Toothy Edges: Which Steels and Which Uses?

[pinnah]

What steels are best sharpened with a toothy edge instead of a polished edge?

And what cutting task (or materials to be cut) are best done with a toothy edge instead of polished edge.


This thread is a branch off a discussion in the Traditional Forum that started talking about the differences between Case SS (420HC hardened at 56Rc or so), Buck 420HC (hardened at 58Rc) and Opinel's Inox (Sandvik 12C27 hardened at 58-59Rc).

I've settled into liking ~320 or so for Case's blades, precisely due their slightly lower hardness. I sort of found this indirectly, in noticing how one of my cheap Japanese-mystery-steel paring knives responded to the coarser grit, when looking for a decent sharpening solution for that one. That knife simply wouldn't retain any bite at anything much finer. I'd even noticed it was easy to over-strop it on simple green compound (on leather); even that would polish finer teeth out of it quickly. With that knife, I think it's issues were all due to a combination of low hardness and coarse grain; it seemed as if the finer 'teeth' on the edge would just crumble away, like sand, with just a little abrasion. Still tends to do this at coarser grit, but at least the bigger teeth last a bit longer before needing touching up.

Case's SS is better than that one, in terms of holding an edge with some bite. But it's still similar in it's ability to sharpen up easily (that's low abrasion resistance, as opposed to hardness), and in how it cuts at a given grit; that's why I tried the coarser grit on the Tru-Sharp, and discovered I really liked it. Buck's 420HC is a little harder (RC), so it tends to finish up at a somewhat finer scratch pattern for the same grit. To get the same 'tooth' out of it, I'd likely take a step down in grit, to ~220 or so.

Opinel's Sandvik stainless is in another league, so far as I'm concerned. Not so much difference in elemental makeup, but their manufacturing process is famous for it's purity and producing even finer grain. Combine that with higher finishing hardness (they spec 12C27Mod up to RC 59), and it makes for some very fine edges that will hold for a while. I've also noticed, for whatever reason that I haven't yet understood, it always seems to retain some 'teeth', even at higher finish (my Opi is finished to above 2000 grit).

I'm coming to the conclusion that softer and less wear-resistant steels like 420HC and similar kitchen-grade cutlery all respond better to a lower-grit, toothier finish. Attempting to polish them too high, even though great shaving edges are possible this way, always seems to degrade durability of the edge. On the other hand, better quality stainless that's taken a bit higher in hardness will take very coarse or very polished edges equally well, and hold them longer. Opinel's stainless is what convinced me of this, in spades.


David

David, I'm super confused by this because of my ignorance. Not sure where to start...

Let's begin with the difference you see in Buck's 420HC and Opinel's Inox. I don't notice much of a difference in them either in sharpening (neither are particularly abrasion resistent and sharpen easily on normal stones or on wet/dry and neither burr up as bad as Case SS or Vic Inox). And I don't notice much of a difference in edge retention but a) I sharpen both to a fine edge and b) am still gaining experience with Opinel's Inox. It may last longer and I'm just not seeing it yet.

I'm confused by why you find that Buck's 420HC does better with a toothy edge. Is this just because Sandvik 12C27 is so much *MORE* fine grained? My (perhaps wrong) understanding is that 420HC was a fairly fined grained steel and roughly in the same camp as 12C27 in that regard. And they're both hardened to close the same 58-59 range. Maybe the Opinel Sandvik is just a tick harder?


The more general question is which steels do best with a toothy edge and which with a polished edge. And after that, which is better for cutting what materials. But one step at a time I think.

As always, in your debt...

-Dave

 

[Vegas Blade]

As I understand, and have played around with, toothy edges do WAY better on hide, meat, rope, basically anything fiberous. Your smooth, mirrored edges will respond much better to paper, woodworking and such. I recently did a test in the Spyderco sub form pitting Cruwear against M4. Bigger than the difference in the steel was the difference I noticed between a 600 grit finish an a 2000 grit finish. The 600 absolulutely, hands down was a better slicer on 3/8 manilla rope. The 2000 grit wanted to "slide" over the material. The 600 bit in hat and cut far more aggressively.

Reference steel types, I've heard the higher alloyed steels do better with the coarser grit for cutting potential and edge holding. Most likely that is a result of the carbide richness in the steel.

This is what I have seen and understand.

 

[Obsessed with Edges]

What steels are best sharpened with a toothy edge instead of a polished edge?

And what cutting task (or materials to be cut) are best done with a toothy edge instead of polished edge.


This thread is a branch off a discussion in the Traditional Forum that started talking about the differences between Case SS (420HC hardened at 56Rc or so), Buck 420HC (hardened at 58Rc) and Opinel's Inox (Sandvik 12C27 hardened at 58-59Rc).




David, I'm super confused by this because of my ignorance. Not sure where to start...

Let's begin with the difference you see in Buck's 420HC and Opinel's Inox. I don't notice much of a difference in them either in sharpening (neither are particularly abrasion resistent and sharpen easily on normal stones or on wet/dry and neither burr up as bad as Case SS or Vic Inox). And I don't notice much of a difference in edge retention but a) I sharpen both to a fine edge and b) am still gaining experience with Opinel's Inox. It may last longer and I'm just not seeing it yet.

I'm confused by why you find that Buck's 420HC does better with a toothy edge. Is this just because Sandvik 12C27 is so much *MORE* fine grained? My (perhaps wrong) understanding is that 420HC was a fairly fined grained steel and roughly in the same camp as 12C27 in that regard. And they're both hardened to close the same 58-59 range. Maybe the Opinel Sandvik is just a tick harder?


The more general question is which steels do best with a toothy edge and which with a polished edge. And after that, which is better for cutting what materials. But one step at a time I think.

As always, in your debt...

-Dave

The differences I noticed between the two (420HC in Case/Buck blades and 12C27Mod in Opinels) were: 1.) edge retention at very thin edge angles, and 2.) the 'bite' which seemed to remain in the Sandvik steel at finish levels way beyond where 420HC lost it's 'teeth'. The edge retention of the Opinel may just be due to heat treat differences; I'm not sure. It's just something I noticed, and it impressed me. The Rockwell HRC scale isn't linear, as I understand it, and a single point, or even a fraction of a point difference, say between 58 and 59, might yield a more noticeable difference in edge retention/hardness than most might assume.

Since I'd thinned my Opinel quite a bit, and also polished it to 2000+ (just for the fun and education of it, basically), I kept noticing that the Opinel continued to 'bite' into the edge of a piece of phonebook paper much more readily than any of the Case/Buck edges that I'd finished to a similar degree. I still notice it to this day, every time I touch up the edge on that knife and do some test-cutting with it. Don't know if it's due to Sandvik's fine-grain process alone (with much emphasis on eliminating impurities and/or making grain structure much more uniform), or Opinel's heat treat afterward, or a combination of the two (but probably this, at least).

The original 420HC 'recipe' from Latrobe has been around for a very long time, and it may be that different manufacturers of this steel, or it's generic equivalents, may not be fine-tweaking the purity or uniformity of it as much. Just speculating, but that's what comes to my mind. Either of these stainless steels should be relatively fine-grained, due to the minimal carbides in them. But, grain size also depends on heat treatment and quench. Quicker cooling of the steel during quench yields finer grain, as I understand it, and slower cooling allows the grains' crystal structure to grow further in size, until sufficiently cooled.


David

 

[AreBeeBee]

As I understand, and have played around with, toothy edges do WAY better on hide, meat, rope, basically anything fiberous. .....

This squares with our experience in the kitchen, where we use one of these on the most often used chef knife. (It's a 5.5" stainless Déglon, but I have no idea what steel it uses):

This has diamond in the crossed steels, which puts a small tooth on the blade that very helpful in cutting up meat and vegetables.

 

[HwangJino]

Maybe im unorthodox, but in my near decade of being a chef, polish trumps toothy.

I cut meat fish veggies pretty much all day all night, toothy not for me.


When I polish the teppan guys knife, he usually asks me to polish it again.

even when chef do polish, I feel they arent hitting the apex and why moat people think polished is no good.

 

[HeavyHanded]

The differences I noticed between the two (420HC in Case/Buck blades and 12C27Mod in Opinels) were: 1.) edge retention at very thin edge angles, and 2.) the 'bite' which seemed to remain in the Sandvik steel at finish levels way beyond where 420HC lost it's 'teeth'. The edge retention of the Opinel may just be due to heat treat differences; I'm not sure. It's just something I noticed, and it impressed me. The Rockwell HRC scale isn't linear, as I understand it, and a single point, or even a fraction of a point difference, say between 58 and 59, might yield a more noticeable difference in edge retention/hardness than most might assume.

Since I'd thinned my Opinel quite a bit, and also polished it to 2000+ (just for the fun and education of it, basically), I kept noticing that the Opinel continued to 'bite' into the edge of a piece of phonebook paper much more readily than any of the Case/Buck edges that I'd finished to a similar degree. I still notice it to this day, every time I touch up the edge on that knife and do some test-cutting with it. Don't know if it's due to Sandvik's fine-grain process alone (with much emphasis on eliminating impurities and/or making grain structure much more uniform), or Opinel's heat treat afterward, or a combination of the two (but probably this, at least).

The original 420HC 'recipe' from Latrobe has been around for a very long time, and it may be that different manufacturers of this steel, or it's generic equivalents, may not be fine-tweaking the purity or uniformity of it as much. Just speculating, but that's what comes to my mind. Either of these stainless steels should be relatively fine-grained, due to the minimal carbides in them. But, grain size also depends on heat treatment and quench. Quicker cooling of the steel during quench yields finer grain, as I understand it, and slower cooling allows the grains' crystal structure to grow further in size, until sufficiently cooled.


David

I've noticed all my 12c27 knives exhibit this tendency - I find i have to take them to a high polish to get a toothy-performing edge, and at lower finishes they just don't seem to cut as well. Bucks 420HC and 440c properly HT seem to be the champ for toothy edges in general.

My experience squares pretty well with most of the responses in general - toothy edge for draw cutting fibrous materials or synthetic materials, polished for chopping, shaving, carving - something in between for EDU.

 

[pinnah]

Interesting and helpful discussion so far. Thanks!!

Perhaps folks could weigh in on how they would sharpen the following steels: toothy or polished. If needed, you can clarify for fibrous materials or not if that makes a difference.

I apologize up front for the entirely self serving aspect of this list. These are steels in my life. If people want to add others, that would be ideal.

Buck 440c (from back in the day)
425Mod
Case SS 420hc
Leatherman 420hc
Buck 420hc
Generic 440a
Schrade + 440A
Schrade 1095
Generic 1095
Opinel Carbone (1086?)
Opinel Inox
Victorinox Inox
Generic Aus 8

Thanks so much!

 

[pinnah]

The original 420HC 'recipe' from Latrobe has been around for a very long time, and it may be that different manufacturers of this steel, or it's generic equivalents, may not be fine-tweaking the purity or uniformity of it as much. Just speculating, but that's what comes to my mind. Either of these stainless steels should be relatively fine-grained, due to the minimal carbides in them. But, grain size also depends on heat treatment and quench. Quicker cooling of the steel during quench yields finer grain, as I understand it, and slower cooling allows the grains' crystal structure to grow further in size, until sufficiently cooled.

I've noticed all my 12c27 knives exhibit this tendency - I find i have to take them to a high polish to get a toothy-performing edge, and at lower finishes they just don't seem to cut as well. Bucks 420HC and 440c properly HT seem to be the champ for toothy edges in general.

Guys, I really appreciate your patience on this. I remain pretty thoroughly confused and this remains pretty counter intuitive that a steel like 12c27 would get more toothy at finer grits. Two conjectures and you can correct me if/when I go in the ditch.

First (and I'm very shaky on this, there are grains and then there grains. The tough ones are the abrasion resistant carbides but there may be others (e.g. pearlite, austenite). 440C and D2 have large carbides. 12C27 has a very fine grain structure all around. And in between, 420HC lacks large carbides but may have other large grains (that aren't as hard as carbides). How am I doing so far?

Second, is it true that to get "toothy" performance from an edge, the grit should somewhat match the size of the grains in the steel (regardless of whether or not the grains are hard carbides)?

In particular, is the problem with taking 420HC down to 2000 grit that the 2000 grit essentially cuts off the soft but large grains where as the 2000 grit reveals or exposes the naturally small grains in 12C27 (even though its about the same in terms of abrasion resistance)?

 

[pinnah]

Anybody?

 

[Obsessed with Edges]

Guys, I really appreciate your patience on this. I remain pretty thoroughly confused and this remains pretty counter intuitive that a steel like 12c27 would get more toothy at finer grits. Two conjectures and you can correct me if/when I go in the ditch.

First (and I'm very shaky on this, there are grains and then there grains. The tough ones are the abrasion resistant carbides but there may be others (e.g. pearlite, austenite). 440C and D2 have large carbides. 12C27 has a very fine grain structure all around. And in between, 420HC lacks large carbides but may have other large grains (that aren't as hard as carbides). How am I doing so far?

That's how I view it. The large carbides in both 440C and D2 are chromium carbides (neither steel has much, if any vanadium carbides; so we can rule those out). Though the chromium carbides aren't as hard as vanadium carbides, they're still quite hard as compared to surrounding steel matrix, and will therefore be more challenging to refine/shape without the right abrasives (diamond, silicon carbide work well). And your assumption about 420HC's grain size/structure matches my view about it as well (if comparing to Sandvik's steels).

Second, is it true that to get "toothy" performance from an edge, the grit should somewhat match the size of the grains in the steel (regardless of whether or not the grains are hard carbides)?

At the very least, I believe the grit used should be adequately hard/aggressive for grinding/shaping the carbides, if any are present. If it is, you should be able to produce a very coarse and effective 'toothy' edge in most any steel, regardless of whether the grit size is similar to grain size. OR, just the opposite, in shaping/refining to a very high polish; still need adequately hard abrasives to do it. In most cases, the grit choice likely won't be same or similar to grain size anyway. With simple carbon steels like 1095, it's possible the grain size may be much finer than the working grits most people will choose for it. This is why I like Schrade's 1095, BTW. With good/great heat-treat & quench, it's grain seems to retain some amazing bite, even at fairly high polish. And the grain size also affects how thick/wide the apex can ultimately be (another reason why I like Schrade's 1095).

In particular, is the problem with taking 420HC down to 2000 grit that the 2000 grit essentially cuts off the soft but large grains where as the 2000 grit reveals or exposes the naturally small grains in 12C27 (even though its about the same in terms of abrasion resistance)?

That's how I see it. I suspect the purity/uniformity of Sandvik's steels is what makes the 'bite' at higher polish more noticeable. With less pure, less uniform grains at the edge, I think the 'bite' or 'micro-tooth' at a given edge finish will be highly variable, and limited or most affected by the largest/bluntest/roundest grains present.

Anybody?

Sorry for my late(ish) reply. I've been somewhat distracted by other things in last few days (not bad things, just busier), so haven't been able to focus quite as much as I'd usually like.


David

 

[pinnah]

David, you have absolutely nothing to apologize for in anyway. I can't tell you how appreciative I am of your time on this.

And of your past posts on the matter. I've been burning up search time with site:bladeforums toothy and such and it's been interesting reading the discussions over the past few years.

I had a terrible habit of annoying my teachers in school with persistent questions and become fearful I'm doing it again.

At the very least, I believe the grit used should be adequately hard/aggressive for grinding/shaping the carbides, if any are present. If it is, you should be able to produce a very coarse and effective 'toothy' edge in most any steel, regardless of whether the grit size is similar to grain size. OR, just the opposite, in shaping/refining to a very high polish; still need adequately hard abrasives to do it. In most cases, the grit choice likely won't be same or similar to grain size anyway. With simple carbon steels like 1095, it's possible the grain size may be much finer than the working grits most people will choose for it. This is why I like Schrade's 1095, BTW. With good/great heat-treat & quench, it's grain seems to retain some amazing bite, even at fairly high polish. And the grain size also affects how thick/wide the apex can ultimately be (another reason why I like Schrade's 1095).

I hesitate to post pictures from a manufacturer's site since we know so little about what they actually show. From Sandvik's site:

12C27 at 1400x

440C at 1400x

If the magnification is the same, I wonder 2 things.
1) How is that the carbides in the 440C have become so vividly exposed? There are visible peaks and valleys between the bumps of the carbides but they clearly aren't from sharpening. Is this what a large hard carbide edge looks like after it's been put through an abrasive medium that has caused the softer blade material to wear away, leaving the peaks of the harder carbides (but before they break out of the steel)? Or, could this be the result of stropping?

2) I wonder what accounts for the wider apex (under the carbides) of the 440C? Is this because they're showing a finally finished 12C27 edge next to a worn down 440C edge to show the exposed carbides or is it possible that this is what happens when they are finished in the same way.

Last comment on those pictures.. would be interesting to see the 12C27 under higher magnification to see if grains become more visible (fractal like).

 

[Obsessed with Edges]

David, you have absolutely nothing to apologize for in anyway. I can't tell you how appreciative I am of your time on this.

And of your past posts on the matter. I've been burning up search time with site:bladeforums toothy and such and it's been interesting reading the discussions over the past few years.

I had a terrible habit of annoying my teachers in school with persistent questions and become fearful I'm doing it again.




I hesitate to post pictures from a manufacturer's site since we know so little about what they actually show. From Sandvik's site:

12C27 at 1400x

440C at 1400x

If the magnification is the same, I wonder 2 things.
1) How is that the carbides in the 440C have become so vividly exposed? There are visible peaks and valleys between the bumps of the carbides but they clearly aren't from sharpening. Is this what a large hard carbide edge looks like after it's been put through an abrasive medium that has caused the softer blade material to wear away, leaving the peaks of the harder carbides (but before they break out of the steel)? Or, could this be the result of stropping?

2) I wonder what accounts for the wider apex (under the carbides) of the 440C? Is this because they're showing a finally finished 12C27 edge next to a worn down 440C edge to show the exposed carbides or is it possible that this is what happens when they are finished in the same way.

Last comment on those pictures.. would be interesting to see the 12C27 under higher magnification to see if grains become more visible (fractal like).

I think there are way (way) too many unanswered questions about how, where and with what those edges came about. The obviously wide apexes on the edges have me scratching my head, in particular; it just looks like these edges weren't finished. I suppose it's possible they were left this way to give a more direct & in-focus look at the carbides in the edge. Might also be an example of what happens as the edge wears; the apex will gradually widen in that circumstance, and the carbides will be further exposed.

Having said that, the part I bolded above is what I imagine happens when using an abrasive that's not aggressive enough to adequately shape the carbides, but still abrasive enough to abrade/erode away the matrix steel around them.


David

 

[me2]

There are carbides, and there are grains. Both can be large or small, and both can be controlled, either by steel selection (choose 440C if large carbides are desired) or processing. Carbide size control is often overlooked. Grain size control is often overemphasized. It's important to distinguish between the 2, as saying something is fine grained then pointing out it's carbide size is confusing. Grains and carbides have a large variation in size, and the processing methods to control them in the same steel are often at odds. High heat makes carbides smaller and grains bigger. Low heat makes carbides bigger and keeps grains small or unchanged.

 

[pinnah]

David, assuming that the edges were worn down makes sense to me.

ME2 (or anybody), I'm hearing at least 3 reasons an edge can be "toothy".
1) As a result of being sharpened with a relatively low grit (under 400) as David, David Martin and HH have advised (in this thread and earlier ones) for steels like 420HC.

2) As a result of exposed but still intact carbides, as in the case of 440C, D2 and others.

3) ??? Low carbide and small grained steels like 1095, 1085? & 12C27 get toothy when polished down to 2000 grit or more because (and I'm unclear on this bit) the fine grit is working well with the small grain size (and lack of carbides)???

I'm pretty confused on that last one.

 

[BluntCut MetalWorks]

2) and 3) are the same concept, except from the example steels, 2) mostly larger carbide (CrC and or VC) compare to 3) where iron-carbide is very small so requires high grit to expose them. It would be simpler to understand the 'what', we separate tooth size from composition from geometry ..

otoh, beware of my babbling:yawn:

ME2 (or anybody), I'm hearing at least 3 reasons an edge can be "toothy".
1) As a result of being sharpened with a relatively low grit (under 400) as David, David Martin and HH have advised (in this thread and earlier ones) for steels like 420HC.

2) As a result of exposed but still intact carbides, as in the case of 440C, D2 and others.

3) ??? Low carbide and small grained steels like 1095, 1085? & 12C27 get toothy when polished down to 2000 grit or more because (and I'm unclear on this bit) the fine grit is working well with the small grain size (and lack of carbides)???

I'm pretty confused on that last one.