Mushet, Robert Forester

SUBJECT AREA: Metallurgy

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b. 8 April 1811 Coleford, Gloucestershire, England

d. 19 January 1891 Cheltenham, Gloucestershire, England

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English steelmaker who invented the first alloy steel.

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Mushet acquired his metallurgical knowledge in his father's ironworks at Coleford in the Forest of Dean. In 1848 his attention seems to have been drawn to the use of manganese in ironworking, in the form of spiegeleisen, an alloy of iron and manganese derived from a Prussian iron ore consisting essentially of a double carbonate of iron and manganese. This alloy came into its own in 1856 with the invention of the Bessemer steelmaking process, for Mushet found that if molten spiegeleisen was added to the Bessemer iron the quality of the product was greatly improved. Mushet patented this process, but when he failed to pay the stamp duty due in 1859 his rights lapsed. Bessemer independently discovered the use of spiegeleisen, although Mushet continued to maintain his priority.

Mushet's most important discovery was that of tungsten steel, the forerunner of a long line of alloy steels. While working a small crucible steelworks at Coleford, he was asked by a Scottish manufacturer to make a hard-metal tool, but he found that the metal was unsatisfactory. After experiments, he found that an alloy steel containing about 8 per cent tungsten possessed remarkable properties. It proved to be self-hardening, i.e. after forging and being allowed to cool, it was found to have become hardened, without the need for the heat treatment that was normally required. Also, unlike other hardened steels, it did not lose its hardness when heated even to dull-red heat. It would thus remain hard in a cutting tool that had run hot through deep cutting. Mushet's tungsten steel was brought into use in 1868 and was of great benefit to engineers, who were making increasing demands on cutting machines.

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Further Reading

Biographical notice, 1878, Journal of the Iron and Steel Institute : 1–4.

LRD