High-carbon ferrochrome and a method of smelting the same

Abstract

The application provides high-carbon ferrochrome and a smelting method thereof. In the method, chromite powder, coke powder and coal pitch are uniformly mixed to prepare a binding mixture, the binding mixture is pyrolyzed and sintered, and then is fed into an electric furnace together with a reducing agent and a slag forming agent to be smelted to be clean, and then is refined by top and bottom combined blowing of a converter, is slagged, and is cast to obtain high-carbon ferrochrome. The method smelts high-carbon ferrochrome by sintering, in-furnace smelting and blowing, and can not only obtain high-quality products, but also effectively reduces power consumption compared with traditional complete in-furnace smelting, because no power is supplied in the blowing process, and almost no power is consumed. The high-carbon ferrochrome has low impurity content of sulfur and phosphorus, and has the characteristics of small amount of inclusions and high alloy purity, because the high-carbon ferrochrome has experienced multiple purification steps of pyrolysis, sintering and converter blowing.

Description

Technical Field

[0001] This application relates to alloy smelting technology, and more particularly to a high-carbon ferrochrome and its smelting method. Background Technology

[0002] High-carbon ferrochrome is the most produced and widely used type of ferrochrome alloy. It is primarily used as an alloying additive in the production of stainless steel, bearing steel, and tool steel to improve the hardness, wear resistance, and corrosion resistance of the steel. High-carbon ferrochrome is mostly produced using submerged arc furnaces (SAF). This is a type of high-power, continuous pyrometallurgical equipment. The core process involves mixing ferrochrome ore, coke, and flux in a specific ratio and then feeding them into the furnace. Electrodes are inserted into the furnace charge to form a submerged arc, and the charge is melted at high temperatures through resistance heating and arc heating. At a high temperature of approximately 1600℃-1800℃, the carbon in the coke reduces the chromium and iron oxides in the chromium ore, generating molten ferrochrome alloy and slag. The final product is obtained through periodic tapping, casting, or granulation. Due to the high power consumption in the smelting process of high-carbon ferrochrome, developing lower-power smelting methods is one direction for process improvement. Summary of the Invention

[0003] This application provides a high-carbon ferrochrome and a smelting method thereof, which provides a low-power smelting path for high-carbon ferrochrome.

[0004] In a first aspect, this application provides a method for smelting high-carbon ferrochrome, comprising the following steps: Chromite powder, coke powder and coal tar pitch are mixed evenly according to the weight parts to make a binder mixture; The binder mixture is fed into a pyrolysis furnace, inert gas is introduced, and the temperature is raised to 800°C for pyrolysis according to the heating regime to obtain the pyrolysis material; The pyrolytic material is sintered to obtain sintered material; The sintering material, reducing agent and slag-forming agent are fed into an electric furnace and smelted until the melt is clear and the smelting temperature is reached to obtain the first melt. The first melt is fed into a converter, and oxygen is blown from the top and inert gas is blown from the bottom to produce the second melt. After slag removal from the second melt, it is transferred to a ladle for casting to obtain high-carbon ferrochrome.

[0005] 1) The method of this application uses sintering, furnace smelting and blowing to smelt high carbon ferrochrome, which can not only obtain products of excellent quality, but also consume almost no electricity because no electricity is supplied during the blowing process. Therefore, it can effectively reduce electricity consumption compared with the traditional completely furnace smelting.

[0006] 2) This application uses coal tar pitch as a binder, mixing fine chromite powder and coke powder to form a binder mixture. Compared with conventional water glass or bentonite binders, coal tar pitch has good plasticity and binding force at room temperature, which can agglomerate the powder into particles, avoid dust flying, and improve the working environment. Moreover, coal tar pitch is converted into pitch coke during subsequent pyrolysis, which is deposited in situ between particles. It does not introduce additional impurities (such as sodium, calcium, etc.) and can form a high-strength porous structure, which is beneficial to the permeability and reduction efficiency of subsequent sintering and electric furnace smelting.

[0007] 3) This application achieves the orderly removal and utilization of volatile matter in coal tar pitch through a two-step pretreatment process of pyrolysis and sintering. The pyrolysis step is carried out under an inert atmosphere, allowing the volatile matter to be centrally recovered as chemical raw materials or fuel, avoiding the waste of thermal energy and environmental pollution caused by the disorderly combustion of volatile matter during direct sintering. The sintering step utilizes the exothermic combustion of the carbonaceous material (coke powder + pitch coke) contained in the pyrolysis material itself, achieving self-sustaining sintering under negative pressure ventilation conditions without the need for additional fuel. This pyrolysis-sintering series process enables the cascade utilization of the chemical energy of coal tar pitch, while feeding the pretreated material into the electric furnace in block form significantly improves the charging density and conductivity of the furnace, effectively reducing power consumption.

[0008] Optionally, the heating process includes the following steps: The binder mixture is placed in a pyrolysis furnace, and an inert gas is introduced. The temperature is raised from room temperature to 230°C at a rate of 2-3°C / min, then to 350°C at a rate of 1-2°C / min, and held for 0.5-1 h. The temperature is then raised to 500°C at a rate of 1°C / min and held for 30-45 min. Finally, the temperature is raised to 800°C at a rate of 1.5-2°C / min and held until no volatiles are discharged. Heating is then stopped, and the temperature is lowered to below 200°C to obtain the pyrolysis material.

[0009] Optionally, the fabric sintering includes: The pyrolysis material is spread on a sintering trolley with a thickness of 800~900mm. It is ignited at 1000~1100℃ and sintered under a negative pressure of 11.0~15.0kPa. The final sintering temperature is 250~400℃. After cooling, the sintered material is obtained.

[0010] Optionally, the power-smelting process includes: The sintering material, reducing agent, and slag-forming agent are fed into an electric furnace and energized. The electrode voltage is 275~280V and the current is 8200~8300A. The AC power is supplied and the smelting is carried out until all the added materials are melted and the smelting temperature reaches 1600℃~1650℃, thus obtaining the first melt.

[0011] Optionally, the blowing process includes: After the first melt is transferred into the converter, the spray gun at the top of the smelting furnace is turned on to blow oxygen into the furnace. At the same time, the spray gun at the bottom of the smelting furnace is turned on to blow inert gas into the furnace for blowing. After blowing until the carbon content in the melt reaches the standard, the oxygen blowing is stopped, and then the inert gas is blown for another 10 to 12 minutes to obtain the second melt. Lime is added during the blowing process to adjust the slag alkalinity to 2.0~2.3, and 5~6% of the weight of lime bauxite is added at the same time.

[0012] Optionally, after slag removal from the second melt, it can be transferred to a ladle, allowed to stand for 5-8 minutes, and then cast.

[0013] Optionally, the weight ratio of chromite powder, coke powder and coal tar pitch in the binder mixture is 100:(12~15):(18~22). The proportion of chromite powder with a particle size of 1-3 mm is greater than 85%; The particle size of the coke powder is 1~3mm; The carbon residue of coal tar pitch is ≥45%.

[0014] Optionally, the weight ratio of the sintering material, reducing agent, and slagging agent is 100:(5~8):(12~15). The reducing agent is coke, semi-coke, or anthracite with a fixed carbon content of ≥83%; The slag-forming agent includes lime and silica, and the weight ratio of lime to silica is (3~3.5):1.

[0015] Optionally, the inert gas is nitrogen or argon; The oxygen injection rate during the blowing process is 0.8~1.2 Nm³. 3 / t·min, the inert gas injection rate is 0.2~0.3Nm. 3 / t·min.

[0016] Secondly, this application provides a high-carbon ferrochrome, which is smelted by the method described in the first aspect above.

[0017] The high-carbon ferrochrome obtained by the method of this application has a low content of impurities such as sulfur and phosphorus, a small number of inclusions, and high alloy purity because it has undergone multiple purification steps such as pyrolysis, sintering and converter blowing. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are also within the scope of protection of this application.

[0019] In a first aspect, this application provides a method for smelting high-carbon ferrochrome, comprising the following steps: Chromite powder, coke powder and coal tar pitch are mixed evenly according to their weight proportions to form a binder mixture.

[0020] In this application, coal tar pitch is used as a binder to agglomerate fine chromite powder and coke powder into a mixture with a certain particle size and strength. As an organic binder, the amount of coal tar pitch added must balance the molding effect with the carbon residue rate during subsequent pyrolysis (e.g., using medium-temperature or high-temperature coal tar pitch with a carbon residue rate greater than 45%). Compared to water or inorganic binders, coal tar pitch transforms into pitch coke at high temperatures, which not only avoids the introduction of additional impurities but also provides a carbonaceous reducing agent for subsequent smelting. Furthermore, this process does not introduce water, eliminating the need for drying before direct pyrolysis in the furnace, thus shortening the processing time to some extent. Moreover, because no water is introduced, the drawbacks of high heat consumption and difficult-to-handle pyrolysis gas during subsequent pyrolysis heating are avoided.

[0021] The binder mixture is fed into a pyrolysis furnace, inert gas is introduced, and the temperature is raised to 800°C for pyrolysis according to the heating regime to obtain the pyrolysis material.

[0022] In this application, this step is carried out in the absence of air (under inert gas protection) to induce thermal decomposition and condensation reactions in the coal tar pitch. During the heating process, volatiles in the pitch (such as low-molecular-weight aromatics and alkanes) are gradually released, while cyclization, aromatization, and dehydrogenation condensation occur simultaneously, ultimately forming solid pitch coke with a porous structure. The final temperature of 800℃ is sufficient to ensure complete carbonization of the pitch (carbon residue can reach over 50%), while avoiding excessive reduction of iron and chromium oxides in the chromite (the significant reduction of iron oxides typically begins at temperatures above 850℃). The main components of the pyrolysis material are chromite powder, coke powder, and pitch coke converted from pitch. These three components are tightly bound together by the in-situ deposition of the pitch coke, forming composite particles with a certain strength. Furthermore, the release of volatiles from the thermal decomposition of pitch creates numerous channels in the final pyrolysis material, which is beneficial for the subsequent sintering process.

[0023] The pyrolytic material is sintered to obtain sintered material.

[0024] In this application, sintering involves laying the material on the sintering machine trolley, igniting it, and then venting the sintering machine to cause localized melting or solid-phase reactions on the surface of the material, thereby solidifying it into blocks. Since the pyrolysis material no longer contains volatile asphalt components, the flue gas during sintering is clean and the material layer has good permeability. The main function of sintering is to create partial solid-phase diffusion or low-melting-point liquid phase (such as iron-carbon eutectic) bridging between chromite particles and carbonaceous particles (coke powder and pitch coke), improving the mechanical strength and particle size of the material to facilitate subsequent electric furnace charging. Simultaneously, during sintering, the carbonaceous particles undergo partial oxidation and combustion (although the negative pressure of the venting creates a reducing atmosphere, oxidation still exists on the surface), thereby adjusting the carbon content and pore structure of the material. Sintered material can significantly improve the permeability of the charge column in the electric furnace, reduce blow-off losses, and improve thermal efficiency.

[0025] The sintering material, reducing agent, and slag-forming agent are fed into an electric furnace and smelted until the molten material is clear and reaches the smelting temperature to obtain the first melt.

[0026] In this application, electric furnace smelting is the core step of reduction smelting. The sintering material provides chromite and some carbon, while additional reducing agents (such as coke) and slagging agents (lime, silica, etc.) are added to adjust the slag composition. Under electric arc heating, the furnace temperature rises to 1600-1650℃, where FeO and Cr2O3 in the chromite are reduced by carbon to form an Fe-Cr-C alloy (i.e., high-carbon ferrochrome). The CO gas produced by the reduction reaction rises and agitates in the molten pool, promoting mass transfer. The slagging agent combines with gangue (SiO2, Al2O3, MgO, etc.) to form liquid slag, covering the alloy surface to prevent oxidation and absorb impurities. Smelting to the point of "crystal clearing" indicates that all solid materials have melted, forming a slag-metal two-phase melt.

[0027] The first melt is fed into a converter, where oxygen is blown from the top and inert gas is blown from the bottom to produce the second melt.

[0028] In this application, a second melt is obtained by top-blowing oxygen and bottom-blowing inert gas. The purpose of this step is not deep decarburization, but rather to fine-tune the composition, raise the temperature, and remove some impurities. The top-blown oxygen reacts with elements such as carbon and silicon in the melt, releasing a large amount of heat and further raising the melt temperature (up to above 1650℃), which is beneficial for slag-iron separation and further reduction of chromium. The bottom-blown inert gas (such as nitrogen or argon) generates a strong stirring effect, promoting the diffusion of oxygen and the removal of reaction products, while avoiding localized overheating.

[0029] After slag removal from the second melt, it is transferred to a ladle for casting to obtain high-carbon ferrochrome.

[0030] In this application, the slag removal operation removes the upper layer of oxidizing slag, preventing it from mixing into the alloy and affecting its quality. Casting can be performed using ingot casting or a granulation process, with the product form determined according to market demand.

[0031] The high-carbon ferrochrome smelting method provided in this application has the following beneficial effects: 1) The method of this application uses sintering, furnace smelting and blowing to smelt high carbon ferrochrome, which can not only obtain products of excellent quality, but also consume almost no electricity because no electricity is supplied during the blowing process. Therefore, it can effectively reduce electricity consumption compared with the traditional completely furnace smelting.

[0032] 2) This application uses coal tar pitch as a binder, mixing fine chromite powder and coke powder to form a binder mixture. Compared with conventional water glass or bentonite binders, coal tar pitch has good plasticity and binding force at room temperature, which can agglomerate the powder into particles, avoid dust flying, and improve the working environment. Moreover, coal tar pitch is converted into pitch coke during subsequent pyrolysis, which is deposited in situ between particles. It does not introduce additional impurities (such as sodium, calcium, etc.) and can form a high-strength porous structure, which is beneficial to the permeability and reduction efficiency of subsequent sintering and electric furnace smelting.

[0033] 3) This application achieves the orderly removal and utilization of volatile matter in coal tar pitch through a two-step pretreatment process of pyrolysis and sintering. The pyrolysis step is carried out under an inert atmosphere, allowing the volatile matter to be centrally recovered as chemical raw materials or fuel, avoiding the waste of thermal energy and environmental pollution caused by the disorderly combustion of volatile matter during direct sintering. The sintering step utilizes the exothermic combustion of the carbonaceous material (coke powder + pitch coke) contained in the pyrolysis material itself, achieving self-sustaining sintering under negative pressure ventilation conditions without the need for additional fuel. This pyrolysis-sintering series process enables the cascade utilization of the chemical energy of coal tar pitch, while feeding the pretreated material into the electric furnace in block form significantly improves the charging density and conductivity of the furnace, effectively reducing power consumption.

[0034] Optionally, the heating process includes the following steps: The binder mixture is placed in a pyrolysis furnace, and an inert gas is introduced. The temperature is raised from room temperature to 230°C at a rate of 2-3°C / min, then to 350°C at a rate of 1-2°C / min, and held for 0.5-1 h. The temperature is then raised to 500°C at a rate of 1°C / min and held for 30-45 min. Finally, the temperature is raised to 800°C at a rate of 1.5-2°C / min and held until no volatiles are discharged. Heating is then stopped, and the temperature is lowered to below 200°C to obtain the pyrolysis material.

[0035] In this application, the pyrolysis process is divided into four stages: The first stage involves heating from room temperature to 230℃ at a rate of 2-3℃ / min. Within this temperature range, the coal tar pitch begins to soften and gradually melts. A relatively rapid heating rate (2-3℃ / min) allows the coal tar pitch to quickly reach a molten state. When the temperature reaches 230℃, the coal tar pitch is completely melted. Due to the small particle size (1-3mm) of coke powder and chromite powder, even though the pitch is completely melted, it can still fully impregnate and coat the chromite powder and coke powder particles.

[0036] The second stage: 230℃ to 350℃, with a heating rate of 1~2℃ / min. This range is the critical temperature zone for the thermal decomposition of coal tar pitch. Low molecular weight components in the coal tar pitch begin to volatilize, and simultaneously, intermolecular cross-linking reactions occur. The aforementioned heating rate is used to ensure the volatiles are discharged quickly and evenly, thereby forming numerous pores or cracks within the material. After heating to 350℃, hold for 0.5~1 hour to allow the cross-linking reaction to proceed fully, forming a preliminary solid framework.

[0037] The third stage: 350℃ to 500℃, with a heating rate of 1℃ / min. In this stage, the temperature continues to rise at an extremely slow rate. The decomposition of coal tar pitch enters the middle stage, with more volatiles (such as methane and hydrogen) escaping, while the degree of carbon condensation deepens. Holding at this temperature for 30 to 45 minutes helps stabilize the mesophase structure.

[0038] Fourth stage: 500℃ to 800℃, heating rate 1.5~2℃ / min. At this stage, the decomposition of coal tar pitch is basically complete, and most of the volatile matter has been released. The heating rate can be appropriately accelerated, as rapid heating promotes the orderly arrangement of carbon atoms and improves the electrical conductivity and mechanical strength of the pitch coke. After reaching 800℃, maintain the temperature until no more volatile matter is released, indicating that the pyrolysis reaction is completely finished.

[0039] During the cooling phase, after heating is stopped, the temperature is lowered to below 200°C under an inert atmosphere to prevent the pyrolysis material from oxidizing upon contact with air at high temperatures.

[0040] Optionally, the fabric sintering includes: The pyrolysis material is spread on a sintering trolley with a thickness of 800~900mm. It is ignited at 1000~1100℃ and sintered under a negative pressure of 11.0~15.0kPa. The final sintering temperature is 250~400℃. After cooling, the sintered material is obtained.

[0041] In this application, the thickness of the material layer on the sintering trolley directly affects the air permeability and heat transfer efficiency of the sintering process. Too thin a thickness (<800mm) leads to rapid heat loss, a thin sintered layer, and low output; too thick a thickness (>900mm) results in the lower layer of material failing to receive sufficient heat due to poor air permeability, potentially leading to under-firing. Furthermore, because the sintered material has high porosity and contains almost no water, its air permeability is good, allowing for a thicker layer to improve processing efficiency.

[0042] A stable combustion layer can be formed at 1000~1100℃, and heat can be transferred to the lower layers.

[0043] The ventilation system creates a negative pressure below the material layer, allowing the hot airflow generated by combustion to pass through the material layer from top to bottom, preheating the lower layer of material and igniting the combustibles within. The magnitude of the negative pressure determines the airflow velocity and combustion intensity. 11.0~15.0 kPa is considered a medium negative pressure range, ensuring sufficient combustion speed without causing excessive material layer contraction or excessive dust removal due to excessive negative pressure.

[0044] The unloading endpoint temperature refers to the temperature at which the sintered material is unloaded from the trolley. Before reaching the unloading endpoint temperature, the material layer has already been burned through. Subsequently, under the suction of the negative pressure at the bottom, outside air enters the sintered material layer to play a cooling role. Controlling this temperature can prevent the high temperature of the sintered material from causing thermal damage to the receiving container.

[0045] Optionally, the power-smelting process includes: The sintering material, reducing agent, and slag-forming agent are fed into an electric furnace and energized. The electrode voltage is 275~280V and the current is 8200~8300A. The AC power is supplied and the smelting is carried out until all the added materials are melted and the smelting temperature reaches 1600℃~1650℃, thus obtaining the first melt.

[0046] In this application, the electrode voltage is 275~280V and the current is 8200~8300A. The ratio of voltage to current determines the arc length and power input characteristics. 275~280V is a relatively low voltage level, which is conducive to forming a short arc operation, making the arc heat more concentrated in the molten pool area below the electrode and reducing heat radiation to the furnace wall. 8200~8300A corresponds to a larger current, indicating that the electrode is inserted deeper into the furnace charge, in a submerged arc state. Because the arc is covered by the furnace charge, heat is directly transferred to the material, and at the same time, the resistance of the furnace charge itself also generates Joule heating (resistive heating), thus reducing heat loss.

[0047] Complete melting, also known as the molten clear state, means that no solid material remains in the furnace; both slag and metal have formed a liquid state and separated into layers. A temperature of 1600℃~1650℃ is the thermodynamic requirement for the chromium reduction reaction. According to the chromium reduction reaction Cr₂O₃ + 3C = 2Cr + 3CO, the initial temperature of this reaction under standard conditions is approximately 1500℃. However, in actual smelting, due to limitations in slag activity and mass transfer, a higher temperature is required to drive the reaction to the right. Temperatures above 1600℃ can ensure the chromium reduction rate, and the slag also has good fluidity, which is beneficial for slag-iron separation.

[0048] Optionally, the blowing process includes: After the first melt is transferred into the converter, the spray gun at the top of the smelting furnace is turned on to blow oxygen into the furnace. At the same time, the spray gun at the bottom of the smelting furnace is turned on to blow inert gas into the furnace for blowing. After blowing until the carbon content in the melt reaches the standard, the oxygen blowing is stopped, and then the inert gas is blown for another 10 to 12 minutes to obtain the second melt. Lime is added during the blowing process to adjust the slag alkalinity to 2.0~2.3, and 5~6% of the weight of lime bauxite is added at the same time.

[0049] In this application, the total refining time is determined based on the grade of the target finished product. During the refining process, decarburization, desiliconization, dephosphorization, and oxidation of iron and other metals (such as vanadium, titanium, etc.) occur.

[0050] During this blowing process, the oxygen supply intensity is low, the reaction is mild, and violent boiling does not occur. After stopping oxygen blowing, inert gas is continuously injected for 10-12 minutes. The purpose is to utilize the agitation effect of bubbles to promote the upward escape of dissolved CO, oxygen, and other bubbles in the melt, while simultaneously causing unreacted micro-droplets between the slag and gold to further coalesce and separate. Inert gas agitation also accelerates the homogenization of the melt temperature and facilitates the upward floating of suspended inclusions into the slag layer.

[0051] The addition of lime (CaO) serves two purposes: first, it reacts with the SiO2 generated during blowing to form calcium silicate (2CaO·SiO2 or 3CaO·SiO2) to form slag; second, it increases the basicity of the slag, which is beneficial for desulfurization and dephosphorization reactions. A basicity of 2.0–2.3 is considered high basicity, at which the slag has a high desulfurization capacity. Furthermore, high basicity is beneficial for enriching and removing metals such as titanium and vanadium from the melt in the slag. Adding bauxite can lower the melting point of the slag layer, preventing the formation of dry slag that makes slag layer separation difficult.

[0052] Optionally, after slag removal from the second melt, it can be transferred to a ladle, allowed to stand for 5-8 minutes, and then cast.

[0053] In this application, after the converter blowing process, the surface of the second melt is covered with a layer of slag. This slag contains high levels of FeO, MnO, and CaO, with a basicity of 2.0–2.3. If this slag is transferred to the ladle along with the alloy, during the subsequent settling and casting processes, the FeO in the slag will react with the carbon in the alloy: FeO + C → Fe + CO, generating gas and causing porosity inside the ingot. Furthermore, the slag mixed into the alloy will increase the inclusion content in the finished ferrochrome, affecting product purity. Therefore, it is essential to remove as much surface slag as possible through slag removal.

[0054] Optionally, the weight ratio of chromite powder, coke powder and coal tar pitch in the binder mixture is 100:(12~15):(18~22). The proportion of chromite powder with a particle size of 1-3 mm is greater than 85%; The particle size of the coke powder is 1~3mm; The carbon residue of coal tar pitch is ≥45%.

[0055] In this application, coke powder provides fixed carbon as a reducing agent. The amount used here is slightly lower because the pyrolysis of coal tar pitch also leaves a large amount of carbon (tar coke), and the total carbon content of both is sufficient to meet the reduction requirements. If too much coke powder is used, the carbon content of the pyrolysis feed will be too high, which may lead to over-reduction of some chromite during subsequent sintering, forming a refractory metallic phase. In chromite, Cr2O3 ≥ 45%, and Cr2O3 / ∑FeO ≥ 2.5. Coal tar pitch serves as a binder and supplementary carbon source.

[0056] If the carbon residue is too low (<45%), there will be insufficient residual carbon after pyrolysis, requiring additional coke powder to be added, which will affect the mix design. A higher carbon residue is also beneficial for forming a more solid pyrolysis material structure and improving the strength of the sinter.

[0057] Optionally, the weight ratio of the sintering material, reducing agent, and slagging agent is 100:(5~8):(12~15). The reducing agent is coke, semi-coke, or anthracite with a fixed carbon content of ≥83%; The slag-forming agent includes lime and silica, and the weight ratio of lime to silica is (3~3.5):1.

[0058] In this application, 5 to 8 parts of reducing agent are mainly used to compensate for the lack of carbon in the sintering material and to deal with the carbon loss during the electric furnace smelting process.

[0059] Chromite powder particles of 1-3 mm form a uniform porous structure after sintering, which is beneficial for the diffusion of reducing gases in the electric furnace. The coke powder particle size is similar to that of the chromite powder, ensuring uniform mixing. If the coke powder is too fine, it is easily coated with pitch coke during pyrolysis and loses its activity; if it is too coarse, it will be unevenly distributed.

[0060] Due to the gangue components (MgO, Al2O3) in chromite and the ash introduced during sintering, slag-forming agents need to be added to form slag. Silica can also play a reducing role while forming slag.

[0061] Optionally, the inert gas is nitrogen or argon; The oxygen injection rate during the blowing process is 0.8~1.2 Nm³. 3 / t·min, the inert gas injection rate is 0.2~0.3Nm. 3 / t·min.

[0062] In this application, top-blown oxygen provides the oxidant and stirring power, while bottom-blown inert gas provides auxiliary stirring. As bottom-blown bubbles rise, they pass through the oxidation zone formed by top-blown oxygen, promoting the generation and escape of CO bubbles while preventing localized over-oxidation.

[0063] Secondly, this application provides a high-carbon ferrochrome, which is smelted by the method described in the first aspect above.

[0064] The high-carbon ferrochrome of this application has undergone multiple purification steps, including pyrolysis, sintering, and converter blowing, resulting in lower levels of impurities such as sulfur and phosphorus, fewer inclusions, and higher alloy purity. Example

[0065] In the following examples, the proportion of chromite powder with a particle size of 1-3 mm is 87.5%; the particle size of coke powder is 1-3 mm; the carbon residue of coal tar pitch is 46.8%; the Cr2O3 content in chromite is 45.6%, and Cr2O3 / ∑FeO = 2.6.

[0066] Example 1 A high-carbon ferrochrome is obtained through the following process: S101. Mix chromite powder, coke powder and coal tar pitch in a weight ratio of 100:12:18 to form a binder mixture.

[0067] S102. Place the binder mixture in a pyrolysis furnace, introduce nitrogen gas, raise the temperature from room temperature to 230°C at a rate of 2°C / min, then raise it to 350°C at a rate of 1°C / min, hold for 0.5 h, raise it to 500°C at a rate of 1°C / min, hold for 30 min, then raise it to 800°C at a rate of 1.5°C / min, hold until no volatiles are discharged, stop heating, and cool down to below 200°C to obtain the pyrolysis material.

[0068] S103. The pyrolysis material is spread on the sintering trolley with a thickness of 800mm. It is ignited at 1000℃ and sintered under a negative pressure of 11.0kPa. The final sintering temperature is 250℃. After cooling, the sintered material is obtained.

[0069] S104. The sintering material, reducing agent, and slag-forming agent are fed into the electric furnace in a weight ratio of 100:8:12. The furnace is powered on with an electrode voltage of 275V and a current of 8300A, using AC power. The furnace is smelted until all the added materials are melted and the smelting temperature reaches 1600℃ to obtain the first melt. The reducing agent is coke with a fixed carbon content of ≥83%. The slag-forming agent includes lime and silica, with a weight ratio of lime to silica of 3:1.

[0070] S105. After transferring the first melt into the converter, turn on the top spray gun of the furnace to inject oxygen into the furnace, and simultaneously turn on the bottom spray gun to inject argon into the furnace for blowing. After blowing until the carbon content in the melt reaches the standard, stop blowing oxygen, and then continue blowing inert gas for 10 minutes to obtain the second melt; the oxygen blowing rate during the blowing process is 0.8 Nm³. 3 / t·min, the inert gas injection rate is 0.2Nm³. 3 / t·min; Lime is added during the blowing process to adjust the slag basicity to 2.0, and 5% of the weight of lime bauxite is added at the same time.

[0071] S106. After removing the slag from the second melt, transfer it to a ladle and let it stand for 5 minutes before casting to obtain high-carbon ferrochrome.

[0072] Example 2 A high-carbon ferrochrome is obtained through the following process: S201. Mix chromite powder, coke powder and coal tar pitch in a weight ratio of 100:12:22 to form a binder mixture.

[0073] S202. Place the binder mixture in a pyrolysis furnace, introduce nitrogen gas, raise the temperature from room temperature to 230°C at a rate of 3°C / min, then raise it to 350°C at a rate of 2°C / min, hold for 1 hour, raise it to 500°C at a rate of 1°C / min, hold for 45 minutes, then raise it to 800°C at a rate of 2°C / min, hold until no volatiles are discharged, stop heating, and cool down to below 200°C to obtain the pyrolysis material.

[0074] S203. The pyrolysis material is spread on the sintering trolley with a thickness of 900mm. It is ignited at 1100℃ and sintered under a negative pressure of 15.0kPa. The final sintering temperature is 400℃. After cooling, the sintered material is obtained.

[0075] S204. The sintering material, reducing agent, and slag-forming agent are fed into the electric furnace in a weight ratio of 100:5:15. The furnace is powered on with an electrode voltage of 280V and a current of 8200A, using AC power. The furnace is smelted until all the added materials are melted and the smelting temperature reaches 1650℃, thus obtaining the first melt. The reducing agent is coke with a fixed carbon content of ≥83%. The slag-forming agent includes lime and silica, with a weight ratio of lime to silica of 3.5:1.

[0076] S205. After transferring the first melt into the converter, turn on the top spray gun of the furnace to inject oxygen into the furnace, and simultaneously turn on the bottom spray gun to inject argon into the furnace for blowing. Blowing continues until the carbon content in the melt reaches the standard, then oxygen blowing is stopped, and inert gas is injected for another 12 minutes to obtain the second melt. The oxygen injection rate during the blowing process is 1.2 Nm³. 3 / t·min, the inert gas injection rate is 0.3Nm 3 / t·min; Lime is added during the blowing process to adjust the slag basicity to 2.3, and 6% by weight of iron bauxite is added at the same time.

[0077] S206. After removing the slag from the second melt, transfer it to a ladle and let it stand for 8 minutes before casting to obtain high-carbon ferrochrome.

[0078] Example 3 A high-carbon ferrochrome is obtained through the following process: S301. Chromite powder, coke powder and coal tar pitch are mixed evenly in a weight ratio of 100:13:20 to prepare a binder mixture.

[0079] S302. Place the binder mixture in a pyrolysis furnace, introduce nitrogen gas, raise the temperature from room temperature to 230°C at a rate of 2.5°C / min, then raise it to 350°C at a rate of 1.5°C / min, hold for 0.75 h, then raise it to 500°C at a rate of 1°C / min, hold for 40 min, then raise it to 800°C at a rate of 1.8°C / min, hold until no volatiles are discharged, stop heating, and cool down to below 200°C to obtain the pyrolysis material.

[0080] S303. The pyrolysis material is spread on the sintering trolley with a thickness of 850mm. It is ignited at 1050℃ and sintered under a negative pressure of 13.0kPa. The final sintering temperature is 300℃. After cooling, the sintered material is obtained.

[0081] S304. The sintering material, reducing agent, and slag-forming agent are fed into the electric furnace in a weight ratio of 100:7:13. The furnace is powered on with an electrode voltage of 278V and a current of 8250A, using AC power. The furnace is smelted until all the added materials are melted and the smelting temperature reaches 1630℃, thus obtaining the first melt. The reducing agent is coke with a fixed carbon content of ≥83%. The slag-forming agent includes lime and silica, with a weight ratio of lime to silica of 3.2:1.

[0082] S305. After transferring the first melt into the converter, turn on the top spray gun of the furnace to inject oxygen into the furnace, and simultaneously turn on the bottom spray gun to inject argon into the furnace for blowing. Blowing continues until the carbon content in the melt reaches the standard, then oxygen blowing is stopped, and inert gas is injected for another 10 minutes to obtain the second melt; the oxygen injection rate during the blowing process is 1.0 Nm³. 3 / t·min, the inert gas injection rate is 0.25Nm. 3 / t·min; Lime is added during the blowing process to adjust the slag basicity to 2.2, and 5.5% of the weight of lime bauxite is added at the same time.

[0083] S306. After removing the slag from the second melt, transfer it to a ladle and let it stand for 7 minutes before casting to obtain high-carbon ferrochrome.

[0084] Comparative Example 1 The remaining operations are the same as in Example 3, except that the converter blowing process is not carried out, but the smelting is carried out in the electric furnace until the carbon content of the melt is the same as in Example 3. Lime is also added during the furnace smelting process to adjust the slag basicity to 2.2, and 5.5% of the weight of lime bauxite is added at the same time.

[0085] High-carbon ferrochrome of grade FeCr55C10.0 was produced using the methods described in Examples 1 to 3 above. The obtained high-carbon ferrochrome was tested, and the results are shown in Table 1. Table 1

[0086] The data in Table 1 show that the energy consumption of smelting high-carbon ferrochrome using the scheme of this application is 240~300 kWh / t Fe lower than that of smelting entirely in an electric furnace, and the chromium recovery rate is also improved. This indicates that the furnace smelting + converter blowing method of this application can effectively reduce power consumption, reduce the electricity cost in smelting, and at the same time improve the chromium recovery rate and reduce the waste of raw materials.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for smelting high-carbon ferrochrome, characterized in that, Includes the following steps: Chromite powder, coke powder and coal tar pitch are mixed evenly according to the weight parts to make a binder mixture; The weight ratio of chromite powder, coke powder, and coal tar pitch in the binder mixture is 100:12~15:18~22; the proportion of chromite powder particles with a diameter of 1~3mm is greater than 85%; the particle size of coke powder is 1~3mm; and the carbon residue of coal tar pitch is ≥45%. The binder mixture is fed into a pyrolysis furnace, inert gas is introduced, and the temperature is raised to 800°C for pyrolysis according to the heating regime to obtain the pyrolysis material; The pyrolytic material is sintered to obtain sintered material; The sintering material, reducing agent and slag-forming agent are fed into an electric furnace and smelted until the melt is clear and the smelting temperature is reached to obtain the first melt. The first melt is fed into a converter, and oxygen is blown from the top and inert gas is blown from the bottom to produce the second melt. After slag removal from the second melt, it is transferred to a ladle for casting to obtain high-carbon ferrochrome. The heating process includes the following steps: The binder mixture is placed in a pyrolysis furnace, and an inert gas is introduced. The temperature is raised from room temperature to 230°C at a rate of 2-3°C / min, then to 350°C at a rate of 1-2°C / min, and held for 0.5-1 h. The temperature is then raised to 500°C at a rate of 1°C / min and held for 30-45 min. Finally, the temperature is raised to 800°C at a rate of 1.5-2°C / min and held until no volatiles are discharged. Heating is then stopped, and the temperature is lowered to below 200°C to obtain the pyrolysis material. The fabric sintering includes: The pyrolysis material is spread on a sintering trolley with a thickness of 800~900mm, ignited at 1000~1100℃, and sintered under a negative pressure of 11.0~15.0kPa. The final sintering temperature is 250~400℃, and the sintered material is obtained after cooling. The blowing process includes: After the first melt is transferred into the converter, the spray gun at the top of the smelting furnace is turned on to blow oxygen into the furnace. At the same time, the spray gun at the bottom of the smelting furnace is turned on to blow inert gas into the furnace for blowing. After blowing until the carbon content in the melt reaches the standard, the oxygen blowing is stopped, and then the inert gas is blown for another 10 to 12 minutes to obtain the second melt. Lime is added during the blowing process to adjust the slag basicity to 2.0~2.3, and 5~6% of the weight of lime bauxite is added at the same time; The weight ratio of the sintering material, reducing agent, and slag-forming agent is 100:5~8:12~15; The reducing agent is coke, semi-coke, or anthracite with a fixed carbon content of ≥83%; The slag-forming agent comprises lime and silica, wherein the weight ratio of lime to silica is 3 to 3.5:

1.

2. The smelting method for high-carbon ferrochrome according to claim 1, characterized in that, The electrified smelting includes: The sintering material, reducing agent, and slag-forming agent are fed into an electric furnace and energized. The electrode voltage is 275~280V and the current is 8200~8300A. The AC power is supplied and the smelting is carried out until all the added materials are melted and the smelting temperature reaches 1600℃~1650℃, thus obtaining the first melt.

3. The smelting method for high-carbon ferrochrome according to claim 1, characterized in that, After slag removal from the second melt, transfer it to a ladle, let it stand for 5-8 minutes, and then proceed with casting.

4. The smelting method for high-carbon ferrochrome according to claim 1, characterized in that, The inert gas is nitrogen or argon; The oxygen injection rate during the blowing process is 0.8~1.2 Nm³. 3 / t·min, the inert gas injection rate is 0.2~0.3Nm. 3 / t·min.

5. A high-carbon ferrochrome, characterized in that, It includes materials smelted by the method described in any one of claims 1 to 4.

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