ATS-34 Stainless Steel for Knife Blades
Hitachi ZDP-189 Stainless Steel
ZDP189 is a fairly recent super-steel that has come to the market from Hitachi, with many people claiming that it is a rip-off of Cowry-X, another Japanese stainless steel that uses 3% Carbon and 20% Chromium. Though many claim that it is the same steel due to similar properties and composition, there is no conclusive evidence that it is.
One of the most remarkable things about ZDP189 is that it can be hardened to RC 65-67 without any problems with chipping, at least nothing in my experience. Sharpening this steel is not easy, and sharpening it with Ceramic stones and rods can cause problems especially when using a lot of pressure as it can cause the steel to chip if the angle is very acute. This steel is extremely hard and can take a very keen edge, and thus taking care when sharpening is important.
I found that sharpening with diamond rods with very light pressure was the best way to maintain this blade. Some people have reported excellent results sharpening with Japanese water stones as well according to Cliff Stamp.