Steel and Heat Treatment
The steel is the soul of a knife, comparable to the engine of a car. Without a powerful engine, a car won’t be fast. Without good steel, a knife won’t cut well, at least not over a longer period of time.
The steel defines the basic properties of a knife, in the areas of
- how sharp a knife can become
- how long it will stay sharp
- how resistant it will be to stains and corrosion
- how resistant the edge will be to damage and chipping
Whereas sharpness and edge retention define the cutting performance of a knife, corrosion resistance and toughness define the usability of it in daily kitchen life. The potential of a knife to excel in those categories depends on the choice of steel, but unlocking this potential depends on its heat treatment, which is explained in different chapters of this site.
What is in a knife steel?
Knife steel largely consists of iron, in small traces Silicon, Mangan, Phosphorus and Sulfur (which inadvertently are added during the production process), and Carbon as the most important alloy. The Carbon content defines the potential hardness of a steel.
When heated, Carbon and other elements in the steel create a compound that is called carbides. In a simple steel, Carbon will form carbides with Iron, called Cementite. If other carbide forming elements are added to the steel, different carbides will be formed and the material properties changed.
Some of those carbide forming elements are Chromium and Molybdenum, and are added to increase corrosion resistance*. Vanadium and Tungsten both form hard carbides, increase toughness and abrasion resistance. Theoretically Tungsten could also be used for improving corrosion resistance, but is considerably more expensive than Chromium, which is why Chromium is preferred for that purpose. Cobalt doesn’t form carbides, but helps to improves microstructure and amplifies the properties of other alloys. It's one of the rarer elements in steel.
*Steel with Chromium content over 13% is called stainless (note: not stain-free!). Steel low on Chromium or without it is called carbon steel and corrodes easily.