HAP-40
Powder steel at 68 HRC: holds its edge 3 to 5 times longer.
Gyuto
Japanese chef's knife: all-round for vegetables, meat and fish.
210 mm
Long: big boards, large vegetables, pro or enthusiast use.
When HAP 40 first became available, Osamu Yoshida quickly bought the steel and tried it out. He was amazed at how incredibly sharp the steel could become and how long it would hold its edge, so he began making kitchen knives using this super steel. Although it is a difficult steel to handle, he feels a great sense of accomplishment when he forges with it compared to other steels.
In addition to laminating their own steel, they also treat their knives with sub-zero heat to purify the steel, which allows the knife to work better and sharpen better. This is done after quenching, treating the knives with liquid nitrogen to remove excess retained impurities that have not been converted to martensite. This prevents the knife from bending over time by "stabilizing" its structure. While this is scientific mumbo jumbo for most, it is a big deal in the knife making world.
The secret of this knife lies in its hard core made of a somewhat exotic Hitachi HAP-40 steel, which falls into the category of modern, technologically advanced steels. HAP-40 is thin enough to sharpen very well, and knives made from it retain their edge 3-5 times longer than traditional knives. An interesting fact is that because it is a powdered steel, it has a very low chromium content (about 4%) and can react like a high carbon steel under specific circumstances.
This steel is heat treated to an incredible 68 HRC, but it can still be sharpened relatively easily on whetstones. It is extremely durable and therefore less likely to chip along the edge than the steel used in traditional knives.
