Iron And Steel (China)

The earliest iron artefacts known from China are a few blades forged from meteoritic iron (see Beijing, Gaocheng, Xincun). Iron does not seem to have been smelted until about the 6th century bc, at which time wrought iron and cast iron appear more or less simultaneously. The iron artefacts of this stage are mostly agricultural tools made of cast iron. A number of such tools were found in a 4th-century bc tomb at Guweicun, and 87 iron moulds for casting iron tools have been unearthed at a foundry site of about the same date at Xinglong in Hebei province. From its beginning Chinese iron technology was dominated by cast iron — so much so that in later centuries whole buildings could be assembled from cast iron parts: a 13-storey cast-iron pagoda erected in Hubei province in ad 1061 still stands. The extensive use of cast iron from the time of the metal’s first exploitation no doubt reflects the Shang and Zhou bronze-workers’ habitual reliance on casting and must have drawn heavily on their expertise (see metallurgy China). Steel was made in China within a few centuries of the first known use of smelted iron. Some was produced by carburizing solid wrought iron, the only method known to Western craftsmen, but the Chinese ironworker’s familiarity with cast iron led him to explore other techniques as well. Steel can be made from cast iron by removing carbon from it; thus prolonged exposure of hot cast iron to air, which eliminates some of the carbon by oxidizing it, can produce a serviceable steel. The oldest steel objects shown by scientific examination to have been made by this method of decarburizing cast iron are arrowheads from the tomb of Liu Sheng (d. 113 bc) at Mancheng, but earlier use of some such process is suggested by the long steel swords (see swords, China) found at many late Eastern Zhou sites (e.g. at Yan Xiadu, where a multiple burial of soldiers contained iron scale armour and 51 iron weapons). Swords of the 1st century ad and later sometimes carry inscriptions describing them as ‘steel of 30 refinings’ (or 50, or 100). These have proved to be decarburized cast iron folded and forged repeatedly to give a laminated structure with the stated number of layers. In texts of the period ‘100 refinings’ denotes the best steel. A second process for decarburizing cast iron, today the most common method of making steel, subjects liquid cast iron to the oxidizing action of air. A third method is to soak solid wrought iron in molten cast iron, allowing it to absorb carbon. All three methods were used in China centuries earlier than in Europe, a consequence of China’s much longer experience with cast iron. In the Han dynasty (206 bc-220 ad) iron production was a government monopoly. An ironworks of this period excavated near Zhengzhou in Henan province, at the site of the Han city of Xingyang, was identified as ‘Henan Prefectural Ironworks No. 1’ by the discovery of moulds that marked the castings made in them with this inscription. Hearths of two very large furnaces were excavated along with 20-ton salamanders (unmanageable masses of iron that collected in the bottom of the furnace and were disposed of by burying them on the spot when the furnaces were rebuilt). The furnaces are described in the excavation report as blast furnaces (i.e. driven by bellows) but are perhaps more likely to have been pottery kiln-like reverberatory furnaces, driven by natural draught, in which reduction of the iron ore, carburization, and melting took place in slow succession. Because of the need for a high flame the fuel was necessarily wood (in later times bituminous coal) rather than charcoal.