A D V A N C E D M A T E R I A L S & P R O C E S S E S | J U L Y / A U G U S T 2 0 2 2 2 0 Thereafter, the single or split pieces of bloom are hand hammer-forged to the required shapes suitable as workpieces for further processing. Examples from experimental archaeometallurgy are shown in Fig. 2. The forging steps usually require intermittent reheating of the bloomery workpieces to maintain sufficient malleability. Bloomery workpieces, today classified as wrought iron, were basically low-carbon steels (< 0.1 wt% C) and invariably contained slag inclusions that actually improved the malleability[9]. Figure 3 shows examples of objects with microstructures essentially the same as bloomery workpieces, namely single phase (ferrite) metal and slag inclusions[10,11]. There were numerous other applications, such as nails, hinges, and– much later–Roman bridge pile-shoes[12]. However, wrought iron is relatively soft and unsuitable for taking cutting edges in tools and weapons. In these applications wrought iron was not competitive with hardened (cold-worked) bronzes until the accidental discovery of steel. This discovery and its exploitation started the Iron Age. DISCOVERY OF STEELS The archaeological evidence indicates that steels (iron-carbon alloys) were first produced accidentally owing to incomplete control of the complex bloomery smelting process (Fig. 1) and Fig. 1 — Schematic of an iron smelting shaft furnace and details of the production stages. Adapted from Thiele[6]. Fig. 2 — Iron bloom processing: (a) slag removal and bloom consolidation, showing pieces of slag surrounding the bloom; (b) a large bloom split using a maul and sledge hammers; (c, d) hammer hand-forging to the required shape. Adapted from various experimental archaeometallurgy sources. (a) (b) (c) (d)
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