Edge retention on cardboard (slicing) : CPM-10V, S30V, 52100 , AISI 420

[Cliff Stamp]

Details on the knives :

Coyote Meadow, CPM-10V (62.5 HRC / actually measured), full deep cryo, ground and heat treated by Wilson.

South Fork, S30V (60 HRC / actually measured), full deep cryo, ground and heat treated by Wilson.

MEUK, 52100, (57/59 HRC on edge), no cold treatment, forged and heat treated by Caffrey, ground by Blade, reground (full height) by Caffrey.

Point Guard (54/56 HRC), no details on hardening, CRK&T.

The blades were used to slice 30 cm (one foot) sections of 1/4" double layered cardboard, against the ridges through 3 cm of edge (just over an inch), on a draw with the edges set at 7-9 degrees per side, no micro-bevel, freehand.The sharpening process in detail :

-shape edge with 200 SiC
-refine with 800 AO
-deburr and reset with 600 DMT
-clean with 3 passes per side on plain leather
-clean with 3 passes per side on CrO/AO loaded leather
-clean on newsprint on leather

The edges were checked under 10x mag to examine burrs, could shave easily on both sides, usually catch hair above the skin, and push cut newsprint at more than an inch where it was being held. All cardboard cutting was done on identical boxes (random sampling through the boxes), and repeated five times with each blade, complete sharpening each time.

What isn't surprising is the order of the blades in regards to how they performed on the cardboard, the Coyote Meadow out cut the South Fork which out cut the MEUK with outcut the Point Guard. What was more interesting was the manner in which they blunted which was very different between the two Wilson blades and the other two knives, easily noticed in the following graph :

http://i7.photobucket.com/albums/y269/CliffStamp/phil%20wilson/south%20fork/cardboard.png

All the blades start off blunting similar with linear relationships with the amount of material cut, however the rate of blunting in Wilson's knives is reduced almost immediately and the rate of loss of sharpness is cut to a small fraction of the initial rate. Specifically, in the last 10 meters they blunt as much as they did in the initial 0.5 meters. However the other two blades keep blunting at the very fast initial rate and thus they are soon not even in the same class.

When I discussed blunting with Wilson many years ago, he proposed initial blunting was deformation and late blunting was carbide and that there were two distinct stages, initial work I did supported this but later more detailed work with more points didn't show two regions but a smooth transfer and it looked like all blades had the same behavior so I was thinking the process was nonlinear as a whole, mainly a log relationship.

It turns out my viewpoint was off because the sample was biased as almost all the knives used had really high carbide volumes and thus high wear resistance. The above graph shows low alloy steels and they have different behavior which supports the carbide hypothesis. As well if you look at the difference between the two Wilson blades in detail you can notice that the Coyote Meadow has a further reduced fall off which is inline with the greater wear resistance it has due to the increased vanadium.

In regards to ease of slicing the cardboard, the cotton cutting well represents the sharpness, as the numbers climb the blades start to be unable to cut the cardboard cleanly and instead is torn. This happens at past 4 meters with the Point Guard and 9 meters with the MEUK. After 18 meters the Wilson blades are still cutting clean, if you extrapolate based on the graph for them to reach the same level of cotton performance it is a many to one advantage due to the fall off in blunting rate.

Consider for example that the South Fork after cutting 18 meters of cardboard has the same sharpness as the PoinT Guard has after cutting 1.8, a difference of a factor of ten, and this ratio actually gets bigger as more cardboard is cut because the Point Guard keeps blunting rapidly and the South Fork is at that point in the region where its blunting is really low.

An additional point of interest, amount of honing for resharpening is identical, all blades are restored back to optimal performance on a 600 DMT rod with one pass per side at 20 degrees, showing the extreme influence of a micro-beveling. Ease of sharpening in terms of setting the initial edge goes South Fork, Coyote Meadow, MEUK, Point Guard. It was very difficult to get the last two softer blades to form clean, I only used the repeat step in the above because it was necessary for them.

As a numerical ranking for sharpening, if the South Fork was a 5 the Coyote Meadow was a 4.5, very close, it was a bit lower because the low grindability requires more precision and my freehand sharpening skills are not what I would call great. If I was using a jig these would be near identical. The MEUK is much lower, easily a three, it tended to burr more readily, and was harder to get crisp and even. The Point Guard was annoying, it was easily a 1, difficult to get a very sharp edge.

In case anyone is wondering, the edge retention of the knives is *greatly* enhanced by the low angles, I also did runs where the edges were set at 10/12 primary and 20 micro-bevel with a 600 DMT rod, the edge retention was much lower on the same class of cardboard. I also ran a Black Jack small also in 52100 against the two Wilson blade in other trials just to confirm the behavior, it was also just as strongly outclassed as the MEUK.

-Cliff

 

[hara-kiri-yogi]

Really interesting, esp. between the Coyote and the Fork -- Thanks very much for your time, effort, and sense of curiosity. -kh

 

[Don M]

Interesting, 7-9 degrees per side with S30V. I don't recall how thin the edge was on the Sebenza you tested, but it was less than this, and it was breaking out. Maybe this is getting close to the limit for S30V, or maybe it is due to Wilson's heat treat that this angle was no problem.

In any case, 7-9 degrees per side would do wonders on cardboard.

 

[digdeep]

Cliff, how critical is the heat treatment? I see heat treats done by Bos, D'holder, and others.
Are some better than others?
Who do you believe does the best heat treat and how is it usually done? Thanks for your input.

 

[Phil Wilson]

Cliff, what you observed is pretty much what I have seen in the field with these two steels. I need to further study your test and maybe relate some in use observations with both hunting knives and fillet knives. I only have one question so far: When you say “massively” slow down are you relating to the fact that the wear slowed down or that the cutting ability slowed down. The graph shows almost a straight line gradual loss of sharpness. Your testing represents a lot of work and is much more precise than what I have done myself. Phil

 

[kel_aa]

What is your conclusion about CMP 30V at 60 vs CMP 10 V at 62.5? Is the 10 V only nominally better in edge retention, considering the extra hardness and Vanadaium?

Can you put your M2 paring knife through the same comparison?

 

[barrabas74]

interesting stuff cliff, thanks for the review.

 

[Joe Talmadge]

Very interesting, Cliff. In regards to the larger-edge-angle testing you mentioned in your last paragraph, did you see any interesting effects regarding Phil's theory about two-stage dulling? If the first stage is dominated by blunting, you'd expect the larger edge angle to start off with much worse performance, but degrade more slowly to the carbide-dominated phase. Were you paying close enough attention to know whether you saw this?

 

[OwenM]

Do you think the harder steels' disproportionate lack of blunting after more extensive cutting is a result of the softer steels being damaged and/or not having the strength to support that geometry?
I have some questions about the "why" behind the 10V blade at 62.5Rc intially blunting faster than the S30V at 60 that are also related to limits of the material vs. edge thickness and angle, but will have to think about how to state them so they are intelligible. I understand you ran the edges the same angle, but am curious as to differences in blade geometry and how close those edges actually are in terms of thickness/support.

Good stuff. While I don't run my edges at angles that low, personally, I think that comparing thin edges at low angles gives us a piece of the puzzle that is often overlooked, and provides a better overall picture of how individual steels perform and compare to others by approaching their functional limits--and since geometry controls performance, and materials control geometry, that's where we really see the difference those materials can make.

 

[Cliff Stamp]

I don't recall how thin the edge was on the Sebenza you tested, but it was less than this, and it was breaking out.

The primary was much more acute, but it was breaking in the micro-bevel which was much more obtuse. I plan to rerun the plywood with this South Fork, I already have a couple of runs, I'll do at least five or so.

Cliff, how critical is the heat treatment?

The composition of the steel defines its limits, the heat treatment attempts to reach them. Consider it like cooking a steak, a dozen people can start out with the same piece of meat, it doesn't all taste the same in the end.

Who do you believe does the best heat treat and how is it usually done?

Wilson has the best performance I have seen so far, easily better than the Sebenza, I have to run it against Spyderco's and Swamp Rat's directly to check them in more detail. Phil has described his exact recipe on the forums.

When you say “massively” slow down are you relating to the fact that the wear slowed down or that the cutting ability slowed down.

I rewrote that section as it was unclear, I meant to say that the two very high wear steels had a dramatic change in behavior almost immediately and the rate of blunting was much induced. They were still cutting quite well at the end, a few minutes of movie capture would be valuable here.

Is the 10 V only nominally better in edge retention, considering the extra hardness and Vanadaium?

It has a slight lead in sharpness at any one point, but it maintains this and thus if you look at the amount of material which needs to be cut to reach the same level of blunting it is much more dramatic. At the end in the above if you extrapolate the graphs the 10V blade looks to be able to cut about twice as much cardboard. A much longer run would need to be done to confirm that this extrapolation is valid.

Can you put your M2 paring knife through the same comparison?

Yes, not on that cardboard though it ran out. That was well over a thousand feet of cardboard cut. Once I get another few thousand feet I have another comparison to run, I would like to see S30V, ZDP-189, SGPS, VG-10 (for baseline), ideally several types of S30V. Then the South Fork vs full hard M2 and 1095. These are all some time away though because of both the massive amount of material it requires and the time.

In regards to the larger-edge-angle testing you mentioned in your last paragraph, did you see any interesting effects regarding Phil's theory about two-stage dulling?

I didn't do it with consistent weights for the tension so you can't plot the same kind of graph and check the rate because cutting ability is nonlinear with applied force. They were more rough runs to benchmark the performance, in all of them the Coyote Meadow had the same long term advantage similar in extent to the above and the Blackjack small (52100) had a more linear blunting responce.

You make an interesting point about deformation vs wear, you would expect if this was indeed the case that you should be able to adjust the curve based on edge angle, however in the past I have found this to be very complex behavior because the edge angles influence the force exerted on the edge, probably by control of the blade.

You would expect, or I would anyway, that from a first gross consideration that as the edge angle is lowered that the blunting would speed up, but this doesn't in fact happen, it usually increases until the point where a critical point is passed and the edge just collapses. I think there are a few effects in competition and they are not linear.

In any case it would be of benefit to repeat the above with a higher and lower angle and see if the shape of the curves would change. It is possible, and very likely that the optimal angle for all of these steels isn't identical. it seems reasonable that the really soft and weak steels would benefit from a more obtuse angle.

You then however end up with the effect of geometry on cutting ability that Mike Swaim noted and that even if you could increase the edge retention, the lifetime of the cutting ability could be lowered because the force to push the blade through the material would be higher at a given sharpness.

I understand you ran the edges the same angle, but am curious as to differences in blade geometry and how close those edges actually are in terms of thickness/support.

The South Fork and Coyote Meadow are near idential in terms of primary grind, block stock and edge thickness/angle. The MEUK is very similar, it is thicker in the spine, but the blade is wider and also has a full height grind, it is convex but *very* light, you need to put a ruler on it to know it isn't flat. The Point Guard has a hollow primary again on similar stock. Note the edges on all of these blades is really wide given the angles are so low, they are about 1/8" wide, so the only part which is stressed is the same for all of them.

Thinking about the influence of geometry, I think there may be an issue with control, and the handle will also influence this. The South Fork for example had the most comfortable grip in hand, however I was doing the cuts in short rotation, and fatigue was not an issue and when they were all really sharp, they all cut the cardboard very well and could easily make very thin slices. In actual use, if I had to just whack up a bunch of cardboard, fatigue and control would be an issue and the performance of the Point Guard for example would be reduced further.

I think that comparing thin edges at low angles gives us a piece of the puzzle that is often overlooked, and provides a better overall picture of how individual steels perform and compare to others by approaching their functional limits--and since geometry controls performance, and materials control geometry, that's where we really see the difference those materials can make.

Yes, I think you need to go low because if you go high enough then everything blurs together. You take a really nice strong steel at 0.035" thick at 20 degrees per side and a really weak steel at the same profile and cut up some rope and neither of them do well and there is a lot of twisting and frustration. Take the same edges down to 0.005" and 10 per side and they will both float through the rope, and one will do it for quite some time.

-Cliff

 

[David Schott]

Cliff, how critical is the heat treatment? I see heat treats done by Bos, D'holder, and others.
Are some better than others?
Who do you believe does the best heat treat and how is it usually done? Thanks for your input.

I was reading through MANY testing threads here, and this is often ignored or not mentioned. Often, so much emphasis is put on which steel is used, what percent of a particular element is existing in a steel, etc etc. Talk to some of the knifemkaers and you will quickly learn that a steel's markings can mean almost nothing compared to what the blade actually is. 1095 has HUGE variances according to tests, and L6 was recently found to be wayyyy off in specs from a particular manufacturer....

It seems that more often than not, these tests are performed assuming both perfect steel composition for its claimed type and perfect thermal cycling, grain refinement, hardening and tempering. Those are some pretty huge factors that will affect performance....I think test on a blade should stay specific to that blade, and not be used as a fool proof test of one steel over another.

After all, I can take a piece of mild steel from home depot and harden it and it will outcut poorly treated steel of any type...

Just throwing that out there...we should always be looking to test, but always be aware of the factors we cannot see and do not have access to...

 

[DGG]

That's a good point. I quess the followup question is, "What is the consistency of heat treatment among manufacuters?"


I'm sure large lots of blades are heat-treated in mass.

 

[Cliff Stamp]

That's a good point. I quess the followup question is, "What is the consistency of heat treatment among manufacuters?"

There have been some problems with some steels, S30V being an obvious one, but the actual reported defect rate is rather low if you consider the volume of units sold. But this of course ignores evaluation strength, what percentage of units sold is subjected to use in depth to produce a failure if one exists and then what percentage of said users would report the failure publically on one of the well known forums.

Deducing actual failure rates from such samples is very difficult because of those two large unknowns which have to be factored in to estimate the actual defect rate from the reported failure rate. The best you can do is look at discriminating users with decent sample sizes and generate an average from them. The statistics are however rarely compiled and even then you are assuming of course it is all factual.

It also changes from one manufacturer to another, take a run through the Swamp Rat forums and see the pictures of blades which have seen so much use there is little coating left on the flats. Swap Rat both encourages use heavily, even extreme use, and the prices are so low that there is (or was anyway) little collector value. They are also promoted simply on performance, so both corrections noted in the above are likely very low. Now take a look around and try and find the same type of reports on other "hard use" knives.

Back to actual defect rates, I have handled, and used extensively, several hundred knives, aside from Ontario, the actual defect rate I have seen is pretty much nothing. In standard scientific work, the criteria commonly used for strength of conclusion is a 1 in 20 error. This means that you are confident that at least 19 times out of 20 the conclusions you have reach are real and that the data is representative. This is the minimum, you aim for higher, but for most fields people will publish at that level.

I would find it very hard to believe that any decent high end manufacturer, and especially custom maker, has a defect rate actually higher than 1 in 20. What you need to consider more critically is the difference, not defect rate, but actual choices made in heat treatement. Note how Fowler and Cashen approach heat treating 52100, it does not produce the same blade, it isn't a question of defects but which attributes are chosen. Alvin Johnston would likely have a different hardening procedure again as would Phil Wilson for the same steel.

It seems that more often than not, these tests are performed assuming both perfect steel composition for its claimed type and perfect thermal cycling, grain refinement, hardening and tempering.

Generally yes, if you assumed otherwise you would likely not use the knife, it is by use that you check these assumptions. You don't of course view the work with blinders, you cross reference it to all other work done as well as other sources you trust as well as consider the expected performance from known materials data and of course the maker, assuming they have actually done any R&D and are willing to share it.

For example I ran two comparisons of 52100 blades vs the South Fork to verify the behavior and it was consistent on both the Blackjack small and MEUK. It also made sense considering the materials data on that steel which has a much lower wear resistance than S30V and both 52100 blades were significantly softer. I have also used other 52100 blades in the past and the behavior seen is also consistent with those two, so I would feel fairly confident that in general if you were to run one of Phil's S30V blades against a standard heat treated 52100 blade, then the S30V would have a large advantage for the above type of work.

Now if you were to take a very non-standard 52100 blade, one at full hardness, with a full cryogenic treatment and a low temper, I would expect it to be different, but even then there are bounds on performance. 52100 no matter how heat treated will never be as corrosion resistant as 440C or have the wear resistance of D2 or have the shock resistance of S7, it is many to one outclassed for each. However if it was 65/66 HRC, with deep cryo, the resistance to deformation would be much higher and thus the intial faster linear responce might have a different shape and the wear resistance would be bumped up a point as Johnston has noted on rec.knives for such class of steels.

I would still however bet that in the long term, for slicing aggression on cardboard, at those edge profiles, then S30V would have the advantage and a significant one at that. However if the profiles were radically altered, specifically if they were hollow ground to edges <0.020" thick at 1/4" back from the edge, and the edges set to primary grinds of 3/4 degrees, with 5/6 degree secondary bevels, then there may be issues of edge stability which Alvin Johnston has noted is a limiting problem with steels with large carbides, work confirmed by Roman Landes, mainly with push cutting sharpness.

I intend to check this to a certain extent by using the Ratweiler for some cardboard cutting as its steel is a varient of 52100 as it harder than the MEUK and Busse has always been an advocate of deep cryogenics, I need to confirm that this is actually used on the SR101 blades, I assume so as it is has been stated for the INFI and the D2 run. Thus I would expect it to have slightly greater edge retention for slicing aggression than the previous blades, but certainly not enough to exceed S30V. If it does I'll give Cobalt my SHBM.

While it would be a fairly extreme viewpoint to assume because you have used one knife in a steel you known how it performs from every maker who uses it, it would be just as extreme to assume that every knife in a steel is so wildly different that you would not be able to make any concrete conclusions about a steel aside from how it works in a knife. This if it was true would lead to the conclusion that the variance in production in both steel and by makers is tremendous. The largest problem as noted is difference in how the steel is hardened. In general, while there are people like Wilson, Johnston and such who run different, in the case of Alvin, radically different, hardening schemes, a large portion of the industry runs the same treatements, often using the same heat treater so you would expect wide runs of consistent performance.

In general when I have such details on non-standard heat treatment I make them available, there are also webpages which the reviews are linked to which note this topic in detail, often constrasting the difference from blades in the same steel from different makers, Doziers vs Swamp Rat's D2, or Johnston vs TOPs in 1095. I intend to compare Phil's S30V to another more standard blade later on in various respects, the review even now contains some details on that work, specifically contrasts the performance on plywood vs the Sebenza.

After all, I can take a piece of mild steel from home depot and harden it and it will outcut poorly treated steel of any type...

I would find it hard to imagine than anyone out there has such variance that this would hold. Have you ever actually made a worked hardened mild steel knife which out performed a custom or production knife?

-Cliff

 

[Ed Fowler]

Mild steel from the 40's has been worked into some very good cutting blades,
A geltleman in Casper Wyo. made knives out of Packard Car Fenders that would put quite a few knives , factory or custom to shame.

 

[Cliff Stamp]

Mild steel from the 40's has been worked into some very good cutting blades,
A geltleman in Casper Wyo. made knives out of Packard Car Fenders that would put quite a few knives , factory or custom to shame.

Which custom and production knifemakers can not get better performance out of their blades than ones made from mild steel and in which attributes is the performance being measured. Was this result ever communicated to those makers so they could address the performance criteria and make sure their knives were being evaluated in a meaningful way?

-Cliff

 

[Cliff Stamp]

I redid the graph to show the trends more clearly using weighted cubic splines :

http://i7.photobucket.com/albums/y269/CliffStamp/phil wilson/south fork/cardboard.png

This shows fairly clearly the dramatic difference in behavior. Note none of the curves can catch the initial blunting point, there needs to be more data taken in that region as the slope is changing so quickly, a check should have been made at 1,2,3,4 cuts instead of just 2 and 4.

It would be interesting to check similar steels to see if the correlation could be made as to what is exactly causing the performance, for example run 0.6 to 1.2% plain carbon steel all at full martensite hardness and see what the curves look like to focus the difference on wear resistance alone.

To clearify, the above just represents edge retention during slicing on abrasive media, it can't be extended directly to push cutting edge retention, nor work done on very hard media, or chopping, or of course cutting in very corrosive enviroments.

-Cliff

 

[magneto]

What a great test Cliff! But I have a question on the S30V steel. How does it take an edge? I purchased a Buck knife in S30V and I can not seem to get it at the hair popping sharpness that I can with other steels. Could that be a trade off with some of these great new steels coming out? Or could it be me?Sure would be nice to be able to get a knife so sharp that the reflection of the blade cuts you, and stay that way!

Phil

 

[Cliff Stamp]

S30V has a low grindability, it takes much more time on an abrasive to remove metal from the edge. In order to compensate for this you have to use micro-bevels. On the simple steels like 52100, they can be ground so easily that you can easily and quickly sharpen very wide edge bevels, but when you move up to really high alloy steels full of hard carbides you want to minimize the contact area, otherwise it just takes way to long. There have been some issues reported of S30V blades with problems and these won't sharpen well, the edge just breaks apart, but ideally it will get very sharp.

-Cliff