Is this carbide tear out, or something else?

C

Clint_Beastwood

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Jul 11, 2022
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I needed a way to keep myself busy during a really long conference call so I grabbed my KME, a new in box QSP Penguin in D2, and my new USB microscope. I didn't spend the time to clean up all the prior scratches because I was really just fixing the edge geometry from the wonky factory grind, not going for a mirror. I started at 100 grit and progressed up through to 15k diamond on a strop, and after the 15k diamond, it looks like there are "holes" all along my edge. What might cause that? Is that carbide tear-out? Here's a link to the images
https://imgur.com/cSC0H4D
 
Testing has demonstrated that carbide tearout is essentially myth, and rather carbides are more likely to crush or shatter. What you see there may be micro-chipping. D2 has notoriously large chromium carbides and if you were using diamond stones, those have pretty high grit protrusion that may have put sufficient side loads on the edge to chip the carbides. But this is just a guess on my part.
 
FortyTwoBlades said:
Testing has demonstrated that carbide tearout is essentially myth, and rather carbides are more likely to crush or shatter. What you see there may be micro-chipping. D2 has notoriously large chromium carbides and if you were using diamond stones, those have pretty high grit protrusion that may have put sufficient side loads on the edge to chip the carbides. But this is just a guess on my part.
Click to expand...

Thanks. It's weird that it looked OK up until I got to the 15k diamond, then there are just... holes all over the edge.
If I am doing D2, should I then be using natural stones instead of diamond ones? Or a combination like diamond for setting the bevel, and then clean/polish using the KME natural arkansas or something?
 
Clint_Beastwood said:
Thanks. It's weird that it looked OK up until I got to the 15k diamond, then there are just... holes all over the edge.
If I am doing D2, should I then be using natural stones instead of diamond ones? Or a combination like diamond for setting the bevel, and then clean/polish using the KME natural arkansas or something?
Click to expand...
Something that's been observed with diamond plates is that above a certain point they end up actually producing a coarser finish due to the change in their size, distribution, and protrusion. Science of Sharp has a blog post about it. I'd switch to fine synthetic bonded abrasives like water stones or India stones to finish and you may find that it fixes the problem.
 
D2 doesn't finish as well on natural or AlOx stones as it does on something like a hardwood strop with diamond compound (3 micron & finer). That's what I've found works the best with D2, for polishing it. I tend to favor going all-diamond in the sequence with it, transitioning to a 3-micron diamond-pasted strop of hardwood, after honing up through 1200 at least (like DMT's EF). At coarser grit, when grinding bevels & such, other coarse stones like AlOx can work OK (and SiC is great for this, with D2 - it eats it for breakfast when hogging off metal). But when looking for mirror polish on D2, a wood strop with diamond compound makes it much easier and keeps the apex much crisper, better able to shape & thin D2's great big carbides at/near the edge. D2 has been known to reveal what's called an 'orange peel' finish when lesser abrasives struggle to polish those big carbides. The finish tends to come out sort of lumpy and/or pitted in appearance (microscopically), when that happens.

And whether there's tearout or chipping going on, I tend to believe that's more a quality issue with the steel itself. D2 has also been known to be very tricky in heat-treating it correctly. At one time, maybe 10 or more years ago, I remember seeing a lot of mention of D2 blades either chipping or breaking, as the 'sweet spot' for heat-treating D2 hadn't been nailed down by many trying to make blades with it.
 
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Ok, I followed the exact same process with a civivi in 14c28n and it looks a ton cleaner, I think that first knife, the QSP Penguin, might not be the best heat treated steel.
NgtkoBH.jpg
 
It's not even so much about the heat treatment of the D2 (although, yes, that's a factor) but rather that D2 "just do be like that". It's notoriously temperamental when it comes to how it's sharpened or polished, and it's mostly because of it's big honkin' chromium carbides.
 
You would need higher levels of magnification to determine what is going on with the carbides is a blade steel (*example: image below - carbide shadows downstream edge trailing).
D2 can have relatively large clumps of carbides, where as CPM D2 carbide distribution with be greater (minimal clumping).
14C28N would be less prone than D2.

*carbide shadows downstream edge trailing
Steel Carbides.jpg

*image from ScienceOfSharp
 
C Clint_Beastwood i love looking at these photos(so much so I’ll probably be getting a USB microscope too). Could you please put a reference park, like a sharpie dot where the cutting edge meets the main bevel, sometimes it seems like we are not looking at the exact same section.
 
As this, as you stated, was a new in box edge, might have just been over heated/cooked at the factory when initially ground - seems to happen a lot on these mass produced blades.
I would stick with the lower grits and regrind a new working apex until the edge degradation is minimal, before working through the finer grades.
It might take a few sharpens until you get passed the heat damaged edge, then I think all will be OK.
Have found that some of the Chinese D2 is hardened quite high and gets very chippy on the factory ground edge until a new edge on fresh steal is achieved.
 
Another vote for the burnt edge hypothesis. A badly burned edge can literally crumble on the stone.
 
Aside from the apparent 'holes' seen along the polished bevels, if the finished edge doesn't exhibit any signs of chipping at the apex after some use, I'd not worry too much about the appearance under the microscope. As mentioned, D2 is kind of known for weird finish issues related to the big chromium carbides. That in itself may not be a functional problem in use, as many decent blades in D2 also exhibit those finish quirks.

But if the edge does show chipping issues in use, then it's back to the possibility of a heat treat issue or a burned edge as mentioned above.
 
I own 5 D2 knives. With each, I call it a day after finishing on a 1000 grit (JIS) whetstone. Finer grits tend to do nothing with respect to knife performance. That's my experience.
 
I personally, have never had good luck taking D2 below 20dps. Below that and I get the edge shown. I have a few inexpensive work knives in D2 and found that regardless of brand, below the 20 mark they are going to be rough. 20-25 do’s and they are fine. I always attributed it to the carbide tearout deal, but regardless, I sharpen to 20 and call it good.
 
Thanks for all the replies!

I pulled another couple NIB knives:
- QSP Penguin D2 satin finish
- QSP Penguin D2 Black Stonewash finish
- pair of civivi elementums in D2

Both Penguins did the same crumbling/chipping thing, so I used the 50 grit KME Beast to grind away quite a bit of steel until it "felt" different, then went through the progression. It looks way better, but still slightly crumble-y (see pic). Probably need to get through more steel but it is improving - the Civivis were totally fine, no issues. I checked my CRKT D2 provoke compact and it's pretty clean too, so I think its just the QSP d2 that I'm having a lot of trouble with.

Side note, the 50 grit KME beast diamonds seem a lot... taller? It's probably because the stones pretty new and needs to wear in, but it adds scratches at the inner edge of the bevel that take a TON of removal to clean up, kinda mitigating the point of the 50 grit stone. Do I just need to take that 50 grit stone and grind through a block of steel or something to wear it in or something? Caliper says its the same height so it's not the angle changing.

cdOm9XO.jpg
 
As others have said, I think it's just chipping along the edge. The chips are way larger than carbides, as Spey mentioned.

The largest carbides in D2 are likely to be 50 microns. A 100-grit stone leaves 150-micron grooves. As you can see, your chips are much larger than the 100-grit grooves. So what you're seeing is not carbide tear out.

Cool photos. Makes it a lot easier to see what's going on.
 
For reference, I did the exact same progression and time spent per stone on the civivis, here's a pic of a civivi after the same progression. Looks like there's maybe still a tiny burr I can't feel or seem to strop away.


KYbNOrB.jpg
 
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