In the Siemens-Martin process, steel is produced either by melting a certain quantity of pig iron in the hearth of a reverberatory furnace and adding wrought iron till the bath attains the desired degree of carbonization, or by mixing cast iron and certain kinds of iron ores. The oxides of the ores are removed and carbon and manganese are added by the introduction of a small quantity of ferromanganese, similar to spiegeleisen. The amount of carbon left in the metal is ascertained by removing a small quantity of metal in a ladle, cooling it, and then breaking it up and testing it. If found satisfactory, the charge is tapped and the metal run into the ingot molds. The ingot is later reduced to a slab, called a bloom, by passing it back and forth between heavy rolls until it is reduced to the thickness desired (Fig. 194). The operation is slower than the Bessemer, but it enables the manufacturer to produce more readily the desired grade of steel. It is the usual method of producing steel of good and uniform quality at a low cost and on a large scale; the product competes with Bessemer steel in price.
Pig. 194. - Blooming Mill Showing Steel Ingot Reduced to Bloom.