JNAT Work Hardening: explain please

[Brooksie967]

Can't remember where I read it but I seem to recall seeing something about jnats being the only stones that will 'work harden' the steel being sharpened on the stone.

Any takers? As detailed as you can be please

 

[Steve56]

So Yamashita's site at Japan Tool is what Ive seen broadly quoted. Maybe So can enlighten us.

http://www.japan-tool.com/toishi/home_toishi_tennen.html

I do know they do something different to the layer of steel that reflects light, the observables are quite different from synthetic. So something different is happening at some level. Whether its related, IDK.

Cheers, Steve

 

[Brooksie967]

So Yamashita's site at Japan Tool is what Ive seen broadly quoted. Maybe So can enlighten us.

http://www.japan-tool.com/toishi/home_toishi_tennen.html

I do know they do something different to the layer of steel that reflects light, the observables are quite different from synthetic. So something different is happening at some level. Whether its related, IDK.

Cheers, Steve

Thanks Steve, that is exactly where I read it, just couldn't remember.

 

[PapaFish]

Can't remember where I read it but I seem to recall seeing something about jnats being the only stones that will 'work harden' the steel being sharpened on the stone.

Any takers? As detailed as you can be please

That's not true, it can't be. If it were true, I would have to buy one!

He doesn't say that JNats are the only stones that harden the edges, but it's the only stone I have seen this type of test done with. He also doesn't say that JNat edges last longer than any other stone, he says that Natural edges last longer than Synthetic edges due to the difference in the particle sizes. I can't prove/disprove any of this, by the way. It makes me want to find a way to test the hardness of edges when sharpened on various stones. This testing sounds like a whole new rabbit hole...

 

[oakeshott]

Of course I could be wrong, but I'm nearly certain that this is nonsense. Most work hardening in steels occurs as a result of impact (though not all, some machining does it as well to certain tool steels, iirc). When honing, however, we are abrading steel and I don't think that can induce work hardening. At a micro level there may be some impact occurring, but if so, only a very thin layer of steel would be hardened. Too thin to be detected by an Rc measuring device.

Of course, metallurgy is tricky. Something may be going on here, but I don't believe it.

 

[BDF]

Right. Work hardening has to involve the deformation of the material and that is not happening with honing, even if one presses <really> hard on the razor. In fact if there was any appreciable deformation, the edge would just bend out of the way and the razor would not actually get sharp. I supposed in a real stretch one could say that a foil edge could be work hardened it is of no relevance as it is so thin that it will be broken off before it can be used in any way.

There is nothing being done to the metallurgy of the steel either; in fact, honing is one of only three processes that will remove an amorphous layer and leave 'correct' steel behind. All machining and almost all grinding processes leave an amorphous layer which is undesirable under any circumstances or usage that I know of.

Brian

Of course I could be wrong, but I'm nearly certain that this is nonsense. Most work hardening in steels occurs as a result of impact (though not all, some machining does it as well to certain tool steels, iirc). When honing, however, we are abrading steel and I don't think that can induce work hardening. At a micro level there may be some impact occurring, but if so, only a very thin layer of steel would be hardened. Too thin to be detected by an Rc measuring device.

Of course, metallurgy is tricky. Something may be going on here, but I don't believe it.

 

[Fuzzy Chops]

There is nothing being done to the metallurgy of the steel either; in fact, honing is one of only three processes that will remove an amorphous layer and leave 'correct' steel behind. All machining and almost all grinding processes leave an amorphous layer which is undesirable under any circumstances or usage that I know of.

Brian

If there is a way to mechanically polish metal without forming a Beilby layer (the amorphous layer) I would like to know more about it. Usually this layer has to be removed chemically.

 

[Seraphim]

The Rockwell testing is suspect in my book here.

If they tested one spot, honed, then tested the exact same spot, the same divot, then the Rockwell testing itself likely caused the work hardening. If they did not use the same test divot, then it could simply be due to different location have a different localized hardness.

Did they really test the hardness right down there on the bevel??? That's a pretty narrow slice of real estate with variable thickness they are trying to measure. Measuring closer to the edge likely would result in a lower apparent RC due to deflection. Conversely, measuring the hardness on the bevel further away from the edge would likely result in a higher score because of increased thickness and therefore stiffness.

I say it's a test result that likely is within the margin of error for any useful data to be had.


The razor did, however, measure 10 points higher on the Mojometer after honing on the JNat!

 

[Steve56]

Coticule garnets are reportedly faceted spheres, so aren't we rolling the blade over little ball peen hammers? Maybe like bead blasting. Random thoughts here...

Cheers, Steve

 

[BDF]

The three ways to remove the amorphous layer from steel are: 1) honing 2) lapping and 3) superfinishing. All these processes have the one thing in common that will remove stock without creating an amorphous layer, which is what amounts to removing the amorphous layer in the first place: they do not create enough point contact temperture to disturb the parent material and yet will slowly abrade the parent material away.

Honing is the slow, moderate pressure wiping of the parent material using pre- formed abrasives. Lapping is similar but uses a lapping compound (the abrasive) between the parent material and the lapping surface, usually a relatively soft material such as cast iron. Superfinishing uses soft, resin bound abrasives moving 90 from the main direction of travel and is by far the most widely used of the three methods.

In addition, all three methods can yield a correct tribological contact surface on the parent material. This is what has allowed relatively 'break-in' free engines in the last 30 or so years. If you picture a series of "V"s across a surface that has been ground, for example, the typical bearing surface would be on the order of 5%. After superfinishing, only the lowest valleys (the inverted "V"s) would be left with 95% of the surface flat and the remaining grooves there to retain lubricant.

Another method that does work is a simple fixture wrapped with sandpaper, used in a drill press at very low rotary speed and pressure. This was the original method used by Chrysler R&D back in the 30's which provided the basis for superfinishing. Unfortunately sanding cannot leave a correct tribolobical surface behind but it can remove the amorphous layer.

Finally, controlled, specific methods of modern CBN grinding leave no amorphous layer behind on most materials, including all forms of steel. If the surface is a bearing surface of any kind, it will still need to be superfinished to acheive an acceptable bearing surface.

Brian

If there is a way to mechanically polish metal without forming a Beilby layer (the amorphous layer) I would like to know more about it. Usually this layer has to be removed chemically.

 

[Brooksie967]

Great info guys!

I'm not sure if the person who wrote on jnats work hardening steel did the test on a razor, a plane or some other tool/steel object so I don't think we should assume it was tested on a razor.

RE coticule: i've heard that too, about the rolling.

Jnats are... silica? I'm wondering what it does to steel. I've never seen any synthetic stones with silica as the abrading material.

 

[alx gilmore]

Can't remember where I read it but I seem to recall seeing something about jnats being the only stones that will 'work harden' the steel being sharpened on the stone.

Any takers? As detailed as you can be please

Brooksie
Here is one reference to that hardening effect:

This is what's going on with Japanese natural sharpening stones. The particles in these stones have been rounded by nature so they produce a scratch that refracts less light. Some natural stones can produce an edge that is sharp but not really shinny. Under powerful magnification the surfaces left by these natural abrasives look beaten more than scratched. Typically, there are some harder particles mixed in with the softer ones so errant scratches occur. The finest Japanese finishing stones have a particle size of about 2.5 microns, really large in terms of modern abrasives. Then why can they produce such great long lasting edges? Those naturally large rounded particles hammer the steel more than they abrade it leaving a "microscopically cold forged surface" in some steels. The problem is finding uniformity in nature. Natural stones can only be divided into families based on geological regions. Stones cut from adjacent layers in the same quarry can have very different characteristics. Even different strata in the same stone vary. This makes prospecting for a good marriage of steel and stone time consuming.

and the source of that quote: http://japanesewoodworking.com/phpB...sid=23623aa9d499de29fb90c70202713f8c&start=15

This is a very indepth thread from TheJapaneseWoodworking forum, razors are mentioned and also some of the effects that chemicals within the natural stones might have on the blades.


Alx

 

[Fuzzy Chops]

The three ways to remove the amorphous layer from steel are: 1) honing 2) lapping and 3) superfinishing. All these processes have the one thing in common that will remove stock without creating an amorphous layer, which is what amounts to removing the amorphous layer in the first place: they do not create enough point contact temperture to disturb the parent material and yet will slowly abrade the parent material away.

Honing is the slow, moderate pressure wiping of the parent material using pre- formed abrasives. Lapping is similar but uses a lapping compound (the abrasive) between the parent material and the lapping surface, usually a relatively soft material such as cast iron. Superfinishing uses soft, resin bound abrasives moving 90 from the main direction of travel and is by far the most widely used of the three methods.

In addition, all three methods can yield a correct tribological contact surface on the parent material. This is what has allowed relatively 'break-in' free engines in the last 30 or so years. If you picture a series of "V"s across a surface that has been ground, for example, the typical bearing surface would be on the order of 5%. After superfinishing, only the lowest valleys (the inverted "V"s) would be left with 95% of the surface flat and the remaining grooves there to retain lubricant.

Another method that does work is a simple fixture wrapped with sandpaper, used in a drill press at very low rotary speed and pressure. This was the original method used by Chrysler R&D back in the 30's which provided the basis for superfinishing. Unfortunately sanding cannot leave a correct tribolobical surface behind but it can remove the amorphous layer.

Finally, controlled, specific methods of modern CBN grinding leave no amorphous layer behind on most materials, including all forms of steel. If the surface is a bearing surface of any kind, it will still need to be superfinished to acheive an acceptable bearing surface.

Brian

Thanks for that Brian, very interesting reading. We work at very different length scales.

 

[BDF]

Probably not so far as you would think- surface finishes are typically sub- micron in maximum change. Piston ring edges are critical both in finish as well as edge geometry. I am not in the automotive industry but a lot of finishing is done for the automotive industry and the rolling element bearing world.

And I bet shaving wise we have very similar size faces, give or take an inch or two.

Brian

Thanks for that Brian, very interesting reading. We work at very different length scales.

 

[Gamma]

Those naturally large rounded particles hammer the steel more than they abrade it leaving a "microscopically cold forged surface" in some steels

Seriously?

Hey Alex - did Sir Issac Stanley ever get back to you with his scientific explanation about that tidbit?

 

[oakeshott]

Those naturally large rounded particles hammer the steel more than they abrade it leaving a "microscopically cold forged surface" in some steels.

There is simply no way this happens. Take a metal like manganese which will naturally work harden. I've seen it used in applications (hammermill in a car recycling plant was quite impressive) where the steel had to take a TREMENDOUS beating to go from Rc in the high 20's to something in the low 40's. The problem was you had to use it in applications where the bulk of the wear was from impact; if there was significant abrasion, then the steel wears away.

Even at the micro level, those "naturally large rounded particles" could not generate enough force of impact to cause a change in the structure of the base steel. Plus, if they're round, then they're more, not less, likely to abrade rather than hammer.

In the metals world there's all kinds of folk tales about why metals behave the way they do. I remember one old time welder, a truly gifted craftsman and a 40 year veteran of the trade, tell me that the reason cast iron is so brittle is because the molecules all point the same way. The metallurgist I worked with at the time was too astonished to say anything.

 

[BDF]

Thank goodness we do not have any of that in the shaving world.



Brian

<snip>

In the metals world there's all kinds of folk tales about why metals behave the way they do.

<snip>

 

[Brooksie967]

Wow, this is WAY more advanced information that I had hope for but it's quite an interesting topic. At this point I think I'm more confused that I was previously; that and sceptical of the fact that these stones 'work harden' steel.

 

[Brianskeet]

Wow!! Really interesting info.

 

[oakeshott]

Thank goodness we do not have any of that in the shaving world.



Brian

Every culture and every sub-culture has its myths.

Anyone heard the one lately about how wet shaving will save them money?