Carbides on Cutting Edge

[Juha Perttula]

I have not found in my cutting tests that carbide-rich steels are better than carbon steels. The reason is that I have tested extremely sharp blades and in that case there is no room for carbides on the thin cutting edge. In the Figure 1. is shown a microscope image of exceptionally good group of carbides on the cutting edge, generally fewer or nil carbides can be found on very sharp edge.


Fig. 1. Microscope photo of carbides (white) on a cutting edge

It is difficult to photograph the cutting edge because the shallow depth of field of light microscope. For that reason I have made for you a hazelnut chocolate demonstration, which clearly simulates the situation. My test equipments are shown in Figure 2.


Figure 2. Marabou hazelnut chocolate demonstration equipment.

Marabou hazelnut chocolate contains 17% nuts. If we think that chocolate is steel matrix and nuts are carbides, it simulates a carbide-rich steel. The chocolate plate can be sharpened by kitchen grater. So we can visualize the fact that, when a blade is sharpened very sharp, there is no many carbides on the cutting edge (Figure 3). Thus, the steel matrix will make the majority of the cutting work. In addition, the carbides on the thin edge are not surrounded at four sides by steel matrix and they may drop off.



Figure 3. Hazelnut chocolate cutting edge (chocolate is steel and nuts are carbides).

So, the hazelnut chocolate demonstration shows it clearly; when the target is ultimate sharpness, carbide-rich alloy steels are not necessarily better than plain carbon steels.

http://www.juhaperttula.com/

 

[PatriotDan]

Juha, most knives made in your country have a quite acute edge angle, would you say that your findings are relevant for lower edge angles also? (Lower as in, say 30...45 deg inclusive)

 

[Juha Perttula]

Juha, most knives made in your country have a quite acute edge angle, would you say that your findings are relevant for lower edge angles also? (Lower as in, say 30...45 deg inclusive)

I have studied inclusive angels about 20 deg. Situation with 30..45 deg angles could be different. However, I think the most important factor is sharpness. If you need a blade which can shave a beard, carbide-rich steel is not necessarily the best. But if you need a blade which is sharp enough to cut a manilla rope, carbide-rich steel is the best. A slightly blunt edge, for instance, if it have roundness of about 0.01 mm, then there is room for many carbides and it can keep the edge "forever".

 

[r8shell]

Finally, a visual demonstration that I can understand. Thank you.

 

[Alberta Ed]

Very interesting. I can get a sharper edge faster on simple carbon steels such as 1070, 1095, 52100 than I can on high carbide steels such as D2 and S30V, but both can achieve mirror-smooth edges. At coarser levels (DMT red hone), the high carbide steels seem like they cut more aggressively. Some high carbide steels like CTS-XHP and S35Vn seem to fall in between; they will take a very fine edge with less time and effort.

 

[Twindog]

I struggle with this issue. In a powder steel, the carbides run 2-4 microns. The edge of a very sharp knife is going to be 1 micron or less. I think straight razors get to 0.35 microns.

So, yes, there is not room on the apex for unsharpened carbides. But who says they are not sharpened? On a coarse steel like D2, the carbides can be 50 microns in size and clumpy, which means that almost any stone will tear out the carbides. So why does D2 steel hold an edge better than 1095? My thinking is that the carbides are sharpened along with the steel matrix. A hard Arkansas stone or an extra fine diamond stone will have a coarseness of 8-15 microns, which seems fine enough to hone the carbides without tearing them out of the matrix.

Also, the carbides on powder steels are fine and well distributed. A Norton 8000 water stone will have a grit at 4-8 microns, which is still the same size or slightly larger than the carbides in a powder steel. But if those stones are also sharpening the carbides, there can be less carbide tear out, especially when the carbides are fully surrounded by steel matrix and not clumped within the matrix, as we fine on super steels.

And we have lots of evidence that high-carbide steels out cut simple steels by a wide margin, including rope cutting, cardboard cutting and well-controlled, scientific CATRA tests. What besides the presence of carbides on the apex could explain that performance advantage over simple steels at the same sharpness?

 

[mete]

Please submit a video of you butchering a reindeer with a chocolate/hazel nuts . That's the only true test !!!
We are now back to the old D2 properties . Lots of carbides ,very wear resistant ,many hunters love that steel . But Roman Landes has described it well .The carbides eventually wear and are pulled out to be replaced by other large carbides . BUT he explained that you cannot get as sharp an edge with D2 because of those large carbides. Sharpness is defined as the smallest radius of the cutting edge you can get with the blade material. So , D2 . wear resistance yes , sharpness no. I'll stick to the " powder steels like S35VN or similar. Carbides are important but make them small !

 

[shinyedges]

Love this thread, thank you for taking the time to post this. I always welcome people testing and sharing information especially when a vivid explanation is provided.

My experience with d2 is it is a very aggressive cutter, I didn't find it painful to sharpen either. Now when compared to say, vg10, which I found sharpened like a dream and achieved an excellent fine edge but would loose that sharpness fairly quickly (depending on media) d2 would carry on. Smaller, more evenly distributed carbides are the cats meow.

 

[Juha Perttula]

I struggle with this issue. In a powder steel, the carbides run 2-4 microns. The edge of a very sharp knife is going to be 1 micron or less. I think straight razors get to 0.35 microns.

So, yes, there is not room on the apex for unsharpened carbides. But who says they are not sharpened? On a coarse steel like D2, the carbides can be 50 microns in size and clumpy, which means that almost any stone will tear out the carbides. So why does D2 steel hold an edge better than 1095? My thinking is that the carbides are sharpened along with the steel matrix. A hard Arkansas stone or an extra fine diamond stone will have a coarseness of 8-15 microns, which seems fine enough to hone the carbides without tearing them out of the matrix.

Also, the carbides on powder steels are fine and well distributed. A Norton 8000 water stone will have a grit at 4-8 microns, which is still the same size or slightly larger than the carbides in a powder steel. But if those stones are also sharpening the carbides, there can be less carbide tear out, especially when the carbides are fully surrounded by steel matrix and not clumped within the matrix, as we fine on super steels.

And we have lots of evidence that high-carbide steels out cut simple steels by a wide margin, including rope cutting, cardboard cutting and well-controlled, scientific CATRA tests. What besides the presence of carbides on the apex could explain that performance advantage over simple steels at the same sharpness?

In my chocolate demonstration nuts were sharpened. But the problem is that the cutting edge have more chocolate (steel) than nuts (carbides). In one dimensional line smaller amount of carbides can not prevent abrasive wear of larger amount of steel. But the situation is different with surfaces or slightly blunt edges; then the carbide particles can block the abrasive particles. In practice this means that a carbide-rich steel blade has fast initial wear, and after that, the wear stagnates and the blade can keep the serviceable sharpness for a long time. For that reason, I think, carbide-rich steels have great success in CATRA and field tests.

Sandvik steel factory has interesting opinion about carbide size and blade sharpness. They think that carbide size limits the sharpness.
http://smt.sandvik.com/en/products/...erent-steel-types/coarse-carbide-tool-steels/
It should be note that many industrial scandinavian puukko knives are made of sandvik 12C27 steel and razor blades are made of Sandvik 13C26.

 

[BITEME]

We hear a lot about carbide pullout ,but wouldn't it be somewhat difficult if the carbides are embedded in the base metal to be pulled out ?,I am sure some will get pulled out but I think that would be a relatively small number?oh btw I will send you my address so you can send the test samples to verify your results

 

[Juha Perttula]

We hear a lot about carbide pullout ,but wouldn't it be somewhat difficult if the carbides are embedded in the base metal to be pulled out ?,I am sure some will get pulled out but I think that would be a relatively small number?oh btw I will send you my address so you can send the test samples to verify your results

I have found with microscope that carbide pullout does not take place when a larger portion of the carbide is hidden than visible. Here is for you a carbide pullout simulation.

 

[BITEME]

If the edge apex is 1 micron and the carbide is 2 microns then the missing piece would be much smaller then the pic,but I agree that pullout will and does happen. Thanks for the excellent topic.another ? would the carbide be sharpened or would it be fractured?

 

[Juha Perttula]

If the edge apex is 1 micron and the carbide is 2 microns then the missing piece would be much smaller then the pic,but I agree that pullout will and does happen. Thanks for the excellent topic.another ? would the carbide be sharpened or would it be fractured?

Carbides will be sharpened just like nuts in chocolate. Carbides do not fracture easily because they are so small, but carbide steel interface fractures easily.

 

[John Stubley]

Some photo`s and information on the amount of Carbides depending on hardening temperature.

Click to open Heat Treatment dropdown in link below.

http://smt.sandvik.com/en/materials-center/material-datasheets/strip-steel/sandvik-12c27/

John.

 

[Sergeua]

This post is useless with a lot of unknowns
Like what kind of testing have you done.?What sharpening medium you used? The obvious questions that arise.

 

[Twindog]

The chocolate visual really represents a steel with an extremely coarse carbide content, with carbides large and poorly distributed.

Like this D2 steel:

But the powder steels don't look like that. The photo below on the right shows a powder steel with the carbides being very small and well distributed.

If I understand you correctly, you're saying that fine-grained, low-carbide steels can give a much finer edge that has superior cutting abilities, at least until the edge begins to dull. I don't doubt that.

My sense is that it's easier to sharpen a fine-grained, low-carbide steel to a high degree of sharpness, but with proper technique and the right equipment, you can get the same results with a high-carbide powder steel. And just about any edge on a high-carbide powder steel will outlast a fine-grained simple steel for cutting abrasive material.

It's difficult for me to see how powder steels are not an advancement for the knife industry. But I do see that simple steels still have strong assets.

 

[Mo2]

Can you cut the chocolate with a wide angle and a narrow angle. Also sharpen each version with a course grit and one with a fine grit.

 

[Twindog]

So this may support Juha’s OP a bit. I have two puukkos, one made by a knife maker Lauri who Juha collaborates with. It uses 80CrV2 steel — a relatively simple carbon steel that is heat treated to Juha's specifications to produce very fine grain and high hardness. The blade’s edge is hardened to 63 Rc. The edge is sharpened about 35 degrees inclusive, but it's difficult to measure with my laser protractor because the edge bevel is so narrow. The edge shoulders are about 0.011 inches.


The other knife is a special project by Deadboxhero, using Vanadis 4 Extra steel handed by Peters to 64 Rc. The edge is about 40 degrees inclusive (but hard to measure because the edge bevel is so narrow), with edge shoulders about 0.006 inches. It’s difficult to measure these edge geometries when the edge bevel is all but invisible. The knife was made by top knifemaker Malanika.


I did two tests. One is my standard test for edge stability: chopping a piece of bailing wire in two on a large flat block of Doug fir. In this case, I used a rubber mallet and tried to chop the wire in two. Only the Malanika could chop the wire in two. No other knife I have can do that. But the edge rolled badly, which seems odd for a steel this hard.


The Juha/Lauri puukko’s edge flattened somewhat, but came out almost intact, which is extremely good edge stability (toughness and strength). It didn’t cut the wire in half.


The other test was to jab the tips of the knives into a piece of Doug fir and pry them out. This was a relatively gentle test meant replicate the most abuse that a pukka would see in normal whittling. Both knives passed that test easily, and both have very pointy tips.


I can’t really say too much about the Vandals 4E blade because it was much thinner than the Juha/Lauri pukka. I’ve had other knives suffer this much damage on the bailing wire test, but none of them were even close to the geometry of the Malanika.

But for sure, Juha's heat treat of a simple steel performed extremely well for edge stability on the bailing wire test. Few of my knives can match that.

 

[mete]

Carbide sharpened or fractured ? Just a note here . The abrasive particles in grinding wheels will round off the sharp corners as it wears. At that point we want a new surface .That means we want to fracture the worn particle with sharp edges and these sharp edges are the real grinding parts. The grinding process should do that but we can also help by dressing the wheel with the proper tool.
I would like to see photos of carbides in steel that have fractured .

 

[Wowbagger]

Finally, a visual demonstration that I can understand.

I don't know . . . I will have to taste it for my self before I can decide