Describe the open hearth process of steel manufacture. What is meant by acid steel and
basic steel?
In the open hearth process a broad shallow furnace is used to support the charge of pig iron and
scrap steel. Pig iron content of the charge may constitute 25% to 75%of the total, which may
vary in size depending upon furnace capacity, between 10 to 50 tonnes. Scrap steel is added to
reduce melting time if starting from cold. Fuel employed in this process may be enriched blast
furnace gas (blast furnace gas may contain 30% CO after cleaning) which melts the charge by
burning across its surface. Reduction of carbon content is achieved by oxidation; this may be
assisted by adding pure iron oxide to the charge. Other impurities are reduced either by
oxidation or absorption in the slag. At frequent intervals samples of the charge are taken for
analysis and when the derived result is obtained the furnace is tapped.
When pig iron is refined by oxidation a slag is produced. Depending upon the nature of the slag
one of two types of processes is employed. If the slag is siliceous it is the acid process. If it is high
in lime content the basic process is used. Hence the furnace lining which is in contact with the
slag is made of siliceous material or basic material according to the nature of the slag. Thus
avoiding the reaction acid plus base =salt plus water. Both acid and basic process can be
operated in the open hearth, Bessemer, LD and electric are furnace.
