In essence, a kitchen knife is simply a piece of steel with a handle. A good kitchen knife is made of steel. Good steel must be considered as a base, a potential which, thanks to the forging, bending and shaping of 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)
Powdered steels (ZDP-189 or R2)
But before diving 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.
STEEL CHEMICAL ELEMENTS AND THEIR EFFECT
Steel is made up of iron (Fe), carbon (C) and smaller amounts of other elements. Carbon (C) is the key steel element. Without carbon, steel could not be forged or bent. More carbon means harder steel. The steel can contain between 0.1 and 3% carbon.
Iron (Fe): main steel element.
Carbon (C): key steel element. This gives the steel the possibility of being 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 the resistance to corrosion, it is often present in stainless steels and contributes to maintain the hardness and the power of the steel in the event of temperature change.
Silicon (Si): increases the positive effects of carbon (C). This increases the hardness and power of the steel.
Cobalt (Co): for greater hardness and corrosion resistance.
Tungsten (W): considerably increases the wear resistance of steel.
Phosphorus (P): impurity present in small amounts in all types of steel.
Sulfur (S): impurity present in small quantities in all types of steel.
The Japanese sword represents traditional Japanese crafts. Made of Japanese steel with iron sand as the raw material, the edge 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 in the mountains of Tottori and Shimane prefectures and has been refined to become Tama Hagane using traditional treatment (Tatara). Hitachi further improved its techniques by establishing its Yasuki factory for the manufacture of steel. 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 package the finished steel for identification.
The Honyaki Knife
They can only be made by a few skilled craftsmen in Japan using the same method as the traditional Japanese saber. It is an art to work with traditional Japanese techniques, with exceptional sharpness and durability. Production is very small, due to the difficulty and the tedious process. To have a few, these knives are amazing. If you are a collector or simply a fan of Japanese kitchen knives, it is a must. Expensive of course, but when you understand the essence of the work for the manufacture of this object, you realize that the price is only fair compensation in the face of this masterpiece.
HIGH CARBON STEELS (TRADITIONAL JAPANESE STEELS)
High carbon steels are the preferred choice of Japanese chefs. Due to their high carbon content (C), these steels can be forged with high hardness (60+ HRC) while being very easy to regrind. Knives made of high carbon steels require special attention during maintenance, wiping them after each use, oiling the blade from time to time, and developing a patina over time. Poor maintenance will develop corrosion.
Japanese blacksmiths have always chosen steel with care. 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 subjected to treatment processes similar to those of katana. There are two main types of steel: shiro-ko (white steel n ° 1, n ° 2) and ao-ko (blue steel n ° 1, n ° 2 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 can 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 is fragile and susceptible to cracking.
White steel no.1 contains iron (Fe), carbon (C) from 1.25 to 1.35%, manganese (Mn) 0.20 to 0.30%, phosphorus (P) to 0 , 03%, sulfur (S) at 0.004% and silicon (Si) at 0.10 to 0.20%. It is very popular with professional chefs who prepare traditional Japanese cuisine, as it can be refined to obtain an extremely fine edge. It has a very good cutting performance 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 a minimum of 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 cutting retention and is very easy to resharpen. Recommended for new users of traditional Japanese knives.
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, blue steel is more durable, slightly more resistant to corrosion, but above all, it has better "kirenaga", a Japanese word for duration and sharpness. Blue steel knives are mainly 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 further improve the retention of cutting performance and toughness. This steel is perhaps most often seen in traditional Japanese high-quality single-edged 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 very similar to No.2 white steel in terms of sharpness of edge. However, it has slightly higher 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 largest Japanese carbon steels in terms of performance. In addition to containing more carbon, chromium and tungsten than blue steel No.1, it also includes molybdenum. It has very good sharpness and excellent edge retention. It is also capable of achieving high hardness without being brittle. Therefore, many knife enthusiasts rank the super aogami among the best high carbon steels in the world.
CORROSION RESISTANT STEELS
By adding chromium (Cr) to the 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 and dried after use, especially if you are cutting fruits and vegetables containing 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. Today, high carbon (C) and corrosion resistant steels are very popular with professional chefs.
VG-1 stainless steel
(Takefu Special Steel Co., Ltd.) is a high quality, high-grade Japanese 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.
It represents the best of the corrosion resistant steel offer. 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 renowned Japanese stainless steels. It has a high resistance to corrosion and can provide very good cutting clarity and good edge retention. VG-10 belongs to the group of steels called "cobalt steels", but it also contains vanadium, which improves its strength and toughness.
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 which can achieve the sharpness and retention of cut comparable to some steels with high carbon content. 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 the VG-10. A steel favorite in this section. Its hardness is well balanced 60-61 HRC (in general).
Tamahagane is considered the mother of all steels. It used to be the case, or it still is when we talk about katanas and Japanese swords, but modern science produces new special steels, much more suited to kitchen blades, like powdered steels. Such steel is more advanced, harder, sharper and has something 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 best fusion of old and modern to produce the best knives or better, the sharpest!
Steels for powder metallurgy are steels often used in industrial applications which require tools capable of cutting steel and withstanding extreme forces and temperatures. Powdered steels are produced using a different manufacturing process, which results in richer chemical ingredients and a very fine grain structure with excellent metallurgical properties.
Knives made from these steels are rare, difficult and expensive to produce, and only the best cutlers are able to forge, laminate and heat treat them. It is a very difficult process that requires a lot of experience, knowledge and a blacksmith inclined to perfection. The steel knives of the properly manufactured powders 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 sharp longer than other traditional steels.
The most common and suitable powdered steels for kitchen cutlery:
“Super steel” powder metallurgy. It has a chemical composition similar to that of 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.
C 3.00% | Cr 20.00%
R2 or (SG2)
It is also a "super steel" of powder metallurgy. It has become one of the most popular steels due to its cutting performance, excellent cutting edge retention and high resistance to corrosion. Unlike the Cowry X and ZDP-189, R2 steel kitchen knives are much more available on the market.
C 1.25-1.45% | Cr 14.00-16.00% | Mo 2.3-3.3% | V 1.8-2.2%
It is a "super steel" of powder metallurgy from Hitachi Metals Ltd. Its rich chemical composition and fine microstructure make it possible to produce knives which have an exceptional balance between hardness and its conservation of the cutting edge.
C 1.27-1.37% | Cr 3.70-4.70% | W 5.60 to 6.40% | Mo 4.60-5.40% | V 2.80-3.30% | Co 7.50-8.50%
Cowry X or (Daido Steel Co., Ltd.)
It is a “super steel” of powder metallurgy with a high carbon and chromium content. Unfortunately, it is expensive and technically difficult to use for cutlers. These superb knives are therefore rather rare.
C 3.00% | Cr 20.00% | Mo 1.00% | V 0.3%
I hope this article has been able to light up your lanterns and solve the puzzles on steels. I really wanted to write about it, since the choices are many and can be difficult, especially when buying a new knife. This article does not fully summarize all types of steels, it is mainly those which are currently on the market.