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Knife Edge Degradation Study - August/September 2005

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Starting Conditions And The Purpose Of The Test

Rinaldi TTKK edge at the beginning of hte testing Benchmade 710 HSSR edge at the beginning of the testing

After getting more or less useful macro equipment obviously, I've started examining the edges of my knives. I personally find it really fascinating and interesting, seeing the cutting edges in great details. Provides valuable information about many aspects of the edge and its characteristics after all. I've posted macro photos of the original edges on custom and production knives and other types of the edges as well. Since then the gallery increased significantly, but I was still lazy to finish this article. Anyway, the idea and purpose of this test was to observe knife edge degradation and deformation under their standard use scenarios. For testing two knives were chosen - my old time EDC BM 710 and Rinaldi TTKK, for more info on the knives check out Benchmade 710HSSR review and Trace Rinaldi TTKK review.

The conditions were to use those two knives exclusively and no sharpening whatsoever, the limitation included steeling or stropping as well. This is rather neglecting and abusing the knife, but that's how most of the people use their knives. So, I was curious what would happen with the knives. Besides, since the degradation(or deformation) was the key point of interest, steeling and stropping would only delay the results. Which is why you should steel or strop your knives, makes the edge last a lot longer ;)

Another condition, no knife abuse per-se, that is using the knives for designated cutting, no bone chopping or anything of that sort, which would constitute an abuse. Again, 99% of the non knife folks do a lot worse to their kitchen knife, but that wasn't the purpose of the test. Thus, BM 710 was restricted to usual EDC cutting chores, whatever small stuff you'd cut with the pocket knife and Rinaldi TTKK was used for everything in the kitchen. Honestly, that was very inconvenient. Especially bread cutting. However, no bone contact. Soft food, vegetables, boneless meat and such.

On the photos attached to this paragraph you can see both blades in their starting condition, just sharpened, both feature 30° angle (included), mirror polished edges. Sharpening was done using Edge-Pro Apex sharpening system. And then the resulting edges were polished using 0.3µm Aluminum Oxide microabrasive film. Benchmade 710 sports M2 steel blade, hardened at 58.8HRC (as I found out later, at that time I was sure it was 60-62HRC) and TTKK has S30V steel blade, 60HRC, heat treated by P. Boss.

Week 1 and 2

Nothing interesting. I could feel the edges becoming slightly duller, but nothing significant visually, I mean photography-wise. I couldn't detect any dents or rolls on the edge using my macro photography setup. Therefore, no photos here :)

Week 3

By the end of the 3rd week things started getting more interesting. Both knives were noticeably duller and with a loupe I could see rolls and chips on both blades. To be more precise both had rolls, but only TTKK had chipping.

Rinaldi TTKK
Rinaldi TTKK edge after 3 weeks of kitchen use. Rinaldi TTKK edge after 3 weeks of kitchen use. Rinaldi TTKK edge after 3 weeks of kitchen use. Rinaldi TTKK edge after 3 weeks of kitchen use. Rinaldi TTKK edge after 3 weeks of kitchen use.

On the first photo attached here, you can see some edge rolling in the mid section of the blade. Quite hard to see on though. So basically, the only way I found to make it work, was the light reflection. Light reflects differently from rolled portions. You can see couple bright spots on this photo, which is around 16x magnification. I just resized original image to show larger section of the edge. Second photo is 1:1 crop of the original image and shows deformations in more blurry details :). Whichever you prefer.


The third photo in the stack is another damaged section of the blade. Still mid section, but closer to the tip. For some reason I got the chip which was unexpected, and some more rolling. Chip and rolls are shown on close-up inserts in the photo.
Next, 4th is the close-up full size crop of the chip in previous photo.
And 5th picture is the second section you see on the collage in 3rd photo.


That's it for TTKK after 3 weeks. The chip was really unexpected because I never cut anything that hard during the whole period (7 weeks). Bread, vegetables, cheese, boneless meat, etc. For the record I always use cutting board, so glass or granite countertop isn't to blame. Nevertheless, chipping occurred.


Benchmade 710 HSSR
Benchmade 710 edge after 3 weeks of kitchen use. Benchmade 710 edge after 3 weeks of kitchen use.

You can clearly see the edge dented and rolled on this image. I assume that came from the wire I cut with it. No significant deformations or degradations otherwise. Rolled edge further back to the handle side. At this stage the blade still shaved and cut through free hanging paper. What I didn't really know at that time, was that the blade was rather on the soft side, 58.8HRC not 60-62HRC. I wrote in details about that in another article The Importance Of Knife Blade Hardness.


Week 7

After 7 weeks of the use. Still no touchups, no sharpening. This time damage is a lot more extensive and visible.

Rinaldi TTKK
Rinaldi TTKK edge after 7 weeks of kitchen use. Rinaldi TTKK edge after 7 weeks of kitchen use. Rinaldi TTKK edge after 7 weeks of kitchen use.

We have a major chip on the tip and a roll. First shot is the overall view and close-up of the roll.
Full size close-up of the chip on the tip on the next picture.
And the third picture in this stack is the badly deformed mid section of the blade. Rolls, chips, dents. It's all there. However, bear in mind here magnification is ~32x, that is screen size vs. real size. So visually it's still nothing like this. You can see rolls on the light and that's pretty much it. Blade won't shave or cut through free hanging paper. Although I am sure it's still a lot sharpen that most of the kitchen knives in average household. Usable in other words. But if you like sharp knives that's not it.


Benchmade 710 HSSR
Benchmade 710 edge after 7 weeks of kitchen use. Benchmade 710 edge after 7 weeks of kitchen use.

Well, rolling is more defined at this stage as you can see. This is the same section as in previous test images 3 after weeks of testing. Next section of the edge towards the serrated portion. Still no chipping, just rolling. That part still can shave with difficulties, when previous one can't.


Conclusions

Well, one is clear, deformed edge degrades much faster. That I knew before all this, just pictures make it clearer. Second, visually, you can't tell much anyway. You either need a loupe or a microscope to get the clearer picture. Third, Not very clear why I got chips on TTKK. Theoretically and practically it was all soft stuff I was cutting on cutting board, no bones, nothing that harsh. I didn't clean potatoes with it either, to blame dirt that is. Other that that... May be that's the "metal fatigue" i.e. edge portion bending to different sides multiple times so it finally falls off. I don't know. Also, Cliff Stamp did note that the damage was too localized to be caused by the metal fatigue effect. Perhaps carbide localization had something to do with it.

Also, worth noting that S30V was rather infamous for its chipping. May be that's what I saw in 2005 testing. M2 steel held up better, which is also visible, however to be fair, it never saw as much cutting as TTKK, although I use it for harsher stuff than food. Considering what I know now, i.e. 58.8HRC of the M2 steel in those tests, that'd easily explain the absence of the chipping on the M2 blade. S30V in this tests was 60HRC. Even at 60HRC M2 would still be tougher than S30V. In the end, it was a good experience. I'm planning to get back to those tests and repeat with more knives. So, I'll finish this article with usual - to be continued ;)

Last updated - 09/01/11