The metallurgical industry that existed between the 10th and 12th centuries at the Chahak site in southern Iran produced crucible steel with the addition of chromium, a mineral that has been used since the 20th century to make rust-resistant steel.
A series of archaeological finds suggests that Iranian metallurgists made an alloy of iron and chromium - which can be considered a forerunner of modern stainless steel- already at the beginning of the second millennium, according to astudy published this Wednesday in the Journal of Archaeological Science.
These are remains of crucibles with slag found inChahak, a metallurgical center in southern Iran, and dated to between the 10th and 12th centuries.
«Crucible steel in general is a steelvery high quality. It contains no impurities and is ideal for the production of weapons and armor and other tools, ”lead study author Rahil Alipour told Gizmodo.
Furthermore, an analysis of the material revealed that it containedchrome, an additivethat began to be used from the 20th century in the manufacture of stainless steel.
«This particular crucible steel made in Chahak contains around1% to 2% chrome, "Alipour detailed, highlighting that the finding" providesthe earliest evidence of the "consistent and intentional addition" of that mineral, although its concentration was insufficient to create a stainless steel.
At the same time, thephosphorus at a concentration of 2% found in the same slag would have made the resulting steelmore fragile. However, this mineral was necessary to lower the melting point.
Scientists previously knew of evidence of crucible steel making in various Asian regions in medieval times, such as today India, Sri Lanka, Turkmenistan and Uzbekistan. However, "none of these [centers] show traces of chromium," explained Alipour, who noted that the discovery of this specific Chahak alloy may be useful for identifying the provenance of steel objects of the time.
“Chromium as an essential ingredient in Chahak's crucible steel production has so far not been identified in any other known crucible steel industry. That is very important, as we can now look for this element in crucible steel objects andtrace them back to your facility or production method«, Concluded the archaeologist.