Maximizing Edge Retention – What CATRA Reveals about the Optimum Edge

Great info. Like most of these things though, lots of makers are gonna jump to conclusions now about edge angles, without understanding the caveats here. It makes total sense to me that more blunt edge geometry would wear quicker in this scenario, it's primarily an abrasion resistance test, and the more friction and surface contact, the higher the wear rate.

However, I would expect to see very different results from impact testing, or variances on cutting harder materials with heavier force. Although, there is definitely a point of diminishing returns here also. With everything, it's a balance.

Had the edge geometry in the above test gone significantly more acute, I'd expect to see performance falling off after a certain point also. At a certain angle, you'd lose enough edge support to maintain it, although it's probably much more acute than most would suspect.


This is just one (important) data set, of a specific cutting scenario, among endless possibles. It should inform you certainly, but don't make giant assumptive leaps based on it, other than; you should probably try grinding thinner and putting a more acute edge on your sharpened crowbars. :p
 
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Willie71 said:
Larrin, if I’m reading this right, pick the steel and hardness that gives you the most stable fine edge, and optimize the heat treat for that to get the best wear resistance? The steel that supports the finest edge will give you the longest lasting edge?
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If that were true, then W2 would be the king of edge retention. However, in this test, I'd expect of any two steels that can support the same edge geometry, the one with higher abrasion resistance to win, unless there's a massively different configuration of carbide sizes and types.

I think it's wrong to jump to conclusions about steel selection based on this test, more that it supports the theory that when it comes to performance cutting abrasive materials at reasonable cut pressures, the more acute edge angles will win. If you consider the lower amount of surface contact and friction generated at equal force between a more acute edge vs a blunt one, this makes obvious sense.
 
javand said:
Great info. Like most of these things though, lots of makers are gonna jump to conclusions now about edge angles, without understanding the caveats here. It makes total sense to me that more blunt edge geometry would wear quicker in this scenario, it's primarily an abrasion resistance test, and the more friction and surface contact, the higher the wear rate.

However, I would expect to see very different results from impact testing, or variances on cutting harder materials with heavier force.
Click to expand...
I don’t believe the more obtuse edge is wearing more quickly. It’s cutting ability is worse to begin with and not as much wear is required to become dull.

I don’t have any control over what random conclusions people might be extrapolating based on one CATRA study. If I was writing a book or an overview article I could give a broader picture.
 
javand said:
If that were true, then W2 would be the king of edge retention. However, in this test, I'd expect of any two steels that can support the same edge geometry, the one with higher abrasion resistance to win, unless there's a massively different configuration of carbide sizes and types.

I think it's wrong to jump to conclusions about steel selection based on this test, more that it supports the theory that when it comes to performance cutting abrasive materials at reasonable cut pressures, the more acute edge angles will win. If you consider the lower amount of surface contact and friction generated at equal force between a more acute edge vs a blunt one, this makes obvious sense.
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A steel with higher hardness and wear resistance at the same angle would win. The question is how hard and wear resistant can you go before it is too brittle to handle the low angle edge. That depends on the person, specific application, etc. It’s a balancing act between toughness and wear resistance along with hardness to avoid rolling.
 
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Larrin said:
I don’t have any control over what random conclusions people might be extrapolating based on one CATRA study. If I was writing a book or an overview article I could give a broader picture.
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Of course not man, I'm certainly not putting that responsibility on you. My response was just encouraging caution, to the other members here, that might not understand the caveats.

Larrin said:
I don’t believe the more obtuse edge is wearing more quickly. It’s cutting ability is worse to begin with and not as much wear is required to become dull.
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Fair point, although I do personally believe surface area of contact that would be a contributing factor in overall abrasive breakdown rates of edges. I don't have any data of course, but there's tons of studies on the subject of edge geometry and material contact levels affecting wear with machining cutters and inserts.
 
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Larrin said:
A steel with higher hardness and wear resistance at the same angle would win. The question is how hard and wear resistant can you go before it is too brittle to handle the low angle edge. That depends on the application, specific application, etc. It’s a balancing act between toughness and wear resistance along with hardness to avoid rolling.
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Exactly!
 
javand said:
Great info. Like most of these things though, lots of makers are gonna jump to conclusions now about edge angles, without understanding the caveats here. It makes total sense to me that more blunt edge geometry would wear quicker in this scenario, it's primarily an abrasion resistance test, and the more friction and surface contact, the higher the wear rate.

However, I would expect to see very different results from impact testing, or variances on cutting harder materials with heavier force. Although, there is definitely a point of diminishing returns here also. With everything, it's a balance.

Had the edge geometry in the above test gone significantly more acute, I'd expect to see performance falling off after a certain point also. At a certain angle, you'd lose enough edge support to maintain it, although it's probably much more acute than most would suspect.


This is just one (important) data set, of a specific cutting scenario, among endless possibles. It should inform you certainly, but don't make giant assumptive leaps based on it, other than; you should probably try grinding thinner and putting a more acute edge on your sharpened crowbars. :p
Click to expand...

Hey, if you’re designing a knife to cut 5 percent silica impregnated card stock you now know exactly the best way to do so ;) If you want a knife to cut things that you might normally want a knife to cut, yeah probably a few more variables to consider that are not represented here.
 
Larrin do you have anything about Dendritic Cobalt and edge retention? I've only just heard of boye knives.

Also, is there any CATRA data on serrated blades?
 
Just like Javan, I see a whole lot of bad conclusions being reached by the folks reading this paper without applying critical thinking. It would be too easy for someone to jump to a conclusion or use the limited and extremely narrow data band produced to reinforce their own skewed agenda.

For an example, I’ll point out two simple features that weren’t utilized to any effect here, but that people seem to be assuming aren’t of any value due to the results of this test: grain size and carbide distribution. With chemical composition being equal, a finer grain steel with more even and perhaps smaller versions of the same carbides will behave differently, but perhaps not at the same hardnesses. The advantage of finer grain may mean that the steel may display improved micro-strength and micro-toughness when used at higher hardnesses than the same composition with larger, clumpier carbides with uneven distribution and larger overall grain. Higher hardness due to improved microstructure leading to improved toughness and wear resistance. How many of you use simple carbon steels? Have you found that through improved grain refinement you can use the same steel at higher rockwell hardnesses with no ill effects compared to the same steel with less fine grain? Anecdotal, to be sure, but I’m hoping you see my point. We would need tests to reach these conclusions, or disprove them, and this test ain’t it!


This, too, could be erroneous - my point is that this single test really doesn’t quantify much of anything, and it would be dangerous to use this singular point of data to generate any conclusion.

Great papers, Larrin - I, too, don’t hold you to blame for how others will mutliate the data, but maybe a bit more translation of the results would help...

“From this study it should be apparent that lower edge angles lead to superior cutting performance. PM vs ingot, cryo, and edge finish appear to be minor factors”


It was this statement from the paper that got me to reply. There’s guys that obviously took this to mean ‘no advantage’. The latter portion of it only holds true if you think ‘equally’. AEBL with a proper - and improved - heat treat will allow for use at higher hardnesses compared to the same steel with ‘lesser processing’ - processing that may require that knife to be used at a lower hardness to allow the edge to hold up. One of those improved processes is grain refinement. Seems like common sense would dictate that PM versions of other steels may produce comparable results, no? Don’t know! We’d need to perform tests to conclude that. :)

Again, Larrin, this isn’t an attack on you - I’m just concerned that others may not be ‘getting it’, and I’m hoping my rebuttal shakes some cages, just not yours. ;)
 
Changing some variables may allow the change of others, like you said. Enhanced toughness from PM may allow you to increase hardness while maintaining similar toughness and therefore have superior cutting performance. However, that isn't necessarily an apples to apples comparison.
 
I agree wholeheartedly! I think you know that, too. But it doesn’t take much reading through this thread alone to see a lot of bad conclusions jumped to, and my example of why ‘equal’ isn’t always a good test is part of the point.

The ONLY thing this test seemed to indicate, aside from the fact that his 8000 grit stone really needs to be checked, was that “lower edge angles lead to superior cutting performance.” Everything past that remains to be isolated and tested properly.
 
... Rick Marchand Rick Marchand would like me to express my regret in not having read the ‘ScienceOfSharp’ discussion of the 8000 grit stone, and it’s explanation of the results.

I have shame. :oops:

Please continue on with the discussion now.
 
There is a great article on Serious Eats that talks about the way we interpret scientific research: Ignore the Headlines: Sometimes Tomatoes Belong in the Fridge. The gist of it is that a research paper came out whose conclusions were that cold storage negatively affects volatile compounds in tomatoes. A wave of articles across the internet came out referencing the paper about how you should "never refrigerate tomatoes". What these articles missed is that the paper was not offering conclusions as to "how you should store your tomatoes".
 
SirSpice said:
There is a great article on Serious Eats that talks about the way we interpret scientific research: Ignore the Headlines: Sometimes Tomatoes Belong in the Fridge. The gist of it is that a research paper came out whose conclusions were that cold storage negatively affects volatile compounds in tomatoes. A wave of articles across the internet came out referencing the paper about how you should "never refrigerate tomatoes". What these articles missed is that the paper was not offering conclusions as to "how you should store your tomatoes".
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I wrote some about the importance of actually reading the original journal articles here: https://knifesteelnerds.com/2018/05/07/is-spider-silk-stronger-than-steel/
 
...AND it’s a great laxative, which should definitely help you, Rick.


o_O
 
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