Japanese Carbon White steel 2 Knives

Shirogami Steel (White paper) is a Japanese high carbon unalloyed steel manufactured by Hitachi Metals Corporation. Translated, Shirogami means "White paper" (“Shiro” means white, and “gami” means paper). Shirogami Steel got its name from the color of the wrapper paper in which the manufacturer wraps it. Steel belongs to the "Gold" (etalons) group of steels with a high degree of purification and the simplest composition. It is a famous fact that Japanese bladesmiths value old traditions very much. The production process, the spiritual content of their craft, the materials used, and the functional properties of the final product are very important in Japan. Shirogami steel is a result of one of the oldest technologies in the production of high-carbon steels, the so-called "pure steels" (free of alloying elements). The simplest, oldest, and at the same time the ideal concept of steel - just iron and carbon. Shirogami steel is just close to this ideal. This steel allows you to achieve almost a reference cutting performance, which is why it is so prized in Japan from time immemorial. In the assortment of Hitachi Metals there are several types of Shirogami slightly differing in purity and carbon content. Shirogam i#1(White paper one); Shirogami #2(White paper two) - High hardness and Sirogam i#3 - Middle hardness (White paper three);

Why do Hitachi Metals make three different types of steel on one name? What are the reasons and differences?

Shirogami #1 and #2 have the same level of purity. Only a small difference in carbon content. Shirogami #1 has a 1.25-1.35% of carbon; highest hardness; longest cutting edge holding but a bit hard to sharp;
Shirogami #2 has a 1.05-1.15% and hardness is a little bit lower; less cutting edge holding but easy to sharp;
Shirogami #3 less purity and less hardness; carbon about 0.80-0.90%. Very easy to sharpen.
Knives made of Shirogami steel have a perfect cutting ability easy to sharpen and hold a cutting edge well. Many experts consider the cutting of Shirogami steel to be a reference but like all carbon steels, Shirogami is not resistant to corrosion and requires careful maintenance. Usual hardness range 60-64 HRc.