Raw Material Preparation
Before smelting, manganese carbonate ore must be roasted and the powdered ore must be sintered and agglomerated. Ores containing high iron and phosphorus can generally only be used together, or manganese-rich slag with low iron and low phosphorus can be produced through selective reduction. Coke is used as a reducing agent during smelting, and some factories also use lean coal or anthracite. The auxiliary raw material is mainly lime, and silica is generally added when smelting manganese-silicon alloy.
Use of Ferromanganese in Steelmaking
Ferromanganese is mainly used in steelmaking as a manganese source: manganese combines with sulfur to reduce hot shortness, acts as a deoxidizer, and alloys the steel to improve strength and toughness. The manganese-rich ferroalloy is added during refining to adjust the melt chemistry.
Steel Casting Heat Treatment
Steel castings should be used after heat treatment. Because there are casting defects such as pores, cracks, shrinkage cavities, shrinkage porosity, coarse grains, uneven structure, and residual internal stress inside the cast steel castings, the strength, especially the plasticity and toughness, of the steel castings are greatly reduced.
In order to refine the grains, uniformize the structure, and eliminate internal stress, steel castings must be normalized or annealed. The mechanical properties of normalized steel are higher than those after annealing, and the cost is lower, so it is widely used. However, since normalizing treatment will cause greater internal stress than annealing, it is only suitable for steel castings with a carbon content of less than 0.35 percent. Because low-carbon steel castings have good plasticity, they are not easy to crack when cooled. In order to reduce internal stress, steel castings should be tempered at high temperature after normalizing. For steel castings with carbon content greater than or equal to 0.35 percent, complex structures, and prone to cracks, only annealing can be performed. Steel castings should not be quenched, otherwise they will easily crack.
Frequently Asked Questions
What raw materials are used for ferromanganese smelting? Roasted and agglomerated manganese ore with coke (or lean coal/anthracite) as the reductant and lime as the auxiliary.
Why must steel castings be heat treated? To refine grains, uniformize the structure, and eliminate internal stress from casting defects.
When is annealing used instead of normalizing? For castings with carbon content at least 0.35 percent, complex structures, or crack tendency.
