Process for reducing the nitrogen content of hot metal

Abstract

The application provides a treatment method for reducing the nitrogen content of molten iron, comprising the following steps: smelting to obtain first molten iron in a blast furnace, sampling and analyzing the first molten iron to obtain a first titanium content and a first nitrogen content in the first molten iron; according to the first titanium content and the first nitrogen content, adding titanium-containing pig iron into an iron ladle and then introducing the first molten iron to obtain second molten iron in the iron ladle, and the precipitation temperature of titanium nitride in the second molten iron is greater than or equal to 1400 DEG C; transporting the second molten iron to a KR process, performing stirring treatment to promote the precipitation of titanium nitride, and performing slagging treatment to obtain molten iron to be used. The application controls the precipitation temperature of titanium nitride to be greater than or equal to 1400 DEG C by adding titanium-containing pig iron, and combines with the KR stirring, so that the nitrogen content of the molten iron can be reduced to less than or equal to 0.0050%, and pure molten iron raw materials are provided for a smelting converter, and the production cost is reduced.

Description

Technical Field

[0001] This application relates to the field of iron and steel metallurgy technology, and in particular to a method for reducing the nitrogen content of molten iron. Background Technology

[0002] Nitrogen readily forms interstitial solid solutions with iron in steel, or forms nitrides with alloying elements such as titanium, aluminum, and vanadium. When steel remains at room temperature or during heating for an extended period, nitrides gradually precipitate and accumulate at grain boundaries or dislocations, leading to increased strength and hardness, but decreased plasticity and toughness, i.e., aging embrittlement.

[0003] Low-nitrogen steel refers to steel with nitrogen content controlled at a low level, usually ≤0.005% by mass. Low-nitrogen steel can significantly reduce aging sensitivity and is especially suitable for structural components that have been in long-term service, such as pressure vessels and bridge steel. How to smelt low-nitrogen steel by reducing the nitrogen content of molten iron is a current issue of great concern. Summary of the Invention

[0004] This application provides a method for reducing the nitrogen content of molten iron, thereby providing pure molten iron raw materials for smelting converters and reducing production costs.

[0005] This application provides a method for reducing the nitrogen content of molten iron, comprising the following steps: smelting to obtain first molten iron in a blast furnace; sampling and analyzing the first molten iron to obtain the first titanium content and the first nitrogen content in the first molten iron; adding titanium-containing pig iron to a ladle according to the first titanium content and the first nitrogen content, and then introducing the first molten iron to obtain second molten iron in the ladle, wherein the precipitation temperature of titanium nitride in the second molten iron is ≥1400℃; transporting the second molten iron to the KR process, performing stirring treatment to promote the precipitation of titanium nitride, and performing slag removal treatment to obtain molten iron ready for use.

[0006] According to an embodiment of this application, in the step of adding titanium-containing pig iron to an iron ladle and then introducing molten iron to obtain molten iron in the iron ladle, based on the first titanium content and the first nitrogen content, the second molten iron has a second titanium content, which is controlled at 0.10% to 0.15%.

[0007] According to embodiments of this application, the titanium-containing pig iron comprises the following components by mass percentage: titanium, 6-12%, carbon, 1-2%, silicon, 2-4%, manganese, 0.2-0.4%, iron, 81-90%; the remainder being unavoidable impurities such as sulfur, phosphorus, and copper.

[0008] According to an embodiment of this application, in the step of adding titanium-containing pig iron to a ladle and then introducing molten iron to make the precipitation temperature of titanium nitride ≥1400°C to obtain molten iron in the ladle, the tapping temperature of the first molten iron in the blast furnace is ≥1490°C when the first molten iron is introduced into the ladle, based on the first titanium content and the first nitrogen content.

[0009] According to an embodiment of this application, the process parameters for the stirring treatment include: a stirring speed of 100-120 r / min and a treatment time of 15-20 min.

[0010] According to an embodiment of this application, the depth to which the stirring head is inserted below the liquid level is 0.6 to 1 m.

[0011] According to an embodiment of this application, in the step of transporting the second molten iron to the KR process, performing stirring treatment to promote the precipitation of titanium nitride, and performing slag removal treatment to obtain molten iron ready for use, the second nitrogen content in the ladle is obtained, and the slag removal treatment is performed when the second nitrogen content is ≤0.0050%.

[0012] According to an embodiment of this application, after stirring, the temperature of the molten iron in the ladle is controlled at 1320-1380°C, and slag removal is performed.

[0013] According to the embodiments of this application, the slag removal cleanliness of the molten iron to be used is ≥70%.

[0014] This application controls the precipitation temperature of titanium nitride to ≥1400℃ by adding titanium-containing pig iron, and combines it with KR stirring, so that the nitrogen content of molten iron can be reduced to ≤0.0050%, providing pure molten iron raw materials for converter smelting and reducing production costs. Attached Figure Description

[0015] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0016] Figure 1 This is a flowchart of the treatment method for reducing nitrogen content in molten iron provided in this application; Figure 2 These are the precipitation temperatures of TiN under different nitrogen contents.

[0017] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0018] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments.

[0019] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0020] 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 application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0021] In steel production, when blast furnace conditions are not optimal, molten iron often exhibits low silicon and titanium content. A decrease in titanium content in the molten iron leads to a drop in the precipitation temperature of titanium nitride (TiN), making it difficult for TiN to fully precipitate during the KR (mechanical stirring) process. This results in ineffective denitrification of the molten iron, ultimately leading to a high nitrogen content, typically between 0.006% and 0.010%. High nitrogen content in molten iron affects the subsequent smelting of low-nitrogen steel. Traditional processes require a high iron-to-metal ratio of over 90% to achieve a final nitrogen content of ≤0.0025% in the converter steel, increasing production costs.

[0022] In view of the above problems, this application provides a method for reducing the nitrogen content of molten iron, which can reduce the nitrogen content of molten iron and save production costs.

[0023] This application provides a method for reducing the nitrogen content in molten iron. Please refer to [link to relevant documentation]. Figure 1 It includes the following steps: S100: Smelting to obtain the first molten iron in the blast furnace, sampling and analyzing the first molten iron to obtain the first titanium content and the first nitrogen content in the first molten iron; S200: Based on the first titanium content and the first nitrogen content, titanium-containing pig iron is added to the iron ladle and then the first molten iron is passed through to obtain the second molten iron in the iron ladle. The precipitation temperature of titanium nitride in the second molten iron is ≥1400℃. S300: The second batch of molten iron is transported to the KR process, where it is stirred to promote the precipitation of titanium nitride, and then slag is removed to obtain molten iron ready for use.

[0024] This application controls the precipitation temperature of titanium nitride to ≥1400℃ by adding titanium-containing pig iron, and combines it with KR stirring, so that the nitrogen content of molten iron can be reduced to ≤0.0050%, providing pure molten iron raw materials for smelting converters and reducing production costs.

[0025] The specific steps for S100 are as follows: In this embodiment of the application, molten iron is obtained through smelting and sampled for analysis. Specifically, in the smelting process, iron ore, coke, and flux are smelted in a blast furnace to generate liquid molten iron under high-temperature reducing conditions. Before the molten iron is received in the ladle, a sample of the molten iron is collected and analyzed to obtain the first titanium content and the first nitrogen content in the molten iron.

[0026] For example, the first titanium content and the first nitrogen content can be determined by spectroscopic analysis (such as ICP-AES) or chemical analysis.

[0027] By measuring the titanium and nitrogen content of the first batch of molten iron, a basis can be provided for calculating the amount of titanium-containing pig iron to be added subsequently, thus avoiding insufficient or excessive titanium content.

[0028] In some embodiments, the first nitrogen content in the first molten iron is 0.0060% to 0.010%. If the first titanium content is <0.10%, it can be determined that titanium-containing pig iron needs to be added to ensure that the composition of the second molten iron meets the standards.

[0029] The specific steps for S200 are as follows: Based on the first titanium content and the first nitrogen content, titanium-containing pig iron is added to the iron ladle, and then the first molten iron is passed through to obtain the second molten iron in the iron ladle. The precipitation temperature of titanium nitride in the second molten iron is ≥1400℃.

[0030] When it is necessary to increase the titanium content, in the empty state of the iron ladle, first add titanium-containing pig iron, and then pass in the first molten iron to make the titanium-containing pig iron and the first molten iron fully mixed.

[0031] When the first batch of molten iron is introduced into the ladle, the titanium-containing pig iron dissolves rapidly through the impact and stirring action of the molten iron, forming the second batch of molten iron, thus ensuring a uniform distribution of titanium content.

[0032] The precipitation behavior of TiN in molten iron is significantly affected by temperature. Temperature determines the precipitation morphology of TiN, which in turn affects the removal efficiency. When the temperature is <1400℃, TiN is easily dispersed uniformly in the molten iron in the form of extremely fine particles, i.e., diffuse precipitation. These fine particles are small in size, numerous, and have strong binding force with the molten iron, making it difficult to separate and remove them from the molten iron in the subsequent slag removal process. However, when the temperature is ≥1400℃, the higher temperature will change the nucleation conditions of TiN, making it more difficult to form fine and diffuse particles. At the same time, the atomic diffusion rate is accelerated, causing the already formed tiny TiN particles to aggregate and grow. Eventually, TiN will transform into larger and more concentrated particles, no longer uniformly dispersed in the molten iron, but more likely to float to the surface of the molten iron or aggregate near the slag phase. This application embodiment controls the precipitation temperature to ≥1400℃, and adjusts the particle growth rate by thermodynamically adjusting the spontaneous tendency of the precipitation reaction and kinetic regulation, so that TiN is transformed from a difficult-to-separate fine and dispersed state to an easily separable coarse and aggregated state. With the help of subsequent KR stirring, this form of TiN can quickly float to the surface and be completely removed by the slag removal process, thereby achieving the core goal of denitrification of molten iron and realizing the control of TiN particle size, distribution and molten steel quality.

[0033] In some embodiments, in the step of adding titanium-containing pig iron to an iron ladle and then passing first molten iron through it to obtain second molten iron in the iron ladle, the second molten iron has a second titanium content, which is controlled at 0.10% to 0.15%.

[0034] Ti and N in molten iron spontaneously combine to form TiN compounds. TiN is insoluble in molten iron, but it will only precipitate from the molten iron when the activity product of Ti and N, aTi⋅aN, reaches a critical value. (See also...) Figure 2This application notes that calculations during the production process show that titanium and nitrogen elements are present in the molten iron, and TiN will precipitate during the cooling process. The precipitation temperature of TiN is positively correlated with the titanium content; the higher the titanium content, the higher the TiN precipitation temperature for the same nitrogen content. When the titanium content reaches 0.10%, the activity product of titanium and nitrogen in the molten iron, aTi⋅aN, can exceed the precipitation critical value, causing TiN to precipitate from the molten iron. When the titanium content is in the range of 0.10% to 0.15%, corresponding to a nitrogen content of 0.0060% to 0.010% in the first batch of molten iron during production, the TiN precipitation temperature can be stably ≥1400℃. When the titanium content in the molten iron is 0.10%, the corresponding TiN precipitation temperatures are 1429℃ and 1489℃ for nitrogen contents of 0.005% and 0.010%, respectively. When the titanium content is increased to 0.12%, the precipitation temperatures for nitrogen contents of 0.005% and 0.010% are 1444℃ and 1505℃, respectively. It is evident that a titanium content within the range of 0.10% to 0.15% ensures a TiN precipitation temperature ≥1400℃, providing a thermodynamic basis for nitrogen precipitation in the form of TiN.

[0035] As mentioned above, when the TiN precipitation temperature is ≥1400℃, large, easily aggregated particles are formed. These particles can quickly float to the surface under the stirring action of KR and be completely separated from the molten iron through the slag removal process, thereby reducing the nitrogen content of the molten iron. Therefore, the embodiments in this application control the titanium content at 0.10% to 0.15%, which can both meet the thermodynamic requirement of TiN precipitation temperature ≥1400℃ and avoid excessive titanium content leading to excessive molten iron composition and increased production costs, or insufficient titanium content failing to achieve the expected denitrification effect.

[0036] If the titanium content is less than 0.10%, such as 0.06%, when the nitrogen content is 0.008%, the TiN precipitation temperature is only 1426℃, close to the lower limit of the process. If the titanium content is further reduced to 0.02%, the precipitation temperature drops to 1340℃. At this point, the KR treatment temperature may be higher than the precipitation temperature. The actual temperature of the molten iron is higher than the TiN precipitation temperature, which is thermodynamically unfavorable for the full precipitation of TiN. Even if a small amount of TiN is generated, the temperature conditions will make nucleation difficult and the precipitation amount insufficient. Ultimately, this results in a decrease in denitrification efficiency and an inability to effectively reduce the nitrogen content of the molten iron.

[0037] In some embodiments, the titanium-containing pig iron comprises the following components by mass percentage: titanium, 6-12%, carbon, 1-2%, silicon, 2-4%, manganese, 0.2-0.4%, iron, 81-90%; the remainder being unavoidable impurities such as sulfur, phosphorus, and copper.

[0038] The titanium content must be ensured to be increased to 0.10%–0.15% in the molten iron, corresponding to a TiN precipitation temperature ≥1400℃. If the titanium content is <6%, more pig iron needs to be added to achieve the target titanium content, increasing transportation and feeding costs; if it is >12%, the enrichment of titanium in the pig iron may lead to insufficient silicon and iron content, affecting the fluidity and dissolution rate of the pig iron. For example, the titanium content is 6%, 7%, 8%, 9%, 10%, 10%, or 12%.

[0039] Titanium can form solid solutions with silicon and carbon, reducing the activity coefficient of titanium and indirectly increasing the driving force for TiN precipitation. Simultaneously, a silicon content of 2-4% can control the melting point of titanium-containing pig iron to 1250-1300℃, lower than the temperature of molten iron, ensuring rapid melting of the pig iron after it is added to the ladle and avoiding cold material residue. If the silicon content is <4%, the melting point of the pig iron rises to above 1350℃, and the dissolution time is extended to more than 10 minutes; if it is >6%, the pig iron becomes too fluid and prone to leakage during transportation. For example, silicon contents of 2%, 2.5%, 3%, 2%, or 4% are used.

[0040] Titanium-containing pig iron uses iron as its base, with a content of 81-90%, matching the composition of molten iron to avoid poor fusion due to excessive compositional differences. For example, the iron content is 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, or 90%.

[0041] Therefore, the composition of titanium-containing pig iron, consisting of 6-12% titanium, 1-2% carbon, 2-4% silicon, 0.2-0.4% manganese, and 81-90% iron, ensures efficient utilization of titanium and full extraction of TiN. Furthermore, the synergistic effect of silicon, carbon, and iron optimizes the solubility and metallurgical reactivity of the pig iron, while keeping impurities such as sulfur and phosphorus within safe limits. This achieves the best balance between denitrification efficiency, process feasibility, and cost.

[0042] In some embodiments, in the step of adding titanium-containing pig iron to the ladle according to the first titanium content and the first nitrogen content, and then introducing the first molten iron to obtain the second molten iron in the ladle, the tapping temperature of the first molten iron in the blast furnace is ≥1490℃ when the first molten iron is introduced into the ladle.

[0043] TiN precipitation requires a molten iron temperature ≥1400℃, but there is a temperature drop from blast furnace tapping to KR treatment. If the tapping temperature is ≥1490℃, the molten iron temperature can still be maintained at the KR treatment target temperature after ladle transportation and alloying process, ensuring that TiN is fully precipitated within the thermodynamically feasible temperature range.

[0044] Meanwhile, the tapping temperature of ≥1490℃ can be higher than the liquidus temperature of molten iron, so that the molten iron remains in a liquid state during transportation and processing, avoiding excessive viscosity of molten iron due to low temperature, which would hinder the aggregation and floating of TiN particles.

[0045] The specific steps for S300 are as follows: The second batch of molten iron is transported to the KR process, where it is stirred to promote the precipitation of titanium nitride, and then slag is removed to obtain molten iron ready for use.

[0046] This application notes that, through calculation, the molten iron contains titanium and nitrogen elements, and TiN will precipitate during the cooling process. The KR stirring process further promotes the combination and precipitation of Ti and N.

[0047] The KR process achieves deep purification of molten iron through mechanical stirring and the synergistic effects of desulfurization and denitrification, providing high-quality molten iron raw materials with controllable composition for converter steelmaking.

[0048] In some embodiments, the process parameters for the stirring treatment include: a stirring speed of 100-120 r / min and a treatment time of 15-20 min.

[0049] In the KR process, stirring breaks down titanium-containing pig iron particles through mechanical shearing, allowing them to come into full contact with the first molten iron at a temperature above 1490°C, thus increasing the dissolution rate.

[0050] Without stirring, the titanium concentration near the point where the titanium-containing pig iron is added may become excessively high instantaneously, causing titanium nitride to precipitate and agglomerate prematurely, making it difficult to remove by slag skimming. Simultaneously, stirring can eliminate temperature stratification within the ladle. While the blast furnace tapping temperature is ≥1490℃, the temperature difference between the bottom of the ladle and the liquid surface is significant. In this embodiment, stirring forces convection, reducing the temperature difference between different areas within the ladle and ensuring that the temperature in the low-temperature zone at the bottom is maintained above 1400℃, thus preventing a reduction in titanium nitride precipitation due to insufficient supercooling.

[0051] When stirring at the above-mentioned speed range, avoid excessive particle breakage or insufficient agglomeration, and ensure that the TiN particle size is conducive to slag removal. When the fluid shear force and particle collision and agglomeration force reach equilibrium, at low speeds (<100 r / min), particles easily agglomerate into large particle clusters, resulting in fast but uneven settling speeds; at high speeds (>120 r / min), particles are broken down to too small, and their floating speed is lower than the flow speed of molten iron, making them difficult to remove.

[0052] In addition, the eddy currents formed by stirring push TiN particles toward the slag-iron interface, increasing their migration rate and effectively reducing the TiN inclusion content in the molten iron, thus providing pure molten iron for subsequent steelmaking.

[0053] Controlling the stirring time can avoid energy waste caused by excessive stirring, and shortening the stirring time can keep the molten iron at a suitable temperature, complete denitrification within a thermodynamically feasible temperature window, avoid the contradiction between temperature drop and energy consumption, maximize denitrification efficiency, and minimize equipment wear and energy consumption.

[0054] For example, the stirring speed is 100 r / min, 110 r / min or 120 r / min.

[0055] For example, the stirring time is 15 min, 16 min, 17 min, 18 min, 19 min or 20 min.

[0056] In some embodiments, the stirring head is inserted to a depth of 0.6 to 1 m below the liquid level.

[0057] In this embodiment, when the insertion depth is 0.6–1 m, the stirring head can penetrate a key depth layer below the molten iron surface, creating a continuous vortex field from the surface to the bottom. Compared to the problem of strong upper fluid and weak bottom flow caused by excessively shallow insertion, or surface air entrapment caused by excessively deep insertion, the above depth range ensures a low velocity difference between the upper and lower layers of molten iron, avoiding dead zones in local areas, thereby improving the mass transfer efficiency of titanium and nitrogen in the molten iron. At the above depth, the shear force generated by the rotation of the stirring head can create a moderate turbulence intensity in the molten iron: ensuring effective collision and aggregation of TiN particles while avoiding excessive turbulence that causes already aggregated particles to break up again, creating conditions for subsequent slag removal. For example, the insertion depth of the stirring head below the liquid level is 0.6 m, 0.7 m, 0.8 m, 0.9 m, and 1 m.

[0058] In some embodiments, in the step of transporting the second molten iron to the KR process, performing stirring treatment to promote titanium nitride precipitation, and performing slag removal treatment to obtain molten iron ready for use, the second nitrogen content in the ladle is obtained, and the slag removal treatment is performed when the second nitrogen content is ≤0.0050%.

[0059] After the second batch of molten iron is transported to the KR process and stirred, molten iron samples are collected from different locations in the ladle using the drill cuttings sampling method, and the nitrogen content is measured in real time.

[0060] For example, the locations for collecting molten iron samples include the center of the ladle and / or the edge of the ladle.

[0061] For example, nitrogen content can be determined in real time using a direct-reading spectrometer or an inert gas melting thermal conductivity method.

[0062] When the nitrogen content in the molten iron is detected to be ≤0.0050%, it is determined that TiN has been fully precipitated and floated to the slag layer, at which point the slag removal operation is initiated. If the nitrogen content does not meet the standard, the stirring time can be appropriately extended or the stirring parameters adjusted until the nitrogen content meets the requirements, to avoid premature slag removal leading to incomplete denitrification.

[0063] By removing slag only after the nitrogen content meets the standard, it can be ensured that the nitrogen content of each furnace of molten iron meets the requirement of ≤0.0050%, thus avoiding abnormal steelmaking quality caused by nitrogen removal fluctuations.

[0064] In some embodiments, after stirring, the temperature of the molten iron in the ladle is controlled at 1320–1380°C, and slag removal is performed.

[0065] During the slag removal process, the temperature of the molten iron needs to be controlled between 1320 and 1380℃ to avoid the slag viscosity increasing due to excessively low temperature, which would affect the removal effect.

[0066] For example, the temperature of molten iron during the slag removal process is 1320℃, 1325℃, 1330℃, 1335℃, 1340℃, 1345℃, 1350℃, 1355℃, 1360℃, 1365℃, 1370℃, 1375℃, or 1380℃.

[0067] In some embodiments, the slag removal cleanliness of the molten iron is ≥70%.

[0068] After stirring, allow the mixture to stand for a preset time, for example, 3-5 minutes, to allow the TiN particles to fully float to the slag layer, which can improve slag removal efficiency. For example, the slag removal cleanliness of the molten iron to be used is 70%, 75%, 80%, 85%, 90%, 95%, or above 95%.

[0069] In some embodiments, during slag removal, the slag removal plate is inserted into the slag layer at an angle of 30° to 45° with the liquid surface. For example, the insertion depth is controlled at 50 to 80 mm, and the translational speed is 0.3 to 0.5 m / s to avoid slag-iron mixing due to excessive speed or slag adhesion due to excessively slow speed. First, the floating slag is slowly removed along the edge of the ladle, and then it is gathered towards the central area to form a slag layer of uniform thickness before being removed in one go.

[0070] For example, a hydraulic slag remover is used, with the slag remover plate inserted into the slag layer to a depth of 50-80 mm and moved horizontally along the liquid surface of the ladle at a speed of 0.3-0.5 m / s to ensure that the TiN-containing slag layer is removed as a whole.

[0071] TiN-containing slag layers typically contain sulfides and unreacted nitrides. If slag removal is incomplete, the residual slag layer can undergo secondary reactions with the molten iron. For example, sulfide dissolution can lead to an increase in the sulfur content of the molten iron; nitride decomposition or nitrogen adsorbed from the slag layer can dissolve into the molten iron, causing an increase in the nitrogen content. A slag removal efficiency of ≥70% can reduce the thickness of the residual slag layer, significantly reducing the aforementioned risks, ensuring stable molten iron composition, and creating conditions for converter smelting of low-nitrogen, low-inclusion steel grades. The nitrogen content of the treated molten iron meets the requirements for low-nitrogen steel smelting. Generally, to produce converter steel with a nitrogen content ≤0.0025% at the end of production, the iron-to-steel ratio must be above 90%. However, this application demonstrates that a lower iron-to-steel ratio can be used to produce steel grades with a nitrogen content ≤0.0025%, allowing converter steelmaking to use an iron-to-steel ratio ≤90%, reducing molten iron consumption, lowering raw material costs, meeting product quality requirements, and increasing output.

[0072] Example The following embodiments describe the disclosure of this application in more detail. These embodiments are for illustrative purposes only, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0073] Example 1: The smelting process yields the first molten iron in the blast furnace. Samples of the first molten iron are taken for analysis to obtain the first titanium content and the first nitrogen content. The blast furnace molten iron has a titanium content of 0.052%, a nitrogen content of 0.0082%, and a quantity of 160 tons. After adding titanium-containing pig iron to an iron ladle, molten iron is passed through, resulting in molten iron in the ladle. The precipitation temperature of titanium nitride in the second molten iron is ≥1400℃. The composition of the titanium-containing pig iron is: titanium 8%, carbon 1.2%, silicon 2.1%, Mn 0.3%, iron 88%, and the remainder being unavoidable impurities such as sulfur, phosphorus, and copper. Adding 1 ton of titanium-containing pig iron results in an iron tapping temperature of 1499℃; the titanium content of the second molten iron is 0.101%. The second batch of molten iron was transported to the KR process and stirred for 18 minutes at a stirring speed of 100 r / min to promote the full precipitation of titanium nitride. After stirring, the temperature was 1345℃, and the molten iron was skimmed off to obtain a nitrogen content of 0.0053%.

[0074] Example 2: The smelting process yields the first molten iron in the blast furnace. Samples of the first molten iron are taken for analysis to obtain the first titanium content and the first nitrogen content. The blast furnace molten iron has a titanium content of 0.058%, a nitrogen content of 0.0092%, and a quantity of 162 tons. After adding titanium-containing pig iron to an iron ladle, molten iron is passed through, resulting in a second batch of molten iron in the ladle. The composition of the titanium-containing pig iron is: titanium 10%; carbon 1.4%; silicon 2.5%; Mn 0.4%; iron 85%; and the remainder consists of unavoidable impurities such as sulfur, phosphorus, and copper. With the addition of 1.2 tons of high-titanium pig iron, the tapping temperature of the molten iron is 1495℃; the titanium content of the second batch of molten iron is 0.136%. The second batch of molten iron was transported to the KR process and stirred for 18 minutes at a stirring speed of 116 r / min to promote the full precipitation of titanium nitride. After stirring, the temperature was 1362℃ and the nitrogen content of the molten iron was 0.0054%.

[0075] Example 3: The smelting process yields the first molten iron in the blast furnace. Samples of the first molten iron are taken for analysis to obtain the first titanium content and the first nitrogen content. The blast furnace molten iron has a titanium content of 0.045%, a nitrogen content of 0.0090%, and a quantity of 161 tons. After adding titanium-containing pig iron to an iron ladle, molten iron is passed through, resulting in a second batch of molten iron in the ladle. The composition of the titanium-containing pig iron is: titanium 9%; carbon 1.9%; silicon 2.3%; Mn 0.3%; iron 86%, with the remainder being unavoidable impurities such as sulfur, phosphorus, and copper. Adding 1.3 tons of high-titanium pig iron resulted in an iron tapping temperature of 1498℃; the titanium content of the second batch of molten iron was 0.117%. The second batch of molten iron was transported to the KR process and stirred for 19 minutes at a stirring speed of 115 r / min to promote the full precipitation of titanium nitride. After stirring, the temperature was 1352℃ and the nitrogen content of the molten iron was 0.0057%.

[0076] Example 4: The smelting process yields the first molten iron in the blast furnace. Samples of the first molten iron are taken for analysis to obtain the first titanium content and the first nitrogen content. The blast furnace molten iron has a titanium content of 0.055%, a nitrogen content of 0.0088%, and a quantity of 162 tons. After adding titanium-containing pig iron to an iron ladle, molten iron is passed through, resulting in a second batch of molten iron in the ladle. The composition of the titanium-containing pig iron is: titanium 11%; carbon 1.2%; silicon 2.3%; Mn 0.3%; iron 85%, with the remainder being unavoidable impurities such as sulfur, phosphorus, and copper. Adding 1.3 tons of high-titanium pig iron, the tapping temperature of the molten iron is 1497℃; the titanium content of the second batch of molten iron is 0.142%. The second batch of molten iron was transported to the KR process and stirred for 18 minutes at a stirring speed of 118 r / min to promote the full precipitation of titanium nitride. After stirring, the temperature was 1363℃ and the nitrogen content of the molten iron was 0.0045%.

[0077] Comparative Example 1: The smelting process yielded the first batch of molten iron in the blast furnace. Samples of this molten iron were taken and analyzed to determine its titanium and nitrogen content. The blast furnace molten iron contained 0.0142% titanium and 0.0098% nitrogen, with a total volume of 160 tons. The molten iron was tapped at a temperature of 1502℃ and then stirred in KR iron for 19 minutes. The molten iron was then skimmed off, and the nitrogen content was 0.0086%.

[0078] Comparative Example 2: The smelting process yields the first molten iron in the blast furnace. The first molten iron is sampled and analyzed to obtain the first titanium content and the first nitrogen content. The titanium content of the blast furnace molten iron is 0.0192%, the tapping temperature is 1489℃, and the nitrogen content is 0.0087%. The molten iron is then stirred and treated with KR for 20 minutes. The slag is removed from the molten iron, and the nitrogen content is 0.0080%.

[0079] In summary, the embodiments of this application control the precipitation temperature of titanium nitride to ≥1400℃ by adding titanium-containing pig iron to molten iron, and combine it with KR stirring, so that the nitrogen content of molten iron can be reduced to ≤0.0050%, providing pure molten iron raw materials for converter smelting and reducing production costs.

[0080] 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 reducing the nitrogen content of molten iron, characterized in that, Includes the following steps: The first molten iron is obtained by smelting in a blast furnace. The first molten iron is sampled and analyzed to obtain the first titanium content and the first nitrogen content in the first molten iron. Based on the first titanium content and the first nitrogen content, titanium-containing pig iron is added to the ladle, and then the first molten iron is passed through to obtain the second molten iron in the ladle. The precipitation temperature of titanium nitride in the second molten iron is ≥1400℃. The second molten iron has a second titanium content, which is controlled between 0.10% and 0.15%. The titanium-containing pig iron comprises the following components by mass percentage: titanium, 6-12%, carbon, 1-2%, silicon, 2-4%, manganese, 0.2-0.4%, iron, 81-90%, with the remainder being sulfur, phosphorus, copper, and unavoidable impurities. When the first molten iron is passed through the ladle, the tapping temperature of the first molten iron in the blast furnace is ≥1490℃. The second molten iron is transported to the KR process for stirring to promote titanium nitride precipitation, and then slag is removed to obtain molten iron ready for use. The process parameters for stirring include: stirring speed of 100-120 r / min, processing time of 15-20 min, and the depth of the stirring head inserted below the liquid level of 0.6-1 m. The second nitrogen content in the ladle is obtained, and the slag removal operation is performed when the second nitrogen content is ≤0.0050%.

2. The method for reducing nitrogen content in molten iron according to claim 1, characterized in that, After the stirring process, the temperature of the molten iron in the ladle is controlled at 1320-1380℃, and slag removal is performed.

3. The method for reducing nitrogen content in molten iron according to claim 2, characterized in that, The slag removal cleanliness of the molten iron to be used is ≥70%.

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