retention of his knives. The primary dendretic carbides dwarf the carbides in S30V.

Also consider other factors like S60V for example was later dropped soft, ~56 HRC, and then people started to complain about the edge denting/rolling and you still had low machinability and now you got burr problems as well. However when left hard guys like Mayo got really promoted extreme numbers of animals cleaned by professional hunters with S60V knives without resharpening.

-Cliff

 

[Blop]

If you look at the parallelogram of a sharp edge, the sharpest point is between 2 and 0,5µm thick up to the point where it is really dull, lets say 30µm thick.

The sharpest edge ever ground was 0.5µm thick. And i once herad, that the usual edge on edc knifes is around 2µm thick

How will the edge come down from 0.5µm to 30µm?

It looses material.

How will the material get lost?

In the way it is glued together, breaking at the weakest point first.

Whatever it is cut and how it is cut determines the time and way this happens.

Some conclude, that the sharpest edge, a material can take is determined by the average grain size of itself.

 

[harrymole]

I have got a question for you Blop and Cliff. If it is true that as you cut the edge breaks away causing it to become dull. Then evetually will it reach a point where the metal is strong enough not to break away? Example : I have a Spyderco Manix I love this knife razor sharp and cuts like a dream, but it wasn't always so. When I first got it I wanted to get rid of it because it would loose an edge so fast. I thought that the blade was to soft it was easy to cut with a medium Lansky stone. I went ahead and used it from what I have seen on BF sometimes the facotry edge is a bit obtuse and needs to be reground. I used it and re-sharpened it about 3 times now the edge seems to last forever. It seems to me that if the edge (factory) is weak and repeated sharpening wil eventually remove the "defective" material this would hold true for all knives. But, here on the forums I have seen many posts that say their knives get dull quick or chip badly. Is this due to the material being used or mabey how the knife was initially sharpened? See where I am going with this. I have had no futher problems with the Mnaix once the "defective" material was removed. Comments? Thanks.

 

[Cliff Stamp]

It seems to me that if the edge (factory) is weak and repeated sharpening wil eventually remove the "defective" material this would hold true for all knives.

Yes, this happens a fair amount of the time.

But, here on the forums I have seen many posts that say their knives get dull quick or chip badly. Is this due to the material being used or mabey how the knife was initially sharpened?

It can be due to many things, the operator's expectations are too high, maybe anything would have chipped, the initial edge may have been burned, or there may be problems with the heat treatment or it may be an inherent limitation of the steel.

The sharpest edge ever ground was 0.5µm thick. And i once herad, that the usual edge on edc knifes is around 2µm thick

Verhoeven has photographed edges under a high polish of less than 0.5 microns, I assume most of the really high polished edges are similar.

How will the edge come down from 0.5µm to 30µm?

It looses material.

How will the material get lost?

In the way it is glued together, breaking at the weakest point first.

This is too simplistic. The edge can simply distort. The metal can stay there, just be out of alignment. This will also reduce cutting ability, this is in fact the majority of blunting in most cases, because you can just take a smooth steel and use it on a knife which removes very little material however can bring a knife from about 5-10% of optimal to 90-95% in just a few passes, this shows the extent of distortion (it also does some cold working).

However even when steels lose material this doesn't mean it is due to carbide fracture. You can see abrasive scratches on the side of a knife after you cut a lot of cardboard or carpet for example, this isn't due to all the carbides on the sides being torn out. The steel is actually worn away from abrasion, this is very different than fracture from ductility or impact failure. This is why CATRA tests show higher results for S30V than something like 440A, the higher carbide steels stay sharper for longer in that medium at those profiles, they don't go dull faster due to excessive fracture.

If the arguement you propose was true then something like L6 in bainite would have optimal edge retention because its resistance to fracture would be extremely high. However would anyone really argue that knife would stay sharper cutting cardboard or rope vs a blade made in D2. Now yes, if you go to very low edge profiles then you can have an issue with edge stability in the really coarse steels, and blunting can be by fracture in chopping and other heavy work, but you can't just generalize that blunting=fracture and carbides=bad for all work in all edge profiles. This is just as wrong as carbides=edge retention which Crucible promotes.

Some conclude, that the sharpest edge, a material can take is determined by the average grain size of itself.

This is trivially not the case because steels can have huge aggregated carbides, D2 can be 30-50 microns and you can take annealed steel and sharpen it to a razor edge and the grain size is huge. There is no reason why the abrasive can't cut the carbides and through the grains in certain conditions. The grain size of steel are just the austenite boundries usually containing carbides and they will be cut just like the martensite inside them.

30 microns by the way is huge, 0.001" is 25 microns and I have knives for which I can set a caliper at 0.001" and it rides up onto the visible primary edge grind, far behind the secondary micro-bevel which can't be seen by eye. I can take a knife down to 5% of optimal during cutting and this small microbevel is still there even after extended blunting, it would take an insane amount of cutting to grind the edge of the knife back to 25 microns.

-Cliff