Silicon Carbide vs. Aluminum Oxide belts

[Himalayan]

For those who belt sharpen, is there much/any difference between these? I've only ever used SC. Primarily I use only 400 & 600 grit. To sharpen the harder steels, would one be better than the other?

 

[Blade Lab]

I don't have much experience with belt sharpening, but silicon carbide is harder than aluminum oxide, so I would imagine that sic would be better for wear-resistant steels. That said, even sic isn't as hard as vanadium carbide, so not ideal for high-vanadium steels.

 

[Obsessed with Edges]

As per Blade Lab's post above, and fully admitting I don't have experience using powered grinders, I'd echo the same:

As used in stones, SiC should be better for more wear-resistant steels. I know there's a big and easily perceptable difference in ease of grinding on stones using SiC instead of AlOx on steels like 440C or D2, for example. And for high-vanadium steels especially, SiC should work better than AlOx.

AlOx is usually popular for its economy, durability & toughness and also for its ability to dissipate heat. This is assuming the abrasive is not clogged or too worn anyway, or being used on steels with too much wear resistance, which would wear out the abrasive much faster and exacerbate heat issues.

SiC usually isn't as tough as AlOx and will be more friable (breaks down more easily to finer grit). So, the SiC belts may not last as long, or may not work at the same finish as long, as will AlOx (again assuming the AlOx isn't wearing too much, or getting too clogged).

 

[Cementite]

My question regarding AlOx vs SiC is more about stones than belts, but does anyone know whether either abrasive will reliably cut CPM M4 high-speed steel?

I recently got a Spyderco PM2 in CPM M4, and I'm curious whether my Norton Crystolon (silicon carbide) and/or Norton India (aluminum oxide) combination stones will cut it.

(Also interested whether either of these abrasives will work with CPM CruWear and/or Carpenter Maxamet steel, since I also have Spyderco PM2s in both of those steels, as well.)

TIA for any help...

 

[Grasshopperglock]

From my understanding and I have a table top belt sander. Aluminium oxide is for wood. Typically a dark red color. It's cheap and you can find it everywhere. And using it on steel, wears it out pretty quick.

Silicon carbide is meant for steel. Being grey-ish blue colored.

Dealing with stones. Aluminum oxide on forged blades. Carbide on powered steel.

 

[FortyTwoBlades]

The abrasive type is only one of many variables that impact the cut speed, wear rate, and finish produced, but in general silicon carbide will cut a little faster and leave a toothier edge, but break down faster.

 

[Obsessed with Edges]

My question about AlOx vs SiC is more about stones than belts, but does anyone know whether either abrasive will reliably cut CPM M4 steel?

I recently got a Spyderco PM2 in CPM M4, and I'm curious whether my Norton Crystolon (silicon carbide) and/or Norton India (aluminum oxide) combination stones will cut it.

(Also interested whether either of these abrasives will work with CPM CruWear and/or Carpenter Maxamet steel, since I also have Spyderco PM2s in both of those steels, as well.)

TIA for any help...

SiC has been known to cut wear-resistant steels pretty easily at coarser grits, which means it can hog off metal for reprofiling jobs pretty easily and quickly. In essence, the large grit would simply be scooping out the carbides along with the matrix steel, so the hardness of the carbides themselves wouldn't be much of an obstacle. The Norton Crystolon has been recommended for such uses by experienced sharpeners here on the forum. But at finishing stages, where vanadium carbides in the steel become closer in size to the finer grits used for finishing, the carbides will be harder and will not be refined as easily by the less-hard SiC grit. Refinement is where you want the abrasive to cleanly, efficiently cut and shape the carbides themselves for the keenest results. And with vanadium carbides, either diamond or CBN are highly favored for that.

And aluminum oxide will be less hard than SiC grit. Again, at very coarse grit sizes, it may do OK for scooping out the carbides+matrix steel for very coarse shaping of the blade. But AlOx will really struggle against the much harder vanadium carbides at finer grits (400+). And aluminum oxide will also wear significantly, if it's used frequently or heavily on vanadium carbide-heavy steels. And the more it wears, the more it'll struggle to cut much of anything. A stone like the Norton India would glaze quickly in such uses, meaning the harder carbides in the steel would essentially polish the grit in the stone and leaving it almost useless on any steel, unless or until it gets resurfaced.

Knoop hardness:
Diamond = 7000 Knoop (hardest of all)
CBN (Cubic Boron Nitride) = ~ 4500 Knoop
Vanadium carbide = ~ 2800 Knoop
Silicon carbide (SiC) = ~ 2600 Knoop
Aluminum oxide (AlOx / Al203 / 'sapphire' etc.) = ~ 2100 Knoop

 

[Blade Lab]

You CAN sharpen wear-resistant blades with AlOx or SIC, contrary to what some may claim, but testing has shown that you sacrifice some edge retention when used against steels with significant vanadium carbide volume. M4 is 4% Vanadium, but I don't know how much of that forms Vanadium carbide. The best bet would be to stick with diamond or CBN.

 

[Cementite]

Thanks for the replies, guys. I appreciate your help.

The Maxamet is 6% vanadium, 13% tungsten and 10% cobalt, so I'm guessing it's definitely diamonds for that high-speed steel on steroids, at least in the higher grits.

I found this chart in another thread, so I'll just put it here, as well, for others' future reference:

 

[Blade Lab]

Oh yeah, you absolutely want diamonds or CBN for Maxamet. It has a lot of Vanadium and Tungsten, and it's almost certainly run very hard, too. I think Spyderco runs it at around 67 hrc.