Bulat steel

Bulat is a type of steel alloy known in Russia from medieval times and regularly mentioned in Russian legends as material of choice for cold steel. The name "bulat" is a Russian transliteration of the Persian word "پولاد" (transliterated "pulad"), meaning steel. There are no known sources indicating that the origin of bulat is Russian while the name suggests that the immediate source of it was Persia. It is highly possible that bulat steel is made using the same process as wootz steel.

History

The secret of bulat manufacturing was lost by the beginning of the 19th century. Pavel Petrovich Anosov eventually managed to duplicate the qualities of that metal in 1838, when he completed ten years of study into the nature of Damascus steel swords. Bulat became popular in cannon manufacturing, until the Bessemer process was able to make the same quality steels for far less money.

Anosov had entered the Saint Petersburg Mine Cadet School in 1810, where a Damascus steel sword was stored in a display case. He became enchanted with the sword, and was filled with stories of them slashing through their European counterparts. In November 1817 he was sent to the factories of Zlatoust mining region in the southern Urals, where he was soon promoted to the inspector of the "weapon decoration department".

Here he again came into contact with Damascus steel of European origin (which was in fact pattern welded steel, and not at all similar), but quickly found that this steel was quite inferior to the original from the Middle East. Anosov had been working with various quenching techniques, and decided to attempt to duplicate Damascus steel with quenching. He eventually developed a methodology that greatly increased the hardness of his steels.

Structure

Carbon steel consists of two components: pure iron, in the form of ferrite, and cementite or iron carbide, a compound of iron and carbon. Cementite is very hard and brittle; its hardness is about 640 by the Brinell hardness test, whereas ferrite is only 200. The amount of the carbon and the cooling regime determine the crystalline and chemical composition of the final steel. In bulat, the slow cooling process allowed the cementite to precipitate as micro particles in between ferrite crystals and arrange in random patterns. The color of the carbide is dark while steel is grey. This mixture is what leads to the famous patterning of Damascus steel.

Since cementite is essentially a ceramic, this also accounts for the famous sharpness of the Damascus (and bulat) steel. This means that the latest invention in kitchen tools - ceramic knives - is not all that original. Cementite is unstable and breaks down between 600-1100°C into ferrite and carbon, so working the hot metal must be done very carefully.

Bibliography

* The Mystery of Damascus Blades, by John D. Verhoeven in Scientific American, No 1, pages 74-79, 2001.
* History of Metallography: The Development of Ideas on the Structure of Metals before 1890. Cyril S. Smith. MIT Press, 1988.
* On Damascus Steel. Leo S. Figiel. Atlantis Arts Press, 1991.
* Archaeotechnology: The Key Role of Impurities in Ancient Damascus Steel Blades. J. D. Verhoeven, A. H. Pendray and W. E. Dauksch in
* JOM: A Publication of the Minerals, Metals and Materials Society, Vol. 50, No. 9, pages 58–64; September 1998. Available at http://www.tms.org/pubs/journals/JOM/9809/Verhoeven-9809.html

See also

* Wootz steel, an Indian crucible steel
* Pattern welded steel