A Treatise On The Principles And Practice Of Dock Engineering

134 DOCK ENGINEERING. A relatively large proportion of carbon induces hardness, strength, incom- pressibility, brittleness, and fusibility. A small proportion tends to toughness, malleability, weldability, and tenacity. Manganèse Steel.—But, as already remarked, there are other constituents,. besides carbon, which are capable of entering very largely into combination with iron, and of exercising an influence equally powerful in determining its characteristics. By far the most remarkable is an element which, according to the proportion in which it is incorporated, imparts the most opposite qualities to the compound. The addition of manganèse to iron was suggested as far back as the 18th century,* and Mushet, who published in 1840 the results of some very interesting experiments, recommended it as an essential accompaniment to the Bessemer process. The quantity recommended was small and in the form of spiegeleisen, and a limit was found at which the steel apparently ceased to benefit by the admixture. A recent and more deeply experimental investigation, by Mr. R. A. Hadfield, has established the important fact that there is a second limit beyond the first, at which the deterioration ceases, and the compound commences to regain in greater intensity the characteris- tics which it had seemingly lost. Mr. Hadfield’s conclusions are as follows : —t 11 Whilst the belief, hitherto held, that steel becomes brittle and com- paratively worthless when the manganese exceeds about 2’75 per cent, is correct, yet it has now been proved that, by adding more of the same metal in such quantifies as to obtain in the material under treatraent not less than about 7 per cent, of manganese, the result is a metal with entirely different characteristics; in fact, the product is a new metal. The apparent paradox thus takes place that, whilst manganese, alloyed with iron, the former being present in the proportion of not less than 2-75 and up to about 7 per cent., gives a very brittle product, when its proportion is inereased to not less than 7 and up to about 20 per cent., . . . the result is a material possessing peculiar and extraordinary strength, toughness,. and other qualities.” Manganese steel is more free from blow holes than are ordinary castings, and the addition ot silicon, in order to prevent unsoundness or honeycombsr is unnecessary. Whilst molten, it gives off a peculiarly strong sulphurous odour, and, though at first very fluid, it cools more rapidly than ordinary steel; its contraction is also greater. Nickel is a second agent capable of entering into an effective combina- tion with iron, and of producing a valuable compound. The following * Early experiments upon manganese were made by Glauber in 1656, and by Wartz in 1705. Hinman (1773) melted equal parts of grey pig-iron and manganese ore, obtaining a non-magnetic produet. Reynolds attempted its use in the manufacture of steel in 1799. + Hadfield on “ Manganese Steel,” Min. Proc. Inst. C.E., vol. xciii.