By forge-welding differing types of metal pieces together and working and manipulating the result, a distinct pattern can result in the final product. Pattern welding, the result of which can b e identified by their banded patterns, can be utilized for cosmetic effect and can be embellished by polishing or acid etching. A more functional use is for combing steels of differing compositions to achieve the desired mix of hardness and toughness.
Early use of pattern welding resulted from the need to produce high strength steel despite the limitations in iron smelting at the time. Bloomeries, furnaces consisting of a chimney and entrances for air near the bottom, could reduce iron oxide ore into pure iron but could not melt it. The resulting mass of “sponge iron” could be processed into wrought iron by continuously working it with hammers and folding it over to remove the slag, impurities in the metal. Carburizing the metal, adding carbon and causing it to be absorbed into the metal while under heat treatment, can form high carbon steel. Forging resulting bars or plates together results in the layered patterns seen in pattern welded metal.
One of the earliest known uses of pattern welding occurred in Europe in between the 2nd and 3rd century by the Celts. The Viking Ulfberht swords were also pattern welded. These swords tended to be durable, and less likely to bend or snap when used.
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