High carbon ferrochrome
It is mainly used as an alloying agent for ball steel, tool steel and high-speed steel with high carbon content, as an additive for cast iron, also as a chromium-containing raw material for the production of silicon-chromium alloys and medium, low and micro-carbon ferrochrome by the slag-free method, and for the production of metallic chromium by electrolysis Chromium-containing raw materials, raw materials for smelting stainless steel by oxygen blowing method.
The smelting methods of high-carbon ferrochromium mainly include blast furnace method and submerged arc furnace method. The raw materials used are chrome ore, coke and silica. High-quality metallurgical grade chrome ore requires Crp0g;>48%, S<0.1%, P<0.1%, Cr0g/FeO>3. The blast furnace method can only produce special pig iron with a chromium content of about 30%. High-carbon ferrochromium with high chromium content is mostly smelted in submerged arc furnaces by flux method. Due to the high melting point of ores and alloys, the required furnace temperature is also high, so high secondary voltage and electrode current density are used for smelting.
Medium, low and micro carbon ferrochrome
Medium and low-carbon ferrochrome is used to produce medium and low-carbon structural steel, chrome steel and alloy structural steel, etc. Micro-carbon ferrochrome is mainly used to produce stainless steel, heat-resistant steel and acid-resistant steel.
Medium, low and micro-carbon ferrochrome (collectively referred to as refined ferrochrome) is generally smelted with silicon-chromium alloy, chromite and lime as raw materials, and is smelted by electrosilicon thermal reduction method. Use 1500~6000 kVA electric furnace for refining and desiliconization, and use high basicity slag operation (CaO/Sio2 is 1.6~1.8). The lower the carbon content of these ferrochrome, the higher the requirements for raw materials.
The smelting of medium and low carbon ferrochrome also adopts the oxygen blowing method, that is, oxygen is directly blown into liquid high carbon ferrochrome to decarburize it. A small amount of lime and fluorite are added to the molten pool during blowing to form slag, and silicon-chromium alloy or ferrosilicon is added before iron tapping to recover chromium in the slag. The oxygen blowing method is to put the liquid high-carbon ferrochromium out of the electric furnace into the converter for oxygen blowing decarburization and refining, so it is also called the converter method.
Low and micro-carbon ferrochrome smelting is also produced on a large scale by the heat transfer method, that is, two electric furnaces are used during production, one furnace smelts silicon-chromium alloy; the other furnace melts slag composed of chromium ore and lime. The desiliconization and refining reaction is carried out in two stages in two ladles: ① After the slag of the slag furnace is injected into the first ladle, the silicon-chromium alloy that has been initially desiliconized in the other ladle is mixed in. There is a large excess of oxidant and sufficient desiliconization, and micro-carbon ferrochrome with a silicon content of less than 0.8% and a carbon content of as low as 0.02% can be obtained. ② After the reacted slag (containing about 15% of CTz0g) in the first basket is moved to the second ladle, the silicon-chromium alloy (containing 45% of silicon) smelted in the silicon-chromium electric furnace is heated into the slag, and the reaction Obtain the silicon-chromium alloy (containing about 25% of silicon) of preliminary desiliconization in the back, blend into the first ladle to further desiliconize, and the slag contains Cr Og can be discarded less than 3%.
Micro-carbon ferrochromium smelting also has a vacuum solid-state decarburization method, that is, high-carbon ferrochrome is ground into powder, mixed with an appropriate oxidant, and produced by mixing, pressing, drying and vacuum smelting to obtain micro-carbon with low carbon content of ferrochrome. The equipment used is a vacuum resistance furnace.