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Ferromanganese, a ferroalloy with high content of manganese, is made by heating a mixture of the oxides MnO2 and Fe2O3, with carbon in a furnace. They undergo a thermal decomposition reaction. It is used as a deoxidizer for steel.
Henry Bessemer invented the use of ferromanganese as a method of introducing manganese in controlled proportions during the production of steel. The advantage of combining powdered iron oxide and manganese oxide together is the lower melting point of the combined alloy compared to pure manganese oxide.
A North American standard specification is ASTM A99. The ten grades covered under this specification include:
Standard ferromanganese
Medium-carbon ferromanganese
Low-carbon ferromanganese
In China the standards of ferromanganese produced by electric arc furnaces can be divided into following grades.

In China the standards of ferromanganese produced by blast furnaces can be divided into following grades.