Ferrum Noricum Hüttenberg, archaeometallurgy

The archaeometallurgical project deals with the investigation of iron/steel objects, other materials specific to smelting (slags, furnace clays, bricks, refractory ceramics) and aggregates particular to smelting technologies (shaft furnaces, roasting beds) of pre-Roman and Roman iron production localised by means of the field archaeometric project and exposed respectively developed through the archaeological project. The investigations include material analysis for the characterisation of material properties as well as studies aimed at the reconstruction of processes and the production of goods in Noric iron production. The working hypothesis is based on contrasting intra and extra-alpine (Celtic) iron production and processing, with the focus set on quality of the steels produced regarding smelting (unalloyed, carbon alloyed phosphorus alloyed) and processing technological (fire welding, carburisation; composite materials) aspects. De facto an attempt will be made to determine phases of development and local variations of Celtic/Roman iron production by contrasting the state of research on the iron finds of Magdalensberg and the finds and findings to be made in the Hüttenberg region (intra-alpine regions) with the Celtic depot found on the Gründberg near Linz (extra-alpine region). Corresponding to the issue at hand, the methodological approach selected included several analytical methods (slag and steel chemistry, section analysis, refractory analysis of smelting plant building materials and refractory ceramics, micro probe, trace element chemistry) which will be performed at the respective specialist institutes of the University of Leoben and in laboratories of the voestalpine Stahl Linz GmbH co-operatively. The interdisciplinary co-operation with the archaeological and archaeometrical/geoscientific projects is centred on field work and interpretation of the total results.

The running slags found at the "Eisner" smelting site in Hüttenberg are silicate slags containing abt. 60 % FeOn ; 10 % MnO and 25 % SiO2 (all percentages by weight). The flow temperature of the slags is around 1500C. The high flow temperature of 1500C is indicative of the fact that the smelters were able to heat the shaft furnaces up to around 1550C. Consequently, the metal workers were able to produce both low- and high-carbon steel loops (=pig iron). Depending on the iron ores used, the steel loops obtained could also be varied with regard to their phosphorus content. First, the low-carbon loops were forged into steel bars. Several of these bars, of different quality, i.e. alloyed or unalloyed, were then made into the finished product by fire-forging. Moreover, the smiths of the Roman era mastered the techniques of carburizing and hardening. The transformation of the brittle pig iron into the desired products requires some sort of refining process. The appropriate technique was probably known to the metal craftsmen in the inner Alpine regions during the time of the Roman Empire. However, we still lack the archaeological evidence to bear out this assumption.