Technological tradition of the Mongol Empire as inferred from bloomery and cast iron objects excavated in Karakorum

Abstract

Iron objects from Karakorum, the former capital of the Mongol Empire, were metallographically examined. Most were forged out of bloomery iron, particularly those requiring superior functional properties. By contrast, approximately one third were made from cast iron, with carbon levels approximating either cast iron or ultrahigh carbon steel. The carbon concentration of the bloomery products was controlled either by a carburization treatment directed at the functional parts or by the welding of a pre-carburized steel plate to a low carbon body. By comparison, cast iron-based steelmaking was achieved by subjecting pieces of solid cast iron to a combined thermal and mechanical treatment aimed at accelerating decarburization. Some anonymous cast objects were circulated as a feedstock for this unique process, naturally taking the form of thin plates. Also, the cast products examined were contaminated with substantial amounts of sulfur and silicon, suggesting that they originated from liquid iron smelted at relatively high temperatures using fossil fuel instead of charcoal. Given these findings, it can be concluded that the Mongol Empire took advantage of an effective multi-faceted iron tradition, which combined bloomery-based and cast iron-based iron technologies. It is important to note, however, that the former still remained the key technological tradition dominating the local contemporary iron industry.