New kitchen knife -- pretty exciting

BTW you can't really compare the wear resistance or cutting ability of 2 different steels, based on hardness alone.

Take for example 2 knives at 58HRC. Some might say they will both have about the same wear resistance or edge retention. However, if one blade is 440c and the other is S90V, the S90V is several times more wear resistant. (http://www.crucibleservice.com/datash/dsS90v7b.pdf)

Why? you have to take into account all sorts of factors, including the type of carbides and grain size and such. For example, ZDP-189 doesn't have any vanadium. And vanadium carbides are much harder and finer than chromium carbides. So for ZDP-189 to compare favorable with a high vanadium steel such as S30V it probably has to be that hard. Which makes it brittle, which requires a laminate, .....

So while it's fun to compare HRC numbers, unless you're keeping the type of steel the same it doesn't mean much.


Stev
 
Sando said:
BTW you can't really compare the wear resistance or cutting ability of 2 different steels, based on hardness and what else I know about the steel.
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Sure, that's true, but ... for kitchen use, we're talking about pretty well-known types of usage. For example, my "go-to" 6" chef's knife is going through some abrasive materials, but not enough that "wear resistance" is usually the dominant factor in edge degradation. In fact, frequent pressure against the cutting board causes the edge to blunt and roll, and this is often the reason the knife stops cutting. This is especially true if I've sharpened to a thinner high-performance cutting edge. Hence the importance of steeling kitchen knives, particularly on softer knives -- if wear resistance were really the problem, steeling would have little effect.

So, we don't know about wear resistance based on hardness alone. But what we're really worried about is edge retention, and in this case, edge retention is more a factor of edge strength (resistance to deformation) than wear resistance. And that, in turn, is directly related to hardness. So I can make guesses -- and usually be right -- on how a steel will perform for me in the kitchen, based on hardness alone, depending on what exactly I want to use the knife for.

So while it's fun to compare HRC numbers, unless you're keeping the type of steel the same it doesn't mean much.
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While it's a mistake to consider hardness directly related to wear resistance in different steels, it's also a mistake to consider wear resistance to always be the dominant factor in edge retention. Cliff Stamp has been pointing out the wear-resistance-is-always-most-important error for years. There are plenty of jobs where other factors -- toughness, strength, etc. -- can be more important factors. Again, in the case of certain kitchen tasks, I'd claim that hardness is a critical factor -- though of course you need to reach an acceptable level of toughness (so the edge doesn't chip out) and wear resistance.

Joe
 
Good point, Joe! (as always)

Didn't think of it in those terms before. Certainly makes sense considering the softness of a Henkle vs. hard custom job. Can't imagine a Henkle at 15 degrees holding up like a fully hardened blade.

I'm going to defer to your knowledge and experience: hardness is the dominate factor.

Still I have to believe that the resistance to deformation is effected by other factors as well. I know the S30V kitchen knives I make at 59-60 HRC and 15 degree edges don't have an edge roll over problem - suckers seem to last forever. I suppose I could make some at 62-64 and see if there is a noticable difference.

Of course you start getting into the brittleness issue. Not all steels can stay together at a given hardness. 440C at 63 would probably crumble to look at, S30V at 63 is still pretty tough.

Maybe Mete can clarify how this gets measured.

Steve
 
hahahhaha, had my head up my butt. Hardness testing is a test of plastic deformation. hahahahhaha ... choke ... spit.

I suppose I was thinking about it's ability to withstand plastic deformation without fracturing. What you're refering to (and rightly so) is resisting the deformation to begin with. And that is the hardness test.

So.....

If different steels are all at, say, HRC 60 they, then by defintion they resist deformation the same amount. However, once they are deformed (by pressing into the cutting board, or the wife hacking beef bones again) one steel might fracture after one bend, one might fracture after 20 bends, another might just stay bent.

But if those steels are limited to pressures below the same amount, they will all perform the same (except for wear resistance). However, above that amount it's going to vary from no ill effect, to rolled over, to chipping.

So.....

The optimum hardness is the minimum amount that will keep the edge from bending during normal use (depends on the type of kitchen work it's designed for). Above that you have the toughness/brittleness scale to contend with and that varies with the steel choice.

(As you can see I'm starting to agree with some of the earier posts in this thread. I'm man enough to admit it.)

I hope this is clearing up someone else's notions besides mine.

Steve
 
mete said:
According to www.agrussell.com the Kai has a center of VG-10 and has a hardness of 65 HRc.
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I am sorry, that is a mistake. I, of course, am responsible for allowing product to be put into the web site without looking at the copy. I hope that most of you recognize that when I put hardness anywhere in my copy I ALWAYS quote it as "55-57 Rc" or for VG-10 I would put it as "59-61 Rc" Any one who quotes one number either has no idea what he is talking about OR he is heat treating and testing the hardness of every piece himself.

In the case of whoever supplied the information on my web site, they obviously had no idea of the facts. changes will begin on monday.
 
A.G.Russell, You're forgiven. ....I've long tried to explain that hardness should always be given as a range rather than one specific number because it can't be controlled that precisely.And the reason (which I also try to explain) is that while composition is often given as a nominal composition , it is always melted to a range for each element......Sando, Hardness testing was originally developed to get an approximate measure of tensile strength. Using it for other purposes can get you in trouble . What often gets the layman confused is that engineering tests are very specific tests for very specific things .For example - while both layman and scientists use the term nonflammable the layman takes that as meaning -it won't burn. The scientist in ASTM tests takes it as reacting to flame in a specific way under specific test conditions .......Knife use - are we talking about a knife to use to skin a warthog ? very thick skin and the hair is packed with abrasive mud ? Skinning a deer where mostly the hide is pulled off with occasional cutting of membrain? impact such as machete or kukri ? slicing veggies with a santoku? The choice of steel very much depends on usage and laboratory tests have to be combined with with experience.
 
ZDP-189 is a powdered steel made by Hitachi. It has been around for quite a while and is capable of 65 HRC. At that hardness it is brittle but the powdered steel structure gives it some ductility so it won't chip too easily.
 
Satrang said:
ZDP-189 is a powdered steel made by Hitachi. It has been around for quite a while and is capable of 65 HRC. At that hardness it is brittle but the powdered steel structure gives it some ductility so it won't chip too easily.
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In practice you will find that a steel supported with softer material on one or both sides will stand a great deal more shock and impact than it would if the support was not there. You can use a much higher hardness with a clad blade than one of a single material.

A. G.
 
Japanese wood carving blades are typically very hard, not 67 HRC, but it isn't uncommon to see them at ~ 64 HRC. I have used a 1095 blade at 66 HRC to carve lots of hardwood with no problems, and it was hollow ground to a thin (<0.010") and acute edge (5-6) degrees. However if I twisted it in a knot I am sure I could break the edge, but the geometry would be the critical factor in that case.

Hardness is just tested by hitting the blade with something hard and measuring how much of a dent is made, usually by the depth of the hole or its width. The amount of energy, the type of indentor, etc., are all well controlled, but in essense it is no difference than testing the hardness of a piece of wood by giving it a whack with a hammer.

(there are a few other types of hardness tests, some of them test indirect properties, such as hitting the material with a ball and seeing how far the ball bounces, these are not the hardness numbers usually quoated though).

-Cliff
 
Are laminated blades with high hardness cores easier to sharpen than a blade that is all of high hardness because the core, though very hard, is also quite thin? I figure that even with a core of 64-66 in hardness, the 420 sides of the WH piece would make that blade not too much of a problem to sharpen.
 
Yes . My scandinavian grind knife is laminated.Many complain that you sharpen the whole bevel but it's not bad since only the center is really hard.
 
Crayola said:
Are laminated blades with high hardness cores easier to sharpen than a blade that is all of high hardness because the core, though very hard, is also quite thin?
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If they are, the sharpening method being applied is very inefficient, as you never sharpen the entire edge bevel anyway. All you need to hone is the last fraction of a mm, "sharpening" anything else is a waste of time, it achieves nothing.

As well, this should not be an issue if the knife is properly ground and the steel chosen to suit the intended purpose of the knife.

This is one of the promoted "advantages" of said blades, but the actual reason for laminates was simply that steel was too expensive to make the whole blade out of, thus wrought iron was used for most of it, after all only the edge has to cut, the rest of the blade is pretty much filler.

That is the Japanese viewpoint, which ignores lateral loads, which are the bane of such blades.

-Cliff
 
Just wanted to add that the view point that hardness is the determining factor edge retention for kitchen knives is not sound. This assumption greatly underestimates the abrasiveness of a wood (or plastic for that matter) cutting board. Just imagine: a few strokes over a (soft) leather belt (stropping) will polish the entire edge bevel (which may be smaller than a millimeter, but is still large to the width of the blade) and if stropped enough will even "pull out" a very fine burr like structure on the edge. Now imagine you are slicing 10 carrots on a wood board. 30 strokes per carot, makes 300 stokes over wood with pressure directly on the edge. Even if you have afforded the luxury of an endgrain board, there will be a large amount of wear and not only deformation or roll. The wear resistant steels will have a much longer lasting edge when hardened to a similar hardness than less wear resistant ones.
 
Try to polish the side of a blade with a piece of wood or plastic. It has little effect as neither material can significantly wear into steel.

Try to lightly steel a kitchen knife after it has blunted. The edge respond greatly, as they have basically rolled.

Even when cutting materials which can abrade an edge (like carpet), roll is still a *huge* factor.

If you have a cheap magnifier (10x-20x) you can look down into an edge and see it has bent. It looks like a sidewinder snake in motion.

Steel it a few times and it is straight again. No significant metal removed. However sharpness is 10x+ times greater.

-Cliff
 
So someone should buy one and let us know how it works. Not me. I am buying a new house and so I will have to sit this one out.
 
Thanks Cliff for that clarification. I am still thinking about it.
Guess I have to try to polish an edge with some wood to get some hands on experience. I can see that an edge that rolls quickly will not be abraded much as the surface area greatly increases. I can also see, that a self-lubricating plastic will not abrade steel very much. I have also read that natural proteins in the leather perform as abrasive particles on a leather strop, so my comparison was probably a bad one, however a canvas strop or a piece of cardboard (Emerson recommends that for stropping) should be very simliar to fibrous wood in its chemical make up, so I don't quite see why a canvas strop would polish steel and wood doesn't? Thinking about it, cardboard contains mostly very fine wood chips?

Also I don't know about the "no significant material removed" while steeling. After several uses I can usually rub a significant amount of metal from my steel. A strop doesn't really remove a "significant" amount of metal either or it would look grayish rather quickly (which is does over time), yet it removes enough metal to polish the edge. Also the pressure when cutting into a material is many times the pressure when polishing the edge bevel as the edge is </= 1 mu while the edge bevel is usually about 3 orders of magnitude larger. Yes, i am aware that the total contact area is larger than the edge when cutting *into* a material, depending on the penetration, but still the basic idea holds, I believe.

I don't doubed that, especially for the soft western kitchen knives, roll is the major factor and that the main function of a steel is the alignment of the edge. I am just surprised that wear shouldn't be a significant effect in dulling a kitchen knife.
 
HoB said:
Also I don't know about the "no significant material removed" while steeling. After several uses I can usually rub a significant amount of metal from my steel.
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This depends on the type of butcher's steel you are using. The coarse grooved steels included with most Western knife sets can wear away metal with sufficient pressure. A smooth or fine grooved steel that is much harder than the blade steel will align the edge and remove virtually no metal in the process.
 
Agreed, I have both a smooth steel and a standard Zwillings steel. The latter removes more material, but after a few weeks of daily steeling you can see that even the smooth one removes material. The new ceramic steels will probably be even more agressive than the coarse grooved ones.
 
Butchers steel will grind metal away readily as they act like files. I have a number of cheap kitchen knives that I sharpen about once a year on a sander and for the rest of the time just hit them with the butcher steel. I should have clarified that I meant a smooth steel.

Getting specific, I recently ran some cutting on cardboard (very abrasive) with a Buck 119, after 15.6 m of 3/8" cardboard cut (2 cm of edge used, push cuts on a 45) the edge had blunted down to 34.1 (4.5) % of its initial sharpness.

After steeling, three passes per side, smooth steel from Razors Edge, the sharpness had jumped up significantly to 65.9 (10.0) % of its initial sharpness.

Thus even on something this abrasive, a large amount of the blunting came from deformation. This was also visible under mag as the edge could be seen to be rolled / dented before steeling and crisp after.

Note as well that wear resistance, as the material property does *not* correlate well to metal removal from a knife edge, as the former is usually abrasive wear (something hard cuts into the steel), which the latter usually happens as the steel just breaks away.

Thus you can take a steel like S90V which has a very high abrasion wear resistance, but leave it soft and the edge will bend and deform, and with continued use fracture away and thus lose metal long before another knife with far less abrasive wear resistance, but which was much harder and thus the edge didn't get floppy and break off.

To clearify, I am not arguing that wear resistance isn't a factor, it is great if you can get it at no cost, but when you have to give up other properties such as hardness, the benefits are not going to be nearly as large as promoted, and in general edge holding is *NEVER* proportional to wear resistance unless you like to use your knives *really* dull.

Smooth steeling can remove metal, but the amounts are trivial. Just try to reprofile an edge with a smooth steel, or try to sharpen a blunted blade. Its major effect is deformation based.

-Cliff
 
Excellent post as usual, Cliff!
Please don't take my persistence to be impertinence: I just want to learn.

What I don't quite understand is your argument that just because you can not reprofile an edge with a smooth steel, the material removal is insignificant. I wouldn't want to reprofile an edge with a #10000 stone either (Quite frankly I doubt it would be possible) and the material removal is *very* small, but obviously not insignificant. I think the SEM images in Leonard Lees book show quite well that major material is not necessessary for edge refinement.

Also, Mr. Glesser has reported on several occations that their tests at Spyderco actually showed that S30V at 57-59 Rc was perfoming better than at harder Rc's and was still having twice the edge retention of ATS-34 hardened to 59-61. If roll is the major factor in edge retention the two steels should have a much more comparable edge retention with the harder steel possibly even pulling ahead.
 
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