The Toughest PM Stainless

me2 said:
It didn't sound metal, but it is full of water and stuff, and on a YouTube video. Regardless, a deformed edge is an indication of insufficient strength/hardness keeping in mind this is only the first stage.
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Me2 does make a good point; one that initially escaped me. The test really showed that Elmax was the strongest of the three blades because it had less deformation (auto correct said defamation) of the edge. You'd expect that result because the Elmax is a bit harder than the others, and strength (resistance to bending, rolling and deformation) is a proxy for hardness.

What you're looking for is resistance to chipping or breaking (toughness). You might look at the edge under high magnification and see if there are any chips. Sometimes, small chips can look like dents to the naked eye.

Because this is such a cool experiment and one that Shawn had to put a lot of time and money into, it's worth it to test it carefully.

I'd can the light taps against the metal pan. They're not a bad informal test, but it could be better. For example, you could tape a nail to a long board that pivots on the opposite end. By adding weight and height to the drop, you could standardize the test, and you could work up to higher loads (heavier, higher drops) without having to destroy the knives. Just make sure the edge is hit at 90 degrees by each blow. You could also add a 45-degree test to see how the edge holds up to lateral stressing.

All you need to demonstrate is that chipping begins at a certain point for each alloy. In the end, you could easily sharpen out the damage, and send the knives out to a wear-resistance tester for cut testing. Then we'd get fuller look at these alloys.

Regardless, this is awesome stuff. Thanks to Shawn for taking the time and thought to do it. Three cheers.
 
Twindog said:
Me2 does make a good point; one that initially escaped me. The test really showed that Elmax was the strongest of the three blades because it had less deformation (auto correct said defamation) of the edge. You'd expect that result because the Elmax is a bit harder than the others, and strength (resistance to bending, rolling and deformation) is a proxy for hardness.

What you're looking for is resistance to chipping or breaking (toughness). You might look at the edge under high magnification and see if there are any chips. Sometimes, small chips can look like dents to the naked eye.

Because this is such a cool experiment and one that Shawn had to put a lot of time and money into, it's worth it to test it carefully.

I'd can the light taps against the metal pan. They're not a bad informal test, but it could be better. For example, you could tape a nail to a long board that pivots on the opposite end. By adding weight and height to the drop, you could standardize the test, and you could work up to higher loads (heavier, higher drops) without having to destroy the knives. Just make sure the edge is hit at 90 degrees by each blow. You could also add a 45-degree test to see how the edge holds up to lateral stressing.

All you need to demonstrate is that chipping begins at a certain point for each alloy. In the end, you could easily sharpen out the damage, and send the knives out to a wear-resistance tester for cut testing. Then we'd get fuller look at these alloys.

Regardless, this is awesome stuff. Thanks to Shawn for taking the time and thought to do it. Three cheers.
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Thanks Josey, great ideas
I agree with you guys
Let's slow down so we can get the most out these blades and repeat this first test a few more times since there is no going back after batoning nails.

There are a few pieces of equipment I'd like to have such as a USB microscope and a dial scale to measure how much force is need to chip the edge with transverse pressure on a nail.

But I don't have the money. Hell I'd love to test what ever comes to mind but I can't.

So I'm going to focus on some higher priorities for now. I'll come back to enrich the thread when the time is right.
 
DeadboxHero said:
There are a few pieces of equipment I'd like to have such as a USB microscope and a dial scale to measure how much force is need to chip the edge with transverse pressure on a nail.

But I don't have the money. Hell I'd love to test what ever comes to mind but I can't.
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Hey Shawn -- I have a new Dino-Lite digital microscope and stand. It's the AM3111T. Haven't even opened the box yet.

I could loan it to you if you want. Being able to see exactly what's going on with the edge apexes would help your tests a lot.
 
Twindog said:
Hey Shawn -- I have a new Dino-Lite digital microscope and stand. It's the AM3111T. Haven't even opened the box yet.

I could loan it to you if you want. Being able to see exactly what's going on with the edge apexes would help your tests a lot.
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That would be sweet for this project, yea man, team effort!
 
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Got the USB microscope from Josey, very exciting. We will do a more controlled test. I did an informal one last night. And checked on the microscope. Still looks like elmax took the least damage, but we need more control, we might have very very fine chipping on Elmax that is hidden.

Either way any flaws will be discovered with more abusive testing. Hammering through nails hides nothing.

We will also do a tip test by dropping the blades from a measured height tip first onto concrete.

Testing will resume mid April.

I've got a the Oregon knife show to gear up for so I'm putting this on the back burner for now.

Come down to Eugene, OR and say hi

Shawn
 
I should also note how the edges came back from the testing in the first video.

CPM 154 had the highest response
with stropping on 1 micron diamond compound on leather. The edge came back to almost full.

ELMAX was the least effected by stropping.

Then S35VN in the middle.

Moving to a ceramic honing rod for a few passes then back to the strop

S35VN came back.

CPM154 seemed fully restored.

But Elmax still had some snags on paper.


This is why I feel like it's worth more investigation before we move to more destructive testing.
 
I've had extremely good luck with CPM-20CV to the point I called it "a more stainless 3V". Insanely tough and ridiculously stainless. It was my favorite until Delta3V from Nathan. Now I just need everything in D3V. I NEED IT!!!!!
 
Twindog said:
Me2 does make a good point; one that initially escaped me. The test really showed that Elmax was the strongest of the three blades because it had less deformation (auto correct said defamation) of the edge. You'd expect that result because the Elmax is a bit harder than the others, and strength (resistance to bending, rolling and deformation) is a proxy for hardness.

What you're looking for is resistance to chipping or breaking (toughness)...
{snip}
...All you need to demonstrate is that chipping begins at a certain point for each alloy...
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^This.
Sucks that they didn't give you a tight 61 Rc on each blade :( You probably would have achieved these same results with three such blanks of all the same steel.
Charpy V-notch test-samples could give you "empirical" toughness values, but I suspect that the longitudinal toughness values for all of these steels would be about the same, composition and carbide loads being similar between them (S35VN on the lower end ~14% and Elmax higher ~18%, of course the HT protocol might impact that and I am not learned enough to declare how much). But that sort of result doesn't really answer your question, I suppose, which trends toward performance differences in knife-edge geometries...

I'll be the idiot and type about the elementary principles for a second:
Every material has its failure point, has its 'stress-strain' curve. Right now, you may have simply demonstrated the limits of the elastic region (Yield Point) on the softer blanks, having not reached it on the harder blank (or you did but it fractured nicely so as to hide any apex 'glint'?). Again, this gets to what you are actually hoping to see. Strength is in the elastic region of that stress-strain curve for a given material, i.e. the amount of stress it can endure before taking a permanent deformation (Yield Point). Toughness is generally characterized as the stress it can endure AFTER taking a permanent deformation until Fracture. That is to say, an edge that deforms but doesn't fracture is "tougher" than an edge that resists permanent deformation but then does fracture at the same or lower stress level.
The edge that resists deformation is stronger but not necessarily tougher than the edge that takes a bend. Of course, once it takes a bend, the steel can 'neck' and become very brittle, refusing to bend further and instead simply cracking away.
The design of the Charpy pendulum is to apply the same stress to all samples and so quickly and forcefully that the material has very little time to bend elastically and there is no repeat impact to push a plastic bend further to the point of cracking, rather it bends as much as possible against the force of the stress and then fractures almost immediately, and toughness is calculated by the amount of energy 'absorbed' by the piece prior to fracture within that plastic region.
For your test, the impacts can squash the apex or bend it to the side, most likely the latter, and all the result of the strength of the steel at the apex. For the latter, a second impact could crack away the bent material, but it was already compromised by the initial bend that resulted from the reduced strength rather than because of lower "toughness". However, if the edge does NOT appear to take a permanent bend but instead chips upon impact, you presume that the same amount of stress toward deflection was imparted and the material simply reached its Yield Point and had a Fracture Point very near thereunto, making it less tough than a material that would have simply deformed under the same level of stress.
The thing is, if your read-out for "toughness" is to look at how much 'glint' appears at the edge or how well the edge slices paper, what is your hypothesis?
If an edge chips, will it present more or less 'glint'? Will it present a more or less 'ragged edge' or cutting?

I would personally expect the "tougher" edge (the one that deforms rather than chipping away) to present more edge-folds that appear as a thicker apex with more 'glint' and evince a more ragged cut against the paper.
I would expect the LESS TOUGH edge (the one that chips rather than rolling/bending) to show LESS 'glint', retaining a generally thinner apex geometry and continuing to cut more cleanly than the rolled edge.
But of course this is all overshadowed by the first principle which is that you expect the stronger edge to better resist rolling/cracking and so retain the thinnest and cleanest apex geometry overall.

So what's my (worth what you paid for it) conclusion?
1) It sucks that the Rc values may present a comparison of strength instead of toughness, and that the Elmax could not be given the "industry standard" HT to at least make it relevant to the majority of consumers.
2) Skip the pot and go straight to the "Jesus Nail" (especially given the significance of this week with regard to that epithet ;) ). Make no room for questions of whether or not the edge reached a limit, squash out all external influences that could impart noise to the results, FORCE THEM ALL TO BEND OR BREAK :mad:
I am not advocating for full-on destruction of the blanks, just a guarantee of a destroyed edge at some single point or region in order to create a visible (maybe with that microscope) bend to ensure that the Yield Point was reached. If they ALL fracture in the midst of the bend/roll, then try to back off on the force until ONLY bends/rolls appear on at least one of the specimens. With the same force applied, the specimen that bends without breaking is your king :)

Remember, what bluntcut has been working on is improving the strength of steels without relevantly compromising toughness to produce that king who first refuses to bend but then also holds back from breaking. If it turns out that your hardest blank (the Elmax) refuses to bend and also keeps from chipping when the softer blanks cannot, then you will have proved his purpose, that "toughness" only matters when your tool is too weak to handle the stress to begin with ;) :D
 
Im game for a group effort to test the steels. I can get repeated edge thicknesses and consistent HT from peters.
Steels i currently have:
Vanax
Z-finit
NItro-V
Z-Wear

I can do testing on my Apex hunter model.
I have 3 in Zwear at 62HRC. And one full convex to 0.
I can send one to someone as a test mule.
 
Sweet.

How much did this cost you? Id like to see this test done with everything at 61. Ill throw down some cash if you ever do a similar test again. Maybe something like 154CM or 440C might be a cool thing to toss in for a standard comparison.
 
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