442 Introduction to the Study of Science 



are consequently being replaced by several kinds of steel and 

 especially by casting steel. The result in the industry is indi- 

 cated by the fact that to-day five sixths of the total output of 

 pig iron is used in making steel. 



215. The manufacture of steel. Pig iron, either the 

 molten or the molded solid pigs, is converted into steel in several 

 ways. These are known as the Bessemer converter, the open- 

 hearth, the electric furnace, the cementation, and the crucible 

 processes. In general the process of steel making is that in 

 which pig iron is freed from its impurities, such as silicon, carbon, 

 phosphorus, sulfur, and so on, through rapid oxidation. The 

 Bessemer converter process, which is of great importance in 

 the development of the steel industry, will make clear the essen- 

 tial features of steel making. The other processes will be easily 

 understood from this. 



The Bessemer converter is a large cylindrical vessel made of 

 steel plates and lined usually with slabs of silica rock or fire- 

 brick. It is provided with cylindrical fire-clay bottoms; in 

 these are many small openings through which heated air is 

 forced under a pressure of from ten to thirty pounds. Molten 

 pig iron is put into the converter. The hot-air blast is turned 

 on and, blowing in a fine but powerful spray through the molten 

 mass, produces by oxidation of the silicon and manganese enough 

 heat to ignite the carbon. The temperature which is thus 

 produced by the combustion of the carbon is such as burns 

 out or converts into molten slag most of the impurities, leaving 

 in the iron not more than one tenth of one per cent each of 

 carbon, silicon, and manganese. As steel to be steel requires a 

 certain percentage of carbon, this may be added by putting into 

 the converter a quantity of molten pig iron, or some iron rich in 

 carbon. In this way, from molten pig iron, steel is produced 

 " without fuel," as Sir Henry Bessemer announced in 1856 

 when he first described his invention. 



Impurities in steel. The Bessemer converter does not 

 produce a steel which is free from the impurities. Sulfur and 



