Blade Geometry + Steel Toughness for Maximum Edge Retention AND Toughness

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mobile1mobile1

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May 23, 2022
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So I was reading this amazing article here about blade geometry impact on edge retention. My mind was blown!

Given these results:

How would a high edge retention steel at a higher edge angle compare to a high toughness steel at a smaller angle in relation to edge retention?
So for example wouldn't a lower edge angle (for example 20 degrees) on a high toughness 3V steel OUTPERFORM a high edge retention steel like S90V at a common 37 degrees edge angle as far as edge retention is concerned? And then at the same time wouldn't the 3V also be vastly superior in regards to toughness compared to S90V as well. Even though the lower edge angle decreases toughness, 3V with 33lb/ft is probably 6x tougher than S90V - which I believe is at 5lb/ft for toughness... so 6x the toughness should provide an overall tougher blade than S90V with the bigger angle? 6x the toughness should make up for half the material missing..

So could high toughness blade at lower angle be the holy grail for high edge retention AND high toughness?

I am sure many smart minds have thought of that, so I would be curious what the issue is with such an approach?
 
mobile1mobile1 said:
So I was reading this amazing article here about blade geometry impact on edge retention. My mind was blown!

Given these results:

How would a high edge retention steel at a higher edge angle compare to a high toughness steel at a smaller angle in relation to edge retention?
So for example wouldn't a lower edge angle (for example 20 degrees) on a high toughness 3V steel OUTPERFORM a high edge retention steel like S90V at a common 37 degrees edge angle as far as edge retention is concerned? And then at the same time wouldn't the 3V also be vastly superior in regards to toughness compared to S90V as well. Even though the lower edge angle decreases toughness, 3V with 33lb/ft is probably 6x tougher than S90V - which I believe is at 5lb/ft for toughness... so 6x the toughness should provide an overall tougher blade than S90V with the bigger angle? 6x the toughness should make up for half the material missing..

So could high toughness blade at lower angle be the holy grail for high edge retention AND high toughness?

I am sure many smart minds have thought of that, so I would be curious what the issue is with such an approach?
Click to expand...
Basically yeah. The phrase is "Geometry cuts."

Sharpen something to 10 million grit diamond at 90 degrees inclusive and 1" behind-the-edge thickness and all you've got is a mirror polished corner. It's not even an edge. It's a corner.

Meanwhile, even box cutter blades that have been used for months will still cut.

To be clear, blade steel is  not a primary consideration. Choice of blade steel is only a consideration as a function of its thinnest possible practical geometry.

Thin geometry is by far the most important question in terms of cutting performance and any change to a higher carbide steel (in pursuit of increased edge retention) must be balanced against that given steel's stability at minimized geometries, otherwise the required increase in thickness will quickly counteract it's enhanced wear resistance as a function of overall edge retention
 
mobile1mobile1 said:
So I was reading this amazing article here about blade geometry impact on edge retention. My mind was blown!

Given these results:

How would a high edge retention steel at a higher edge angle compare to a high toughness steel at a smaller angle in relation to edge retention?
So for example wouldn't a lower edge angle (for example 20 degrees) on a high toughness 3V steel OUTPERFORM a high edge retention steel like S90V at a common 37 degrees edge angle as far as edge retention is concerned? And then at the same time wouldn't the 3V also be vastly superior in regards to toughness compared to S90V as well. Even though the lower edge angle decreases toughness, 3V with 33lb/ft is probably 6x tougher than S90V - which I believe is at 5lb/ft for toughness... so 6x the toughness should provide an overall tougher blade than S90V with the bigger angle? 6x the toughness should make up for half the material missing..

So could high toughness blade at lower angle be the holy grail for high edge retention AND high toughness?

I am sure many smart minds have thought of that, so I would be curious what the issue is with such an approach?
Click to expand...
As an example, a ton of the insane supersteels we use today are actually die steels that are used in manufacturing. Dies are "sharpened" with 90 degree "edges" and gross pressure is used to make the cut or stamp the medium. In this use case, the more highly alloyed steel, the better. Just slam as much tungsten and vanadium in there as you can get because your "edge" stability at 90 degrees is extremely high so stability isn't really a concern so you can strive for insane wear resistance.

But in blade geometries, fully hardened Rex 121 at 20 degrees inclusive, 16th inch at the spine, 10 thou BTE thickness, would be a joke. It'd chip and shatter under those demands, even though it is one of the "best" "blade" steels in the world, insofar as manufacturing is concerned
 
Well, then there is abrasion resistance that figures in. Yes geometry and toughness matter but so does the elements that are hard enough to not wear much cutting tough abrasive materials.
 
isnt abrasion resistance same as edge retention? hmm google says no.. so abrasion resistance requires hardness. Which 3v isn't super great at.

Then again the article I quoted says even after the edge has worn down to the same width at the tip for different edge angles - the lower edge angles still continues to keep cutting better.. so my suggestion for high toughness steel at lower edge angle still would outperform anything else in a practical scenario, no?

The article says that edge angle has 58x the impact on edge retention than the next important factor (Hardness) :oops: wow
 
willc said:
Good edge geometry is not a very good sales pitch though.
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Buck's Edge 2X blade profile was pretty good for sales, I suspect, though a lot of people probably didn't (or don't) understand much about the reasoning behind it. It certainly interested me when Buck came out with that around 1999.
 
There’s going to be a limit to every aspect. That’s why I carry more than one knife especially outdoor activities. I usually have a folder edc type knife hollow ground with 20cv or s35vn sharpened to 15 degrees per side 30 inclusive. Then a fixed blade in 420hc or 3v full flat ground at 13-15 dps. I’ve had very good results with these examples.
 
mobile1mobile1 said:
isnt abrasion resistance same as edge retention? hmm google says no.. so abrasion resistance requires hardness. Which 3v isn't super great at.

Then again the article I quoted says even after the edge has worn down to the same width at the tip for different edge angles - the lower edge angles still continues to keep cutting better.. so my suggestion for high toughness steel at lower edge angle still would outperform anything else in a practical scenario, no?

The article says that edge angle has 58x the impact on edge retention than the next important factor (Hardness) :oops: wow
Click to expand...
Abrasion resistance is an element of edge retention. The concept of edge retention is actually metaphysical. Edge retention is something that is perceived rather than being something that can be measured via a theoretical edge retention measurement device.

A blade is determined to have lost its edge after passing a given threshold of cutting performance. A knife is deemed dull when it can no lobger cut cleanly through printer paper, for example. Abrasive resistance will enhance perceived edge retention because it physically defends the apex of the edge from damage, thereby increasing the edge's service life, as a damage apex will inhibit, but not utterly determine, it's cutting performance in, for my example, the printer paper test.

An edge, even perfectly sharpened, such as my aforementioned 10 million grit corner, will also fail the printer paper cut test, thereby forcing a failing grade on sharpness, thereby indicating the edge as "dull" even though it is perfectly "sharp" it just has shit geometry. This theoretical blade, then, technically rates at  zero edge retention, even if it has been made from the world's most extreme wear resistant steel.

In essence, then, edge retention is defined as the hollistic perception of a blade's capacity to continue cutting above threshold performance over time, of which a given steel's abrasion resistance characteristic will have a tangible effect (albeit greatly beneath the effect of overall geometry).
 
Take a look at Larrin’s articles on “edge stability.” The way I see it, the thinner the edge, the better it cuts, and the two main factors in keeping a thin edge from failing are toughness (prevents chipping) and hardness (prevents rolling).
 
As said, edge retention is a board term, so is wear resistance, as other sirs here already mentioned.
A low angle will cut better, doesn't matter the steel, or material for that matter (there is a japanese youtuber made knives from many random substances).
How long it will last, on the other hand, does depend on the steel. CATRA test is not a sharpness test, but an edge endurance test, therefore high wear resistance steel will last longer. A sharpness test would be something like Brubacher Edge Sharpness Scale (BESS C) test, which test how much force to cut the same media.
Carbide volume and size are what decide the wear resistance vs the toughness. Low carbide = more toughness, high carbine = more wear resistance. Small carbine size (more refinement) = more toughness for the same amount of carbide.
Hardness, in my opinion, is the way to achieve that balance in form on the result. In a later article from the website (I trust Larrin), he shows that 420 steels have similar CATRA score and higher toughness at lower hardness than 1095, which has a lot of iron carbide.
I read these from Larran's Knifesteelnerd and his reference sources.
 
mobile1mobile1 said:
So I was reading this amazing article here about blade geometry impact on edge retention. My mind was blown!

Given these results:

How would a high edge retention steel at a higher edge angle compare to a high toughness steel at a smaller angle in relation to edge retention?
So for example wouldn't a lower edge angle (for example 20 degrees) on a high toughness 3V steel OUTPERFORM a high edge retention steel like S90V at a common 37 degrees edge angle as far as edge retention is concerned? And then at the same time wouldn't the 3V also be vastly superior in regards to toughness compared to S90V as well. Even though the lower edge angle decreases toughness, 3V with 33lb/ft is probably 6x tougher than S90V - which I believe is at 5lb/ft for toughness... so 6x the toughness should provide an overall tougher blade than S90V with the bigger angle? 6x the toughness should make up for half the material missing..

So could high toughness blade at lower angle be the holy grail for high edge retention AND high toughness?

I am sure many smart minds have thought of that, so I would be curious what the issue is with such an approach?
Click to expand...
It very much depends on how your edge fails. Lets forget geometry for a second and pretend geometry is set. Then if you are chipping your edge you need tougher steel if you are bending your edge you need stronger/harder steel. Geometry can mitigate some of this for either case. So you can take a low toughness steel like 1095 for example and modify geometry to make it more durable, this will decrease its cutting ability and theoretical edge holding, but you might be ok with this compromise because your edge will last longer overall because it doesn’t chip anymore. Alternatively, you might have a tough steel like 3V, set a very acute edge and find out that your edge deforms or bends. In this case you need to again use geometry to mitigate this issue. You can increase the angle and stop deformation. Once again you are loosing cutting ability and theoretical edge holding, but in reality your edge holding can improve. The best combination is a steel that is very tough at high hardness, this allows thin acute edges that will last a long time, longer than wear resistance would indicate. Of course, if said steel also has high wear resistance that would be the best combination. Unfortunately, steel attributes are a set of compromises, in general the harder the steel gets the lower the toughness is, the higher the wear resistance the lower the toughness. Some steels seem to have a good combination of these attributes, so they work well for general purpose knives, especially when the geometry also takes advantage of the attributes such steels have.
 
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so what minimum angles are suggested for 3V, s90v and m390...if sharpness is a priority - but without it being ridiculously susceptible to damage?
 
mobile1mobile1 said:
so what minimum angles are suggested for 3V, s90v and m390...if sharpness is a priority - but without it being ridiculously susceptible to damage?
Click to expand...
Depends entirely on what you’re cutting. If it’s just raw fish - you can get away with something much thinner than if you were whittling wood.

I personally tend to favor toughness over wear resistance in part because I like sharpening and like most of my knives to be able to cut a wide range of materials without damage.

I’m much happier sharpening a dull edge than repairing a chipped one.
 
scdub said:
Depends entirely on what you’re cutting. If it’s just raw fish - you can get away with something much thinner than if you were whittling wood.

I personally tend to favor toughness over wear resistance in part because I like sharpening and like most of my knives to be able to cut a wide range of materials without damage.

I’m much happier sharpening a dull edge than repairing a chipped one.
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Agreed. No way for anyone to know what will work for you in your use. You have to start with something and work from there, increase/decrease angle depending on how your edges fail. Use matters a lot, noone can tell you "use m4 at 12°". Heat treat and use matter. There is a difference if you are using a single bevel yanagiba to make sushi or chopping wood with a camp knife for camp fire even if the steel were the same. For sushi knife made out of m4 at 64 hrc you might be able to get away with relatively tiny angles. You would not want same hardness and angles for wood chopping. Besides, if you are not using something like a laser goniometer the angles quoted are a rough approximation at best. Especially on longer knives or freehand sharpened knives. Even on systems like sharpmaker where the rods are set at a certain angle you can't be sure that your whole edge is at that angle.
 
The fun part about sharpening is trying different angles and seeing how thin you can go until you start to get micro-chipping. Even if we had an exact use-case and knew exactly what it would take for a failure for a certain use case, you couldn't recommend a specific angle to people because it would also vary based on the hardness of the steel. Another factor that prevents giving general recommendations for edge angle is because hand sharpening leads to convexity so the functional angle is higher than you think you are sharpening to. A fixed angle sharpening system would have to use a more obtuse angle for the same result.
 
Thanks for the explanation.. .I have ordered your book - so should learn more about all this.
I think I'll try CPM-M4 or maybe Cruwear, which should allow for the thinnest edge given toughness and hardness is needed. Should be fun to play around with.
 
I think this is a question that only the individual can answer for themselves. You can only read, research, and test so much. I personally started just freehanding everything nearly flat as acute as I can go regardless of the steel. If it breaks, just go less thin. So far it’s worked for me. I only use folders and I do not use them to pry or baton wood like the kids on YouTube. I know for sure my knives cut way better with more acute angles. I don’t even bother measuring my ugly uneven edges, but if I had to guess they have to be 10 degrees per side on most.
I am actually most impressed with a k390 stretch that I sharpened as flat as I could. Totally outperforms my pm2. It’s amazing how much of a difference .7mm or so can make.
 
golddots said:
I think this is a question that only the individual can answer for themselves. You can only read, research, and test so much. I personally started just freehanding everything nearly flat as acute as I can go regardless of the steel. If it breaks, just go less thin. So far it’s worked for me. I only use folders and I do not use them to pry or baton wood like the kids on YouTube. I know for sure my knives cut way better with more acute angles. I don’t even bother measuring my ugly uneven edges, but if I had to guess they have to be 10 degrees per side on most.
I am actually most impressed with a k390 stretch that I sharpened as flat as I could. Totally outperforms my pm2. It’s amazing how much of a difference .7mm or so can make.
Click to expand...
wow 10 degree a side... interesting.. I have noticed hardness is as important as toughness... m4 so far has been great I have noticed. Havent tried k390.. will take a look. I am curious about s90v.. have you tried 10 degree on that one. I don't whack things.. mostly cut amazon boxes.. for prying stuff m4 seems to do the job so I use that.
 
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