chiral.grolim
Universal Kydex Sheath Extension
- Joined
- Dec 2, 2008
- Messages
- 6,422
"the strength of the martensite structure" = rockwell hardness => harder material has greater edge stability
This is absolutely the case :thumbup: and is WHY we use >90% carbide hard-metals to achieve the finest edges, apices that are 10 - 100X smaller than can be achieved with ANY steel.
As for the sharpening you describe, YES I have done it, and my experience is that the low-carbide steel (2-5%) rolls easily due to lower martensite hardness (usually <58 Rc) while the high-carbide steel (>10%) is usually accompanied by higher hardness (60+) and resists any deformation under the same stress BUT may present micro-chipping at HIGHER stress, stress levels where the lower-carbide steel already folded over on itself.
But don't take my word for it. http://bladetest.infillplane.com/html/bevel_angles.html
Here is an SEM from ToddS of a low-carbide straight-razor blade sharpened at 15-inclusive (though it must be noted that the apex-angle is actually closer to 30-inclusive at 0.5um back) after it cut through a few centimeters of printer paper:
Again, that's after cutting through printer paper, not carving wood. On wood, you can kiss that first couple of microns good-bye, it'll fold over and snap away PDQ due to insufficient material support from a) such a low angle that reduces edge-thickness/strength ENORMOUSLY and b) too low martensite hardness.
"The fact" is that edge-angle relates to edge strength through edge thickness at a given distance behind the apex, and that thickness relates cubically to strength, i.e. an edge sharpened at at 10-inclusive is ~8X weaker (more susceptible to folding/breaking) than one sharpened at 20-inclusive, and the 20-inclusive edge is ~3.5X weaker than the 30-inclsuive edge. Rather than mess around with the sharpening angle, you're better of sticking with 30-inclusive and then just thinning the blade at the bevel shoulder to achieve the performance desired, which can be seen in Jim's edge-retention thread. Please note again where well-done AEB-L falls compared to high-carbide steels with similar geometry.
Another thing to take into account is the balance between carbide-volume reducing toughness & edge-stability vs carbide fraction increasing toughness and edge-stability. Quoting from the paper I linked in my last post:
This is why we see an increase in toughness in some steels when Rc goes up a couple of points, rather than the inverse.
It is more complicated than you pretend. Again, look at the image I posted of CPM-M4, which has 3-4X the carbide volume of AEB-L. CPM-M4 is a high-carbide steel and the "edge-structure" between it and AEB-L would be almost indistinguishable, the Charpy data I've seen suggests that toughness would be about the same, but CPM-M4 can obtain MUCH higher hardness for even more edge-stability and it is already much more wear-resistant due to the carbide volume. Where AEB-L wins is cost (it's cheaper) and corrosion resistance (it's stainless).
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Choice of steel gives you carbon and alloy content, higher carbide steel requires higher carbon which allows for higher hardness which is why CPM-M4 can achieve 65 Rc even after tempering and AEB-L cannot. Above 0.5% carbon, the excess carbon doesn't play a role in martensite hardness, instead it forms carbides with allowing elements, including forming cementite with iron. These higher hardness particles contribute to rockwell hardness of the steel. Clear?
Why not just present S125V as a comparison to AEB-L while you are at it? I presented the micrograph of CPM-M4 as a closer comparator, but it is STILL more carbide-rich than AEB-L and yet... not all that distinguishable. Same grain size, same carbide size, edge-stability will be the same. CPM-3V is closer in carbide content to AEB-L, i didn't see you present that. But you think CPM-154, with >17% large chromium-carbide aggregates, is the "very best" of powder steels? That is NOT "fact", that is most definitely "opinion".
