So what is the finest particle size micro grain carbide for purposes of obtaining the sharpest possible polished carbide cutting edge? I know about "breaking in" edges, dulling the edge, chipping etc. Most interested in the finest grain size, strongest, hardest carbide composition that will give the smoothest polished surface and near razor edge sharpness. Toughness to resist chipping is important but for very fine cutting on an extremely smooth and rigid machine edge wear is the failure mode.
Strongest and hardest are opposites in carbide. More cobalt in the mix makes the tool stronger, less cobalt makes for a harder tool.
Real high cobalt content makes for good pulverizing hammers.
Low cobalt content makes for good fine finishing tools but they chip and break easily.
The primary advantage of micrograins is that cracks do not propagate as easily through them. Since the grains are smaller the cracks have to turn more times as they reach the boundary of each grain. This makes the tool harder to break in half. This is kinda simplified but hopefully you get the idea.
Until you are working with 2000-3000 grit wheels and very specialized machines grain size is not a problem for edge sharpness.
One of the things I see a lot on the net that always makes me roll my eyes is the statement that you can't get a razor sharp edge on carbide. This is absolute bull.
People see a 2000x picture of carbide structure and think "Oh yea, I see you can't sharpen it cause each particle falls out of the bond."
Ever look at a razor blade or a hand stoned piece of HSS at 2000x ? Kinda looks like a picture of the Rocky Mountains.
Fine grain carbides are at the 1-2 micron size. You need at least 1500x and very good optics just to see the particles.
Micrograins are 0.5 to 1 micron. This is approaching the resolution limit of any optical microscope made. The grooves from your 400 grit grinding wheel will span 10 or more grains.
Nanograin carbides, which are only used in very strange circumstances due to their cost, can only be seen using a SEM.
Getting a sharp edge is all about grinding technique. The wheel must enter the part at the cutting edge keeping the material in compression.
If you surface grind a piece of flat carbide and look at it under a reasonable magnification the right edge where the wheel is entering the part will be clean and chip free (assuming a good grinding wheel and good coolant flow).
The trailing left side of the part will be chipped. The size of these chips will depend on the wheel being used but they will be 10 to 100s of grains in size.
Every few years I'll see a rookie at the sink, red paper towels everywhere, and a trail of blood on the floor leading back to his machine.
I'll say "What happened?" and inevitably the answer is "I wiped off the edge on one of the finishing blades with my finger".
I give them the where were you when they passed out the brains look and ask "Who wants to drive numnuts to the hospital so they can stitch up his fingers?".
Bob