Knife Edge degradation Macro Photos.

Gator97

Gator97

Joined
Apr 10, 2000
Messages
3,794
Hi All.
In jun I've posted magnified pix of edges. Original thread can be found here.
At the same time I decided to see what would happen to the edge durign prolonged and unsharpened use. For observation I selected Trace Rinaldi TTKK
which was used in the kitchen during those 7 weeks exclusively, which means it was the only knife I've used in the kitchen, have to say, it was rather inconvenient :)
Second was my edc folder, good old trusty BM 710 HSSR. Used as edc blade for medium/heavy cutting. Although no heavy duty stuff during these 7 weeks was cut.

In next msg there are pictures after 3 weeks of use. And msg afterwards is 7 weeks of the use. Edges in starting state are posted in the original thread referenced above.

During those 7 weeke I haven't sharpened or steeled those 2 knives.

NOTE - If you have disabled inline links you'll have to either enable them or go to links manually by getting link location from your browser. Alternatively all the pictures are posted here:

NIB edges and degradation study edge pix.
 
After 1st week there was no visible difference. During second week I could feelthe edge was duller, but nothing significant visually, I mean photography. So, after 3 weeks this is what happened:

TTKK S30V:

Some edge rolling in the mid section of the blade. Quite hard to see on the photos. So basically the only way I found to work was light reflection. Light reflects differently from rolled portions. You can see couple bright spots on this pic, which is around 16x magnification. I just resized original image to show larger section of the edge.

This one is the full size picture, shows close up of the rolled edge.

mid section of the blade, little bit closer to the tip compared to prev. pix. For some reason I got the chip which was unexpected, and some more rolling. Chip and rolls are shown on closeup inserts in the pic.

this is the closeup full size crop of the chip in prev. pic.

And this is second section from the collage above showing minor chipping.

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

BM 710 HSSR after 3 weeks.

You can clearly see the edge dented and rolled on this pic. 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 stil shaved and cut through free hanging paper.
 
After 7 weeks of the use. Still no touchups, no sharpening. This time damage is a lot more extensive and visible.

TTKK S30V:

We have a major chip on the tip and a roll. Overall view and closeup of the roll.

Full size closeup of the chip on the tip.

Badly deformed mid section of the blade. Rolls, chips, dents. It's all there. However, bear in mind here magnification is ~32x, that is scren 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.

BM 710 HSSR after those same 7 weeks.

Well, rolling is more defined at this stage as you can see. This is the same section as in prev. msg 3 weeks after.

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.

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 potatos 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 donno.

M2 steel held up better, wchich is also visible, however to be fair, it never saw as much cutting as TTKK, although I use it for harsher stuff than food.

At this point I'll be sharpening both blades again :) It's about time. Later I'll try to see if I can photo particular edge damage types.

And a bonus:

NIB edge of Phil Wilson's hunter CPM 10V steel, 64HRC.
closer to the hilt.
mid section.
and the tip.

And NIB edge of Himalayan imports AK bowie that came in on saturday:
 
Those are some amazing pictures!
Very interesting, thank you for posting these.
 
Gator97 said:
The chip was really unexpected because I never cut anything that hard during the whoel period (7 weeks).
Click to expand...

Coarse grained steels break down like this in use even on soft materials, it has its advantages in slicing as it keeps them sawing, it isn't what you want in heavier use as it makes the edge weak to impacts and lowers push cutting ability.

I don't think it is general fatigue as it is way too localized, I think it is more to do with carbide distribution at that particular point. If you check the edge at sharpening at really low angles you can see chips form similar while sharpening on such steels.

Nice work.

-Cliff
 
Pretty strange :) I mean grain size compaerd to the size othe missing chunk. As for the edge that one was 15 degrees per side, which is pretty low. Well, for the kitchen knife at least.
Do you think it is worth trying to get lower angle on that blade and try the whole thing again in the kitchen?
 
Gator97 said:
I mean grain size compaerd to the size of he missing chunk.
Click to expand...

Some quick math which is likely wrong :

3/32/10/2.54/1.2/1000 = 3 microns

The chip looks 3 mm deep, adjust for 32 mag, convert from mm to cm and then cm to inches, convert from width to thickness assuming a ~20 degree microbevel, and finally convert to microns.

When I go really low, that angle adjustement factor increases radically and thus edges start breaking apart, even under 10x mag they won't be smooth. Alvin noted the same thing years ago when he tried to sharpen stainless at 3-5 degrees per side, and yes some of it was even Bos hardened.

Do you think it is worth trying to get lower angle on that blade and try the whole thing again in the kitchen?
Click to expand...

It is always good to repeat just to make sure it isn't a fluke of some kind like dirt on the food. Because it only happened on one spot on the edge the probability is low anyway. Note when you get grain sizes for steel these are averages, some are much higher in the steel at other places, some are lower.

-Cliff
 
3-5 degrees per side? Man, that IS low. Never thought. Well, if I get M2 blade at high RC sometimes I'll try to do that. Interesting what'll happen.
I guess I'll try to resharpen at lower angle and try again. I think chipping will be more severe though.
 
Yes, the blade is right to the stone, you can't hone this low on flat or convex grinds unless you basically hone the full primary grind.

-Cliff
 
what was the condition of the blade before this test.. Used ? I can't see tip damage from cutting soft material on one of Trace's blade....
 
Send that knife back and I will figure out what if anything is wrong... I have never seen that sort of damage on a knife under normal kitchen use I made ever.

Take Care
Trace.
 
Trace, nothing wrong with the knife, at least from my point of view.
Like Cliff ponted, the chip in there is magnifyed 32 times. Barely visible with unarmed eye.
As for the starting conditions, I sharpened it with edge pro and pictures of the original edgte ar posted in another thread, linked in 1st message. Mirror polished edge @ 15 deg. per side.
 
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