Science: Bessemer Eye

Up to about 1870 railroad rails were made of iron because the cost of making steel in quantity was prohibitive. Then the converters invented by Henry Bessemer got going and steel became much cheaper. In Bessemer converters—little changed after 70 years—a powerful blast of air is forced through molten pig iron as it lies in the converter's capacious belly. The air oxidizes impurities which form a slag or pass off as gases through the converter mouth. After the slag has formed, the steel is poured into molds to make ingots.

Since 1920 steelmaking has had a big swing to the open-hearth...

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