Ferro-Alloy Production: Part One

Ferro-alloys are master alloys containing iron and one or more non-ferrous metals as alloying elements. The ferro-alloys are usually classified in two groups: bulk ferro-alloys (produced in large quantities in electric arc furnaces), and special ferroalloys (produced in smaller quantities, but with growing importance). Bulk ferro-alloys are used in steel making and steel or iron foundries exclusively, while the use of special ferroalloys is far more varied. In total, about 90 % of the ferroalloys produced are used in the steel industry.

As mentioned above, ferro-alloys can be divided into two main categories: bulk alloys and special alloys. Bulk ferro-alloys (ferro-chrome, ferro-silicon, ferro-manganese, silico-manganese and ferro-nickel).

Compared to bulk ferro-alloys, the production rate of special ferro-alloys is rather small. Special ferro-alloys (ferro-vanadium, ferro-molybdenum, ferro-tungsten, ferro-titanium, ferro-boron, and ferro-niobium) are mostly used in the iron, steel and cast-iron industries. Besides this, some special ferro-alloys are increasingly also used in other industry sectors, e.g. aluminum and chemical industries.

The ferro-alloy industry is associated with the iron and steel industries, its largest customers. Ferro-alloys impart distinctive qualities to steel and cast iron and serve important functions during iron and steel production cycles. The principal ferroalloys are those of chromium, manganese, and silicon.

Chromium provides corrosion resistance to stainless steels. Manganese is essential to counteract the harmful effects of sulfur in the production of virtually all steels and cast iron. Silicon is used primarily for deoxidation in steel and as an alloying agent in cast iron. Boron, cobalt, columbium, copper, molybdenum, nickel, phosphorus, titanium, tungsten, vanadium, zirconium, and the rare earths impart specific characteristics and are usually added as ferro-alloys.

A variety of furnace types, including submerged electric arc furnaces, exothermic (metallothermic) reaction furnaces, and electrolytic cells can be used to produce ferroalloys. Furnace descriptions and their ferroalloy products are given in Table 1.
Table 1: Ferro-alloy processes and respective product groups Legend for Table 1:
a - Process by which metal is smelted in a refractory-lined cup-shaped steel shell by submerged graphite electrodes.
b - Process by which molten charge material is reduced, in exothermic reaction, by addition of silicon, aluminum, or a combination of the 2.
c - Process by which simple ions of a metal, usually chromium or manganese in an electrolyte, are plated on cathodes by direct low-voltage current.
d - Process by which carbon is removed from solid-state high-carbon ferrochrome within vacuum furnaces maintained at temperatures near melting point of alloy.
e - Process that converts electrical energy into heat, without electrodes, to melt metal charges in a cup or drum-shaped vessel.