How quickly should an edge lose "Super Scary Sharpness"?

Sodak,

You have to go to www.amazon.de and look for Messerklingen und Stahl.

There are two ISBN's (so it's twice as international!)
3938711043
978-3938711040

Uncle Rukus,

All steels; surprizingly, even S30V; have their weak points. If you plan for their weak-points, you can take advantage of their strengths. S30V's greatest strength is its wear-resistance and some folks get the most of it with a thin and toothy edge and others go for a thick and polished it. A lot of us go for a thin and polished edge and just resharpen a lot and consider it a fact of life (I know I do!) when the edge blows out while pruning weeds. I think a little extra time resharpening (which I love doing anyways) is worth the joy of gardening with a tactical folder.
 
When sharpening or when carbides chip out is it the carbide that chips or is the carbide coming out its self? Also how is the carbide held in place in the steel matrix? Is it bonded to the matrix, or does it need the matrix around the carbide to hold it in place?
 
I always figured there are going to be carbides that flick out when sharpening and when cutting but that more stayed in place in the steel matrix than were lost and further, that the larger of these carbides that remained were honed down to the final bevel along with the steel matrix. So, in effect you changed the size of the carbide with the abrasive stone when they stayed in place.

Is this not what is seen in micrographs? I find it hard to believe that all carbides would be affected by flicking out so something has to be going on with that where they get some reshaping during sharpening.

Nevertheless, I like D2, don't much care for S30V at all, and much prefer Sandviks 13C26. The average carbide size of this steel is very small, the edge stays very true and to an apex for a very long time in my cutting tests and its become my favorite stainless to date above anything else I've used.

In my carpet and cardboard cutting trials 13C26 blades vastly out cut the D2 and S30V blades I ran it against. All sharpening was done first with factory edges. Then with my sharpening using my EdgePro 120 grit to reprofile and finished up with the 220 grit followed by two to four swipes on the 1200 grit ceramic rod.

After cutting approximately 5 yards of carpet and four large priority mail boxes up to throw them out the edge of the 13C26 blade Kershaw not only reflected less light back when looking down on it, proving it did less chipping out but it also required less effort to make cuts than either the Spyderco Military in S30V or the Kabar Dozier D2 blade. Not only that but the Kershaw required far less to get that original edge back up to snuff.

I will admit that initially the D2 and S30V blade out performed the 13C26. All lost their biting sharp edge quickly in the carpet which was cut first, but about half way through it became apparent to me that the 13C26 had reached a point where it just kept going and going and going with no noticable change in the edge or effort to cut. The others got tougher and tougher to control until you were eventually forced to straighten the edges out.

Now to me this was what makes the 13C26 an ideal steel for the masses because in my experience most good ole boys (the non knife knut types) don't spend a lot of time sharpening their knives if any time is spent on it at all. They start using it when they get it and with the factory edge. They dull it immediately on the first few cuts where it loses that bite and go from there. To this type the longer that edge stays to a better apex remaining thin enough to be forced through a cut the better.

I grant you things can be affected by edge geometry and profiles but all these I picked were pretty much sharpened down to the same 15 degree angles with the same stones and ceramic for the second run and the results while better for all three were much the same. This simple test that anyone can do has caused me to relook at carbide size and consider that it really can make a difference depending on the type cutting you do and the type edge you expect to keep on a user.

STR
 
question for roman:

does grasinsize have anything to do with how long the steel will hold an edge?
 
does grasinsize have anything to do with how long the steel will hold an edge?
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Of course,

We talk about 2 types of grain size commonly mixed up and causing troubles understanding for most ppl.

Grainsize is austenit grain size (measured in martensitc nedle length or amount of primay austenit grains cuu by a definde line on the SEM)

And we have carbide size (measured in the average diameter with a SEM)

both effect the edge stability intensly the coarser both are, the less the edge will take, hence last.
 
Roman, if you willing to take the time, could you give a short (or long :) ) explanation by what mechanism the small grainsize (austenite) stabilizes the edge? I have no problem seeing the carbide argument thanks to your excellent Hazelnut chocolate model :), but I have trouble visualizing what is going on in the grains. Is the reason that the smaller grainsize makes shorter slip-planes and hence reduces edge deformation?
 
Is the reason that the smaller grainsize makes shorter slip-planes
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OK,

this can be read in any good book of material science HBO incl. Verhoeven.

Toughness of a steel is ruled by many factores such as chemical composistion, microscopic stucture (HT), impurities, segregations, carbide size distributions, austenit grain size...

Lets do an example:

In this example we assume we talk about the same result on hardness, let it be 60 HRC here, but for some reason one pice of steel got coarse grains the other one got fine.

In a martensitic steel the former grain boundaries are formed, while austenizing, and are used as an indicator for toughness on hardened steel. So does the martensitic nedle length, that also indicates the former austenit grainsize.

The more grains per measurement were formed during the HT, the shorter the matensitic nedle lenght is, hence the more slip/gliding-planes u get in the same volume fration of the observed body.

U can compare these grains with allot of small springs with a high sensitivity and spring rate, 3dimensionaly taking loads. So it will take allot more elastic deformations on a high level, before plastic deformation takes place.

The bigger the grains gets the the more ridgid the system is and the distance between elastic deformation and plastic deformations is closer and on a lower level in relation to the grain size (Lack of toughness).

For an edge this means, fine grains will allow more force to be absorbed before it chips at the same hardness of the same steel. This becomes more and more obviours to a user the finer the edge gets steeper the edge angle and the thiner the blade is e.g. razors.
As "micro chipping" is the main wear mechanism of fine edges, every bit of grain size counts as well as carbide size.

Since we want more performace out of a good blade, the construction figures are, to achieve the the slimmest geometry and finest edge to last for maximum time of use.
Hence u have to look for a steel and HT that can provide maximum hardness combined with maximum toughness and for that specific application.
 
Friends and fellow collectors,
Cardboard and a fine knife edge don't really get along well, I use a cheap Stanley with a replaceable blade and save my knives for important tasks, like splitting hairs and cutting single sheet bathroom tissue. A larger angle on the blade will serve better for cardboard.
 
deancase3@aol.com said:
Friends and fellow collectors,
Cardboard and a fine knife edge don't really get along well, I use a cheap Stanley with a replaceable blade and save my knives for important tasks, like splitting hairs and cutting single sheet bathroom tissue. A larger angle on the blade will serve better for cardboard.
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Thank you for contributing such useful information to the thread...

So Roman, when you say scary sharpness for you is anything below 1µm of edge radius, just how sharp is that? I have no idea how to measure that except in a comparison to something like push cutting phonebook paper or single ply toilet paper.
 
Roman Landes said:
U can compare these grains with allot of small springs with a high sensitivity and spring rate, 3dimensionaly taking loads. So it will take allot more elastic deformations on a high level, before plastic deformation takes place.
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Thanks, Roman, for taking the time. So it is because of the lower ductility due to shorter slip planes, increasing both strength and resiliance.


Uncle Rukus said:
I have no idea how to measure that except in a comparison to something like push cutting phonebook paper or single ply toilet paper.
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There is really no good way of measuring edge radius unless you have access to a SEM (like Roman does). You could resolve a micron with a light microscope but the depth of field is so small that imaging an edge straight on is near impossible. But for comparison: a commercial razor blade has according to Verhoeven an edge *diameter*/width of around 0.6 microns.

If you can find, get some old fashion double edge razorblades by the brand "Feather". They make for an excellent reference. A bit more difficult to handle if you do things like paper cutting, but also a good reference are the blades of a standard big razor, which you have to pry out of the head (they are molded into the head). Both have a level of sharpness that is very difficult to doublicate on a "normal" knife. However, both have edges that are very fragile. The edge will significantly and visibly (under magnification) deform on cutting tasks as simple as cutting thread. They will very quickly degrade when cutting paper.
 
Roman Landes said:
With this, and the information that came before it, wouldn't it be possible to come up with a chart of the optimum edge angle/polish level for each steel at different hardness levels? Is this available somewhere?

Thanks to all the knowledgeable people who take the time to contribute to these discussions! :thumbup:
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M Wadel said:
HoB is´nt that higher ductility? or am i just misunderstanding?
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Plastic deformation (ductility) is essentially slip along the slip/glide planes of the crystal. If you had a perfect single crystal, you have very high ductility because the atoms can slip along the slipplanes for a large distance (theoretically infinitely) while encounter an equivalent environment every few angstroms within the periodic lattice. When the grains are small, the slipplanes are short. So when one row of atoms slips over the other it quickly runs into the grainboundary of the next grain were the slipplanes are oriented differently, which prevents the rows from slipping very far. This limits ductility and increases strength. Instead of slipping you push the atomes only a little out of the equilibrium position which causes the grain to act, like Roman said, like little springs. Whether that increases or decreases toughness is not directly clear from this alone, since toughness is the integral under the stress/strain curve. While you have higher ductility and hence a "longer curve", the plastic deformation occurs at much lower force, because the slipping is much easier when you have large grains. But in any event the yield strength will be lower and resiliance likely, too, weakening the edge.
 
I don't know anything about slip planes, but I do know that a finer grain increases both strength and toughness.
 
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