BESSEMER STEEL-Bessemer process
Steel made by blowing air through molten iron. The original pneumatic process, which for the first time made possible the production of steel on a large scale, involved blowing air through molten pig iron held in a bottom-blown vessel lined with acid (siliceous) refractories, and thus is commonly referred to as the acid Bessemer process. It was developed independently by Henry Bessemer of England, whose U.S. patent was issued in 1856, and by William Kelly, Eddyville, Kentucky, who didn’t apply for a patent until 1857 but proved that he had been working on the process as early as 1847. Bessemer built a steel works in Sheffield, England, and began operating in 1860. In the United States, where both men shared rights to the process, Kelly Pneumatic Process Co. was formed in 1863. By 1871, some 55% of total U.S. steel production was made by this process, and it remained the significant steelmaking process for many years until it was eventually replaced worldwide by the open-hearth process, which, in turn, was replaced by the basic-oxygen process.
The acid Bessemer process was the major steelmaking process until 1908. Among the product forms made were free-machining bars, flat-rolled stock, seamless and welded tubing, wire, and castings. Fully killed (deoxidized) acid Bessemer steel was first used by U.S. Steel for making steel pipe, and the dephosphorized steel was used extensively in the production of welded pipe and galvanized sheet. The basic Bessemer process, or Thomas process, patented in 1879 by Sidney G. Thomas in England, involved use of a basic lining and flux in the converter, making it possible to use the pneumatic process to refine pig iron smelted from high-phosphorus ores common in Europe. The process was never used in the United States, and production developed more widely in other European countries than in England. Steel produced by the process was called Thomas steel. In the acid Bessemer process, ferromanganese and sometimes steel scrap were added to the steel when pouring into the ladle in order to regulate the content. In the blowing process, the chemical action between the oxygen of the air and the molten mass increases the temperature, and air
then forms the chief fuel as carbon is oxidized and driven off. The blowing required only a few minutes, and carbon was reduced to 0.04% or less. The carbon desired in the steel was then regulated by the addition of carbon to the melt. The two processes, acid and basic, differ in the type of refractories employed for lining the converters, and there is a difference in the resulting steel since the acid process does not remove as much sulfur and phosphorus.

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