A medium bounds for performance : chopping

[Jerry Hossom]

The point I was making is that Rockwell hardness, which does in fact measure the force needed to deform steel using a penetrator, does not accurately predict plastic deformation as it might be experienced by a knife edge. In the case you cite, I would expect CPM-3V to experience plastic deformation and 440C to experience brittle failure when they are both pushed to their limits. The "limit" for CPM-3V will be higher than that for 440C, however.

Hardness is not strength. And that's where the simple solution of finding a steel that can get hard but do so without a lot of carbon falls apart. That's why people competing in the Professional Cutting Competitions are not using low alloy steels.

 

[cds4byu]

The point I was making is that Rockwell hardness, which does in fact measure the force needed to deform steel using a penetrator, does not accurately predict plastic deformation as it might be experienced by a knife edge. In the case you cite, I would expect CPM-3V to experience plastic deformation and 440C to experience brittle failure when they are both pushed to their limits. The "limit" for CPM-3V will be higher than that for 440C, however.

Hardness is not strength. And that's where the simple solution of finding a steel that can get hard but do so without a lot of carbon falls apart. That's why people competing in the Professional Cutting Competitions are not using low alloy steels.

There are lots of different things that are commonly called strength, and we need to clarify what we mean, or we end up talking around in circles.

Two of the strengths are materials properties. The first is yield strength, which is the amount of stress required to create 0.2% (or 2 parts per 1000) permanent deformation in the metal. Yield strength is related to load required to bend a knife or roll an edge. Rockwell, Knoop, Brinell, and Vickers hardness values have been successfully correlated with yield strength; therefore hardness can be used to assess yield strength.

The second strength that is a material property is ultimate tensile strength, or UTS. UTS is the amount of stress required to cause the metal to break (generally "engineering stress", not "true stress", but that's another story). Hardness tests cannot be used to measure ultimate tensile strength.

One of the challenges related to knives and strength is that we sometimes don't distinguish between yield and ultimate strengths. For soft steel (steel that is far from its maximum possible hardness), there is a big difference between the yield strength and the ultimate strength. For hard steels (steels that are close to their maximum possible hardness), there is almost no difference between the yield strength and the ultimate strength. Thus, a soft steel will permanently bend substantially before it breaks, and a hard steel will have almost no permanent deformation before it breaks.

Note that the comment above refers not to absolute hardness, i.e. a RC value, but relative hardness (the actual hardness compared to the maximum possible hardness). And it's a bit of a generalization. But it helps to understand some of what is going on in knife edge performance. If one steel (probably 440C in your example) is closer to its maximum possible hardness than the other (probably CPM-3V in your example) at equivalent hardness values, it's more likely to chip while the other is more likely to deform. That's because the yield stress is almost the same as the ultimate stress, and when it gets to the bending point, it breaks.

Another meaning for strength is "edge strength", which isn't a material property at all, but a combination of the yield and ultimate strengths of the material and the geometry of the edge. The edge strength is generally not well defined, but generally refers to the ability of the edge to avoid damage in response to some kind of usage.

A final strength that is sort of a material property is fracture toughness. Toughness represents the ability to withstand fast fracture. Fracture can occur at gross loads below the yield and ultimate strengths of a material, due to the presence of flaws. For example, in the "famous" YouTube video of the salesman whacking a "katana" sword against the table, only to have the blade snap and the broken piece bounce back and hit him, the blade was not stressed beyond its yield point, and most likely not beyond its ultimate strength. Rather, the impact caused a high load in the area where a flaw existed, which caused the blade to break.

The reason I say that toughness is "sort of a material property" is that the most commonly used measure of toughness, Charpy Impact Energy, doesn't directly measure toughness. The best test for directly measuring toughness, using a pre-cracked compact tensile specimen, only works in thick steels. So you couldn't measure the toughness of a knife blade; you could only measure the toughness of the steel the knife blade was made from, but in a different geometry. Because of this, toughness is extremely difficult to quantify and use in a knife.

Bottom line: Hardness measures yield strength. Fracture tendency is related to the difference between yield strength and ultimate strength. Toughness is difficult to measure, but if it's too low, blades will break under impact loading. Both blade and edge strengths are combinations of material properties and geometry.

If we want to avoid confusion, we probably ought to be careful about which type of strength we reference when we say "strength".

Carl

 

[Jerry Hossom]

I was probably referring to yield strength in stating my views on steels that will deform on hard impacts. The problem I have with the statement that "Hardness measures yield strength" is that my experience and that of some other knifemakers argue otherwise. Under similar loads, two different steels at virtually identical Rc hardness can exhibit greater or lesser degrees of plastic deformation. Similar edges in CPM-1V and A2, both at Rc59 have exhibited substantially different levels of plastic deformation on hard impacts. M60S at Rc60 deformed badly in a test that caused no plastic deformation in two other steels at Rc61.

Carl, you're in a much better position than I am to confirm or refute these findings, but I'd suggest you try for yourself hard impacts on fine edges in CPM-1V, A2, and maybe a couple other steels at the same Rc to see what happens. (Got any nails? ) In a discussion with a steel company metallurgist, I was told that Rc measurements are biased by carbide sizes and distribution. In another discussion, Questek, the company who introduced (almost) M60S acknowledged the problem of excessive plastic deformation in blade sections, even though their steel achieved Rc60, and they had strong commercial incentives to believe otherwise.

It might be difficult to "avoid confusion".

 

[hardheart]

So we need steels with high maximum hardnesses, as well as high UTS, so we can temper down to a high yield strength, still retain a gap between it & the UTS, and resist fracture? And hope that the steel is manufactured properly and that we process it accordingly when making the blades?

it sounds so easy

 

[Jerry Hossom]

One of the challenges related to knives and strength is that we sometimes don't distinguish between yield and ultimate strengths. For soft steel (steel that is far from its maximum possible hardness), there is a big difference between the yield strength and the ultimate strength. For hard steels (steels that are close to their maximum possible hardness), there is almost no difference between the yield strength and the ultimate strength. Thus, a soft steel will permanently bend substantially before it breaks, and a hard steel will have almost no permanent deformation before it breaks.

Note that the comment above refers not to absolute hardness, i.e. a RC value, but relative hardness (the actual hardness compared to the maximum possible hardness). And it's a bit of a generalization. But it helps to understand some of what is going on in knife edge performance. If one steel (probably 440C in your example) is closer to its maximum possible hardness than the other (probably CPM-3V in your example) at equivalent hardness values, it's more likely to chip while the other is more likely to deform. That's because the yield stress is almost the same as the ultimate stress, and when it gets to the bending point, it breaks.

Another meaning for strength is "edge strength", which isn't a material property at all, but a combination of the yield and ultimate strengths of the material and the geometry of the edge. The edge strength is generally not well defined, but generally refers to the ability of the edge to avoid damage in response to some kind of usage.

As I reread this, I'm having trouble with a couple of your assertions. For starters, we certainly do distinguish between "yield and ultimate strengths". Ultimate strength is a threshold I'm not sure I've even encountered in practical knife experience. I've broken knives, but that was under conditions I've rarely approached in actual knife use. The yield strength being associated with relative hardness doesn't completely wash either if you look at the hardening schedules of most of the steels we use in knifemaking. Most of us operate with our steels at no more than 2-3 points below as quenched hardness. In the case of CPM-3V, I use it at only 1 point below quench hardness, having gained back a point or two from cryogenic quenching. With 440C, it's frequently used just 2-3 points below as quenched hardness. I use 154CM AT the published as quenched hardness, again having gained a couple points in cryo. Since these steels exhibit different plastic deformation at similar hardness, relative hardness doesn't explain it either.

Your use of the term "edge strength" isn't what I was referring to either. We understand the relationships between steel properties and edge geometry sufficiently to not confuse or intermix them in the discussion.

I think the issue lies in the cracks between "correlation" and fact.

 

[Cliff Stamp]

L6 is hardly similar to 12C27M. For starters it has over 40% more carbon than 12C27M, and little chromium.

Jerry as I noted before, the carbon percentage alone is not the controlling factor, what is in solution in the austenite. 52100 for example has a lot more carbon than 12C27M but when heat treated the same amount of carbide is in solution in both steels so they will both form similar lathe martensite even though the absolute carbon percentage of 52100 is enough to form plate martensite.

I don't know where you got your strength numbers ...

Carpenter Steel.

This is a complete change of subject, since L6 is not among the steels we were discussing and nothing like the steels we were discussing, e.g. 12C27M, 420HC and 440A.

No Jerry it is perfectly valid because it is a low carbide steel and you were generalizing on carbide fraction. I cited direct material properties to show a much lower carbon/carbide steel is in fact much stronger and tougher than a higher carbon/carbide volume steel.

If you want direct measurements on the edge itself in regards to deformation actually on the micron level, then Landes has done just than and 12C27M is actually much stronger than 440C, 154CM, RWL34, S90V, etc. . This strength is directly correlated to hardness and inversely correlated to carbide volume.

There is a of course a small increase in gross compressional strengh with carbide volume. Compare D2 vs O1 for example which are at extremes of carbide size/volume, the compressive strength of D2 is only 5% greater at 55 HRC and both are identical at 2150 MPa at 60 HRC.

Impact toughness (at least as measured by Charpy testing) may relate to blade toughness, but it tells us nothing about a tendancy for plastic deformation.

Well yes, Charpy toughness is a measurement of toughness not strength. For strength you would look at tensile, torsional and compressive strengths. These are all highly correlated to hardness.

You're saying edges don't deform, as in rolling? You're suggesting a crack will form somewhere besides the edge?

It can yes, it happens all the time in nail contacts. As noted, the deformation of the Fiskars axes was far above the actual micron thickness of the very edge. The edge can still be crisp and sharp while the bevel is deformed to the side. This is usually the case in lateral loading by definition because the loads are on the side of the edge.

Cliff, to suggest that knifemakers necessarily lack intellectual credibility and/or integrity because they're knifemakers is a little off the edge.

I am friends with many knifemakers, all of them are open about the fact they are selling knives and it is obvious they are going to be biased when discussing their products publically. This is of course the same as any other professional selling something. Some will even say that publically such as Bill Martino who used to tell people to not ask him about the products he was selling, ask his customers instead.

At times some knifemakers have broken kayfabe, they all did on the knife list when they noted they would use L6 for their personal knives, they only used the high carbide stainless because it was easy to sell. Alvin noted that he read an article by Loveless who noted that he favored low carbide tool steels vs the high carbide stainess for performance, but what sells is what he makes.

I guess I'm saying, if a steel dents, make it harder, if it then chips, choose a different steel. Does that sound right?

It does according to every steel reference guide you will read.

This post got started way back when by saying that a Fiskars hatchet was of medium quality, and could chop lots of wood.

I just finished one run with the Bruks, it was not significantly different than the Fiskars. It lost the blazing push cutting sharpness at about the same point, and after 852 chops could not shave without a lot of force and draw which was likely to cut the skin. I will do another trial just to bound this and verify that this was not just a run on really abrasive wood.

The point I was making is that Rockwell hardness, which does in fact measure the force needed to deform steel using a penetrator, does not accurately predict plastic deformation as it might be experienced by a knife edge.

Take your S30V blade and temper it progressively softer. Does the edge get more or less resistant to damage when chopping the nails? As I noted, more and more carbide is forming in the steel when you draw the hardness because the carbon and alloy is coming out of the matrix and aggregating on existing carbide. So you are getting more carbide but less and less strength, the latter being directly shown by the loss of hardness.

So we need steels with high maximum hardnesses, as well as high UTS, so we can temper down to a high yield strength, still retain a gap between it & the UTS, and resist fracture? And hope that the steel is manufactured properly and that we process it accordingly when making the blades?

There are lots of steels like that, they are all low carbide and designed to provide high toughness and high strength, you just don't get high wear resistance. it is actually not difficult to get any two of those properties very high, you just can not maximize three of them at the same time.

-Cliff

 

[thombrogan]

Why bother with steel? Some maraging alloys can be hardened to the low sixties on the RC scale and with less than 0.005% cardbon by weight, they won't have so many pesky carbides to clot and weaken the edge.

 

[Cliff Stamp]

I checked the Bruks again, 894 this time. But to be frank, the precision on this is really low. If I did this with a blind run I doubt I could get better than 10%. So in short, there is no way I could tell these two axes (Fiskars/Bruks) apart by checking shaving ability with both at similar edge profile.

If I measured the sharpness on thread maybe, as the Bruks did seem to keep the push cutting sharpness a little longer, but in actual use, I would be surprised if anyone would see a difference. Time to try the Tramontina Bolo if I can find it and maybe break the Battle Mistress out of retirement.

-Cliff

 

[Broos]

I am slowly reading through this thread, but thought I'd give it a shot with an old beater 440C tanto. Edge angle at around 35-40 degrees total. 2.5" nail, and a big nylon hammer. I cut through about 40%, maybe a little less. I had a hard time figuring out why technique could be an issue - hold the knife straight and strong, and hit it with a hammer. I guess the knife could slip as you hit it, though. If I would have done it on a harder surface I could have ounded through, but I drove the nail into the wood and bent it before I could cut through.

Pictures of edge damage:

Some nice dents and one chip.

My conclusion is that this is a test you should not do with your nice knives.

 

[thombrogan]

Yeah, please don't try that with your Lairsson competition cutter.

 

[hardheart]

I had a hard time figuring out why technique could be an issue - hold the knife straight and strong, and hit it with a hammer.

I destroyed a ocuple knives just from the awkward position I was in (not working on a table) and not having the best grip on them.

I guess the knife could slip as you hit it, though. If I would have done it on a harder surface I could have ounded through, but I drove the nail into the wood and bent it before I could cut through.

Happened to me as well, then I put the nail on top of a bit of steel to remedy that. But then it could shift around as I started to apply pressure before the hit, which didn't help with lining up.

It would just take a minute to set up a guide for this sort of thing, which I'll probably do once I redo the HT on some Old Hickories.

 

[Jerry Hossom]

Cliff, we are destined to never agree on knife steel metallurgy. What you are saying flies in the face of all knifemaking experience and knowhow. Lots of outstanding swordmakers use L6 for swords and you're saying they could just as well use 12c27m.

There is not a clear correlation between hardness and strength as it relates to thin sections. Hardness is measured, as you know, with a penetrator that dimples the steel given sufficient force. The strength I'm referring to is that required to resist exactly the king of damage depicted in this photograph. The top blade is 154CM at Rc61. The bottom blade is M60S at Rc60. While there is major deformation above the edge, the edge itself is crushed on the M60S blade. CPM-1V failed in a similar but not nearly as dramatic manner. I would expect the same of 12C27M. I may buy some cheap cutlery and test it the same way. One problem there is finding something with an adequately robust blade above the edge so it won't go Home Shopping Network on me. (Then again, maybe I won't do that...) Cheap is OK, but I wouldn't try it with anything thinner than 1/8" unless I knew what steel I was using.

Broos, it's interesting to see how that blade failed. For starters, the ONLY test conditions I can attest to are using an 8d Common Bright nail from Home Depot. If you use a different weight of nail, I don't know what you might expect. The tanto was clearly not very hard, probably Rc54-55 would be my guess, which is probably where many factories harden 440C. Except for the small chip, those failures are plastic deformation. I got the same kind of failure with an Ontario Machete, which is 1095 at Rc53-55. That damage, while looking pretty dramatic, isn't really too bad when you think about it. The knife is still useful and you can sharpen those dings out of the edge rather easily, especially if you use a small belt sander method. You should try that. Given a convex edge, a repeat of the same test will likely result in less damage.

If a "Competition" cutter can't cut an 8d nail with almost invisible damage, it probably can't cut the hardwood dowel without a ding in the competition. The Professional Cutting Competition is a very serious test of steel. The knife has to have an edge that will easily cut rings off the paper towel tube, slice empty aluminum cans, and/or other very fine cutting challenges, PLUS be able to go through the 2 x 4 in under 10 seconds and slice through a 1" dowel of some unknown tropical hardwood. The tasks vary with each competiton, but they all place a very demanding requirement for an extremely fine cutting edge as well as a very durable chopping edge. Any detectable rolling, flattening, chipping or any other damage results in disqualification.

They do not use 12c27m in these knives.

I need to back up for a second and note that the plastic deformation damage in Broos' knife is not the same as the plastic deformation in the M60S blade. The message from the M60S blade is that the steel can deform beyond the immediate area of contact. What I can therefore expect of both those steels is that a fine edge in made in them will roll or deform easily on even moderate impacts or on hard materials, just like happens with most kitchen cutlery, including some of the better stuff like Henckels. Most kitchen knives, except the real expensive Japanese kind, use steels having those attributes preferentially to harder, more robust steels that might chip. Nothing sadder than a broken point on a $200 chef's knife. A rolled edge that can be quickly straightened with a steel is far preferrable.

So what does this have to do with the subject of the thread? Well, it's what those more robust steels are capable of enduring in edges that are designed for chopping. As you can see in the 154CM blade above, there is fairly modest damage from cutting the nail. Compared with Broos' knife, the 154CM blade has very minor chipping at the very edge. What you see extending up from the chipped area is nail steel that is smeared on the surface of the harder steel.

A well designed edge in GOOD steel that is properly heat treated is capable of amazing cutting potential. Even some steels that are considered less than tough can exhibit a lot of toughness when they are used properly, but there is no remedy for weakness.

 

[cds4byu]

The point I was making is that Rockwell hardness, which does in fact measure the force needed to deform steel using a penetrator, does not accurately predict plastic deformation as it might be experienced by a knife edge. In the case you cite, I would expect CPM-3V to experience plastic deformation and 440C to experience brittle failure when they are both pushed to their limits. The "limit" for CPM-3V will be higher than that for 440C, however.

Hardness is not strength. And that's where the simple solution of finding a steel that can get hard but do so without a lot of carbon falls apart. That's why people competing in the Professional Cutting Competitions are not using low alloy steels.

For a homogenous metal, Rockwell hardness does accurately predict yield strength. (Rockwell hardness, by the way, measures depth of penetration under a fixed load. Brinell, Vickers, and Knoop hardness measure the area of the resulting dimple under a fixed load).

However, in a steel containing primary carbides (such as D2), the steel is no longer homogeneous. The steel consists of very hard carbides in a less hard matrix. In thin sections, such as a blade edge, the matrix strength limits the resistance to deformation, and the hardness of the carbides has little effect. However, when the same steel is Rockwell tested, the hard carbides interact with the indenter and create a larger effective area (the carbides themselves don't deform much, but they push through the matrix around them), which gives a larger Rockwell hardness number.

In our work developing the FFD2 process, we used Vickers microhardness, rather than Rockwell hardness. The indentations that we made were smaller than the separation between primary carbides, so we were able to measure the hardness of the matrix independently from the hardness of the primary carbides. The FF process raised the matrix hardness up to nearly the hardness of the primary carbides.

For steels without primary carbides, the secondary carbides that form during tempering are small enough to increase the strength of the matrix. For these steels, a Rockwell hardness test will give a good indication of yield strength.

If CPM-3V will experience plastic deformation when pushed to its "limit", why not make it harder, which will make the limit higher still? I guess, that as a knife manufacturer, you prefer plastic deformation damage, which is easily repairable, to chipping, which must be ground out.

Thanks for the discussion. I'm enjoying refining my understanding of knife steels.

Carl

 

[hardheart]

I read something about DMT diasharps that stated the surface hardness was around 72. Diamonds aren't 72 Rc, so that must be the measured hardness of the entire surface, the diamonds embedded in the nickel. I kinda figured the same was true for steel with lots of carbides, I thought martensite itself only gets so hard. Same for the complaints about machining very high vanadium content, like S90V or S125V.

 

[Cliff Stamp]

Lots of outstanding swordmakers use L6 for swords and you're saying they could just as well use 12c27m.

No, I am saying that they would be far closer to L6 with 12C27M than they would be with S30V. L6 would be expected to be stronger and tougher than 12C27M because it is stainless which inherently weakens and embrittles the steel.

While there is major deformation above the edge, the edge itself is crushed on the M60S blade.

That is compressive brittle failure and fairly interesting, though not unexpected in a high carbide steel. I would like to see micrographs of the steel, surely this was done when the failure was reported as well as material properties checked on the exact hardening method used. What were the results of that analysis?

I may buy some cheap cutlery and test it the same way.

The cheap ones would not be representative of the ability of the steel as they can have large pockets of retained austenite and often blown grain, they get as soft as close to 50 HRC on the production ones. Get some pieces professionally hardened by someone like Landes who has specialized in those types of steels.

If a "Competition" cutter can't cut an 8d nail with almost invisible damage, it probably can't cut the hardwood dowel without a ding in the competition.

A hardwood dowel is much softer than a nail and the impact area is much larger. The stress on the knife is not even close. The actual working knives which are used to cut hardwoods are often just pearlite, rather surprising to me at first, but it is only wood after all.

They do not use 12c27m in these knives.

Many of the competions have been won by steels with the same carbon content (in solution) and very low carbide volume. That you can use very brittle high carbide steels does not mean you can infer the steels are tough, it could simply means the competition is not demanding on the blades in that regard. It is however a very high test of user skill.

However, when the same steel is Rockwell tested, the hard carbides interact with the indenter and create a larger effective area (the carbides themselves don't deform much, but they push through the matrix around them), which gives a larger Rockwell hardness number.

As a first pass, can you assume an influence of the size of the carbide volume, i.e., dHRC~dCV ?

In our work developing the FFD2 process, we used Vickers microhardness, rather than Rockwell hardness.

Did you perform HRC checks and then transform the Vickers to see the difference?

In regards to the CPM steels and hardness, often the maximum is limited by the furnace tolerance on maximum temperature.

-Cliff

 

[Jerry Hossom]

Many of the competions have been won by steels with the same carbon content (in solution) and very low carbide volume. -Cliff

Which Professional Cutting Competition was ever won by a low carbon steel? You've said "many", now name one.

Cliff, if you think cutting a hardwood dowel is easy, do so with an edge that can also do the fine cutting tasks in that competition. It is easy if the edge is designed to cut hardwood dowels, but it's not so easy if the edge is designed to cut ping pong balls also. Better still, bring whatever you like to one of those competitions and compete in it. See what you're talking about, and talk to some people who actually make it happen. Saying it is "easy" without having ever done it with a competitive knife is arrogant.

Carl, I susect there is an explanation in there somewhere. I appreciate yours. Since most of the high alloy steels we use in knifemaking, and certainly the stainless steels have some primary carbides, the apparent Rockwell hardness might be distorted. What is actually "yielding" though is a very thin piece of steel called a knife edge and I don't know if the correlation studies were focussed on that kind of geometry. You can certainly get a box of nails and see what I'm talking about though.

I might be doing some further testing with CPM-3V at a higher Rc to see what happens. 3V at Rc61 cuts the nail with an almost indiscernible flat spot where the contact was made, not visible from the side - at least not with my eyes. It's a very tough steel. One evaluator tested an Rc61 3V blade by sinking the point 2" into a stump and bending the blade over until the handle touched. Yes, it showed plastic deformation, taking about a 1" set to one side. He bent it back to the opposite side, again touching the handle, then repeated that back and forth until the fourth bend when it finally snapped from fatigue. RC61! Not much reason to want to change anything. BUT, that is steel at Rc61 which does exhibit plastic deformation (reduced yield strength) in excess of what you might expect from another steel at Rc61.

 

[noss4]

I'm surprised with you gentlemen. Chopping nails with a knife and hammer. Shame on you. I would never engage in such an abusive and destructive act.

 

[Cliff Stamp]

Which Professional Cutting Competition was ever won by a low carbon steel?

As noted many times, 52100 has the same carbon in solution in austenite as 12C27M. In solution is what controls the hardening responce. There are also many knife makers who are known for very high performance knives (high sharpness, cutting ability and edge retention) who use steels with well below 1% C, Tai Goo for example.

... if you think cutting a hardwood dowel is easy, do so with an edge that can also do the fine cutting tasks in that competition.

The standard edge on my wood cutting knives is 8/10:0.030"-12/14:0.015". They are actually more acute than most factory folders. That easily cuts hardwood dowels. It does not need to be nearly that obtuse to cut the dowels readily, I only go that thick to cut the seasoned deadwood limbs that are common here which I clear a lot.

The thickness of 0.030" is also not needed for chopping that is just for splitting, if I did not want to baton through knots I could reduce both thickness by about 0.005" . I could cut a couple of degrees off of it if I was willing to not make bad cuts where I know the blade will hit poor angles such as when I have to cut through multiple limbs at odd angles. But that is not practical because there are lots of times in actual work where the cuts are not going to be perfect anyway.

The steels on those blades are also not ideal. An L6 blade at 66 HRC should be close to the limit of how thin the edge can get. I am trying to get a custom in 13C26 at 65 HRC which should benchmark the same for stainless, though frankly 12C27M at 59/60 HRC is a better functional knife steel for that use, the 13C26 is just an extreme benchmark for edge thinness.

One evaluator tested an Rc61 3V blade by sinking the point 2" into a stump and bending the blade over until the handle touched.

Wood deforms, you might want to note the degree the actual blade itself bent. I have bent many knives flat to a piece of wood digging through it without the knife even taking a set. This does not prove the steel was super tough, the wood just bent and not the blade. This is also not impact toughness but ductility.

The edge is also not fracturing at a micron level in the above nail pictures, it is on a much larger scale which will be the area of the initial contact (this includes any side loading effects). Again as noted, if you actually want to see the results of micro loading of an edge then Landes work shows this directly and 12C27M takes less damage than 154CM, S90V, etc. . The carbides just fracture out of the edge and magnify the damage on the high carbide volume steels, it makes them weaker, not stronger.

-Cliff

 

[Jerry Hossom]

Cliff, stop talking about it and do it. If you can make those cuts, do so in a competition in front of witnesses where other people can see you do it. Clearly, you are claiming greater skill and understanding of edges than the best of the knifemakers who are competing in these competitions. For reasons I can't fathom, they seem to think the competitions and the cuts required are pretty challenging.

Tai Goo is a wonderful bladesmith. He does not make competition cutting blades. He is best known for his artistic and primitive bladesmithing craftsmanship. As I think I said, I have one of his knives and admire his work.

If you can do that 3V bending task with something else, do so and take photos. The testing I was referring to was done and reported on here by Gadi Blilious some years ago. All we have from you here is talk and unproven claims. It sounds a lot like Hype. Chop a nail with 12C27M and take some photos. Sink a point 2" into a stump and bend the blade over until the handle touches. You can let the wood bend as much as you like, but take some photos...

52100 has 1.0-1.1% Carbon. 12C27M has 0.52% Carbon. 12C27M has 14.5% Chromium. 52100 has 1.5% Chromium. Don't look much alike to me. Regardless, which Professional Cutting Competition contest was won by a blade in 52100? I'm not suggesting a 52100 blade might not have won one of the contests, though I'm pretty certain that didn't happen. What I am saying is that you don't know a 52100 blade won even though you claimed one did, thus hyping your own storyline with nonfacts - a fairly common tactic. For the record, CPM-M4 is the reigning champion. And that's a fact.

 

[hardheart]

Lin Rhea won in 06 with 5160, AC Richards won at Pomona Forging Clinic in 2005 with 52100, Adam Desrosier won at some time with a damascus blade (according to a Blade show picture thread by RogerP) I don't know what Reggie Barker wins with, but he wins all the time. The Browning competition cutter by he & Jim Crowell is 1084. According to Jeremy Reynolds' memory, the top five finishers in 03 used 1084, 5160, 52100, and a damascus with L6 (I'd bet the other steel was O1, it was Kevin Cashen's)

It's not so easy to see what steels are used, all the cutting competition stats follow the men, not the knives.