Chromium iron is divided into high carbon chromium iron, medium carbon chromium iron, low carbon chromium iron, and micro carbon chromium iron according to their carbon content.
The carbon content of high carbon ferrochrome is 4-8%, the carbon content of medium carbon ferrochrome is 0.4%, the carbon content of low-carbon ferrochrome is 0.15-0.50%, and the carbon content of low-carbon ferrochrome is 0.06%
Chromium iron is mainly used as an important alloy additive in steelmaking, which was previously added in the later stage of steelmaking refining. Now, the focus of chromium iron production is on refining carbon chromium iron.
The main uses of high carbon ferrochrome include:
(1) Used as an alloying agent for ball steel, tool steel, and high-speed steel with high carbon content, to improve the hardenability of steel, increase its wear resistance and hardness;
(2) Used as an additive for cast iron to improve its wear resistance and hardness, while also giving it good heat resistance;
(3) Used as a chromium containing raw material for the production of silicon chromium alloys and medium, low, and micro carbon ferrochrome using slag free method;
(4) Used as a chromium containing raw material for electrolytic production of metallic chromium;
(5) Used as a raw material for oxygen blowing smelting of stainless steel.
The smelting methods of high carbon ferrochrome include blast furnace method, electric furnace method, plasma furnace method, etc. The use of blast furnaces can only produce special pig iron with a chromium content of about 30%. At present, high carbon ferrochrome with high chromium content is mostly smelted using the electric furnace method in a
Dc Submerged Arc Furnace.
The basic principle of electric furnace smelting high carbon ferrochrome is to reduce chromium and iron oxides in chromium ore with carbon. The starting temperature for carbon reduction of chromium oxide to produce Cr2C2 is 1373K, the starting temperature for the reaction of producing Cr7C3 is 1403K, and the starting temperature for the reaction of reducing to produce chromium is 1523K. Therefore, during carbon reduction of chromium ore, chromium carbides are obtained, not metallic chromium. The carbon content in ferrochrome depends on the reaction temperature. It is easier to generate carbides with high carbon content than carbides with low carbon content.
The raw materials for smelting high carbon ferrochrome include chromium ore, coke, and silica.
In chromium ore, Cr2O3 ≥ 40%, Cr2O3/∑ FeO ≥ 2.5, S<0.05%, P<0.7%, MgO and Al2O3 content should not be too high, with a particle size of 10-70mm.
Coke requires a fixed carbon content of no less than 84%, an ash content of less than 15%, S<0.6%, and a particle size of 3-20mm.
Silicone requires a content of SiO2 ≥ 97%, Al2O3 ≤ 1.0%, good thermal stability, no soil, and a particle size of 20-80mm.
March 12, 2024