Method for scrap smelting and method for producing steel

Abstract

The present application relates to a method for scrap smelting and a method for preparing steel. The method for scrap smelting comprises the following steps: adding calcium aluminate refining slag and a first batch of scrap steel into a smelting furnace with first solid slag adhered, wherein the calcium aluminate refining slag contains 3CaO.Al2O3 phase and 12CaO.7Al2O3 phase; heating to a first temperature to melt the first batch of scrap steel to obtain first molten iron and second solid slag, and to partially melt the calcium aluminate refining slag, and the first solid slag falls off; adding a second batch of scrap steel into the smelting furnace, heating to a second temperature to melt the second batch of scrap steel to obtain second molten iron and third solid slag, completely melting the calcium aluminate refining slag, and converting the first solid slag, the second solid slag and the third solid slag into liquid slag; heating to a third temperature to smelt; and removing the liquid slag. The method realizes effective prevention and treatment of slag sticking to the furnace lining, and improves the smoothness of scrap smelting and production capacity.

Description

Technical Field

[0001] This invention relates to the technical field of steelmaking, and in particular to a method for smelting scrap steel and a method for preparing steel products. Background Technology

[0002] Scrap steel smelting is a steelmaking technology that transforms scrap steel into high-quality steel through processes such as slag treatment and high-temperature smelting. It typically uses an induction furnace to smelt scrap steel into molten iron. Scrap steel comes from diverse sources and often contains large amounts of SiO2 impurities. Furthermore, the alloying elements within the scrap steel are prone to oxidation during smelting, forming oxide slag containing components such as MgO, SiO2, and Al2O3. This oxide slag selectively reacts with the refractory material of the induction furnace lining, further forming high-melting-point, high-viscosity slag such as pure corundum and magnesium-aluminum spinel phases, which adhere to the furnace lining, hence the term "furnace lining slag adhesion." During scrap steel smelting, the slag adhesion continuously grows inward, gradually clogging the induction furnace and necessitating shutdown. During the blockage process, the adhered material hinders the flow and mixing of molten metal in the upper and lower parts, resulting in increased energy consumption and reduced production efficiency, ultimately impacting the production capacity of scrap steel smelting. Summary of the Invention

[0003] Therefore, it is necessary to provide a method for smelting scrap steel and a method for preparing steel products to overcome the problem of slag adhesion to the furnace lining during scrap steel smelting.

[0004] The above-mentioned objective of this invention is achieved through the following technical solution:

[0005] In a first aspect, the present invention provides a method for smelting scrap steel, comprising the following steps:

[0006] Calcium aluminate refining slag and the first batch of scrap steel are added to a smelting furnace with the first solid slag attached, wherein the calcium aluminate refining slag contains 3CaO·Al2O3 phase and 12CaO·7Al2O3 phase;

[0007] The temperature is raised to a first temperature to melt the first batch of scrap steel, resulting in the first molten iron and the second solid slag, and the calcium aluminate refining slag is partially melted, and the first solid slag falls off.

[0008] A second batch of scrap steel is added to the smelting furnace and heated to a second temperature to melt the second batch of scrap steel, resulting in a second batch of molten iron and a third solid slag. This completely melts the calcium aluminate refining slag and transforms the first solid slag, the second solid slag, and the third solid slag into liquid slag.

[0009] The temperature is raised to the third temperature for smelting.

[0010] Remove the liquid slag.

[0011] In one embodiment, the first temperature is ≥1300°C and the second temperature is ≥1400°C.

[0012] In one embodiment, the third temperature is 1450°C to 1550°C.

[0013] In one embodiment, the mass fraction of CaO in the calcium aluminate refining slag is ≥48%, and the mass fraction of Al2O3 is ≥30%.

[0014] In one embodiment, the mass ratio of the 3CaO·Al2O3 phase to the 12CaO·7Al2O3 phase in the calcium aluminate refining slag is (3~5):(2~5).

[0015] In one embodiment, the capacity of the smelting furnace to smelt molten iron is denoted as A tons, and the amount of calcium aluminate refining slag added is 5A kg to 15A kg.

[0016] In one embodiment, the step of adding other batches of scrap steel to the smelting furnace is included before heating to the third temperature for smelting.

[0017] In one embodiment, the mass ratio of the first batch of scrap steel to the total mass of the first batch of scrap steel, the second batch of scrap steel, and the other batches of scrap steel is 1:(2~4).

[0018] In one embodiment, one or more of the following conditions are met:

[0019] 1) The step of adding calcium aluminate refining slag and the first batch of scrap steel to the smelting furnace also includes the step of adding a first additive;

[0020] 2) The step of adding a second batch of scrap steel to the smelting furnace also includes the step of adding a second additive;

[0021] 3) The addition of other batches of scrap steel to the smelting furnace also includes the step of adding a third additive.

[0022] In one embodiment, the first additive, the second additive, and the third additive each independently comprise one or more of carbon powder, ferrosilicon powder, aluminum powder, and ferromanganese powder.

[0023] In one embodiment, removing the liquid slag includes the following steps:

[0024] Adding a slag remover causes the liquid slag to solidify and aggregate, resulting in solid slag.

[0025] Remove the solid scum.

[0026] In a second aspect, the present invention provides a method for preparing steel, which includes the steps of the scrap steel smelting method described above.

[0027] The present invention has the following beneficial effects:

[0028] In this invention, the calcium aluminate refining slag contains 3CaO·Al2O3 phase and 12CaO·7Al2O3 phase. The 3CaO·Al2O3 phase reacts with high-melting-point phases such as magnesium aluminum spinel phase and corundum phase to form low-melting-point phases such as 12CaO·7Al2O3 phase. The 12CaO·7Al2O3 phase is the phase with the lowest melting point in the CaO-Al2O3 system and can be rapidly liquefied during the heating process. This changes the reaction between the calcium aluminate refining slag and the three solid slags from a solid-solid reaction to a solid-liquid reaction. While accelerating the reaction rate, it can also react with the three solid slags to form low-melting-point phases such as CaO·Al2O3 phase and promote the formation of liquid slag.

[0029] At the first temperature, the calcium aluminate refining slag partially melts into a liquid state. This liquid slag adheres to the first and second solid slags, aiding in the melting and desorption of the first solid slag and preventing the second solid slag from contacting and reacting with the furnace lining. At the second temperature, the calcium aluminate refining slag completely melts and undergoes a solid-liquid reaction with the first, second, and third solid slags, forming a low-melting-point, low-viscosity liquid slag that floats to the surface of the molten iron. At the third temperature, the scrap steel in the furnace is completely melted into molten iron. Simultaneously, this gradient heating smelting method not only effectively prevents slag adhesion to the furnace lining and increases the output and energy efficiency of scrap steel smelting, but also reduces the reaction between the calcium aluminate refining slag and the refractory material of the furnace lining, preventing its erosion of the furnace lining. Attached Figure Description

[0030] Figure 1 This is a diagram showing the cold state inside the medium-frequency furnace after smelting 25 heats in Comparative Example 1.

[0031] Figure 2 This is a diagram showing the internal thermal state of the medium-frequency furnace after 15 heats in Example 1.

[0032] Figure 3 The slag phase change curve during the scrap steel smelting process of Comparative Example 1 is shown.

[0033] Figure 4 The curves show the phase change of slag during the scrap steel smelting process in Example 1. Detailed Implementation

[0034] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0035] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0037] Medium-frequency furnace steelmaking is a steelmaking process that uses the principle of medium-frequency electromagnetic induction to melt scrap steel and other waste metals, and then continuously casts and rolls them into steel products of various specifications. The furnace linings of a medium-frequency furnace are made of acidic SiO2-based or neutral Al2O3-based refractory materials. During scrap steel smelting, oxide slag containing components such as MgO, SiO2, and Al2O3 is usually formed. This slag selectively reacts with the refractory materials in the furnace lining to form pure corundum phase (Al2O3) and magnesium aluminum spinel phase (MgAl2O4) slag. The melting points of pure corundum and magnesium aluminum spinel phases are above 1800℃, far exceeding the smelting temperature of molten iron, and they also have high viscosity, causing them to adhere firmly to the furnace lining. This is known as furnace lining slag adhesion. The presence of furnace lining slag adhesion gradually clogs the medium-frequency furnace, continuously reducing its smelting capacity and severely impacting the production capacity of scrap steel smelting.

[0038] After gaining a thorough understanding of the formation principle and main phases of slag adhesion in furnace linings, the inventors believe that the basic approach to preventing slag adhesion in furnace linings is as follows: 1) Prevent the generation of new high-melting-point, high-viscosity solid slag during the scrap steel smelting process to avoid further deterioration of the slag adhesion phenomenon in furnace linings; 2) For existing high-melting-point, high-viscosity solid slag, use physicochemical methods to reduce its melting point and viscosity, so that it desorbs from the furnace lining and floats to the surface of the molten iron, and is finally removed by slag removal treatment.

[0039] Based on this, in a first aspect, the present invention provides a method for smelting scrap steel that can effectively remove old furnace lining slag and prevent the generation of new furnace lining slag.

[0040] In some embodiments, the method of scrap steel smelting includes the following steps:

[0041] Calcium aluminate refining slag and the first batch of scrap steel were added to a smelting furnace with the first solid slag attached. The calcium aluminate refining slag contained 3CaO·Al2O3 phase and 12CaO·7Al2O3 phase.

[0042] The temperature is raised to the first temperature, which melts the first batch of scrap steel, resulting in the first molten iron and the second solid slag. The calcium aluminate refining slag is partially melted, and the first solid slag falls off.

[0043] A second batch of scrap steel is added to the smelting furnace and heated to a second temperature to melt the second batch of scrap steel, resulting in a second batch of molten iron and a third batch of solid slag. This completely melts the calcium aluminate refining slag and transforms the first, second, and third batches of solid slag into liquid slag.

[0044] The temperature is raised to the third temperature for smelting.

[0045] Remove liquid slag.

[0046] Understandably, the first solid slag adheres to the furnace lining of the smelting furnace, also known as furnace lining slag adhesion; the second and third solid slags originate from solid inclusions generated during the melting of scrap steel, including impurities in the scrap steel and oxidation products of alloying elements.

[0047] In this invention, the calcium aluminate refining slag contains 3CaO·Al2O3 phase and 12CaO·7Al2O3 phase. The 3CaO·Al2O3 phase reacts with high-melting-point phases such as magnesium aluminum spinel phase and corundum phase to form low-melting-point phases such as 12CaO·7Al2O3 phase. The 12CaO·7Al2O3 phase is the phase with the lowest melting point in the CaO-Al2O3 system and can be rapidly liquefied during the heating process. This changes the reaction between the calcium aluminate refining slag and the three solid slags from a solid-solid reaction to a solid-liquid reaction. While accelerating the reaction rate, it can also react with the three solid slags to form low-melting-point phases such as CaO·Al2O3 phase and promote the formation of liquid slag.

[0048] At the first temperature, the calcium aluminate refining slag partially melts into a liquid state. This liquid slag adheres to the first and second solid slags, aiding in the melting and desorption of the first solid slag and preventing the second solid slag from contacting and reacting with the furnace lining. At the second temperature, the calcium aluminate refining slag completely melts and undergoes a solid-liquid reaction with the first, second, and third solid slags, forming a low-melting-point, low-viscosity liquid slag that floats to the surface of the molten iron. At the third temperature, the scrap steel in the furnace is completely melted into molten iron. Simultaneously, this gradient heating smelting method not only effectively prevents slag adhesion to the furnace lining and increases the output and energy efficiency of scrap steel smelting, but also reduces the reaction between the calcium aluminate refining slag and the refractory material of the furnace lining, preventing its erosion of the furnace lining.

[0049] Optionally, the smelting furnace is a medium-frequency furnace.

[0050] Induction furnaces are commonly used for smelting scrap steel. They have the characteristic of cold slag, and the slag temperature is lower than that of molten iron, which easily leads to slag adhesion to the furnace lining. Therefore, it is very necessary to prevent and control slag adhesion to the furnace lining.

[0051] Optionally, the first temperature is ≥1300℃. In some specific examples, the first temperature can be 1300℃, 1310℃, 1320℃, 1330℃, 1340℃, 1350℃, 1360℃, 1370℃, 1380℃, 1390℃, or 1400℃, etc.

[0052] Optionally, the second temperature is ≥1400℃. In some specific examples, the second temperature can be 1400℃, 1405℃, 1410℃, 1415℃, 1420℃, 1425℃, 1430℃, 1435℃, 1440℃, 1445℃, or 1450℃, etc.

[0053] Optionally, the third temperature is 1450℃~1550℃. In some specific examples, the third temperature can be 1450℃, 1460℃, 1470℃, 1490℃, 1500℃, 1510℃, 1520℃, 1530℃, 1540℃ or 1550℃, etc.

[0054] Understandably, in the actual scrap steel smelting process, the heating temperature of the smelting furnace may fluctuate significantly, ensuring that the first temperature is not lower than the second temperature. However, as long as the smelting temperature meets the requirements of the first temperature ≥ 1300℃ and the second temperature ≥ 1400℃, slag adhesion to the furnace lining can be prevented while minimizing erosion. Controlling the third temperature at 1450℃~1550℃ ensures that the scrap steel is completely melted into molten iron while preventing damage to the smelting furnace from excessively high smelting temperatures.

[0055] Besides CaO and Al2O3, calcium aluminate refining slag typically contains SiO2, MgO, K2O, Na2O, and CaF2, resulting in a melting point lower than that of the 12CaO·7Al2O3 phase (≈1415℃). By appropriately setting the first, second, and third temperatures, the calcium aluminate refining slag can be gradually melted into a liquid phase. Through physicochemical processes such as adhesion, fluxing, and reaction, all solid slag can be transformed into liquid slag, thereby preventing slag adhesion to the furnace lining and smelting scrap steel.

[0056] Optionally, in the calcium aluminate refining slag, the mass fraction of CaO is ≥48%, and the mass fraction of Al2O3 is ≥30%. In some specific examples, the mass fraction of CaO in the calcium aluminate refining slag can be 48%, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, or 70%, etc., and the mass fraction of Al2O3 can be 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, or 52%, etc.

[0057] By controlling the CaO and Al2O3 content, it is possible to ensure that the calcium aluminate refining slag contains sufficient 3CaO·Al2O3 phase and 12CaO·7Al2O3 phase to react with the slag adhering to the furnace lining and the solid slag in the molten iron.

[0058] Optionally, in the calcium aluminate refining slag, the mass ratio of the 3CaO·Al2O3 phase to the 12CaO·7Al2O3 phase is (3~5):(2~5).

[0059] Further optionally, the mass fraction of the 3CaO·Al2O3 phase in the calcium aluminate refining slag is 30%~50%.

[0060] Further optionally, the mass fraction of the 12CaO·7Al2O3 phase in the calcium aluminate refining slag is 20%~50%.

[0061] The content of the 3CaO·Al2O3 and 12CaO·7Al2O3 phases is crucial for preventing slag adhesion to the furnace lining. Adjusting the content of these two phases based on the amount of first solid slag adhesion and the impurity content of the scrap steel can accelerate the removal efficiency. In specific examples, in calcium aluminate refining slag, the mass fraction of the 3CaO·Al2O3 phase can be 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, or 50%, and the mass fraction of the 12CaO·7Al2O3 phase can be 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, or 50%.

[0062] Optionally, let A tons be the capacity of the molten iron that the smelting furnace can produce, and let 5A kg to 15A kg be the amount of calcium aluminate refining slag added, where A > 0. In some specific examples, based on the capacity of the smelting furnace, the mass of calcium aluminate refining slag added per ton of molten iron can be 5A kg, 6A kg, 7A kg, 8A kg, 9A kg, 10A kg, 11A kg, 12A kg, 13A kg, 14A kg, or 15A kg, etc.

[0063] Before smelting scrap steel, the amount of calcium aluminate refining slag required can be estimated based on the amount of slag adhering to the furnace lining and the impurity content in the scrap steel, so as to avoid waste of calcium aluminate refining slag or incomplete removal of slag adhering to the furnace lining.

[0064] Optionally, before heating to the third temperature for smelting, the process also includes adding other batches of scrap steel to the smelting furnace.

[0065] During scrap steel smelting, after the first and second batches of scrap steel melt, the molten iron level is still some distance from the furnace opening, which is not conducive to removing the liquid slag floating on the surface of the molten iron, and the smelting furnace capacity is not fully utilized. Therefore, before heating to the third temperature for smelting, other batches of scrap steel must be gradually added so that the molten iron level gradually rises to 5cm to 15cm below the furnace opening.

[0066] Optionally, the ratio of the mass of the first batch of scrap steel to the total mass of the first batch, the second batch, and other batches of scrap steel is 1:(2~4). In some specific examples, the ratio of the mass of the first batch of scrap steel to the total mass of the first batch, the second batch, and other batches of scrap steel can be 1:2.0, 1:2.2, 1:2.4, 1:2.6, 1:2.8, 1:3.0, 1:3.2, 1:3.4, 1:3.6, 1:3.8, or 1:4.0, etc.

[0067] The first batch of solid slag mostly adheres to the lower and middle parts of the smelting furnace, especially the furnace lining below one-third of the furnace's maximum capacity. By controlling the quality of the first batch of scrap steel to one-quarter to one-half of the total scrap steel, the first batch of solid slag in the lower and middle parts of the smelting furnace can be effectively cleaned.

[0068] Optionally, adding calcium aluminate refining slag and the first batch of scrap steel to the smelting furnace also includes the step of adding a first additive.

[0069] Optionally, adding a second batch of scrap steel to the smelting furnace also includes the step of adding a second additive.

[0070] Optionally, adding other batches of scrap steel to the smelting furnace also includes the step of adding a third additive.

[0071] Further optionally, the first additive, the second additive, and the third additive each independently include one or more of carbon powder, ferrosilicon powder, aluminum powder, and ferromanganese powder.

[0072] Adding additives such as carbon powder, ferrosilicon powder, aluminum powder, and ferromanganese powder during the scrap steel smelting process can regulate the composition of molten iron and deoxidize, desulfurize, or dephosphorize the slag, thereby improving the quality of steel.

[0073] Optionally, the composition of the first batch of scrap steel, the second batch of scrap steel, and other batches of scrap steel may each independently include one or more of Fe, Si, C, Al, Mn, and Cr.

[0074] Alternatively, the mass fraction of Cr in the first batch, the second batch, and other batches of scrap steel is independently <1%, because Cr tends to form high-melting-point chromium compounds during smelting, which is not conducive to the removal of slag adhering to the furnace lining.

[0075] Optionally, removing molten slag includes the following steps:

[0076] Adding a slag remover causes the liquid slag to solidify and aggregate, resulting in solid slag.

[0077] Remove solid scum.

[0078] Understandably, the method for removing molten slag is slag removal.

[0079] Alternatively, the slag remover may include carbonate components such as sodium carbonate, potassium carbonate, and calcium carbonate. After the slag remover is sprinkled on the molten slag, the carbonates decompose at high temperatures and absorb heat, causing some of the molten slag to cool and solidify, thus achieving a good agglomeration effect. During slag removal, it is usually not necessary to completely solidify the molten slag; instead, it is necessary to transform the molten slag into a solid-liquid mixture, which makes it easier to remove the molten iron.

[0080] Alternatively, the molten slag may be removed multiple times.

[0081] In a second aspect, the present invention provides a method for preparing steel, which includes the steps of the scrap steel smelting method described above.

[0082] Optionally, the mass fraction of the steel composition satisfies: C≥2.0%, Si≥0.6%.

[0083] The present invention will be further described in detail below with reference to specific embodiments. Unless otherwise specified, the raw materials and equipment used in the following embodiments are all commercially available products.

[0084] Example 1

[0085] In this embodiment, a 3T medium-frequency furnace is selected as the smelting furnace, with a molten iron capacity of 3 tons (t). The first, second and third additives all include carbon powder and ferrosilicon powder, so that the mass fraction of the molten iron in the smelting process meets the following conditions: C≈2.1wt.%, Si≈0.6wt.%.

[0086] The method for smelting scrap steel includes the following steps:

[0087] 1) Add 15~45kg of calcium aluminate refining slag, 1t of the first batch of scrap steel and the first additive to the medium frequency furnace. The furnace lining of the medium frequency furnace is covered with the first solid molten slag.

[0088] 2) The temperature is raised to above 1300℃ to completely melt the first batch of scrap steel, resulting in the first molten iron and the second solid slag; at the same time, the calcium aluminate refining slag is partially melted, and the molten calcium aluminate refining slag and the first solid slag adhere to each other, which helps the first solid slag to melt and fall off.

[0089] 3) Add 1.2t of the second batch of scrap steel and the second additive to the medium-frequency furnace, and raise the temperature to above 1400℃ to completely melt the second batch of scrap steel, obtaining the second molten iron and the third solid slag; during the heating process, the calcium aluminate refining slag completely melts. In the presence of the completely melted calcium aluminate refining slag, the first solid slag, the second solid slag and the third solid slag can fully react to form a low melting point and low viscosity liquid slag, thereby causing the first solid slag on the furnace lining to fall off.

[0090] 4) After the molten slag floats to the surface of the molten iron, add 0.8t of other batches of scrap steel and the third auxiliary agent to the medium-frequency furnace, and heat to 1520℃ for smelting; then perform multiple slag removal processes until the molten slag on the surface of the molten iron is completely cleaned. The slag removal process specifically involves: sprinkling a slag remover onto the molten slag on the surface of the molten iron, causing the molten slag to solidify and aggregate, resulting in solid slag; and then removing the solid slag using a slag removal rod.

[0091] Comparative Example 1

[0092] The scrap steel smelting process in this comparative example is basically the same as that in the embodiment, except that calcium aluminate refining slag is not added. The specific steps are as follows:

[0093] 1) Add 1 t of the first batch of scrap steel and the first additive to the medium-frequency furnace with the first solid slag attached to the furnace lining, and raise the temperature to above 1300℃ to completely melt the first batch of scrap steel, so as to obtain the first molten iron and the second solid slag.

[0094] 2) Add 1.3t of the second batch of scrap steel and the second additive to the medium-frequency furnace, and raise the temperature to above 1400℃ to completely melt the second batch of scrap steel, so as to obtain the second molten iron and the third solid slag.

[0095] 3) After the molten slag floats to the surface of the molten iron, add 0.8t of other batches of scrap steel and the third auxiliary agent to the medium-frequency furnace, and heat to 1520℃ for smelting; then perform multiple slag removal processes until the molten slag on the surface of the molten iron is completely cleaned. The slag removal process specifically involves: sprinkling a slag remover onto the molten slag on the surface of the molten iron, causing the molten slag to solidify and aggregate, resulting in solid slag; and then removing the solid slag using a slag removal rod.

[0096] Test case

[0097] Following the scrap steel smelting method described in Comparative Example 1, after smelting 25 heats in an intermediate frequency furnace, the condition of the first solid slag on the furnace lining was observed, and the results were as follows: Figure 1 As shown. By Figure 1 It can be seen that without the addition of calcium aluminate refining slag, after smelting 25 heats, a large amount of first solid molten slag adhered to the furnace lining of the intermediate frequency furnace, which significantly reduced the actual capacity of the intermediate frequency furnace and seriously affected the scrap steel smelting capacity.

[0098] Following the scrap steel smelting method described in Example 1, after smelting 15 heats in an intermediate frequency furnace, the condition of the first solid slag on the furnace lining was observed, and the results were as follows: Figure 2 As shown. By Figure 2 It can be seen that, with the addition of calcium aluminate refining slag, after smelting 15 heats, there is almost no first solid molten slag on the lining of the intermediate frequency furnace, and the intermediate frequency furnace can still maintain good production capacity.

[0099] The composition of impurities in calcium aluminate refining slag and scrap steel was tested using X-ray fluorescence spectrometry. The obtained composition was then input into the thermochemical software FactSage for calculation, thereby obtaining the slag phase change curve during the scrap steel smelting process. The results are as follows: Figures 3-4 As shown, where, Figure 3 The curves showing the phase change of the slag during the scrap steel smelting process in Comparative Example 1 are shown. Figure 4 The curves show the phase change of slag during the scrap steel smelting process in Example 1.

[0100] Depend on Figure 3 It can be seen that when scrap steel is smelted without the addition of calcium aluminate refining slag, the main phase of the slag below 1300℃ is pseudosapphire phase (Mg4Al). 10 Si2O 23 M4A5S2), calcium feldspar phase (CaAl2Si2O8, CAS2), magnesium aluminum spinel-calcium hexaaluminate complex phase (CaMg2Al 16 O 27The phases are MgO (M), Al2O3 (A), SiO2 (S), and CaO (C). These phases originate from impurities in scrap steel, oxidation products of alloying elements, additives added during smelting, refractory materials in the furnace lining, and their reaction products. When the temperature is raised above 1300℃, the pseudosapphire phase, calcium feldspar phase, magnesium aluminum spinel-calcium hexaaluminate composite phase, and fluorite phase almost completely disappear, while pure corundum phase (Al2O3, A) and magnesium aluminum spinel phase (MgAl2O4, MA) are formed. These two phases have high melting points and high viscosity, and easily adhere to the furnace lining, resulting in a large amount of first solid slag adhering to the lining of the medium-frequency furnace. As the temperature continues to rise from 1300℃ to 1700℃, the mass percentage of liquid slag gradually increases, reaching a maximum of 70%. The remaining slag exists in the form of first solid slag, second solid slag, or third solid slag, which reduces the capacity and quality of scrap steel smelting.

[0101] Depend on Figure 4 It can be seen that when calcium aluminate refining slag is added for scrap steel smelting, below 1300℃, the main phase of the slag is cordierite (Mg2Al4Si5O). 18 The phases consist of M2A2S5, anorthite (CaAl2Si2O8, CAS2), and pseudosapphire (Mg4Al). 10 Si2O 23 These phases originate from calcium aluminate refining slag, impurities in scrap steel, oxidation products of alloying elements, additives used in smelting, refractory materials in the furnace lining, and their reaction products. Upon heating above 1300℃, the cordierite, anorthite, and pseudosapphire phases almost completely disappear, while a very small amount of pure corundum (Al2O3, A) is generated between 1300℃ and 1400℃, but no magnesium aluminum spinel (MgAl2O4, MA) is formed. Upon heating above 1400℃, only liquid slag remains as a phase. This liquid slag is an amorphous, non-crystalline phase containing the following mass fractions: 16.4% CaO, 31.9% Al2O3, 44.3% SiO2, 5.8% MgO, and 1.6% CaF2. At smelting temperatures ranging from 1400℃ to 1700℃, the mass percentage of liquid slag was close to 100%, indicating that the use of calcium aluminate refining slag can almost completely convert all solid slag in the furnace into liquid slag, avoiding the formation of high-melting-point phases such as pure corundum and magnesium aluminum spinel. This not only thoroughly removes the first solid slag adhering to the furnace lining but also helps prevent the second and third solid slags from transforming into new first solid slags, demonstrating excellent prevention and control effects. Thanks to the thorough prevention of slag adhesion to the furnace lining, this scrap steel smelting method can not only improve steelmaking capacity and quality but also extend the life of the induction furnace lining, reduce the energy consumption of the induction furnace, and save on the production costs of scrap steel smelting.

[0102] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0103] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A method for smelting scrap steel, characterized in that, Includes the following steps: Calcium aluminate refining slag and the first batch of scrap steel are added to a smelting furnace with the first solid slag attached, wherein the calcium aluminate refining slag contains 3CaO·Al2O3 phase and 12CaO·7Al2O3 phase; The temperature is raised to a first temperature to melt the first batch of scrap steel, resulting in the first molten iron and the second solid slag, and the calcium aluminate refining slag is partially melted, and the first solid slag falls off. A second batch of scrap steel is added to the smelting furnace and heated to a second temperature to melt the second batch of scrap steel, resulting in a second batch of molten iron and a third solid slag. This completely melts the calcium aluminate refining slag and transforms the first solid slag, the second solid slag, and the third solid slag into liquid slag. The temperature is raised to the third temperature for smelting. Remove the liquid slag; The first solid slag includes a corundum phase and a magnesium aluminum spinel phase; In the calcium aluminate refining slag, the mass fraction of CaO is ≥48%, and the mass fraction of Al2O3 is ≥30%.

2. The method for smelting scrap steel as described in claim 1, characterized in that, The first temperature is ≥1300℃, and the second temperature is ≥1400℃.

3. The method for smelting scrap steel as described in claim 2, characterized in that, The third temperature is 1450℃~1550℃.

4. The method for smelting scrap steel as described in claim 1, characterized in that, In the calcium aluminate refining slag, the mass fraction of CaO is 48%-58%, and the mass fraction of Al2O3 is 30%-44%.

5. The method for smelting scrap steel as described in claim 4, characterized in that, In the calcium aluminate refining slag, the mass ratio of the 3CaO·Al2O3 phase to the 12CaO·7Al2O3 phase is (3~5):(2~5).

6. The method for smelting scrap steel according to any one of claims 1 to 5, characterized in that, Let A be the capacity of the smelting furnace to produce molten iron, and let A be the amount of calcium aluminate refining slag added, which is 5A kg to 15A kg.

7. The method for smelting scrap steel as described in claim 6, characterized in that, Before smelting at the third temperature, the process also includes adding other batches of scrap steel to the smelting furnace.

8. The method for smelting scrap steel as described in claim 7, characterized in that, The ratio of the mass of the first batch of scrap steel to the total mass of the first batch of scrap steel, the second batch of scrap steel, and the other batches of scrap steel is 1:(2~4).

9. The method for smelting scrap steel as described in claim 7, characterized in that, One or more of the following conditions must be met: 1) The step of adding calcium aluminate refining slag and the first batch of scrap steel to the smelting furnace also includes the step of adding a first additive; 2) The step of adding a second batch of scrap steel to the smelting furnace also includes the step of adding a second additive; 3) The addition of other batches of scrap steel to the smelting furnace also includes the step of adding a third additive.

10. The method for smelting scrap steel as described in claim 9, characterized in that, The first additive, the second additive, and the third additive each independently include one or more of carbon powder, ferrosilicon powder, aluminum powder, and ferromanganese powder.

11. The method for smelting scrap steel according to any one of claims 1 to 5, characterized in that, The removal of the liquid slag includes the following steps: Adding a slag remover causes the liquid slag to solidify and aggregate, resulting in solid slag. Remove the solid scum.

12. A method for preparing steel, characterized in that, It includes the steps of the scrap steel smelting method as described in any one of claims 1 to 11.

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