Continuous casting method for casting molten steel with high hydrogen content

Abstract

The application provides a continuous casting production method for casting high-hydrogen-content molten steel, comprising the following steps: detecting the content of H element in the molten steel in a continuous casting tundish; selecting molten steel with the content of H element reaching a preset range a as target molten steel according to the detection result, wherein 8.5ppm≤a; pouring the target molten steel into a crystallizer by using a low tundish superheat degree, and the tundish superheat degree is controlled to be 0-20℃; adopting a strong cooling process for the molten steel in the crystallizer, the water flow rate of the wide surface of the crystallizer is 5200L / mim-6000L / mim, and the flow speed is 9.5m / s-11.0m / s; the water flow rate of the narrow surface of the crystallizer is 580L / mim-660L / mim, and the flow speed is 9.4m / s-10.8m / s; and the continuous casting speed is 0.8m / min-1.2m / min. The problems of frequent speed reduction caused by sticking alarm and frequent molten steel leakage accidents caused by high hydrogen content in the molten steel can be solved.

Description

Technical Field

[0001] This application relates to the field of steel preparation, specifically to a continuous casting production method for casting molten steel with high hydrogen content. Background Technology

[0002] Hydrogen in molten steel is a harmful element. High hydrogen content in molten steel can cause frequent sticking alarms and speed reductions in continuous casting, and in severe cases, can lead to serious production accidents such as sticking and steel leakage. According to production statistics, when the hydrogen content in molten steel is >8.5 ppm, the sticking alarm speed reduction index increases dramatically, with 21.82 sticking alarm speed reductions per 100 heats of steel, and a sticking and steel leakage incidence rate of 0.54%; this seriously affects the smooth operation of continuous casting and product quality. Therefore, in existing technologies, molten steel is generally dehydrogenated before continuous casting. However, this increases the number of processes, causes material flow chaos, and increases production costs. Summary of the Invention

[0003] In view of this, the embodiments of this application provide a continuous casting production method for casting molten steel with high hydrogen content, which can solve the problems of frequent sticking alarms and speed reductions and frequent steel leakage accidents in continuous casting when the hydrogen content in the molten steel is high.

[0004] The continuous casting production method for casting high-hydrogen-content molten steel provided in this application includes:

[0005] The hydrogen (H) content in the molten steel in the continuous casting tundish was detected. Based on the detection results, molten steel with an H content within a preset range 'a' was selected as the target molten steel, where 8.5 ppm ≤ 'a'. The target molten steel was poured into the crystallizer using a low tundish superheat, with the tundish superheat controlled between 0-20℃. A strong cooling process was used for the molten steel in the crystallizer. The water flow rate on the wide side of the crystallizer was 5200 L / min-6000 L / min, with a flow velocity of 9.5 m / s-11.0 m / s; the water flow rate on the narrow side of the crystallizer was 580 L / min-660 L / min, with a flow velocity of 9.4 m / s-10.8 m / s; and the continuous casting speed was 0.8 m / min to 1.2 m / min.

[0006] According to the embodiments of this application, the thickness of the billet shell exiting the crystallizer is 15mm to 22mm.

[0007] According to the embodiments of this application, the argon flow rate of the stopper rod is controlled to be 5L / min-10L / min; the argon flow rate of the inlet is 4L / min-8L / min.

[0008] According to the embodiments of this application, the argon flow rate of the stopper rod is controlled to be 6L / min-8L / min; the argon flow rate of the inlet is 5L / min-7L / min.

[0009] According to the embodiments of this application, the insertion depth of the drain outlet in the middle package is 90mm-120mm.

[0010] According to the embodiments of this application, the insertion depth of the drain outlet in the middle package is 90mm-100mm.

[0011] According to the embodiments of this application, the crystallizer vibration frequency is 100-120 times / min, the vibration amplitude is 3.0mm-4.5mm, and the skewness is 20%.

[0012] According to the embodiments of this application, the superheat of the low-medium ladle is controlled at 0-10°C.

[0013] Compared with the prior art, the continuous casting production method for casting high-hydrogen-content molten steel provided in this application has at least the following beneficial effects:

[0014] The continuous casting production method for casting high-hydrogen-content molten steel provided in this application uses molten steel with a hydrogen content within the range of 8.5ppm≤a as the target molten steel. By adjusting the process parameters, the superheat of the tundish is controlled at 0-20℃ during the casting of the target molten steel. At the same time, a strong cooling process is adopted, combined with an appropriate continuous casting speed. The purpose is to form a thick billet shell on the meniscus of the crystallizer, increase the strength of the billet shell, increase the gap between the copper plate of the crystallizer and the billet shell, and reduce the friction between the copper plate of the crystallizer and the billet shell. This solves the problems of frequent adhesion alarms and speed reductions and steel leakage accidents in continuous casting with high hydrogen content in molten steel, and makes production run smoothly. Detailed Implementation

[0015] To make the purpose, technical solution, and beneficial technical effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the embodiments described in this specification are merely for explaining this application and are not intended to limit it.

[0016] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, although not explicitly stated, every point or individual value between the endpoints of the range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit and combined with any other point or individual value or with other lower or upper limits to form a range not explicitly stated.

[0017] In the description of this application, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, and "multiple" in "one or more" means two or more.

[0018] The foregoing description of this application is not intended to describe every disclosed implementation or method. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are representative only and should not be construed as exhaustive.

[0019] Hydrogen in molten steel is a harmful element. High hydrogen content in molten steel can cause frequent sticking alarms and speed reductions in continuous casting, and in severe cases, can lead to serious production accidents such as sticking and steel leakage. According to production statistics, when the hydrogen content in molten steel is >8.5 ppm, the sticking alarm speed reduction index increases dramatically, with 21.82 sticking alarm speed reductions per 100 heats of steel, and a sticking and steel leakage incidence rate of 0.54%; this seriously affects the smooth operation of continuous casting and product quality. Therefore, in existing technologies, molten steel is generally dehydrogenated before continuous casting. However, this increases the number of processes, causes material flow chaos, and increases production costs.

[0020] In view of this, the inventors of this application have conducted extensive research with the aim of providing a continuous casting production method for casting molten steel with high hydrogen content, the method comprising:

[0021] The continuous casting production method for casting high-hydrogen-content molten steel provided in this application includes:

[0022] The hydrogen (H) content in the molten steel in the continuous casting tundish was detected. Based on the detection results, molten steel with an H content within a preset range 'a' was selected as the target molten steel, where 8.5 ppm ≤ 'a'. The target molten steel was poured into the crystallizer using a low-temperature tundish superheat, with the tundish superheat controlled between 0-20℃. In the crystallizer, a strong cooling process was used for the molten steel. The water flow rate on the wide side of the crystallizer was 5200 L / min-6000 L / min, with a flow velocity of 9.5 m / s-11.0 m / s; the water flow rate on the narrow side of the crystallizer was 580 L / min-660 L / min, with a flow velocity of 9.4 m / s-10.8 m / s; and the continuous casting speed was 0.8 m / min to 1.2 m / min.

[0023] The inventors observed in actual production that research revealed a dramatic increase in the adhesion alarm rate reduction index when the H content in molten steel was ≥8.5ppm, with 21.82 adhesion alarm rate reductions per 100 heats and an adhesion leakage rate of 0.54%, severely impacting continuous casting production and product quality. Therefore, molten steel with an H content ≥8.5ppm was selected as the target molten steel.

[0024] Specifically, the hydrogen content in the molten steel in the continuous casting tundish is detected by a hydrogen determination device. Molten steel with an hydrogen content ≥ 8.5 ppm is used as the target molten steel. When casting the target molten steel, the tundish superheat is controlled at 0-20℃. The tundish superheat is the measured molten steel temperature minus the steel grade liquid level temperature. At the same time, a strong cooling process is adopted, with the water flow rate on the wide side of the crystallizer being 5200 L / min-6000 L / min and the flow velocity being 9.5 m / s-11.0 m / s; and the water flow rate on the narrow side of the crystallizer being 580 L / min-660 L / min and the flow velocity being 9.4 m / s-10.8 m / s. The purpose is to form a thick billet shell on the meniscus of the crystallizer, increase the strength of the billet shell, increase the gap between the copper plate of the crystallizer and the billet shell, and reduce the friction between the copper plate of the crystallizer and the billet shell. This solves the problems of frequent sticking alarms and speed reductions and steel leakage accidents caused by high hydrogen content in the molten steel, and ensures smooth production.

[0025] For example, the superheat of the intermediate ladle is 1°C, 2°C, 3°C, 4°C, 5°C, 6°C, 7°C, 8°C, 9°C, 10°C, 11°C, 12°C, 13°C, 14°C, 15°C, 16°C, 17°C, 18°C, 19°C, 20°C or any two of the above values.

[0026] Preferably, in some embodiments, the superheat of the low-temperature and medium-temperature package is controlled at 0-10°C.

[0027] For example, the water flow rate across the crystallizer is 5200 L / min, 5250 L / min, 5300 L / min, 5350 L / min, 5400 L / min, 5450 L / min, 5500 L / min, 5550 L / min, 5600 L / min, 5650 L / min, 5700 L / min, 5750 L / min, 5800 L / min, 5850 L / min, 5900 L / min, 5950 L / min, 6000 L / min, or a range of any two of the above values.

[0028] For example, the water flow velocity across the wide face of the crystallizer is 9.5 m / s, 9.6 m / s, 9.7 m / s, 9.8 m / s, 9.9 m / s, 10.0 m / s, 10.1 m / s, 10.2 m / s, 10.3 m / s, 10.4 m / s, 10.5 m / s, 10.6 m / s, 10.7 m / s, 10.8 m / s, 10.9 m / s, 11.0 m / s, or any range of two of the above values.

[0029] For example, the water flow rate of the narrow face of the crystallizer is 580L / min, 585L / min, 590L / min, 595L / min, 600L / min, 605L / min, 610L / min, 615L / min, 620L / min, 625L / min, 630L / min, 635L / min, 640L / min, 645L / min, 650L / min, 655L / min, 660L / min, or a range of any two of the above values.

[0030] For example, the water flow velocity in the narrow face of the crystallizer is 0.8 m / s, 0.9 m / s, 1.0 m / s, 1.1 m / s, 1.2 m / s, 1.3 m / s, 1.4 m / s, 1.5 m / s, 1.6 m / s, or any combination of two of the above values.

[0031] In this embodiment, the water flow rate and casting speed in the crystallizer are matched to obtain a cast billet with good surface quality. The continuous casting speed is set to 0.8 m / min to 1.2 m / min. Within this range, the billet shell thickness exiting the crystallizer can be 15 mm to 22 mm. This shell thickness is sufficient to support the static pressure of the molten steel inside the crystallizer. Simultaneously, a suitable casting speed reduces center segregation in the fan-shaped section of the billet, lowering the risk of cracking and improving the quality of the steel plate.

[0032] For example, the continuous casting speed is 0.8 m / min, 0.9 m / min, 1.0 m / min, 1.1 m / min, 1.2 m / min, 1.3 m / min, 1.4 m / min, 1.5 m / min, 1.6 m / min or any range of two of the above values.

[0033] In some embodiments, the thickness of the billet shell exiting the crystallizer is 15 mm to 22 mm. For example, the thickness of the billet shell exiting the crystallizer is 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, 20 mm, 21 mm, 22 mm, or any combination of two of the above values.

[0034] In some implementations, the argon flow rate of the stopper rod is controlled at 5 L / min-10 L / min; the argon flow rate of the inlet is controlled at 4 L / min-8 L / min.

[0035] By controlling a larger argon flow rate in the stopper rod, the melting of the protective slag can be promoted, the slag consumption can be increased, and the slag renewal rate can be improved. At the same time, the rising of argon bubbles can carry away hydrogen bubbles in the liquid slag film, reducing the number of pores in the solid slag film of the protective slag.

[0036] For example, the argon flow rate of the stopper is 5 L / min, 6 L / min, 7 L / min, 8 L / min, 9 L / min, 10 L / min or any range of two of the above values.

[0037] For example, the argon flow rate at the water inlet is 4L / min, 5L / min, 6L / min, 7L / min, 8L / min, or any range of two of the above values.

[0038] In some implementations, the argon flow rate of the stopper rod is controlled at 6 L / min-8 L / min; the argon flow rate of the inlet is 5 L / min-7 L / min.

[0039] In some embodiments, the insertion depth of the tundish drain outlet is 90mm-120mm. By controlling the shallow insertion depth of the tundish drain outlet and coordinating it with a larger argon flow rate, the melting of the protective slag can be promoted, slag consumption can be increased, thereby improving the slag renewal rate. At the same time, the rising of argon bubbles can carry away hydrogen bubbles in the liquid slag film, reducing the number of pores in the solid slag film of the protective slag. For example, the insertion depth of the tundish drain outlet is 90mm, 92mm, 94mm, 96mm, 98mm, 100mm, 102mm, 104mm, 106mm, 108mm, 110mm, 112mm, 114mm, 116mm, 118mm, 120mm, or any range of two of the above values.

[0040] In some implementations, the insertion depth of the drain outlet is 90mm-100mm.

[0041] In some embodiments, the crystallizer oscillation frequency is 100-120 times / min, the oscillation amplitude is 3.0mm-4.5mm, and the skewness is 20%.

[0042] In this embodiment, the vibration frequency, amplitude, and pulling speed are matched. By adopting a low-frequency, high-amplitude process, the positive sliding time of the vibration is increased to 0.36-0.38s, thereby increasing slag consumption. The negative slip advance of the vibration is increased to 3.4-4.5mm, thereby improving the healing ability of the billet shell after adhesion.

[0043] The present application will now be described in conjunction with specific embodiments.

[0044] Example 1

[0045] Composition of high-hydrogen molten steel: C: 0.17wt%, Si: 0.12wt%, Mn: 0.27wt%, P: 0.027wt%, S: 0.006wt%, H: 11.7ppm, balance being Fe and unavoidable impurities.

[0046] Production steps:

[0047] (1) Use low tundish superheat casting, with the tundish superheat controlled at 3-8℃.

[0048] (2) The crystallizer adopts a strong cooling process. The water flow rate of the wide face of the crystallizer is 6000L / min and the flow velocity is 11.0m / s; the water flow rate of the narrow face of the crystallizer is 660L / min and the flow velocity is 10.8m / s.

[0049] (3) Argon flow control: Argon flow rate of stopper rod is 9L / min; Argon flow rate of inlet is 7L / min.

[0050] (4) Insertion depth of the middle package drain outlet is 95mm.

[0051] (5) The crystallizer vibration frequency is 120 times / min, the vibration amplitude is 3.5mm, and the skewness is 20%.

[0052] (6) Pulling speed 1.0m / min.

[0053] Example 2

[0054] Composition of high-hydrogen molten steel: C: 0.21wt%, Si: 0.2wt%, Mn: 1.20wt%, P: 0.013wt%, S: 0.0020wt%, H: 10.8ppm, balance being Fe and unavoidable impurities.

[0055] Production steps:

[0056] (1) Use low tundish superheat casting, with the tundish superheat controlled at 5-10℃.

[0057] (2) The crystallizer adopts a strong cooling process. The water flow rate of the wide face of the crystallizer is 5800L / min and the flow velocity is 9.76m / s; the water flow rate of the narrow face of the crystallizer is 580L / min and the flow velocity is 10.1m / s.

[0058] (3) Argon flow control: Argon flow rate of stopper rod is 7L / min; Argon flow rate of inlet is 4-6L / min.

[0059] (4) Insert the drain outlet of the middle package to a depth of 100mm.

[0060] (5) The crystallizer vibration frequency is 115 times / min, the vibration amplitude is 3.7mm, and the skewness is 20%.

[0061] (6) Pulling speed 1.10m / min.

[0062] Example 3

[0063] Composition of high-hydrogen molten steel: C: 0.07wt%, Si: 0.02wt%, Mn: 0.23wt%, P: 0.019wt%, S: 0.0060%, H: 11.6ppm, balance being Fe and unavoidable impurities.

[0064] Production steps:

[0065] (1) Use low tundish superheat casting, with the tundish superheat controlled at 10-15℃.

[0066] (2) The crystallizer adopts a strong cooling process. The water flow rate of the wide face of the crystallizer is 6000L / min and the flow velocity is 11.0m / s; the water flow rate of the narrow face of the crystallizer is 660L / min and the flow velocity is 10.8m / s.

[0067] (3) Argon flow control: Argon flow rate of stopper rod is 7L / min; Argon flow rate of inlet is 6L / min.

[0068] (4) Insert the drain outlet of the middle package to a depth of 100mm.

[0069] (5) The crystallizer vibration frequency is 100 times / min, the vibration amplitude is 4.5mm, and the skewness is 20%.

[0070] (6) Pulling speed 1.2m / min.

[0071] Example 4

[0072] Composition of high-hydrogen molten steel: C: 0.09wt%, Si: 0.02wt%, Mn: 0.95wt%, P: 0.019wt%, S: 0.0060%, H: 11.6ppm.

[0073] Production steps:

[0074] (1) Use low-temperature tundish superheat casting, with the tundish superheat controlled at 7-10℃.

[0075] (2) The crystallizer adopts a strong cooling process. The water flow rate of the wide face of the crystallizer is 5200L / min and the flow velocity is 9.5m / s; the water flow rate of the narrow face of the crystallizer is 580L / min and the flow velocity is 9.4m / s.

[0076] (3) Argon flow control: Argon flow rate of stopper rod is 8L / min; Argon flow rate of inlet is 6L / min.

[0077] (4) Insertion depth of the middle package drain outlet is 90mm.

[0078] (5) The crystallizer vibration frequency is 120 times / min, the vibration amplitude is 3.2mm, and the skewness is 20%.

[0079] (6) Pulling speed 0.9m / min.

[0080] Comparative Example 1

[0081] The production steps are similar to those in Example 1, except that the pulling speed is 1.5 m / min.

[0082] Comparative Example 2

[0083] The production steps are similar to those in Example 1, except that the superheat of the intermediate package is controlled at 30°C.

[0084] Comparative Example 3

[0085] The production steps are similar to those in Example 1, except that the water flow rate on the wide side of the crystallizer is 4500 L / min and the flow velocity is 8 m / s; the water flow rate on the narrow side of the crystallizer is 500 L / min and the flow velocity is 9.4 m / s-10.8 m / s; and the continuous casting speed is 0.5 m / min.

[0086] Comparative Example 4

[0087] The production steps are similar to those in Example 1, except that the crystallizer vibration frequency is 150 times / min and the vibration amplitude is 2.7 mm.

[0088] Comparative Example 5

[0089] The production steps are similar to those in Example 1, except that the argon flow rate of the stopper is 3L / min.

[0090] Performance testing

[0091] Example 1 21mm 0 No steel leakage Example 2 19mm 0 No steel leakage Example 3 16mm 0 No steel leakage Example 4 21mm 0 No steel leakage Comparative Example 1 12mm 2 Steel leakage Comparative Example 2 20mm 3 No steel leakage Comparative Example 3 22mm 4 No steel leakage Comparative Example 4 21mm 3 No steel leakage Comparative Example 5 21mm 2 No steel leakage

[0092] Examples 1-4 employ the continuous casting production method for casting high-hydrogen-content molten steel provided in this application. The hydrogen content in the molten steel in the continuous casting tundish is detected using a hydrogen determination device. When the hydrogen content is ≥8.5ppm, the tundish superheat is controlled between 0-20℃ during casting of the target molten steel. The tundish superheat is the measured molten steel temperature minus the steel grade liquid level temperature. Simultaneously, a strong cooling process is used, with a water flow rate of 5200L / min-6000L / min on the wide side of the crystallizer and a flow velocity of 9.5m / s-11.0m / s; and a water flow rate of 580L / min-660L / min on the narrow side of the crystallizer and a flow velocity of 9.4m / s-10.8m / s. The resulting cast billet exhibits good quality and no alarms were detected.

[0093] In Comparative Example 1, the casting speed was 1.5 m / min. Due to the high casting speed, the thickness of the billet shell exiting the crystallizer was 12 mm. The billet shell was insufficient to support the static pressure of the molten steel inside the crystallizer, which ultimately led to the leakage of steel.

[0094] In Comparative Example 2, the tundish superheat was controlled at 30°C. Due to the excessively high tundish superheat, the strength of the billet shell formed on the meniscus of the crystallizer may be insufficient. During the friction between the copper plate of the crystallizer and the billet shell, although no steel leakage occurred, it led to a large number of sticking alarms.

[0095] In Comparative Example 3, due to the low cooling intensity, the strength of the billet shell formed on the meniscus of the crystallizer may be insufficient, resulting in a high number of adhesion alarms during friction between the copper plate of the crystallizer and the billet shell.

[0096] In Comparative Example 4, the crystallizer vibration frequency was 150 times / min. The high vibration frequency of the crystallizer may be due to the reduction of the positive sliding time of the vibration, which reduced slag consumption and failed to form effective lubrication, resulting in a large number of sticking alarms.

[0097] In Comparative Example 5, the argon flow rate of the stopper rod was 3L / min. The argon flow rate of the stopper rod was too low, which may have caused the protective slag to not melt effectively, resulting in reduced slag consumption. Consequently, the slag renewal rate was insufficient, and effective lubrication was not formed, leading to a higher number of adhesion alarms.

[0098] In summary, the continuous casting production method for casting high-hydrogen-content molten steel provided in this application uses molten steel with a hydrogen content within the range of 8.5ppm≤a as the target molten steel. When casting the target molten steel, the superheat of the tundish is controlled at 0-20℃, and a strong cooling process is adopted to form a thick billet shell on the meniscus of the crystallizer, increasing the strength of the billet shell and increasing the gap between the copper plate of the crystallizer and the billet shell, thereby reducing the friction between the copper plate of the crystallizer and the billet shell. This solves the problems of frequent adhesion alarms and speed reductions and frequent steel leakage accidents in continuous casting with high hydrogen content in molten steel, and ensures smooth production.

[0099] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A continuous casting production method for casting molten steel with high hydrogen content, characterized in that, include: The content of hydrogen (H) in the molten steel in the continuous casting tundish is detected. Based on the test results, molten steel with H content reaching the preset range a was selected as the target molten steel, where 8.5ppm≤a; The target molten steel is poured into the crystallizer using a low-temperature tundish superheat, wherein the tundish superheat is controlled at 0-20°C. The molten steel is subjected to a strong cooling process in the crystallizer to obtain a cast billet. The water flow rate on the wide side of the crystallizer is 5200L / min-6000L / min, and the flow velocity is 9.5m / s-11.0m / s; the water flow rate on the narrow side of the crystallizer is 580L / min-660L / min, and the flow velocity is 9.4m / s-10.8m / s. The continuous casting speed is 0.8 m / min to 1.2 m / min.

2. The continuous casting production method for casting high-hydrogen-content molten steel according to claim 1, characterized in that, The thickness of the billet shell exiting the crystallizer is 15mm to 22mm.

3. The continuous casting production method for casting high-hydrogen-content molten steel according to claim 1, characterized in that, The argon flow rate of the stopper rod is controlled at 5L / min-10L / min; the argon flow rate of the inlet is 4L / min-8L / min.

4. The continuous casting production method for casting high-hydrogen-content molten steel according to claim 3, characterized in that, The argon flow rate of the stopper rod is controlled at 6L / min-8L / min; the argon flow rate of the inlet is 5L / min-7L / min.

5. The continuous casting production method for casting high-hydrogen-content molten steel according to claim 3, characterized in that, The insertion depth of the drain outlet in the middle package is 90mm-120mm.

6. The continuous casting production method for casting high-hydrogen-content molten steel according to claim 5, characterized in that, The insertion depth of the drain outlet in the middle package is 90mm-100mm.

7. The continuous casting production method for casting high-hydrogen-content molten steel according to claim 1, characterized in that, The crystallizer has a vibration frequency of 100-120 times / min and a vibration amplitude of 3.0-4.5mm; the skewness is 20%.

8. The continuous casting production method for casting high-hydrogen-content molten steel according to claim 1, characterized in that, The superheat of the low-temperature and medium-temperature ladle is controlled at 0-10℃.