6.3 MVA To 63 MVA Submerged Arc Furnace For High Carbon Ferrochrome Production

Ferrochrome is classified into high carbon ferrochrome, medium carbon ferrochrome, low carbon ferrochrome, and micro carbon ferrochrome based on carbon content. High Carbon Ferrochrome is a ferroalloy with a carbon content of 4%–8%, mainly used in the production of stainless steel and tool steel. Due to its high carbon content, high carbon ferrochrome is suitable for improving the hardness and wear resistance of steel, whereas low-carbon and micro-carbon ferrochrome are more suitable for steel that requires high corrosion resistance.

Medium Carbon Ferrochrome: Carbon content 0.5%–4%

Low Carbon Ferrochrome: Carbon content 0.15%–0.5%

Micro Carbon Ferrochrome: Carbon content <0.15%, mainly used to improve the oxidation resistance and corrosion resistance of steel.

(1) Used as an alloying agent for high-carbon bearing steel, tool steel, and high-speed steel to improve hardenability, wear resistance, and hardness.

(2) Used as an additive in cast iron to improve wear resistance and hardness, while also providing good heat resistance.

(3) Used as a chromium-containing raw material for the slag-free production of silicochromium and medium, low, and micro carbon ferrochrome.

(4) Used as a chromium-containing raw material for the electrolytic production of chromium metal.

(5) Used as a raw material for stainless steel production via the oxygen blowing method.

High carbon ferrochrome can be produced by blast furnace, electric furnace, or plasma furnace processes. Blast furnaces can only produce special pig iron with a chromium content of about 30%. Currently, high carbon ferrochrome with high chromium content is mostly smelted in submerged arc furnaces using the flux method.

The basic principle of electric furnace smelting for high carbon ferrochrome is to reduce chromium and iron oxides in chromite using carbon. The initial temperature for Cr₂C₂ formation from carbon reduction of chromium oxide is 1373 K, for Cr₇C₃ formation is 1403 K, and for metallic chromium formation is 1523 K. Therefore, carbon reduction of chromite yields chromium carbides rather than metallic chromium. The carbon content of ferrochrome depends on the reaction temperature, with higher carbon carbides forming more readily than lower carbon ones.

The raw materials for smelting high carbon ferrochrome include chromite, coke, and silica.

Chromite: Cr₂O₃ ≥ 40%, Cr₂O₃/∑FeO ≥ 2.5, S < 0.05%, P < 0.07%, MgO and Al₂O₃ content not too high, particle size 10–70 mm (refractory ores should have appropriately smaller particle sizes).

Coke: Fixed carbon ≥ 84%, ash < 15%, S < 0.6%, particle size 3–20 mm.

Silica: SiO₂ ≥ 97%, Al₂O₃ ≤ 1.0%, good thermal stability, no clay contamination, particle size 20–80 mm.

High Carbon Ferrochrome is widely used in the steel industry:

Stainless steel production: As a key raw material for 300 series stainless steel, it improves the steel's corrosion resistance and hardness.

Tool steel and high-speed steel: Used as an alloy additive to enhance hardenability, wear resistance, and hardness.

Cast iron modification: Improves the wear resistance and heat resistance of cast iron.

Alloy production: Used in the slag-free process to produce silicon-chromium alloys as well as medium-carbon, low-carbon, and micro-carbon ferrochrome.

Electrolytic production of chromium metal: Serves as a chromium-containing raw material.

Stainless steel refining by oxygen blowing: Provides a source of chromium.