A process for converting pig iron from a blast furnace into steel.

The molten pig iron is loaded into a refractory-lined tilting furnace, (bessemer converter) at about 125° C. Air is blown into the furnace from the base and spiegal is added to introduce the correct amount of carbon. Impurities (especially silicon, phosphorus and manganese) are removed by the converter lining to form a slag. Finally the furnace is tilted so that the molten steel can be poured off.

In the modern VLN (very low nitrogen) version of this process, oxygen and steam are blown into the furnace in place of air to minimize the absorption of nitrogen from the air by the steel. The process is named after the British engineer Sir Henry Bessemer (1813-98) who announced it in 1856.