Steel categories
In essence, a kitchen knife is simply a piece of steel with a handle. A good kitchen knife is made of steel. Good steel should be considered as a base, a potential which, thanks to the processes of forging, bending and shaping the blade, can only be exploited by experienced craftsmen.
There are three main categories of steels used in the manufacture of kitchen knives. Each category has its advantages and disadvantages, depending on the use of the knife.
High Carbon Steels (Traditional Japanese Steels)
Corrosion resistant steels (VG10)
Powder steels (ZDP-189 or R2)
But before we dive into different types of steel, let's first explore the main chemical elements of steel and their effect on the characteristics of the kitchen knife.
CHEMICAL ELEMENTS IN STEEL AND THEIR EFFECT:
Steel is made up of iron (Fe), carbon (C) and smaller amounts of other elements. Carbon (C) is the key element in steel. Without carbon, steel could not be forged or bent. More carbon means harder steel. Steel can contain between 0.1 and 3% carbon.
CHEMICAL ELEMENTS:
Iron (Fe): main steel element. Carbon (C): key element in steel. This gives the steel the ability to be hardened during the heat treatment process. It reduces corrosion resistance and makes steel brittle. Chromium (Cr): greatly increases the corrosion resistance of steel and, at a certain level, increases its hardness. Manganese (Mn): improves the structure of the steel and increases the possibility of further hardening of the steel. Vanadium (V): the key element to increase the hardness of steel. This increases the possibility of having a sharper blade and maintains sharpness longer. Molybdenum (Mo): increases resistance to corrosion, it is often present in stainless steels and helps to maintain the hardness and strength of the steel in the event of temperature changes. Silicon (Si): increases the positive effects of carbon (C). This increases the hardness and strength of the steel. Cobalt (Co): for greater hardness and corrosion resistance. Tungsten (W): considerably increases the wear resistance of steel. Phosphorus (P): an impurity present in small quantities in all types of steel. Sulfur (S): impurity present in small quantities in all types of steel.
Yasuki Steel
The Japanese sword represents traditional Japanese craftsmanship. Made of Japanese steel with iron sand as the raw material, the sharpness of a Japanese sword is well known around the world. Hitachi Metals Co., Ltd. produces Yasuki steel from raw materials for Japanese steel. In the past, iron sand with a high degree of purity could be excavated from the mountains of Tottori and Shimane prefectures and refined into Tama Hagane using traditional processing (Tatara). Hitachi further improved its techniques by establishing its Yasuki plant for steelmaking. The steel is called blue steel, white steel and yellow steel in order of quality. These names are said to be derived from the fact that blue and white papers were used to wrap the finished steel for identification purposes.
The Honyaki knife
They can only be made by a few skilled artisans in Japan using the same method as the traditional Japanese sword. It is an art to work with traditional Japanese techniques, with exceptional sharpness and durability. The production is very small, due to the difficulty and time-consuming process. Having owned a few, these knives are amazing. If you are a collector or just a fan of Japanese kitchen knives, it is a must. Expensive certainly, but when you understand the essence of the work for the manufacture of this object, you realize that the price is only fair compensation for this masterpiece.
High Carbon Steels (Traditional Japanese Steels)
High carbon steels are the preferred choice of Japanese chefs. Due to their high carbon (C) content, these steels can be forged with high hardness (60+ HRC) while being very easy to resharpen. Knives made from high carbon steels require special care in maintenance, wiping them down after each use, oiling the blade occasionally, and developing a patina over time. Improper maintenance will develop corrosion.
Japanese blacksmiths have always chosen steel carefully. The traditional katana is made from tamahagane steel, produced only in the western part of Japan. Traditional Japanese steel is made using similar techniques. This steel is used in the manufacture of knives that undergo treatment processes similar to those of the katana. There are two main types of steel: shiro-ko (#1, #2 white steel) and ao-ko (#1, #2 blue steel, and Aogami steel).
White Steel or Shiro-ko (Shirogami)
White steel is an extremely pure steel with a high percentage of carbon and no additional ingredients (it may contain phosphorus (F) and sulfur (S) as impurities). There are two types of white steel: white steel 1 and white steel 2. Forging white steel is extremely difficult and requires highly skilled craftsmen. A knife made from this steel has an extremely sharp edge, but it is brittle and susceptible to cracking.
White steel no.1 contains iron (Fe), carbon (C) 1.25-1.35%, manganese (Mn) 0.20-0.30%, phosphorus (P) 0 .03%, sulfur (S) at 0.004% and silicon (Si) at 0.10 to 0.20%. It is very popular with professional chefs preparing traditional Japanese cuisine because it can be refined to an extremely fine edge. It has a very good cutting edge and is easy to resharpen.
White steel no.2 contains iron (Fe), carbon (C) 1 – 1.15%, manganese (Mn) 0.20 – 0.30%, phosphorus (P) 0.03%, sulfur (S) 0.004% and silicon (Si) 0.10 – 0.20%. It has minimal impurities and a very fine grain structure, so it is ideal for fine cutting tools such as traditional Japanese style knives. It also has very good cut retention and is very easy to resharpen. Recommended for new users of traditional Japanese knives.
Corrosion resistant steels
By adding chromium (Cr) to steel, we increase its resistance to corrosion. Chromium oxide forms a protective film on the surface of the steel, which prevents any contact between iron and water or oxygen. If the base steel alloy contains 12% or more chromium, we call it stainless steel. Even stainless steel kitchen knives should be wiped dry after use, especially if you are cutting fruits and vegetables that contain acids (lemon, onions, tomatoes, etc.). If we leave the knife dirty and wet for a long time, even the stainless steel can corrode.
Due to technological development, we have witnessed the emergence of new types of steels, which combine the quality of steel with a high percentage of carbon and the practicality of corrosion-resistant steel. High carbon (C) and corrosion resistant steels are popular with professional chefs today.
VG-1 stainless steel
(Takefu Special Steel Co., Ltd.) is a quality Japanese high carbon stainless steel popular for making cutlery. It has good corrosion resistance, good edge retention and good sharpness. The hardness of Rockwell is also relatively high.
The VG-10
It represents the best of the corrosion resistant steel offering. It contains iron (Fe), carbon (C) 0.95 – 1.15%, chromium (Cr) 14.50 – 15.5%, cobalt (Co) 1.30 – 1.50%, manganese (Mn) 0.50%, molybdenum (Mo) 0.90 – 1.20%, phosphorus (P) 0.03% and vanadium 0.10-0.3%. It is one of the most popular and well-known Japanese stainless steels. It has strong corrosion resistance and can provide very good cutting sharpness and edge retention. VG-10 belongs to the group of steels called “cobalt steels”, but it also contains vanadium, which improves its strength and toughness.
Ginsan
Known as Ginsan-ko or silver no.3, containing iron (Fe), carbon (C) 0.92 – 1.10%, chromium (Cr) 13.00 – 14.5%, manganese (Mn) 0.60 – 1.00%, phosphorus (P) 0.03%, sulfur (S) 0.02% and silicon (Si) 0.35%. It is a very fine grain stainless steel that can achieve sharpness and cut retention comparable to some high carbon steels. It has even been used to create corrosion-resistant versions of traditional Japanese single-edged knives. It is very popular with professionals and cooks. It is generally considered to be slightly easier to sharpen than VG-10. A favorite steel in this section. Its hardness is well balanced 60-61 HRC (in general).
Blue steel or Ao-ko (Aogami)
If we add chromium and tungsten to extremely refined white steel, we get blue steel. Thanks to the additives, the blue steel is more durable, slightly more resistant to corrosion, but above all, it has a better "kirenaga", the Japanese word for duration and sharpness. Blue steel knives are used in Japanese restaurants, where the chef needs a knife that stays sharp for a long time.
Blue steel no.1 contains iron (Fe), carbon (C) 1.25 – 1.35%, chromium (Cr) 0.20 – 0.50%, manganese (Mn) 0.20 – 0.30%, phosphorus (P) 0.03%, sulfur (S) 0.004% and silicon (Si) 0.10 – 0.20%. The additional carbon and tungsten improve tool life retention and toughness. This steel is perhaps most commonly seen in high quality traditional Japanese single edge knives.
Blue steel no.2 contains iron (Fe), carbon (C) 1.05 – 1.15%, chromium (Cr) 0.20 – 0.50%, manganese (Mn) 0.20 – 0.30%, phosphorus (P) 0.03%, sulfur (S) 0.004%, silicon (Si) 0.10 – 0.20% and tungsten (W) 1.00 – 1.58%. Many chefs have noted that this steel is similar to No.2 white steel in terms of edge sharpness. However, it has slightly better edge retention.
Aogami Super Steel
Contains iron (Fe), carbon (C) 1.40 – 1.50%, chromium (Cr) 0.30 – 0.50%, manganese (Mn) 0.20 – 0.30%, molybdenum (Mo) 0.30 – 0.52% and phosphorus (P) 0.03%, sulfur (S) 0.004%, silicon (Si) 0.10-0.20%, tungsten (W) 2.00 – 2.50% and vanadium (V) 0.30 – 0.50%.
It is one of the greatest Japanese carbon steels in terms of performance. In addition to containing more carbon, chromium and tungsten than blue steel No.1, it also contains molybdenum. It has very good sharpness and excellent edge retention. It is also capable of reaching high hardness without being brittle. Therefore, many knife enthusiasts rank aogami super among the best high carbon steels in the world.
Powder steels
Tamahagane is considered the mother of all steels. This is always the case when we talk about katanas and Japanese swords, but modern science is producing new special steels, much more suitable for kitchen blades, such as powder steels. Such steel is more advanced, harder, sharper and has one thing in common with the old tamahagane: they are both made in Japan! Japanese high-tech steel is forged the old-fashioned way by the same families of blacksmiths who made katanas. It is the fusion of the old and the modern to produce the best knives or better, the sharpest!
Powder metallurgy steels are steels often used in industrial applications that require tools capable of cutting steel and withstanding extreme forces and temperatures. Powder steels are made using a different manufacturing process, resulting in richer chemical ingredients and a very fine-grained structure with excellent metallurgical properties.
Knives made from these steels are rare, difficult and expensive to produce, and only the best knife makers are able to forge, laminate and heat treat them. It is a very difficult process that requires a lot of experience, knowledge and a smith inclined towards perfection. Properly made powder steel knives are among the elite of kitchen blades.
Advantages of powder coated steel kitchen knives
Very high hardness up to 67 on the Rockwell C scale (HRC) and good toughness.
Satisfactory corrosion resistance.
Easy to sharpen steel, with a fine microstructure for a fine edge and the ability to stay sharper longer than other traditional steels.
ZDP-189
“Super steel” powder metallurgy. It has a similar chemical composition to Cowry X and offers a similar level of performance. Unfortunately, due to the difficulty of producing ZDP-189 and the special forging and heat treatment, few blacksmiths are able to process it.
Obviously these knives are very expensive.
3.00% | 20.00%
R2 OR (SG2)
It is also a powder metallurgy "super steel". Became one of the most popular steels due to its cutting performance, excellent edge retention and high corrosion resistance. Unlike Cowry X and ZDP-189, R2 steel kitchen knives are much more available in the market.
C 1.25-1.45% | Cr 14.00-16.00% | Mo 2.3-3.3% | V 1.8-2.2%
HAP-40
It is a powder metallurgy “super steel” from Hitachi Metals Ltd. Its rich chemical composition and fine microstructure produce knives that have an exceptional balance between hardness and edge retention.
C 1.27-1.37% | Cr 3.70-4.70% | W 5.60 to 6.40% | MB 4.60-5.40% | V 2.80-3.30% | Co 7.50-8.50%
Cowry X or (Daido Steel Co., LTD.)
It is a powder metallurgy "super steel" with a high carbon and chromium content. Unfortunately, it is expensive and technically difficult for knife makers to use. These superb knives are therefore rather rare.
3.00% | 20.00% | MB 1.00% | 0.3%