Super Hard vs. Soft Edges
Or Are Very Hard Edges Really That Brittle

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Lessons Learned and Conclusions

As usual, the following is strictly my own opinion and conclusions, the outcome of my not so scientific testing. Keep that in mind when you read all that. It's not designed neither for promotion nor demotion of knives of any kind. Just the observations, based on the test, and conclusions regarding the widespread knife myths listed at the beginning of this article ;) If you feel you agree strongly with the 4 statements at the top of this article, then perhaps you should skip the rest of the page.

Ease Of Sharpening

- The number one busted myth for me, was the proverbial ease of sharpening of the soft edges. While it is true on its own, as in, it is easier and takes less amount of time to remove the same X amount of metal from 56HRC steel compared with 64HRC steel, in real life, with knives and actual edges used for cutting, things don't play out as simple as that statement implies. Harsh material can very easily induce the type of damage on the soft edge, that is not repairable using simple steeling or stropping. And that is one of the major pros of the softer edges, they can be realigned easily, but and that's an important but, only if the deformation is not deep. If the deformation goes in too deep, like it happened to my calphalon parer in both tests, doesn't really matter how hard and how long you steel, it's not going back. Most likely you will induce further damage. There is a reason why all the pros advise to use light or no pressure during steeling. Any more than that and you risk the new deformations. As you can see from the results and photos in this article, hard edges not only lasted longer times sharper, but they required very little time to restore their original sharpness. To be fair, the very first edge restoration on Calphalon, in the test #1 went fairly quickly too, just 10 strokes per side, but for the sake of the same fairness, I have to mention that not the whole test section was brought back to shaving sharpness. Subsequent dulling occurred much faster compared to the initial dulling, I am assuming it was due to weakened metal on the edge, and edge restoration was far less successful duringthe first test, and pretty much impossible using given tools in the second test. To summarize, if the load on the edge is up to X amount and that X load or a force can bend or rip the soft edge, but can't deform the hard edge, it is obvious hard edge is preferable.

Soft Edge Durability

- That's a derivative from the above. I don't think anyone seriously believes that soft edges can stay sharp longer, given the same alloy. Simply, the idea is that, soft edge will slightly roll if it encounters harder obstacle during cutting, and that roll is quickly fixed by using a smooth steel, and voila, you're back in business with razor sharp edge, in a minute. Hard edges on the opposite, when they encounter the staple or something like that in the cutting medium, they will chip. And obviously, a chipped edge can't be repaired using smooth steel or a plain strop, you really need to sharpen it, perhaps remove considerable amount of metal to get the good edge too. As with the previous one, this statement is also true, both parts (soft and hard edges) are true, in a very broad sense. However, practice is different and can make very significant corrections. using the same hypothetical scenario, if I was cutting cardboard and there was a staple made of aluminum embedded in it, my hard knife either would cut through it with no damage, if I was using enough force, or hit the staple and stop, in either case there would be no damage to speak of. No restoration would be needed either. Now, replace that hard steel with a softer one like in Calphalon, and at best you are off to steeling for few minutes, at worst you will have to do exactly what the myth says about hard steel knives, sit down and sharpen a new bevel.

Yes, it is absolutely true, on certain occasions hard steel will chip, but given the results I saw myself in this test, I can't imagine soft steel knife in the same situation surviving with the edge damaged just enough to be realigned with a simple smooth steel. Unless that hard knife edge was made out of glass, or it somehow failed the heat treatment, there is no way to achieve that result. Case to the point - GRS Kukri damaged edge image gallery, that kukri apparently wasn't hard enough to chip or break, but look what happened to it when the edge hit a nail during chopping. There is no way anyone could've realigned damage that intensive using any sort of smooth steel. Actually, I couldn't push back the ripped out metal using a hammer. The deformation was so great that the blade had trouble going back into the sheath. I can't see how a small or medium size chip would have been any worse than that. If it was up to me, I'd rather have a small chip or few small chips instead of the mess I got on that kukri.

The one possibility I can think of, that is when it comes close to the softer edge is more durable scenario, when a softer blade is made out of relatively tough steel, INFI, S7, 5160 etc, about 58-60HRC range and hard steel is something like ZDP-189, CPM110V above 65HRC. Then, if you start chopping with both blades, hard one sure will suffer more chipping and you can possibly even break it. The only thing is, nobody makes chopping knives out of ZDP-189, and the designated uses of those two knives will be different. If you take small knife made from those tougher steels, then harder steel will outperform them in light cutting anyway, but yes, it can sustain more damage if abused. However, the question is why would you do that. In the end, there is very specific conditions for the myth to be 100% true and it shouldn't be used universally. Visuals above ;)

Hard Edges Are Difficult To Sharpen

- No they're not :) I don't want to elaborate on the hardships of rebeveling hard and especially, highly wear resistant steels here. In the context of the tests described above, and quickie restoration, hard edges were both, more durable and easier to restore. On top of that, steel composition influences ease of difficulty of steel sharpening to greater extent compared to Rockwell hardness. E.g. Aritsugu A-Type gyuto, with its gokinko steel, which is about 60-61HRC is much harder to grind than ZDP-189 steel above 65 HRC. In the context of these tests, what mattered was the little damage sustained by those hard edges, consequently very little work was required to restore them. There's another aspect to consider too, hard edge in general means the ability to have more acute edges and thinner blades, or at least thin blade behind the edge. That means there is very little metal to remove, even if you have to put a new bevel on the knife. Soft steel simply can not sustain that kind of edge, it will bend and fold, hence the necessity to remove more metal, thus in the end that is debatable as well, what's easier to sharpen. If you manage to have super thick edge on super hard steel, then yeah, you're in for a treat ;) However, normally, you would grind thin edge and metal behind the edge is thin too, and then it is a different matter altogether.

Hard Edges Are Brittle And Chippy

- I don't like and disagree with this statement 100%. It is way too general and misleading. Unless you specify the steel, hardness, designed use, and specific blade geometry/angle it is pretty much meaningless statement, at least in the context of knife edges and cutting stuff with them. 67HRC in the test #2 was not brittle, and sustained very little, if any damage, compared to much tougher and softer steel at the same angle, on the same medium. Is it a good reason to say no it is not brittle at all? Depends what is the baseline and what do you want to cut, or if you are planning to chop with it. Depending on the steel, the same hardness can make it brittle or not, 61HRC is pretty much the limit for CPM S90V steel, but it is soft and low hardness for ZDP-189. My Sanetsu Gyuto never chipped, and it is 64-66HRC. I don't consider it to be brittle at all, for its designed use, but if someone asks about it as a chopper, I will agree, it is brittle. The same is true for the steel. ZDP-189 is brittle? Yeah, it is brittle for a sword or a kukri. Otherwise, it is not brittle for chef's knife or a paring knife. Use the right tool for the right job, and the right steel, with the right hardness and heat treatment for the job. You'll do fine. Those who stick to gold old classic steels and medium hardness, do miss out a lot in the cutting performance and edge holding department. All in the name of that dubious ease of sharpening and durability, as if chopping down the trees with 4" folders or kitchen knives is something one has to do on daily basis. Anyhow, to each his own, but I think hard knives and edges are getting a lot of undeserved bad rap.

Sharpening On A Rock

- One of the popular arguments in favor of the soft(er) edges is that, should you end up in the woods or other wilderness environment, with one knife, and not having a knife sharpener with you, it is easy to sharpen your knife on a flat rock, which you will easily find in the wild, but if you have a hard steel on you, then it is very difficult or impossible to sharpen your knife with the same flat rock you just picked up.

Obviously, this is the worst case scenario, because normally, why would you venture in the wilderness for a day or more, having a knife on you without a small sharpener, especially if you know you will use it[the knife], depend on it, and you know how to sharpen it. Lots of fixed blades sold today have either a sharpening stone pouch on the sheath, or a small medium grit stone on the sheath. It's kind of hard to imagine loosing only a sharpener and still having your knife. Well, ok, accidents, even the most weird ones happen. So, you ended up with a knife, but no sharpener. Then what? Depends how much cutting you will have to do, and what will you cut. How long will you be stuck in that wilderness alone, and how long will you survive. For certain types of cutting CPM 10V at 64-65HRC can outlast average mainstream steels, with average hardness more than 5:1 ratio. So, if your soft knife lasted a day and then it needed sharpening, then your CPM 10V would've lasted 5 days w/o sharpening. Chances are high, that's enough to get back and make sure you pack a sharpener next time, just in case ;) Most of the people who die out there, they die because of various reasons, and dull knives, or even lack of the knives are not in the top 100 reasons of fatalities.

Let's say one possesses all the skills required to survive, and the only thing missing is that sharpener. So, you are somewhere in the woods and then go looking for that flat tone, because you have to sharpen your knife. You know what? Depending on the area you are in, you might end up severely disappointed. Extreme environments such as deserts, tundra and glaciers notwithstanding, even more friendly areas can be very scarce on rocks, or may have soft rocks predominantly. The thing is, not every rock will do for sharpening, the rock itself, besides being flat enough, has to be also hard enough to actually remove metal from your knife. Otherwise, you can rub that steel on the rock all day and not get too far. The problem, and I think it's the part of the rock sharpening myth, common sharpening stones work very poorly on high alloy, high carbide steels. And in those cases, even if the steel is softer, it doesn't help the situation, it's the composition that is more of a problem than the hardness. However, finding a stone that has hardness above 7 on Mohs scale(mineral hardness, analog of Rockwell Hardness for metals) will sharpen high alloy carbide steels as well. Slower, but it will still sharpen them. Plus, unless you managed to cause a real disaster to the edge of your hard knife, then the amount of sharpening you have to do should be minimal. And restoration will be quick. If you somehow ended up in the situation where you need to put a new bevel on the 67HRC ZDP-189 or other steel like that and have nothing but a flat rock on you, I feel really sorry for you.

I know some of survivalist schools teach hot to sharpen things on the rock. Although, it is the very same freehand sharpening skill many people have. I think the idea is to learn freehand sharpening, not to rely on dumb luck helping you find the suitable rock. In one discussion about this topic on bladeforums, several members mentioned that, i.e. being on the wilderness tour, which included sharpening the knife on the rock, on daily basis, by the way. When I asked about the details, turned out the rock was not your average rock you pick up on the shore of any river. One of the examples was Ohio Sandstone. As the name suggests it is primarily found in quarries in Ohio. So, relying on that... For me it is easier to obtain DMT diamond sharpener or Japanese whetstone than to find that Ohio Sandstone. Besides, natural quartz and garnet stones can sharpen high alloys and hard steels. So, if you are gong about chances of finding a stone in random places, then to get the real advantage on sharpening for that soft knife, the area has to have flat rocks hard enough to sharpen the soft steel knife, but not hard enough to sharpen hard steel. I am sure areas like that exist. May be even in greater quantity than the areas with quartz based stones. However, should you or should you not base the choice of your knife on the wilderness stone compositions and the possibility of loosing a sharpener, is a personal choice. Once again, in my opinion you are loosing a lot of performance for your knife based on that choice. What's really beyond me is some people picking soft steel kitchen knives for the ease of sharpening. Besides more frequent sharpenings, the loss of cutting performance and edge holding/edge stability is simply enormous.


- That is one long report, but testing was long too and I wanted to cover quite a few topics here. To summarize in simpler terms let's say we have two knives, one is about 58HRC and the other is 64HRC. Same steel or different steel it doesn't matter too much, hardness controls the edge strength, so that's what we are focusing on. It will take X amount of force to bend the edge on the soft knife and Y amount of the force to bend or chip the hard blade. Obviously, Y is greater than X. What many people don't realize or underestimate,myself included before this testing, is the difference between X and Y, which can easily be 2x, 4x or even greater value. That's what it all comes down to in the end. If your designed use doesn't imply forces greater than Y, you have absolutely no reason to settle for the knife with lower strength. If the load will be greater than Y then you will get chips and nicks on the hard knife, that's certain, but what is also certain, a soft steel knife will get severe damage as well. In my tests, as you can easily deduce, I never went above Y value, and I got hard knives with no damage, and anywhere from bad to really bad damage on the softer edge. Obviously, if the Y is too big it can break hard knife, and softer one might survive, because it has better elasticity. Point is, there is no universal hardness, no universal X and Y in real life and you have to choose what do you do with a given tool, if you want at least better than average performance from your knives. Settling for 60HRC on ZDP-189 steel is pretty much the same as buying a top of the line sports car and driving it at 40mph on a highway. Nobody will give you a ticket for your knife underuse, but why ;).

See also Hard vs. Soft edges image gallery for additional images of the tested edges.

Prev - Test #2, Kershaw and William Henry ZDP-189 vs. Calphalon

Last updated - 05/19/19