Like any number of knifemakers, but certainly not all, The Nubatama knifemaker has kept this information proprietary. Yes this is frustrating to steel junkies, but consider the fact that even two vendors making white steel knives can get very different results. Try to get the details of HOW they temper and forge their blades and you don't get answers to these questions. The Nubatama knifemaker DOES make [excellent] white and blue steel knives at a lower cost, but his black steel formulation is proprietary. I don't know the formulation so I can't disclose it. This certainly makes for a tougher sale on my part.
Consider this from the knifemaker's perspective. You open up the kimono to reveal all and guess what happens? Another knifemaker immediately begins duplicating your product. Now if they are a larger company you may be undercut and pushed out of business and wind up working FOR the larger company and paid a pittance for your work and nothing for your efforts to come up with the initial product.
I have run into this problem with MANY products that I have introduced to the market, so I have full sympathies for the knifemaker in this regard. It's no fun seeing others making profit from your IP when you are unable to defend it. But it can and usually does happen.
What I can say about the steel comes from my experience with it and the experience of my customers and what I can share. It is a steel that develops a patina, so it is not stainless. Edge retention is exceptionally high. It is far easier to sharpen than your high vanadium steels, so the combination of edge retention and easy sharpenability makes it exceptional. If you like sharpening your knife everyday, this is not the knife for you
It holds up very well in a commercial or home environment. It takes natural stone and synthetic stone edges quite well, as well as responding to CBN compounds. I rarely do more than stropping the edge typically at 0.75 microns or 24000 grit. If I touch it up I rarely go below a 15k Nubatama stone. The original 'factory edge' is done by a sword polisher, who also does the custom engraving, using natural stones to produce the edge. I have been told that Rockwell hardness testing produced values of HRC 64 and that the forging process requires higher temperatures and more precise control than what is required for Hitachi white or blue steels.
Hope this information helps.