The science behind the Hamon on Japanese swords, and how Katanas can cut through iron materials

In Japan, we defined the real Katana as a sword with a sharp blade created using Tamahagane by the traditional process. After the WW2, only the licensed swordsmith can create a Katana. It is prohibited to create swords using iron, steel other than Tamahagane. There are swords created using a different kind of iron in the world, we don t call it Katana (it is called Mozouto or replica sword). We described that Katana can easily cut through iron materials, but of course, Katana cannot magically cut throug