The edge gets dull WITHOUT cutting?

I have a few knives that seem to exhibit this kind of behavior. Strange thing is that two are Sandvik Kershaws. They seem to always want a quick stropping whenever I pull them out, even if they were put up keen as a razor. I have a couple low end 420j2 Kershaws that behave better in this respect. The other is a Tekna in 420HC that I swear goes dull by looking at it too hard.

These oddities remain a mystery to me.
 
We can guess all day (and have fun doing it). But whether it's corrosion at the edge or an edge memory issue, the only way to know for sure what the problem is is to check the edge with a microscope. Check right after sharpening to your best edge and then again after leaving it alone for a few days. If you snap pictures of the before and after edge, say with a USB microscope, that's even better.
 
This happens to me. It happened to my brand new Stretch II. I carried it for about 2 months without ever using it (factory edge), and it did become rather dull after that time period. Same happened to my D4W.
 
winbag338 said:
How in the world can you carry a knife for 2 months without useing it?
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Bill1170 said:
My thought exactly.
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lol I got it back in early October and I never used it because I didn't want it to get dull and have to sharpen it (which would mean reprofiling since it would be the first time). I didn't have time to reprofile it because of school and all, but now that the semester is over I finally used it. And it is certainly the best cutter I have ever used :thumbup:
 
Thanks to everyone who responded with ideas and experience, etc.

In no particular order:

I think I'm getting rid of the burr. If it was as big as knifenut says it could be, I'd feel it. I'm pretty sure this is not the case.

Corrosion: I guess it's possible. I live a few miles from the coast, and it's really, really humid here nearly all the time, but it's not "salt air" and I don't store the blade in salt water as someone asked. :P

As for metal "memory", I can sorta see this happening, but how would I have formed memory for a slightly dull, slightly leaned over edge? Maybe this steel is just not "good enough" to keep the edge that I've put on it.

Is the edge hitting something inside the handle of the folder? I've looked carefully and it's not.

Thanks again.

Brian.
 
I have no proof, but I think the issue is one of corrosion. All steels are prone to corrosion, "stainless steel" is well named. It stains (corrodes) less. But it still corrodes, and minute changes are going to be most noticeable at the edge.

Corrosion is the result of the oxidation of iron by oxygen. moisture promotes the reaction, though it is not absolutely necessary. You can place steel wool in a pure O2 atmosphere, apply a spark and watch the stuff burn producing a flame.

All steel oxidizes (corrodes) on a surface exposed to air and moisture. For a non-stainless steel, the oxidation products are only loosely adhering and more oxygen gets at the surface to cause continued corrosion. For "stainless alloys" the corrosion products adhere tightly to the surface and prevent further access by oxygen and water, so the corrosion process stops.

At a knife edge, the oxide layer has a hard time remaining attached to the surface. It is, after all, a knife edge. So there should be a tendency for more corrosion to occur at a knife edge than on just a sheet of stainless steel. This would lead to the situation that even a fairly corrosion resistant grade of stainless steel such as 420 or 440A will lose some material at a knife edge, even though the flat part of the blade does not show corrosion.

The above is a hypothesis based on theory. I have seen no photo-micrographic studies on the subject. But it is theoretically sound and would explain the phenomenon, which I also have noticed on occasion. But for me, I notice it as much on my non-stainless blades as on my stainless unless I keep the non-stainless oiled, which I often do.

my 2 cents.
 
You know, I don't know *why* I neglected to mention this the first time around.

Regarding corrosion: In the past I haven't used oil on the blade surface itself and was lax about wiping it down after touching the blade. After a while (not sure how long) the blade surface (the sides) developed some corrosion: Not classic orange rust, but more like black circles and teeny tiny pits. This, despite the fact that the blade is "440" (probably 440A based on all the commentary here) and that the blade was coated with some sort of gray-ish finish on it. The web site says "bead blasted", but I'm not sure. The point is, it corroded despite these two things.

That coating is now gone as a friend of mine sanded off the corrosion, along with the coating (finish) and most of the writing on the blade. :)

So I guess corrosion is absolutely possible. I'm just not sure how long it takes or if it would appear on the edge or not. Interesting stuff.

Brian.
 
Reading Knarfeng's post makes me wonder what about H1 steel? Does it also degrade at the edge in storage, and is it due to corrosion or some other dynamic?

I personally suspect that there are processes that occur at a very sharp edge which cannot be adequately explained by the existing language of our science. If this is a correct suspicion, then it may help to explain some of the mystical/mythical associations we have with blades.

Bill
 
Knarfeng-
I have had carbon steel knives in the same cas with the stainless ones. Carbon steel remained sharp. This seems to negate corrosion-although the carbon knives were oiled, stainless was not.
 
Bill DeShivs said:
Knarfeng-
I have had carbon steel knives in the same cas with the stainless ones. Carbon steel remained sharp. This seems to negate corrosion-although the carbon knives were oiled, stainless was not.
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The oil forms a barrier to moisture and oxygen. And because it is a liquid, it is easier for the oil to remain in place around the edge than an oxide layer.

Usually I store carbon blades oiled. Sometimes not (Bad Knarfeng!). I think I've noticed that it makes a difference on the edge staying sharp, though I have not done a side-by-side comparison. The loss in cutting performance is so little, I'd have a hard time documenting it anyway.
 
Hi
One of the ways to stop the knife dulling,after stropping, Lightly steel your knife,
Ben Dale of Edge Pro gave me that info,it works.You may also be aligning a very ,very
small burr that deteriorates,folds over.
 
Knarfeng
I understand what you are saying. Because the stainless was not oiled, that corrosion at the thin edge may have taken place. Interesting. I may sharpen one up and oil it to see.
Thanks.
 
bgentry said:
The web site says "bead blasted", but I'm not sure. The point is, it corroded despite these two things.
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I just thought I'd point out that if it is in fact bead blasted, not coated, it would actually rust MORE than if it were satin- or even better mirror-finished. The bead blasting causes tiny dents/pits (thus the matte gray color) in the surface, which hold onto liquids and corrosive byproducts, making the end product less rust resistant than one would expect for the given steel.
 
Bill DeShivs said:
Knarfeng
I understand what you are saying. Because the stainless was not oiled, that corrosion at the thin edge may have taken place. Interesting. I may sharpen one up and oil it to see.
Thanks.
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I'd be interested in hearing about your results.
 
Could it be that the stainless is "passivating" itself at the new edge?
 
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