Why can I get VG-10 sharper than S35VN?

[kjos]

I'm fairly new to the knife world and still trying to learn about blade steels and sharpening. My question is stated above, but I use the Spyderco Sharpmaker, medium, fine, ultra fine stones, then strop on my knivesplus strop block. I am referring to my Spyderco Endura 4 full flat-ground, and my small Sebenza 21 Insingo S35VN. I sharpen both knives the same, at 20 degrees, and with much patience and care. I can just seems to get a much sharper edge on my Endura with the VG-10 and didn't know why.

Thanks for any info guys.

 

[Obsessed with Edges]

VG-10 is a lot less wear-resistant than S35VN, which has much more vanadium (10-30X as much as in VG-10) and higher carbon content (half again as much, as in VG-10), and therefore a ton of vanadium carbides in it. Vanadium carbides are extremely hard and much more challenging to abrade. That doesn't mean S35VN can't get as sharp, but it does likely mean it takes more aggressive abrasives, and more time and effort to get it there.

I'm sure there are other factors, because these are completely different steels. But, the vanadium carbide content is the biggest difference, as I see it.


David

 

[bgentry]

I don't know much about this, so I'm really here to ask questions of my own.

I've read that vanadium carbides are so hard that many abrasives won't grind them. Instead, the abrasive grinds the steel around the VCs until there's so little left holding them on, that the VCs tear out of the matrix. Presumably leaving behind a very tiny hole or chip in the edge. Does this mean that when using most abrasives a high vanadium carbide blade will seem more toothy or rough? Less good at push cutting (shaving) and better at slicing?

What if you use diamonds on this type of steel, which is supposed to be able to actually grind down the carbides. Will you get a finer edge?

Or is the whole problem for the OP that he's not getting a burr on S35VN because it's so wear resistant that he's not grinding for long enough?

To the OP: Are you getting a burr with your S35VN blade?

Brian.

 

[Bo T]

VG-10 is a lot less wear-resistant than S35VN, which has much more vanadium (10-30X as much as in VG-10) and higher carbon content (half again as much, as in VG-10), and therefore a ton of vanadium carbides in it. Vanadium carbides are extremely hard and much more challenging to abrade. That doesn't mean S35VN can't get as sharp, but it does likely mean it takes more aggressive abrasives, and more time and effort to get it there.

I'm sure there are other factors, because these are completely different steels. But, the vanadium carbide content is the biggest difference, as I see it.


David

+1 The heat treatment also has something to do with it as it is possible to produce vanadium carbides of different sizes depending on the purpose of the knife.

 

[Obsessed with Edges]

I don't know much about this, so I'm really here to ask questions of my own.

I've read that vanadium carbides are so hard that many abrasives won't grind them. Instead, the abrasive grinds the steel around the VCs until there's so little left holding them on, that the VCs tear out of the matrix. Presumably leaving behind a very tiny hole or chip in the edge. Does this mean that when using most abrasives a high vanadium carbide blade will seem more toothy or rough? Less good at push cutting (shaving) and better at slicing?

What if you use diamonds on this type of steel, which is supposed to be able to actually grind down the carbides. Will you get a finer edge?

Or is the whole problem for the OP that he's not getting a burr on S35VN because it's so wear resistant that he's not grinding for long enough?

To the OP: Are you getting a burr with your S35VN blade?

Brian.

Prefacing my reply with this quoted text from Crucible's data sheet for S35VN (I added the bold emphasis):

(text quoted from -->: http://www.crucible.com/PDFs\DataSheets2010\dsS35VNrev12010.pdf )

"CPM S35VN is a martensitic stainless steel designed to offer
improved toughness over CPM S30V. It is also easier to machine
and polish than CPM S30V. Its chemistry has been rebalanced
so that it forms some niobium carbides along with vanadium and
chromium carbides. Substituting niobium carbides for some of the
vanadium carbides makes CPM S35VN about 15-20% tougher
than CPM S30V without any loss of wear resistance. CPM S35VN’s
improved toughness gives it better resistance to edge chipping.
Because both vanadium and niobium carbides are harder and more
effective than chromium carbides in providing wear resistance,
the CPM stainless blade steels offer improved edge retention
over conventional high chromium steels such as 440C and D2."

I interpret this to mean S35VN won't be as prone to the 'coarse edge' resulting from carbides chipping out, as compared to S30V. Still don't know how that would compare to VG-10, which has no vanadium carbides at all (just chromium carbides, which are often larger, but not as hard and easier to grind; maybe molybdenum carbides as well). I'd assume the CPM process helps to keep the carbide size relatively small in S35VN, which might minimize how difficult it may be to get a real fine edge. CPM-S30V's vanadium carbides are described by Crucible as averaging 2-4 microns in size; don't know if the assumption is the same for S35VN.

I do agree, that any steel with relatively high vanadium carbide content (maybe above 2% or so), is going to grind & refine more easily with diamond, at least, especially when done by hand. Powered (driven) grinding tools could do it with other abrasives (Crucible recommends a given type of AlOx or CBN wheel, for this steel, in their data sheet).


David

 

[Magnaminous_G]

Sigh...

OP, the Sebenza is convexed from the factory. You are not hitting your apex. You need to grind it down to a V to get there, which is practically impossible with the medium rods as they are not coarse enough. Get the diamond rods. Payce.

 

[Ben Dover]

Sigh...

OP, the Sebenza is convexed from the factory. You are not hitting your apex. You need to grind it down to a V to get there, which is practically impossible with the medium rods as they are not coarse enough. Get the diamond rods. Payce.

Mag is correct. The Convex must be converted to "V" for using the SM.

The other option is to use sandpaper and strops and resharpen the convex. At one time, Bark River Knife and Tool had a tutorial on their website for convex sharpening.:thumbup:

It isn't difficult, but it can a bit time consuming if the blade is dull. I use 3M wet/dry sandpaper, very wet, over a mouse pad to re-establish the edge, and loaded strops to refine it.

If you go to you tube and search for convex sharpening, I'll betcha you'll find at least several videos on the topic.

 

[fervens]

Sigh...

He didn't say he couldn't get it sharp. He said he couldn't get it as sharp. Even with the Sebenza being convex, the SM's angles can still hit the apex. It depends on the angle at the apex. As for VG10 being sharper than S35VN. S35VN has lots of chunky carbides to keep it from abrading easily. you will need CBN or diamond abrasives to cut the carbides. Otherwise, you will sharpen away the steel matrix and eventually pull out the carbides. CBN and diamond will cut the carbides as well as the steel leaving a cleaner apex. Also, VG10 was picked as a knife steel for it's ability to hold a very fine edge. For kitchen knives mostly. S35VN was picked for it's extreme abrasion wear resistance that allows it to hold a "working" or courser edge for a really long time.

 

[Obsessed with Edges]

Unless CR Knives has changed the way they do their edges, the 'convex' on them is so subtle as to not matter substantially anyway, nor does it have to remain convex. The subtle convex on their blades is introduced in the way they finish/polish the edge, after grinding the bevels. Any method used for V-edges can touch them up. As mentioned, for high-wear steels, diamond/CBN will be more effective. I've used wet/dry paper for light touch-ups on my S30V Sebenza, but it doesn't quite impart the same 'bite' to the edge, on this steel. The carbides in it are almost as hard as the abrasive itself (SiC). S35VN is supposed to be somewhat easier to grind/shape (according to Crucible), so that might make a difference in sharpening on wet/dry paper.

Chris Reeve even recommends the Sharpmaker (or Lansky) as a maintenance sharpener for their knives (see quote from their FAQ page, below). With the diamond rods, it could do fine or even excellently, so long as re-bevelling isn't needed. Re-bevelling would be very slow-going on the small abrasive surface area of the SM's rods, otherwise.

( from site: http://chrisreeve.com/FAQs )

"What is the best way to keep my Chris Reeve Knife sharp?
One important thing to remember with any knife is to maintain the edge – it is better to keep it reasonably sharp rather than let it get completely dull and then try to get the edge back. To maintain an optimal cutting edge on a Chris Reeve knife, we recommend the use of the Spyderco Tri-Angle Sharpmaker or a Lansky Sharpener. If you prefer to use a stone, the angle at which to sharpen will be best achieved at 18 – 20 degrees. We will sharpen any knife we have made free of charge. We ask only that you pay for the return shipping. Simply return the knife (in its sheath if applicable), make sure that you include your address and phone number and we will restore that famous, hair-popping sharp, Chris Reeve Knives edge."

David

 

[Magnaminous_G]

I hope the OP posts again with his results.

 

[Ben Dover]

Excellent points, David. Personally, I wouldn't want a convex in any steel much past 154CM, unless I used a power belt sander. Linen belts, and CBN or diamond on a belt sander would make quick work of the super steels, but doing any of them by hand with sandpaper would severely test even my stubborn nature.

It will be interesting to see if linen or leather belts are offered for the Worksharp Ken Onion. If they are, I will, in all likelihood acquire one, even though my convex sharpening is limited.