O1 vs 5160

sunshadow said:
Roman Landes showed some micrographs of several popular blade steels on saturday at Ashokan that have carbides considerably larger than than 3 or 4 microns. A truly sharp blade has an edge radius of aproximately 1 micron. large carbides are exremely brittle and also readily pull out during the sharpening process leaving gaps and holes. Many finer grained steels without large chunks of carbide will sharpen to and hold a 1 micron edge. Large carbides make for good surface wear resistance they do not however contribute to fine edge stability

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Page,

Did Roman Landis talk about general sizes of different carbides... like chromium carbides, tungsten carbides, vanadium carbides? I'm wondering if different steel chemistries lend themselves to better edge stability by the nature of their carbide size.

Mike
 
I'm not Page, but the gist of what he was saying was that the larger the carbide, no matter what type alloy involved, the less edge stability.
 
Not specifically. Roman only dealt with properly heat treated steels and implied but did not
explicitly state that carbide size generally increases with increasing alloy content,
with the exception that powder metallurgy causes the sizes of carbides to decrease and
the distribution of carbides to improve (e.g. moving D2 from the largest carbide range to
the middle one of five). His position was basically that carbide size and distribution was the
major factor in the ability to form a very sharp and stable edge. This must be qualified
by his repetition that you must first select the application and behavior you want from your knife,
not the steel.

Not all applications get most benefit from very sharp stable edges with minimal carbide tear out.
One example he gave was a hunting knife, defined as a knife used to skin and gut game (not whittle,
chop wood, etc.). For that application a knife with larger carbides that have significant tear out but
good wear resistance result in a microscopically (1000x) saw toothed edge which might work very well
for the task.

Someone asked what would be the best steel for what we might call a hunting knife; a general
knife-of-all-tasks EDC sort. He basically refused to answer because no one steel would be optimum
for all the different tasks.

Most of his own knives were (drop dead gorgeous) cooking knives with very hard, very thin blades and
edges. He had a couple of hunting pattern knives; the ones I remember had damascus blades. His
personal EDS is a little, well used, san mai pukko style.
 
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Dan, the question that Mr. Landes would not answer was for a "bushcraft" knife.
(Sorry, didn't mean to "split hairs" - get it?:D)
 
sunshadow said:
Roman Landes showed some micrographs of several popular blade steels on saturday at Ashokan that have carbides considerably larger than than 3 or 4 microns. A truly sharp blade has an edge radius of aproximately 1 micron. large carbides are exremely brittle and also readily pull out during the sharpening process leaving gaps and holes. Many finer grained steels without large chunks of carbide will sharpen to and hold a 1 micron edge. Large carbides make for good surface wear resistance they do not however contribute to fine edge stability

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That is very fascinating research. I have found many high carbide steels to chip/dent easily at thinner angles, even when the hardness is lowered for toughness.

That said, John Verhoeven showed electron microscope pictures of various knife edges, and the sharpest he can get them to was 0.4 micron. What was interesting was that even the steels with 3-4 micron carbides he could get the same edge because of the steel matrix. It seems like any steel can take an equally fine edge (even D2) but the simple alloys like 1060-1084 are best at holding the finest edges.

Mike Krall said:
Page,

Did Roman Landis talk about general sizes of different carbides... like chromium carbides, tungsten carbides, vanadium carbides? I'm wondering if different steel chemistries lend themselves to better edge stability by the nature of their carbide size.

Mike
Click to expand...

I wasn't there at the Landes lecture but I do know that niobium carbides are the smallest, followed by vanadium, then tungsten/molybdenum, and chromium carbides are the largest. Not sure where cementite goes, but alloyed steels tend not to contain that.
 
cotdt said:
That is very fascinating research. I have found many high carbide steels to chip/dent easily at thinner angles, even when the hardness is lowered for toughness.

That said, John Verhoeven showed electron microscope pictures of various knife edges, and the sharpest he can get them to was 0.4 micron. What was interesting was that even the steels with 3-4 micron carbides he could get the same edge because of the steel matrix. It seems like any steel can take an equally fine edge (even D2) but the simple alloys like 1060-1084 are best at holding the finest edges.



I wasn't there at the Landes lecture but I do know that niobium carbides are the smallest, followed by vanadium, then tungsten/molybdenum, and chromium carbides are the largest. Not sure where cementite goes, but alloyed steels tend not to contain that.
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It is possible to sharpen a blade with large carbides like ATS34, however teh large carbides are likely to chip and tear out more readily than abrade. I polish metalurgical samples as part of my day job, and carbide pullout is one of the biggest nuisances. Carbides are like large chunks of peanut in a chocolate bar. They are harder and brittler than the surrounding matrix, and not all that well attached. Try cutting a chocolate bar with large chunks of peanut to a 20 degree included angle using a horse rasp and you will see what I mean.
a jagged edge will feel sharp and will tear meat just fine, a truly sharp knife will cut freehanging individual strands of hair with the blade moving slowly

-Page
 
I'll have to read the Verhoeven sharpening paper again. I dont remember him making any comments regarding carbide size in the steels tested. Most of the tests were done on AEB-L. Is its carbide size in the 3-4 micron range? Some were 52100, which has carbides 1 micron or less, as taken from his book. I have no idea what the carbide morphology is for the Al Pendray original damascus blades he tested. IRRC, these were pearlitic, not martinsitic. I assume the carbides would be thin and layered, but cant guess how that would affect sharpening.
 
Thanks Page & 'me2'... but now I'm confused. 'cotdt' mentioned chromium carbides are the largest. Other indication is D2 has large carbides and I presume from the high Cr%. AEB-L is a stainless with large carbides. Both of those with 3-4 micron carbides. How do the carbides (chromium carbides) in 52100 end up less than a micron? Would that be true also for 5160?

Mike
 
Mike Krall said:
Thanks Page & 'me2'... but now I'm confused. 'cotdt' mentioned chromium carbides are the largest. Other indication is D2 has large carbides and I presume from the high Cr%. AEB-L is a stainless with large carbides. Both of those with 3-4 micron carbides. How do the carbides (chromium carbides) in 52100 end up less than a micron? Would that be true also for 5160?

Mike
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D2 has a lot of carbon so it can form carbides with the Cr. I've read that the D2 actually has some carbides much larger than 3-4 microns but it's very dependant on the heat treat. AEB-L is much more fine-grained because it has less carbon. It is much more fine-grained than the CPM stainless steels, for example.

5160 is expected to be more fine-grained than 52100 because it has less carbon but 52100 is already one of the most fine-grained steels out there.
 
If I remember correctly D2 carbides run up to 20-30 microns, and that's with proper heat treat, ATS 34 if I remember correctly runs 5-15 microns

-Page
 
Mike Krall said:
AEB-L is a stainless with large carbides.
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Actually AEB-L has tiny carbides, around the size of 52100. The size of the carbide is controlled by the volume of carbides and the process by which the steel was made and forged. You'd have to get into more complex subjects to answer what controls the volume of carbides. There is no one paragraph answer.
 
Grain size and carbide size are not really related. In fact, larger grains often indicate over heating in which case carbides will be smaller. 5160 is technically a hypoeutectoid steel, meaning when austenized and quenched it will not have any undissolved carbides, though this is a little complicated by the chromium pushing the eutectoid composition down. Chromium carbides come in different forms and size varies a lot from one alloy to the other. Steels like 5160, AEB-L, 12C27, and many others have both chromium and carbon, but in the quenched and tempered condition do not form large chromium carbides, if any at all.
 
Guys if one wants to get the model of the edge slide shown at the presentation just drop me a mail and Ill send it back to you for free distribution.

It will show carbide size and distribution in 1000x Mag for 5 typical alloys

BTW. Larrin and Kevin Cashen do have a copy to
 
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