The Japanese ZDP-189 is one of the world’s hardest blade steel types. With its hardness of 65-70 HRC, it is almost matchless. However, its excellent edge retention comes with a certain brittleness. Spyderco, for instance, ceased its production of serrated blades made from ZDP-189, because the teeth of the serrated edge broke off too easily. Apart from Spyderco, who have been using this steel product successfully for many years, it is also used by manufacturers like Al Mar and some Japanese producers.