The world of knife steel can be daunting and overwhelming at times. We hope that this guide helps you to understand some of the steel used to make Japanese Knives.
Steel is an alloy of iron and other elements, but mainly carbon. Just a couple of percent of carbon, gives iron hardness, ductility and tensile strength which pure iron does not have.
Some ‘carbon steel’ knives are made from similar types of steel, although are very susceptible to rusting and must be very carefully looked after. High carbon steels are easier to sharpen and so prized by some chefs.
Whilst basic steel contains mixes of iron and carbon, with stainless steel including chromium and nickel. Japanese steel used for kitchen knives regularly contains two other elements, Vanadium and Molybdenum. The Vanadium increases the strength, wear resistance and toughness of the steel.
It also provides corrosion resistance by contributing to the oxide coating. Molybdenum increases the strength, hardness, harden-ability and toughness. Global Knives use Chromova18 (Chromium, Molybdenum, Vanadium) their own special mix of these steels.
VG-10 is a high grade stainless steel made in Japan. The name stands for V Gold 10, literally meaning ‘gold quality’. It is steel with a high carbon content containing 1% Carbon, 15% Chromium, 1% Molybdenum, 0,2% Vanadium, 1.5% Cobalt and 0.5% Manganese.
Generally considered to be the ultimate stainless steel for kitchen knives, it holds an edge very well, can be sharpened to an extremely fine edge and is very rust resistant. Other materials such as AUS 10, MBS 26 offer slightly different mixes of the above alloy but produce similar results with the knife blade.
Damascus steel is easily identifiable by wavy patterns on the blade. Damascus knives look beautiful and have an allure about them. The procedure to make Damascus steel involves molten layers of metal that are folded over each other.
Typically this is done 32 or 62 times, but can be folded further to create thinner layers. The idea is to fold two different kinds of steel. One soft, but ductile, the other hard, but brittle. The soft layer allows the knife blade to adsorb shock and avoid damage. The hard or brittle layer allows the knife to retain edge sharpness (A bit like VG-10 cores).Mixing the two layers allows the knife to carry characteristics of both hard and soft steels. Damascus knife blades cut easily and hold their edge for a long time.
Ceramic Knives are made from Zirconium Dioxide, which is generally manufactured by dry pressing ceramic ‘zirconia’ powder through sintering. Ceramic knives are prized because they are so much harder than a stainless steel knife, above 80 on the Rockwell Scale. Secondly, ceramic knives are totally inert, meaning that they will not leave a hint of metallic taste on food.
Ceramic knives will hold their edge for a lot longer than steel knives and will not need re-sharpening often. However they will never be as sharp as a steel knife. Ceramic knives are also brittle and the blades may break if dropped or if used when cutting through bones, hard vegetables and frozen food.
3 Ply refers to the three separate and different layers of steel used to make a knife blade. Imagine a sandwich with two layers of bread and a middle layer which is the filling. Knives that are made using 3 ply steel will typically have the middle ‘core’ made from very hard steel, such as VG-10 which will provide the cutting edge of the knife.
However these kinds of ultra-hard materials are usually delicate and brittle. In order to protect against corrosion, these ‘cores’ are covered by an outside layer of softer and more corrosion resistant stainless steel. The benefit is that the cutting edge of the knife is made from the ultra-hard steel to provide the best possible cutting edge, whilst the knife in general is protected by a softer material.
The Rockwell scale is used to measure the hardness of a material. Typically knives range from the mid 40’s to the low 60’s depending on the material used in the blade and the manufacturing method. Knives that have harder blades ultimately can hold a sharper edge.
However blades that are too hard effectively can become brittle. A blade made from steel with a lower Rockwell rating will be softer, will become blunt quite quickly but will be easier to sharpen and will be more robust. Japanese knives (Global, Kai, Kasumi etc) which are typically 55-62 on the Rockwell scale are far harder than their European counterparts (Wustof and Henckels). Their hardness means that they are far sharper and will hold their edges for much longer.
Click here to see a short summary of some other steels used in Japanese knives