Medium carbon ferrochromium is used in the production of low carbon structural steel, chromium steel and alloy structural steel. Chromium steel is often used to manufacture gears, gear shafts, etc. There are two main smelting methods of medium carbon ferrochromium: high carbon ferrochromium refining method and electro-silicothermic method.
High carbon ferrochromium refining process is divided into chromium ore refining high carbon ferrochromium and oxygen refining high carbon ferrochromium. When high carbon ferrochromium is used in chromium concentrate, the refining slag has higher viscosity and melting point, and the smelting temperature must be higher. Therefore, high power consumption, short lining life, carbon content is not easy to fall. Oxygen blowing of high carbon ferrochromium has great advantages, such as high productivity, low cost and high recovery. At present, the traditional production method is electro-silicothermic method. Electro-silicothermic process is to produce medium and low carbon ferrochromium by reducing the oxides of chromium and iron with silicon in the silicon-chromium alloy under the condition of making alkaline slag in the electric furnace.
Medium and low carbon ferrochromium smelting by electro-silicothermic method is carried out in a fixed three-phase electric arc furnace. Self-baking electrodes can be used. The lining of the furnace is made of magnesia bricks (dry lining). Short lining life is an important problem in the production of medium and low carbon ferrochromium. Because of the high smelting temperature (up to 1650 degrees Celsius), the lining life is generally shorter. The raw materials for smelting medium and low carbon ferrochromium are chromium ore, silicon chromium alloy and lime. Chromium ore should be dry and pure lump ore or concentrate powder. The higher the content of Cr2O3, the better the impurity content. The content of phosphorus in chromite should not be more than 0.03% and the particle size should be less than 60 mm. Silicon-chromium alloy should be crushed, with particle size less than 30 mm and no slag. Lime should be freshly fired with a CaO content of not less than 85%.
Oxygen blowing process is to produce medium and low carbon ferrochromium by directly blowing oxygen into liquid high carbon ferrochromium to decarburize it. The main elements in high carbon ferrochromium are chromium, iron, silicon and carbon, which can be oxidized. The main task of oxidative blowing of high carbon ferrochromium is decarbonization and chromium retention. When oxygen is blown into liquid high carbon ferrochromium, the content of chromium and iron accounts for more than 90% of the total alloy, so chromium and iron are oxidized first, and then the silicon in the alloy is oxidized by these oxides. Because of the oxidation of chromium, iron and silicon, the temperature of molten pool increases rapidly and decarbonization reaction develops rapidly. The higher the temperature, the more conducive to decarbonization reaction and can inhibit the oxidation reaction of chromium, the lower the carbon content in the alloy.