Tundish protection pouring method for large high-quality steel ingot

Abstract

The invention discloses an intermediate tank protection pouring method for a large-scale high-quality steel ingot, which comprises the following steps of: additionally arranging an argon protection cover (2) on an intermediate tank (1) to form a sealed environment in the tank, specifically, opening an argon pipeline (4) of a cover plate (21) for one time 30-60 minutes before casting, filling argon, controlling the pressure of the argon pipeline to be 0.3-0.6 MPa and the purity of argon to be gt; the flow rate is 200-400 L / min, and the steel casting condition is met after the oxygen content in the closed space of the tank body is lower than 100 ppm; the long nozzle (3) is inserted into the intermediate tank (1) through the secondary light cover plate (22), and then the secondary light cover plate (22) is dragged to be connected with a steel ladle collector nozzle; the radar automatic control system (23) controls an oil cylinder and adjusts the pouring speed of the molten steel; and after pouring is finished, the long nozzle is moved out, argon is closed, and steel pouring is completed. The method has the advantages of avoiding oxidation pollution of molten steel, and improving the internal quality of steel ingots and the flaw detection qualification rate of super-thick steel plates.

Description

Technical Field

[0001] The present invention belongs to the technical field of mold casting of steel, and particularly relates to a tundish protected casting method for large high-quality steel ingots. Background Art

[0002] In the process of ingot mold casting, pouring is the most important link. With the development of metallurgical technology, the quality requirements for large single-weight and extra-thick steel ingots are continuously increasing. Some finished products of offshore extra-thick plates even require meeting the special first-class flaw detection standard of energy consumption. Therefore, higher requirements are put forward for mold casting technology.

[0003] Currently, most mold castings adopt the open bottom-pouring method. Molten steel is quickly poured from the ladle into the tundish, and then flows from the runner brick at the bottom of the tundish to the bottom of the ingot mold to complete the mold filling. However, since the molten steel is exposed during pouring, the molten steel is easily re-oxidized by air, forming a large number of endogenous inclusions, which affects the purity of the molten steel. To avoid the above situation, materials such as protective slag or covering agent are mostly added to the tundish to prevent the oxidation of molten steel. However, often due to the too-fast pouring speed in the tundish, the molten steel rolls severely, causing slag entrainment and resulting in unqualified flaw detection of extra-thick steel plates. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems of slag entrainment of molten steel, easy oxidation, low purity of steel ingots, and low qualified rate of flaw detection of steel plates during the existing pouring process, and provides a tundish protected casting method for large high-quality steel ingots, which effectively avoids the oxidation and pollution of molten steel and improves the internal quality of large steel ingots and the qualified rate of flaw detection of extra-thick steel plates.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions: A tundish protected casting method for large high-quality steel ingots includes installing an argon protection cover on the tundish to form a sealed environment inside the tundish. The argon protection cover consists of a primary cover plate, a secondary lightweight cover plate, and a radar automatic control system. After the molten steel is poured, the long nozzle is removed, and the argon protection of the tundish is closed. The specific steel pouring process includes the following steps: (1) Open the argon gas pipeline of the primary cover plate of the tundish to fill argon 30 - 60 minutes before starting pouring. Set the pressure of the argon gas pipeline to 0.3 - 0.6 MPa, the argon gas purity > 99.999%, and the flow rate to 200 - 400 L / min. When the oxygen content in the sealed space of the tundish is lower than 100 ppm, the pouring condition is met; (2) Insert the long nozzle into the tundish through the secondary lightweight cover plate of the argon protection cover; (3) Drag the secondary lightweight cover plate of the argon protection cover by the long nozzle to connect with the sub-ladle nozzle; (4) Control the oil cylinder through the radar automatic control system, and then adjust the opening and closing degree of the slide plate to control the pouring speed of the molten steel; After the pouring is completed, remove the long nozzle and close the argon gas of the first cover plate of the tundish to complete the steel pouring.

[0006] Furthermore, the first cover plate of the argon gas protection cover is a steel cover plate, and the inner diameter of the argon gas pipeline therein is 18 mm and the outer diameter is 22 mm.

[0007] Furthermore, the entire argon gas pipeline of the first cover plate is in a U shape and covers above the inner cavity of the tundish. An argon gas outlet hole is opened every 30 - 50 mm on the argon gas pipeline. The diameter of the argon gas outlet hole is 5 mm and the opening is downward. The argon gas is discharged into the tundish through the argon gas outlet holes of the pipeline to achieve the purpose of protecting the pouring.

[0008] Furthermore, the second light cover plate is made of high-temperature resistant fiberboard material, and the second light cover plate slides on the first cover plate.

[0009] Furthermore, the radar automatic control system is installed on the first cover plate, with a detection distance of 0 - 30 m and a detection temperature range of -40 - 1600 °C. After processing the measured liquid level height signal, the radar transmits it to the oil cylinder, so as to achieve the purpose of controlling the steel pouring speed.

[0010] Furthermore, during the process of the radar controlling the steel pouring speed, the long nozzle drags the second light cover plate, so that the inside of the tundish is always in a sealed state during the steel pouring process to prevent secondary oxidation of the molten steel.

[0011] Furthermore, in the step (1), an argon gas outlet hole with a diameter of 5 mm and opening downward is opened every 30 mm on the argon gas pipeline. The argon gas purity is set >99.999%, the argon gas flow rate is 380 L / min, the argon gas pressure is 0.57 MPa, and the argon gas of the tundish is filled 40 minutes before the start of pouring.

[0012] Furthermore, in the step (1), an argon gas outlet hole with a diameter of 5 mm and opening downward is opened every 50 mm on the argon gas pipeline. The argon gas purity is set >99.999%, the argon gas flow rate is 260 L / min, the argon gas pressure is 0.39 MPa, and the argon gas of the tundish is filled 60 minutes before the start of pouring.

[0013] Furthermore, in the step (1), an argon gas outlet hole with a diameter of 5 mm and opening downward is opened every 50 mm on the argon gas pipeline. The argon gas purity is set >99.999%, the argon gas flow rate is 260 L / min, the argon gas pressure is 0.39 MPa, and the argon gas of the tundish is filled 40 minutes before the start of pouring.

[0014] Further, in the step (1), argon gas outlet holes with a diameter of 5 mm downward are opened every 30 - 50 mm on the argon gas pipeline. The purity of argon gas is set to be >99.999%, the argon gas flow rate is 200 - 400 L / min, the argon gas pressure is 0.3 - 0.6 MPa, and the argon gas filling for the tundish is started at least 30 minutes before pouring.

[0015] Compared with the prior art, the advantages of the technical solution of the present invention are specifically as follows: (1) Through the perfect cooperation of the primary cover plate, secondary cover plate of the tundish protection cover and the radar liquid level automatic control system, the present invention ensures the tightness of the tundish during the whole process of pouring molten steel, realizes the whole-process argon gas protection pouring, avoids the contact between molten steel and air, prevents the secondary oxidation of molten steel, and has a good protection pouring effect; (2) The present invention installs a radar liquid level automatic control device on the tundish protection cover. By measuring the height of the molten steel liquid level in the tundish through radar signals, the opening degrees of the oil cylinder and the slide plate are controlled. On the one hand, the instability of manual operation is avoided, and the pouring speed of molten steel is ensured; on the other hand, through radar control, the synchronous movement of the long nozzle and the secondary lightweight cover plate is realized, further ensuring the full sealing of the tundish, preventing the secondary oxidation of molten steel and the generation of inclusions; (3) After the whole-process argon gas protection, the present invention does not need to add flux or covering agent, avoiding the slag entrainment of molten steel, improving the purity of molten steel, and enhancing the flaw detection qualification rate and product quality of extra-thick steel plates. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is the assembly structure schematic diagram of the argon gas protection cover and the tundish of the present invention; Figure 2 is the top view of the primary cover plate of the present invention. DETAILED DESCRIPTION OF THE INVENTION Example 1

[0017] To make the present invention clearer and more understandable, a tundish protection pouring method for a large high-quality steel ingot of the present invention is further described below. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0018] See Figure 1 and Figure 2 , an argon gas protection cover 2 is provided on the upper part of the tundish 1 to form a sealed environment inside the tundish 1. The argon gas protection cover 2 is composed of a primary cover plate 21, a secondary lightweight cover plate 22 and a radar automatic control system 23. The entire argon gas pipeline 4 of the primary cover plate 21 is in a U shape and covers above the inner cavity of the tundish 1. One end of the argon gas pipeline 4 is connected with a quick-change joint 5, and the other end is connected with an argon gas valve 6. A rectangular notch 21a is provided on the side of the primary cover plate 21 facing the long nozzle 3, and lifting lugs 7 are provided on the other three sides. The secondary lightweight cover plate 22 is arranged above the rectangular notch 21a.

[0019] In this embodiment, the argon gas pipeline 4 on the primary cover plate 21 above the tundish 1 has an outer diameter of 22 mm and an inner diameter of 18 mm. An argon gas outlet hole with a diameter of 5 mm downward is opened every 30 mm on the argon gas pipeline 4. The argon gas purity is set to >99.999%, the argon gas flow rate is 380 L / min, the argon gas pressure is 0.57 MPa, and the argon gas filling for the tundish is turned on 40 minutes before casting. During the casting process, a radar liquid level automatic control system is used. A total of 90 tons of Q355 molten steel is cast, and the total casting time is 17 minutes. When casting 50 ± 5 tons of molten steel, 3 samples are randomly taken at the overflow port of the tundish, and 3 comparative samples are taken after the refining is completed to detect the acid-soluble aluminum loss. The higher the ratio of acid-soluble aluminum to total aluminum (acid-soluble aluminum + aluminum oxide), the less the aluminum oxidation of the molten steel and the better the protective casting effect.

[0020] The ratios of acid-soluble aluminum in the molten steel in refining and the tundish are shown in Table 1 below:

[0021] As can be seen from Table 1 above, during the casting process in the tundish, the ratio of acid-soluble aluminum decreased from an average of 0.9717 to 0.9139, and the average reduction ratio of acid-soluble aluminum loss was 5.95%. Example 2

[0022] In this embodiment, the argon gas pipeline 4 on the primary cover plate 21 above the tundish 1 has an outer diameter of 22 mm and an inner diameter of 18 mm. An argon gas outlet hole with a diameter of 5 mm downward is opened every 50 mm on the argon gas pipeline 4. The argon gas purity is set to >99.999%, the argon gas flow rate is 260 L / min, the argon gas pressure is 0.39 MPa, and the argon gas filling for the tundish is turned on 60 minutes before casting. During the casting process, a radar liquid level automatic control system is used. A total of 90 tons of Q355 molten steel is cast, and the total casting time is 17 minutes. When casting 50 ± 5 tons of molten steel, 3 samples are randomly taken at the overflow port of the tundish, and 3 comparative samples are taken after the refining is completed to detect the acid-soluble aluminum loss. The higher the ratio of acid-soluble aluminum to total aluminum (acid-soluble aluminum + aluminum oxide), the less the aluminum oxidation of the molten steel and the better the protective casting effect.

[0023] The ratios of acid-soluble aluminum in the molten steel in refining and the tundish are shown in Table 2 below:

[0024] As can be seen from Table 2 above, during the casting process in the tundish, the ratio of acid-soluble aluminum decreased from an average of 0.9407 to 0.8720, and the average reduction ratio of acid-soluble aluminum loss was 7.29%. Example 3

[0025] In this embodiment, the outer diameter of the argon gas pipeline 4 of the primary cover plate 21 above the tundish 1 is 22 mm, and the inner diameter is 18 mm. An argon gas outlet hole with a diameter of 5 mm downward is opened every 50 mm on the argon gas pipeline 4. The purity of the argon gas is set to be >99.999%, the argon gas flow rate is 260 L / min, and the argon gas pressure is 0.39 MPa. The argon gas filling of the tundish is started 40 minutes before the start of casting. During the casting process, a radar liquid level automatic control system is used. A total of 90 tons of Q355 molten steel is cast, and the total casting time is 17 minutes. When casting 50 ± 5 tons of molten steel, 3 samples are randomly taken at the overflow port of the tundish, and 3 comparative samples are taken after the refining is completed to detect the loss of acid-soluble aluminum. The higher the ratio of acid-soluble aluminum to total aluminum (acid-soluble aluminum + aluminum oxide), the less the aluminum oxidation of the molten steel and the better the effect of protected casting.

[0026] The ratios of acid-soluble aluminum in the molten steel during refining and in the tundish are shown in Table 3 below:

[0027] As can be seen from Table 3 above, during the casting process in the tundish, the ratio of acid-soluble aluminum decreased from an average of 0.9629 to 0.8924, and the average loss ratio of acid-soluble aluminum decreased by 7.31%.

[0028] In summary, there is a small amount of acid-soluble aluminum loss during the production process of protected casting from refining to the tundish. The ratio of acid-soluble aluminum decreased by 5.95% - 7.31%, meeting the production requirements of extra-thick slabs. The primary cover plate and the secondary lightweight cover plate of the tundish protection cover can form a closed environment in the tundish. During the filling process of argon gas, the excess air can be quickly expelled before the start of casting in the tundish, and a stable argon gas atmosphere can be formed above the molten steel surface in the tundish during the production process, ensuring that the molten steel does not come into contact with air throughout the casting process, thereby ensuring the purity of the molten steel during casting, making the produced large extra-thick slabs have better internal quality. At the same time, after full argon protection, there is no need to add protective slag or covering agent, avoiding problems such as molten steel slag entrainment and flaw detection problems caused by ingot slag entrainment in extra-thick plates, improving the flaw detection qualification rate and product quality.

[0029] In addition to the above embodiments, the present invention can also have other implementation manners. All technical solutions formed by equivalent replacement or equivalent transformation fall within the protection scope required by the present invention.

Claims

1. A tundish protective casting method for large-sized high-quality steel ingots, characterized in that: It includes installing an argon protection cover (2) on the tundish (1) to form a sealed environment inside the tundish (1). The argon protection cover (2) consists of a primary cover plate (21), a secondary lightweight cover plate (22), and a radar automatic control system (23). After the molten steel is poured, the long nozzle (3) is removed, and the argon protection of the tundish is closed. The specific steel pouring process includes the following steps: Step 1: Open the argon gas pipeline (4) of the primary cover plate (21) of the tundish (1) to fill argon 30 - 60 minutes before pouring. Set the pressure of the argon gas pipeline to 0.3 - 0.6 MPa, the argon gas purity > 99.999%, and the flow rate to 200 - 400 L / min. When the oxygen content in the closed space of the tundish (1) is lower than 100 ppm, the steel pouring condition is met; Step 2: Insert the long nozzle (3) into the tundish (1) through the secondary lightweight cover plate (22) of the argon protection cover (2); Step 3: The long nozzle (3) drags the secondary lightweight cover plate (22) of the argon protection cover (2) to connect with the sub - nozzle of the ladle; Step 4: Control the oil cylinder through the radar automatic control system (23), and then adjust the opening and closing degree of the slide plate to control the molten steel pouring speed; Step 5: After the pouring is completed, remove the long nozzle (3), and close the argon gas of the primary cover plate (21) of the tundish (1) to complete the steel pouring.

2. The tundish protection pouring method for large - sized high - quality steel ingots according to claim 1, characterized in that: The primary cover plate (21) of the argon protection cover (2) is a steel cover plate, and the inner - diameter of the argon gas pipeline (4) arranged therein is 18 mm and the outer - diameter is 22 mm.

3. The tundish protection pouring method for large - sized high - quality steel ingots according to claim 1 or 2, characterized in that: The entire argon gas pipeline (4) of the primary cover plate (21) is in a U - shape, covering the upper part of the inner cavity of the tundish (1). An argon gas outlet hole is opened every 30 - 50 mm on the argon gas pipeline (4). The diameter of the argon gas outlet hole is 5 mm and the opening is downward. The argon gas is discharged into the tundish (1) through the argon gas outlet holes of the pipeline.

4. The tundish protection pouring method for large - sized high - quality steel ingots according to claim 1 or 2, characterized in that: The secondary lightweight cover plate (22) is made of high - temperature - resistant fiberboard material, and the secondary lightweight cover plate (22) slides on the primary cover plate (21).

5. The tundish protection pouring method for large - sized high - quality steel ingots according to claim 1 or 2, characterized in that: The radar automatic control system (23) is installed on the primary cover plate (21), with a detection distance of 0 - 30 m and a detection temperature range of - 40 - 1600 °C. The radar processes the measured liquid level height signal and transmits it to the oil cylinder to control the molten steel pouring speed.

6. The tundish protection pouring method for large - sized high - quality steel ingots according to claim 5, characterized in that: During the process of the radar controlling the molten steel pouring speed, the long nozzle (3) drags the secondary lightweight cover plate (22) to keep the inside of the tundish (1) in a sealed state during the steel pouring process.

7. The tundish protection pouring method for large - sized high - quality steel ingots according to claim 3, characterized in that: In the first step, an argon gas outlet hole with a diameter of 5 mm facing downwards is opened every 30 mm on the argon gas pipeline (4). The purity of the argon gas is set to be >99.999%, the argon gas flow rate is 380 L / min, the argon gas pressure is 0.57 MPa, and the argon gas filling of the tundish is started 40 minutes before casting.

8. The tundish protective casting method for large-sized high-quality steel ingots according to claim 3, wherein: In the first step, an argon gas outlet hole with a diameter of 5 mm facing downwards is opened every 50 mm on the argon gas pipeline (4). The purity of the argon gas is set to be >99.999%, the argon gas flow rate is 260 L / min, the argon gas pressure is 0.39 MPa, and the argon gas filling of the tundish is started 60 minutes before casting.

9. The tundish protective casting method for large-sized high-quality steel ingots according to claim 3, wherein: In the first step, an argon gas outlet hole with a diameter of 5 mm facing downwards is opened every 50 mm on the argon gas pipeline (4). The purity of the argon gas is set to be >99.999%, the argon gas flow rate is 260 L / min, the argon gas pressure is 0.39 MPa, and the argon gas filling of the tundish is started 40 minutes before casting.

10. The tundish protective casting method for large-sized high-quality steel ingots according to claim 3, wherein: In the first step, an argon gas outlet hole with a diameter of 5 mm facing downwards is opened every 30 - 50 mm on the argon gas pipeline (4). The purity of the argon gas is set to be >99.999%, the argon gas flow rate is 200 - 400 L / min, the argon gas pressure is 0.3 - 0.6 MPa, and the argon gas filling of the tundish is started at least 30 minutes before casting.

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