A production method for controlling the cleanliness of steel for seamless pipes

Abstract

The application discloses a production method for controlling the cleanliness of seamless steel pipe steel, and relates to the technical field of iron and steel metallurgy.The application discloses an economical production method for controlling the cleanliness of seamless steel pipe steel.The production method adopts a converter primary refining-LF refining-round billet continuous casting-slow cooling process flow, and cancels a VD degassing process compared with conventional seamless steel pipe steel, so that the production energy consumption and production cost of the medium and high-grade seamless steel pipe steel are reduced while the high cleanliness and good quality of the steel are ensured.The application can obtain a production method for controlling the cleanliness of seamless steel pipe steel.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, specifically to a production method for controlling the cleanliness of steel used in seamless steel pipes. Background Technology

[0002] Heilongjiang Jianlong Steel Co., Ltd. has one round billet production line consisting of converter primary refining - ladle refining furnace (LF refining) - vacuum degassing (VD degassing) - continuous casting; one Φ180mm continuous rolling seamless steel pipe production line; one Φ273mm ACCU-ROLL skew rolling seamless steel pipe production line; and one quenching and tempering heat treatment production line. It mainly produces medium- and high-grade seamless steel pipes, including oilfield pipes, high-temperature and high-pressure pipes, and mechanical structure pipes. Among these, medium- and high-grade seamless steel pipes all have strict requirements for steel cleanliness. Therefore, while maintaining high cleanliness and good quality, reducing the energy consumption and production costs of steel used in medium- and high-grade seamless steel pipe production is of paramount importance. Summary of the Invention

[0003] The purpose of this invention is to solve the problems of high production cost, high energy consumption and how to maintain the cleanliness of steel used in traditional seamless steel pipes, and to provide a production method for controlling the cleanliness of steel used in seamless steel pipes.

[0004] A production method for controlling the cleanliness of steel used in seamless steel pipes comprises the following steps:

[0005] Step 1: Converter primary refining process:

[0006] Steel and silicon-carbon alloy are charged into a converter for smelting. The basicity of the final slag in the converter ranges from 2.5 to 3.5, the mass fraction of FeO is 10 to 16%, the mass fraction of carbon at the end point is 0.05 to 0.10%, the end point temperature is 1600 to 1630℃, the mass fraction of P at the end point is ≤0.010%, and the carbon-oxygen product in the molten steel at the end point is ≤0.0025.

[0007] Step 2: Ladle pre-deoxidation, alloying, and slag-making process:

[0008] After smelting, steel is tapped. Before tapping, argon gas is blown into the bottom of the ladle at a pressure of 0.3-0.5 MPa. When 1 / 5 of the steel is tapped, a deoxidizer is added. When 1 / 3 of the steel is tapped, high-alumina refining slag and alloy are added, followed by lime. After tapping, argon gas is blown for 2-3 minutes to obtain the metallurgical melt.

[0009] Step 3, LF refining process:

[0010] The metallurgical melt obtained in step two is transferred to the refining station, and aluminum wire is added to the metallurgical melt. The mass fraction of acid-soluble aluminum in the metallurgical melt is 0.020~0.030%. Power is supplied at an argon flow rate of 3~4 NL / (min•t). Slag is added after 1~2 minutes. Then lime and high-alumina refining slag are added to the metallurgical melt. White slag is formed by deoxidation with aluminum particles and silicon carbide. The refining time of the white slag is greater than 15 minutes. The mass fraction of acid-soluble aluminum in the entire refining process is ≥0.015%. 5~10 minutes before tapping, low power supply and low flow rate argon bottom blowing are used.

[0011] Step 4: Barium treatment and soft blowing process:

[0012] Three minutes before tapping, add silicon-barium alloy at a ratio of 0.8~1.2 kg / ton of steel for deep deoxidation and barium treatment of inclusions in the steel; after tapping, add carbonized rice husks to evenly cover the entire slag surface and adjust the argon flow rate for soft blowing, with a soft blowing time of ≥15 min.

[0013] Step 5: Continuous casting of round billets:

[0014] The entire process of casting is protected, and the fluctuation range of the liquid level in the crystallizer is controlled within ±3mm.

[0015] Step Six: Slow Cooling Process

[0016] The continuous casting round billet enters the pit at a temperature ≥500℃, with a temperature drop rate ≤15℃ / h during slow cooling, and an exit temperature ≤200℃, to obtain steel for seamless steel pipes. The chemical composition of the steel for seamless steel pipes has the following mass fractions: C 0.15~0.35%, Si 0.15~0.35%, Mn 0.40~1.60%, Cr 0.02~1.20%, Mo 0.005~1.10%, Nb 0.005~0.050%, V 0.005~0.12%, P≤0.015%, S≤0.005%, O≤0.0020%, and N≤0.005%, with the balance being Fe.

[0017] The beneficial effects of this invention are:

[0018] (1) The present invention adopts converter primary refining-LF refining-round billet continuous casting-slow cooling to produce clean medium and high grade seamless steel pipes. The content of harmful elements in the steel is controlled as follows: [H]≤0.0002%, [N]≤0.005%, [O]≤0.0012%, [S]≤0.005%, [P]≤0.015%. The metallographic inclusion rating results of the seamless steel pipes produced by it are as follows: coarse inclusions of categories A, B, C and D are all grade 0, fine inclusions of category A are ≤0.5, fine inclusions of category B are ≤1.0, fine inclusions of category C are grade 0, and fine inclusions of category D are ≤0.5. This achieves the same quality level of cleanliness as steel produced by converter primary refining-LF refining-VD degassing-round billet continuous casting-slow cooling.

[0019] (2) Compared with the process of using converter primary refining-LF refining-VD degassing-round billet continuous casting-slow cooling, the present invention adopts the process of converter primary refining-LF refining-round billet continuous casting-slow cooling to produce clean medium and high grade seamless steel pipes. The VD degassing process is reduced, steam consumption is reduced by 0.12 tons / ton of steel, refining power consumption is reduced by 122 kwh / ton of steel. According to the carbon dioxide emission factor, carbon dioxide emissions are reduced by 0.126 tons / ton of steel, and the cost per ton of steel is reduced by 63.37 yuan / ton.

[0020] (3) The present invention adopts a process flow of converter primary refining-LF refining-VD degassing-round billet continuous casting-slow cooling. Its characteristics are: high cleanliness, good product quality, high energy consumption and high production cost. Through technical breakthroughs and innovations, the production process and flow are optimized to reduce the production energy consumption and production cost of steel for medium and high-grade seamless steel pipes while maintaining the high cleanliness and good quality of steel.

[0021] This invention provides a production method for controlling the cleanliness of steel used in seamless steel pipes. Detailed Implementation

[0022] Specific Implementation Method 1: This implementation method describes a production method for controlling the cleanliness of steel used in seamless steel pipes, which is carried out according to the following steps:

[0023] Step 1: Converter primary refining process:

[0024] Steel and silicon-carbon alloy are charged into a converter for smelting. The final slag has a basicity range of 2.5-3.5, an FeO mass fraction of 10-16%, a final carbon mass fraction of 0.05-0.10%, a final temperature of 1600-1630℃, a final P mass fraction ≤0.010%, and a carbon-oxygen product in the final molten steel ≤0.0025. This is achieved by controlling the bottom blowing intensity at 0.12-0.15 NM within 2 minutes before the final stage of the converter process. 3 This is achieved by / (t•h), which reduces the [%O] in the final steel of the converter, controls the FeO content in the final slag, and reduces the burden of refining to remove inclusions;

[0025] Step 2: Ladle pre-deoxidation, alloying, and slag-making process:

[0026] After smelting, steel is tapped. Before tapping, argon gas is blown into the bottom of the ladle at a pressure of 0.3-0.5 MPa. When 1 / 5 of the steel is tapped, a deoxidizer is added. When 1 / 3 of the steel is tapped, high-alumina refining slag and alloy are added, followed by lime. After tapping, argon gas is blown for 2-3 minutes to obtain the metallurgical melt.

[0027] Strict control over the argon flow rate, aluminum ingots, carbon raiser, high-alumina refining slag, alloy, and lime in this step is to ensure good alloy melting and uniform composition, good deoxidation of molten steel, and good melting of ladle top slag, thereby achieving the goal of producing refining slag in advance.

[0028] Step 3, LF refining process:

[0029] The metallurgical melt obtained in step two is transferred to the refining station, and aluminum wire is added to the metallurgical melt. The mass fraction of acid-soluble aluminum in the metallurgical melt is 0.020~0.030% to ensure that Als≥0.015% throughout the refining process, thus ensuring good deoxidation. Power is supplied at an argon flow rate of 3~4 NL / (min•t). After 1~2 minutes, slag is added, followed by lime and high-alumina refining slag. Aluminum particles and silicon carbide are used for deoxidation to create white slag. Then, a refined steel sample is taken for analysis. Power is then supplied again at an argon flow rate of 3~4 NL / (min•t) for steel, and silicon carbide is added to maintain the white slag. After the analysis results of the refined steel sample are obtained, power is cut off, and alloys and carbon raisers are added. Power is supplied again after 3 minutes, and then cut off after 5~7 minutes. Then, a steel sample is taken for analysis. Finally, argon is blown at a flow rate of 1~1.2 NL / (min•t) for steel, and power is supplied until the steel is tapped. The refining time of the slag is greater than 15 minutes, the mass fraction of acid-soluble aluminum in the whole refining process is ≥0.015%, and low power supply and low flow rate argon bottom blowing are used 5 to 10 minutes before tapping. The ladle top slag melts well after argon, and the color of the ladle top slag after cooling is white or yellowish-white.

[0030] In actual production during this step, if the argon system is not functioning properly, such as abnormal air permeability of the permeable bricks or leaks in the pipes and interface valves, the argon gas should be adjusted according to the actual stirring effect to ensure good stirring performance.

[0031] The slag material mentioned in this step consists of high-alumina refining slag and lime. The amount of high-alumina refining slag and lime added is calculated and controlled based on the total amount of slag in the ladle top slag and the percentage content of each component in the ladle top slag.

[0032] Step 4: Barium treatment and soft blowing process:

[0033] Three minutes before tapping, add silicon-barium alloy at a ratio of 0.8~1.2 kg / ton of steel for deep deoxidation and barium treatment of inclusions in the steel; after tapping, add carbonized rice husks to evenly cover the entire slag surface and adjust the argon flow rate for soft blowing, with a soft blowing time of ≥15 min.

[0034] Adding a silicon-barium alloy 3 minutes before tapping the steel serves to perform deep deoxidation, modify inclusions in the molten steel, and promote the floating and removal of inclusions, thereby reducing the TO content in the steel.

[0035] Adding carbonized rice husks to evenly cover the entire slag surface helps to keep the molten steel warm, ensures that the top slag of the ladle remains liquid and does not form a crust, facilitates the full floating and discharge of steel inclusions, and helps to achieve uniform temperature throughout the molten pool and stability of superheat during continuous casting.

[0036] Step 5: Continuous casting of round billets:

[0037] After the soft blowing is completed, the molten steel ladle is transferred to the continuous casting machine. The entire process is protected during pouring, and the fluctuation range of the liquid level in the crystallizer is controlled within ±3mm. The continuous casting machine then produces a continuous casting round billet of the target fixed length from the molten steel.

[0038] The purpose of continuous casting with full protection is to reduce secondary oxidation and contamination of the molten steel by air intake during the continuous casting process.

[0039] Step Six: Slow Cooling Process

[0040] The continuous casting round billet enters the pit at a temperature ≥500℃, with a temperature drop rate ≤15℃ / h during slow cooling, and an exit temperature ≤200℃, to obtain steel for seamless steel pipes. The chemical composition of the steel for seamless steel pipes has the following mass fractions: C 0.15~0.35%, Si 0.15~0.35%, Mn 0.40~1.60%, Cr 0.02~1.20%, Mo 0.005~1.10%, Nb 0.005~0.050%, V 0.005~0.12%, P≤0.015%, S≤0.005%, O≤0.0020%, and N≤0.005%, with the balance being Fe.

[0041] The strict slow cooling process is designed to further promote the escape of hydrogen from the steel and reduce its hydrogen content.

[0042] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that: in step one, the steel material consists of vanadium-extracting semi-steel and scrap steel, with a mass ratio of vanadium-extracting semi-steel to scrap steel of (9~9.5):1; the amount of silicon-carbon alloy added is 0.3~0.5% of the mass of the vanadium-extracting semi-steel, which is to compensate for insufficient heat in the semi-steel, and at the same time, it is beneficial to stabilize and control the basicity, slag quantity, final carbon content, FeO content in the slag, and final temperature of the converter slag; the mass fraction of the chemical composition of the silicon-carbon alloy is: C≥2% and Si≥45%, with the balance being Fe.

[0043] The other steps are the same as in Specific Implementation Method 1.

[0044] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: in step one, the bottom-blown argon flow rate is controlled to be 0.12~0.15 NM before the converter endpoint. 3 / (t•h), the carbon-oxygen product in the molten steel at the endpoint is ≤0.0025.

[0045] The other steps are the same as in specific implementation method one or two.

[0046] Specific Implementation Method Four: The difference between this implementation method and Specific Implementation Methods One to Three is that the deoxidizer mentioned in step two is aluminum ingot. The amount of aluminum ingot added is determined based on the final carbon content, alloy type, and amount of alloy added, which are determined according to the specific steel grade.

[0047] The other steps are the same as those in Specific Implementation Methods One to Three.

[0048] Specific Implementation Method 5: The difference between this implementation method and Specific Implementation Methods 1 to 4 is that: in step 2, when the steel tapping is finished, a sliding plate is used to block slag and reduce the amount of slag.

[0049] The other steps are the same as those in Specific Implementation Methods One through Four.

[0050] Specific Implementation Method Six: The difference between this implementation method and Specific Implementation Methods One to Five is that the mass fraction of the silicon carbide chemical composition in step three is: SiC≥75%, free carbon≤6%, SiO2≤15%, S≤0.020% and H2O≤0.5%, and the particle size of silicon carbide is 2~5mm.

[0051] The other steps are the same as those in Specific Implementation Methods 1 to 5.

[0052] Specific Implementation Method Seven: The difference between this implementation method and Specific Implementation Methods One to Six is ​​that: 5 to 10 minutes before tapping the steel in step three, the power supply voltage is 180 to 196V and the current is 6000 to 10000A; the flow rate of argon bottom blowing is 1 to 1.2 NL / (min•t), in order to create foamy slag, increase the contact area between steel and slag, and promote the full floating and discharge of inclusions in the steel.

[0053] The other steps are the same as those in Specific Implementation Methods 1 to 6.

[0054] Specific Implementation Method Eight: The difference between this implementation method and Specific Implementation Methods One to Seven is that: the mass fraction of the chemical composition of the silicon-barium alloy in step four is: Ba≥25% and Si≥50%, with the balance being Fe; the elements and mass fractions contained in the carbonized rice husk in step four are: fixed carbon≥40%, moisture≤2.0% and volatile matter≤45%.

[0055] The other steps are the same as those in Specific Implementation Methods 1 to 7.

[0056] Specific Implementation Method Nine: The difference between this implementation method and Specific Implementation Methods One to Eight is that the flow rate of argon gas soft blowing in step four is 10~25NL / min, which is preferably not exposed to the surface of the molten steel. This is to ensure that the inclusions in the molten steel are fully denatured and floated to the surface for discharge, and to prevent the absorption of gas and secondary oxidation.

[0057] The other steps are the same as those in Specific Implementation Methods 1 to 8.

[0058] Specific Implementation Method Ten: The difference between this implementation method and Specific Implementation Methods One through Nine is that the specific steps of full-process protective casting in step five are as follows: The molten steel from the ladle to the tundish is protected by a long nozzle + argon seal, and the long nozzle is inserted into the molten steel in the tundish to a depth ≥250mm; the tundish body and the ladle cover are sealed with refractory material; the molten steel in the tundish is protected by an tundish covering agent; the molten steel from the tundish to the crystallizer is protected by an integral submerged nozzle, and the submerged nozzle penetrates into the molten steel in the crystallizer to a depth of 80~120mm; the molten steel in the crystallizer is protected by crystallizer protective slag.

[0059] The other steps are the same as those in Specific Implementation Methods 1 to 9.

[0060] The beneficial effects of the present invention are verified using the following embodiments:

[0061] Example 1: A production method for controlling the cleanliness of steel used in seamless steel pipes, comprising the following steps:

[0062] Step 1: Converter primary refining process:

[0063] Steel and silicon-carbon alloy are charged into a converter for smelting. The basicity of the final slag in the converter is 2.7, the mass fraction of FeO is 13%, the mass fraction of carbon at the end is 0.05%, the end temperature is 1610℃, the mass fraction of P at the end is ≤0.010%, and the carbon-oxygen product in the molten steel at the end is 0.0023.

[0064] In step one, the steel material consists of vanadium-extracting semi-steel and scrap steel, with a mass ratio of vanadium-extracting semi-steel to scrap steel of 9:1; the amount of silicon-carbon alloy added is 0.4% of the mass of vanadium-extracting semi-steel, and the mass fraction of the chemical composition of the silicon-carbon alloy is: C≥2% and Si≥45%, with the balance being Fe.

[0065] In step one, the bottom-blown argon flow rate is controlled to 0.12 NM before the converter endpoint. 3 / (t•h), the carbon-oxygen product in the molten steel at the endpoint is 0.0023.

[0066] Step 2: Ladle pre-deoxidation, alloying, and slag-making process:

[0067] After smelting, steel is tapped. Before tapping, argon gas is blown into the bottom of the ladle at a pressure of 0.3 MPa. When 1 / 5 of the steel is tapped, a deoxidizer is added. When 1 / 3 of the steel is tapped, high-alumina refining slag and alloy are added, followed by lime. After tapping, argon gas is blown for 2 minutes to obtain the metallurgical melt.

[0068] The deoxidizer mentioned in step two is aluminum ingot.

[0069] In step two, a sliding plate is used to block slag at the end of the steel tapping process.

[0070] Step 3, LF refining process:

[0071] The metallurgical melt obtained in step two is transferred to the refining station, and aluminum wire is added to the metallurgical melt to achieve a mass fraction of 0.025% acid-soluble aluminum. Power is supplied at an argon flow rate of 3 NL / (min•t), and slag is added after 1 minute. Then, lime and high-alumina refining slag are added to the metallurgical melt, and aluminum particles and silicon carbide are used for deoxidation to form white slag. The refining time of the white slag is greater than 15 minutes, and the mass fraction of acid-soluble aluminum is ≥0.015% throughout the refining process. In the 7 minutes before tapping, low-power power supply and low-flow argon bottom blowing are used.

[0072] The mass fraction of the silicon carbide chemical composition mentioned in step three is: SiC ≥ 75%, free carbon ≤ 6%, SiO2 ≤ 15%, S ≤ 0.020% and H2O ≤ 0.5%, and the particle size of silicon carbide is 2~5mm.

[0073] In step three, 7 minutes before tapping the steel, the power supply voltage is 180V and the current is 25KA; the flow rate of argon bottom blowing is 1.2NL / (min•t).

[0074] Step 4: Barium treatment and soft blowing process:

[0075] Three minutes before tapping, add silicon-barium alloy at a ratio of 1 kg / ton of steel for deep deoxidation and barium treatment of inclusions in the steel; after tapping, add carbonized rice husks to evenly cover the entire slag surface and adjust the argon flow rate for soft blowing, with a soft blowing time of ≥15 min.

[0076] The mass fraction of the chemical composition of the barium silicon alloy in step four is: Ba ≥ 25% and Si ≥ 50%, with the balance being Fe; the mass fraction of the chemical composition of the carbonized rice husk in step five is: fixed carbon ≥ 40%, moisture ≤ 2.0%, and volatile matter ≤ 45%.

[0077] In step four, the flow rate of argon gas during soft blowing is 20 NL / min.

[0078] Step 5: Continuous casting of round billets:

[0079] The entire process of casting is protected, and the fluctuation range of the liquid level in the crystallizer is controlled within ±3mm.

[0080] The specific steps for full-process protective casting in step five are as follows: The molten steel from the ladle to the tundish is protected by a long nozzle + argon seal, with the long nozzle inserted into the molten steel in the tundish to a depth ≥250mm; refractory material is used to seal the tundish body and the ladle cover; the molten steel in the tundish is protected by an tundish covering agent; the steel flow from the tundish to the crystallizer is protected by an integral submerged nozzle, with the submerged nozzle penetrating the molten steel in the crystallizer to a depth of 85mm; the molten steel inside the crystallizer is protected by crystallizer protective slag.

[0081] Step Six: Slow Cooling Process

[0082] The continuous casting round billet enters the pit at a temperature ≥500℃, with a temperature drop rate ≤15℃ during slow cooling, and an exit temperature ≤200℃, to obtain steel for seamless steel pipes. The chemical composition of the steel for seamless steel pipes has the following mass fractions: C 0.25%, Si 0.25%, Mn 1.20%, Cr 0.020%, Mo 0.005%, Nb 0.005%, V 0.005%, P ≤0.015%, S ≤0.005%, O ≤0.0020%, and N ≤0.005%, with the balance being Fe.

Claims

1. A production method for controlling the cleanliness of steel used in seamless steel pipes, characterized in that... The production method is carried out according to the following steps: Step 1: Converter primary refining process: Steel and silicon-carbon alloy are charged into a converter for smelting. The basicity of the final slag in the converter ranges from 2.5 to 3.5, the mass fraction of FeO is 10 to 16%, the mass fraction of carbon at the end point is 0.05 to 0.10%, the end point temperature is 1600 to 1630℃, the mass fraction of P at the end point is ≤0.010%, and the carbon-oxygen product in the molten steel at the end point is ≤0.0025. Step 2: Ladle pre-deoxidation, alloying, and slag-making process: After smelting, steel is tapped. Before tapping, argon gas is blown into the bottom of the ladle at a pressure of 0.3-0.5 MPa. When 1 / 5 of the steel is tapped, a deoxidizer is added. When 1 / 3 of the steel is tapped, high-alumina refining slag and alloy are added, followed by lime. After tapping, argon gas is blown for 2-3 minutes to obtain the metallurgical melt. Step 3, LF refining process: The metallurgical melt obtained in step two is transferred to the refining station, and aluminum wire is added to the metallurgical melt. The mass fraction of acid-soluble aluminum in the metallurgical melt is 0.020~0.030%. Power is supplied at an argon flow rate of 3~4 NL / (min•t). Slag is added after 1~2 minutes. Then lime and high-alumina refining slag are added to the metallurgical melt. White slag is formed by deoxidation with aluminum particles and silicon carbide. The refining time of the white slag is greater than 15 minutes. The mass fraction of acid-soluble aluminum in the entire refining process is ≥0.015%. 5~10 minutes before tapping, low power supply and low flow rate argon bottom blowing are used. Step 4: Barium treatment and soft blowing process: Three minutes before tapping, add silicon-barium alloy at a ratio of 0.8~1.2 kg / ton of steel for deep deoxidation and barium treatment of inclusions in the steel; after tapping, add carbonized rice husks to evenly cover the entire slag surface and adjust the argon flow rate for soft blowing, with a soft blowing time of ≥15 min. Step 5: Continuous casting of round billets: The entire process of casting is protected, and the fluctuation range of the liquid level in the crystallizer is controlled within ±3mm. Step Six: Slow Cooling Process The continuous casting round billet enters the pit at a temperature ≥500℃, with a temperature drop rate ≤15℃ / h during slow cooling, and an exit temperature ≤200℃, to obtain steel for seamless steel pipes. The chemical composition of the steel for seamless steel pipes has the following mass fractions: C 0.15~0.35%, Si 0.15~0.35%, Mn 0.40~1.60%, Cr 0.02~1.20%, Mo 0.005~1.10%, Nb 0.005~0.050%, V 0.005~0.12%, P≤0.015%, S≤0.005%, O≤0.0020%, and N≤0.005%, with the balance being Fe.

2. The production method for controlling the cleanliness of steel for seamless steel pipes according to claim 1, characterized in that... In step one, the steel material consists of vanadium-extracting semi-steel and scrap steel, with a mass ratio of vanadium-extracting semi-steel to scrap steel of (9~9.5):1; the amount of silicon-carbon alloy added is 0.3~0.5% of the mass of vanadium-extracting semi-steel, and the mass fraction of the chemical composition of the silicon-carbon alloy is: C≥2% and Si≥45%, with the balance being Fe.

3. A production method for controlling the cleanliness of steel for seamless steel pipes according to claim 1 or 2, characterized in that... In step one, the bottom-blown argon flow rate is controlled to be 0.12~0.15 NM before the converter endpoint. 3 / (t•h), the carbon-oxygen product in the molten steel at the endpoint is ≤0.0025.

4. The production method for controlling the cleanliness of steel for seamless steel pipes according to claim 1, characterized in that... The deoxidizer mentioned in step two is aluminum ingot.

5. A production method for controlling the cleanliness of steel for seamless steel pipes according to claim 1, characterized in that... In step two, a sliding plate is used to block slag at the end of steel tapping.

6. A production method for controlling the cleanliness of steel for seamless steel pipes according to claim 1, characterized in that... The mass fraction of the silicon carbide chemical composition mentioned in step three is: SiC ≥ 75%, free carbon ≤ 6%, SiO2 ≤ 15%, S ≤ 0.020% and H2O ≤ 0.5%, and the particle size of silicon carbide is 2~5mm.

7. A production method for controlling the cleanliness of steel for seamless steel pipes according to claim 1, characterized in that... In step three, 5 to 10 minutes before tapping the steel, the power supply voltage is 180 to 196V and the current is 6000 to 10000A; the flow rate of argon bottom blowing is 1 to 1.2 NL / (min•t).

8. A production method for controlling the cleanliness of steel for seamless steel pipes according to claim 1, characterized in that... The mass fraction of the chemical composition of the barium-silicon alloy in step four is: Ba ≥ 25% and Si ≥ 50%, with the balance being Fe; the elements and mass fractions contained in the carbonized rice husk in step four are: fixed carbon ≥ 40%, moisture ≤ 2.0%, and volatile matter ≤ 45%.

9. A production method for controlling the cleanliness of steel for seamless steel pipes according to claim 1, characterized in that... In step four, the flow rate of argon gas during soft blowing is 10~25 NL / min.

10. A production method for controlling the cleanliness of steel for seamless steel pipes according to claim 1, characterized in that... The specific steps for full-process protective casting in step five are as follows: The molten steel from the ladle to the tundish is protected by a long nozzle + argon seal, with the long nozzle inserted into the molten steel in the tundish to a depth ≥250mm; refractory material is used to seal the tundish body and the ladle cover; the molten steel in the tundish is protected by an tundish covering agent; the steel flow from the tundish to the crystallizer is protected by an integral submerged nozzle, with the submerged nozzle penetrating the molten steel in the crystallizer to a depth of 80~120mm; the molten steel inside the crystallizer is protected by crystallizer protective slag.