Laminated steel blade

Piled steel developed out of the necessarily complex process of making blades that were both hard and tough from the erratic and unsuitable output from early iron smelting in bloomeries.

[1] The bloom must then be heated and hammered to work out the impurities, resulting in the relatively soft wrought iron.

The ideal sword is one with a hard, sharp edge, and tough enough to bend, but not to shatter.

The very hard, but brittle, edge made the swords stay extremely sharp, while the spine gave the blade flexibility, so that it would bend rather than break.

Laminated steel also finds use in the construction of padlocks, where the structure of the material makes it more difficult for the lock to be destroyed by tools like hammers and drills.

A Japanese katana made of laminated steel. The outer skin is forged from alternating layers of steel with differing carbon content, and folded upon itself many times, producing a mokume (wood-eye) pattern.