Some Super Steels don't seem to hold a fine edge

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Aug 3, 2009
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I have very few blades made of super steels. One in ZDP-189, and one I just got in S30V. In particular the S30V is a Spyderco Yojimbo 2. I opened a few boxes with it and noticed the front part seemed kinda dull; sliding over material. Looked at it in the light and found light reflected back from the edge at the front in about a 1 inch long section.

I microbeveled that section and the rest of the blade, spending much more time on the reflective flat area, using the SharpMaker medium stones. Opened a few more boxes and now had a larger flat reflective area. Ok, 10 more minutes on the SharpMaker and it's very sharp again. I opened *1* box, with tape that was reinforced with string in the tape and looked at the blade: Reflective and flat along the entire length!!! Won't even catch phonebook paper. Barely catches and slices/tears printer paper. Not super dull, but not what I think of as sharp.

I've been trying to decide how long to use the blade in this condition, as everyone seems to say something like: S30V loses it's fine edge quickly, but retains a "working edge" for a long long time. Is a flat reflective edge (very, very narrow reflection) a "working edge"? An edge that will NOT clean slice printer paper?

I did a little informal testing with my ZDP-189 and sliced up some cardboard. Not much; about as much as had dulled the S30V blade. The ZDP blade still shaved roughly and sliced phonebook paper, though not cleanly. My previous experiments with the ZDP blade yielded that it would go through maybe 10 to 20 feet of cardboard before the shaving sharp edge was gone completely.

To be fair, I have not yet reprofiled, or even "erased" the factory edge on either blade with a proper sharpening starting with a coarse stone. Should I regrind the edge (keeping the factory angle) on the S30V blade right away? I was thinking DMT C, then DMT EF and see where that gets me. Or can I expect more of the same: Open 1, 2, or 5 boxes, and the shaving edge is completely gone? I bought this blade to *use* it and use it a lot. I like even my box opening knife to clean slice the paper tape that holds a lot of boxes together. If I have to muscle it at all, I want a sharper blade.

Color me completely unimpressed with my experience so far with S30V and not very impressed with ZDP-189 either, though it's clearly better than S30V. Perhaps my expectations were too high. I was expected at least 2 or 3X the life that I'm used to with steel like 8Cr18Mov. S30V seems worse than 8Cr18Mov.

Thanks for reading a semi-rant; and thanks for any input. :)

Brian.
 
If it were me, only having experience with a s30v Blur, I d take care to sharpen to apex and make sure the wire edge is removed. It sounds to me that you have a flat spot on the edge that needs to be addressed.
I find that my blur had poor edge retention from the factory. I sharpened to about 6000 grit and stropped with green compound on balsa. Now all I do is strop now and then, I cut a lot of cardboard and paper daily and it seems to hold very well now.

BTW what angle is that edge?
 
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Yes, I'd check what cschol suggested. Plus, my blades of S30V steel cuts more like 100' of cardboard before it starts to show me much drag. But I sharpen to only the level of a coarse diamond. DM
 
If neither blade has been re-profiled, and only the factory edge is still present, my first thought is that the underlying geometry of the edge is most of the problem. Especially if they're not even cutting paper well; takes a pretty wide edge to behave like that. The geometry of the edge is what will do the most work, most of the time, with any blade or steel. If it's relatively wide, thinning the edge to 30° inclusive or less can make a big difference.

2nd thought:
Though it's relatively uncommon, the persistent return of the 'flat reflective' area on the edge might be indicative of weakened steel from the factory grinding. Some blades need to have a little more steel removed from the factory edge, to get rid of steel weakened by overheating during factory sharpening.

My preference with S30V is to not take it much finer than about 600 mesh (as in DMT's 'Fine'). S30V does tend to lose a hair-whittling edge very fast, due to relatively large carbides tearing out of the edge during use. The 'working edge' that remains, however, will benefit from the wear-resistance of those same carbides, albeit at not such a fine/thin finish. This is why I don't like to go much past 600 grit, because that finish seems to emulate and/or enhance the naturally coarse & toothy character of the steel. At 30° inclusive or less, edges finished like this (and FULLY apexed, of course) will cut printer paper viciously (or phonebook paper, or cardboard, for that matter).

For a long time, with several S30V blades, and ONE ZDP-189 blade, I also didn't know what to think about these steels. Finally got around to thinning the edge grinds on all of them, and figuring out S30V's positive response to a coarser finish. With those two variables changed to my liking, my perception of the steels has improved considerably. The additional thing to watch, with ZDP, is to avoid going too thin with it. Assuming it's hardened into the 60s RC, as is it's most-hyped attribute, it'll also be more brittle and prone to chipping/cracking/breaking if it's honed too thin. I discovered this the hard way, in snapping the pointy tip off of my ZDP Kershaw Leek, only a few hours after re-bevelling it to a MUCH thinner profile. Slices like a demon now, but after seeing how easily the tip snapped off, I'm afraid to use it for anything substantial anymore. :(


David
 
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Diamonds can cut carbides so you will actually form the edge in them instead of potentially tearing them out with softer abrasives while forming the edge in what's left of the softer steel. Might not be noticeable when the scratch pattern is bigger than the carbides, but when the abrasive is finer than the carbides themselves, it's another story. What angle are you sharpening at? May be too low an angle for the steel to handle. You can try a microbevel in that case. It is possible for the carbides to be wider that the majority of your apexed bevel. Vanadium carbides on average are 2-4 microns(sourced form crucible). All this can get worse if it isn't a PM steel.

ETA: How new are these blades and is this their first sharpening? The edge could have been all show from the factory and put on overstressed steel. This mean you may have to just cut into a stone a couple times to get to good steel and start fresh.
 
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Your experience with S30V mirrors mine. i've gotten rid of all my knives in that steel and it's now a deal breaker for me. Holding a fine edge? I've yet to have a knife in S30V hold ANY edge. Period. I've tried a half dozen knives from various manufacturers with different types of sharpening, all with the same result. Whatever the reason, I just avoid the S30V and use other steels that are far superior IMO. Vg10, CPM M4, CPM 3V, S90V, S110V, CPM 10V, all blow it out of the water based on my usage. YMMV.
 
If it's relatively wide, thinning the edge to 30° inclusive or less can make a big difference.
Hey David, being an Spyderco It doesn't seems probable. All of mine came around 30º out of the box


2nd thought:
Though it's relatively uncommon, the persistent return of the 'flat reflective' area on the edge might be indicative of weakened steel from the factory grinding. Some blades need to have a little more steel removed from the factory edge, to get rid of steel weakened by overheating during factory sharpening.

My preference with S30V is to not take it much finer than about 600 mesh (as in DMT's 'Fine').

David
^THIS!!!
my para2 improved a lot by the 3rd sharpening, the first and second were actually touch ups. So the first real sharpening. So, I can only suspect that the grinding overheated the superficial layer of steel and when it was removed the edge retention improved.
I also agree with the finishing grit, 600 DMT gives you an easily shaving edge but with a LOT!! of bite, really scary sharp.

Mateo
 
As several of you have asked, yes these are the factory angles and the factory sharpened edges. I've only touched up and mircobeveled the edges. Both micros were applied at 20 dps with a SharpMaker. So their grinds are definitely under 20 dps, since the SM makes a micro on them at that setting.

Regarding the reflective edge of the S30V: I keep thinking I've got bad factory metal at the very edge like I hear people here talk about a lot. But I thought that was extremely rare? I guess today or tomorrow I'll regrind the edge with DMT plates and see where it goes from there.

Thanks for the ideas and discussion so far.

Brian.
 
Funny, I too used my yojimbo 2 for everyday carry plus an endura 4 zdp-189. I only cut food and paper, but have noticed that the sv30 doesn't hold an edge for too long. The zdp-189 definitely holds an edge MUCH longer. I have never resharpened either blade, I just strop them daily with .5 micron diamond paste and that brings them back to hair shaving sharp.
That being said, I have now switched to a spyderco tuff with the cpm 3v because it is tougher and holds an edge longer than sv30 and won't chip as zdp-189 is prone to do in tougher use. I also admit to snubbing the LESSER steels :) in favor of the new super steels and this now dictates my decision in future purchases.
 
If you have light reflecting off of an edge only used on paper and string and you have sharpened it and removed the burr... You have crap steel or crap HT or a burnt edge (possibly some combination)

S30V is not a horrible steel, I've used it and will still use it, in my book it's a step above 440C and 154CM.

You aren't looking at a steel issue.

You are looking at HT and burnt edge with some small allowance for sharpening being the culprit.
 
TIFWIW, but there are some vids on YT from guys like Smokeeater908 that have done cut tests, and according to those, S30V seems to hold up very well compared to more "premium steels" (these were all comparing like 6 different Para 2 sprint runs in different steels to the standard S30V). Not saying these videos are the gospel by any means whatsoever, and I can't attest to their accuracy since I do not own and have not used any of those sprint run steels.

However, I do own Benchmade and Spyderco S30V and have had good experiences with both. I'm curious whether it could be a possible HT issue.

I'd also consider investing in a strop and maybe the ultra fine Sharpmaker rods to make sure you're actually getting the wire edge off. When I very first started on the SM, I had what I thought were some razor sharp edges but would dull after cutting a couple pieces of cardboard. Turned out there was still a very fine wire edge that would roll and reflect light when cutting anything else besides paper. Time, better technique, light pressure, and lots of practice stropping finally resolved this issue for me.
 
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Hey David, being an Spyderco It doesn't seems probable. All of mine came around 30º out of the box

(...)

Most of the Spydercos I've got also were pretty good, if not excellent, from the factory. I do have a couple that were more obtuse though, one of which was WAY outside 40°; it was downright blunt. Spyderco does their edges better than most production knife companies, but mistakes sometimes happen; nobody's completely immune to that. That's why I brought it up as a possibility. Even some relatively 'good' edge grinds at ~35° inclusive can see big improvement in cutting performance, just by taking them to 30° or lower.


David
 
You might want to take care minimizing burr formation when you are apexing the edge, that can seriously impact edge retention.

But yeah, that's kind of how high carbide steels will behave. ZDP is interesting in the respect that it can be sharpened by simpler abrasives than high vanadium steels, as well as being able to attain high sharpness. I don't mind S30V, but I prefer low carbide steels for their toughness compared to high carbide steels.
 
Another possibility is that one side of the edge is at a different angle than the other. When you work up a burr on the side where the stone meets the apex, the wire edge is formed. When you switch to the other side, the stone never reaches the burr so the wire edge remains. It will break off when you use it, leaving a dull edge.

You might want to check that the burr is raised on both sides, and then be careful to fully remove it.

It shouldn't take 10 minutes to raise a microbevel -- just a few passes -- so it's possible you're dealing with two different angles. A good loupe and a sharpie should let you diagnose any issues with geometry.
 
I would definitely grind all the factory edge off and start over. Many edges from the factory have wasted steel along the cutting edge. I don't care if its a cheap kitchen knife, should be able to cut many feet of cardboard without failing as you describe.
 
Sounds like you have a wire edge that you haven't removed. The wire edge will feel razor sharp after you've sharpened the knife, but a few passes through cardboard will break it off, leaving an unapexed edge in it's place. Take it easy on those final finishing strokes, make sure you use light pressure, and you'll be much more likely to remove the burr rather than straighten it.

S30V shouldn't have any trouble cutting through a lot of cardboard if properly sharpened. It's a pretty tried and true steel.
 
To address various comments: Each time I've used the SharpMaker on this blade, I've raised a burr on both sides, and then removed it. I won't claim master status in sharpening, but I'm very familiar with forming, detecting, and removing the burr. ...and yes, it did take me around 10 minutes to microbevel the edge on this blade *after* it was flat and reflective on the edge as I described. Maybe I'm slow? :)

Today, after cutting a few things, I got mildly disgusted with the knife and decided to try the SharpMaker *one* more time before breaking out the DMT stones. After spending 5 to 8 minutes on the SM, the edge was sharp again, and cleanly sliced phonebook paper. Shaved, but not super clean. I cut a half dozen slices from medium cardboard and it sliced nicely. Observing the edge, I couldn't see much of a reflection, except in this one spot near the front that I've been having trouble with. I have not yet to date been able to get this small area (1/4 to 1/2 inch long) to stop reflecting light. I figured I'd have to take it to the stones to remove enough metal to get that one spot perfect. But YAY, no reflections on the rest of the edge after mild cutting. Still slices phonebook paper.

On to cardboard boxes. I started with a double layer box I had played with previously, and saw the evidence that the blunt edge yesterday was just tearing and pushing this soft-ish double thick cardboard. I cut in next to a torn spot and.... *smooth* slice all the way until my arm stopped. I cut the rest of that box to big pieces and noticed that it felt correct now.

On to other boxes and some cardboard wrapping. Three or four different thicknesses and grades of cardboard totaling maybe 20 feet of cutting. Plus or minus. All sliced well, and half way through I realized that it had never felt like this in any of my previous tests. Even when freshly sharpened before, it was almost as if the edge was deforming in the first cut and not really smooth slicing on any cut. I checked the edge after: No reflections at all. This is the crazy part: There's no reflection up front where it was before. I checked 4 or 5 times under three different light sources. It's *gone*. Slices phonebook paper still, but it's rough and tears in some spots. Fairly clean slices magazine and printer paper. Very acceptable sharpness for what I do with this blade. Mostly won't shave at all, except in the first half inch. Again, no problem, it's still performing well.

Something has changed. I'm now thinking that there really was weak steel at the apex that was ground away through 3 sharpenings on the SM. I'm also pretty sure that one "real" sharpening on bench stones (or my DMTs) would have done this in one go instead of three. I'm going to play with this edge for a day or two (or three) to see how it continues to work.

I'm much happier with this current result. :)

You know, I considered just doing all of this experimentation on my own and not writing anything here until I was done. Now I'm happy that I decided to share early, as I think this is a good story of a badly performing blade and the process I've gone through of testing and attempting to fix it. I'll update here with more results as they come.

Brian.
 
It shouldn't take ten minutes to microbevel, you are probably overstressing the edge and it is prematurely collapsing.
 
Brian,

I was looking at an older thread today, one with a good deal of mention/discussion of S30V and (apparently) some tendency for it to be more easily damaged by overheating during powered grinding/sharpening. On some level, it seems to make sense, in that the high wear-resistance given by the vanadium carbides might also make it more difficult to grind/abrade (obviously, this is no secret), and therefore create more opportunity for overheating it; especially on older/worn belts that may be a little slower than when new & fresh. I honestly don't know myself how much of the discussion's content is true or accurate, but it seems like it could be a factor in creating new edges with damaged (weakened) steel on S30V; edges which either chip or otherwise degrade very quickly in use, until the weakened steel is eventually stripped away from the edge.

Glad to hear you're seeing some progress, and I'll keep my fingers crossed in hoping it's now 'fixed' (or soon will be). :thumbup:


David
 
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If you're noticing a difference from a few touch ups, take the time to sharpen it properly on your stones, I've heard of edge retention issues on some blades until a few sharpenings have ground away the bad steel. I haven't personally ran into that yet that I know of.

My first reaction would be to toss on my 120 grit diamond stone and put a new lean V bevel on, leave the edge at 400 grit and put it to work. I will say that cardboard is (as you probably know) some really nasty stuff and should quickly show if that area of the blade is still nasty. I would request a replacement knife if after the first few sharpenings the blade is still jacked up, it would point to a bad HT and the blade could be more prone to failure.
 
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