Method for improving denitrification capacity in converter smelting process

Abstract

The invention relates to the technical field of steelmaking, in particular to a method for improving the denitrification capacity in the converter smelting process. Argon is blown from the bottom in the whole converter smelting process, converter smelting is started to blowing for 5-6 min, and the oxygen supply intensity is gt; 3.5 Nm < 3 > / (t.min) control is conducted, and slagging materials are added after ignition is sufficient; after the materials are added, the oxygen supply intensity is controlled according to 3.0-3.1 Nm < 3 > / (t.min); 1-2 min before oxygen supply is finished, the oxygen supply intensity is gt; and 3.5 Nm < 3 > / (t.min) control is carried out. In the converter smelting process, an oxygen lance adopts an oxygen supply intensity step regulation method, the oxygen supply intensity is high-low-high in sequence from the smelting early stage to the smelting later stage, and bottom argon blowing is carried out in the whole process by combining a bottom blowing system of the converter, so that the end-point nitrogen content is reduced, the subsequent refining burden is reduced, and the production of low-nitrogen steel is realized.

Description

Technical Field

[0001] This invention relates to the field of steelmaking technology, and more particularly to a method for improving denitrification capacity in a converter smelting process. Background Technology

[0002] In recent years, guided by the "dual carbon" goals, the global steel industry has actively promoted a low-carbon transformation, with the research and development of key technologies for reducing carbon emissions becoming a priority. By improving the recycling rate of scrap steel and optimizing the resource utilization of slag, steel companies have effectively reduced the consumption of primary resources and significantly lowered their carbon emission intensity.

[0003] In practice, steel companies have mainly adopted two technical approaches: one is to reduce iron consumption by increasing the scrap ratio in converters; the other is to use a semi-steel process where scrap is smelted in an electric arc furnace and then mixed with molten iron. While these measures have reduced the consumption of molten steel per ton of steel and carbon emissions, they have also brought new technical challenges: because scrap steel itself has a high nitrogen content (usually >0.0050%), and the nitrogen content of molten steel is generally high during electric arc furnace smelting, although the RH refining unit has a certain denitrification capacity, it is limited by the potential nitrogen increase risk in the LF refining process and the secondary nitrogen increase phenomenon in the continuous casting process, ultimately resulting in the finished steel's nitrogen content failing to meet the production requirements of high-end steel grades.

[0004] Low-nitrogen steels hold an irreplaceable position in high-end manufacturing due to their superior mechanical properties, excellent weldability, and stable resistance to aging. They are primarily used in automotive steel (such as IF steel), electrical steel (such as grain-oriented silicon steel), pipeline steel (such as X80), and high-strength steel (such as DP980). The influence of nitrogen on steel properties is mainly reflected in three aspects: 1) Mechanical properties: Excessive nitrogen content will enhance the solid solution strengthening effect, impair the ductility and deep drawing performance of steel, and is not conducive to the development of lightweight automobiles; 2) Welding performance: Increased nitrogen content will exacerbate the tendency of the heat-affected zone to become embrittled, increasing the risk of welding cracks; 3) Regarding resistance to aging: Nitrogen readily forms AlN / TiN precipitates with elements such as Al and Ti, leading to aging hardening problems.

[0005] Converter smelting is a key step in denitrification of molten steel. Currently, nitrogen content is mainly controlled by optimizing the scrap steel ratio, adopting a full-process argon bottom blowing process, precisely controlling the smelting endpoint, adding special denitrification agents, and adjusting the composition of furnace gas.

[0006] However, existing denitrification technologies have significant bottlenecks in efficiency, with converter smelting achieving a maximum denitrification rate of only 60%. Particularly when using high scrap ratios (>50%) or electric arc furnace molten iron mixing processes, the nitrogen content in the tapped steel often exceeds 0.0025%, even reaching over 0.0030%, posing a significant challenge to the production of low-nitrogen steel grades (requiring nitrogen content <0.0020%). Overcoming these bottlenecks and achieving more efficient nitrogen content control has become a critical technical challenge urgently needing to be addressed in the steel industry. Summary of the Invention

[0007] The purpose of this invention is to provide a method for improving denitrification capacity in the converter smelting process. By adopting a "step-by-step control method for oxygen supply intensity" in the oxygen lance during the converter smelting process, the oxygen supply intensity is successively high-low-high from the early stage of smelting to the later stage of smelting. Combined with the bottom blowing system of the converter for full-process bottom blowing of argon, the final nitrogen content is reduced, the subsequent refining burden is reduced, and the production of low-nitrogen steel grades is achieved.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: This invention provides a method for improving denitrification capacity in a converter smelting process. Argon is blown into the bottom throughout the converter smelting process, with an oxygen supply intensity >3.5 Nm for the first 5-6 minutes of blowing from the start of smelting. 3 Control the oxygen supply rate (t·min) and add slag-forming materials after complete ignition; after all materials have been added, maintain the oxygen supply intensity at 3.0-3.1 Nm³. 3 / (t·min) control; 1-2 minutes before the end of oxygen supply, the oxygen supply intensity should be >3.5Nm 3 / (t·min) control.

[0009] During converter smelting, the nitrogen content in molten steel changes as the smelting process progresses. In the initial blowing stage, due to the lower temperature, nitrogen has a higher solubility in the molten steel, and the reaction between oxygen and nitrogen is less, so the nitrogen content in the molten steel gradually increases. As blowing continues, the temperature rises, the decarburization reaction intensifies, and the formed CO bubbles act like a "vacuum pump," promoting the removal of nitrogen. At this point, the nitrogen content in the molten steel gradually decreases.

[0010] The dissolution behavior of nitrogen in molten steel follows Sievts' law, which states that the solubility of nitrogen is proportional to the square root of the partial pressure of nitrogen in the gas phase: (1) in: The equilibrium solubility of nitrogen in molten steel (ppm); The nitrogen dissolution equilibrium constant is taken as 0.042 ppm·atm⁻⁵ at 1600℃; The nitrogen partial pressure (atm) at the gas-liquid interface.

[0011] Formula (1) shows that reducing nitrogen partial pressure can reduce nitrogen content in molten steel. Using weak oxygen supply intensity during the blowing process can prolong the time for reducing nitrogen partial pressure and extend the denitrification time, thereby reducing nitrogen content in molten steel and improving the denitrification capacity of the smelting process.

[0012] The contradiction between oxygen supply intensity and nitrogen content: high oxygen supply intensity (>3.5 Nm³) 3 While oxygen supply intensity ( / (t·min)) can accelerate decarburization, it also intensifies turbulence in the molten pool and promotes air entrainment. However, air entrainment increases the nitrogen content of the molten steel. Therefore, a weak oxygen supply intensity is adopted to reduce the risk of air entrainment increasing the nitrogen content of the molten steel.

[0013] In the above technical solution, the slag-forming materials are dolomite and lime, which are added in multiple batches.

[0014] In the above technical solution, the specific strategy for adding slag-forming materials is as follows: after the dolomite has been fully ignited, the first batch of lime is added at 30%-50% of the total amount of lime, and the remaining lime is added at 0.5-1 ton / furnace every 30-60 seconds until it is all added.

[0015] In the above technical solution, sintered return ore is further used as a cooling material in conjunction with smelting. After ignition is complete, 0.5-1.0 tons of sintered return ore is added every 30-60 seconds until it is completely added.

[0016] In the above technical solution, the argon gas supply intensity is further specified as 0.008-0.01 Nm. 3 / (t·min).

[0017] In the above technical solution, the period from the start of converter smelting to 5-6 minutes of blowing is the early stage of smelting, and the oxygen lance position is controlled at 1.8-2.0 meters.

[0018] In the above technical solution, the period from the completion of material addition to 1-2 minutes before the end of oxygen supply is the middle stage of smelting, and the oxygen lance position is controlled at 1.8-2.2 meters.

[0019] In the above technical solution, the period from 1-2 minutes before the end of oxygen supply to the end of blowing is the later stage of smelting, and the oxygen lance position is controlled at 1.6-1.8 meters.

[0020] The beneficial effects of this invention are as follows: 1. This invention employs a "step-wise control method for oxygen supply intensity" in the oxygen lance during converter smelting. High oxygen supply intensity is used in the early and late stages of smelting to meet the needs of lance ignition during initial blowing and carbon removal at the final stage. In the middle stage, weak oxygen supply is used, utilizing the CO bubbles formed during the decarburization reaction to act like a "vacuum pump," extending the denitrification time. Combined with the converter's bottom blowing system's continuous bottom blowing with argon, nitrogen removal is promoted. Another function of weak oxygen supply is to reduce the intensity of the deoxidation reaction, which helps reduce slag drying during the strong decarburization period. Liquid slag covering the molten steel surface reduces contact between the steel and air, avoiding secondary contamination and reducing the nitrogen content in the molten steel, ultimately improving the denitrification capacity of the converter smelting process. Compared to existing technologies, this invention achieves nitrogen reduction through oxygen lance process optimization, making it suitable for rapid application in existing converter production lines. While ensuring normal converter production, it reduces the final nitrogen content, decreases the burden on subsequent refining, and enables the production of low-nitrogen steel grades.

[0021] 2. The converter bottom blowing system of this invention adopts argon blowing operation throughout the smelting process, which agitates the molten steel to facilitate the uniformity of temperature and composition in the furnace, the normal progress of the dephosphorization reaction, and the smooth removal of nitrogen.

[0022] 3. The denitrification capacity of the converter using the method of this invention is increased from a maximum of 60% in traditional converter smelting to 80%, reaching a leading level in China. In the traditional converter smelting process, it is usually difficult to stably control the nitrogen content of molten steel below 20 ppm. The nitrogen content of molten steel in the converter of this invention is reduced to below 0.0016%, which not only reduces the pressure of controlling the nitrogen content of molten steel in subsequent processes and meets the needs of smelting low-nitrogen steel grades, but also improves product quality and the development of specialty steels. Attached Figure Description

[0023] Figure 1 This is a graph showing the relationship between blowing time and oxygen supply intensity in Example 1. Detailed Implementation

[0024] The following examples are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0025] Example 1 The ironworks uses torpedo ladles to transport molten iron to the steel plant. Tests show the nitrogen content in the molten iron is 0.0050%. Due to the use of a composite injection method (magnesium powder + lime) for desulfurization of the molten iron, with nitrogen as the carrier, the nitrogen content in the molten iron after desulfurization and slag removal is 0.0075%, the silicon content is 0.40%, and the temperature is 1340℃. The steel grade to be smelted is SPHC. Calculations show the total amount of dolomite is 2.5 tons, the total amount of lime is 6 tons, and the amount of sintering return ore added is 1.0 ton.

[0026] After scrap steel is added to the molten iron in the converter, the lance is lowered to begin smelting, with the oxygen lance supplying an oxygen intensity of 3.8 Nm. 3 / (t·min), lance position 2.0 meter, after complete ignition, add 2.5 tons of dolomite and 2.0 tons of lime. After 60 seconds, add 1.0 ton of lime and 1.0 ton of sintered return ore. After 120 seconds, add 1.0 ton of lime. After 180 seconds, add 1.0 ton of lime. After 240 seconds, add 1.0 ton of lime. At this point, all materials have been added. After 300 seconds, the oxygen supply intensity of the oxygen lance is reduced to 3.0 Nm³. 3 / (t·min), the oxygen lance position is flexibly adjusted according to the slag melting situation in the furnace, with the principle of no splashing and no back drying. The oxygen lance position is 1.8 meters to 2.2 meters. 1-2 minutes before the end of blowing, the oxygen supply intensity of the oxygen lance is increased to 3.8 Nm. 3 / (t·min), oxygen lance position 1.6 meters for carbon extraction until the blowing is completed, argon gas is blown from the bottom of the converter throughout the process, with a gas supply intensity of 0.009 Nm. 3 The lance was lifted at a rate of / (t·min), and then an endpoint test was performed. After confirming that the composition and temperature met the requirements, the steel was tapped. The nitrogen content of the molten steel was tested to be 0.0015%, and the denitrification rate reached 80%.

[0027] Example 2 The ironworks uses torpedo ladles to transport molten iron to the steel plant. Testing showed the nitrogen content in the molten iron to be 0.0052%. Due to the use of a composite injection method (magnesium powder + lime) for desulfurization of the molten iron, with nitrogen as the carrier, the nitrogen content in the molten iron after desulfurization and slag removal was 0.0078%, the silicon content was 0.35%, and the temperature was 1330℃. The steel grade to be smelted is Q235B. Calculations show that 2.2 tons of dolomite, 5.5 tons of lime, and 0.5 tons of sintered return ore were added.

[0028] After scrap steel is added to the molten iron in the converter, the lance is lowered to begin smelting, with the oxygen lance supplying an oxygen intensity of 3.8 Nm. 3 / (t·min), lance position 2.0 meter, after complete ignition, add 2.2 tons of dolomite and 2.0 tons of lime. After 60 seconds, add 1.0 ton of lime and 0.5 tons of sintered return ore. After 120 seconds, add 1.0 ton of lime. After 180 seconds, add 1.0 ton of lime. After 240 seconds, add 0.5 tons of lime. At this point, all materials have been added. After 300 seconds, the oxygen supply intensity of the oxygen lance is reduced to 3.0 Nm³. 3 / (t·min), the oxygen lance position is flexibly adjusted according to the slag melting situation in the furnace, with the principle of no splashing and no back drying. The oxygen lance position is 1.8 meters to 2.2 meters. 1-2 minutes before the end of blowing, the oxygen supply intensity of the oxygen lance is increased to 3.8 Nm. 3 / (t·min), oxygen lance position 1.6 meters for carbon extraction until the blowing is completed, argon gas is blown from the bottom of the converter throughout the process, with a gas supply intensity of 0.009 Nm. 3 The lance was lifted at a rate of / (t·min), and then an endpoint test was performed. After confirming that the composition and temperature met the requirements, the steel was tapped. The nitrogen content of the molten steel was 0.0016%, and the denitrification rate reached 79.5%.

[0029] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A method for improving denitrification capacity in a converter smelting process, characterized in that, Argon is blown into the bottom throughout the converter smelting process. From the start of converter smelting to 5-6 minutes of blowing, the oxygen supply intensity is >3.5 Nm. 3 Control the oxygen supply rate (t·min) and add slag-forming materials after complete ignition; after all materials have been added, maintain the oxygen supply intensity at 3.0-3.1 Nm³. 3 / (t·min) control; 1-2 minutes before the end of oxygen supply, the oxygen supply intensity should be >3.5Nm 3 / (t·min) control.

2. The method for improving denitrification capacity in a converter smelting process according to claim 1, characterized in that, The slag-forming materials are dolomite and lime, which are added in multiple batches.

3. The method for improving denitrification capacity in a converter smelting process according to claim 1, characterized in that, The specific strategy for adding slag-forming materials is as follows: after the dolomite has been fully ignited, the first batch of lime should be 30%-50% of the total lime content. The remaining lime should be added at a rate of 0.5-1 ton / furnace every 30-60 seconds until it is completely added.

4. The method for improving denitrification capacity in a converter smelting process according to claim 3, characterized in that, Sintered return ore is used as a cooling material in the smelting process. After the ignition is complete, 0.5-1.0 tons of sintered return ore is added every 30-60 seconds until all the ore is added.

5. The method for improving denitrification capacity in a converter smelting process according to claim 1, characterized in that, Argon gas supply intensity: 0.008-0.01 Nm 3 / (t·min).

6. The method for improving denitrification capacity in a converter smelting process according to claim 1, characterized in that, The period from the start of converter smelting to 5-6 minutes of blowing is the early stage of smelting, during which the oxygen lance position should be controlled at 1.8-2.0 meters.

7. The method for improving denitrification capacity in a converter smelting process according to claim 1, characterized in that, The period from when the materials are added to when oxygen supply ends is 1-2 minutes before the end of the smelting process, during which the oxygen lance position is controlled at 1.8-2.2 meters.

8. The method for improving denitrification capacity in a converter smelting process according to claim 1, characterized in that, The period from 1-2 minutes before the end of oxygen supply to the end of blowing is the later stage of smelting, and the oxygen lance position should be controlled at 1.6-1.8 meters.

Images