Silicon-chromium-iron with low admixture content, method for its production and use thereof in production of low-carbon chromium iron

Abstract

This invention relates to silicon-ferrochrome with low doping content, comprising, by weight percentage of total alloy weight: not less than 33% chromium, not less than 47% silicon, not more than 0.025% carbon, not more than 0.02% phosphorus, not more than 0.015% nitrogen, not more than 0.03% hydrogen, not more than 0.4% oxygen, and not more than 0.005% sulfur, with the balance being iron and trace impurities, and a chromium-to-iron ratio of not less than 2.0. This invention also relates to a method for producing silicon-ferrochrome with low doping content and its use in the production of low-carbon ferrochrome.

Description

Technical Field

[0001] This invention relates to silicon-chromium ferrochrome with low doping content, comprising no more than 0.025 wt% carbon, no more than 0.02 wt% phosphorus, no more than 0.03 wt% hydrogen, no more than 0.4 wt% oxygen, no more than 0.005 wt% sulfur, and no more than 0.015 wt% nitrogen, and a chromium-to-iron ratio of not less than 2.0. This invention also relates to a method for producing silicon-chromium ferrochrome with low doping content, and the use of silicon-chromium ferrochrome in the production of low-carbon ferrochrome (FeCr LC). This invention belongs to the field of metallurgy.

[0002] Ferrosilicon is produced in a submerged arc furnace using the carbothermic reduction reaction of silicon dioxide and iron oxide in the presence of high-carbon ferrochrome. It is then refined in a ladle to reduce the carbon content and cast and cooled by restricting gaseous inclusions from entering the alloy. Background Technology

[0003] In the prior art, various types of silicon-chromium-iron alloys are known, including those described in the international standard ISO 5449:1980 (silicon-chromium-iron—specifications and delivery conditions), which describes a chromium-silicon-iron alloy obtained by reduction or fusion, with a chromium content of 20.0 to 65.0 wt% and a silicon content of 10.0 to 60.0 wt%.

[0004] International patent application WO2019240589A1 discloses a silicon-based alloy containing 45-95 wt% silicon, no more than 0.05 wt% carbon, 0.4-30 wt% chromium, 0.01-10 wt% aluminum, 0.01-0.3 wt% calcium, no more than 0.10 wt% titanium, no more than 25 wt% manganese, 0.005-0.07 wt% phosphorus, and 0.001-0.02 wt% sulfur, with the balance being iron and incidental impurities in conventional amounts. The alloy described in that international patent application differs from the alloy described in this patent application in terms of calcium content.

[0005] European patent application EP3075869A1 discloses a method for producing FeSiAl alloys, wherein carbonaceous rock is mixed with quartzite, iron-containing materials, wood chips, and, if necessary, highly volatile carbon in specific amounts, and the homogenized furnace charge mixture is charged into a furnace to produce the FeSiAl alloy. The furnace charge contains 1.5-4.5% Fe₂O₃, 55-65% SiO₂, 25-35% Al₂O₃, 32-34% CaO, 0.3-3% MgO, 0.3-2% TiO₂, and trace amounts of phosphorus and sulfur. The alloy obtained by the process contains (by weight%): 40-85% silicon, 1-40% aluminum, 0.001-1.0% carbon, up to 2% titanium, up to 1.0% calcium, and trace amounts of phosphorus and sulfur, with the balance being iron.

[0006] On the other hand, European patent EP2295614B1 discloses an alloy composition for deoxidation and the introduction of alloying additives, which contains 45.0-63.0% by weight of silicon, 10.0-25.0% by weight of aluminum, 1.0-10.0% by weight of calcium, 1.0-10.0% by weight of barium, 0.3-0.5% by weight of vanadium, 1.0-10.0% by weight of titanium, 0.1-1.0% by weight of carbon, and the balance being iron.

[0007] Currently, silicon-chromium ferrochrome with low dopant content (especially carbon and nitrogen) is a particularly popular product. This type of alloy is used to produce low-carbon ferrochrome (FeCr LC), which in turn is used in the steel industry to produce specialty alloy steels and materials, including corrosion-resistant, heat-resistant, acid-resistant, and high-strength steels for demanding applications such as aerospace, defense, chemical, and energy. However, achieving low levels of dopant (especially carbon and nitrogen) in silicon-chromium ferrochrome presents a significant technical challenge. Summary of the Invention

[0008] The object of this invention is to provide silicon ferrochrome with low dopant content (especially carbon and nitrogen), and to develop a method for manufacturing it and its use in the production of low-carbon ferrochrome.

[0009] The purpose of this invention is to provide a silicon-chromium ferrochrome with low dopant content, characterized by comprising, by weight percentage of the total alloy weight: not less than 33% chromium, not less than 47% silicon, not more than 0.025% carbon, not more than 0.02% phosphorus, not more than 0.015% nitrogen, not more than 0.03% hydrogen, not more than 0.4% oxygen, and not more than 0.005% sulfur, with the balance being iron and trace impurities, and a chromium-to-iron ratio of not less than 2.0. The proportion of chromium not less than 33% and the proportion of silicon not less than 47% ensure that the silicon-chromium ferrochrome has sufficient reducing power. Lower chromium content reduces the efficiency of the FeCr LC production process and its performance in alloy steel production. Lower silicon content leads to a decrease in the alloy's reducing power.

[0010] Preferably, the low-doped silicon-chromium-iron alloy is characterized by comprising, by weight percentage relative to the total weight of the alloy, 33 to 36% chromium, 47 to 50% silicon, 0.020 to 0.025% carbon, 0.01 to 0.02% phosphorus, 0.01 to 0.015% nitrogen, 0.01 to 0.03% hydrogen, 0.2 to 0.4% oxygen, and 0.001 to 0.005% sulfur, with the balance being iron and trace impurities.

[0011] Preferably, the low-doped ferrosilicon is characterized by comprising, by weight percentage of the total alloy weight: 34.02% chromium, 49.12% silicon, 0.019% carbon, 0.013% phosphorus, 0.011% nitrogen, 0.026% hydrogen, 0.24% oxygen, and 0.0015% sulfur, with the balance being iron and trace impurities. This chemical composition ensures high reducing power relative to chromite and minimizes non-metallic inclusions in the finished alloy steel.

[0012] Preferably, the low-doped ferrosilicon silicon is characterized by a chromium-to-iron ratio of 2.0. Lower values ​​will adversely affect the chemical composition of FeCrLC and its performance in alloy steel production.

[0013] On the other hand, the present invention relates to a method for producing silicon-chromium ferrochrome with low dopant content, characterized in that, in a submerged arc furnace, silicon oxide (SiO2) and iron oxide (FeO) are reduced by carbothermal reduction in the presence of chromium and iron derived from high-carbon ferrochrome, followed by ladle decarburization refining using silica fume, and then the melt is cooled using water jets. Controlling the carbon content in the alloy steel is extremely important because the mechanical properties of the finished product vary with the iron-carbon ratio and M. 23 The changes are due to the precipitation of C6 carbides, while M 23 C6 carbides are the primary cause of intergranular corrosion. The results showed that the expected use of an argon atmosphere for protection and argon cooling during the cooling process to isolate the nitrogen content in the silicon-chromium-iron alloy and thus reduce it to a satisfactory low level did not achieve the desired effect (Table 6). This method neither ensured sufficiently rapid cooling nor adequately limited the alloy's absorption of gases. Furthermore, the use of argon protection proved to be a complex process to implement on an industrial scale. Surprisingly, water jet cooling (pouring water onto the metal) proved to be extremely effective in reducing air contact with the alloy (the protective layer of water vapor formed during contact with the high-temperature metal limited the contact time between the high-temperature metal and air), and cooling occurred very rapidly, resulting in silicon-chromium-iron alloys with the expected sufficiently low nitrogen content.

[0014] Preferably, the method for producing silicon-chromium ferrosilicon with low admixture content is characterized in that ladle decarburization refining using silica fume is carried out at temperatures up to 1400°C. Refining at higher or lower temperatures does not yield favorable results and is inefficient.

[0015] On the other hand, the present invention relates to the use of low-doped silicon ferrochrome in the production of low-carbon ferrochrome.

[0016] The main advantage of this invention lies in the appropriate ferrochrome mass ratio (not less than 2.0), chromium content not less than 33%, and silicon content not less than 47%, ensuring sufficient reducing power for the silicon ferrochrome. Another advantage is that it reduces gaseous inclusions (particularly nitrogen, oxygen, and hydrogen) in the alloy to below the limits required by manufacturers of low-carbon ferrochrome, as well as manufacturers of high-grade stainless steel, heat-resistant steel, acid-resistant steel, and high-strength alloy steel. Low-gaseous-inclusion silicon ferrochrome is a precursor for the production of low-carbon ferrochrome (FeCr LC) and is used as a reducing agent in its manufacturing process; therefore, with the development of the steel market and metallurgical science, the requirements for these alloys are becoming increasingly stringent. Nitrogen is an austenite-forming element and therefore significantly affects the microstructure of steel, which is a major factor influencing the properties of alloy steels. Hydrogen is an element that reduces the mechanical properties of steel through hydrogen embrittlement and its tendency to diffuse in the crystal lattice. Oxygen directly causes corrosion of steel, and increased oxygen content leads to chromium depletion in the steel grains through an increased oxide layer ratio. Another advantage of this invention is its low carbon, low phosphorus, and low sulfur content. Controlling the carbon content in alloy steel is extremely important because the mechanical properties of the finished product vary greatly depending on the iron-carbon ratio and M. 23 The changes are due to the precipitation of C6 carbides, while M 23 C6 carbides are a major cause of intergranular corrosion. Phosphorus is an element that degrades the mechanical properties of steel through so-called cold brittleness, due to its dissolution in ferrite and its effect on the formation of banded structures in the steel. Sulfur combines with iron to form sulfides, which in turn triggers so-called hot brittleness, adversely affecting the mechanical properties of the steel. On the other hand, a key advantage of this invention is the use of water jet cooling (pouring water onto the metal), which greatly reduces air contact and allows cooling to occur very rapidly, thereby obtaining silicon-chromium ferrochrome that meets the desired low nitrogen content. Detailed Implementation

[0017] The purpose of this invention is illustrated by examples, which are not intended to limit its scope.

[0018] The silicon-chromium-ferrochrome alloy presented in the embodiments is obtained through the following process: a mixture of raw materials for alloy production is periodically added to the working space of a semi-enclosed low-profile submerged arc furnace in a specified proportion; the process includes: simultaneous liquid transformation of high-carbon ferrochrome (parameters of high-carbon ferrochrome are listed in Table 1), reduction of SiO2 contained in quartzite (parameters of quartzite are listed in Table 2) by elemental carbon contained in hard coal (parameters of hard coal are listed in Table 4) and chromium carbide contained in high-carbon ferrochrome, reduction of FeO contained in mill scale (parameters of mill scale are listed in Table 3), then dissolving the obtained Si-Fe alloy in liquid ferrochrome, tapping the smelting product from the bottom of the submerged arc furnace to the ladle, transferring the alloy to a refining ladle for decarburization, then casting the alloy into a set of cast iron ingot molds, and using water jets to strongly cool the alloy.

[0019] Table 1. Chemical composition of high-carbon ferrochrome

[0020] Table 2. Chemical composition of quartzite

[0021] Table 3. Chemical composition of iron oxide scale in terms of pure elements

[0022] Table 4. Parameters and chemical composition of hard coal

[0023] The furnace for producing the iron-silicon-chromium alloy according to the embodiment is equipped with a 12 MVA three-phase transformer, a circular molten pool, three self-baking electrodes with a diameter of 900 mm, a hood with five windows (the windows are used to introduce batch mixtures through the loader's hopper), and a tap for periodically discharging the smelted product. The furnace operates in continuous mode with an active power of 7.8 MW and an electrode current ranging from 32 to 35 kA.

[0024] Ferro-silicon chromium with low admixture content (particularly carbon and nitrogen) was smelted using raw materials with consumption rates shown in Table 5. Iron oxide scale was added to achieve a chromium-to-iron ratio of at least 2:1. The chemical composition of FeSiCr is shown in Table 6. Refining of the finished product was based on coating the metal surface with a layer of silica fume, using 50 kg of silica fume per 8000 kg of refined alloy. This silica fume incorporates silicon carbide formed during the temperature drop from 1650-1550°C to 1400°C. Tapping was to be carried out through a hole on the side of the ladle in an argon atmosphere, and cooling was also performed under argon protection at a flow rate of 50 dm³. 3This method cannot guarantee rapid cooling, nor can it adequately suppress the alloy's absorption of gases. Therefore, the cooling method was modified to obtain a specific chemical composition. To this end, the metal stream was poured directly from the ladle into the mold, bringing the two as close to each other as possible (the maximum length of the metal stream was 50 cm), at a pouring rate of 1600 kg / min. Water was then poured onto the metal with sufficient intensity to cover the entire metal surface with a water layer of minimum thickness of 1-3 mm, thereby increasing the cooling rate and generating a protective vapor layer, reducing the contact time between the high-temperature liquid metal and air.

[0025] Table 5. Raw material consumption rate for producing the alloy according to the present invention

[0026] Table 6. Comparison of the chemical composition of the alloy with the preset composition at each stage.

[0027] *Samples: 1—Unrefined FeSiCr; 2—FeSiCr after decarburization and refining; 3—FeSiCr after decarburization and argon cooling; 4—FeSiCr after decarburization and water cooling; 5-8—Reference samples of FeSiCr after decarburization and water cooling.

[0028] Table 6 shows the chemical composition [%] of the alloys obtained according to the applied treatments. The unrefined alloy contained high levels of carbon (0.170%) and nitrogen (0.023%), making it unsuitable for further production of low-carbon ferrochrome. Decarburization improved the alloy parameters in terms of carbon content, achieving a carbon value (0.020%) that made the alloy usable for further production of low-carbon ferrochrome; however, the nitrogen content (0.025%) remained too high. Argon cooling was intended to limit air contact with the melt and reduce the content of undesirable gaseous impurities in the melt, but the expected nitrogen content was not achieved (the obtained nitrogen content was 0.017%). Furthermore, the argon cooling process was difficult to implement on an industrial scale. Only water cooling unexpectedly yielded a product with the expected nitrogen content (0.011%).

[0029] Low-carbon ferrochrome is produced based on the reduction of chromite with ferrosilicon. Because of the reduction reaction between silicon and Cr₂O₃, no additional carbon is needed to supplement the reaction, thus maintaining a low carbon content in the finished alloy. Ferrochrome prepared in this way can be successfully used in the production of austenitic stainless steel; however, strict control of the carbon content is essential during production to ensure sufficient mechanical properties in the finished product.

Claims

1. A silicon-chromium-ferrosilicon with low dopant content, characterized in that, It includes, by weight percentage of the total weight of the alloy, Chromium content not less than 33 Silicon of not less than 47 Carbon particles no larger than 0.025 Phosphorus concentration not exceeding 0.02 mg / L Nitrogen concentration not exceeding 0.015 Hydrogen concentration not exceeding 0.03 Oxygen concentration not exceeding 0.4 Sulfur not exceeding 0.005, with the balance being iron and trace impurities. The chromium / iron ratio is not less than 2.

0.

2. The silicon-chromium-ferrosilicon with low dopant content according to claim 1, characterized in that, It includes, as a weight percentage relative to the total weight of the alloy, Chromium content of 33 to 36 47 to 50 silicon, 0.020 to 0.025 carbon, 0.01 to 0.02% phosphorus, 0.01 to 0.015 nitrogen, 0.01 to 0.03% hydrogen, 0.2 to 0.4% oxygen Sulfur content of 0.001 to 0.005, with the balance being iron and trace impurities.

3. The silicon-chromium-ferrosilicon with low dopant content according to claim 1, characterized in that, It comprises, by weight percentage of the total weight of the alloy, 34.02% chromium, 49.12% silicon, 0.019% carbon, 0.013% phosphorus, 0.011% nitrogen, 0.026% hydrogen, 0.24% oxygen, and 0.0015% sulfur, with the balance being iron and trace impurities.

4. The silicon-chromium ferrosilicon according to any one of claims 1 to 3, characterized in that, The chromium-iron ratio is 2.

0.

5. A method for producing silicon-chromium ferrosilicon with low dopant content according to any one of claims 1 to 4, characterized in that, In a submerged arc furnace, in the presence of chromium and iron derived from high-carbon ferrochrome, oxides SiO2 and FeO are reduced by a carbothermal process, followed by ladle decarburization and refining using silica fume, and then the melt is cooled using a water jet.

6. The method for producing silicon-chromium ferrosilicon with low dopant content according to claim 5, characterized in that, The decarburization and refining of the ladle using silica fume is carried out at temperatures up to 1400°C.

7. The use of silicon-chromium ferrosilicon with low dopant content according to any one of claims 1 to 4, characterized in that, It is used to produce low-carbon ferrochrome.

Images