Do you need special equipment to sharpen high carbide steels?

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test18258
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Do you need special equipment to sharpen high carbide steels?

Post by test18258 »

I recently saw a video talking about sharpening really high carbide steels on alumina based stones, and they suggested that since alumina is softer than tungsten carbide or molybdenum carbide (not sure which) that sharpening a knife with a high amount of carbides can result in the tearing out of carbides and therefore a weaker edge.

Do I need to use stick to diamond stones for something like cpm 20cv? Does using a alumina based stone like the spyderco stones make the knife weaker?
Jason B.
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Re: Do you need special equipment to sharpen high carbide steels?

Post by Jason B. »

Short answer, Yes you will need diamond plates for that steel.

The alloy element most problematic is Vanadium. It's harder than all but diamond and CBN so using an Aluminum Oxide or Silicon Carbide stone will only kinda work. A lot of factors can play into it but as a general rule any steel with 4% or greater Vanadium will be best sharpened by an abrasive that can actually handle it.
test18258
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Re: Do you need special equipment to sharpen high carbide steels?

Post by test18258 »

Do you have a grit level of diamond stone that you would reccomend going to before it stops being helpful anymore?
and can you do finish work on a non diamond stone?
As in do all the main grinding on a diamond stone but finish with a ceramic like the spyderco ultra fine?

Also is a strop with green compound on it still useful for a steel like that? Or would I possibly need a different stropping compound?
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Re: Do you need special equipment to sharpen high carbide steels?

Post by ken123 »

Depends on what you mean by 'special' :)

Not all waterstones are created equally. I have found the Nubatama Platinum stones to handle a much wider range of steels than other stones - available from 320 to 3000 grit. A surprising range of steels, even a few beyond 4% and steels with high chromium carbide content like zdp-189. So for most sharpening stones, Jason's comments are valid. These are exceptional.

So for abrasion resistant steels, abrasives harder than the carbides [on the Mohs hardness scale] in the steel will allow you to cut THROUGH the carbides allowing further refinement rather than abrasives that erode around the carbides until they lack support and fall out. Mostly this includes various forms of diamond and CBN (cubic boron nitride).

So in terms of equipment you have these options:
1) Better stones
2) Putting CBN or diamond [only water soluble!!] ON the stones in the slurry. For synthetic stones, match the grits to the stones, so for a 1k stone =16 microns, 2k-8 microns, 4k-4 microns, etc
3) Diamond plates These are available from 46 grit to 3000 grit
4) Diamond films available in a wide variety of grits, but these are flimsy and easily damaged.
5) Strops with diamond and cbn compounds on it - These are more robust than films and renewable.

So the heavy lifting is done at the lower grits. You can switch to stones (including Spyderco UF) past the solutions mentioned above or transition to CBN or diamond strops at this point as well.

Green compounds are highly variable, not as hard and far less precise than my CBN and diamond preparations (other brands may vary and be less optimal).

---
Ken
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Re: Do you need special equipment to sharpen high carbide steels?

Post by Jason B. »

test18258 wrote: Thu Nov 02, 2017 9:18 pm Do you have a grit level of diamond stone that you would reccomend going to before it stops being helpful anymore?
and can you do finish work on a non diamond stone?
As in do all the main grinding on a diamond stone but finish with a ceramic like the spyderco ultra fine?

Also is a strop with green compound on it still useful for a steel like that? Or would I possibly need a different stropping compound?
Because these steels have a lot of wear resistance they tend to do best with a very Coarse edge that is followed by a quick polish.

When it comes to sharpening it's actually the fine grits that will have the most issue. Coarse grits of nearly any abrasive will grind through tough alloy steels because the abrasive size is larger than the carbides in the steel so they are simply scooped out as bulk steel is removed. As you move finer in the grit scale the carbide and abrasive size starts to equal out and this is when the real issue of abrasive hardness occurs.

So, at a Coarse level the abrasive type is less important that it is at the fine level.
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Re: Do you need special equipment to sharpen high carbide steels?

Post by Georgek »

One of my favorite edges is the one i get from 20cv on the nubatama ume 2k, dopped with 1 drop of 1micron diamond solution.
Then strop with 1 micron loaded balsa.

The edge just lasts forever (> 6months in a home environment)
test18258
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Re: Do you need special equipment to sharpen high carbide steels?

Post by test18258 »

Jason B. wrote: Fri Nov 03, 2017 6:17 am

Because these steels have a lot of wear resistance they tend to do best with a very Coarse edge that is followed by a quick polish.

When it comes to sharpening it's actually the fine grits that will have the most issue. Coarse grits of nearly any abrasive will grind through tough alloy steels because the abrasive size is larger than the carbides in the steel so they are simply scooped out as bulk steel is removed. As you move finer in the grit scale the carbide and abrasive size starts to equal out and this is when the real issue of abrasive hardness occurs.

So, at a Coarse level the abrasive type is less important that it is at the fine level.
Do most steels have a similar size to the carbides? And if they do what grit would I be able to go to before I have to start using more specialized stones? As of right now The highest grit Diamond stone that I have is a DMT 600.
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Re: Do you need special equipment to sharpen high carbide steels?

Post by Radar53 »

Hi There test. My understanding is that different carbides are different sizes.
Cheers Grant

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test18258
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Re: Do you need special equipment to sharpen high carbide steels?

Post by test18258 »

OK What would be a good grit to go to stop at before I run into the carbide removal issue? If I dont have high grit cbn or diamond stuff?
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Re: Do you need special equipment to sharpen high carbide steels?

Post by Bensbites »

test18258 wrote: Fri Nov 03, 2017 6:06 pm
Jason B. wrote: Fri Nov 03, 2017 6:17 am

Because these steels have a lot of wear resistance they tend to do best with a very Coarse edge that is followed by a quick polish.

When it comes to sharpening it's actually the fine grits that will have the most issue. Coarse grits of nearly any abrasive will grind through tough alloy steels because the abrasive size is larger than the carbides in the steel so they are simply scooped out as bulk steel is removed. As you move finer in the grit scale the carbide and abrasive size starts to equal out and this is when the real issue of abrasive hardness occurs.

So, at a Coarse level the abrasive type is less important that it is at the fine level.
Do most steels have a similar size to the carbides? And if they do what grit would I be able to go to before I have to start using more specialized stones? As of right now The highest grit Diamond stone that I have is a DMT 600.
My understanding from reaearch on forging and heat treating is that carbide size is dependent on the skill of the person forging/heat treating. Too much heat and you have large carbides.
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Re: Do you need special equipment to sharpen high carbide steels?

Post by ken123 »

Jason could you please clarify the seeming contradiction between your first and second post? MY experience agrees with the first post, where especially at lower grits, the use of CBN and diamond is most helpful and at higher grits as well.

The issue of carbide fallout is something that occurs when the matrix surrounding the carbides is abraded away by softer abrasives as you see with most natural stones and even synthetic stones based on silicon carbide and aluminum oxide. There are however various forms of SIC and Alox with slightly different properties as I referenced earlier. These steel carbides - particularly Vanadium and Niobium, but also tungsten, etc resist abrasion at all grits - that's why they are there. You can see that even at coarser grits, the doping of the stone slurry with e.g. CBN at say 80 microns will enhance the effectiveness of a coarser stone as well against an abrasion resistant steel. This becomes even more obvious as you start going into even higher vanadium content steels like s90v and k390 and Rex 121 which are in the 9% + range. Even more extreme are ceramic knives which REQUIRE diamond to sharpen at any grit.

---
Ken
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Re: Do you need special equipment to sharpen high carbide steels?

Post by samuraistuart »

Carbide size isn't so straightforward. Off the top of my head, without actually researching this further, the size will generally go (from small to large), Niobium then Tungsten/vanadium, then silicon, then moly, then chromium. There are primary carbides that are present in the steel when it is smelted (like vanadium carbide VC, Tunsten carbide WC, SiC, and then a couple different Chromium carbides we use the short term K1, and K2, but they are Cr23C6 and Cr7C3 respectively), and then you also will have tempering carbides that form upon tempering (very very very small carbides). Primary carbides can be big, like in D2, which has a lot of Chromium carbides, and can be 30-50 microns in size. Compare that to AEBL, also has chromium carbides, which are only a micron or few in size. Carbon content will dictate a lot of carbide size, as evidenced by D2 vs AEBL. More carbon will allow more/larger carbides, whereas a lower carbon content will allow fewer/smaller carbides. Chromium carbides (primary) tend to be large, but there is also the issue of carbide networking, where the carbides will clump together to form even larger carbides. This usually occurs when annealing is done without care. Vanadium carbides, as well as Tungsten, tend to be much smaller than Chromium carbides (dependent again upon steels carbon content and HT), but can also clump together if a bad anneal was done. The CPM process allows for much smaller primary carbides in the steel. Many makers who like the properties of ingot D2 (large primary Chromium carbides) find that CPM D2 behaves much differently because they are much smaller due to the CPM process. Those smaller carbides change the characteristics of ingot D2, and the smiths who like D2, don't really care for CPM D2, for that reason. Tempering carbides are generally very very small, but for the most part when we talk carbide size, we are discussing primary carbides. Many forget that annealed steel has more primary carbides in it than steel that has been heat treated. The higher the heat you use, the more carbides actually dissolve. When you use too much heat, then even vanadium carbides will dissolve, and this causes excessive aus grain growth, because the carbides are no longer there to pin the grain boundaries, allowing them (the aus grain) to grow. The higher the heat, the more carbides are dissolved. When cooling happens, the carbides then will reform upon cooling. If the cooling/anneal is done too slowly, the carbides tend to congregate into networks, which sometimes we can see as carbide banding. When this occurs, it's back to a normalizing heat to re-dissolve those carbide networks, break them up, and then on to a better anneal on the next go around to make sure they are dispersed evenly.
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Re: Do you need special equipment to sharpen high carbide steels?

Post by Jason B. »

ken123 wrote: Mon Nov 06, 2017 3:49 am Jason could you please clarify the seeming contradiction between your first and second post? MY experience agrees with the first post, where especially at lower grits, the use of CBN and diamond is most helpful and at higher grits as well.

The issue of carbide fallout is something that occurs when the matrix surrounding the carbides is abraded away by softer abrasives as you see with most natural stones and even synthetic stones based on silicon carbide and aluminum oxide. There are however various forms of SIC and Alox with slightly different properties as I referenced earlier. These steel carbides - particularly Vanadium and Niobium, but also tungsten, etc resist abrasion at all grits - that's why they are there. You can see that even at coarser grits, the doping of the stone slurry with e.g. CBN at say 80 microns will enhance the effectiveness of a coarser stone as well against an abrasion resistant steel. This becomes even more obvious as you start going into even higher vanadium content steels like s90v and k390 and Rex 121 which are in the 9% + range. Even more extreme are ceramic knives which REQUIRE diamond to sharpen at any grit.

---
Ken
I don't see a contradiction but I will explain it again.

Large abrasive grains will remove larger filings of steel, larger than the carbides. Therefore diamond or CBN is not necessary at Coarse grits. With extreme alloy content it's advisable to use diamonds because the concentration of carbides is much higher but if all you have is a Norton Alox stone then it is still going to work.

Fine stones are more problematic because the abrasive size and carbide size start to equal out and have greater interaction with one another. And because the carbide is harder than the abrasive the carbide starts winning.
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Re: Do you need special equipment to sharpen high carbide steels?

Post by Chefcallari »

samuraistuart wrote: Mon Nov 06, 2017 1:08 pm Carbide size isn't so straightforward. Off the top of my head, without actually researching this further, the size will generally go (from small to large), Niobium then Tungsten/vanadium, then silicon, then moly, then chromium. There are primary carbides that are present in the steel when it is smelted (like vanadium carbide VC, Tunsten carbide WC, SiC, and then a couple different Chromium carbides we use the short term K1, and K2, but they are Cr23C6 and Cr7C3 respectively), and then you also will have tempering carbides that form upon tempering (very very very small carbides). Primary carbides can be big, like in D2, which has a lot of Chromium carbides, and can be 30-50 microns in size. Compare that to AEBL, also has chromium carbides, which are only a micron or few in size. Carbon content will dictate a lot of carbide size, as evidenced by D2 vs AEBL. More carbon will allow more/larger carbides, whereas a lower carbon content will allow fewer/smaller carbides. Chromium carbides (primary) tend to be large, but there is also the issue of carbide networking, where the carbides will clump together to form even larger carbides. This usually occurs when annealing is done without care. Vanadium carbides, as well as Tungsten, tend to be much smaller than Chromium carbides (dependent again upon steels carbon content and HT), but can also clump together if a bad anneal was done. The CPM process allows for much smaller primary carbides in the steel. Many makers who like the properties of ingot D2 (large primary Chromium carbides) find that CPM D2 behaves much differently because they are much smaller due to the CPM process. Those smaller carbides change the characteristics of ingot D2, and the smiths who like D2, don't really care for CPM D2, for that reason. Tempering carbides are generally very very small, but for the most part when we talk carbide size, we are discussing primary carbides. Many forget that annealed steel has more primary carbides in it than steel that has been heat treated. The higher the heat you use, the more carbides actually dissolve. When you use too much heat, then even vanadium carbides will dissolve, and this causes excessive aus grain growth, because the carbides are no longer there to pin the grain boundaries, allowing them (the aus grain) to grow. The higher the heat, the more carbides are dissolved. When cooling happens, the carbides then will reform upon cooling. If the cooling/anneal is done too slowly, the carbides tend to congregate into networks, which sometimes we can see as carbide banding. When this occurs, it's back to a normalizing heat to re-dissolve those carbide networks, break them up, and then on to a better anneal on the next go around to make sure they are dispersed evenly.
Hahahahahaha!...
"Well just off the top of my head"... Lol jesus christ man your like a fucking encyclopedia!
Sorry... That shit just made me laugh.
I was expecting this real simple answer... Then BOOM!
test18258
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Re: Do you need special equipment to sharpen high carbide steels?

Post by test18258 »

So in terms of grit size for japanese waterstones in general what grit level would be relatively safe from carbide tear out? Im assuming that carbides being 45-50 is not the norm.
Is a 1200 grit waterstone going to have issues with carbides falling out of the knives?
And if I go diamond like with DMT would it be better to stop at 600 or 1200? Im thinking of getting one or both diamond sharpeners but I dont know if 1200 would result in a weaker edge/be redundant.
test18258
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Re: Do you need special equipment to sharpen high carbide steels?

Post by test18258 »

Actually thats the video that inspired me to ask this question.
Since I dont have any high grit diamond stones I was wondering how much of an issue the carbide tear out is. He only finished the knife on a spyderco ultra fine.
Thats also why im trying to figure out if its worth getting some higher grit diamond stones (600 and 1200) Because I will probably be getting more knives in the future that have these super carbide laden steels.
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Re: Do you need special equipment to sharpen high carbide steels?

Post by pjwoolw »

The tear out stuff is something I believe is overstated and overthought. I'm sure there is truth to it but all the hullabaloo gives me a headache. So I ignore it and sharpen the darn knife.

That being said having the 600 and 1200 diamond plate, presuming Atoma, couldn't hurt. Very versatile items. If one were to concentrate on the end result an investment in high grade CBN and diamond compounds / emulsions / strops would also be great tools. Both ends of the spectrum in other words.
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Re: Do you need special equipment to sharpen high carbide steels?

Post by Radar53 »

@Ken123. I found that video really interesting from a couple of perspectives.

Firstly, I quite like refined edges. I would probably finish my good euros (58 HRC) at 5 or 8k and I don't notice a lack of "bite" on say soft tomatoes and I don't notice a quick loss of that initial sharpness. I have put that down to the fact that I'm pretty careful with my toys and being a home cook, I don't do a lot of prepping or cutting work. So its interesting to see a more highly refined edge being stress tested.

Of late I have been sharpening my lesser knives freehand and because I'm still very much in the learning phase here, I have been stopping at my Kohetsu 2k. And I have to say that's a pretty cool edge. It's different for sure, but still performs very well in my "sheltered" environment. I'll definitely investigate & play more with less refined edges.

Secondly, the carbide discussion, especially regarding pm steels, intrigues me. I have three R2 knives, an HAP40 and soon a ZDP189. Having done a fair amount of reading on the subject, I'm leaning towards the view that carbide tearout can be a factor. I sharpen these knives on the EdgePro using a tight progression of 3M diamond films & finish at 10 or 15k. These edges perform & last really well & the films work on the EP for a couple of good reasons. But the PSA films come as a 6 X 3" sheet & could be stuck onto float glass and used freehand. (My skills would have to improve significantly before I would commit to sharpening these knives freehand though haha.)

Again it works for me because of my situation, in that I don't need to sharpen my knives that often & I only use the films on my pm steels. The film route could get to be a bit expensive I think if doing a lot of sharpening.

So Ken, thanks for sharing.
Cheers Grant

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test18258
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Re: Do you need special equipment to sharpen high carbide steels?

Post by test18258 »

pjwoolw wrote: Tue Nov 07, 2017 8:42 pm The tear out stuff is something I believe is overstated and overthought. I'm sure there is truth to it but all the hullabaloo gives me a headache. So I ignore it and sharpen the darn knife.

That being said having the 600 and 1200 diamond plate, presuming Atoma, couldn't hurt. Very versatile items. If one were to concentrate on the end result an investment in high grade CBN and diamond compounds / emulsions / strops would also be great tools. Both ends of the spectrum in other words.
I did notice from the video that he said it seems like its not a big deal, though that was with just finishing on the spyderco ultra fine, In my case its all spydercos and aluminum oxide waterstones beyond the DMT stones for reprofileing. His closing comments of if your just finishing with ceramic its fine is what made me want to know how much of a problem carbide tear out can be in terms of weakening the final edge.

If I was to get some a 600 and 1200 grit diamond stone they would probably be DMT, unless I can find a compelling reason why atoma are enough of an improvement that they are worth spending 60% more each.

Would the 600 or 1200 atoma work as a lapping plate? or would it be too slow? I do have an issue with my current DMT stones sticking really badly when trying to flatten a stone.
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