What are the reasons for it?
Silica. this is because of the earthy material that goes in with the iron ore, although most of that should be removed by the limestone in the blast furnace charge. CaCO3 --- CaO + CO2 CaO + SiO2 -- CaSiO3 slag The coke, used as the reducing agent in the BF, is carbon. Most reacts in that way but a fair amount dissolves in the molten iron formed. This is the main reason why pig iron needs further refining before use it makes it too brittle.
