A method for preparing deoxidized slag by applying an electric field

Abstract

The present application relates to a kind of preparation methods of electric field deoxidation slag, comprising S1, converter boiling tapping;S2, after tapping into argon station, molten steel tank bottom is connected argon and is stirred;S3, after deoxidation slag is added to electric field, it is placed 1-3min after lower deoxidation electrode, and additional electric field equipment is opened.The present application can make full use of the refining slag resources of steel plant first, realize the secondary use of waste heat, waste slag, energy saving and emission reduction;Second, it is favorable to improve the deoxidation efficiency of additional electric field, reduce deoxidation time, improve production efficiency;Finally, the composition of synthetic slag is simple, preparation process is simple, easy to operate, easy to implement.

Description

Technical Field

[0001] This invention relates to the field of steelmaking technology, and in particular to a method for preparing deoxidized slag under an applied electric field. Background Technology

[0002] The cleanliness of molten steel largely determines the quality of rolled products, especially the total oxygen content in the molten steel. Molten steel with high total oxygen content must undergo deoxidation treatment. Currently, the main deoxidation method still relies on alloy deoxidation, such as conventional aluminum deoxidation. However, when aluminum and other alloys are deoxidized, metal oxides are inevitably produced. These metal oxides cannot be completely removed from the molten steel, and when they accumulate to a certain extent, they will cause various problems.

[0003] When alumina inclusions accumulate on the inner wall of the submerged entry nozzle, they can cause interruptions in casting, increasing steelmaking costs. When the accumulated material falls into the molten steel in the crystallizer and remains in the billet, it can cause inclusion defects in the rolled plate, such as peeling defects, linear defects, and pinhole defects in cold-rolled plates. In severe cases, it can even cause pores. Therefore, researchers have developed various inclusion removal processes. For example, the literature "Removal of Inclusion Particles from Molten Steel by Small Bubbles" (Acta Metallurgica Sinica, 2004, Vol. 3) analyzes the relationship between the efficiency of inclusion particle removal by argon blowing in molten steel and the diameter of argon bubbles, inclusion diameter, area of ​​permeable bricks, pore size of permeable bricks, argon blowing flow rate, and argon blowing time. It discusses methods for obtaining small bubbles in molten steel and demonstrates the effectiveness of argon blowing for inclusion removal in the refining of spring steel in a 70t LF ladle furnace, which effectively reduced the number of oxide inclusions and the proportion of inclusion particles larger than 40μm in the steel. The literature "Application Research of Composite Powder Cored Wire," Steelmaking, No. 2, 2022, analyzes the mechanism and effect of using ferrosilicon and calcium oxide powder cored wire for inclusion removal. Industrial tests show that the application of a certain amount of composite powder cored wire does not affect the control of steel composition, and no excessive silicon or calcium content was observed. From the T[O] content and inclusion inspection results of the cast billet, it can reduce the total amount of inclusions in the molten steel and change the size distribution of residual inclusions in the cast billet. In the ladle batches using composite cored wire, the residual inclusions were mainly smaller than 4μm, while in the comparative ladle batches, the residual inclusions in the cast billet were mostly large-sized inclusions. The literature "Research on Oxide Inclusion Control in Steel", Shanxi Metallurgy, No. 3, 2014, analyzes the transformation process of inclusions in steel during various steelmaking processes and the corresponding relationship between total oxygen content and inclusions during steelmaking. It proposes a series of measures to reduce the oxygen content in steel. After implementation, the oxide inclusion content in steel can be reduced to the greatest extent and the total oxygen content (mass fraction of oxygen) of the finished product can be maintained below 30×10-6.

[0004] The aforementioned literature focuses on improving the purity of molten steel by removing deoxidation products. Methods employed include internal air blowing to promote inclusion flotation, adding fluxes to create easily floating inclusions, and controlling oxygen content at each stage. However, these approaches do not aim to reduce inclusion formation. With the increasing interdisciplinary influence, a new method of deoxidation using an external electric field has emerged, offering researchers a new option for inclusion removal. This method, called slag-metal external electric field deoxidation, is a novel, pollution-free deoxidation method based on solid electrolyte deoxidation. It uses slag instead of the solid electrolyte as a channel for dissolved oxygen to be transported outwards. An external electric field is applied between the molten metal and the slag covering it, controlling the direction of oxygen ion transport within the slag system and accelerating its conduction rate to achieve deoxidation. The literature "Pollution-Free Deoxidation of Slag and Metal Under an Applied DC Electric Field," *Journal of Process Engineering*, 2006, Vol. 1, details the independently developed applied electric field equipment and demonstrates successful electro-deoxidation experiments in the laboratory. Results show that applied electric field deoxidation can significantly reduce the oxygen content of molten steel and accelerate the deoxidation rate. The literature "Pollution-Free Deoxidation Process of Molten Steel under an Applied Electric Field," *Iron and Steel*, 2016, Vol. 9, explores the effects of different applied electric fields and electrodes on pollution-free deoxidation of molten steel. Based on the electrochemical reaction mechanism, an applied electric field molten steel purification and refining device suitable for industrial testing was designed and fabricated, and corresponding numerical simulations and industrial experimental studies were conducted. The research shows that applying an applied electric field between molten slag and molten steel can achieve a maximum deoxidation rate of 0.00186% / min. Patent document CN101435009A describes a synthetic slag for pollution-free deoxidation under an external electric field between slag and metal. The slag's chemical composition and weight percentages are: CaO: 40-55%, Al2O3: 40-55%, MgO: 1-10%, FeO: 0.01-1%, MnO: 0-1%; and CaO / Al2O3 = 0.8-1.2. The slag features a low melting point, fast melting speed, good fluidity, low volatility, and high oxygen ion conductivity. Patent document CN102321784A discloses a pre-melted conductive slag for electrochemical deoxidation and its preparation method. The pre-melted conductive slag for electrochemical deoxidation has the following composition and mass percentage: CaO: 35%-45%, Al2O3: 30%-40%, MgO: 7%-12%, SiO2: <1%, FeO: 1%-15%, Fe2O3: 0.1%-5%, BaO: 0.1-10%, and other unavoidable impurities, and the sum of the mass percentages of the above components is 100%; the particle size of this pre-melted slag is 0.1-100mm.

[0005] Based on the existing technologies mentioned above, new methods for deoxidizing molten steel using an external electric field are attracting attention in the industry. However, as can be seen from the known literature, the slag produced by the external electric field requires additional preparation, and the composition and preparation requirements are relatively high, which increases the production cost. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to provide a method for preparing deoxidized slag under an applied electric field. This method can fully utilize the refining slag resources of steel plants, achieve secondary utilization of waste heat and slag, and save energy and reduce emissions. It is also beneficial to improve the deoxidation efficiency of the applied electric field, reduce deoxidation time, and improve production efficiency. The synthesized slag has a simple composition, a simple preparation process, is easy to operate, and is easy to implement.

[0007] The technical solution adopted in this invention is as follows:

[0008] The present invention proposes a method for preparing deoxidized slag under an applied electric field, comprising the following steps:

[0009] S1, converter boiling tapping;

[0010] S2. After tapping, the steel enters the argon station, and argon gas is introduced to the bottom of the molten steel ladle for stirring.

[0011] S3. After the deoxidizing slag is added to the electric field, let it stand for 1-3 minutes before lowering the deoxidizing electrode and turning on the external electric field equipment.

[0012] Furthermore, in step S1, the converter tapping temperature is ≥1700℃, the slag discharge is controlled at 30-50kg, and the ladle clearance is 70-100mm.

[0013] Furthermore, in step S2, the argon gas flow rate is 30-50 m³ / h. 3 / h, add hot or cold slag from LF furnace smelting to the steel ladle, along with cerium oxide and sodium oxide.

[0014] Furthermore, the composition of the hot or cold slag, by mass percentage, includes: CaO: 40%–60%, SiO2: 20%–40%, MgO: 10%–20%, Al2O3: 15%–30%, and (FeO+MnO) ≤ 4%.

[0015] Furthermore, the amount of hot or cold slag added is 2.0-4.0 kg / ton of steel; the amount of cerium oxide added is 0.05-0.1 kg / ton of steel; and the amount of sodium oxide added is 0.05-0.1 kg / ton of steel.

[0016] Furthermore, in step S3, the anode of the deoxidizing electrode is inserted into the slag layer at a distance of 5-10 cm from the steel slag interface, and the cathode is inserted into the molten steel at a distance of 5-10 cm from the steel slag interface. A voltage of 5-20V and a current of 1000-4000A are applied, and the processing time is 5-10 min.

[0017] Furthermore, in step S3, the final deoxidized slag includes, by mass percentage: CaO: 30%–50%, SiO2: 10%–30%, MgO: 5%–10%, Al2O3: 10%–20%, (FeO+MnO) ≤ 4%, Na2O: 2.5%–5%, and CeO2: 2.5%–5%.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. This invention can reduce the amount of deoxidizing alloy used and lower costs, as well as reduce steel defects caused by residual deoxidizing inclusions;

[0020] 2. The preparation of electro-deoxidation slag is simple, and the LF furnace refining slag can be reused to reduce the amount of steelmaking flux used;

[0021] 3. The processes are closely linked and do not change the existing production process of the steel plant. Attached Figure Description

[0022] Figure 1 This is a schematic flowchart of a method for preparing deoxidized slag under an applied electric field proposed in this invention. Detailed Implementation

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] See appendix Figure 1 The present invention proposes a method for preparing deoxidized slag under an applied electric field, which specifically includes the following steps:

[0025] S1. Converter boiling tapping; wherein, the converter tapping temperature is ≥1700℃, the slag amount is controlled at 30-50kg, and the ladle clearance is 70-100mm.

[0026] S2. After tapping, the steel enters the argon station, where argon gas is introduced to the bottom of the molten steel ladle for stirring; the argon gas flow rate is 30-50 m³ / h. 3 / h, and add hot or cold slag smelted in the LF furnace to the molten steel ladle;

[0027] The composition of the hot or cold slag must meet the following requirements, by mass percentage: CaO: 40%–60%, SiO2: 20%–40%, MgO: 10%–20%, Al2O3: 15%–30%, (FeO+MnO) ≤ 4%, with the balance being unavoidable impurities; the amount of hot or cold slag added is 2.0–4.0 kg / ton of steel;

[0028] Simultaneously, cerium oxide and sodium oxide are added to the molten steel ladle, with the amount of cerium oxide added being 0.05-0.1 kg / ton of steel and the amount of sodium oxide added being 0.05-0.1 kg / ton of steel.

[0029] S3. After the deoxidizing slag is added to the electric field, let it stand for 1-3 minutes, then lower the deoxidizing electrode and turn on the external electric field equipment. The anode of the deoxidizing electrode is inserted into the slag layer 5-10 cm from the steel-slag interface, and the cathode is inserted into the molten steel 5-10 cm from the steel-slag interface. Apply a voltage of 5-20V and a current of 1000-4000A for 5-10 minutes.

[0030] The final deoxidized slag (refining slag) includes, by mass percentage: CaO: 30%–50%, SiO2: 10%–30%, MgO: 5%–10%, Al2O3: 10%–20%, (FeO+MnO) ≤4%, Na2O: 2.5%–5%, CeO2: 2.5%–5%, with the balance being unavoidable impurities.

[0031] The technical solution of the present invention will be further described below through specific embodiments:

[0032] Example 1

[0033] Using ordinary low-carbon low-alloy steel SPCC as the test object, the production process route is BOF-external electric field molten steel purification-RH-continuous casting, and the specific implementation plan is as follows:

[0034] S1. Converter boiling tapping, tapping capacity is 200 tons, alloy composition (including carbon raiser) is not adjusted, tapping temperature is 1710℃, ladle hanging temperature is 1670℃, slag discharge is 30kg, and ladle clearance is 80mm.

[0035] S2. After entering the argon station, argon gas is introduced to the bottom of the molten steel tank for stirring, with an argon gas flow rate of 30 m³ / h. 3 / h, add 400kg of hot slag from the LF furnace to the steel ladle, along with 10kg of cerium oxide and 10kg of sodium oxide, and let stand for 1min;

[0036] S3. Turn on the external electric field equipment. Insert the anode into the molten slag layer 5cm from the steel slag interface and insert the cathode into the molten steel 10cm from the steel slag interface. Apply a voltage of 5V and a current of 1000A for 5min.

[0037] After deoxidation treatment by the above-mentioned external electric field, the total oxygen content of the molten steel after tapping from the converter decreased from 0.06% to 0.03% (mass percentage), and the deoxidation rate reached 50%, which can save 67.5 kg of subsequent deoxidized aluminum.

[0038] Example 2

[0039] Using ordinary low-carbon low-alloy steel Q345B as the test object, the production process route is BOF-external electric field molten steel purification-RH-continuous casting, and the specific implementation plan is as follows:

[0040] S1. Converter boiling tapping, tapping capacity is 200 tons, alloy composition (including carbon raiser) is not adjusted, tapping temperature is 1720℃, ladle hanging temperature is 1680℃, slag discharge is 50kg, and ladle clearance is 100mm.

[0041] S2. After entering the argon station, argon gas is introduced to the bottom of the molten steel tank for stirring, with an argon gas flow rate of 50 m³ / h. 3 / h, add 450kg of cold slag smelted in the LF furnace to the steel ladle, along with 15kg of cerium oxide and 15kg of sodium oxide, and let stand for 3min;

[0042] S3. Turn on the external electric field equipment. Insert the anode into the molten slag layer 10cm away from the steel slag interface and insert the cathode into the molten steel 10cm away from the steel slag interface. Apply a voltage of 50V and a current of 4000A for 10min.

[0043] After deoxidation treatment by the above-mentioned external electric field, the total oxygen content of the molten steel after tapping from the converter decreased from 0.07% to 0.03% (mass percentage), and the deoxidation rate reached 57%, which can save 90 kg of subsequent deoxidized aluminum.

[0044] The working principle of this invention is as follows: the electric furnace slag is based on the LF furnace slag, and its basic components are CaO, Al2O3, SiO2, a small amount of MgO, FeO, and MnO. It has good fluidity and low viscosity. At the same time, due to the low content of FeO and MnO, it has a high oxygen melting capacity. After adding cerium oxide and sodium oxide, it can provide a certain amount of free oxygen ions to the slag without being reduced by the molten steel. At the same time, it further reduces the melting point and viscosity, so that the slag has better fluidity and oxygen ion migration capacity, accelerates the migration of oxygen ions in the slag, and thus shortens the reaction time of electro-deoxidation.

[0045] All matters not covered in this invention are common knowledge.

[0046] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing deoxidized slag under an applied electric field, characterized in that, The method includes the following steps: S1, converter boiling tapping; S2. After tapping, the steel enters the argon station, and argon gas is introduced to the bottom of the molten steel ladle for stirring. S3. After the electric field deoxidation slag is added, let it stand for 1-3 minutes, then lower the deoxidation electrode and turn on the external electric field equipment. In step S1, the converter tapping temperature is ≥1700℃, the slag discharge is controlled at 30-50kg, and the ladle clearance is 70-100mm. In step S2, the argon gas flow rate is 30-50 m³ / h. 3 / h, add hot or cold slag from LF furnace smelting to the steel ladle, along with cerium oxide and sodium oxide; The amount of hot or cold slag added is 2.0-4.0 kg / ton of steel; the amount of cerium oxide added is 0.05-0.1 kg / ton of steel; and the amount of sodium oxide added is 0.05-0.1 kg / ton of steel.

2. The method for preparing deoxidized slag under an applied electric field according to claim 1, characterized in that: The composition of the hot or cold slag, by mass percentage, includes: CaO: 40%–60%, SiO2: 20%–40%, MgO: 10%–20%, Al2O3: 15%–30%, (FeO+MnO) ≤ 4%.

3. The method for preparing deoxidized slag under an applied electric field according to claim 1, characterized in that: In step S3, the anode of the deoxidizing electrode is inserted into the slag layer 5-10 cm from the steel slag interface, and the cathode is inserted into the molten steel 5-10 cm from the steel slag interface. A voltage of 5-20V and a current of 1000-4000A are applied, and the processing time is 5-10 min.

4. The method for preparing deoxidized slag under an applied electric field according to claim 3, characterized in that: In step S3, the final deoxidized slag includes, by mass percentage: CaO: 30%–50%, SiO2: 10%–30%, MgO: 5%–10%, Al2O3: 10%–20%, (FeO+MnO) ≤ 4%, Na2O: 2.5%–5%, CeO2: 2.5%–5%.

Images