Hypothetical secondary effect of stropping

Gentlemen, for your consideration:

A hypothetical secondary effect of stropping.

The conventional wisdom regarding stropping is that it aligns and straightens microserrations along the razor’s edge.

It has been observed that with several cycles of shaving and stropping, the edge improves after honing before reaching a point where the keenness of the edge declines thus requiring honing or pasting.

Since plain stropping does not seem to be removing metal only moving it, the question is raised regarding work hardening of the metal.

Work hardening is a well known and readily observable phenomenon. When metal is manipulated, that is bent or hammered, it becomes harder. This can easily be demonstrated by bending a paper clip back and forth. The clip quickly loses its ductility (if ductility is the word I want) until brittleness overtakes it and it snaps.

Or, one could repeatedly strike a copper penny and observe that more deformation occurs with the initial blows and that further shaping becomes difficult as the copper becomes harder.

So:

Does stropping harden the edge of the razor? Does this explain the bell curve of shaving comfort? Does the edge become harder to the point that it starts becomes too brittle thus requiring honing to expose fresh steel?

Does a slack strop strop bend the edge more causing a greater hardening?

I’ll leave it to better minds to ponder. I’m just an idea man.

Happy trails,
LG Roy

interesting idea. Sounds like it could have a point....unfortunately I'm not much of a metal man....so I can't really say if it's true.

Now that's a perfect example of thinking outside the box. Good brain, LG.
I've got no answer either, but I sure will ponder this one and await the metalurgists to weigh in.

X

The scyte is also hammered between honings. that makes sence...

My take on it, for what it's worth:

Work hardening requires overstressing a metal. Low carbon steel and stainless steel are two that can work harden rapidly when deformed beyond their normal stress tolerances. Stropping can't possibly provide enough heat and stress to cause work hardeining.

Instead, consider this. Stropping DOES remove and shape th metal. It does it at a slower rate than hone, by far, but leather will definitly polish metal and polishing is caused by removing metal at a micro-scale. This forms a very fine micro bevel, which is more obtuse and, therefore, more risistant to dulling. Until the micro bevel becomes so large and obtuse as to restrict the cutting ability of the edge, the edge will continue to become a little stronger and a little more durable with each time the blade is stropped.

I have not made up my mind if stropping does work harden it or not. As papa bear pointed out you have to stress the metal and deform it. to get work hardening you really have to exceed the yeild stress of the metal. This does happen when you strop. If stroping moves the "teeth" so that the "teeth" do nto spring back to their original position then stropping does create stresses that exceed the yeild stress of the steel. In that case I would expect the metal to have been work hardened some.

I'm with Robert. I think the blade does reform with stropping. And I think we are just beginning to understand the benefit of extra stropping passes and more aggressive stropping.

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Originally Posted by trapperjohnme

If stroping moves the "teeth" so that the "teeth" do nto spring back to their original position then stropping does create stresses that exceed the yeild stress of the steel. In that case I would expect the metal to have been work hardened some.

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That would mean that shaving work hardens the steel, too, then. Because it moves the "teeth" out of alignment so they don't spring back to their origninal position. Cutting or dulling of a blade doesn't work harden it, so I think there's little chance that stropping would stress the metal enough to work harden it - at least to any practical degree. I don't think that the purpose of stropping really is about realigning the "teeth" so much as polishing the micro-bevel with the silica naturally in the leather, which is a very mild abrasive.

I'll have to go with you on this one PapaBull.

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That would mean that shaving work hardens the steel, too, then. Because it moves the "teeth" out of alignment so they don't spring back to their origninal position

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that is correct pappabull it would.
But who is to say that saving doesnt work harden part of it?
You have to realize that you can work harden an incredible small area. moving the tooth of the razor either by shaving or stropping will cause work hardening somewhere if the yield stress is exceeded, most likely the root of the tooth, not the very edge. So even though work hardening is occuring it may not be close enough to the edge to benifit.


working high carbon steel to the point that the yield stress is exceeded will result in some work hardening were the stress is great enough to exceed the yield stress, that is just a law of physics.

Work hardening is not always a good thing. Fatigue failures in moving parts are due to a larg extent on localized work hardening.

As a matter of fact one way of dulling a blade is the "teeth" breaking off, they would be more prone to do this if they had been work hardened.

If shaving and stropping both work harden the steel, albiet extremely mildly, and do so at the 'root' of the fins then that effect, over a period of the first few strops and shaves, would continue up to the tip of the cutting tooth. This would very well explain why newly honed razors tend to act up a bit. The fact as well that it is a very low degree of work stress would also agree with why the teeth aren't broken off easily. It's also an argument to strop after the shave.

I think the thought experiment part of this discussion so far can be said to support the work stress theory. How to test it. Perhapse observation under a high powered microscope before and after each stropping which should also perhaps be done both before and after the shave, with careful notes taken on each observation, might prove somewhat conclusive.

This could be The Miniscule Experiment ! :D

X

The only problem I see with this is that as you shave those micro teeth or serrations are being worn down and disappearing so even if the metal is being work hardened at that very thinest edge how long does that edge last before you have to start the whole work hardening process all over again.

Actually what I should have added is that as an edge dulls what is really happening there. Is it just becoming rounded off or is it actually undergoing some major physical change or is it wearing away and saying bye-bye to us?

I don't think so

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Originally Posted by thebigspendur

...how long does that edge last before you have to start the whole work hardening process all over again.

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About 15 or 20 shaves it seems.

Xman, if work hardening was the effect and purpose of stropping, why would it matter when you stropped? Why also, would it matter how many strokes you gave it - or on what type of surface. The canvas side would work just as well as the leather side and a couple strokes would do it because once you "straightened out the teeth", and so "work hardened" them, there would be nothing more the strop would do for you. I'll bow out of this discussion now, though.

Frustrated? LOL....I'm lost too.

Lets go back to the initial example. If I bend a paperclip back and forth it breaks and that proves its harder? Can someone explain that example to me?

If stropping work hardens the blade why does it need stropping on successive shaves? Shouldn't it be hard at that point?

Why can't the strop simply align the edge of the razor because of its consistency?

Are you suggesting that the tip of the bevel is moving back and forth enough to harden the blade and that makes it shave better?

Perhaps your referring more to the ideas presented by Herbert in 1927 when he suggested that steels harden via abrasion. So unlike the need to hammer at steel it simply receives a like molecular compression by abrading it against the strop. This was demonstrated by the hardening of rail ties against repeated train movement. Surely banging a hammer to harden metal and locomotive wheel abrasion hardening aren't taking place here on our razors.

Why the original assumption that hardening of steel is creating a better shave?

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Lets go back to the initial example. If I bend a paperclip back and forth it breaks and that proves its harder? Can someone explain that example to me?

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Bending the paperclip so that it is permanantly deformed work hardens a small area of the paperclip. particularly the area that had the yeild stress exceeded.

when the metal is made harder its strength increases. BUT its ability to withstand deformation DECREASES. In other words it gets mor brittle. you can take a soft steel and bend it without breaking it. take that same steel and heat treat it so that it is as ahrd as possible and then try to bend it. IT doesnt Bend, it breaks. The heat treated steel is harder and stonger but it is more brittle.

work hardening a material likewise makes it more brittle. That is why i stated earlier that work hardening is a primary component of fatigue failures. when a steel is repeatedly flexed it gets harder and more brittle on the surface, eventually a crack can form in the work hardened region. once a crack forms it tends to grow untill the part fails.

Sorry for the can of worms. Just idle speculation on my part.

For the record, I don't know what happens when I strop apart from the edge is made better for shaving.

It's interesting how the simplest things can be so confounding.

The thinking cap is now OFF.

&C &C
LG Roy

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Originally Posted by PapaBull

... if work hardening was the effect and purpose of stropping, why would it matter when you stropped?

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A good question. Clearly other factors are at play, like what the metal does on its own between shaving and stropping.

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Originally Posted by PapaBull

... Why also, would it matter how many strokes you gave it - or on what type of surface. The canvas side would work just as well as the leather side and a couple strokes would do it because once you "straightened out the teeth", and so "work hardened" them, there would be nothing more the strop would do for you.

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More strokes equal more stress, and it's far too assumptive to say that different materials wouldn't matter. They provide a different stress. eg. What would you expect to happen if you stropped on the 4000 grit Norton? Perhaps I like my canvass before my leather because it does more stressing while the leather does more aligning.

If work hardening can be upheld, we would perhaps see that lots of early stropping would benefit the shaving edge. Perhaps not all at once though, 5000 strokes with an hour between sets of fifty for example should bypass the testy early stage. Less stropping toward the end of the edge's life would also be an indicator. After 12 or 15 shaves a dozen or so passes might be enough.

X

P.S. Thanks for the worm LG. :)

If work hardening can be upheld, heat treating could be proven to be irrelevant :) Nice soft steel that's easy to hone would work just fine since the edge is hardned by stropping, right? Lead process heat treating.... what a bunch of nonsense .....I always did think the French were a bunch of big fat stewpid loosers, anyway. ;)

How good a blade we have is more determined by the quality of the heat treat than the quality of the steel, itself. Two blades of the same steel can be perform very, very differently and that's all dependent on the heat treating.

I've taken some old beaters and drawn them down with a torch and re-treated them. It's pretty interesting to see it work and to see what it takes to harden steel.

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Originally Posted by PapaBull

If work hardening can be upheld, heat treating could be proven to be irrelevant :) Nice soft steel that's easy to hone would work just fine since the edge is hardned by stropping, right? Lead process heat treating.... what a bunch of nonsense .....I always did think the French were a bunch of big fat stewpid loosers, anyway. ;)

How good a blade we have is more determined by the quality of the heat treat than the quality of the steel, itself. Two blades of the same steel can be perform very, very differently and that's all dependent on the heat treating.

I've taken some old beaters and drawn them down with a torch and re-treated them. It's pretty interesting to see it work and to see what it takes to harden steel.

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This makes sence to me.

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Originally Posted by PapaBull

How good a blade we have is more determined by the quality of the heat treat than the quality of the steel, itself.

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:nono: The good razor steel has to have at least 0.6% carbon in it, very important variable in the steel quality equation. Without it, all the heat treating in the world wouldnt produce shaving edge...

Nenad

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If work hardening can be upheld, heat treating could be proven to be irrelevant

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in a word no.

Again any work hadening that accorus would occur mostly at the root.

the other reason that heat treating is needed is it assures a uniform hardness. when a metal is work hardened the work hardening is proportional to how much it has been deformed. stroping does not creat uniform deformation throughout the razor, it doesnt even cause uniform deformation thoughout the teeth. the largest stresses would occur at the root that woudl tend to act as a cantilever as it is dislocated.

the hardness of the razor is most determined by the carbon content and the heat treating process. yes, it should have a carbon content of at least .6% also important in the quality of the edge is the carbide distrubition as well. this can be affected by alloying agents, processing of the steel etc.

I may not be an honemeister or a razor expert, but i am an engineering professor that teaches materials science and mechanical design.

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Originally Posted by trapperjohnme

Again any work hadening that accorus would occur mostly at the root.

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This might be a bit of a misleading way of putting it since we're really talking about grooves, striations.

Trapper, I was trying to make a point. I certainly wasn't seriously implying that heat treatment is irrlevant. That's what makes a razor's edge hard enough to hold up or not. Stropping merely polishes a more obtuse secondary micro-bevel which makes the edge stronger. But that's just from an engineering perspective. From an alchemist's perspective, work-hardening the teeth of a razor by stropping it is what makes a razor's edge durable. I'm not much into alchemy, though.

I think it's important in a discussion like this that we look to the relevant experimental data that we can get our hands on. The best electron micrographs of the razor's edge are from Prof. Verhoeven's paper "Experiments on knife sharpening." He has micrographs of straight razors. These micrographs show no evidence whatsoever of "teeth", but instead just a clean smooth edge that is about 0.3-0.4 microns wide.

I agree that stropping definitely does something, but what that is I don't exactly know. I don't think I would rule out work hardening at the very surface of the metal. While we are clearly not bending the metal back and forth, we are putting shear stress on the metal at the razor edge by dragging it across the leather. I suspect that it is possible to introduce lattice strain and defects which produce a harder 'skin' on the edge. It might be possible to observe this with a transmission electron microscope (TEM).

E

It's all very interesting, but there's no reason to reinvent the wheel. The existence of the teeth is well established. It's not the striationsbut the raised part next to it. The micrographs we saw were probably too close to see the striations. If you worked an edgw with a 8K stone, magnified 10,000x the spacing between striations would be 1.2 inches.

There is a old German story that razors should not be stropped right after shaving because it doesn't allow the teeth to return to their normal, nearly upright positions. Stropping would then force the teeth back, eventually causing them to break off from stress. This tells us that the teeth are elastically deformed when we shave and slowly return to some position short of being aligned. After that stropping probably causes additional elastic deformation as the teeth are stood up. This can go on for many shaves, and it does. Eventually, the blade pulls a little even after stropping. That's because of the slight frictional wear caused by shaving. All you need to do is a few touch up swipes on a Swaty and you're back to the original condition after you strop. As we know, this can go on indefinitely without major stropping.

So, with the normal routine, there should be no work hardening and no major honing required. That only happens if we do something out of the ordinary lkie, according to the Germans, always stropping right after you shave.

As for an edge improving after a few hone/strop cycles, that could just be a function of zeroing in an edge that's not quite there.