Method for controlling nitrogen content at smelting end point of converter by using KR desulfurization solid waste

Abstract

The invention discloses a method for controlling the content of nitrogen at the smelting end point of a converter by using KR desulfurization solid waste, and belongs to the technical field of converter steelmaking. The method comprises the following steps that when the oxygen blowing amount of converter smelting reaches 70%-80%, KR desulfurization solid waste is added into molten steel in a converter, the lance position of an oxygen lance is controlled to be 100-150 mm lower than the normal lance position, and S in the KR desulfurization solid waste enters the molten steel to reduce surface nitrogen absorption of the molten steel. According to the scheme, KR desulfurization is reused for converter smelting, and the reuse process is optimally designed, so that the nitrogen content of molten steel at the converter smelting end point can be stably controlled, and meanwhile, the resource utilization of KR desulfurization solid waste can be realized.

Description

Technical Field

[0001] This invention relates to the field of converter steelmaking technology, and more specifically, to a method for controlling the nitrogen content at the end point of converter smelting using KR desulfurization solid waste. Background Technology

[0002] For most steel grades, nitrogen is a harmful element that causes aging and blue brittleness. For steel grades with high formability requirements, there are usually strict limits on the nitrogen content. Nitrogen in molten steel mainly comes from raw materials and air. While the RH process has some denitrification capability in steelmaking, this capability is very limited when the nitrogen content in the steel is below 50 ppm. The converter process has the strongest denitrification capability; therefore, controlling the nitrogen content at the end of converter smelting has a crucial impact on the production of low-nitrogen steel.

[0003] Existing research suggests that reducing the final nitrogen content in converters is mainly achieved through technical solutions such as controlling the scrap ratio, using bottom blowing argon throughout the process, and reducing supplementary blowing. For example, Chinese patent application CN110106304A discloses a converter smelting method for ultra-low nitrogen IF steel, which reduces the nitrogen content at the converter endpoint by using a high scrap ratio and full-process argon blowing; Chinese patent application CN107236839A discloses a method for reducing the nitrogen content of molten steel in the converter steelmaking process, which reduces the nitrogen content of molten steel in the converter steelmaking process by using full-process bottom blowing argon and reducing converter make-up blowing; Chinese patent application CN107974528A discloses a method for reducing the nitrogen content of molten steel at the converter endpoint, which reduces the nitrogen content at the converter endpoint by controlling the scrap ratio below 10% and controlling the carbon content at the converter endpoint above 0.04%; and patent CN114737007A discloses a method for controlling the nitrogen content in the converter high scrap ratio smelting furnace, which mainly stabilizes the endpoint nitrogen content by using a temperature-raising agent and controlling the scrap structure, oxygen supply, feeding, bottom blowing, and hood lowering operation.

[0004] The above-mentioned improvements can all reduce the nitrogen content of the molten steel at the end of converter smelting, but their application also has certain limitations. For example, when the nitrogen content in the molten iron is high, it is difficult to achieve good results, and the phenomena of supplementary blowing and gas absorption during converter smelting are difficult to avoid, which can easily cause fluctuations in the nitrogen content of the molten steel at the end of smelting. Therefore, the above technical solutions have certain limitations in application.

[0005] KR desulfurization solid waste is the slag produced in the KR desulfurization process, mainly composed of CaO, Fe, CaF2, and CaS. During the desulfurization process, because the desulfurization product CaS coats the surface of lime, the utilization efficiency of CaO in the KR desulfurizing agent is less than 20%, with most CaO not participating in the reaction. Furthermore, although slag removal is required after KR desulfurization, poor slag-iron separation results in an iron content exceeding 50% in the KR slag. Due to its high sulfur content, the subsequent comprehensive utilization rate of KR desulfurization solid waste is low, leading to significant resource waste and environmental pollution.

[0006] The inventors had previously conducted research on recycling KR desulfurization solid waste for converter smelting, aiming to recover the CaO and iron elements, which required corresponding design of the recycling process. Currently, there are no reports on recycling KR desulfurization solid waste for converter smelting to control the nitrogen content of the resulting molten steel. Summary of the Invention

[0007] 1. Technical problems to be solved To address the technical challenges in controlling nitrogen content in molten steel at the end of converter smelting, this solution offers a novel method utilizing KR desulfurization solid waste. This method, by recycling KR desulfurization solid waste into converter smelting and optimizing the recycling process, not only achieves stable control of nitrogen content in molten steel at the end of converter smelting but also realizes the resource-based reuse of KR desulfurization solid waste.

[0008] 2. Technical solutions adopted To achieve the above objectives, the technical solution provided by the present invention is as follows: This invention provides a method for controlling the nitrogen content of molten steel at the end point of converter smelting using KR desulfurization solid waste, comprising the following steps: when the oxygen blowing rate in converter smelting reaches 70% to 80%, KR desulfurization solid waste is added to the molten steel in the converter, and the oxygen lance position is controlled to be 100 to 150 mm lower than the normal lance position, so that the S in the KR desulfurization solid waste enters the molten steel to reduce nitrogen absorption on its surface.

[0009] It should be noted that, on the one hand, the inventor's previous research on recycling KR desulfurization solid waste for converter smelting aimed to reuse the CaO and iron elements within it. This required a specific design for the recycling process. Specifically, after oxygen blowing begins, a composite oxidant is added to the converter to control the slag basicity and oxidizing properties in the early stages of oxygen blowing. After 1 minute of oxygen blowing, KR desulfurization slag is added to the converter, and smelting continues. By adding the composite oxidant, the sulfur elements contained in the KR desulfurization solid waste are vaporized, and the reaction between the vaporized SO2 and Ca is further prevented, allowing the SO2 generated by oxidation to escape. On the other hand, existing methods for recycling KR desulfurization solid waste for converters, except for some steel grades with high sulfur content, aim to minimize the introduction of sulfur elements into the molten steel.

[0010] This invention utilizes the sulfur element carried by KR desulfurization solid waste to enter the molten steel in order to reduce the nitrogen content in the molten steel. The specific principle is as follows: As the converter smelting continues, when the oxygen blowing rate is 70%~80%, the carbon-oxygen reaction is weak, that is, the CO bubbles produced are significantly reduced. Therefore, the molten steel is more likely to absorb nitrogen, so KR desulfurization solid waste is added at this time.

[0011] It should also be noted that lowering the lance position helps reduce the Fe2O3 content in the slag, preventing sulfur from undergoing a gasification reaction and allowing sulfur from the desulfurization waste to enter the molten steel. Simultaneously, utilizing the sulfur (S) in the KR desulfurization waste, which enters the molten steel during the later stages of blowing, can increase the sulfur content in the steel. S is a surface-active element that can migrate to the surface, reducing nitrogen adsorption sites and thus decreasing nitrogen absorption in the later stages of converter smelting. Generally, KR desulfurization waste contains both Al2O3 and CaF2. 2同样 It is a surface-active element and can also synergistically improve the foaming performance of slag in the later stage of blowing, reduce the amount of nitrogen absorbed by molten steel when in contact with air, thereby reducing the nitrogen content of molten steel at the end of converter smelting. In addition, desulfurization solid waste contains a large amount of free CaO and Fe, which allows KR desulfurization solid waste to be utilized as a resource in the converter.

[0012] Furthermore, the amount of KR desulfurization solid waste added is 10-20 kg / t of steel. If the amount of KR desulfurization solid waste added is too low, the sulfur content in the molten iron may be insufficient, thus failing to effectively inhibit nitrogen addition. Conversely, if the amount added is too high, although the effect of inhibiting nitrogen addition is good, it may cause the sulfur content of the steel to exceed the limit, or increase the burden on subsequent desulfurization processes. For example, for steel grades produced by direct combustion, it may exceed the upper limit of sulfur content in steel; for refined steel grades, it will increase the burden on refining desulfurization.

[0013] Furthermore, during the converter smelting process, the pressure at the furnace opening is maintained at 0~25 Pa, with argon gas being blown from the bottom throughout the process. By maintaining the pressure at the furnace opening at 0~25 Pa, i.e., maintaining a slight positive pressure inside the converter, the intake of nitrogen gas from the furnace opening is reduced.

[0014] Furthermore, when the oxygen blowing rate in the converter smelting exceeds 80%, the intensity of the bottom-blown argon gas is controlled to be 0.12~0.2m. 3 / t / min. By controlling the intensity of bottom-blowing argon, not only is the S in the KR desulfurization waste introduced into the molten steel, but it is also beneficial to form a large number of Ar bubbles, thereby increasing the denitrification capacity.

[0015] Furthermore, when the oxygen blowing rate during converter smelting is less than 0% to 30%, the bottom-blown argon intensity is controlled at 0.03 to 0.05 m. 3 / t / min; When the oxygen blowing rate in the converter smelting is between 30% and 80%, the bottom blowing argon intensity is controlled at 0.08~0.1m. 3 / t / min. When the oxygen blowing rate in the converter is less than 30%, that is, in the early stage of converter smelting, a lower bottom blowing intensity is used to ensure slag formation, promote slag foaming, and prevent nitrogen absorption.

[0016] Furthermore, the final slag composition at the converter smelting endpoint is as follows: basicity 2.0~3.0, FeO 10%~20%, MgO 7%~10%; molten steel temperature 1580~1630℃. At the converter smelting endpoint, by reducing the final slag basicity and temperature, the desulfurization capacity of the slag is reduced, so that sulfur can enter the molten steel as much as possible and exert its role as a surface-active element.

[0017] Furthermore, the smelting raw materials of the converter include molten iron, scrap steel, and slag-forming materials. The sum of molten iron and scrap steel is called the metal charge, wherein the proportion of scrap steel in the metal charge is ≤15%, and the proportion of heavy scrap steel in the metal charge is ≤5%. Because the melting rate of heavy scrap steel is relatively slow, if its addition is too large, its melting may continue into the later stages of the converter process, leading to an increase in the nitrogen content of the molten steel in the later stages of the converter process. By controlling the proportion of heavy scrap steel to ≤5%, the increase in nitrogen content caused by the melting of heavy scrap steel in the later stages of the converter process is avoided.

[0018] Furthermore, the molten iron used contains the following composition by mass percentage: C 4.0%–5.0%, Si 0.1%–1.0%, Mn 0.1%–0.4%, P ≤0.12%, N 0.006%–0.014%, S ≤0.01%, and the molten iron temperature is 1250–1450℃. This smelting method is particularly suitable for molten iron with low S content. In the early to mid-stages of converter smelting, when the oxygen blowing rate is less than 70%, the S content in the molten iron is at a low level, which can reduce denitrification resistance and thus accelerate the denitrification reaction.

[0019] Furthermore, the KR desulfurization solid waste used contains the following components by mass percentage: CaO 30%–60%, SiO2 5%–10%, Al2O3 1%–5%, CaF2 1%–5%, S 1%–3%, with the remainder being iron and unavoidable impurities.

[0020] Compared with the prior art, the technical solution provided by this invention has the following advantages: (1) This invention optimizes the process design of the converter smelting process. Specifically, when the oxygen blowing rate in the converter reaches 70% to 80%, KR desulfurization solid waste is added to the molten steel in the converter, and the oxygen lance position is controlled to be lower than the normal lance position. This scheme, by lowering the oxygen lance position, helps to reduce the Fe2O3 content in the slag, thereby preventing sulfur from undergoing a gasification reaction, which in turn facilitates the entry of sulfur from the desulfurization solid waste into the molten steel. At the same time, the sulfur in the KR desulfurization solid waste, after entering the molten steel in the later stage of blowing, can increase the sulfur content in the molten steel. S is a surface-active element that can migrate to the surface, reducing the nitrogen adsorption sites and reducing the amount of nitrogen absorbed in the later stage. In addition, the desulfurization solid waste contains a large amount of free CaO and Fe, which allows the KR desulfurization solid waste to be utilized as a resource in the converter.

[0021] (2) The present invention further optimizes the design of the intensity of bottom-blown nitrogen gas during the converter smelting process. Specifically, when the oxygen blowing rate in the converter smelting is greater than 80%, that is, after adding KR desulfurization solid waste to the converter, the intensity of bottom-blown argon gas is controlled to be 0.12~0.2m. 3 The / t / min ratio not only promotes the entry of sulfur from KR desulfurization waste into molten steel, but also facilitates the formation of a large number of Ar bubbles, thereby increasing denitrification capacity. Furthermore, when the oxygen blowing rate in converter smelting is less than 0%–30%, the bottom-blown argon intensity should be controlled at 0.03–0.05 m³ / min. 3 / t / min; When the oxygen blowing rate in converter smelting is between 30% and 80%, the bottom blowing argon intensity should be controlled at 0.08~0.1m. 3 / t / min. In the early stages of converter smelting, a lower bottom blowing intensity is used to ensure slag formation, promote slag foaming, and prevent nitrogen absorption.

[0022] (3) This invention further controls other process parameters during the converter process. Specifically, the pressure at the furnace mouth is maintained at 0~25 Pa, thereby reducing the intake of nitrogen gas from the furnace mouth. Furthermore, the final slag composition at the converter smelting endpoint is: basicity 2.0~3.0, FeO 10%~20%, MgO 7%~10%. During the converter smelting process, by reducing the final slag basicity and molten steel temperature, the desulfurization capacity of the slag is reduced, allowing sulfur to enter the molten steel as much as possible and exert its role as a surface-active element. In summary, this invention achieves the goal of reducing nitrogen absorption by molten steel during the smelting process from multiple aspects, thus optimizing the control of nitrogen content in molten steel at the converter smelting endpoint. Detailed Implementation

[0023] To further understand the content of this invention, the invention will be described in detail with reference to the embodiments.

[0024] The following examples and comparative examples were conducted on a 120t converter, and the experimental steel was HRB400, which has a sulfur content limit of 0.045% according to the national standard.

[0025] It should be noted that the sulfur content of the molten iron used in the following embodiments is ≤0.008%, which should not be construed as a limitation on the sulfur content of molten steel to which this invention is applicable. This invention is applicable to molten iron with S≤0.01%.

[0026] Example 1 This embodiment provides a method for controlling the nitrogen content of molten steel at the endpoint of converter smelting using KR desulfurization solid waste. The method includes the following steps: a. Add scrap steel and molten iron into the converter, then blow oxygen with an oxygen lance, and add slag-forming materials such as lime, dolomite, and iron ore; the temperature of the molten iron used is 1286℃. More parameters of molten iron and scrap steel are detailed in Table 1. Calculated with the sum of the mass of molten iron and scrap steel as 100%, the mass ratio of scrap steel is 13.3%, and the mass ratio of heavy scrap steel is 4.8%.

[0027] b. During the blowing process, based on the decarburization reaction rate, the furnace mouth pressure is controlled between 0-25 Pa during converter smelting. Ar is blown from the bottom throughout the process, with the bottom blowing argon intensity controlled at 0.03 m³ when the oxygen blowing rate is less than 30%. 3 / t / min; when the oxygen blowing rate is between 30% and 80%, the bottom blowing argon intensity is controlled at 0.09m. 3 / t / min; When the oxygen blowing rate is greater than 80%, control the bottom blowing argon intensity to 0.18m. 3 / t / min; where, when the oxygen consumption during blowing reaches 78% of the total, KR desulfurization solid waste is added to the converter at a rate of 12kg / t steel. The composition of the KR desulfurization solid waste used is detailed in Table 2. The oxygen lance position is adjusted to control the oxygen lance position to be 120mm lower than the normal position and maintained at this position until the converter end point. The normal position of the oxygen lance refers to 1.1m.

[0028] c. When the oxygen blowing volume reaches 100% of the total, TSO measurement is performed using a secondary lance. The slag composition at the end of the converter smelting is: basicity 2.7, FeO 15.8%, MgO 8.2%, and molten steel temperature 1593℃. The basicity is calculated as the ratio of CaO / SiO2. For details on the parameter control, molten steel obtained, and material consumption at the end of the converter smelting, please refer to Table 3.

[0029] Comparative Example 1 This comparative example provides a conventional converter smelting method, which includes the following steps: a. Add scrap steel and molten iron into the converter, then blow oxygen with an oxygen lance, and add slag-forming materials such as lime, dolomite, and iron ore; the temperature of the molten iron used is 1328℃. More parameters of molten iron and scrap steel are detailed in Table 1. Calculated with the sum of the mass of molten iron and scrap steel as 100%, the mass ratio of scrap steel is 24.0%, of which the mass ratio of heavy scrap steel is 7.9%.

[0030] b. During the refining process, Ar is blown from the bottom throughout, and the intensity of the bottom-blown argon gas is controlled at 0.12m. 3 / t / min.

[0031] c. When the oxygen blowing volume reaches 100% of the total, TSO measurement is performed using a secondary lance. The slag composition at the end of the converter smelting is: basicity 3.5, FeO 18.4%, MgO 7.3%; molten steel temperature 1651℃. The basicity is calculated as the ratio of CaO / SiO2. For details on the parameter control, molten steel obtained, and material consumption at the end of the converter smelting, please refer to Table 3.

[0032] Comparative Example 2 This comparative example provides a method for controlling the nitrogen content of molten steel at the endpoint of converter smelting, the method comprising the following steps: a. Add scrap steel and molten iron into the converter, then blow oxygen with an oxygen lance, and add slag-forming materials such as lime, dolomite, and iron ore; the temperature of the molten iron used is 1302℃. More parameters of molten iron and scrap steel are detailed in Table 1. Calculated with the sum of the mass of molten iron and scrap steel as 100%, the mass ratio of scrap steel is 12.4%, of which the mass ratio of heavy scrap steel is 3.6%.

[0033] b. During the blowing process, based on the decarburization reaction rate, control the furnace mouth pressure at 0-25 Pa during converter smelting. Perform bottom blowing with Ar throughout the process. When the oxygen blowing rate is less than 30%, control the bottom blowing argon intensity at 0.05 m³ / s. 3 / t / min; when the oxygen blowing rate is 30% to 80%, the bottom blowing argon intensity is controlled at 0.09m. 3 / t / min; When the oxygen blowing rate is greater than 80%, control the bottom blowing argon intensity to 0.15m. 3 / t / min.

[0034] c. When the oxygen blowing volume reaches 100% of the total, TSO measurement is performed using a secondary lance. The slag composition at the end of the converter smelting is as follows: basicity 2.7, FeO 13.9%, MgO 8.5%, and molten steel temperature 1625℃. Among them, basicity is calculated as the ratio of CaO / SiO2. The parameter control, molten steel obtained, and material consumption at the end of the converter smelting are detailed in Table 3.

[0035] Comparative Example 3 This comparative example provides a method for controlling the nitrogen content of molten steel at the endpoint of converter smelting, the method comprising the following steps: a. Add scrap steel and molten iron into the converter, then blow oxygen with an oxygen lance, and add slag-forming materials such as lime, dolomite, and iron ore; the temperature of the molten iron used is 1300℃. More parameters of molten iron and scrap steel are detailed in Table 1. Calculated with the sum of the mass of molten iron and scrap steel as 100%, the mass ratio of scrap steel is 13.3%, of which the mass ratio of heavy scrap steel is 4.8%.

[0036] b. During the blowing process, based on the decarburization reaction rate, control the furnace mouth pressure at 0-25 Pa during converter smelting. Maintain bottom blowing with Ar throughout the process. When the oxygen blowing rate is less than 30%, control the bottom blowing argon intensity at 0.03 m³ / s. 3 / t / min; when the oxygen blowing rate is 30% to 80%, the bottom blowing argon intensity is controlled at 0.09m. 3 / t / min; When the oxygen blowing rate is greater than 80%, control the bottom blowing argon intensity to 0.18m. 3 / t / min; when the oxygen consumption during blowing reaches 60% of the total, KR desulfurization solid waste is added to the converter at a rate of 12kg / t steel. The composition of the KR desulfurization solid waste used is detailed in Table 2. The oxygen lance position is adjusted to control the lance position to be 120mm lower than the normal lance position.

[0037] The composition of the KR desulfurization solid waste used is the same as that in Example 1.

[0038] c. When the oxygen blowing volume reaches 100% of the total, TSO measurement is performed using a secondary lance. The slag composition at the end of the converter smelting is as follows: basicity 2.8, FeO 16.8%, MgO 7.6%, and molten steel temperature 1593℃. Among them, basicity is calculated as the ratio of CaO / SiO2. The parameter control, molten steel obtained, and material consumption at the end of the converter smelting are detailed in Table 3.

[0039] Comparative Example 4 This comparative example provides a method for controlling the nitrogen content of molten steel at the endpoint of converter smelting, the method comprising the following steps: a. Add scrap steel and molten iron into the converter, then blow oxygen with an oxygen lance, and add slag-forming materials such as lime, dolomite, and iron ore; the temperature of the molten iron used is 1300℃. More parameters of molten iron and scrap steel are detailed in Table 1. Calculated with the sum of the mass of molten iron and scrap steel as 100%, the mass ratio of scrap steel is 13.3%, of which the mass ratio of heavy scrap steel is 4.8%.

[0040] b. During the blowing process, based on the denitrification reaction rate, control the furnace mouth pressure at 0-25 Pa during converter smelting. Perform bottom blowing with Ar throughout the process. When the oxygen blowing rate is less than 30%, control the bottom blowing argon intensity at 0.03 m³ / s. 3 / t / min; when the oxygen blowing rate is 30% to 80%, the bottom blowing argon intensity is controlled at 0.09m. 3 / t / min; When the oxygen blowing rate is greater than 80%, control the bottom blowing argon intensity to 0.18m. 3 / t / min; whereby, when the oxygen consumption during blowing reaches 85% of the total, KR desulfurization solid waste is added to the converter at a rate of 12kg / t steel. The composition of the KR desulfurization solid waste used is detailed in Table 2. The oxygen lance position is adjusted to control the lance position to be 120mm lower than the normal lance position and maintained at this lance position until the converter ends.

[0041] The composition of the KR desulfurization solid waste used is the same as that in Example 1.

[0042] c. When the oxygen blowing volume reaches 100% of the total, TSO measurement is performed using a secondary lance. The slag composition at the end of the converter smelting is: basicity 2.5, FeO 13.5%, MgO 8.2%, and molten steel temperature 1600℃. Among them, the basicity is calculated as the ratio of CaO / SiO2. The parameter control, molten steel obtained, and material consumption at the end of the converter smelting are detailed in Table 3.

[0043] Comparative Example 5 This comparative example provides a method for controlling the nitrogen content of molten steel at the endpoint of converter smelting, the method comprising the following steps: a. Add scrap steel and molten iron into the converter, then blow oxygen with an oxygen lance, and add slag-forming materials such as lime, dolomite, and iron ore; the temperature of the molten iron used is 1300℃. More parameters of molten iron and scrap steel are detailed in Table 1. Calculated with the sum of the mass of molten iron and scrap steel as 100%, the mass ratio of scrap steel is 12.4%, of which the mass ratio of heavy scrap steel is 3.6%.

[0044] b. During the blowing process, based on the decarburization reaction rate, control the furnace mouth pressure at 0-25 Pa during converter smelting. Maintain bottom blowing with Ar throughout the process. When the oxygen blowing rate is less than 30%, control the bottom blowing argon intensity at 0.03 m³ / s. 3 / t / min; when the oxygen blowing rate is 30% to 80%, the bottom blowing argon intensity is controlled at 0.09m. 3 / t / min; When the oxygen blowing rate is greater than 80%, control the bottom blowing argon intensity to 0.18m. 3 / t / min; where, when the oxygen consumption during blowing reaches 75% of the total, KR desulfurization solid waste is added to the converter at a rate of 12kg / t steel. The composition of the KR desulfurization solid waste used is detailed in Table 2. The oxygen lance position is controlled to be the normal position, where the normal position of the oxygen lance refers to 1.1m.

[0045] The composition of the KR desulfurization solid waste used is the same as that in Example 1.

[0046] c. When the oxygen blowing volume reaches 100% of the total, TSO measurement is performed using a secondary lance. The slag composition at the end of the converter smelting is as follows: basicity 2.9, FeO 15.2%, MgO 7.0%, and molten steel temperature 1615℃. Among them, basicity is calculated as the ratio of CaO / SiO2. The parameter control, molten steel obtained, and material consumption at the end of the converter smelting are detailed in Table 3.

[0047] Example 2 This embodiment provides a method for controlling the nitrogen content of molten steel at the endpoint of converter smelting using KR desulfurization solid waste. The method includes the following steps: a. Add scrap steel and molten iron into the converter, then blow oxygen with an oxygen lance, and add slag-forming materials such as lime, dolomite and iron ore; the temperature of the molten iron used is 1354℃, and more parameters of molten iron and scrap steel are detailed in Table 1. Calculated with the sum of the mass of molten iron and scrap steel as 100%, the mass ratio of scrap steel is 11.8%, of which the mass ratio of heavy scrap steel is 0%.

[0048] b. During the blowing process, based on the decarburization reaction rate, control the furnace mouth pressure at 0-25 Pa during converter smelting. Perform bottom blowing with Ar throughout the process. When the oxygen blowing rate is less than 30%, control the bottom blowing argon intensity at 0.04 m³ / s. 3 / t / min; when the oxygen blowing rate is 30%~80%, the bottom blowing argon intensity is controlled at 0.08m. 3 / t / min; When the oxygen blowing rate is greater than 80%, control the bottom blowing argon intensity to 0.2m. 3 / t / min; when the oxygen consumption of blowing reaches 75% of the total, KR desulfurization solid waste is added to the converter, and the addition amount is controlled at 15kg / t. The composition of the KR desulfurization solid waste used is detailed in Table 2. The oxygen lance position is adjusted to control the lance position to be 150mm lower than the normal lance position.

[0049] c. When the oxygen blowing volume reaches 100% of the total, TSO measurement is performed using a secondary lance. The slag composition at the end of the converter smelting is as follows: basicity 2.2, FeO 12.4%, MgO 9.5%, and molten steel temperature 1628℃. Among them, basicity is calculated as the ratio of CaO / SiO2. The parameter control, molten steel obtained, and material consumption at the end of the converter smelting are detailed in Table 3.

[0050] Example 3 This embodiment provides a method for controlling the nitrogen content of molten steel at the endpoint of converter smelting using KR desulfurization solid waste. The method includes the following steps: a. Add scrap steel and molten iron to the converter, then blow oxygen with an oxygen lance, and add slag-forming materials such as lime, dolomite, and iron ore; the temperature of the molten iron used is 1314℃. More parameters of molten iron and scrap steel are detailed in Table 1. Calculated with the sum of the mass of molten iron and scrap steel as 100%, the mass ratio of scrap steel is 14.9%, and the mass ratio of heavy scrap steel is 1.2%.

[0051] b. During the blowing process, based on the decarburization reaction rate, control the furnace mouth pressure at 0-25 Pa during converter smelting. Maintain bottom blowing with Ar throughout the process. When the oxygen blowing rate is less than 30%, control the bottom blowing argon intensity at 0.03 m³ / s. 3 / t / min; when the oxygen blowing rate is 30~80%, the bottom blowing argon intensity is controlled at 0.08m. 3 / t / min; When the oxygen blowing rate is greater than 80%, the bottom blowing argon intensity is controlled at 0.17m. 3 / t / min; when the oxygen consumption of blowing reaches 72% of the total, KR desulfurization solid waste is added to the converter at a rate of 13kg / t. The composition of the KR desulfurization solid waste is detailed in Table 2. The oxygen lance position is adjusted to control the lance position to be 120mm lower than the normal lance position.

[0052] c. When the oxygen blowing volume reaches 100% of the total, TSO measurement is performed using a secondary lance. The slag composition at the end of the converter smelting is: basicity 2.8, FeO 17.6%, MgO 7.3%, and molten steel temperature 1586℃. Among them, basicity is calculated as the ratio of CaO / SiO2. The parameter control, molten steel obtained, and material consumption at the end of the converter smelting are detailed in Table 3.

[0053] Example 4 This embodiment provides a method for controlling the nitrogen content of molten steel at the endpoint of converter smelting using KR desulfurization solid waste. The method includes the following steps: a. Add scrap steel and molten iron into the converter, then blow oxygen with an oxygen lance, and add slag-forming materials such as lime, dolomite, and iron ore; the temperature of the molten iron used is 1372℃. More parameters of molten iron and scrap steel are detailed in Table 1. Calculated with the sum of the mass of molten iron and scrap steel as 100%, the mass ratio of scrap steel is 14.8%, of which the mass ratio of heavy scrap steel is 2.3%.

[0054] b. During the blowing process, based on the decarburization reaction rate, control the furnace mouth pressure at 0-25 Pa during converter smelting. Perform bottom blowing with Ar throughout the process. When the oxygen blowing rate is less than 30%, control the bottom blowing argon intensity at 0.05 m³ / s. 3 / t / min; when the oxygen blowing rate is 30~80%, the bottom blowing argon intensity is controlled at 0.08m. 3 / t / min; when the oxygen blowing rate is greater than 80%, the bottom blowing argon intensity is controlled at 0.12m. 3 / t / min; when the oxygen consumption of blowing reaches 79% of the total, KR desulfurization solid waste is added to the converter, and the addition amount is controlled at 18kg / t. The composition is shown in Table 2. The oxygen lance position is adjusted to control the lance position to be 110mm lower than the normal lance position.

[0055] c. When the oxygen blowing volume reaches 100% of the total, TSO measurement is performed using a secondary lance. The slag composition at the end of the converter smelting is: basicity 2.5, FeO 13.0%, MgO 8.6%, and molten steel temperature 1621℃. Among them, basicity is calculated as the ratio of CaO / SiO2. The parameter control, molten steel obtained, and material consumption at the end of the converter smelting are detailed in Table 3.

[0056] Example 5 This embodiment provides a method for controlling the nitrogen content of molten steel at the endpoint of converter smelting using KR desulfurization solid waste. The method includes the following steps: a. Add scrap steel and molten iron to the converter, then blow oxygen with an oxygen lance, and add slag-forming materials such as lime, dolomite, and iron ore; the temperature of the molten iron used is 1372℃. More parameters of molten iron and scrap steel are detailed in Table 1. Calculated with the sum of the mass of molten iron and scrap steel as 100%, the mass ratio of scrap steel is 14.8%, of which the mass ratio of heavy scrap steel is 2.5%.

[0057] b. During the blowing process, based on the decarburization reaction rate, control the furnace mouth pressure at 0-25 Pa during converter smelting. Perform bottom blowing with Ar throughout the process. When the oxygen blowing rate is less than 30%, control the bottom blowing argon intensity at 0.05 m³ / s. 3 / t / min; when the oxygen blowing rate is 30% to 80%, the bottom blowing argon intensity is controlled at 0.1m. 3 / t / min; when the oxygen blowing rate is greater than 80%, the bottom blowing argon intensity is controlled at 0.2m. 3 / t / min; when the oxygen consumption of blowing reaches 80% of the total, KR desulfurization solid waste is added to the converter, and the addition amount is controlled at 20kg / t. The composition is shown in Table 2. The oxygen lance position is adjusted to control the lance position to be 100mm lower than the normal lance position.

[0058] c. When the oxygen blowing volume reaches 100% of the total, TSO measurement is performed using a secondary lance. The slag composition at the end of the converter smelting is: basicity of 3, FeO 19.5%, MgO 9.5%, and molten steel temperature of 1620℃. Among them, basicity is calculated as the ratio of CaO / SiO2. The parameter control, molten steel obtained, and material consumption at the end of the converter smelting are detailed in Table 3.

[0059] Table 1 Information on molten iron and scrap steel used in each embodiment and comparative example

[0060] Table 2. KR desulfurization solid waste components and dosages used in each embodiment.

[0061] Table 3. Converter endpoint control and raw material consumption for each embodiment and comparative example.

[0062] The following conclusions can be drawn from Table 3: (1) Compared with Comparative Example 1, i.e. compared with the existing conventional smelting process, the nitrogen content of the molten steel obtained at the converter smelting endpoint in Examples 1-5 was significantly reduced and stably controlled below 0.0012%, with an average endpoint nitrogen reduction of more than 50%, and lime consumption decreased by 8.1 kg / t, 5.8 kg / t, 4.6 kg / t, 7.1 kg / t and 7.3 kg / t respectively, and steel material consumption decreased by 7.8 kg / t, 8.5 kg / t, 7.1 kg / t, 10.2 kg / t and 9.3 kg / t respectively.

[0063] (2) Compared with Comparative Example 2, i.e., converter smelting without the addition of KR desulfurization solid waste, the nitrogen content of the molten steel obtained at the end of the converter smelting in Examples 1-4 decreased by an average of more than 40%, and the consumption of lime and steel materials was also significantly reduced.

[0064] (3) Compared with Comparative Example 3 and Comparative Example 4, the nitrogen content in molten steel increased significantly when KR desulfurization solid waste was added too early or too late.

[0065] (4) Compared with Comparative Example 5, if only KR desulfurization solid waste is added, and the oxygen lance position is not controlled, some of the sulfur in the KR desulfurization solid waste will be oxidized and enter the furnace gas, making it difficult to exert the effect of KR desulfurization solid waste.

Claims

1. A method for controlling the nitrogen content of molten steel at the endpoint of converter smelting using KR desulfurization solid waste, characterized in that, Includes the following steps: When the oxygen blowing rate in the converter reaches 70% to 80%, KR desulfurization solid waste is added to the molten steel in the converter. The oxygen lance position is controlled to be 100 to 150 mm lower than the normal position, so that the S in the KR desulfurization solid waste enters the molten steel to reduce nitrogen absorption on its surface.

2. The method for controlling the nitrogen content of molten steel at the endpoint of converter smelting using KR desulfurization solid waste according to claim 1, characterized in that, The amount of KR desulfurization solid waste added is 10~20 kg / t steel.

3. The method for controlling the nitrogen content of molten steel at the endpoint of converter smelting using KR desulfurization solid waste according to claim 1, characterized in that, The pressure at the furnace mouth is maintained at 0~25Pa during the converter smelting process, and argon gas is blown from the bottom throughout the process.

4. The method for controlling the nitrogen content of molten steel at the endpoint of converter smelting using KR desulfurization solid waste according to claim 1, characterized in that, When the oxygen blowing rate in the converter smelting exceeds 80%, the intensity of bottom-blown argon gas should be controlled at 0.12~0.2m. 3 / t / min.

5. The method for controlling the nitrogen content of molten steel at the endpoint of converter smelting using KR desulfurization solid waste according to claim 4, characterized in that, When the oxygen blowing rate in the converter smelting is less than 30%, the bottom blowing argon intensity is controlled at 0.03~0.05m. 3 / t / min; When the oxygen blowing rate in the converter smelting is between 30% and 80%, the bottom blowing argon intensity is controlled at 0.08~0.1m. 3 / t / min.

6. The method for controlling the nitrogen content of molten steel at the endpoint of converter smelting using KR desulfurization solid waste according to claim 1, characterized in that, The final slag composition of the converter smelting is as follows: basicity 2.0~3.0, FeO 10%~20%, MgO 7%~10%; molten steel temperature 1580~1630℃.

7. The method for controlling the nitrogen content of molten steel at the endpoint of converter smelting using KR desulfurization solid waste according to claim 1, characterized in that, The smelting raw materials of the converter include molten iron, scrap steel and slag-forming materials. The total mass of molten iron and scrap steel is calculated as 100%, of which the mass of scrap steel accounts for ≤15% and the mass of heavy scrap steel accounts for ≤5%.

8. The method for controlling the nitrogen content of molten steel at the endpoint of converter smelting using KR desulfurization solid waste according to claim 7, characterized in that, The molten iron used contains the following components by mass percentage: C 4.0%~5.0%, Si 0.1%~1.0%, Mn 0.1%~0.4%, P≤0.12%, N 0.006%~0.014%, S≤0.01%, and the molten iron temperature is 1250~1450℃.

9. The method for controlling the nitrogen content of molten steel at the endpoint of converter smelting using KR desulfurization solid waste according to any one of claims 1-8, characterized in that, The KR desulfurization solid waste used contains the following composition by mass percentage: CaO 30%–60%, SiO2 5%–10%, Al2O3 1%–5%, CaF2 1%–5%, S 1%–3%, with the remainder being iron and unavoidable impurities.

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