Folding steel - what does that mean?

Folding is one of the old secrets in blacksmithing. How it works and what it does for you can be found in this article. Also, why Damascus steel has its special structure, and why wrinkles are the reason behind the incredible sharpness of Japanese swords.

Process when folding

When a blacksmith folds a steel, he does the following:

  • the heated blank will stretch first
  • partially split the blank
  • Turn over at the breaking edge
  • forge together again

This folding process is repeated over and over. In this way, alloys are created that can be very selectively influenced. This serves on the one hand to create a completely homogeneous steel, in which one also "unwraiths" unwanted components almost completely over time - or creates a steel with many different layers. Both are done on the same basis, namely by folding.

Homogenization of steel

Especially in the past, iron was not obtained by melting, as in today's blast furnace, but it was used as a raw material in the form of inferior sponge iron (lumps). Sponge iron has a relatively low carbon content, but contains much unwanted slag.

This was first coarsely forged, then forged further and further processed by folding. As a result, the iron was decarburized (that is, the carbon removed), the folding of the original structure was reduced further and further until the structure was finally homogeneous.

Forging layers

The visually impressive structure of Damascus steel is created by etching the steel. The pattern that becomes visible shows only the different layers of steel. These layers are produced by fusing different types of steel, which were (classically) first joined by means of fire welding (joining of different steels at approx. 1300° C welding temperature in the furnace under exclusion of air).

If different layers are repeatedly folded and forged together, one can produce with appropriate skill a steel with "mixed" properties. The best example of this is a Japanese katana sword. - Forged in traditional technique, a Katana can have 30,000 wafer-thin, different layers.

Essentially, the goal is to make the steel hard on the outside, but tough-elastic on the inside, so that the blade becomes very sharp, but does not break. In addition, the initially unequal carbon content in the iron (as described above) is homogenized in the starting steel. The performance of traditional Japanese knife steels is still impressive and can only be achieved today with great effort.

Tips & Tricks

The Japanese folding technique is extremely complicated and very complex and labor intensive. Even the folding, as it was carried out by Western blacksmiths, requires a high level of expertise and above all experience and "feeling". That is why, like fire welding, only a very few blacksmiths are masters today.