\\ ben air is blotto thiough pig in a Itessem•r converter, the tirst element effected is the silicon. and when the silicon is eliminated the carbon begins to burn and continues until there is only about 0.5 ler cent. I 'p to the point where the carbon content has been reduced to 0.5 per cent.. the reactions of the acid end of the basic processes arc the same, lint at this point the similarity ceases, for here the acid process ends, while the basic process begins it, char neteristic work of eliminating the phosphorus and sulphur. For practical purposes it may be assumed that neither the phosphorus nor sulphur it Monts of the original pig iron have altered at the time that the carbon content has re:wiled 0.5 per cent. From that time tilt the phosphorus seizes the oxygen in the same way as the silicon and carbon had done before. the phosphoric acid immediately uniting with the lime which in the basic process is added to the metal at the begin ning of the blow. The basic lining of the furnace is employed so that the lime may do its work without being affected by the lining material; were an acid lining used the silica would corn bino with the lime. thus rendering much of it incapable of doing useful WO•k on the metal. The decarbonization. d•phosphorization, etc., effected by the blowing process require to be supplemented by a further process before the final product of the converter is steel. This process is known as recarburization, and consists in adding carbon and manganese to the molten metal by the use of spiegeleisen or ferromanga nese; the manganese promotes the removal of the sillphur with the slag. The amount of theso materials to be added varies with the character of steel it is required to produce. and also with the process.
As has been stated. the process of steel-making which has just been described was the invention of Henry Bessemer, an Englishman. It developed from his efforts to produce a stronger metal than cast iron for the manufacture of ordnance. In 1;7.54 dames Nasin•th had patented a process for oxidizing the impurities of molten east iron by introducing steam belo• the surface of the metal. Bessemer substituted air for steam, and patented the process in 1855. In his first exp6ri melds, Itessem•r devoted his attention to the production of malleable iron, and such was his success that in IS50 he announced his work to the public, At this time, however, tlne 1111)(!(•Si was far from perfect. Bessemer soon discovered that, while his process remove silicon, manganese, and carbon from east iron, it would not. when eonducted in an aeid-lined conceder, remove pliosidiortis and sulphur. .1fter some attempts to aceomplish the removal of the last two elements, which met with poor success. Bes semer was compelled to revert to the Use of iron so low in phosphorus and sulphur that it would make steel without any further diminution of these elements. Thus arose a classification of Bessemer pig, which still exists (see previous section on Cast Iron), and which means simply pig iron so low in phosphorus and sulphur that it may be made into steel without removal of these elements. The question of phosphorus
being thus satisfaetorily settled, Bessemer was eonfronted with the difficulty of so regulating the period of blowing that carbon should not be eliminated below the amount required in steel. As stated, this problem was solved by burning out practically-all of the carbon and than adding a definite amount in the form of a reearburizer. In the same way. the necessary quantity of manganese was supplied. The success of the Bessemer process was not established commer cially until 1860; from that date it has grown by leaps and bounds, until to-day it is perhaps the most important of the steel-making processes. Bessemer reaped famo and wealth from his inven tion, of which it has been truly remarked that it was of far more importance to the world than all the gold of California and Australia.
The open-hearth process of steel-making con sists in making pig iron mixed with a greater or less quantity of wrought iron, steel, or similar iron products by exposure to the direct action of flame in a regenerative gas-furnace, and convert ing the resultant bath into fluid steel. Like the Bessemer process. the open-hearth process is divided into an acid process and a basic process; in the first the hearth is lined with sand and the slag is siliceous, and in the seccad the hearth is lined with a. basic material and the slag is basic. Like the Bessemer process, also, the con the hearth. From the hearth the hot gases pass down through the briekwork of the second cham ber and serve to heat it. after which they escape at the bottom into the smokestack Hue. soon as the briekwork of the first chamber has become cooled below a certain point, the current of gases is reversed, so that they enter at the bottom of the second chamber and pass out of the bottom of the first clamber after being heated and ignited by time hot brickwork through which they have passed, and after passing over the hearth giving up their waste heat to the brick work of the first chamber. By repetitions of this process of reversing the current of gases, the regenerative process is continuous, and a steady, intense heat is maintained on the hearth.
The hearth is usually a fixed structure, as shown by Fig. 3, but in some American works it is so constructed that it can he tilted like a Bessemer converter to receive its charge and to discharge its molten contents. This form of hearth is claimed to have several material ad vantages over the fixed hearth in ease of opera tion and in producing steel from certain mate rials for certain special purposes. Whether fixed or tilting, the con-truetion of the hearth consists sideration of the open-hearth process may bo divided into a discussion, first of the plant and mechanical operations. and then of the diem ical reactions.