So, you are thinking of buying a knife and budget is of no real concern, and you have owned a Japanese knife for years, so what do you buy? First, no steel is truly rust proof, with the addition of chromium in an alloy the chromium will bond with itself forming a film that will reduces oxidation and makes life easier.
However, it is key to understand steel basics to understand how knives are forged:
Chemical elements in steel:
- Iron (Fe): Main element in steel.
- Carbon (C): Key element in steel. It gives steel the possibility to be hardened during the process of heat treatment. It reduces resistance to corrosion and makes steel brittle.
- Chromium (Cr): strongly increases the corrosion resistance of steel, and to a certain level increases its hardness.
- Manganese (Mn): improves the structure of steel and increases the possibility for higher hardening of steel.
- Vanadium (V): the key element in increasing the hardness of steel. It increases the possibility to have a sharper blade and maintains the sharpness for a longer period.
- Molybdenum (Mo): increases the resistance to corrosion, it is frequently present in corrosion-resistant steel, and it helps maintain the hardness and the power of steel in case of temperature changes.
- Silicon (Si): increases the positive effects of chromium (C). It increases the hardness and the power of steel.
- Cobalt (Co): for higher hardness and corrosion resistance.
- Tungsten (W): highly increases the wear resistance of steel.
- Phosphorus (P): impurity, which is present in all types of steel in small quantities.
- Sulfur (S): impurity, which is present in all types of steel in small quantities.
Steel is a compound mostly of iron and carbon. Yet to be classified as high-carbon steel, it needs to have anywhere from 0.6% to 1.7% carbon by weight. Knives made of high-carbon steels need extra attention with maintenance, wiping them dry after every use and improper maintenance will develop corrosion and rust stains, frankly a pain in the ass for most home chefs.
White steel is extremely pure steel with a high percentage of carbon and no additional ingredients, but it can contain some phosphorus (F) and sulfur (S) as impurities. There are two types of white steel, white steel #1 and white steel #2 but the difference lies in the amount of carbon content, and of course the knife maker.
White steel #1 contains iron (Fe), carbon (C ) 1.25 – 1.35 %, manganese (Mn) 0.20 – 0.30 %, phosphorus (P) 0.03 %, sulphur (S) 0.004 % and silicon (Si) 0.10 – 0.20 %.
White steel #2 contains iron (Fe), carbon (C ) 1 – 1.15 %, manganese (Mn) 0.20 – 0.30%, phosphorus (P) 0.03 %, sulphur (S) 0.004% and silicon (Si) 0.10 – 0.20 %.
Now, if we add chromium and tungsten to extremely refined white steel, we get blue steel. Due to the additives, blue steel is more durable, more corrosion-resistant, but above all, it has better “kirenaga”, which is a Japanese word for the duration of sharpness. Knives made of Blue steels are primarily used in Japanese restaurants, where the chef needs a knife which stays sharp for a long period of time. The same applies to blue steel one and two, carbon content.
Blue steel #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 %, sulphur (S) 0,004 % and silicon (Si) 0.10 – 0.20 %.
Blue steel #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 %, sulphur (S) 0.004 %, silicon (Si) 0.10 – 0.20 % and tungsten 1.00 – 1.58 %.
Blue steel is also named Aogami Super steel made by Hitachi, and it can contain higher (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 %, phosphorus (P) 0.03 %, sulphur (S) 0.004 %, silicon (Si) 0.10-0.20 %, tungsten 2.00 – 2.50 % and vanadium (V) 0.30 – 0.50 %.
By adding chromium (Cr) to steel we increase its resistance to corrosion. Chromium oxide forms a protection film on the surface of steel, which prevents the contact between iron and water or oxygen.
For premium knives, the higher carbon content is the more expensive knife but it also depends the knife maker and his ranking. But no doubt higher carbon allows for a sharper cutting edge. But do not confuse these knives with stainless steel, because these must have a chromium content of more than 12%. While all steel contains carbon, typically steels that do not contain chromium are referred to as carbon steels.
The differences between high carbon steel can be subtle, but each knife experience becomes obvious. Below we explain the differences between white steel, blue steel, as well as the different types of each.
(These two knife photos are my Blue Steel #1 and Blue Steel #2)
White steel is made from finely grained carbon steel that lacks a lot of contaminates within the iron, meaning that knives made from white, high-carbon steel sharpen into a razor-like edge. Many sushi chefs use white steel knives because the cut exactly as the chef demands. But white steel varies in its level on carbon content and white has the highest and will, therefore, hold its cutting edge the best. However, it is also brittle.
As stated above, steel consists of iron and carbon but different alloys can be added to create different types of steel. For example, stainless steel is created from added chromium. Blue steel has tungsten and chromium added to the iron and carbon to create an easier tempering process and also a knife that holds its edge longer than a white steel knife.
Blue steel is more complex and is engineered differently and the white steel required more know-how to pull the full potential, but I wouldn’t say one is noticeably better when sharpened correctly.
All made from white steel, they are very low in contaminates. In the end, blue steels have high carbon 1.1-1.5% and 0.5% chromium for carbide formation, and a tungsten for edge life with added vanadium for wear resistance. Typically blue super has the longest edge life, has the best edge formation and the best toughness.
If you need help just ask.