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Self-Sharpening blades : a side effect of acute edge angles
- Thread starter Cliff Stamp
- Start date
- Joined
- Feb 22, 2002
- Messages
- 131
Burke2:
Any steel has carbide particles in it. Stainless has chromium carbide particles.
Any steel has carbide particles in it. Stainless has chromium carbide particles.
Burke,
Carbides "melt" or dissolve into the iron solution at high temps. When cooled, carbon precipitates out and combines with some of the other elements (such as iron, chromium, vanadium, molybdenum, tungsten ect.), forming carbides.
Carbides should not explode when heated, they should just dissolve.
Carbides "melt" or dissolve into the iron solution at high temps. When cooled, carbon precipitates out and combines with some of the other elements (such as iron, chromium, vanadium, molybdenum, tungsten ect.), forming carbides.
Carbides should not explode when heated, they should just dissolve.
Singularity,
Most of your statements are correct, and as you pointed out, not surprising.
Every knife maker knows the importance of the quality of the steel and it's heat treatments - pretty obvious. Most reputable knife companies have an independent metalurgist analyse the steel to ensure it is free of impurities and large primary carbides, and they do take alot of care in their heat treatments (this includes a cryo quench for stainless steels).
I agree that such things as blade geometry and ergonomics are more important than blade steel/heat treatment in terms of overall knife performance, but that dose not mean that steel's composition should be disregarded. Vanadium has a huge effect on grain size (I wish I had some photomicrographs to post showing this), and small grains allow a keener edge to be attained. Besides, any respectable Swedish stainless steel, should have a bit of Vanadium, it did get it's name form the Norse goddess of beauty and fertility, after all (http://www.vanadium.com.au/vanadium_facts.htm).
Could you give some details on number 5? In what way dose 12C27 perform 8-9 times better than a 1% carbon steel?
Edit - I saw the ref. in the article you posted about the 8-9 times improvemnet in "behaviour of cut", but I think the translator lost much of the meaning of that sentence - at least it did for me!
- Frank.
Most of your statements are correct, and as you pointed out, not surprising.
Every knife maker knows the importance of the quality of the steel and it's heat treatments - pretty obvious. Most reputable knife companies have an independent metalurgist analyse the steel to ensure it is free of impurities and large primary carbides, and they do take alot of care in their heat treatments (this includes a cryo quench for stainless steels).
I agree that such things as blade geometry and ergonomics are more important than blade steel/heat treatment in terms of overall knife performance, but that dose not mean that steel's composition should be disregarded. Vanadium has a huge effect on grain size (I wish I had some photomicrographs to post showing this), and small grains allow a keener edge to be attained. Besides, any respectable Swedish stainless steel, should have a bit of Vanadium, it did get it's name form the Norse goddess of beauty and fertility, after all (http://www.vanadium.com.au/vanadium_facts.htm).
Could you give some details on number 5? In what way dose 12C27 perform 8-9 times better than a 1% carbon steel?
Edit - I saw the ref. in the article you posted about the 8-9 times improvemnet in "behaviour of cut", but I think the translator lost much of the meaning of that sentence - at least it did for me!
- Frank.
I found some CATRA test results, in a Ka-Bar catalog, that compares 12C27 vs 1095 and D2.
12C27 had a intial cut of 22.5 mm and a total cut depth of 168.8 mm.
1095 had an intial cut of 19.4 mm and a total of 146.3 mm.
D2 had an intitial cut of 19.5 mm and a total of 300.6 mm.
All edges were 40 degrees included (20 per side). The hardness of the test blades was not listed, but Ka-Bar's nominal hardness is 55-57RC for 12C27, 56-58RC for 1095, and 59-60 for D2.
Based on the initial cuts, 12C27 is about 15-16% sharper than D2 and 1095 (which indicates a fine grain stucture).
12C27's edge holding is about 15% better than 1095, but only about 56% of that of D2.
12C27 had a intial cut of 22.5 mm and a total cut depth of 168.8 mm.
1095 had an intial cut of 19.4 mm and a total of 146.3 mm.
D2 had an intitial cut of 19.5 mm and a total of 300.6 mm.
All edges were 40 degrees included (20 per side). The hardness of the test blades was not listed, but Ka-Bar's nominal hardness is 55-57RC for 12C27, 56-58RC for 1095, and 59-60 for D2.
Based on the initial cuts, 12C27 is about 15-16% sharper than D2 and 1095 (which indicates a fine grain stucture).
12C27's edge holding is about 15% better than 1095, but only about 56% of that of D2.
- Joined
- Feb 22, 2002
- Messages
- 131
Frank,
Agreed on Vanadium, in addition vanadium in absolutley necessary to the (re)production of Wootz steel. It is naturally found in some ores, and seem to have been present in the production of many fine old-times swords makers (indians and vikings)
The good point about the article, is that it stays with simple steels. The sandvik series were originally designed for razor blades, and thus, machineability, level of sharpness are quite important. Also, it is typically a production where you'd cut, harden, temper and sharpen continuous lengths of steel.
The last paragraph agrees that for applications requiring cutting abrasive materials such as rope, clothing, plastics, some other steels are more appropriate.
Point 5 only tells that independant testings from a knife manufacturer, shows a 8 to 9 times better resistance to abrasion for 12c27 compared to 1% plain carbon... No more precisions... Yes the translator has been a bastard with this one... I'll correct when I have time...
The CATRA test result, thanks a lot for these numbers, very interesting!
Now that is interesting, and totally in the measure of what I would have expected. D2 is a machine tool steel, designed to cut metal, among other things, and also considering that one of the parameters of 12C27 is machinability.
(I still would not give D2 to everybody, one must learn to sharpen first)
OK, we have 2 different comparison of 12c27 and 1095, and I'd bet your number are more accurate (at least we know the procedure used).
We are on an interesting path:
1) In opposition to what is mainly beleived so far, some stainless perform better than plain carbon steels, at equal hardness!
2) There are steels which, while not being performers on a specific parameter (edge-holding, rust-resistance, brittleness), show average caracteristics, and have a very coherent profile for cutlery, this is what makes them good: ease of sharpening, reasonable edge-holding, ability to take a very sharp edge, lack of brittleness.
3) It seems to me that while we talk of edge-holding, we miss an important parameter: ability to take a sharp fine edge. Some have been talking (read joes FAQ) about coarse vs polished edge sharpening, and I am also sure that some steels get a better, finer edge than others. So, while D2 performs fine in slicing rope, it would not play the same in push-cutting penetration. We often measure how long will cut, rarely how easy it cuts at first. Being an occasional wittler, I find there is a difference in different steels, and while d2 lasts forever, it takes significantly more force than say a SAK's blade (of similar geometry and edge) to cut the same chip. Sure you need to resharpen more often, but surely after an hour, you are less tired too.
I have one whish about this CATRA test:
I'd like to see this kind of results for materials with different abrasiveness and hardness, and with blades of different hardness.
Tahnks I enjoy the discussion.
Agreed on Vanadium, in addition vanadium in absolutley necessary to the (re)production of Wootz steel. It is naturally found in some ores, and seem to have been present in the production of many fine old-times swords makers (indians and vikings)
The good point about the article, is that it stays with simple steels. The sandvik series were originally designed for razor blades, and thus, machineability, level of sharpness are quite important. Also, it is typically a production where you'd cut, harden, temper and sharpen continuous lengths of steel.
The last paragraph agrees that for applications requiring cutting abrasive materials such as rope, clothing, plastics, some other steels are more appropriate.
Point 5 only tells that independant testings from a knife manufacturer, shows a 8 to 9 times better resistance to abrasion for 12c27 compared to 1% plain carbon... No more precisions... Yes the translator has been a bastard with this one... I'll correct when I have time...
The CATRA test result, thanks a lot for these numbers, very interesting!
Now that is interesting, and totally in the measure of what I would have expected. D2 is a machine tool steel, designed to cut metal, among other things, and also considering that one of the parameters of 12C27 is machinability.
(I still would not give D2 to everybody, one must learn to sharpen first)
OK, we have 2 different comparison of 12c27 and 1095, and I'd bet your number are more accurate (at least we know the procedure used).
We are on an interesting path:
1) In opposition to what is mainly beleived so far, some stainless perform better than plain carbon steels, at equal hardness!
2) There are steels which, while not being performers on a specific parameter (edge-holding, rust-resistance, brittleness), show average caracteristics, and have a very coherent profile for cutlery, this is what makes them good: ease of sharpening, reasonable edge-holding, ability to take a very sharp edge, lack of brittleness.
3) It seems to me that while we talk of edge-holding, we miss an important parameter: ability to take a sharp fine edge. Some have been talking (read joes FAQ) about coarse vs polished edge sharpening, and I am also sure that some steels get a better, finer edge than others. So, while D2 performs fine in slicing rope, it would not play the same in push-cutting penetration. We often measure how long will cut, rarely how easy it cuts at first. Being an occasional wittler, I find there is a difference in different steels, and while d2 lasts forever, it takes significantly more force than say a SAK's blade (of similar geometry and edge) to cut the same chip. Sure you need to resharpen more often, but surely after an hour, you are less tired too.
I have one whish about this CATRA test:
I'd like to see this kind of results for materials with different abrasiveness and hardness, and with blades of different hardness.
Tahnks I enjoy the discussion.
Cliff Stamp
BANNED
- Joined
- Oct 5, 1998
- Messages
- 17,562
James :
These are generally push cut motions and thus they would not tend to degrade the blade in this manner, and even if they did, it would induce a loss in performance. High impact work like chopping would quickly mangle such thin and acute aggressive toothed edge as well.
Singularity :
You can generalise based on components as their behaviour is known. Yes, you can't be 100% confident and all inclusive, but neither are you wandering in the dark from a spec sheet either.
In regards to "sharpness", I think it is of benefit to discuss optimal sharpness limits as it is often ignored with all the talk of edge holding. That approach is wrong as the edge holding aspect might not be as critical to max sharpness to some. Jeff Clark has been saying this for many years and has specifically compared steels like ATS-34 to the finer grained types and commenting on the advantages of the latter, which often get wrote off as directly inferior. Alvin Johnson has also discussed this on rec.knives describing the limitations of the D family of steels and the 440 class stainless grades in regards to the ability to take a fine edge.
However, that article comes off to me as just as one sided. Only in the very last bit is a comment is made that for a lot of materials, other steels are useful. The other materials include fabrics, ropes and papers, etc. . Which materials are you more likely to cut on a regular basis with your knife, these materials or human flesh? For a lot of people I would argue that these materials which are barely given a mention are in fact frequently more commonly cut. While I think that sharpness is a worth while aspect to consider, a more balanced perspective would be beneficial, this article swings too far the other way and comes off very promotional.
This is indeed a common knife myth (stainless steels are directly inferior if you ignore corrosion resistance). If they are at similar hardness levels (as is common in production and custom cutlery) they will have similar resistance to rolling, and the higher wear resistance of the stainless steels will tend to give it an advantage in edge life on certain materials. However consider that simple carbon steels have a higher max hardness than the stainless steels, and are tougher and more ductile at high hardness levels thus it doesn't make sense to compare them at the same hardness. Compare 1095 at 64-66 RC with 12C27 at <60 RC and note how fast the stainless steel edge rolls and thus blunts. This has been covered on rec.knives (very hard 1095 vs ~60 RC stainless steels of various types at acute edge profiles). Now you could argue that people would have trouble sharpening the hard carbon steels, however I would argue that anyone with the skill to see the difference in sharpness being considered here would not. It is also a very big myth that high hardness = hard to sharpen. Even the hardest of steels is very soft compared to hones.
While this is critical on highly polished scalpels, the reason that it tends to get ignored is that amount of people who sharpen their knives at acute enough angles, and with enough skill to notice the limitations of the coarse grained steels are very few. While the pictures of Sandvik vs 440C are very dramatic, if you compared them with the average sharpening job they would not look nearly as different. This needs to be mentioned, it is not a trivial matter to obtain such a level of sharpness. If you take someone like Jeff Clark who has a very high sharpness standard, a lot of skill, and who sharpens frequently, they will obviously appreciate the ability to take a very fine edge and don't really look down that much at the frequent sharpening as it is not a chore to do. However the average user tends to use their knives at far less than their optimal sharpness and thus the initial high cutting ability isn't that critical, but how long they can go between having to do the "chore" of sharpening, or getting someone else to do it for them, is very critical.
You can sharpen D2 to such an extent that it will push right down into a sheet of newsprint. Few knives, custom or production come this sharp, and few people keep their knives this sharp. And even very small geometry changes will totally swamp out the inherent steel effects. How many people do you see commenting on the low sharpness of Doziers D2, or Blackwood etc. ? I am not arguing that D2 doesn't have an inherent limitation on maximal push cutting sharpness, and I think max sharpness is an aspect which should be considered when discussing steels. However it is a fairly fine aspect compared to edge holding and will only be appreciated by very few.
Note as well that all the talk about primary carbides ignores the fact that these carbides can be dissolved into the matrix if the soak temps are high enough, and that these primary carbides are actually nucleation sites for the crystal transformation which can act to increase the hardening process as well as grain refinement. And of course the CPM process avoids formation of highly segregated carbide clusters in the first place, so the generalisations about alloy content limiting grain structure and thus max sharpness (toughness etc. ) are not accurate.
Interesting comments all.
-Cliff
These are generally push cut motions and thus they would not tend to degrade the blade in this manner, and even if they did, it would induce a loss in performance. High impact work like chopping would quickly mangle such thin and acute aggressive toothed edge as well.
Singularity :
You can generalise based on components as their behaviour is known. Yes, you can't be 100% confident and all inclusive, but neither are you wandering in the dark from a spec sheet either.
In regards to "sharpness", I think it is of benefit to discuss optimal sharpness limits as it is often ignored with all the talk of edge holding. That approach is wrong as the edge holding aspect might not be as critical to max sharpness to some. Jeff Clark has been saying this for many years and has specifically compared steels like ATS-34 to the finer grained types and commenting on the advantages of the latter, which often get wrote off as directly inferior. Alvin Johnson has also discussed this on rec.knives describing the limitations of the D family of steels and the 440 class stainless grades in regards to the ability to take a fine edge.
However, that article comes off to me as just as one sided. Only in the very last bit is a comment is made that for a lot of materials, other steels are useful. The other materials include fabrics, ropes and papers, etc. . Which materials are you more likely to cut on a regular basis with your knife, these materials or human flesh? For a lot of people I would argue that these materials which are barely given a mention are in fact frequently more commonly cut. While I think that sharpness is a worth while aspect to consider, a more balanced perspective would be beneficial, this article swings too far the other way and comes off very promotional.
This is indeed a common knife myth (stainless steels are directly inferior if you ignore corrosion resistance). If they are at similar hardness levels (as is common in production and custom cutlery) they will have similar resistance to rolling, and the higher wear resistance of the stainless steels will tend to give it an advantage in edge life on certain materials. However consider that simple carbon steels have a higher max hardness than the stainless steels, and are tougher and more ductile at high hardness levels thus it doesn't make sense to compare them at the same hardness. Compare 1095 at 64-66 RC with 12C27 at <60 RC and note how fast the stainless steel edge rolls and thus blunts. This has been covered on rec.knives (very hard 1095 vs ~60 RC stainless steels of various types at acute edge profiles). Now you could argue that people would have trouble sharpening the hard carbon steels, however I would argue that anyone with the skill to see the difference in sharpness being considered here would not. It is also a very big myth that high hardness = hard to sharpen. Even the hardest of steels is very soft compared to hones.
While this is critical on highly polished scalpels, the reason that it tends to get ignored is that amount of people who sharpen their knives at acute enough angles, and with enough skill to notice the limitations of the coarse grained steels are very few. While the pictures of Sandvik vs 440C are very dramatic, if you compared them with the average sharpening job they would not look nearly as different. This needs to be mentioned, it is not a trivial matter to obtain such a level of sharpness. If you take someone like Jeff Clark who has a very high sharpness standard, a lot of skill, and who sharpens frequently, they will obviously appreciate the ability to take a very fine edge and don't really look down that much at the frequent sharpening as it is not a chore to do. However the average user tends to use their knives at far less than their optimal sharpness and thus the initial high cutting ability isn't that critical, but how long they can go between having to do the "chore" of sharpening, or getting someone else to do it for them, is very critical.
You can sharpen D2 to such an extent that it will push right down into a sheet of newsprint. Few knives, custom or production come this sharp, and few people keep their knives this sharp. And even very small geometry changes will totally swamp out the inherent steel effects. How many people do you see commenting on the low sharpness of Doziers D2, or Blackwood etc. ? I am not arguing that D2 doesn't have an inherent limitation on maximal push cutting sharpness, and I think max sharpness is an aspect which should be considered when discussing steels. However it is a fairly fine aspect compared to edge holding and will only be appreciated by very few.
Note as well that all the talk about primary carbides ignores the fact that these carbides can be dissolved into the matrix if the soak temps are high enough, and that these primary carbides are actually nucleation sites for the crystal transformation which can act to increase the hardening process as well as grain refinement. And of course the CPM process avoids formation of highly segregated carbide clusters in the first place, so the generalisations about alloy content limiting grain structure and thus max sharpness (toughness etc. ) are not accurate.
Interesting comments all.
-Cliff
I would like to see those test results (they are kind of hard to believe).
This is not suprising, since chrome increases wear resistance (which is why D2 has so much.
That is what the CATRA initial cut measures.
Sal Glesser discussed this in this thread: http://www.bladeforums.com/forums/showthread.php?s=&threadid=83050&highlight=CATRA.
Cliff Stamp
BANNED
- Joined
- Oct 5, 1998
- Messages
- 17,562
A normal light microscope, a stereo microscope would be better. Even a cheap hand held magnifier like you can find at Radio Shack is enough to be a huge benefit and can solve a lot of sharpening problems.
-Cliff
-Cliff