I don't know, how we got on to this topic but it is certainly true, but then again, it is possible to get a shaving edge which is not much larger than a micron on D2 which has carbides that are in the range of 50 mircrons (average). Edgestability is not only a function of carbide size though but dependent on the combination of carbide size and geometry. You can hone an edge to an edge radius of <1 mircon and still have a very obtuse geometry which will then support the carbides. That is the basic principle of Landes' "Schneidenmodel".
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How quickly should an edge lose "Super Scary Sharpness"?
- Thread starter Uncle Rukus
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I don't know, how we got on to this topic but it is certainly true, but then again, it is possible to get a shaving edge which is not much larger than a micron on D2 which has carbides that are in the range of 50 mircrons (average). Edgestability is not only a function of carbide size though but dependent on the combination of carbide size and geometry. You can hone an edge to an edge radius of <1 mircon and still have a very obtuse geometry which will then support the carbides. That is the basic principle of Landes' "Schneidenmodel".
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I did some testing a while back and found the best edge retention in slicing rope to be with a 600 grit DMT (25 micron, fine). 325 and 600 grit cut about the same as far as edge retention, but the 600 grit was sharper, the 9 micron cut about 1/3 as long as 600 grit.
It would be interesting to see if sharpening actually sharpened the carbides or tore them out, assuming the sharpening media was finer than the carbide. If they get torn out, then the edge, rather than looking like a nice even line, would look like a mountain range, with the valleys being the place where the carbides got torn out, the "toothy" edge that everyone talks about.
I'd think it would also depend on the type of sharpener, diamonds, high speed wet wheel grinder, belt grinder, water stones, etc, as to how the carbides are effected. I've gotten D2 pretty darn sharp and long lasting, witch goes against the large carbide dropping out theory.
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This is interesting reading because I've always been under the impression that S30V has relatively small carbides and a fine grain structure. Because of that i always take S30V up to a high polish. I'll try only taking it up to about 800 grit and see if the scary edge lasts much longer.
According to Crucible, S30V does have small as well as evenly dispersed carbides in the 2 to 4 micron range. According to some people here they have much larger (though still smaller than D2) carbides. I'm not 100% sure who to trust, but I'm leaning towards Crucible. Even on their material data sheet, the microphotos comparing it to 440C show S30V having smaller carbides for the most part.
Not necessarily. It depends on the edge geometry. If the edge is thin then you are right because the carbides are not sufficiently embedded in the matrix and tend to break out. The carbides themselves also often contain fractures so they may fracture first which then facilitates the break-outs. However, if the edge angle is larger, the carbides are better embedded and don't break down as quickly. As a matter of fact, they may lend strength to the edge, which is why at large enough angles the abrasion resistance is higher for these high carbide steels (ledeburitic). But not only carbide size but also carbide fraction is important here. If the carbide fraction is higher, each carbide is surrounded by more carbides and less of the matrix which again destabilizes the carbides at the edge if the profile is too thin (for the given steel).
This is supported by common experiences. If the edge would really break down quickly to the carbide size regardless of geometry, you would be able to maintain a shaving edge on D2 only for the briefest of times (the carbide size is about 50 microns and 50 micron edge radius is not shaving anymore), which is contrary to what many people have experienced.
That has been done already. With fresh hones with sufficiently hard abrasives (doesn't have to be diamond, but novaculite may not be hard enough) it is perfectly possible to sharpen the carbides as long as you don't reduce the edge angle to far and the carbides retain sufficient support from the matrix. This is the problem with the propagation of the "Schneidenmodell". People are suddenly surprised, that highly ledeburitic steels can actually get sharp. There was a case on the german Messerforum, were someone was clearly surprised that the ZDP Caly Jr. was performing very well. That person had thought that a steel with such an enormous carbide fraction could not possibly take a "fine edge" (which is another often misunderstood term)....
With dull hones, tear-out of carbides is not unlikely. Which is why you hear of problems of some people trying to sharpen these steels (D2, S30V etc.) with traditional Arkansas stones. These stones are often too soft and glazed over to sharpen the carbides (especially the VaC), while others using ceramic hones, diamond hones or waterstones, have no trouble getting good edges.
2 to 4 microns seems on the small side judging from what I have read which seems to agree with the information that Larrin has aswell, but the order of magnitude seems right. I would have said more like 3-5 microns, but that is still much smaller than 440C or 154CM not to mention D2. Never really read of anyone claiming a much larger carbide size than that.
However, that is still SIGNIFICANTLY larger than the carbide size in O1 for example and many other simple tool steels which are easily sub-micron size.
Don't worry about it, whether 2-4 or 4-6 makes really no practical difference. And the structures showes that to be about the right size even though the magnification is way too small to make a qualitative analysis. The point is more that there are other steels (mostly non-stainless steels, that have much smaller carbides
Yes, M. Wadel, as far as I understand grainsize has also to be considered.
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Grains don't affect how fine something can be sharpened. Grains are just what iron is made up of. They can be ground away in to any shape you want.
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According to Roman Landes' graphs on how different steels wear (which takes in to account thicker edges for larger carbide steels), the finer carbide steels lose their fine edges gradually while larger carbide steels lose it quickly, but the larger carbide steels hold a medium amount of sharpness for a lot longer than the fine carbide steels do. I think you can view those graphs on Cliff Stamp's site if you don't have his book.
The carbides still tear out, regardless of the abrasive you are using. That's why it is possible to get a fine edge on D2, because the carbides tear out so that you can refine the matrix, otherwise it would be impossible to get D2 as sharp as other steels.
I very much doubt that this is happening the way you describe it, but I am happy to agree to disagree. If a 50 micro carbide breaks out, it leaves a hole almost large enough to see with the naked eye. I don't see how you would refine the matrix to cover a hole that size. Just because the larger carbide steels lose the fine edge quickly doesn't mean that it is impossible to shape the carbides. As a matter of fact, it also goes against a discussion that I had with Landes a while back on the Messerforum. Finally, you would have to examine what "medium sharpness" means, if carbide size would truely be the limit of edge radius, the edge radius for D2 would be 25 microns. That is not medium sharpness. That is plain blunt.
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I'm so glad to see someone ask this question! At the age of 39, I finally got some good blades and a Sharpmaker and learned how to get a really good edge. It seems like I can hardly use my knives without them losing their fine edge. I've gotten to where I almost don't want to use my Manix, so it won't lose it's razor sharpness. Guess I'll just have to settle for fairly sharp in a user knife...........
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@Larrin @HBO!
U both on a right track.
1 of cours u get D2 and simmilar ledeburitc steels sharp, and it is also possible to grind the carbides with standard abrasives.
2 the mentioned "scary sharpness" for me personally beginns below 1µm of edge radius
3 this kinda sharpness can be reached with good equipment such as japanese waterstones (Grit 6000-10000) and a propper strop and good skills
4 At these levels of sharpness u will find a clear manually detectible difference in the sharpening behavior and the edge stability within differnt types of steel (e.g. O1 vs D2)
5 Large carbides tend to chip while grinding when the edge has a low angle 25° and below see pic of ATS 34, page 55 Abb. 22 in my book
6 These large carbides are prone to fracture since they do not have a elastic stable matrix around to absorb sideloads in use.
7 small carbide steel O1, AEB L do have the same behavior on a level about 50 times smaller since carbide sizes are that much smaller
8 With improper mechanical properties due to bad HT carbides can be torn out of the compound while grinding, wo beeing positioned on the edge.
Finally u get the ledeburitc steel sharp for average use and they fit well to slicing cutting action.
Whereas scary sharpness that can be reached with steels like O1 , AEB L can be reached by "Monster-carbide-steels" at the edge parts where there is only a low volume of small carbides inbetween the segregation lines of the large ones.
The stability of this kinda edges (whitch is the core of edgeholding) is due to these facts very different.
High sharpness to hold for longer is dedicatet to small carbide sizes and fair volume fractions of carbides (O1, AEBL)
So for future discussions one has to bare in mind, getting sharp is one thing hold this level of sharpness that can be reached (edge stability) is another.
BTW: Almost all of these facts have been figured out by scientists with the beginning of the 20th century in Germany, Japan, Russia, GB and US (see literature list in my book)
The more improtant question to me here is, how thin can I have my blade/edge geomety according to the properties provided by the steel?
Cause geomety cuts,..... steel determines the level and the duration
U both on a right track.
1 of cours u get D2 and simmilar ledeburitc steels sharp, and it is also possible to grind the carbides with standard abrasives.
2 the mentioned "scary sharpness" for me personally beginns below 1µm of edge radius
3 this kinda sharpness can be reached with good equipment such as japanese waterstones (Grit 6000-10000) and a propper strop and good skills
4 At these levels of sharpness u will find a clear manually detectible difference in the sharpening behavior and the edge stability within differnt types of steel (e.g. O1 vs D2)
5 Large carbides tend to chip while grinding when the edge has a low angle 25° and below see pic of ATS 34, page 55 Abb. 22 in my book
6 These large carbides are prone to fracture since they do not have a elastic stable matrix around to absorb sideloads in use.
7 small carbide steel O1, AEB L do have the same behavior on a level about 50 times smaller since carbide sizes are that much smaller
8 With improper mechanical properties due to bad HT carbides can be torn out of the compound while grinding, wo beeing positioned on the edge.
Finally u get the ledeburitc steel sharp for average use and they fit well to slicing cutting action.
Whereas scary sharpness that can be reached with steels like O1 , AEB L can be reached by "Monster-carbide-steels" at the edge parts where there is only a low volume of small carbides inbetween the segregation lines of the large ones.
The stability of this kinda edges (whitch is the core of edgeholding) is due to these facts very different.
High sharpness to hold for longer is dedicatet to small carbide sizes and fair volume fractions of carbides (O1, AEBL)
So for future discussions one has to bare in mind, getting sharp is one thing hold this level of sharpness that can be reached (edge stability) is another.
BTW: Almost all of these facts have been figured out by scientists with the beginning of the 20th century in Germany, Japan, Russia, GB and US (see literature list in my book)
The more improtant question to me here is, how thin can I have my blade/edge geomety according to the properties provided by the steel?
Cause geomety cuts,..... steel determines the level and the duration
Roman Landes,
This is getting too interesting for me to remain ignorant.
I apologize if this has been discussed before, but where can I buy your book? I did a quick search on Amazon, and didn't see it. Do you have an ISBN number or a retailer I can contact?
Thanks!
This is getting too interesting for me to remain ignorant.
I apologize if this has been discussed before, but where can I buy your book? I did a quick search on Amazon, and didn't see it. Do you have an ISBN number or a retailer I can contact?
Thanks!