Temporal Edge Retention

[Manifestgtr]

I’ve been noticing a phenomenon for the last few years…some steels keep their front end sharpness over time without any use and others seem to very subtly dull, even without use. I’m not sure what makes this happen…it seems to be a subcategory or edge stability. Maybe it’s corrosion on a microscopic level that certain steels handle better than others.

It started when I pulled my FRN chaparral out yesterday and noticed it was still aggressively, hair splitting sharp after a month or so of storage. Rest assured, this doesn’t happen with every knife I pull out of the drawer.

Thus far, I’ve checked two steels off that seem to exhibit really good “temporal edge retention”:

XHP and Z-wear

I’m going to check out others in the future and see which steels exhibit which characteristics in this realm

[Evil D]

Corrosion will degrade sharpness over time, on such a small level you won't actually see it as rust or patina.

[WilliamMunny]

I could be nuts, but I always felt my S30V Manix is like this. I will sharpen it, let it sit for awhile, few weeks, then it just does not have the same bite.

[Deadboxhero]

You probably just deburred those edges better on Cruwear and XHP.

So its nothing to do with the name of the steel as much as it has to due with 1. Sharpening technique 2. Microstructure of the steel

Most folks have a difficult time deburring to a truly sharp edge, they end up straightening out the remains of a burr at the edge which is a wispy bit of metal at the apex.

This type of burr is microscopic and not stable. Sometimes called a wire edge or foil edge.

The exact mechanism of why it moves is not known. However there are some clues that could be in understanding more about the elastic/plastic transition of knife steels on a microscopic scale since bulk properties of a material can be different than on a microscopic scale.

However there are also the details and nuisances of dislocations at the atomic scale. These are things that need to be ruled out with testing not just reading and making things up.

Regardless of how its happening, it is a phenomenon that is happening but saying it only happens with Steel A and not Steel B is incorrect.




One can see the effect with a low grit extremely coarse edge that the sharpness can change over several hours if steps are not taken to remove/reduce unseen burr that has been straightened out microscopically at the edge that may fold over slightly overtime decreasing the sharpness.

[wrdwrght]

You probably just deburred those edges better on Cruwear and XHP.

So its nothing to do with the name of the steel as much as it has to due with 1. Sharpening technique 2. Microstructure of the steel

Most folks have a difficult time deburring to a truly sharp edge, they end up straightening out the remains of a burr at the edge which is a wispy bit of metal at the apex.

This type of burr is microscopic and not stable. Sometimes called a wire edge or foil edge.

The exact mechanism of why it moves is not known. However there are some clues that could be in understanding more about the elastic/plastic transition of knife steels on a microscopic scale since bulk properties of a material can be different than on a microscopic scale.

However there are also the details and nuisances of dislocations at the atomic scale. These are things that need to be ruled out with testing not just reading and making things up.

Regardless of how its happening, it is a phenomenon that is happening but saying it only happens with Steel A and not Steel B is incorrect.




One can see the effect with a low grit extremely coarse edge that the sharpness can change over several hours if steps are not taken to remove/reduce unseen burr that has been straightened out microscopically at the edge that may fold over slightly overtime decreasing the sharpness.

So, not corrosion per se, but a failed deburring that may or may not involve corrosion…. Is that what you’re hypothesizing?

[vandelay]

I've had this sort of thing happen and my guess is that it's due to sharpening technique leaving a weak edge. I had one S35VN knife that would mysteriously gain some dull spots on the blade fairly quickly, regardless of how much I used it. I switched sharpening stones and refined my technique a lot and it stopped happening. I'm not sure if I failed to deburr the edge, I somehow caused carbides at the edge to fracture or something else.

[RustyIron]

One can see the effect with a low grit extremely coarse edge that the sharpness can change over several hours if steps are not taken to remove/reduce unseen burr that has been straightened out microscopically at the edge that may fold over slightly overtime decreasing the sharpness.

I don't doubt that the edge can change shape over time. It makes sense. It stands to reason that if the burr moves around, so does the fatter part of the blade, although at different amounts and in different directions.

So let's assume we've done a good job of sharpening. Even though there's no burr, the edge is going to move around a bit over several hours. Would it not make sense to let the blade "rest," and then go back and give it a little more finish sharpening? The edge could be even BETTER!

This is just a hypothetical question, of course. It's quesitonable whether I have the skills to sharpen at this level, and if I did, I don't have the tools for testing. Anyway, it's interesting to think about.

[zhyla]

I don't doubt that the edge can change shape over time. It makes sense. It stands to reason that if the burr moves around, so does the fatter part of the blade, although at different amounts and in different directions.

I think you’re misunderstanding what a burr is. It’s a deformed edge that has been stretched. It’s very thin and so it’s flexible. It’s not moving around over time, it will be in whatever state you leave it. But when you go to cut something it rolls over easily.

So let's assume we've done a good job of sharpening. Even though there's no burr, the edge is going to move around a bit over several hours. Would it not make sense to let the blade "rest," and then go back and give it a little more finish sharpening? The edge could be even BETTER!

This is not the case. The edge does not “move” or “settle”. Aside from the corrosive degradation of edges in non-stainless steels you should assume an edge retains its state indefinitely.

I would caution against this kind of speculation in the absence of data. Sharpness is an elusive thing to judge without measurements. Either a microscope or an objective slicing test is necessary. Even a burr can be difficult to detect without magnification (though it is usually easily avoided).

[RustyIron]

I think you’re misunderstanding what a burr is.

Um... ok.
Thank you.

[Deadboxhero]

Awesome effort on this thread. But guys. Burrs are the enemy. Don’t form them in the first place, you’re just weakening the steel.

viewtopic.php?f=2&t=90520

This subject doesn't seem to be something you are experienced with however since you claim to not be forming a burr which is also not really possible. There is always some burr.

It appears you also have empirical information and data to share beyond just what you are saying.

I don't doubt that the edge can change shape over time. It makes sense. It stands to reason that if the burr moves around, so does the fatter part of the blade, although at different amounts and in different directions.

I think you’re misunderstanding what a burr is. It’s a deformed edge that has been stretched. It’s very thin and so it’s flexible. It’s not moving around over time, it will be in whatever state you leave it. But when you go to cut something it rolls over easily.

So let's assume we've done a good job of sharpening. Even though there's no burr, the edge is going to move around a bit over several hours. Would it not make sense to let the blade "rest," and then go back and give it a little more finish sharpening? The edge could be even BETTER!

This is not the case. The edge does not “move” or “settle”. Aside from the corrosive degradation of edges in non-stainless steels you should assume an edge retains its state indefinitely.

I would caution against this kind of speculation in the absence of data. Sharpness is an elusive thing to judge without measurements. Either a microscope or an objective slicing test is necessary. Even a burr can be difficult to detect without magnification (though it is usually easily avoided).

[zhyla]

viewtopic.php?f=2&t=90520

This subject doesn't seem to be something you are experienced with however since you claim to not be forming a burr which is also not really possible. There is always some burr.

It appears you also have empirical information and data to share beyond just what you are saying.

I’ve already said my peace in that thread pretty much. Always some burr? I’m not sure why you would say that. Sharpen edge leading, alternate sides, there will be no burr. We’ve been sharpening razors this way for centuries.

[Deadboxhero]

Always some burr? I’m not sure why you would say that.

Unless proven otherwise its safe to assume an edge is in two states; either not fully apexed or a little bit of burr hiding.

Sharpen edge leading, alternate sides, there will be no burr.

It doesn't appear to be that simple especially when we dive deeper into the work of Todd Simpson and Dr Vadim Kraichuk.

We’ve been sharpening razors this way for centuries.

"This is the way we have always done it" is not direct evidence of no burr.

We can still cut things with many types of burr at the edge.

[Cheddarnut]

Is it cold in here or is it just me?

Brrrrrrrrr

[vandelay]

viewtopic.php?f=2&t=90520

This subject doesn't seem to be something you are experienced with however since you claim to not be forming a burr which is also not really possible. There is always some burr.

It appears you also have empirical information and data to share beyond just what you are saying.

I’ve already said my peace in that thread pretty much. Always some burr? I’m not sure why you would say that. Sharpen edge leading, alternate sides, there will be no burr. We’ve been sharpening razors this way for centuries.

With a razor, you'll typically strop it on a hanging strop with abrasive to convex the edge to remove the burr and convex the edge after honing. Alternating sides on the strop is essential to preventing burr formation but I don't think burr formation matters when you're just honing.

There are some SEM images of a razor edge here: https://scienceofsharp.com/2016/04/14/s ... or-honing/

[zhyla]

With a razor, you'll typically strop it on a hanging strop with abrasive to convex the edge to remove the burr and convex the edge after honing. Alternating sides on the strop is essential to preventing burr formation but I don't think burr formation matters when you're just honing.

Terminology is tricky. Razor guys say “hone” to describe the act of sharpening. They then “strop” to do what I’ve always thought knife people describe as honing.

I’ll admit I don’t fully understand the strop story with razors. I’ve heard some people say it actually just removes the corrosion layer on the edge. I’ve not personally notice much benefit to stropping with a leather strop. But maybe my strip just sucks — or maybe I don’t have a burr.

There are some SEM images of a razor edge here: https://scienceofsharp.com/2016/04/14/s ... or-honing/

Isn’t that article showing the effect of sharpening with edge-trailing strokes? Of course there’s a burr in that case. Nobody sharpens razors that way.

[vandelay]

With a razor, you'll typically strop it on a hanging strop with abrasive to convex the edge to remove the burr and convex the edge after honing. Alternating sides on the strop is essential to preventing burr formation but I don't think burr formation matters when you're just honing.

Terminology is tricky. Razor guys say “hone” to describe the act of sharpening. They then “strop” to do what I’ve always thought knife people describe as honing.

I’ll admit I don’t fully understand the strop story with razors. I’ve heard some people say it actually just removes the corrosion layer on the edge. I’ve not personally notice much benefit to stropping with a leather strop. But maybe my strip just sucks — or maybe I don’t have a burr.

I notice a substantial difference when stropping with an abrasive. It's removing metal so it'll sharpen the tip one way or another.

There are some SEM images of a razor edge here: https://scienceofsharp.com/2016/04/14/s ... or-honing/

Isn’t that article showing the effect of sharpening with edge-trailing strokes? Of course there’s a burr in that case. Nobody sharpens razors that way.

people who follow that guide sharpen edge trailing. It does demonstrate that stropping on a hanging strop removes the burr pretty effectively.

[Manifestgtr]

You probably just deburred those edges better on Cruwear and XHP.

I’ve considered that and it’s not impossible. I’m typically very meticulous about burr removal…alternating strokes and passes through wood before stropping…that Murray Carter influence…

I’ve been trying to knock out as many variables as humanly possible and it takes more than qualitative evidence to come to any real conclusions long term. Just some observations in the meantime

[USMC-88]

I’ve been noticing a phenomenon for the last few years…some steels keep their front end sharpness over time without any use and others seem to very subtly dull, even without use. I’m not sure what makes this happen…it seems to be a subcategory or edge stability. Maybe it’s corrosion on a microscopic level that certain steels handle better than others.

It started when I pulled my FRN chaparral out yesterday and noticed it was still aggressively, hair splitting sharp after a month or so of storage. Rest assured, this doesn’t happen with every knife I pull out of the drawer.

Thus far, I’ve checked two steels off that seem to exhibit really good “temporal edge retention”:

XHP and Z-wear

I’m going to check out others in the future and see which steels exhibit which characteristics in this realm

You got the burrs man!

[Unluckycharm]

One thing to consider is that most individuals are going to test the “sharpness” of their knife directly after sharpening and stropping. Since the burr is so fine and mailable we create enough energy and heat during the sharpening process that it is able to pass the cut test, once the metal cools the burr will not maintain its original form, oh so slightly, leading to a more dull knife than what we originally had. Zero evidence of this and I am hypothesizing, but I have a strong background in chemistry and material science that would lead me to believe it is entirely possible.

DBH might be able to provide insight to the validity, far more knowledgeable than I in the steel science.

[Manifestgtr]

Made a quick video of the “methodology” involved…posted it to my long-neglected secondary YouTube channel. Since this is potentially a phenomenon that affects the users in the real world, I’m not doing anything funny. Just a typical, freehand, Delica sharpening…put it away til march then check it out and see what’s doing.



This is SUPER preliminary…I’m also one guy and can only contribute so much to the zeitgeist of knife geekdom. Any results I get are from a sample size of precisely one. That doesn’t escape me…I know that science thrives on repeatability and objectivity above all else.