Stainless Steel

There is no steel but rusts

Iron(Fe) is a very unstable element and always unites with the other chemical elements when it exists on the earth, that means it has properties to unite with the other elements very easily. That is why we can say the Carbon Steel, which consists of it’s main ingredients iron(Fe), unites with oxygen and that means it rusts easily.

However, if we add more than 12% of chrome(Cr), oxide film(passivation film) is made by a chemical reaction with the chrome(Cr) and oxygen(O) on the surface. This film protects the material form corrosion and is what we call stainless steel. It literally stands for “Stain” ,“less” steel.Because the passivation film has just 1/100mm thickness, it cannot protect the steel perfectly and sometimes get rusty by external factors such as dirt, water, scratches and so on. In other words, stainless steel does not become quite another substance that never rusts by adding chrome but just becomes hard to get rusty being covered by the protection film. This means that there is no steel but rusts.

 Because stainless steel materials used for kitchen knives include carbon(C) can be harden, they rust easier compared to the ones that do not have less carbon(C). You need to recognize that stainless steel rusts and it is not extraordinary. It is the key to deal with stainless tools.

Mechanism of rusting

There are two mechanisms for rusting kitchen knives. One is touching different kind of steels.　When you keep a knife, if it touches with different kind of steel for many hours, electron transfer occurs between each metal and the molecules unite with oxygen by molecule separation from the touching part, then rust occurs. This theory is put to practical use for batteries. Electron transfer always happens when different kind of metals touch with each other.
 Especially, you must be careful not to touch with different metals such as aluminum foils in your kitchen and sometimes even tap water includes very small amount of minerals (metals) and it causes the rust on the surface as well.

 Another reason to cause rust is leaving a knife alone without removing dirt or water after use. In this case, small amount of air is shut between the dirt(or water) and blade then the air is oxidized. This acts on the surface and get rusty as a result. You may think this kind of rust does not seems to be serious problem when you find it out, however, the corrosion gradually goes inside of the blade. Even if it is very small rust, we highly recommend removing it with cleanser or whetstone as soon as possible. Once you remove, you can use the knife with no problem.

The important thing is to maintain the knives in order not to cause the rust. Washing with a kitchen mild detergent and rinse it well after each use is one of the proper way to deal with and you also need to wipe off water to keep them in a dry condition to prevent them from the rust. If you find rust, please take it away as soon as possible.