Medium, low, and micro-carbon ferrochrome are generally produced using silicon-chromium alloy, chromite, and lime as raw materials. The process involves refining and desiliconizing in a 1500–6000 kVA electric furnace, employing high-basicity slag (CaO/SiO2 ratio of 1.6–1.8). Low and micro-carbon ferrochrome are also produced on a large scale using a hot-mixing method. This method uses two electric furnaces: one for smelting the silicon-chromium alloy, and the other for melting the slag composed of chromite and lime. The refining reaction is carried out in two stages in two containers: ① After the slag from the slag furnace is poured into the first container, the silicon-chromium alloy, which has already undergone preliminary desiliconization, is added to the second container. Due to the large excess of oxidant in the slag, desiliconization is thorough, resulting in micro-carbon ferrochrome with a silicon content below 0.8% and a carbon content as low as 0.02%. ② After the slag from the reaction in the first container (containing approximately 15% Cr2O3) is transferred to the second container, a silicon-chromium alloy (containing 45% silicon) refined in a silicon-chromium electric furnace is hotly added to the slag. After the reaction, a partially desiliconized silicon-chromium alloy (containing approximately 25% silicon) is obtained and added back to the first container for further desiliconization. The slag containing less than 2-3% Cr2O3 can be discarded.
The oxygen blowing method for refining medium and low carbon ferrochrome uses liquid carbon ferrochrome as raw material. During blowing, a small amount of lime and fluorite is added to the molten pool to form slag. Before tapping, silicon-chromium alloy or ferrosilicon is added to recover chromium from the slag. The blowing of low-carbon ferrochrome is only possible under a certain vacuum.
Vacuum solid-state decarburization refining uses finely ground high-carbon ferrochrome as raw material. A portion of the finely ground high-carbon ferrochrome is oxidized and roasted as an oxidant, mixed with water glass or other binders, pressed into lumps, dried at low temperature, and then heated and reduced in a car-bottom vacuum furnace at a vacuum degree of 0.5–10 mmHg and a temperature of 1300–1400℃ for 35–50 hours to obtain micro-carbon ferrochrome with a carbon content of less than 0.03% or even less than 0.01%.
