Chromium crucible steel was first made in Persia

Abstract

For more than a century, evidence for the production of crucible steel in Central and Southern Asia, prior to the European Industrial Revolution, has fascinated and challenged material scientists, historians and archaeologists. At the same time, chromium-alloyed stainless steel was developed in the early 20 th century, building upon 19 th century experiments with low chromium steel. Here we demonstrate new evidence of the intentional addition of chromium to steel nearly a millennium earlier, as part of the Persian crucible steel (pulad) tradition including the production of low-chromium crucible steel in early 2 nd millennium CE Persia. We analysed archaeological finds from the 11 th c. CE site of Chahak in Iran showing the intentional and regular addition of chromium mineral to the crucible charge, resulting in steel containing around 1 wt% chromium. A contemporaneous crucible steel flint striker held in the Tanavoli Collection is reported to also contain chromium, suggesting its origin from Chahak. We argue that the mysterious compound 'rusakhtaj' from Biruni's (10 th -11 th c. CE) recipe for crucible steel making refers to the mineral chromite. Additional historical sources up to the mid-2 nd millennium CE refer to crucible steel from Chahak as being particularly brittle, consistent with its increased phosphorous content.

A Droplet of Liquid Steel: Prills in Crucible Steel Production Remains

“…This raises the question why MnO has been added to the crucible charge, where it affected the slag composition, but had no discernible alloying effect on the crucible slag prills and presumably the main ingot. This is in contrast to the observation in Güder, et al (2022) who report up to 1.7 wt.% Mn in an ingot fragment and around 21 wt.% MnO in the attached slag, but consistent with the analyses in Alipour, Rehren and MartinónTorres (2021) and Alipour and Rehren (2023) where prills embedded in highMnO slag did not show elevated Mn content. It is thought ( Rostoker and Bronson, 1990, pp.107113;Truffaut, 2014) that MnO in slag facilitates carburisation of iron, even without contributing to the alloy itself.…”

“…With very few exceptions (Jaikishan, Desai and Rehren, 2021;Güder, et al, 2022), the study of crucible steel production is restricted either to contemporary written sources, or the analysis of the production waste, while the ingots themselves are not available for characteri sation. The composition of the ingots, however, plays a significant role in the literature (Verhoeven, Pendray and Dauksch, 2018;Wadsworth and Sherby, 1980;Alipour, Rehren and MartinónTorres, 2021). This raises the question whether the prills identified here can be used as a proxy for the ingot composition.…”

“…Two other prills were analysed from the Melsiruvalur crucible fabric showed no phosphorus elevation. Alipour (2017) and Alipour and Rehren (2021) reported metallic iron prills in the Chāhak crucible bodies from southern Iran, based also on ferruginous clays and various levels of phosphorus in prills in the FAG and the crucible slag fins; the latter also contained manganese and chromium. The phosphorus content in the Chāhak FAG prills is higher in compar ison to prills in the crucible body and crucible slag fin (Alipour, 2017, p.315).…”

“…In contrast, Central Asian crucible steel making is characterised by the addition of significant amounts of mineral additives to the charge, resulting in much more slag formation (e.g., Rehren and Papakhristu, 2000). This has been well studied in the medieval Persian Chāhak crucibles, that hold significant amounts of crucible slag rich in prills including phos phorous, chromium and manganese from the crucible charge (Alipour, 2017, pp.316319;Alipour and Rehren, 2021;2023). Due to the intimate relationship between the crucible slag and the crucible steel ingot forming during the process, it is likely that the prills trapped in the crucible slag are compositionally close to the final ingot.…”

Interpreting the Chemical Variability of Iron Smelting Slag: A Case Study from Northeastern Madagascar

“…Phosphorus (P) is reduced under conditions very close to the ones of iron [39]. Chromium (Cr), manganese (Mn) and vanadium (V) demand stronger conditions, but these are not impossible to reach during the bloomery process [40,41]. At very high conditions, silica (SiO 2 ) begins to react, and a few percent silicon (Si) are a common feature in cast irons.…”