Page:The American Cyclopædia (1879) Volume XV.djvu/375

 STEEL 363 and Martin of the " triple compound " of iron, carbon, and manganese (spiegeleisen). The chief difficulty with all these attempts to manufacture steel by fusion in the reverbera- tory was the lack of efficient and economical means for the maintenance of the intense tem- perature required. This was supplied by the important invention of Siemens, the regenera- tive gas furnace (see FURNACE), in which the use of gas as fuel was perfectly realized. The effect of this invention was great and immedi- ate in every branch of metallurgy involving very high temperatures, and nowhere more signal than in the remelting and subsequently in- the direct manufacture of steel by fusion. Sudre, Alexandre, Attwood, and Brigues, Ram- bourg and co. (the last at Montlucon, under the advice of 0. "W. Siemens himself) attempted with the aid of the new system of heating to fuse cast iron with wrought iron or oxides of iron for the production of steel, and procured patents on the strength of their experiments. But the first practical success was that of Pierre and Emile Martin, whose method is set forth in their patents of 1865 and 1867. These me- tallurgists, after a series of experiments ex- tending over many years, arrived at a combi- nation of .features, most of them separately known before, but constituting as a whole a new process, by which they were enabled to manufacture open-hearth steel of all grades, from the homogeneous metal approaching wrought iron to the hardest varieties, on a commercial scale and with profit. Naturally their claims as inventors, among so many eager competitors, were for a time contested ; but the report in their favor of MM. Jordan and Burat, made in November, 1874, after an investigation extending over many months, for the tribunal of the Seine, will probably be ac- cepted as conclusive. The Martin process is now widely employed in England, on the con- tinent of Europe, and in the IJnited States, and constitutes the only rival of the Bessemer method for the production of cheap steel. It consists essentially in the decarburization of cast iron by fusion with wrought iron, iron sponge, steel scrap, or iron oxide, in the hearth of a reverberatory furnace, heated with gas, the flame of which assists the reaction, and the subsequent recarburization or deoxidation of the bath by the addition at the close of the process of white iron, spiegeleisen, or ferro- manganese. The period of fusion and decar- burization lasts from four to eight hours ; the amount of spiegeleisen or f erro-manganese add- ed depends upon the condition of the bath, the grade of steel desired, and the percentage of manganese in the alloy used. The first of these elements is determined by samples taken from time to time during the process and tested. The advantages claimed for the Mar- tin as compared with the Bessemer process are : its less expensive plant ; the greater du- ration of the operation permitting by means of sampling more complete -control of the quality of the product, and also conducing to greater uniformity of result ; and, as a conse- quence of the foregoing, the practicability of employing materials which have not hitherto been considered suitable for the -Bessemer con- verter. The greater variety of materials avail- able for the Martin process also renders the direct conveyance of the molten pig from the blast furnace to the steel furnace an easier matter in this process than in the other, since the initial quality of the pig is of less impor- tance. Yet this direct conveyance of the cast iron has thus far been practised in certain Bessemer works alone. The Martin process has been employed at Terre Noire in France, and by Mr. Slade at Trenton, N. J., for the production of phosphoric steel mentioned above. The production of Martin steel in this country has risen from 3,000 net tons in 1872 to 7,000 tons in 1874. The number of estab- lishments using the process in 1874 was 13, and its introduction was in progress in other works. 35. Indian Steel, or Wootz. This is produced by fusion of wrought iron with coal or carbonaceous substances in crucibles. Small pieces of iron made in the small native fur- naces are put into a clay crucible with some dried wood and leaves, and covered securely with tempered clay. The crucibles are then heated until fusion is complete, when they are broken bpen, and a cdnical mass of steel weigh- ing 2 or 2 Ibs. is obtained. This steel is gen- erally very highly carburized, and requires to be worked at a low heat. It is much esteemed for its purity, but the production is small in amount. About the beginning of this cen- tury David Mushet carried out an extensive series of experiments on the fusion of wrought iron and charcoal in crucibles, and determined the amount of charcoal necessary for the production of steel of different degrees of hardness. Since then numberless patents have been secured for mixtures for fusing in crucibles, comprising mainly the different varieties of pig iron, wrought iron, carbon, and oxide or other compound of manganese. The crucible steel of the present day is largely made from such mixtures, the quality of the product depending on the materials used. Be. Cement Steel. The production of steel by heating wrought iron in charcoal without fusion (cementation) is a very old process, but its origin is unknown. It was described by Re'aumur in 1722, and has not been material- ly changed since. Notwithstanding the in- troduction of modern processes, this method is still employed for the manufacture of the higher grades of steel for tools and other fine purposes. The iron is in the form of flat bars about f in. thick. These are arranged in layers in long boxes or chests of fire brick, each layer being covered with charcoal about i in. thick. When the box is full, it is covered with clay or other impervious material, and heated to bright redness for seven to ten days, according to the degree of carburization re-