Stainless steel...not powdered... 60hrc. Takes a pretty good edge for stainless, holds it decently well, and is pretty tough (it takes abuse well). A lot of pro cooks here in LA are using them now for those very reasons.
I cant get quite as good of an edge off of them as i can my gesshin ginga, the edge retention is not quite as good as my INOX Honyaki (which holds an edge pretty well considering how thin it is), and the toughness is not as good as an a-type, but its a good balance in all areas. Not too thick, not too thin. Not too hard, not too soft... well you get the point.