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High carbon ferrochrome production technology

High carbon ferrochrome production technology

High carbon ferrochrome production technology

Anyang Weiyuan Alloy provides professional High carbon ferrochrome price information, high-quality products, and excellent delivery services.

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Market Details

Ferroalloys are composed of one or more metal or non-metallic elements and iron elements. High-carbon ferrochromium is an alloy used as a deoxidizer, alloy additive, reducing agent, etc. in the steel and foundry industries. Chromium is one of the most versatile and widely used alloying elements in steel. Chromium has the effect of significantly changing the corrosion resistance and oxidation resistance of steel, and helps improve wear resistance and maintain high-temperature strength.

 

 Chromium is an essential ingredient in various stainless steels. my country’s national standards stipulate that the carbon content of high-carbon ferrochromium alloys is 4 to 10%. In fact, there are an increasing number of users who require the carbon content of high-carbon ferrochrome to be narrower than the above range, and there are also some special requirements such as improving the crushing performance by controlling the carbon content of the alloy. Therefore, how to control the carbon content of alloys during the smelting process of high-carbon ferrochromium has become an important technical issue.

High carbon ferrochrome production technology

 

ferro chrome chemical composition


 

Category Grade Chemical composition (mass fraction) “%
Cr C Si P S
Scope
High Carbon Ferro chrome FeCr67C6. 0 62.0-72.0 6.0 1.0 0.03 0.04 0.06
FeCr67C9.5 62.0-72.0 9.5 1.0 0.03 0.04 0.06
FeCr55C1000 60.0 52.0 10.0 1.5 5.0 0.04 0.06 0.04 0.06

High carbon ferrochrome production technology


Many people have discussed the formation mechanism of various chromium carbides and the factors affecting the carbon content of the alloy during the smelting process of high-carbon ferrochrome, but the research needs to be further deepened. Many people have discussed the formation mechanism of various chromium silicides and the factors affecting the silicon content of the alloy during the smelting process of high-carbon ferrochrome, but the research needs to be further deepened. Reducing the sulfur content of high-carbon ferrochrome is an important issue in the production of high-carbon ferrochrome.

During the smelting process, the distribution of sulfur is as follows: 50-60% enters the slag, 20-30% volatilizes, and about 8-15% enters the alloy. How to reduce the sulfur entering the alloy is an issue that ferroalloy workers have always been concerned about [There are many factors that affect the sulfur content of the alloy, such as the sulfur content of the coke, the carbon and silicon content in the alloy, the alkalinity of the slag and the furnace temperature, etc. Desulfurization has an impact. Chromium element can make steel, alloys and certain metal materials have special physical and chemical properties, and can improve the performance of materials. It has been widely valued and used as one of the important alloy elements. Chromium is obtained from the reduction of Cr2O3 in chromium ore.

Carbon content control of high carbon ferrochrome


ferroalloy manufacturingIn a submerged arc furnace, when coke is used as a reducing agent to reduce chromium ore, the carbothermal reduction reaction of chromium trioxide and the change in standard free energy are as follows: 2/3Cr2O3+26/9C=4/9Cr3C2+2CO
(1)=478233.8-349.03T(J)Topen=1100℃2/3Cr2O3+18/7C=4/21Cr7C3+2CO
(2)=482288.4-343.14T(J)Topen=1130℃2/3Cr2O3+54/23C=4/69Cr23C6+2CO
(3)=494368.6-341.72T(J)T open=1175℃

As the charge decreases and the furnace temperature increases, Cr3C2 reacts with Cr2O3 to form Cr7C3: 5(Cr2O3)+27[Cr3C2]=13[Cr7C3]+15CO
(4)=3863480-231.32T(J)Topen=1385℃2/3[Cr2O3]+14/5[Cr3C2]=4/3[Cr]+6/5[Cr7C3]+2CO
(5)=543609-309.45T(J)Topen=1484℃

In actual production, sometimes the minerals entering the furnace are refractory and difficult to reduce due to different structures; or the ore blocks entering the furnace are too large to be reduced in time and fall to the lower layer of the slag to form a residual ore layer, which interacts with the molten iron at a temperature of up to 1700°C. A violent decarburization reaction occurs when liquid or falling alloy droplets come into contact:

3[Cr7C3]+(Cr2O3)=[Cr23C6]+3CO
(6)=621148-328.13T(J)Topen=1620℃[Cr23C6]+2(Cr2O3)=27[Cr]+6CO

(7)=682594-344.22T(J)Topen=1710℃, physical and chemical properties of chromium ore The difference directly affects its reactivity in the furnace. Different chromium ores have greatly different reduction rates of Cr2O3 under the same temperature conditions. The starting reduction temperature of Cr2O3 in general chromium ores is 1100°C; at 1400°C, the reduction reaction rates of Cr2O3 in different chromium ores are basically similar; actual tests on several chromium ores below 1200°C show that the reduction reactions of Cr2O3 in different chromium ores are The speed varies greatly. Therefore, if the chemical composition and mineral structure of chromium ore can ensure a high degree of reduction of Cr2O3 below 1200°C, Cr3C2 and Cr7C3 with higher carbon content will be generated preferentially.

As a result, the alloy has a higher carbon content; for chromium ore with a lower degree of reduction, when the temperature is higher than 1200°C, a certain amount of Cr23C6 will be generated while Cr3C2 and Cr7C3 are generated, thereby reducing the alloy’s Carbon content. When the structure of chromium ore is dense, the crystals are coarse and the blockiness is large, the chromium complex oxide is difficult to decompose and reduce. During the smelting process, only entering the high-temperature arc zone can the rapid reaction occur, thereby causing the Cr23C6 and Cr The proportion increases, and at the same time, the generated chromium carbide reacts with Cr2O3 in the slag and the refining and decarburization continues to reduce the carbon content of the alloy [2]. Therefore, it is important to rationally select and use chromium ore according to the product content requirements and the properties of different chromium ores. The deposit is aluminum chromite, which is a dense phenocryst ore (also known as hard chromium spinel). It is refractory and has poor reducibility. It is suitable for smelting low-carbon products. The particle size of chromium ore is between 20 and 80 mm.

During the smelting process of high-carbon ferrochrome, when the smelting temperature reaches about 1200°C, silicon begins to be reduced (SiO2+2C=Si+2CO), and the reduced Si further reacts with chromium carbides to form stable chromium silicide (Cr7C3+7Si=7CrSi+3C, Cr7C3+10Si=7CrSi+3SiC)〔3〕.
Production practice shows that when using chromium ore that can produce a carbon content of more than 8%, as the carbon content of the alloy increases, its silicon content decreases or tends to remain unchanged [2]. When using difficult-to-reduction ores for production In FeCr67C6.0 grade ferrochrome, due to the formation of a “residual ore layer” on the alloy, at high temperatures above 1700°C, when molten alloy drops pass through the residual ore layer, a violent decarburization reaction occurs. At this time, the decarburization reaction is far more intense than the reduction reaction of silicon, and the desiliconization reaction occurs simultaneously with the decarburization reaction (3CrSi+2Cr2O3=7Cr+3SiO2) [4], making the carbon content of the resulting alloy relatively stable, and the increase in silicon content has an impact on Its impact is not significant, so when producing FeCr67C6.0 grade ferrochromium from refractory ores, the purpose of carbon reduction cannot be achieved by adding silicon to the alloy.

The greater the MgO/Al2O3 ratio in the slag, the higher the carbon content of the alloy; conversely, the lower the carbon content of the alloy. The ratio of MgO/Al2O3 is relatively high, making it difficult to continuously and stably produce products containing C≤6.0%. Therefore, through production practice, the author believes that when producing products with C ≤ 6.0%, using chromium ore with high alumina content or appropriately adding residue with high alumina content to the raw materials can achieve better results. When producing high-carbon ferrochrome with C≤6.0%, the tapping temperature is crucial. In order not to produce high-carbon carbides, the tapping temperature is generally 1700°C.

During the smelting process of high carbon ferrochromium, the silicon content of its alloy is actually only the average silicon content of the molten iron accumulated in the lower part of the furnace during the two tapping intervals, while the silicon content of the metal in different areas of the furnace during the smelting process Not the same.
① The area of ​​increased silicon content in the alloy: starting from the bulk material layer to the junction of the molten layer and the residual coke layer, as the metal particles sink to the depth of the furnace, the silicon content in the alloy continues to rise.
② The area where the silicon content of the alloy decreases: from the interface layer between the molten layer and the residual coke to the tap hole
③ The silicon-containing unstable area of ​​the alloy: refers to the iron deposited layer at the furnace bottom. For the same electric furnace, within a certain time range, the silicon content of the molten iron in this layer is basically stable. However, due to different mineral types, changes over time and the thickness of the iron deposited layer The silicon content changes, which is called the silicon-containing unstable region. During the smelting process of high-carbon ferrochrome, the silicon in the alloy comes from SiO2 in the ore and solvent silica. The specific reaction is as follows: 1/2SiO2+C=1/2Si+CO; SiO2+C=SiO+CO; SiO+C= Si+CO

High carbon ferro chrome sulfur content control


process of FeSiThe sulfur in high-carbon ferrochrome comes from raw materials, of which coke and chromium ore bring in the majority of the sulfur. The sulfur in coke exists in the form of sulfide (FeS, CaS) or organic sulfur. In the actual production process, the raw materials 8% to 15% of the sulfur in the alloy enters the alloy, 20% to 30% volatilizes, and 60% to 70% enters the slag. The sulfur entering the alloy will form a series of sulfides with chromium, such as CrS, Cr2S3, etc. CrS melts without decomposing at 1565°C, and decomposes to form Cr15S6 below 800°C. Since the melting point of sulfides is lower than the melting point of ferrochrome, these sulfides are distributed on the surface of ferrochrome. There are several main ways to reduce the sulfur content in high-carbon ferrochrome alloys: increasing the furnace temperature to increase the equilibrium constant of the chemical reaction.

 

Reduce the Cr2O3 content in the slag and maintain a higher melting point during the production process. The level of Cr2o3 content reflects the degree of reduction of useful elements. A lower Cr2o3 content means that various reactions in the furnace are carried out more thoroughly, and the reducing agent coke is excess. In actual operation, it is more beneficial to the desulfurization effect to properly control the melting point of the slag, avoid operations with too low a melting point, and ensure sufficient dosage of reducing agent. However, the melting point of the slag should not be too high, otherwise the slag will become sticky and the slag iron will overheat, causing the furnace condition to deteriorate. Increasing the alkalinity of the slag means increasing the cao content in the slag, reducing the viscosity of the slag, and increasing the conductivity of the slag. Both increases can improve the kinetic conditions of the reaction in the furnace, ensure uniform power distribution in the furnace, and expand the crucible, but At the same time, unfavorable factors such as excessive electrode consumption, reduced slag hanging on the furnace wall, and heat loss also occurred.

 

Increasing the percentage content of c and si in the alloy, selecting appropriate chromium ore and controlling the appropriate melting point of slag, and sometimes adding desulfurizers such as lime to the ladle can also have a certain effect. After adding lime, the melting point of the slag is lowered, resulting in carbonization of the alloy and also reducing the chromium recovery rate.
Cause Analysis:
(1) During the slag formation process, lime forms gehlenite with Mgo and AL2O3 in the slag. Its melting point is around 1500°C, which lowers the reduction temperature and increases the concentration of cr2o3 in the slag, resulting in carburization of the alloy.

(2) Due to the increase in the amount of lime, the amount of cac2 in the slag increases, resulting in carbonization of the alloy.

(3) The desulfurization capacity of the cao-Mgo-SiO2-AL2O3 quaternary slag system is much greater than that of the MgO-SiO2-AL2O3 ternary slag system. After adding lime, the viscosity of the melt can be reduced and the conductivity of the melt can be increased.

(4) When smelting high carbon ferrochromium using quaternary slag, the CaO content in the slag should not be controlled too high, otherwise it will cause negative effects. For a certain molten slag, the electrical conductivity of high carbon ferromanganese is inversely proportional to the viscosity. Therefore, adding lime can reduce the viscosity of the slag and at the same time increase the electrical conductivity of the slag.

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About WeiYuan Alloy Co., Ltd was established in 2011. We specialize in producing various alloys for steel making, including Ferro Silicon, Ferro Chromium, Silicon Manganese, Ferro
Manganese, Calcium Silicon Barium, Metallurgy Nodulant, Silicon Calcium Powder, carbon raiser, etc.

Advanced equipment and strict QC Procedures ensure our products are of high quality.

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