In the 19th century there were two methods of primary steel making from pig iron and these were the Bessemer converter (Henry Bessemer, 1813/98) and open hearth furnace (Carl Wilhelm Siemens, 1823/83 & Pierre-Émile Martin, 1824-1915).
This was a large tiltable egg-shaped refractory-lined vessel in which air was blown through the molten pig iron to oxidise unwanted impurities such as carbon, manganese and silicon, resulting in the production of steel in a relatively short time.
The refractory lining of the converter could contain dolomite (calcium magnesium carbonate) which had a role in the conversion process by promoting the removal of impurities and these converters were referred to as basic Bessemer converters. Conversely, an acid Bessemer converter had a refractory lining containing ganister sandstone.
This was a refractory-lined furnace that consisted of a shallow charge container with a low-arched roof where a flame heated the charge to oxidise impurities. The charge consisted of pig iron and steel scrap. It was considered to be an improvement in steel manufacture because it was easier to control than the Bessemer converter and eventually it replaced it, although it was slower in operation. This method of making steel was also known as the Siemens-Martin process or acid open hearth process.
Both of the above processes were eventually replaced following the development of the basic oxygen furnace in 1948 by Robert Durrer (1890-1978) and in essence this was a refinement of the Bessemer converter. The furnace consists of a refractory-lined, tiltable container that can hold up to 400 tons of pig iron. In operation, oxygen is blown through the molten pig iron to oxidise impurities. It is described as ‘basic’ because fluxes of dolomite (calcium magnesium carbonate) are added to the furnace to promote the removal of impurities from the pig iron.