S30V vs M390 Toughness?

Jerry Hossom said:
I have never seen 3V chip from a single impact, even on steel. It will deform for sure, but I've not seen it chip. Then again, I don't make "fine" edges. Sharp edges but not thin, fine edges.



Wild ass guess, M390, but "it depends". :)

Here is a photo of a test done on S30V and another steel that is particularly noted for its toughness. Same test, same impact on the same target for both steels. S30V chipped, the other was deformed. Same damage to both. Picture a scale, extreme brittleness on one end and extreme weakness on the other. The ideal blade steel will fall exactly in the middle; it won't chip, it won't deform. There is no such steel, but some come close.

View attachment 480086

Here's another photo. Two steels, the bottom one is 154CM, the top one is a steel that scored high on CATRA and had great Charpy marks, but... Both were hammered through a nail with as close to the same impact force as I could achieve. See what happened to the high scoring steel? The company had high hopes for this in the knife world, but decided to look elsewhere for a market. Numbers...

View attachment 480090

Edited to clarify. "Bottom one" meaning the one underneath - top edge in the photo. Sorry.
Click to expand...

Wow, Jerry this is awesome, can I ask knowing what I just saw in your photo, for someone with some bench stones and regular sharpening equipment, all things being equal, which is easier to reprofile and fix?
 
It's pretty much the same task regardless of how it failed. You need to level out the edge and get it back to smooth, even and sharp in either case. Remember, though, in both these cases the intent was to create failure so I wouldn't expect such chipping or deformation you might see in any reasonable use to be this dramatic.
 
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This is a 3V knife blade with chipping along the edges. I partially removed the chips with a WorkSharp. I believe the chips — which occurred while using the 12-inch blade as a machete in heavy brush (no rocks) — happened because of deep grind lines left behind by the maker. The chips line up with the deep grooves. The heat treat was by Peters at 59-60 Rc.

It will take a long time to get rid of the grind lines, but I’d guess that the chipping would stop once I do. But since I’m using this knife as a machete, I’m not concerned.

For me, the lesson is that chips can result from a number of factors: the steel, the heat treat, the use, and the grinding.
 
If the edge were finished the lines left from the grinding shouldn't matter, though they can result in other issues. I'd really like to look at one of these blades with chips in 3V. As I've said, I've never seen that happen and I'd like to examine the exact nature of the deformations. In any case, this absolutely should not happen with 3V and in fact I'd be surprised if they happened in a decent stainless with a properly shaped and finished edge without hitting something a lot harder than "heavy brush". Twindog, would you be interested in sending me that knife for a free sharpening?
 
Sure, Jerry. You can test out the edge with heavy chopping, too, if you like. I did remove most of the chips, which were not that deep. The ones left were deeper.

If you send me your address, I'll get it in the mail tomorrow.

joseypaul (at) starband.net
 
This will be interesting! Thanks Jerry and Twindog for taking the time to examine this... I look forward to your findings. :)
 
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