can all knives be equally sharpened?

[Jason B.]

Haha, to look that close we need a SEM

A steel having a "toothy edge" when finished is a product of the sharpening. Just like how D2 takes on a "Orange peel" texture when polished, its not the steel but the lack of polishing that caused the Orange peel. When it comes to comparing sharpness it really takes pushing the edge to the limits, .5 micron and smaller abrasives and hours of tedious polishing to feel a slight difference in tingle to the finger is not something that comes easy. There is way more to it than this knife got sharper than the other.

As you said 3rd gen. 3rd gen PM steel is cleaner than previous steels and has less "junk" mixed in to distort the structure of the edge. When sharpening you can literally describe the finished edge as crisp and clean. Sharpen a lower grade non-PM steel and you will see how burrs, deformations, and debris like to hang out.

 

[hardheart]

You're using some strange terms there. A "radius" to me generally refers to the distance from the center of a circle to the outside. I assume you mean the apex of the edge or the bevel itself?

It's certainly true that D2 and 154CM takes a razor edge much better than S30V, but I have a theory on that. According to Crucible, Chromium carbides are around Rc 66-68 whereas Vanadium carbides are Rc 82-84. I'm thinking because the Chromium carbides are softer, they would be easier to polish to a fine edge compared to vanadium carbides.

That's not to say it can't be done, as I did manage to put an edge on my R.J. Martin Overkill in S110V that can cut free-hanging hair. Though I was not able to get quite as sharp an edge on S90V and CTS-20CP with any consistency. The difference isn't drastic, as they can both whittle hair easily. It's just that I found M390 and Elmax take that stupid sharp edge without as much effort.

Didn't you own a Fantoni folder in S125V in the past? Didn't you observe the same thing with that? Or did you not attempt to take it down to submicron levels? To be honest, I think the difference in sharpness would be subtle, like comparing a 1 micron finished edge to a 0.25 micron edge.

Also, I have to ask how much truth is in the statement that reducing grain size cuts down on hardenability, as CPM-D2 and CPM 154 seems to get as hard as their non-powder counterparts.

As knifenut said, an edge is rounded at high magnification. Verhoeven's paper on knife sharpening experiments has some pretty nice images. You can also check the honing forums on B&B or SRP for some high power pics of razors, and there are multiple other peer reviewed papers online with images from electron microscopy used in knife/razor experiments.

Yes, the whole reason to use large quantities of V is to increase wear resistance, and sharpening an edge is abrasive wear against the steel. Higher amounts of harder carbides increase the time and effort of sharpening. You can have a steel with no carbides, steels with cementite as the only carbide, which is iron carbide, and you can have lots of chromium, tungsten, vanadium, etc carbide. But these carbides can be shaped and polished with the right sharpening media and technique.

The S125V folder did take a long time to sharpen, partially because I was using a jig to hold the angle and was using low pressure. It took more concentration and more passes on the stone. But the steel has the highest working hardness of the stainless CPM grades and 5% more carbide volume than S90V. I did polish it to 0.5 diamond. I also have a 15V custom that had a hair popping edge out of the box.

Decreasing grain size decreases hardenability. Metallurgists caution against too many normalizing and quenching cycles because of this. The larger the grains, the less grain boundary area. Pearlite nucleates from grain boundaries, so reducing the area slows down ferrite/pearlite and increase hardening. As you mentioned there is a trade off of finer grain size meaning greater toughness and shock resistance, while increasing hardness means greater strength and wear resistance.

The CPM steels get as hard because the process creates a homogeneous carbide structure, it isn't about grain size. Grain size changes with heat treatment, you can blow up the grain size of a steel with too much heat. But you can also bring that grain size back down with good temperature through phase changes .