"True Damascus Steel": History, Metallurgy, Production скачать в хорошем качестве

"True Damascus Steel": History, Metallurgy, Production

This is going to be a rather long, and in depth video on hypereutectoid crucible steel, a historical steel known by many names, from Pulad (Persian), Wootz (Indian), Fulad (Arabic) and Bulat (Russian) and many other. Today, we'll uncover its history, metallurgy, and production. For the most part, it is based upon excellent academic work by Ann Feuerbach and metallurgical experimentation by John Verhoeven. Historically (prior to the 18th century), "Damascus Steel" also referred to crucible steel, which was produced all over South East and Central Asia and the middle east. In order to differentiate between the two forms of “Damascus”, I will be using the nomenclature of pattern welded steel, and wootz steel. Also known as pulad, fulad or bulat, wootz is an ancient crucible steel, which was produced from as early as the first century, CE. It is typified by being high in carbon content, usually between 1 and 2 percent and a low slag content. Metallurgical identification of wootz steel is problematic, as no single criteria can be used to differentiate between crucible steel, and decarburised wrought iron. In order to confidently say whether a sword is crucible steel or not, the blade must be polished and then etched in nital, and examined via low magnification microscopy. The presense of spheroidised cementite is considered evidence of a crucible produced steel. Wootz can occur in two different forms according to Ann Feuerbach, soft wootz with less than 0.8% carbon, and hard wootz with greater than 0.8%. The vast majority of pattern presenting wootz and historical wootz is hard wootz, whereas the majority of crucible steel that produces no pattern is soft wootz. The names Pulad and Fulad derive their meaning from the words for Purified, and fittingly Wootz also typically contains lower levels of slag than other steels, such as bloomery iron or decarburised wrought iron, however if the wootz was made using one of these as a source of iron, this can introduce slag into the final product. For the most part, the clay crucible would be filled with a charge. This crucible charge would contain iron, often a mix of “soft and hard iron”, referred to by Al Kindi as male and female iron, as well as some form of plant matter such as rice husks, pomegranate peels, wood chips, leaves or vines. These served two purposes: Firstly, to provide carbon to the steel, without which it would not melt and would not produce useable steel, and secondly to produce gasses as they pyrolise, protecting the steel from the atmosphere of the furnace. Some processed such as the Deccani process utilised in Hyderabad used glass as a protective flux. The crucible was heated for anywhere between 6 hours (as in the south Indian process) to two days, as in the Deccani process, or as much as 6 days in the Isfahan process. The resulting wootz button or egg was then polished in order to check the quality of the wootz. In the Isfahan process, the wootz ingots were taken from their crucibles after firing, and placed in a heated room or compartment for two days, to temper them and relieve stresses prior to forging. Isfahan wootz is particularly well known, as is Khorasani steel. The most famous of persian swordmakers hailed from Isfahan, Assad Allah, during the reign of Shah Abbas. There is an interesting legend as to how he rose to such prominence. According to this legend, Shah Abbas held a competition with the intention of finding a new shamshiraz, or swordmaker for his court. In order to root out the best of the best, he offered a prize for a swordsmith who could cut an iron helmet given to him by an ottoman sultan, without damaging their sword. All failed, but one. Assad Allah, whose name literally translates to Lion of God, approached the helmet, swung, and cleaved it in two, without rolling an edge. The secret to producing wootz steel was lost for a long time, as the ore sourced dried up around 1750, and wootz production ground to a halt. Crucible steel was still being made, but it lacked the distinct patterns in the steel, which had served as a guarantee of quality. It was only recently through the combined efforts of John Verhoeven and the late Al Pendray that it was revealed that trace amounts of carbide forming elements are responsible for the formation of wootz patterns. In particular, the pair discovered that vanadium was a vital alloying element in pattern formation. Recently, Verhoeven has revisited the topic with a 2018 paper titled Damascus Steel Revisited, in which experimentation solidified his claim that internal banded microstructures resulted from microsegregation of Vanadium between dendritic and interdendritic regions of the ingot during solidification. Vanadium therefore acts as a nucleation point for cementite spheroid formation, leading to linearly aligned bands of cementite after forging.