Are we actually sharpening the carbides?

[Bolster]

Bearfaced addressed a question in another thread that has been nagging me for some time: when we are sharpening, are we actually sharpening (abrading) the carbides? Are we taking these hard little nuggets and sharpening them into a wedge shape?

Sharpness is defined as the thickness of the apex measured in microns. A 1 micron edge is stupid sharp and a 0.1 micron edge is insanely sharp and maybe not even possible. Powdered steels have carbides in the 3-8 micron size range so we are talking about edges that are thinner than the size of the carbides in it. Both are sharper than most folks need or can achieve. Some steels may struggle to achieve that 0.1 micron edge but only elite sharpeners can even think of getting close to that sharp.

So I guess the steel solution/matrix that surrounds the carbides is strong enough to keep those little nuggets of carbides in place along the edge while we abrade them? Previously I had assumed that when you got the edge to the size of the carbides, they'd just be scraped out. But maybe they remain, and take on the edge themselves? If so, that's very nifty.

Care to edge-u-ma-cate me further on this issue?

[Bolster]

Making wedges of the carbides?

[spoonrobot]

I've been reading about this myself, today.

So I guess the steel solution/matrix that surrounds the carbides is strong enough to keep those little nuggets of carbides in place along the edge while we abrade them? Previously I had assumed that when you got the edge to the size of the carbides, they'd just be scraped out. But maybe they remain, and take on the edge themselves?

I believe this article about Maxamet answers your questions with pictures:https://scienceofsharp.com/2019/11/03/c ... n-maxamet/

However, as noted, this may or may not generalize to other knives/steel.

I also found this thread informative for actually sharpening the carbides themselves: https://bladeforums.com/threads/carbide ... t.1705186/

Much has changed in sharpening knowledge since I first learned a few decades ago.

[sal]

Hi Bolster

Excellent question !

sal

[bearfacedkiller]

With an abrasive that is harder than the carbides I think that the answer is yes. Diamonds will cut vanadium carbides. Abrasives that are hard enough to cut the steel matrix but not the carbide will still sharpen the edge but they can “plow” the carbides through the steel instead of cutting them.

There have been some good threads on Bladeforums with microscopic photos showing this. This has led to the belief that you must have diamonds or CBN stones to sharpen high carbide steels.

My experience is that high carbide steels can be sharpened on most quality stones but that diamond/CBN does work better and they cut faster. It is probably worth noting that I like coarse edges so maybe that is why I don’t mind using ceramic stones too. If I finish on the Spyderco medium stone that is equivalent to about a 15 micron grit size which is larger than the vanadium carbides in a powdered steel. I then follow that with a 1 micron diamond strop to clean up the edge.

My point? I think that when you go to finer edges it may be increasingly important to use diamond or CBN stones. With a coarse edge it may be less important. Hopefully somebody like BBB or Larrin who knows way more than me will chime in. :)

[The Meat man]

I've been reading about this myself, today.

So I guess the steel solution/matrix that surrounds the carbides is strong enough to keep those little nuggets of carbides in place along the edge while we abrade them? Previously I had assumed that when you got the edge to the size of the carbides, they'd just be scraped out. But maybe they remain, and take on the edge themselves?

I believe this article about Maxamet answers your questions with pictures:https://scienceofsharp.com/2019/11/03/c ... n-maxamet/

That article, and those pictures, are absolutely fascinating.

[Deadboxhero]

Bearfaced addressed a question in another thread that has been nagging me for some time: when we are sharpening, are we actually sharpening (abrading) the carbides? Are we taking these hard little nuggets and sharpening them into a wedge shape?

Sharpness is defined as the thickness of the apex measured in microns. A 1 micron edge is stupid sharp and a 0.1 micron edge is insanely sharp and maybe not even possible. Powdered steels have carbides in the 3-8 micron size range so we are talking about edges that are thinner than the size of the carbides in it. Both are sharper than most folks need or can achieve. Some steels may struggle to achieve that 0.1 micron edge but only elite sharpeners can even think of getting close to that sharp.

So I guess the steel solution/matrix that surrounds the carbides is strong enough to keep those little nuggets of carbides in place along the edge while we abrade them? Previously I had assumed that when you got the edge to the size of the carbides, they'd just be scraped out. But maybe they remain, and take on the edge themselves? If so, that's very nifty.

Care to edge-u-ma-cate me further on this issue?

Yes, you shape the hard carbides by using the appropriate abrasive.




According to the BESS tester folks a sub 50g Bess reading is a sign of a sub micron apex.
If you looks at the Micrograph of Rex 121 you can see it has a high volume of carbides much larger than the sub micron range.

If I used softer abrasive I would not be able to get the same crisp definition at the apex, can't seem to burnish and break carbides to shape with softer abrasive to the same definition.

Todd Simpson at Science of Sharp showed with his Maxamet Native 5 the Carbides are very firmly held in place in the matrix although the Maxamet steel does have a hard matrix to support the carbides.

Tear out may be likely with soft annealed steel.

Almost like a shovel being able to scoop out rocks in loose dirt versus when the dirt is compacted and hard and the rocks almost seem to reinforce the dirt making it all feel like rock when digging a hole.

An interesting note about annealed steel is that the carbide volume is higher when a steel is in its soft annealed state.

[Pancake]

What about some medium volume carbide steels, like CPM 3V?
Is the Spyderco medium ceramic stone good or not so good choice?

[jpm2]

This is a most interesting subject to be investigated.

If high carbide steels are not being sharpened with appropriate abrasives, the fine edge advantage of the carbide might not be realized .

[Deadboxhero]

https://knifesteelnerds.com/2019/05/26/ ... fe-steels/

This is article is the best place to "visualize" things

Think of each micrograph folded in half to a point and that what the edge looks like.

[Bolster]

This is soooo interesting. Thanks to all who posted. Spoon's link blew my mind.

[sal]

Kinda looks like a serrated edge to me. :p

sal

[Bemo]

Best thread since I joined. I think the point about highly polished versus course edge cannot be understated in terms of sharpening medium and carbides.