Introduction and use of ferrochrome

High-carbon ferrochrome (4-8% carbon), medium-carbon ferrochrome (0.5-4% carbon), low-carbon ferrochrome (0.15-0.5% carbon), micro-carbon ferrochrome (0.06% carbon %), ultra-fine carbon ferrochromium (carbon content less than 0.03%), metal chromium, silicon chromium alloy ferrochromium: a ferroalloy composed of chromium and iron, is an important alloy additive for steelmaking. The chromite ore used for smelting ferrochrome is generally required to contain 40-50% Cr2O3, and the ratio of chromium to iron is greater than 2.8. This year, the mass-produced "feeding grade ferrochrome" containing 50% chromium is used to contain Cr2O3 and the ratio of chromium to iron is lower. of ore.

1. Definition

Ferrochrome is a ferroalloy mainly composed of chromium and iron. It is one of the main alloying agents used in the iron and steel industry. In addition to the main components of chromium and iron, it also contains carbon, silicon, sulfur, phosphorus and other impurities. Ferrochromium contains 55%-75% chromium, which can be divided into high carbon (4%-10%C), medium carbon (0.5%-4%C), low carbon (>0.15%-0.5%C) and Micro carbon (≤0.15%C) ferrochrome. High-carbon ferrochrome is also called carbon ferrochrome, and medium, low and micro-carbon ferrochrome is also called refined ferrochrome. A kind of high-carbon ferrochrome produced by ferrochrome with low chromium-iron ratio, containing CR50%-55% is called charge-grade ferrochrome, and nitrogen-containing ferrochrome containing N2%-10% is used as nitrogen alloy agent, and It is called ferrochromium nitride.
Ferrochrome is mainly used as an alloy additive for steelmaking, and was added in the late stage of steelmaking in the past. Smelting stainless steel and other low-carbon steel grades requires the use of low and micro-carbon ferrochrome, so the production of refined ferrochrome was once deeply developed on a large scale. Due to the improvement of the steelmaking process, when the AOD method is used to produce stainless steel and other steel grades, carbon ferrochrome is used to charge the furnace, so it is only necessary to add low-carbon ferrochrome to adjust the composition in the later stage, so the production of ferrochrome is mainly the refining of carbon Plain ferrochrome.

2. Carbon ferrochrome

It is smelted in a reduction electric furnace, using coke as a reducing agent, and silica or bauxite as a flux. The slag composition is generally SiO227-33%, MgO30-34%, Al2O326-30%, Cr2O3<9%. The product contains 4-9% carbon due to the formation of chromium carbides. The reduction electric furnace capacity of modern ferrochromium smelting is 10000-48000 kVA, generally adopts closed and fixed type, and the power consumption of smelting is 3000-4000 kW∙h/ton. The electric furnace for smelting silicon-chromium alloy is similar to the ferrochrome reduction electric furnace, and there are two smelting methods: one-step method and two-step method. One-step smelting with chromite, silica, coke and flux. The two-step method uses carbon ferrochromium, silica, and coke as raw materials for slag-free smelting, and the smelting process is roughly similar to the production of ferrosilicon. Smelting power consumption is about 3000-4000 kW∙h per ton.

3. Purpose

Adding chromium to steel can significantly improve the oxidation resistance of the main steel and increase the corrosion resistance of the steel. Chromium is contained in many steels with special physical and chemical properties. Chromium in steel is added with ferrochrome. High-carbon ferrochromium 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 performance and hardness of steel. Adding chromium to cast iron can improve the hardness, the effect is the main performance, and the chromium content of 0.5%-1.0% can be the main effect and its mechanical properties. High-carbon ferrochrome and charge-grade ferrochrome are widely used as charge for smelting stainless steel (AOD or VOD method), reducing production costs. 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. Micro-carbon ferrochromium is used in the production of stainless steel, acid-resistant steel, heat-resistant steel and electric heating alloys.