So here are my notes on the crystal structures inside steel. -Austenite: cube structure with all its carbon molecules intact. From there, you can heat your piece and transform the austenite into -martensite: carbon molecules are still intact, but the cell structure is stretched into a rhombus shape. This is achieved via a ‘quick’ cool such as a brine quench. This cell structure is hard as shit and is the hard, cutting edge of a katana. By itself, it would shatter since it’s a very rigid cell structure. -ferrite: is a cube cell-structure like austenite, but has lost its carbon content. You heat austenite, then let it have a very long cool down time by, for example, leaving it to cool to room temp by itself. It’s the flexible cell used in the spine of a katana to keep the whole damn thing from breaking in two.