Yoshida Hamono is located in Saga prefecture, a very rural area on the island of Kyushu. Like many blacksmiths in rural areas, they specialized in making farming tools such as sickles and hoes, but they are nationally recognized for their incredible kitchen knives. The first generation of the Yoshida family was, like many, a swordsmith. After WWII, they decided to open a small workshop to produce knives and other steel tools, and in 1971 they expanded to a large scale production to meet a growing demand from all over Japan. They invested early in modern machinery that made large-scale production possible, which is one of the reasons why they have the ability to clad their own steel, rather than buying it pre-laminated. Because Saga is not a major production center for knives and there are not many other craftsmen, they have built a facility that can handle the knife making process entirely from start to finish, whereas most knife-makers outsource their steel lamination and sharpening.
In 2017 when the ZDP-189 became first available, Osamu Yoshida quickly purchased the steel and tried it out. He was amazed by how insanely sharp the steel could get and how long it would keep its edge, so he started making kitchen knives using this super steel. Despite being hard steel to deal with, 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 sub-zero heat treat their knives to purify the steel, which allows the knife to perform and sharpen better. This is done after quenching, by treating the knives with liquid nitrogen to remove excess retained austenite which hasn’t been converted to martensite. This prevents the knife from bending with time by “stabilizing” its structure. While scientific gibberish to most, this is a seriously big deal in the knife making world.
