A steelmaking method for reducing nitrogen content in molten steel at the end point of a converter

Abstract

The present application relates to metallurgical technology, and in particular to a steelmaking method for reducing nitrogen content of converter end-point molten steel, comprising: determining target mass percentages of each component in main raw materials according to the temperature of molten iron, wherein the molten iron is 78.0wt.%-83.0wt.%, scrap steel is 11.5wt.%-14.0wt.% and pig iron block is 5.5wt.%-8.0wt.%; adding the converter according to the target mass percentages; blowing mixed gas containing CO2 with a volume percentage of 5.0%-10.0% during the blowing process; and obtaining molten steel at the end of the blowing process. The method effectively reduces the nitrogen content of the end-point molten steel by optimizing the ratio of molten iron, scrap steel and pig iron block, using CO2 top blowing gas, delaying the heating of pig iron block with high carbon content, increasing CO bubbles and prolonging the blowing time, and combining the characteristics of CO2 and carbon reaction to generate double volume CO.

Description

[0001] Technical Field Background Technology Nitrogen is a common interstitial atom in steel and is considered a harmful element for most steel grades. High-end steel grades have strict limits on the nitrogen content of the finished product, and controlling the nitrogen content of the molten steel at the end of the converter is the key to ensuring that the nitrogen content of the finished product meets the standards.

[0002] The denitrification principle in conventional converter smelting lies in the intense carbon-oxygen reaction that occurs during the smelting process, generating a large number of CO bubbles. These bubbles act as a vacuum chamber for nitrogen, carrying away nitrogen from the molten steel as they rise and dissipate. Based on this principle, current technologies for smelting low-nitrogen steel typically use low-sulfur molten iron mixed with pure, high-quality scrap steel as the main raw material for the furnace, and continuously top-blown oxygen with a purity of not less than 99.5 vol.%, utilizing the CO bubbles generated by the carbon-oxygen reaction to achieve denitrification.

[0003] Regarding the technical problem of reducing the nitrogen content of molten steel at the converter endpoint, existing research has proposed corresponding solutions, such as controlling the converter blowing time and the amount of coolant added to control the nitrogen content at the endpoint, or adjusting the furnace charge structure by taking technical measures such as reducing the scrap ratio, increasing the amount of pellets added, and increasing the carbon content at the endpoint to suppress the increase of nitrogen content in molten steel at the converter endpoint.

[0004] However, the aforementioned existing technologies still have shortcomings in practical applications. In traditional converter steelmaking processes, the main raw materials fed into the furnace typically consist only of molten iron and scrap steel. Due to the high melting point of high-quality scrap steel, the nitrogen it carries is only released into the molten steel during the later stages of smelting, when the carbon-oxygen reaction weakens. By this time, the denitrification capacity of the molten pool has significantly decreased, leading to high denitrification pressure in the later stages. Simultaneously, the traditional process involves top-blowing oxygen with a purity of no less than 99.5 vol.% throughout the process. This method cannot effectively increase the generation of CO bubbles, the core of denitrification, in the later stages of smelting, especially when the carbon content decreases and the carbon-oxygen reaction weakens, thus limiting further improvements in the denitrification effect of the molten steel. Summary of the Invention

[0005] To address the technical problems of existing converter steelmaking methods that use low-sulfur molten iron with pure, high-quality scrap steel and top-blown high-purity oxygen throughout the process, utilizing CO bubbles generated by the carbon-oxygen reaction for denitrification, this invention provides a steelmaking method to reduce the nitrogen content of molten steel at the converter's final stage. This method optimizes the ratio of molten iron, scrap steel, and pig iron blocks, and uses a mixed top-blown gas containing CO2 for blowing. By utilizing the high carbon content of the pig iron blocks to slow down the temperature rise, increase CO bubbles, and extend the blowing time, combined with refined ratios at different molten iron temperatures and the characteristic that CO2 reacts with carbon to generate double the volume of CO, the nitrogen content of the molten steel at the converter's final stage can be stably controlled at an extremely low level.

[0006] The technical solution of this invention is as follows: In a first aspect, the present invention provides a steelmaking method for reducing the nitrogen content of molten steel at the converter endpoint, comprising the following steps: S1. Based on the temperature of the molten iron entering the furnace, determine the target mass percentage of each component in the main raw material entering the furnace. The main raw material includes molten iron, scrap steel, and pig iron, with molten iron accounting for 78.0 wt.%-83.0 wt.%, scrap steel accounting for 11.5 wt.%-14.0 wt.%, and pig iron accounting for 5.5 wt.%-8.0 wt.%. S2. Add the main raw materials to the converter according to the target mass percentage; S3. The main raw materials fed into the converter are blown, and mixed top-blown gas is blown into the converter during the blowing process. The mixed top-blown gas contains CO2 with a volume percentage of 5.0%-10.0%. S4. The smelting process is complete, and molten steel is obtained.

[0007] In step S1, the target mass percentages of the main raw materials entering the furnace are determined based on the temperature of the molten iron: molten iron (78.0 wt.%-83.0 wt.%), scrap steel (11.5 wt.%-14.0 wt.%), and pig iron (5.5 wt.-8.0 wt.%). By utilizing the high carbon content and relatively low melting point of pig iron, the proportions of the three raw materials are dynamically adjusted under different molten iron temperatures. This slows down the heating rate of the molten pool and delays the start time of the carbon-oxygen reaction in the early stage of blowing, allowing the slag sufficient time to completely melt and evenly cover the surface of the molten metal to isolate it from the air. At the same time, it avoids the problems of slag fluidity deterioration and poor covering effect caused by premature consumption of FeO in the slag due to excessively rapid heating in traditional processes.

[0008] Step S3 involves blowing the main raw materials into the converter and blowing a mixed top-blown gas containing 5.0%-10.0% CO2 by volume into the converter. The CO2 reacts with the carbon in the molten metal (reaction equation: C + CO2 = 2CO), so that each CO2 molecule generates two CO bubbles after participating in the reaction. Compared with using oxygen alone, where each O2 molecule generates two CO bubbles (i.e., 2C + O2 = 2CO), the number of CO bubbles generated by CO2 is twice that of oxygen when consuming the same volume of carbon. This significantly increases the amount of CO bubbles generated throughout the blowing process, especially when the carbon-oxygen reaction weakens in the later stages of smelting. At the same time, since the reaction between CO2 and carbon is an endothermic reaction, it also slows down the carbon oxidation rate and prolongs the effective denitrification time.

[0009] The molten steel obtained after step S4 blowing has a very low nitrogen content at the end point. This is because the slag coverage and air isolation ability in the early stage of blowing were increased by optimizing the main raw material ratio in the previous steps, and the amount of CO bubbles generated during the smelting process was greatly increased by using mixed top-blown gas containing CO2 to enhance the denitrification efficiency of nitrogen carried by the bubbles to float and be discharged. At the same time, the reduction of scrap steel ratio reduced the release of nitrogen in the later stage, the addition of pig iron blocks increased the carbon content of the molten pool, and extended the decarburization time.

[0010] Furthermore, in step S1, the carbon content of the pig iron block is 3.0 wt.% - 4.3 wt.%.

[0011] By limiting the carbon content of pig iron blocks to 3.0 wt.%-4.3 wt.%, sufficient carbon source is ensured in the main raw materials fed into the furnace. During the blowing process, this carbon generates a large number of CO bubbles through the carbon-oxygen reaction to carry nitrogen out. On the other hand, since the carbon content of pig iron blocks is significantly higher than that of ordinary scrap steel, it continuously provides carbon elements to the molten pool during the melting process. Thus, even when the carbon content naturally decreases in the later stages of blowing, a certain intensity of carbon-oxygen reaction can still be maintained. This avoids the problem of a sharp decrease in the amount of CO bubbles generated and a decline in denitrification capacity in the later stages due to insufficient carbon source in traditional processes.

[0012] Furthermore, in step S1, the particle size of the pig iron blocks is 30mm-80mm.

[0013] By limiting the pig iron block size to 30mm-80mm, a suitable melting rate and reaction surface area are ensured in the converter molten pool. If the particle size is too small, the pig iron block will melt too early in the early stage of blowing and will not be able to play the role of delaying the temperature rise. If the particle size is too large, the pig iron block will melt too late or even remain until the end of the blowing process, and will not be able to provide carbon source and CO bubbles in the critical middle and late stages of smelting. The particle size range of 30mm-80mm allows the melting process of the pig iron block to match the temperature rise curve of the molten pool and the required duration of the carbon-oxygen reaction, thereby achieving the synergistic effect of the pig iron block delaying the temperature rise in the early stage of blowing and continuously supplying carbon to generate CO bubbles in the middle and late stages of blowing.

[0014] Furthermore, in step S1, the temperature of the molten iron entering the furnace is 1300℃-1400℃.

[0015] By limiting the temperature of the molten iron entering the furnace to 1300℃-1400℃, the initial thermal state of the molten iron in the main raw materials entering the furnace is kept within a relatively stable and controllable range. Within this temperature range, in conjunction with the mass percentage range of molten iron, scrap steel, and pig iron blocks set in claim 1, it can be ensured that the initial thermal balance of the molten pool is not disrupted after the addition of pig iron blocks. This prevents the pig iron blocks from failing to melt properly due to excessively low molten iron temperature, and also prevents them from melting prematurely due to excessively high molten iron temperature, thus losing their effect of delaying the temperature rise. This provides the prerequisite for subsequent fine adjustment of the main raw material ratio based on the molten iron temperature.

[0016] Furthermore, in step S1, the rules for determining the target mass percentage of each component in the main raw material fed into the furnace based on the temperature of the molten iron include: When the temperature of the molten iron entering the furnace is ≥1400℃, the proportion of molten iron entering the furnace is 77.5wt.%-78.5wt.%, the proportion of scrap steel is 13.5wt.%-14.5wt.%, and the proportion of pig iron blocks is 7.5wt.%-8.5wt.%. When the temperature of molten iron entering the furnace is between 1380℃ and 1400℃, the proportion of molten iron entering the furnace is 78.5 wt.%-79.5 wt.%, the proportion of scrap steel is 13.0 wt.%-14.0 wt.%, and the proportion of pig iron is 7.0 wt.%-8.0 wt.%. When the temperature of molten iron entering the furnace is between 1360℃ and 1380℃, the proportion of molten iron entering the furnace is 79.5 wt.%-80.5 wt.%, the proportion of scrap steel is 12.5 wt.%-13.5 wt.%, and the proportion of pig iron is 6.5 wt.%-7.5 wt.%. When 1340℃ ≤ molten iron temperature < 1360℃, the proportion of molten iron in the furnace is 80.5 wt.%-81.5 wt.%, the proportion of scrap steel is 12.0 wt.%-13.0 wt.%, and the proportion of pig iron is 6.0 wt.%-7.0 wt.%. When 1320℃ ≤ molten iron temperature < 1340℃, the proportion of molten iron in the furnace is 81.5wt.%-82.5wt.%, the proportion of scrap steel is 11.5wt.%-12.5wt.%, and the proportion of pig iron is 5.5wt.%-6.5wt.%. When the temperature of molten iron entering the furnace is between 1300℃ and 1320℃, the proportion of molten iron entering the furnace is 82.5wt.%-83.5wt.%, the proportion of scrap steel is 11.0wt.%-12.0wt.%, and the proportion of pig iron is 5.0wt.%-6.0wt.%.

[0017] By setting the mass percentage ranges of molten iron, scrap steel, and pig iron blocks according to six different temperature ranges (from ≥1400℃ to 1300℃-1320℃) of the molten iron entering the furnace, adaptive adjustment to changes in the thermal state of the molten iron is achieved. When the molten iron temperature is high, the proportion of pig iron blocks and scrap steel is increased to absorb excess heat and delay the carbon-oxygen reaction. When the molten iron temperature is low, the proportion of molten iron is increased and the proportion of pig iron blocks and scrap steel is reduced to ensure that the molten pool has sufficient initial heat and fluidity. Thus, low-nitrogen molten steel can be stably obtained under different blast furnace tapping temperature fluctuations.

[0018] More preferably, in step S1, the rules for determining the target mass percentage of each component in the main raw material fed into the furnace based on the temperature of the molten iron include: When the temperature of the molten iron entering the furnace is ≥1400℃, the proportion of molten iron entering the furnace is 78.0 wt.%, the proportion of scrap steel is 14.0 wt.%, and the proportion of pig iron blocks is 8.0 wt.%. When the temperature of molten iron entering the furnace is between 1380℃ and 1400℃, the proportion of molten iron entering the furnace is 79.0 wt.%, the proportion of scrap steel is 13.5 wt.%, and the proportion of pig iron is 7.5 wt.%. When 1360℃ ≤ molten iron temperature < 1380℃, the proportion of molten iron in the furnace is 80.0 wt.%, scrap steel is 13.0 wt.%, and pig iron is 7.0 wt.%. When the temperature of molten iron entering the furnace is between 1340℃ and 1360℃, the proportion of molten iron entering the furnace is 81.0 wt.%, the proportion of scrap steel is 12.5 wt.%, and the proportion of pig iron is 6.5 wt.%. When 1320℃ ≤ molten iron temperature < 1340℃, the proportion of molten iron in the furnace is 82.0 wt.%, scrap steel is 12.0 wt.%, and pig iron is 6.0 wt.%. When 1300℃≤molten iron temperature<1320℃, the proportion of molten iron in the furnace is 83.0wt.%, the proportion of scrap steel is 11.5wt.%, and the proportion of pig iron is 5.5wt.%.

[0019] By further setting specific values ​​for molten iron, scrap steel, and pig iron blocks according to the six different temperature ranges of the molten iron entering the furnace, an optimized fixed ratio scheme is provided. This scheme eliminates the uncertainty of operators when taking values ​​within the range, and makes the ratio of main raw materials in each temperature range unique and repeatable. This simplifies on-site operation while ensuring denitrification effect and is conducive to quality stability control in large-scale industrial production.

[0020] Furthermore, the mixed top-blown gas is a mixture of CO2 and O2 with a purity of not less than 99.5 vol.%.

[0021] By limiting the mixed top-blown gas to a mixture of CO2 and O2 with a purity of not less than 99.5 vol.%, the amount of CO bubble generation is increased and the excessively rapid rise in the molten pool temperature is suppressed. At the same time, the high-purity oxygen ensures that the oxidation reaction efficiency of elements such as carbon, silicon, and phosphorus in the molten pool meets the basic requirements of steelmaking. Thus, the dual effects of enhanced denitrification and regulation of molten pool temperature are achieved without extending the overall smelting cycle.

[0022] Furthermore, the mixed top-blown gas includes a first mixed top-blown gas and a second mixed top-blown gas; Before the first temperature measurement and sampling at the secondary gun, the first mixed top-blown gas is blown into the converter. After the first temperature measurement and sampling at the secondary gun, a second mixed top-blown gas is blown into the converter. The volume percentage of CO2 in the first mixed top-blown gas is 5.0%-6.0%. The volume percentage of CO2 in the second mixed top-blown gas is 8%-10.0%.

[0023] By blowing a first mixed top-blown gas with a CO2 volume percentage of 5.0%-6.0% into the converter before the first temperature sampling at the secondary lance, and a second mixed top-blown gas with a CO2 volume percentage of 8.0%-10.0% after the first temperature sampling at the secondary lance, the low CO2 ratio in the early and middle stages of blowing ensures rapid slag formation and preliminary denitrification. In the later stage of blowing, when a large amount of scrap steel melts and the nitrogen it carries is released into the molten steel, the CO2 ratio is increased to further increase the amount of CO bubbles generated, thereby enhancing the denitrification capacity during this period. This ensures that the denitrification intensity matches the nitrogen release rate in the molten pool, resolving the contradiction in traditional processes where the demand for denitrification increases in the later stages but the amount of CO bubbles generated decreases.

[0024] More preferably, the volume percentage of CO2 in the first mixed top-blown gas is 5.0%; The volume percentage of CO2 in the second mixed top-blown gas is 10.0%.

[0025] By further limiting the volume percentage of CO2 in the first mixed top-blown gas to 5.0% and the volume percentage of CO2 in the second mixed top-blown gas to 10.0%, two optimal specific ratio points are provided. Among them, 5.0% CO2 can stably increase the amount of CO bubble generation in the early and middle stages of blowing without significantly affecting slag formation and heating rhythm. 10.0% CO2 can maximize the use of remaining carbon to generate CO bubbles in the later stage of blowing when the carbon content is already low. The denitrification effect is maximized by the two-stage ratio scheme.

[0026] Furthermore, the nitrogen content of the molten steel obtained in step S4 is ≤0.0015 wt.%.

[0027] By limiting the nitrogen content of the molten steel obtained in step S4 to ≤0.0015 wt.%, the endpoint nitrogen content level of molten steel that this method can achieve is clarified. This value is far lower than the conventional requirement of ≤0.0025 wt.% for the nitrogen content of finished products for high-end steel products. In addition, considering the nitrogen increase phenomenon that usually exists in subsequent refining and continuous casting processes, sufficient nitrogen increase space is reserved for subsequent processes, thereby ensuring that the nitrogen content of the final steel product can still meet the strict standards for high-end applications.

[0028] The beneficial effects of this invention are as follows: 1. The steelmaking method for reducing the nitrogen content of molten steel at the converter endpoint provided by the present invention optimizes the ratio of molten iron, scrap steel and pig iron blocks in the main raw materials fed into the furnace, and uses mixed top-blown gas containing CO2 for blowing, which can effectively reduce the nitrogen content of molten steel at the converter endpoint and stably control the nitrogen content of molten steel at the converter endpoint below 0.0015wt.%.

[0029] 2. This invention, by adding a specific proportion of pig iron blocks to the main raw materials fed into the furnace, utilizes the high carbon content and low melting point of the pig iron blocks to slow down the heating rate and the start time of the carbon-oxygen reaction in the early stage of blowing, promotes the uniform melting of slag to better cover the molten metal and isolate it from air, and at the same time increases the amount of CO bubble generation throughout the smelting process, especially in the later stage, and extends the blowing time for effective denitrification.

[0030] 3. By limiting the carbon content of the pig iron block to 3.0wt.%-4.3wt.%, this invention ensures that the pig iron block can provide a sufficient carbon source, thereby continuously generating CO bubbles during the blowing process, effectively diluting and removing nitrogen from the molten steel.

[0031] 4. Based on the different temperature ranges of the molten iron entering the furnace, this invention precisely sets the specific target mass percentages of the molten iron, scrap steel, and pig iron blocks entering the furnace, thereby achieving refined control over the structure of the main raw materials under different thermal states and ensuring that stable low-nitrogen molten steel can be obtained under various molten iron temperature conditions.

[0032] 5. This invention uses a mixed top-blown gas containing CO2, taking advantage of the chemical property that CO2 reacts with C to generate twice the volume of CO. Under the same carbon consumption, more CO bubbles can be generated, thereby enhancing the denitrification kinetics of the molten pool. Detailed Implementation

[0033] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions in the embodiments of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0034] Example 1 A steelmaking method for reducing the nitrogen content of molten steel at the converter endpoint includes the following steps: S1. Determine the target mass percentage of each component in the main raw material fed into the furnace based on the temperature of the molten iron. The main raw material fed into the furnace includes molten iron, scrap steel and pig iron blocks. The carbon content of the pig iron blocks is 3.8wt.% - 4.2wt.%, with an average carbon content of 4.0wt.% and a particle size of 30mm-80mm. The rules for determining the target mass percentage of each component in the main raw materials fed into the furnace based on the temperature of the molten iron are shown in Table 1: Table 1 Correspondence between molten iron temperature and main raw material composition before furnace entry

[0035] In this embodiment, the molten iron temperature is 1370℃, corresponding to a target mass percentage of 80.0 wt.% for molten iron, a target mass percentage of 13.0 wt.% for scrap steel, and a target mass percentage of 7.0 wt.% for pig iron blocks. Specifically, the molten iron is 200t, the scrap steel is 32.5t, and the pig iron blocks are 17.5t. S2. Add the main raw materials to the converter according to the target mass percentage; S3. The main raw materials fed into the converter are blown, and mixed top-blown gas is blown into the converter during the blowing process. The mixed top-blown gas contains CO2 with a volume percentage of 5.0%-10.0%. The mixed top-blown gas is a mixture of CO2 and O2 with a purity of not less than 99.5 vol.%, including a first mixed top-blown gas and a second mixed top-blown gas. Before the first temperature measurement and sampling at the secondary gun, a first mixed top-blown gas was blown into the converter. The volume percentage of CO2 in the first mixed top-blown gas was 5.0%. After the first temperature measurement and sampling at the secondary gun, a second mixed top-blown gas was blown into the converter. The volume percentage of CO2 in the second mixed top-blown gas was 10.0%. S4. After blowing, molten steel is obtained with a nitrogen content ≤0.0015 wt.%.

[0036] Comparative Example 1 A steelmaking method includes the following steps: S1. Determine the target mass percentage of each component in the main raw material fed into the furnace. The main raw material fed into the furnace includes molten iron and scrap steel. The molten iron temperature is 1370℃, the target mass percentage of the molten iron is 80.0 wt.%, and the target mass percentage of the scrap steel is 20.0 wt.%, specifically 200t of molten iron and 50t of scrap steel are charged into the furnace. S2. Add the main raw materials to the converter according to the target mass percentage; S3. The main raw materials fed into the converter are blown, and the purity of the top blown O2 during the blowing process is not less than 99.5 vol.%; S4. After the blowing process is completed, molten steel is obtained. The mass of each component in the main raw material fed into the furnace in Example 1 and Comparative Example 1 is shown in Table 2: Table 2 Comparison of the mass of each component in the main raw material fed into the furnace

[0037] If the average carbon content of both molten iron and pig iron is 4.0 wt.%, then: The theoretically calculated CO production for Comparative Example 1 is:

[0038] The theoretically calculated CO production amount before the first temperature measurement and sampling of the secondary gun in Example 1 (corresponding to the early and middle stages of the blowing process) was:

[0039] Example 1: After the first temperature measurement and sampling of the secondary gun (corresponding to the later stage of blowing), the theoretically calculated CO production was:

[0040] Of which, the early and middle stages of the blowing process accounted for the following percentage of the total blowing time: ; The later stage of the blowing process accounts for 20% of the total blowing time. The ratio of the relative molecular weight of CO to the relative atomic weight of C is ; For the same amount of C, the ratio of CO generated when the CO2 content of the top-blown gas is 5.0 wt.% to that generated when only oxygen is blown from the top is [value missing]. ; For the same amount of C, the ratio of CO generated when the CO2 content of the top-blown gas is 5.0 wt.% to that generated when only oxygen is blown from the top is [value missing]. ; That is, the theoretically calculated CO production amount in Example 1 during the entire blowing process is:

[0041] It can be seen that, compared with Comparative Example 1, the amount of CO generated during the blowing process in Example 1 increased by the following percentage:

[0042] Furthermore, the blowing time of Comparative Example 1 was 12.3 min in the early and middle stages, 3.2 min in the later stage, and 15.5 min in total; while the blowing time of Example 1 was 13.72 min in the early and middle stages, 3.66 min in the later stage, and 17.38 min in total, representing increases of 11.54%, 14.47%, and 12.14% respectively compared to Comparative Example 1.

[0043] It is evident that the technical solution of this application increases the amount of CO bubbles generated and extends the blowing time, thereby controlling the nitrogen content of the molten steel at the converter endpoint at a low level.

[0044] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A steelmaking method for reducing the nitrogen content of molten steel at the converter endpoint, characterized in that, Includes the following steps: S1. Based on the temperature of the molten iron entering the furnace, determine the target mass percentage of each component in the main raw material entering the furnace. The main raw material includes molten iron, scrap steel, and pig iron, with molten iron accounting for 78.0 wt.%-83.0 wt.%, scrap steel accounting for 11.5 wt.%-14.0 wt.%, and pig iron accounting for 5.5 wt.%-8.0 wt.%. S2. Add the main raw materials to the converter according to the target mass percentage; S3. The main raw materials fed into the converter are blown, and mixed top-blown gas is blown into the converter during the blowing process. The mixed top-blown gas contains CO2 with a volume percentage of 5.0%-10.0%. S4. The smelting process is complete, and molten steel is obtained.

2. The steelmaking method as described in claim 1, characterized in that, In step S1, the carbon content of the pig iron block is 3.0 wt.% - 4.3 wt.%.

3. The steelmaking method as described in claim 1, characterized in that, The particle size of the pig iron blocks is 30mm-80mm.

4. The steelmaking method as described in claim 1, characterized in that, In step S1, the temperature of the molten iron entering the furnace is 1300℃-1400℃.

5. The method as described in claim 1, characterized in that, In step S1, the rules for determining the target mass percentage of each component in the main raw material fed into the furnace based on the temperature of the molten iron include: When the temperature of the molten iron entering the furnace is ≥1400℃, the proportion of molten iron entering the furnace is 77.5wt.%-78.5wt.%, the proportion of scrap steel is 13.5wt.%-14.5wt.%, and the proportion of pig iron blocks is 7.5wt.%-8.5wt.%. When the temperature of molten iron entering the furnace is between 1380℃ and 1400℃, the proportion of molten iron entering the furnace is 78.5 wt.%-79.5 wt.%, the proportion of scrap steel is 13.0 wt.%-14.0 wt.%, and the proportion of pig iron is 7.0 wt.%-8.0 wt.%. When the temperature of molten iron entering the furnace is between 1360℃ and 1380℃, the proportion of molten iron entering the furnace is 79.5 wt.%-80.5 wt.%, the proportion of scrap steel is 12.5 wt.%-13.5 wt.%, and the proportion of pig iron is 6.5 wt.%-7.5 wt.%. When 1340℃ ≤ molten iron temperature < 1360℃, the proportion of molten iron in the furnace is 80.5 wt.%-81.5 wt.%, the proportion of scrap steel is 12.0 wt.%-13.0 wt.%, and the proportion of pig iron is 6.0 wt.%-7.0 wt.%. When 1320℃ ≤ molten iron temperature < 1340℃, the proportion of molten iron in the furnace is 81.5wt.%-82.5wt.%, the proportion of scrap steel is 11.5wt.%-12.5wt.%, and the proportion of pig iron is 5.5wt.%-6.5wt.%. When the temperature of molten iron entering the furnace is between 1300℃ and 1320℃, the proportion of molten iron entering the furnace is 82.5wt.%-83.5wt.%, the proportion of scrap steel is 11.0wt.%-12.0wt.%, and the proportion of pig iron is 5.0wt.%-6.0wt.%.

6. The method as described in claim 5, characterized in that, In step S1, the rules for determining the target mass percentage of each component in the main raw material fed into the furnace based on the temperature of the molten iron include: When the temperature of the molten iron entering the furnace is ≥1400℃, the proportion of molten iron entering the furnace is 78.0 wt.%, the proportion of scrap steel is 14.0 wt.%, and the proportion of pig iron blocks is 8.0 wt.%. When the temperature of molten iron entering the furnace is between 1380℃ and 1400℃, the proportion of molten iron entering the furnace is 79.0 wt.%, the proportion of scrap steel is 13.5 wt.%, and the proportion of pig iron is 7.5 wt.%. When 1360℃ ≤ molten iron temperature < 1380℃, the proportion of molten iron in the furnace is 80.0 wt.%, scrap steel is 13.0 wt.%, and pig iron is 7.0 wt.%. When 1340℃ ≤ molten iron temperature < 1360℃, the proportion of molten iron in the furnace is 81.0 wt.%, the proportion of scrap steel is 12.5 wt.%, and the proportion of pig iron is 6.5 wt.%. When 1320℃ ≤ molten iron temperature < 1340℃, the proportion of molten iron in the furnace is 82.0 wt.%, scrap steel is 12.0 wt.%, and pig iron is 6.0 wt.%. When 1300℃≤heat temperature of molten iron into the furnace<1320℃, the proportion of molten iron into the furnace is 83.0wt.%, the proportion of scrap steel is 11.5wt.%, and the proportion of pig iron blocks is 5.5wt.%.

7. The steelmaking method as described in claim 1, characterized in that, The mixed top-blown gas is a mixture of CO2 and O2 with a purity of not less than 99.5 vol.%.

8. The steelmaking method as described in claim 1, characterized in that, The mixed top-blown gas includes a first mixed top-blown gas and a second mixed top-blown gas; Before the first temperature measurement and sampling at the secondary gun, the first mixed top-blown gas is blown into the converter. After the first temperature measurement and sampling at the secondary gun, a second mixed top-blown gas is blown into the converter. The volume percentage of CO2 in the first mixed top-blown gas is 5.0%-6.0%. The volume percentage of CO2 in the second mixed top-blown gas is 8%-10.0%.

9. The steelmaking method as described in claim 8, characterized in that, The volume percentage of CO2 in the first mixed top-blown gas is 5.0%; The volume percentage of CO2 in the second mixed top-blown gas is 10.0%.

10. The steelmaking method according to claim 1, characterized in that, The nitrogen content of the molten steel obtained in step S4 is ≤0.0015 wt.%.

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