ELEMENTS OF STEEL
(The picture on the left shows unworked iron and steel, and a forge burning brightly. These are the beginnings of a Sakai knife.)
IRON - Primary element of steel
CARBON - The most important element for hardening, and for strength
MANGANESE - Grain structure of the steel, hardening and wear resistance
MOLYBDENUM - Prevents brittleness and maintains the steel’s strength at high temperatures
COBALT - For hardness and corrosion resistance
CHROMIUM - Important for corrosion resistance. Steel having 11.5% to 13% chromium is considered stainless
VANADIUM - Essential for giving the blade its ability to harden. Also for wear resistance and toughness of the blade, as well as the ability to take a very sharp edge.
Types Of Japanese Steel
Carbon knives are highly recommended for work that requires precision, as they have an extremely sharp, fine edge. Carbon steel knives are made of iron combined with 0.1 - 2.7% carbon. Carbon knives are very easy to sharpen despite their hardness, and will become significantly sharper than stain resistant knives. However, please be aware that carbon knives should be wiped dry even during use to avoid rusting. Acidic ingredients will cause the steel to discolor. This discoloration will not affect the functionality of the knife, however, Korin does offer a service to clean minor rusting.
-White Carbon Steel #1 (Shiroichi-ko, Shirogami #1)
White steel #1 is the purest form of carbon, making it the closest material to tamahagane steel, which was originally used to craft Japanese swords. Forging a knife out of white steel #1 is extremely difficult and very few highly skilled craftsmen are still able to forge kitchen knives with this material, making knives made out of white steel #1 exceedly rare. Using a knife forged out of white steel #1 also requires great skill, as these knives are brittle and difficult to maintain. However knives forged out of this material will have the sharpest edge achievable.
-White Carbon Steel #2 (Shironi-ko, Shirogami #2)White steel #2 is the most commonly used type of white steel. This steel achieves a harmonious balance between sharpness and brittleness, making it easier to use than white steel #1.
-White Carbon Steel #3 (Shirosan-ko, Yasuki-ko)
White steel #3 has a slightly lower carbon content than white steel #2. The material is therefore not as hard or pure as other white steels, but if sharpened properly it can attain a similar edge. This grade of steel was developed and manufactured in Shimane prefecture in the Western region of Japan.
-Blue Carbon Steel #2 (Aoni-ko, Aogami #2)
Blue steel #2 is a mixture of chromium, tungsten, and white steel #2. The addition of chromium and tungsten to white steel gives it added hardness, making it a good compromise for those who want a carbon knife with a longer edge retention.
Stain Resistant Steel
Adding at least 12% chromium-oxide to the basic mixture of iron and carbon produces the stain resistant steel commonly used by Japanese knife brands. A chromium-oxide film forms on the metal’s surface that prevents the iron from coming into contact with oxygen and water. However, stain resistant knives must still be washed after each use as salt and acidic ingredients can erode the chromium-oxide film and reduce the knife’s rust resistant.
As Technology advances, new types of steel are being developed that increase the performance of carbon steel with practical benefits of stain-resistant steel. High-carbon, stain resistant steels such as Ginsan-ko, Inox, VG-10, and 8A are becoming increasingly popular with professionals and are used in the production of both traditional and western style knives.
Ginsan-ko is a stain resistant steel that is created by adding 13% additional chromium to white steel. By using high quality white steel to produce a stain resistant blade, this makes a great alternative to carbon steel traditional Japanese knives. High carbon stain resistant steels such as Ginsan-ko, Inox, VG-10, and 8A are becoming increasingly popular among professionals for their easy maintenance.
Cobalt is a naturally occurring inclusive mineral found in various ores used in the preparation of magnetic, wear-resistant, and high strength alloys. Knife manufacturers who are forging knives from metals such as VG-10 and Ginsan-ko have an added benefit due to the cobalt content already present in these two types of steel.
Tamahagane is a rare and precious metal that is used to forge the katana. Tamahagane steel is only produced two to four times a year due to the tremendous amount of the labor, material and wasted material that is required to make a very small amount of it. 13 tons of iron sand and 13 tons of coal must be smelted, then hammered for three days and three nights to produce a mere 2.8 tons of raw steel (kera). Once the kera is produced, less than 1 ton of the kera is considered tamahagane steel. The 1 ton of tamagane steel is controlled by the Society for Preservation of Japanese Art Swords, which is sponsored and established by the Japanese Government. The tamahagane steel is sold exclusively to katana craftsmen a few times a year. However, even within the 1 ton of tamahagane steel only 200 kg is considered usable high quality A1 steel, and katana craftsmen are limited to 10 kg of this A1 steel.
Damascus steel is layered hammered steel with a symmetrical 50:50 bevel. The number of layers of steel varies per knife and these knives are becoming increasingly popular for their beautiful patterns that the layered steel creates. Damascus style knives are perfect for both left and right handed users and make popular gifts.