ZDP-189 is an ultra high carbon steel knife manufactured by Hitachi Steel. ZDP is the highest carbon concentration (~3%) meaning it will be extremely hard (the hardest) blade tip on the planet however it will have slightly higher corrosion and reduced ductility which may lead to chipping.
High end well known knife brands such as Miyabi (owned by Zwilling who terms the same metal as MC66) use this ultra high carbon steel composition when making Miyabi knife collections.
The ZDP-189 / MC66 has the following specs:
|Elements||ZDP-189 / MC66|
|Quenching Hardness||HRC60 +|
If you're after ultra hard and have time to hone and stone your knife from time to time this is one of the best steels to use - only be careful that the knife needs (like a Ferrari needs) a little more care.