I have long noticed that in very high carbide steels the following can happen :
-the edge retention can at times act like there was little carbide or even worse (blunt faster than a low carbide steel)
-the blunting is highly random (both in each use and even along the edge in any given use)
-the edge at times would get get "sharper" during the cutting but it was obviously getting more worn
However this did not correlate at all to grinding the steel or the materials data on wear resistance which was very consistent. You don't find anyone saying D2 is very easy to grind for example but you can easily find people saying Elmax has poor edge retention and some people say it is great even when they were all doing the same thing (cutting rope of cardboard).
Now you can just say this is all due to people not knowing what they are doing and introducing random variation, and this is true, but it happens so often and I saw it myself that I knew it had to me more than that and specifically that there was a very different mechanism happening between the steel and the belt when grinding the knife than in the steel and material being cut (rope, cardboard, etc.) when the knife was used.
I had concluded that what was happening was a combination of the following effects (all of these I have wrote on before over the years) :
-the amount of carbide in the edge is random and is just a consequence of the random distribution of the carbide in the steel and thus when you form an edge some parts of it have a lot of carbide and some don't.
This means that you get very random behaviour along the edge as it reacts in a very inconsistent manner. This gets worse with very large aggregate carbides (D2 is much more extreme for example than MBS-26).
-when very large particles hit an edge they are hitting basically a chunk of matrix + carbide and thus they always have a consistent effect
That is why abrasive grinding is always the same result, everyone says D2 is hard to grind, S60V is more difficult to grind, 121 REX is extremely difficult to grind, etc. .
-however when very small particles hit an edge sometimes they hit the carbides and some times they hit the matrix
This means the wear can be both very random and at worse often dramatic as if they tear out the steel between the carbides the carbide can be torn out and thus you have a steel which acts (in those spots) even worse than if it had no carbides at all.
Now again while I thought these were true, and the data supported it, and it made sense I didn't have direct evidence (you have to etch steel and do high mag shots to directly confirm carbide behaviour).
A few years back Roman wrote about edge stability and talked about many of these issues indirectly. However very recently doing a search on the material properties of Vascowear this paper turned up :
It has a wealth of data, but among it it specifically talks about the difference between :
-grinding a flat piece of steel to determine wear resistance and wear at the edge of a cutting tool
-the difference between large abrasive particles and small abrasive particles hitting the edge of a cutting tool
It is a very interesting read and covers a lot of ground, but in particular it was nice to finally get independent confirmation of what I had held to be true.
Now what does all of that mean to a regular ELU, well basically this - assuming you are cutting something which has very fine abrasives then you can expect to see :
-parts of the edge will blunt much more than others
-sometimes the edge will blunt much faster than other times
These effects get stronger as :
-the angle gets lower
-the carbide volume increases
-the carbide size increases
This is one of the reasons why you can find people doing rope cutting tests on S90V, Elmax, D2 etc. and finding average to poor performance and then other people do the same thing and find extreme performance. It doesn't matter how well you try to control the "variables" there is going to be inherent variation due to the random way that small abrasive particles can interact with a composite system of carbides + matrix in the edge of a steel knife.
(Ironically this means that the people who report the "odd" findings are most likely presenting real data, the people who always match the wear resistance tables are most likely making up data or having it be seriously perception biased.)
What is the basic lesson here - simple, don't be do quick to judge and use and sharpen the knife a few times and look at the average performance, especially with high carbide steels.