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Introduction to the archaeometallurgy of iron
Donald B. Wagner

Steelmaking by cementation

Steelmaking at Derwentcote

Here are some illustrations of the Derwentcote furnace. There is more information in Barraclough 1976a; 1976b; and 1984. Percy (1864: 768–773) has more on this type of furnace.

1960’s.

1980’s, after restoration work by English Heritage.

Explanatory signs for tourists.

The term cementation covers a variety of ancient and modern processes in which iron in the solid state takes up carbon from an atmosphere rich in carbon monoxide. An example is case hardening: a smith may pack a semi-finished knife in charcoal in a sealed container and heat it to a fairly high temperature (typically about 950°C) for a period of hours in order to produce a hard steel surface layer, a few millimetres thick. Carbon is taken up at the surface of the iron and diffuses slowly into the interior. On an industrial scale essentially the same process was widely used in Europe in the 18th and 19th centuries to produce high-carbon steel bars for the cutlery trade. Large furnaces were used like one still standing at Derwentcote near Newcastle, England. In this furnace about ten tonnes of wrought-iron bars were packed with charcoal in two sandstone chests. These were heated with a coal fire to about 1100°C for a week or more, after which the furnace was allowed to cool for about a week The bars of steel could then be removed and processed further.

The basic reactions involved here are

CO2 + C (charcoal) = 2CO
2CO = CO2 + C (in Fe)

The conditions under which these reactions proceed to the right are shown here. In addition an accelerator is normally mixed into the charcoal packing: in modern practice barium carbonate (BaCO3), in earlier times usually calcium carbonate (CaCO3) or sodium carbonate (NaCO3). When heated the accelerator gives off carbon dioxide (e.g. CaCO3 = CaO + CO2); this replaces nitrogen in the packing atmosphere, increasing the partial pressures of both CO2 and CO, permitting a faster uptake of carbon and also increasing the equilibrium carbon content at the surface of the iron.

It is a surprise and a puzzle to find the European process in use in Sichuan in the 1930’s. A survey of the Sichuan iron industry (Luo Mian 1936: 35–38) describes a cementation steelmaking furnace in Weiyuan County 威远县, and gives the diagram here on the left. It is clearly of foreign design. The cementation steelmaking process was a German invention of the late 16th century, and developed into the most important steelmaking process of the early 19th century. The introduction of the Bessemer process provided a cheaper means of making steel, and by 1900 the cementation process was essentially obsolete, though it continued in use in Sheffield and a few other places until as late as the 1950’s. When was it introduced in Sichuan, and by whom?

Chinese traditional cementation methods

Yang Kuan 1960: 195–197, citing 冶金工业出版社编,土法炼钢,第四辑。第一篇:怎样炒铁和焖钢。第二篇:怎样焖钢并用焖钢方法制滚珠轴承.

In China, steelmaking by cementation is traditionally called men 焖. Not much is known about Chinese traditional methods of cementation steelmaking, but the historian Yang Kuan has given some interesting information from a handbook published in connection with the Great Leap Forward.

The furnaces are essentially the same as those used for crucible smelting. The cementation pots (crucibles) are ceramic or iron. Low temperatures are used, not over 900°C, and the annealing time ranges from 9 to 24 hours. Such low temperatures and short times would give a carburised layer of only a millimetre or two, but the steel material used by smiths, judging from artefacts I have seen, seems to have been very thin (sometimes less than a millimetre), so this was an appropriate technique.

At some works charcoal alone is used for the packing, but a bewildering variety of accelerators are also seen. At a works in Lushan County 鲁山县, Henan, for example, to make steel from 60 kg of wrought iron, the packing is 6 kg charcoal, 3.6 kg powdered ox-bone, and 2.4 kg saltpetre (potassium nitrate, KNO3). The bone supplies calcium carbonate. Saltpetre is a powerful oxidising agent; it is difficult to understand what function, real or imagined, it might have here. Still other recipes include sodium carbonate, which functions like other metal carbonates, releasing carbon dioxide when heated. One recipe includes ‘salt’, presumably sodium chloride; what function might this serve?

At a works in Yidu County 宜都, Hubei, the packing material is 2.4 kg charcoal, 12 kg powdered ox-bone, and 3 kg sawdust. Here the bone supplies both calcium carbonate and the greater part of the necessary carbon. The sawdust, which is also seen in several other of the recipes, supplies carbon, but what other function might it serve?

References

Barraclough, Kenneth C. 1976a. ‘The development of the cementation process for the manufacture of steel’. Post-medieval archaeology 10: 65–88 + fold-out figures + plates 9–13.

Barraclough, K. C. 1976b. Sheffield steel. (Historic industrial scenes). Hartington: Moorland.

———. 1984. Steelmaking before Bessemer. Vol. 1: Blister steel: The birth of an industry. Vol. 2: Crucible steel: The growth of technology. 2 vols. London: The Metals Society. The PhD thesis on which this book is based is available at etheses.whiterose.ac.uk/14433/.

Percy, John. 1864. Metallurgy . . . [Vol. 2:] Iron; steel. London: John Murray. archive.org/details/metallurgyartex02percgoog

Luo Mian 羅冕. 1936. Zhongguo Gongchengshi Xuehui Sichuan Kaochatuan baogao: Gang tie 中國工程師學會四川考查團報告•鋼鐵 (Reports of the Sichuan Investigation Group, Chinese Engineering Society: Iron and steel). N.p.: Zhongguo Gongchengshi Xuehui. N.d.; preface dated 1936.

Yang Kuan 杨宽. 1960. Zhongguo tufa yetie lian’gang jishu fazhan jianshi 中国土法冶铁炼钢技术发展简史. 上海: 人民出版社.

Last edited by DBW 24 February 2023