The addition of chromium to steel can significantly improve the oxidation resistance of steel and increase the corrosion resistance of steel. Chromium is contained in many steels with special physical and chemical properties. Chromium in steel is added with ferrochrome.
According to the carbon content, ferrochrome is divided into high-carbon ferrochrome, medium-carbon ferrochrome, low-carbon ferrochrome and micro-carbon ferrochrome.
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 micro carbon ferrochrome is 0.06%.
Ferrochrome with different carbon content has different uses.
1. High-carbon ferrochrome is used as an alloying agent for ball steel (0.5%-1.45%Cr), tool steel, die steel (5%-12%Cr) and high-speed steel (3.8%-4.4%Cr), which can improve the quenching of steel. Permeability, increase the wear resistance and hardness of steel. Adding chromium to cast iron can increase hardness and improve wear resistance, and 0.5% to 1.0% chromium can improve its mechanical properties. High-carbon ferrochrome and charge-grade ferrochrome are widely used as charge for smelting stainless steel to reduce production costs.
2. Medium and low-carbon ferrochromium is used to produce medium and low-carbon structural steel, carburizing steel, gears, high-pressure blower blades, valve plates, etc.
3. Micro-carbon ferrochromium is used in the production of stainless steel, acid-resistant steel, heat-resistant steel and electric heating alloys.
The smelting process of ferrochrome with different carbon content is different.
1. Low-carbon ferrochrome: There are two main smelting methods for low-carbon ferrochrome: high-carbon ferrochrome refining method and electric silicon thermal method. The high-carbon ferrochrome refining method is divided into refining high-carbon ferrochrome with chromium ore and refining high-carbon ferrochrome with oxygen. When high-carbon ferrochrome is used as chromium ore concentrate, the refining slag has a higher viscosity and a higher melting point, and the temperature in the smelting process should be higher. The traditional production method is still electric silicon thermal method. The electric silicon thermal method is to use the silicon in the silicon-chromium alloy to reduce the oxides of chromium and iron under the condition of creating alkaline slag in the electric furnace, so as to produce medium and low carbon ferrochromium.
2. Micro-carbon ferrochrome: Micro-carbon ferrochrome is mainly used to produce stainless steel, acid-resistant steel and heat-resistant steel. Micro-carbon ferrochromium smelting methods include electric silicon heating method and thermal conversion method. The electrosilicon thermal micro-carbon ferrochromium smelting is to add chromium ore, silicon-chromium alloy and lime into the electric arc furnace. The electric silicon thermal micro-carbon ferrochrome smelting mainly relies on electric heating to melt the charge, and the silicon in the silicon-chromium alloy is reduced to the chromium ore. Made of Cr2O3. The micro-carbon ferrochromium smelting process of the hot mixing method is to heat the pre-melted chromium ore-lime melt and the silicon-chromium alloy in the molten iron ladle outside the furnace, so as to produce the micro-carbon ferrochrome.
3. High-carbon ferrochrome: The smelting methods of high-carbon ferrochrome include blast furnace method, electric furnace method, plasma furnace method and so on. Using a blast furnace can only produce special pig iron with a chromium content of about 30%. As of 2012, most of the high-carbon ferrochrome with high chromium content is smelted in submerged arc furnaces by flux method.