Optimum steel refinement

[dkb45]

Learning about carbides and steel matrices I have started learning that not every steel is made equal. Some steels work best with a mirror polish, others should be nice and toothy. I did a search here and didn't get anything, so I figured I would ask for optimum refinement for various steels.

Only few steels I know from my own testing are 154cm, CPM-154, VG-10, and AUS-8 all work well with a mirror polish. I have also heard that S30V is best toothy (all steels with high vanadium carbides too), but Elmax has a pretty high carbide content and it has worked wonderfully with a high polish for me.

The steels I am specifically concerned about are Elmax, ZDP-189, S35VN, S110V, and D2. If you know a specific steel, don't hesitate to post it, though. I want this to be a resource for all aspiring sharpeners (maybe a comprehensive list can be made into a sticky at some point).

 

[mknife]

Damasteel RWL and Bohler N690c very fine for mirror polish.

 

[Obsessed with Edges]

My belief is that any steel with fine & uniform grain, and good heat-treat, can take most any edge finish desired. Some steels with large carbides, like D2 (non-CPM version), can still be worked & finessed to a high polish, if one is willing to take the time to get it there (I like 1000-2000+ grit finish on D2). Same for steels with very hard carbides (vanadium), like S30V, etc. With high-carbide content, choosing the right abrasives makes all the difference, if wanting to go finer in finish. Polishing with abrasives that are barely hard enough, or less hard, is counter-productive, because the abrasives won't abrade or shape the carbides as cleanly; the apex will never be quite as crisp as it could be.

Regarding S30V, it's MUCH, MUCH easier to put a nice, toothy edge on it, and the steel performs well with such an edge. Something like a DMT 'Fine' hone can set it up very quickly, so I can see some justification for preferring to sharpen it as such.

I have some 'cheap' stainless kitchen knives, and one or two other folders, with steel that simply won't hold high-grit edges at all, above about 400 grit. Very soft & coarse-grained; really fine edges just seem to get immediately scrubbed away in use, and there's no reward in taking extra time to refine the edges on them. For these knives, a coarser & toothy edge is about the only thing that lasts and works relatively well. Something like 220-320 grit, or very, very light passes with a coarse diamond, is what I usually use on these knives.

The size & uniformity of grain, in any steel, is hugely impacted by the quality of heat-treat. So, when you really get down to it, the maker's skill with hardening & tempering the steel is more important than anything else. To clarify the point about heat-treat, one of my 'poor' knives mentioned above, that won't hold a polished edge, is in 1095 steel. I was tinkering with it yesterday, using a relatively coarse diamond rod pocket sharpener to put some 'bite' in the edge, using minimal passes and feather-light pressure; that's about the only thing that works for it, or doing the same with 220-grit sandpaper works similarly. On the other end of the spectrum, my 'best' knife of all is another 1095-bladed folder from Schrade USA. I've yet to find any edge finish that doesn't stay wicked-sharp on this one; my sharpening & stropping habits leave a near-mirror on the thinly-convexed bevels, and I couldn't be happier with that one.


David

 

[dkb45]

I have done all of my knives with a higher polish (as best as I can) finish and they all seem to perform just fine. I just figured that every steel reacts differently, and since I don't use diamonds there are issues with carbides.

 

[HeavyHanded]

From my POV it comes down to the chore I have in mind for the tool, and then it depends on the steel if its a good fit. IMHO most of the higher RC steels that are not high carbide content will not hold a toothy edge and in some cases won't even take one well. Some of the lower RC steels that can take and hold a toothy edge very well will also hold a fine edge reasonably well though will need a lot more routine maintenance.

And that's not bringing up the differences in HT among mfgs working the same steel...

 

[Sadden]

David hit the nail on the head.

 

[Obsessed with Edges]

I have done all of my knives with a higher polish (as best as I can) finish and they all seem to perform just fine. I just figured that every steel reacts differently, and since I don't use diamonds there are issues with carbides.

I used to scratch my head over S30V, because I was trying to polish edges on it with wet/dry sandpaper. At coarser grits up to about ~600, the edges were pretty decent, but they'd quickly round off and lose their bite at higher finish (above ~800 grit or so). My eyes really popped open when I started using a progression of Fine > EF diamond hones, followed by stropping on wood with 3µ > 1µ diamond paste. High polish very fast, and edges crisper than I ever thought possible on this steel. The biggest jump in noticeable sharpness (at high polish) came with the 3µ Dia-Paste stropping. The 1µ paste refines it a bit beyond, but the difference made by the 3µ was eye-popping. That hammered home the importance of using abrasives suited to the hardness and size of the carbides involved (2-4µ average, for CPM-S30V's vanadium carbides).

( I have a Kershaw Leek in S30V, which was the first to get the diamond progression treatment as above. It's thin-slicing profile mimics that of my 'best' edge, on a Schrade USA Old Timer in 1095. I'd never thought I'd see the day when I could say both cut equally well at high polish. But they do. )


David

 

[james terrio]

What David said :thumbup:

...best toothy (all steels with high vanadium carbides too)...

Nope! One of the lovely things about vanadium carbides is that they tend to be quite small, and V in even very small quantities helps prevent grain growth overall. 3V and Elmax (both have about 3% V, which is fairly high) do very well with a crisp highly-polished edge.

Sorry to nitpick, but that's just one of the problems with trying to categorize steels in this fashion... the fact that commonality/correlation doesn't prove causality. One steel (which just happens to have a lot of V) develops a reputation (rightly or not) for not working well with a fine edge finish, and people automatically assume that all Vanadium-bearing steels can only work well with toothy edges. That's simply not the case... no matter how many times it's repeated on the internet

 

[dkb45]

So... How do you optimally finish the steels I listed? S30V loses the razor edge too quickly for it to he worthwhile, but the steels I listed keep the razor edge a lot longer.

 

[BluntCut MetalWorks]

S30V when properly sharpened, it capable of holding a razor edge in similar retention proportion as other steels you mentioned. For an instance, my s30v blade with 22-24* inclusive back bevel and 32-36* inclusive micro bevel will keep its shaving edge after whittled pine & a bit of dry oak. I used whatever abrasives (alox, sic, diamond) up to 1K grit set the back bevel. Use dmt ee to set micro bevel. Strop with 0.25um diamond paste on a paper towel wrap over a new bastard file.

Understanding carbide & grain size would help in figuring out what cutting edge angle is sustainable/stable, especially for high alloy steels. Of course when at certain level of refinement, one need to use correct abrasive type & size & sharpness. Sharpening stroke direction & backing & pressure & velocity also determine the outcome whether a truly clean strong razor edge or weak/burr/wire/rounded edge.

I've tendency to complicated thing, don't I:foot:

So... How do you optimally finish the steels I listed? S30V loses the razor edge too quickly for it to he worthwhile, but the steels I listed keep the razor edge a lot longer.

 

[Jason B.]

The magic number is 4% on the vanadium. At or higher and the edge will do best toothy and below that it can usually be taken a bit higher in refinement.

 

[dkb45]

So Elmax is perfectly fine polished, along with S35VN. M390, S30V, and S110V are best left toothy. How should I do ZDP? Looking at the composition it is mostly carbon and chromium in the steel matrix, and doesn't match up with any other steels (other than Cowry X). The additional elements should give it a small grain size, but the absurd levels of carbon and chromium might screw that all up.

As for S30V keeping its razor edge, I gotta call bull on that. I had S30V with a well refined edge lose the hair popping edge in a few minutes cutting cardboard (thin stuff like a flat rate box), while my VG-10 knife cut the same and while it was dulled it was still close to razor sharp. I know S30V keeps a working edge damn near forever, but I haven't heard a single person say that it keeps a razor edge worth a damn.

 

[HeavyHanded]

...

As for S30V keeping its razor edge, I gotta call bull on that. I had S30V with a well refined edge lose the hair popping edge in a few minutes cutting cardboard (thin stuff like a flat rate box), while my VG-10 knife cut the same and while it was dulled it was still close to razor sharp. I know S30V keeps a working edge damn near forever, but I haven't heard a single person say that it keeps a razor edge worth a damn.

This was my experience as well, with s30v Bos HT. It took a face-shaving edge fine, but lost it fairly quickly. Nothing alarming, but it didn't even seem to hold as long as some of my carbon steel knives. At a lower finish it didn't even seem to dull with normal use, lost a small amount of its initial catchiness but just kept cutting after that.

This was also my experience with D2 in my BK24. It would take a fine edge and hold OK, not really any better than most common steels but when left at a medium finish it just keeps going. I suspect a lot of this might come down to the HT, it isn't my imagination.

 

[BluntCut MetalWorks]

...
As for S30V keeping its razor edge, I gotta call bull on that. I had S30V with a well refined edge lose the hair popping edge in a few minutes cutting cardboard (thin stuff like a flat rate box), while my VG-10 knife cut the same and while it was dulled it was still close to razor sharp. I know S30V keeps a working edge damn near forever, but I haven't heard a single person say that it keeps a razor edge worth a damn.

How many cutting linear feet of cardboard are we talking about? S30V will loose less than a handful of partially-shaped carbides here & there on the apex but the edge remain razor sharp. Would clean phonebook slicing be consider sharp enough as starting point? It would be easy for me to make a little video to show bull or fact.

edit: If I make this video, s90v & k390 knives will be in there too.

 

[Twindog]

The S30V knives I use on a regular basis -- Manix original, Rukus, Sebenza, Skirmish -- hold a sharp edge quite well. I sharpen them with diamonds up through 800-grit and finish with 1600-grit ceramic stones, followed by stropping on green compound.

What would make S30V steel incapable of holding a sharp edge? The vanadium carbides are small and hard. The steel's grain structure is fine. The vanadium helps defend the steel's basic matrix. I'd guess that most reports of S30V losing a sharp edge quickly have more to do with incomplete burr removal.

 

[Obsessed with Edges]

The S30V knives I use on a regular basis -- Manix original, Rukus, Sebenza, Skirmish -- hold a sharp edge quite well. I sharpen them with diamonds up through 800-grit and finish with 1600-grit ceramic stones, followed by stropping on green compound.

What would make S30V steel incapable of holding a sharp edge? The vanadium carbides are small and hard. The steel's grain structure is fine. The vanadium helps defend the steel's basic matrix. I'd guess that most reports of S30V losing a sharp edge quickly have more to do with incomplete burr removal.

I seem to recall reading somewhere, that some makers might've had trouble earlier on with heat treat issues. I'd actually forgotten about it 'til now, but I have one knife (maybe two, come to think of it) in S30V, that seem more prone to losing their razor-sharpness after cutting into cardboard or even through a stack of paper (this is how I first noticed it, with an S30V ZT-0350). In at least some respect, that could be burr-related. The characteristic thing I noticed most was, the 'razor' edge that quickly came off was replaced with that 'toothy' character so often described in relation to this steel. Not necessarily a loss of functional sharpness, but a change in the working character of the edge, to what I've seen so often described as a good 'utility' edge, that's very durable in hard use. As compared to other steels with little/no carbides and very fine grain, which can still retain razor sharpness after shedding burrs, this steel seemed very different in the coarser/toothy edge left behind.

The S30V Leek I mentioned earlier, is the one that really seemed different to me after finising the edge on it. I haven't noticed the same tendency to lose the razor edge quickly, in that blade. That's meaningful to me, because it's also got the thinnest grind of any of my S30V blades; the fact that it seems to hold the fine edge very well is impressive to me. I've also noticed this somewhat in an S30V Sebenza, though I haven't yet polished that one as high as the Leek's finish.


David

 

[HeavyHanded]

I seem to recall reading somewhere, that some makers might've had trouble earlier on with heat treat issues. I'd actually forgotten about it 'til now, but I have one knife (maybe two, come to think of it) in S30V, that seem more prone to losing their razor-sharpness after cutting into cardboard or even through a stack of paper (this is how I first noticed it). In at least some respect, that could be burr-related. The characteristic thing I noticed most was, the 'razor' edge that quickly came off was replaced with that 'toothy' character so often described in relation to this steel. Not necessarily a loss of functional sharpness, but a change in the working character of the edge, to what I've seen so often described as a good 'utility' edge, that's very durable in hard use. As compared to other steels with little/no carbides and very fine grain, which can still retain razor sharpness after shedding burrs, this steel seemed very different in the coarser/toothy edge left behind.


David

This describes my experience exactly. Its not as if the steel won't take a fine edge and hold it for a bit, its that it doesn't do it anywhere near as well as other steels - I'd swear all my Sandvik knives among others, can hold a fine edge longer than my s30v. And the functional edge that gets left behind after the initial fizz wears off doesn't cut with as much authority as the edge I could make if I intentionally stop at a less refined finish from the get-go. As always, the devil's in the details, and a tool with a different HT might perform a bit differently. Quick example, the Aus8 from Al Mar is so different from what I get from Cold Steel you'd swear they weren't the same material.

 

[Jason B.]

Polished can be thought of in many ways, I use waterstones so for me a "polish" starts to occur around 2k. A stropped polish would be comparable to a 10k+ waterstone, which I don't often use and almost never use on a folding knife.

S30V is a tough subject because every knife maker has a noticeable difference in the heat treatment. I sharpen enough S30V to see that difference and have even noticed changes over the years to the heat treatment from popular knife makers. It's for the better too, S30V today is harder and has a tighter grain than in years past from production companies which makes it tougher, easier to sharpen (less burr, easier to remove, and can handle a little finer of a edge), and really brings it to the level of the "super steel" it was originally claimed to be.

For me I like a coarse or fine diamond finish or if I am using waterstones a 1k with a few passes to deburr on a finer stone. Sharp but toothy seems to do it, which is the case with a lot of steels but obviously so with the S series from crucible.

 

[bpeezer]

As for S30V keeping its razor edge, I gotta call bull on that.

As mentioned repeatedly, it is very difficult to make blanket statements about a steel in general. Keeping the S30V example, my Spyderco PM2 likes a polished edge for a short time like you mentioned but really shines with a coarser edge. My Leatherman Charge TTi somehow does very, very well with a polished edge for quite a long time. It will stop whittling hairs after some use, but it keeps shaving my arm like crazy.

hugely impacted by the quality of heat-treat.

And that's not bringing up the differences in HT among mfgs working the same steel...

I suspect a lot of this might come down to the HT, it isn't my imagination.

S30V is a tough subject because every knife maker has a noticeable difference in the heat treatment.

 

[dkb45]

How many cutting linear feet of cardboard are we talking about? S30V will loose less than a handful of partially-shaped carbides here & there on the apex but the edge remain razor sharp. Would clean phonebook slicing be consider sharp enough as starting point? It would be easy for me to make a little video to show bull or fact.

edit: If I make this video, s90v & k390 knives will be in there too.

I probably only cut like 10-15 feet of cardboard. The knife was still sharp, it just wouldn't cleanly slice receipt paper any more when it was damn near repelling it before I started cutting. The VG-10 was dulled and snagged in a few spots but it was overall sharper. The S30V in question was a Bos HT Buck model. The VG-10 was my Delica. Not good comparison in knives, but the steels still did what they do.

For the record, my S30V from Spyderco and Benchmade have kept a razor edge longer. It really is all in the HT.