A method for removal of inclusions in an RH refining process

Abstract

The application discloses a method for removing inclusions in RH refining process, which reduces the number of driving gas nozzles on the left side of the riser pipe in the early stage of inclusion generation and removal after aluminum deoxidization; and reduces the outlet flow rate of the molten steel in the down pipe in the small-size inclusion removal stage after all alloy addition until the breaking process, so that the method can create suitable kinetic conditions for the early stage of inclusion removal after aluminum deoxidization and the small-size inclusion removal stage after all alloy addition until the breaking process, and high-efficiency removal of inclusions can be realized without additional addition of additional materials. The method is simple and controllable, consumes less argon and steam, and has small temperature loss.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel smelting technology, and specifically relates to a method for removing inclusions during RH refining. Background Technology

[0002] Inclusions in steel are generally considered harmful. For steel grades produced using the "hot metal pretreatment-converter-RH-continuous casting" process, the primary site for inclusion removal is the RH refining process. The RH metallurgical reactor mainly consists of a ladle, a vacuum chamber, and immersion pipes connecting them, forming a space for molten steel flow. Its working principle is that, under vacuum and with the driving gas performing work, molten steel flows from the ladle through the riser into the vacuum chamber and then back into the ladle through the downcomer, continuously circulating in this manner. Upon entering the vacuum chamber, the bubbles from the driving gas burst like a fountain as they leave the molten steel surface, undergoing degassing and decarburization reactions within the vacuum chamber. The molten steel stream entering the ladle through the downcomer stirs and mixes the molten steel within the ladle.

[0003] Steel circulation flow rate is a key parameter in RH refining, referring to the flow rate of molten steel passing through the vacuum chamber per unit time. Its magnitude primarily depends on the vacuum level, the inner diameter of the immersion tube, and the flow rate of the driving gas. Simultaneously, the circulation flow rate also determines the outlet velocity of the molten steel in the downcomer. Generally, it is necessary to control the circulation flow rate to ensure an appropriate velocity of the molten steel returning to the ladle. This avoids both excessive velocity that causes the steel to directly impact the bottom of the ladle and insufficient velocity that would immediately draw the returning molten steel into the vacuum chamber, creating a short circuit in the circulation.

[0004] Inclusions begin to form during deoxidation. In subsequent circulation, these inclusions grow, collide, and float to the surface, resulting in a continuous decrease in both the number and size of inclusions remaining in the steel. The net force acting on the remaining small inclusions in the steel is insufficient to support their ascent, and they are entrained by the steel flow, making separation from the molten steel difficult. Therefore, promoting the removal of small inclusions is a key technological challenge.

[0005] Chinese patent CN111944953A discloses a method for reducing the number of small-sized non-metallic inclusions in steel. Specifically, it discloses the use of nitrogen addition and nitrogen precipitation to remove inclusions by utilizing the principle of removing inclusions by precipitating tiny bubbles in molten steel, thus solving the problem of high requirements for inclusions in high-quality special steel and the difficulty in effectively removing small-sized inclusions.

[0006] Chinese patent CN101323894A discloses a process for removing fine inclusions through ladle refining, specifically disclosing that the removal of inclusions is promoted by using small bubbles generated by feeding wire (core wire containing calcium carbonate).

[0007] Chinese patent CN108504822A discloses a method for controlling the morphology of small-particle-size alumina inclusions in ultra-low carbon steel. Specifically, it discloses adding quicklime to the vacuum chamber in the later stage of RH refining to modify the surface of small-particle-size Al2O3 inclusions that have not been removed by flotation, generating CaO-Al2O3 inclusions to avoid clogging of the nozzle.

[0008] The methods described above either extend the RH process to allow inclusions to float to the surface, but these methods are often ineffective due to time constraints imposed by production schedules. Alternatively, they involve adding modifiers such as calcium ferric sulfate to the RH process to alter the inclusion properties, but this can easily result in large-particle calcium aluminates or inclusions containing modifiers, potentially affecting the steel's machinability or service performance. No existing technology discloses a method for achieving efficient inclusion removal by adjusting the RH process itself without adding additional materials. Summary of the Invention

[0009] To address the aforementioned technical problems, this invention provides a method for removing inclusions during RH refining. This method relies on adjusting the number of driving gas nozzles, vacuum level, and driving gas flow rate during the RH process to create suitable kinetic conditions for the early stages of inclusion removal after aluminum addition and deoxidation, as well as for the removal of small-sized inclusions after all alloys have been added and during the void-breaking process. This method achieves efficient inclusion removal without the need for additional materials. It is simple and controllable to operate, consumes little argon and steam, and experiences minimal temperature loss.

[0010] The technical solution adopted in this invention is as follows:

[0011] A method for removing inclusions in RH refining involves reducing the number of drive gas nozzles located on the left side of the riser in the early stage of inclusion formation and removal after aluminum deoxidation; and reducing the outlet flow rate of molten steel in the downcomer in the small inclusion removal stage after all alloys are added until the cavitation process.

[0012] The method for removing inclusions during the RH refining process includes the following steps:

[0013] (1) After aluminum deoxidation is completed, close some of the driving gas nozzles located on the left side of the riser to reduce the number of nozzles and keep the vacuum and driving gas flow rate consistent with those before deoxidation.

[0014] (2) Determine the cycle time based on the activity oxygen before aluminum deoxidation;

[0015] (3) After the cycle is completed, open all the driving gas nozzles, add the alloy, and let the molten steel circulate 2 to 3 times;

[0016] (4) Reduce the outlet flow rate of molten steel in the downcomer by 20% to 50%, continue to circulate for 3 to 6 minutes, then break the vent, and pour the molten steel onto the continuous casting platform. Continue to circulate for 3 to 6 minutes, then break the vent, and pour the molten steel onto the continuous casting platform.

[0017] In step (1), the number of nozzles is reduced by 1 / 8 to 1 / 4.

[0018] In step (2), when the active oxygen before aluminum deoxidation is ≤250ppm, the cycle is performed for 3 minutes.

[0019] In step (2), when the active oxygen before aluminum deoxidation is 251-300 ppm, the cycle is performed for 4 minutes.

[0020] In step (2), when the active oxygen before aluminum deoxidation is 301-350 ppm, the cycle is performed for 5 minutes.

[0021] In step (2), when the active oxygen before aluminum deoxidation is >350ppm, the cycle is 6 minutes.

[0022] In step (3), the vacuum level and driving gas flow rate remain the same as before deoxidation during the alloying process.

[0023] In step (4), the outlet flow rate of molten steel in the downcomer is reduced by 20% to 50% by turning off the first-stage vacuum pump, adjusting the vacuum level to 3 to 8 kPa, and reducing the driving gas flow rate by 20% to 50%.

[0024] After removal by the aforementioned method, the number density of oxide inclusions in the molten steel is less than 0.96 inclusions / mm. 2 The number density of inclusions larger than 15 μm is less than 0.03 inclusions / mm. 2 .

[0025] The movement of inclusions depends on the magnitude and direction of the combined force of gravity, buoyancy, and the drag force of the molten steel. In a vacuum chamber, it is desirable for inclusions in the molten steel to move upwards from the interior of the molten pool, and the upward distance should be as short as possible to facilitate rapid removal from the molten steel. During the process of the molten steel entering the ladle through the downcomer, inclusions are subjected to gravity, buoyancy, the drag force of the molten steel, and the downward pulling force of the molten steel. The downward pulling force of the molten steel is related to the flow velocity of the molten steel at the outlet of the downcomer. It is desirable for inclusions to move upwards while experiencing a smaller downward pulling force from the molten steel, and for the upward movement to be as short as possible. This invention promotes inclusion removal by adjusting the RH process parameters to ensure that the movement trajectory of inclusions develops in the direction of detachment from the molten steel and shortens the movement distance.

[0026] The method for removing inclusions in the RH refining process provided by this invention, in the early stage of inclusion formation and removal after aluminum deoxidation, reduces the number of driving gas nozzles so that the height and flow rate of molten steel near the left sidewall of the vacuum chamber are lower than those in other areas. This allows the bubbles from the easily broken driving gas to splash inclusions in the molten steel onto the refractory material on the sidewall of the vacuum chamber for removal. In the stage after all alloys are added until the removal of small-sized inclusions during the vacuum breaking process, the outlet flow rate of molten steel in the downcomer is reduced, thereby reducing the travel distance of the molten steel stream after entering the ladle and shortening the path of inclusions in the molten steel within the ladle.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The method provided by this invention creates reasonable kinetic conditions for the early stage of inclusion removal after aluminum deoxidation and for the small-sized inclusion removal stage after all alloys are added until the void breaking process, achieving efficient inclusion removal without the need for additional materials.

[0029] 2. The method provided by this invention is simple and controllable to operate, consumes less argon and steam, and has minimal temperature loss. Detailed Implementation

[0030] The present invention provides a method for removing inclusions during RH refining, comprising the following steps:

[0031] (1) After deoxygenation is completed, close some of the driving gas nozzles located on the left side of the riser pipe to reduce the number of nozzles by 1 / 8 to 1 / 4, and keep the vacuum and driving gas flow rate consistent with those before deoxygenation.

[0032] (2) The circulation time is determined based on the active oxygen before aluminum deoxidation. When the active oxygen before aluminum deoxidation is ≤250ppm, the circulation time is 3 minutes; when the active oxygen is 251~300ppm, the circulation time is 4 minutes; when the active oxygen is 301~350ppm, the circulation time is 5 minutes; when the active oxygen is >350ppm, the circulation time is 6 minutes.

[0033] (3) After circulating for 3 to 6 minutes, open all the driving gas nozzles and add other alloys according to the steel grade requirements. After the alloys are added, let the molten steel circulate 2 to 3 times. The vacuum degree and driving gas flow rate should be kept consistent with those before deoxidation.

[0034] (4) After 2 to 3 cycles, turn off the first-stage vacuum pump, adjust the vacuum level from less than 1 kPa to 3 to 8 kPa, reduce the driving gas flow rate by 20% to 50%, continue to circulate for 3 to 6 minutes, break the vacuum, and pour the molten steel onto the continuous casting platform.

[0035] The present invention will now be described in detail with reference to the embodiments.

[0036] Example 1

[0037] Smelting ultra-low carbon steel, IF steel, grade DC04. The vacuum degree before deoxidation is 85 Pa, the RH driving gas nozzles are all 16 fully open, and the driving gas flow rate is 180 m³ / s. 3 / h.

[0038] After aluminum addition and deoxidation, close the three nozzles on the left side of the riser pipe, keeping the vacuum and driving gas flow rate unchanged. When the active oxygen level before aluminum addition and deoxidation is 276 ppm, after 4 minutes of circulation, open all driving gas nozzles and add alloy manganese and ferrotitanium. After adding the alloys, circulate the molten steel twice, keeping the vacuum and driving gas flow rate consistent with before deoxidation. After two cycles, turn off the primary vacuum pump, adjust the vacuum from 85 Pa to 3.5 kPa, and adjust the driving gas flow rate from 180 m³ / s. 3 / h adjusted to 140m 3 / h. After circulating for 5 minutes, the air is broken, and the molten steel is poured onto the continuous casting platform.

[0039] After the RH cavity was broken, a bucket sampler was used to collect molten steel samples for inclusion analysis. The oxide inclusion number density of the samples was 0.96 inclusions / mm². 2 The number density of inclusions larger than 15 μm was 0.03 inclusions / mm. 2 .

[0040] Example 2

[0041] Smelting ultra-low carbon steel, IF steel, grade DC04. The vacuum degree before deoxidation is 101 Pa, the RH driving gas nozzles are all 16 fully open, and the driving gas flow rate is 180 m³ / s. 3 / h.

[0042] After aluminum addition and deoxidation, close the three nozzles on the left side of the riser pipe, keeping the vacuum and driving gas flow rate unchanged. When the active oxygen level before aluminum addition and deoxidation is 268 ppm, circulate for 4 minutes, then open all driving gas nozzles and add alloy manganese and ferrotitanium. After adding the alloys, circulate the molten steel twice, keeping the vacuum and driving gas flow rate consistent with before deoxidation. After two cycles, turn off the primary vacuum pump, adjust the vacuum from 101 Pa to 5 kPa, and adjust the driving gas flow rate from 180 m³ / s. 3 / h adjusted to 110m 3 / h. After circulating for 5 minutes, the air is broken, and the molten steel is poured onto the continuous casting platform.

[0043] After the RH cavity was broken, a bucket sampler was used to collect molten steel samples for inclusion analysis. The oxide inclusion number density of the samples was 0.74 inclusions / mm². 2 The number density of inclusions larger than 15 μm was 0.01 inclusions / mm. 2 .

[0044] Example 3

[0045] Smelting ultra-low carbon steel, IF steel, grade DC04. The vacuum degree before deoxidation is 65 Pa, the RH driving gas nozzles are all 16 fully open, and the driving gas flow rate is 180 m³ / s. 3 / h.

[0046] After aluminum addition and deoxidation, close the three nozzles on the left side of the riser pipe, keeping the vacuum and driving gas flow rate unchanged. When the active oxygen level before aluminum addition and deoxidation is 218 ppm, circulate for 3 minutes, then open all driving gas nozzles and add alloy manganese and ferrotitanium. After adding the alloys, circulate the molten steel twice, keeping the vacuum and driving gas flow rate consistent with before deoxidation. After two cycles, turn off the primary vacuum pump, adjust the vacuum from 65 Pa to 7 kPa, and adjust the driving gas flow rate from 180 m³ / s. 3 / h adjusted to 100m 3 / h. After circulating for 5 minutes, the air is broken, and the molten steel is poured onto the continuous casting platform.

[0047] After the RH cavity was broken, a bucket sampler was used to collect molten steel samples for inclusion analysis. The oxide inclusion number density of the samples was 0.48 inclusions / mm². 2 The number density of inclusions larger than 15 μm was 0.004 inclusions / mm. 2 .

[0048] Comparative Example 1

[0049] Smelting ultra-low carbon steel, IF steel, grade DC04. The vacuum degree before deoxidation is 98 Pa, the RH driving gas nozzles are all 16 fully open, and the driving gas flow rate is 180 m³ / s. 3 / h.

[0050] The number of driving gas nozzles, vacuum level, and driving gas flow rate remain constant from the start of aluminum deoxidation until the cavitation process. When the active oxygen level before aluminum deoxidation is 236 ppm, after 4 minutes of circulation, alloy manganese and ferrotitanium are added. After the alloys are added, the molten steel is circulated for 6 minutes, the cavitation is broken, and the molten steel is poured onto the continuous casting platform.

[0051] After the RH cavity was broken, a bucket sampler was used to collect molten steel samples for inclusion analysis. The oxide inclusion number density of the samples was 2.23 inclusions / mm². 2 The number density of inclusions larger than 15 μm was 0.24 inclusions / mm. 2 .

[0052] Comparative Example 2

[0053] Smelting ultra-low carbon steel, IF steel, grade DC04. The vacuum degree before deoxidation is 100 Pa, the RH driving gas nozzles are all 16 fully open, and the driving gas flow rate is 180 m³ / s. 3 / h.

[0054] The number of driving gas nozzles, vacuum level, and driving gas flow rate remain constant from the start of aluminum deoxidation until the cavitation process. When the active oxygen level before aluminum deoxidation is 321 ppm, after 4 minutes of circulation, alloy manganese and ferrotitanium are added. After the alloys are added, the molten steel is circulated for 6 minutes, the cavitation is broken, and the molten steel is poured onto the continuous casting platform.

[0055] After the RH cavity was broken, a bucket sampler was used to collect molten steel samples for inclusion analysis. The oxide inclusion number density of the samples was 3.19 inclusions / mm². 2 The number density of inclusions larger than 15 μm was 0.17 inclusions / mm. 2 .

[0056] Comparative Example 3

[0057] Smelting ultra-low carbon steel, IF steel, grade DC04. The vacuum degree before deoxidation is 78 Pa, the RH driving gas nozzles are all 16 fully open, and the driving gas flow rate is 180 m³ / s. 3 / h.

[0058] The number of driving gas nozzles, vacuum level, and driving gas flow rate remain constant from the start of aluminum deoxidation until the cavitation process. When the active oxygen level before aluminum deoxidation is 211 ppm, after 4 minutes of circulation, alloy manganese and ferrotitanium are added. After the alloys are added, the molten steel is circulated for 6 minutes, the cavitation is broken, and the molten steel is poured onto the continuous casting platform.

[0059] After the RH cavity was breached, a bucket sampler was used to collect molten steel samples for inclusion analysis. The oxide inclusion number density of the samples was 2.08 inclusions / mm². 2 The number density of inclusions larger than 15 μm was 0.21 inclusions / mm. 2 .

[0060] The above detailed description of a method for removing inclusions in an RH refining process, with reference to the embodiments, is illustrative rather than limiting. Several embodiments may be listed within the defined scope. Therefore, variations and modifications that do not depart from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A method for removing inclusions during RH refining, characterized in that, In the early stages of inclusion formation and removal after aluminum deoxidation, reduce the number of driving gas nozzles located on the left side of the riser. After all alloys are added until the removal of small-sized inclusions during the void-breaking process, reduce the outlet flow rate of molten steel in the downcomer. Specifically, by turning off the first-stage vacuum pump, adjusting the vacuum level to 3~8 kPa, and reducing the driving gas flow rate by 20%~50%, the outlet flow rate of molten steel in the downcomer is reduced by 20%~50%.

2. The method for removing inclusions during RH refining according to claim 1, characterized in that, Includes the following steps: (1) After aluminum addition and deoxidation are completed, close some of the driving gas nozzles located on the left side of the riser pipe to reduce the number of nozzles and keep the vacuum and driving gas flow rate consistent with those before deoxidation. (2) Determine the cycle time based on the activity oxygen before aluminum deoxidation; (3) After the cycle is completed, open all the driving gas nozzles, add the alloy, and let the molten steel circulate 2 to 3 times; (4) Reduce the outlet flow rate of the molten steel in the downcomer by 20% to 50%, continue to circulate for 3 to 6 minutes, then break the air and pour the molten steel onto the continuous casting platform.

3. The method for removing inclusions during RH refining according to claim 2, characterized in that, In step (1), the number of nozzles is reduced by 1 / 8 to 1 / 4.

4. The method for removing inclusions during RH refining according to claim 2, characterized in that, In step (2), when the active oxygen before aluminum deoxidation is ≤250ppm, the cycle is performed for 3 minutes.

5. The method for removing inclusions during RH refining according to claim 2, characterized in that, In step (2), when the active oxygen before aluminum deoxidation is 251~300ppm, the cycle is 4 minutes.

6. The method for removing inclusions during RH refining according to claim 2, characterized in that, In step (2), when the active oxygen before aluminum deoxidation is 301~350ppm, the cycle is 5 minutes.

7. The method for removing inclusions during RH refining according to claim 2, characterized in that, In step (2), when the active oxygen before aluminum deoxidation is >350ppm, the cycle is 6 minutes.

8. The method for removing inclusions during RH refining according to claim 2, characterized in that, In step (3), during the alloying process, the number of nozzles, vacuum level, and driving gas flow rate remain the same as before deoxidation.

9. The method for removing inclusions during RH refining according to any one of claims 1-8, characterized in that, After removal by the aforementioned method, the number density of oxide inclusions in the molten steel is less than 0.96 inclusions / mm. 2 The number density of inclusions larger than 15 μm is less than 0.03 inclusions / mm. 2 .