BURNING OUT THE CARBON
The production of steel economically and on a large scale dates back to the inventions of Henry Bessemer. While searching for an improved method of making big guns, Bessemer hit upon the idea of forcing a blast of air through the molten iron and thus burning away carbon, silicon, and manganese in the cast iron. No fuel was supplied except the carbon and silicon in the iron itself. In burning out this carbon sufficient heat was generated to keep the metal fluid.
When Bessemer made the announcement of his new process before the British Association in 1856, his paper met with skepticism, but he was able to demonstrate by actual experiment that cast iron could be converted into malleable iron in this way. However, when several firms operating under licenses from the inventor endeavored to reproduce his experiment on a commercial scale they were unsuccessful, and after costly experiments the process was given up as a failure. Bessemer, however, persisted in his efforts and succeeded eventually in producing malleable iron of a quality equal if not superior to that on the market. But iron makers after the failure of the first experiments would have nothing to do with the new process until Bessemer began to turn out quantities of iron at $100 a ton below the prevailing market price. Then iron makers woke up and Bessemer had no difficulty in placing his process with numbers of firms on a very profitable royalty basis.
This process pertained to the making of iron and not steel. When Bessemer tried to produce steel he was confronted with serious difficulties. The steel he obtained was very brittle. He tried purer ores with little better success. Then a solution of his problem was offered by Robert F. Mushet, who discovered a compound which would be added to the molten metal to purify it. This compound which is known as “spiegeleisen” is composed of iron, carbon, and manganese. It removes the oxide of iron and the sulphur and regulates the amount of carbon in the steel.
A Bessemer converter furnishes by far the most spectacular operation in steel manufacture. The converter consists of a large bottle-shaped vessel lined with refractory material. In the bottom of the vessel there are openings through which the air blast is admitted. The molten metal is poured into the flask and then the air blast is turned on. The metal begins to boil violently. A dazzlingly brilliant blast of flame and sparks comes roaring out of the mouth of the converter. Bubbles of metal are thrown high into the air where they burst into showers of sparks. The effect is similar to that of a volcanic eruption. In from ten to twenty minutes the eruption subsides and then a quantity of spiegeleisen is added. The converter is mounted on trunnions so that when the operation is completed the vessel is tilted over and the charge of molten metal now converted into steel is poured out.