Tamahagane is a steel with 1-1.5% of carbon, and its composition is most appropriate for edges.
Sagegane has 0.7% of carbon, houcyoutesu has 0.1-0.3% of carbon and their compositions
are appropriate to extend.
All of them has few impure element, so they are said to be very pure material for steel.
However, compared to modern steel, they include much oxygen (O).
Therefore, the slag (non-metal inclusion) in the steel has more oxygen inclusion.
Although, this oxygen inclusion is much softer than common steel inclusion, stretchable,
so by forging repeatedly, it won’t be dispersed into small elements and become harmless
but will strengthen Japanese sword, create beautiful surface, and straighten the effect of sharpening.
In short, usual non-metal inclusion in steel is bad, but non-metal inclusion in Japanese steel
is good inclusion that revives the material by forging repeatedly.
In this way, you can say Japanese steel is much purer in material than modern steel.
As mentioned above, Japanese steel’s (steel made by tatara forging) material is extremely pure,
so they have the characteristics below:
- Easy to forge
- By heating, it may become stretchable, not being hard or winded
- Easy to sharpen, and can make a good edge
- Rarely become rusty
- The pattern of forging appears clearly, so it will make a beautiful pattern on the edge
Therefore, Japanese sword is said to be the best steel article using this Japanese steel’s characteristic.
Tamahagane is manufactured at tatara forge, which is a Japanese traditional forge.
To understand the way, you may watch this video and see how it works.