Tundish casting process for reducing inclusions in molten pipeline steel

Abstract

The invention relates to the technical field of tundish casting, in particular to a tundish casting process for reducing inclusions in molten pipeline steel, which comprises the following steps: controlling the superheat degree of the molten steel in the steel ladle to be 25-35 DEG C, controlling the entry temperature of the steel ladle to be 1580-1590 DEG C, casting the steel ladle under the protection of argon, and when the mass of the molten steel in the tundish is 15 tons, stopping casting the steel ladle; and a tundish covering agent and carbonized rice husks are sequentially added into the tundish, when the mass of the molten steel in the tundish is 30 tons, adding is finished, when the mass of the molten steel in the tundish is 35 tons, the stopper rod is opened, and the tundish is poured to a crystallizer. According to the tundish casting process for reducing the inclusions in the molten pipeline steel, the molten steel can be prevented from being polluted by the inclusions in the initial casting stage of the steel ladle, the flaw detection qualification rate of steel plates corresponding to casting blanks of later sections such as a pipeline steel head blank (an initial blank), a head + 1 blank (the section 3-6 m after the head blank), a head + 2 blank (the section 3-6 m after the head + 1 blank) and the like is increased, and the quality of pipeline steel products is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of tundish starting casting, and particularly relates to a tundish starting casting process for reducing inclusions in pipeline steel molten steel. Background Art

[0002] Pipeline steel is a low-alloy high-strength steel specifically used for manufacturing pipelines for transporting oil, natural gas, water, and other fluids. Compared with ordinary steel, pipeline steel not only has high strength, good corrosion resistance, and reliable fracture toughness, but also can ensure that the pipeline does not deform, leak, or rupture under long-term high-intensity and high-temperature, high-pressure environments. Therefore, it is widely used in pipelines for transporting oil, natural gas, water, and other fluids.

[0003] During the pipe-making process of pipeline steel, there are approximately 5-7 times of flaw detection inspections. Moreover, during the pipeline construction process of steel pipes, within a range of 100 mm at both ends of the steel pipe, phased array or TOFT (non-destructive testing) and other special flaw detection equipment are required for re-inspection. In the initial stage of starting casting of the continuous casting ladle, the molten steel is easily contaminated by inclusions such as drainage sand and refractories, resulting in non-compliance with flaw detection. Currently, the conventional starting casting process is generally used, and it is difficult for the quality of the cast billet in the initial stage of starting casting to meet the quality requirements of pipeline steel with increasingly strict flaw detection requirements.

[0004] After retrieval, the relevant literatures and patents on starting casting of continuous casting tundishes currently disclosed mainly focus on preventing steel leakage accidents and low-temperature solidified steel stopping casting accidents. Although a few disclosed patents involve the quality control of the starting casting first billet, the technical details of the starting casting tonnage and the control of inclusions during the starting casting process are not involved.

[0005] For example, the patent with the publication number CN 114472836 A discloses a method for preventing steel leakage during the starting casting of high-carbon steel slabs for continuous casting, including the following steps: Step 1: Install the dummy bar; Step 2: Seal the dummy bar during the starting casting of high-carbon steel; Step 3: Control the process during the starting casting; Step 4: End the entire process of preventing steel leakage during the starting casting of high-carbon steel. This solution mainly optimizes and improves key continuous casting process parameters such as the carbon content setting of the sealed dummy bar material, the optimization of the sealed dummy bar parameters, the setting of the mold taper, the superheat control of the starting casting molten steel, and the optimization of the starting casting process parameters, and well solves the problem of steel leakage accidents during the starting casting of high-carbon steel caused by insufficient strength of the first billet shell due to solidification characteristics. This patent mainly optimizes and improves key continuous casting process parameters such as the carbon content setting of the sealed dummy bar material, the optimization of the sealed dummy bar parameters, the setting of the mold taper, the superheat control of the starting casting molten steel, and the optimization of the starting casting process parameters, and well solves the problem of steel leakage accidents during the starting casting of high-carbon steel caused by insufficient strength of the first billet shell due to solidification characteristics. This method does not involve the control of molten steel inclusion pollution in the initial stage of starting casting at all.

[0006] As disclosed in the patent with publication number CN 114769573 A, a stopper rod and a method for preventing low-temperature accidents during continuous casting tundish pouring are disclosed. The method is to blow inert gas into the tundish with the above-mentioned stopper rod before the tundish pouring. The flow rate of the blown inert gas is selectively controlled according to the number of flat gas channels, achieving the effect of preventing low-temperature accidents during continuous casting tundish pouring. There is no need to transform the existing equipment, and only the argon gas channels of the stopper rod need to be redesigned. Therefore, it is easy to manufacture, low in cost, and convenient to operate; the molten steel temperature is evenly stirred by argon gas, and heat exchange is carried out between the low-temperature molten steel at the tundish bowl mouth and the high-temperature molten steel at the upper part. This patent mainly blows inert gas into the tundish with the stopper rod invented in this patent before the tundish pouring, and selectively controls the flow rate of the blown inert gas according to the number of flat gas channels, achieving the effect of preventing low-temperature accidents during continuous casting tundish pouring. This method does not involve the control of molten steel inclusion pollution at the initial stage of pouring at all.

[0007] As disclosed in the patent with publication number CN 113664171 A, a method for controlling the quality of continuous casting first billets is disclosed. The method includes the following steps: (1) adding refined lime with a single power supply at the refining position; (2) the deep vacuum degree at the vacuum position ≤ 67 Pa and the time ≥ 5 min; (3) coating the tundish and controlling the temperature between 100 - 200 °C; (4) tundish baking: baking with low fire, medium fire, and high fire; (5) argon blowing operation, using an argon blowing pipe to blow argon gas into the impact zone and the pouring area, the argon gas pressure is above 1.0 Mpa, and the argon blowing time for each area is less than 3 min; (6) when the tundish liquid level reaches the pouring liquid level, start the pouring operation; (7) carry out continuous casting and billet forming operations. This patent solves the problem of poor quality of continuous casting first billets in the prior art and improves the purity of the quality of the first billets. This patent mainly conducts control from aspects such as refining treatment, tundish baking, and argon protection. Among them, in step (6) of this patent, when the tundish liquid level reaches the pouring liquid level, start the pouring operation; however, it does not involve the process control that the tundish pouring liquid level can affect the floating and removal of inclusions at the initial stage of pouring.

[0008] In the above-mentioned continuous casting tundish pouring process in the iron and steel industry, most focus on preventing steel leakage accidents and low-temperature solidified steel pouring stop accidents, and the control technology for the problem of increased inclusions caused by molten steel pollution at the initial stage of pouring is weak. Summary of the Invention

[0009] Aiming at the technical problem that inclusions in molten steel increase at the initial stage of tundish pouring in the prior art, which affects the quality of pipeline steel products, the present invention provides a tundish pouring process for reducing inclusions in pipeline steel molten steel, which can avoid the pollution of molten steel by inclusions at the initial stage of ladle pouring, and improve the flaw detection qualification rates of subsequent cast billets such as the first billet (initial billet) of pipeline steel, the first + 1 billet (the section 3 m - 6 m after the first billet), and the first + 2 billet (the subsequent 3 m - 6 m of the first + 1 billet) corresponding steel plates.

[0010] The technical solution adopted by the present invention is as follows: The present invention provides a tundish starting casting process for reducing inclusions in pipeline steel molten steel, including: controlling the superheat of the ladle molten steel to be 25°C - 35°C, controlling the ladle inlet temperature to be 1580°C - 1590°C, starting the ladle casting under argon protection. When the mass of the molten steel in the tundish is 15 tons, add tundish covering agent and carbonized rice husk to the tundish in sequence. When the mass of the molten steel in the tundish reaches 30 tons, the addition ends. When the mass of the molten steel in the tundish is 35 tons, open the stopper rod, and start casting from the tundish to the mold.

[0011] Further, pre-treat the tundish before starting the ladle casting. The pre-treatment includes cleaning and baking the inside of the tundish.

[0012] Further, the baking treatment includes baking the inside of the tundish until the temperature of the tundish impact zone ≥ 1200°C. The function is that the baking treatment eliminates the moisture and volatile substances in the tundish, prevents the pollution of molten steel, and at the same time preheats the tundish material to avoid the thermal stress impact caused by the temperature difference inside and outside the refractory material when the cold tundish directly contacts the high-temperature molten steel.

[0013] Further, the baking treatment adopts a three-stage baking process, including baking for 1 - 2 hours under the condition of temperature ≤ 400°C, baking for 0.5 - 1.5 hours under the condition of temperature 400°C - 800°C, and baking for 1 - 3 hours under the condition of temperature ≥ 1000°C, baking until the temperature of the tundish impact zone ≥ 1200°C.

[0014] Further, after the pre-treatment of the tundish, perform pre-blowing argon treatment. The pre-blowing argon treatment includes inserting two argon blowing pipes into the argon passage of the tundish steel receiving hole respectively, inserting one argon blowing pipe into the argon passage of the tundish temperature measuring hole, opening the argon valve to pre-blow argon, and the pre-blowing time is 30 seconds - 40 seconds. When the tundish is filled with air, the first ladle of molten steel for starting casting in the continuous casting tundish is prone to oxidation, resulting in an increase in the gas content in the molten steel, thereby causing subcutaneous bubble defects in the continuous casting billet. By pre-blowing argon, the air in the tundish can be effectively discharged, preventing secondary oxidation and reducing the occurrence of defects such as subcutaneous bubbles.

[0015] Further, the flow rate of argon during ladle casting is controlled at 90 L / min - 100 L / min.

[0016] Further, the control mode of the stopper rod is that when the liquid level in the mold rises to the set liquid level, the control of the stopper rod is changed from manual to automatic control.

[0017] Further, the starting drawing speed after starting casting from the tundish to the mold is 0.1 m / min - 0.2 m / min, and then the drawing speed is gradually increased to 0.8 m / min - 0.9 m / min according to the temperature - drawing speed system.

[0018] Furthermore, the argon flow rate between the submerged entry nozzle slide plates of the tundish crystallizer is controlled at 3 L / min to 10 L / min, and the back pressure between the plates is ≥ 0.1 bar.

[0019] Furthermore, a tundish starting pouring process for reducing inclusions in pipeline steel molten steel provided by the present invention specifically includes the following steps: (1) Bake the inside of the tundish until the temperature of the tundish impact zone ≥ 1200 °C; (2) After baking the inside of the tundish, pre-blow argon into the tundish, and the pre-blow time is 30 seconds to 40 seconds; (3) Control the superheat of the ladle molten steel to be 25 °C to 35 °C, and control the ladle inlet temperature to be 1580 °C to 1590 °C; (4) Pour the ladle under argon protection. When the mass of the molten steel in the tundish is 15 tons, close the pre-blow argon valve, and sequentially add tundish covering agent and carbonized rice husk into the tundish. When the mass of the molten steel in the tundish is 30 tons, the addition is completed; (5) When the mass of the molten steel in the tundish is 35 tons, open the stopper rod, and pour the tundish into the crystallizer. The control mode of the stopper rod is that when the liquid level in the crystallizer rises to the set liquid level, the control of the stopper rod is changed from manual to automatic control. The starting pouring speed after pouring the tundish into the crystallizer is 0.1 m / min to 0.2 m / min, and then the speed is gradually increased to 0.8 m / min to 0.9 m / min according to the temperature-pouring speed system.

[0020] The beneficial effects of the present invention are as follows: (1) The tundish starting pouring process for reducing inclusions in pipeline steel molten steel provided by the present invention provides support conditions for tundish starting pouring by controlling the superheat of molten steel, ladle inlet temperature, etc. The increase in superheat can reduce the viscosity of molten steel, accelerate the floating of inclusions, delay the crust formation in the tundish, and improve the cleanliness of the molten steel for tundish starting pouring.

[0021] (2) In the range where the mass of the molten steel in the tundish is 15 - 30 tons, the tundish covering agent and carbonized rice husk are sequentially added into the tundish. The tundish covering agent and carbonized rice husk mainly play roles such as heat preservation, air isolation, and reduction of molten steel oxidation, etc., to avoid an increase in new inclusions.

[0022] (3) The tundish starting casting process provided by the present invention for reducing inclusions in pipeline steel molten steel, compared with the conventional starting casting process when the tundish reaches 15 tons - 20 tons, in the conventional starting casting process, it takes about 1.5 minutes from the ladle starting casting to the tundish reaching 20 tons. In the present invention, when the mass of molten steel in the tundish is 35 tons, the stopper rod is opened for starting casting, and the time from the ladle starting casting to the tundish starting casting can be extended to 3.5 minutes, making the tundish starting casting time about 2 minutes later than the conventional 15 tons - 20 tons starting casting time. Thus, the floating and removal time of the flow guiding sand, refractory inclusions, etc. flushed in the initial stage of ladle starting casting in the tundish molten steel is extended, and the secondary oxidation of molten steel is effectively avoided, improving the cleanliness of molten steel. Detailed implementation manners

[0023] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0024] Embodiment 1 A tundish starting casting process for reducing inclusions in pipeline steel molten steel, with the working capacity of the tundish used being 45 tons and the working liquid level height being 1240 mm, includes the following steps: (1) Cleaning and baking of the tundish: Before baking the tundish, it is fully cleaned using a high-power vacuum cleaner; baking is carried out in the order of first low fire then high fire. Baking at low fire (≤400 °C) for 1.5 hours, medium fire (400 °C - 800 °C) for 1 hour, and high fire (≥1000 °C) for 2 hours, and measuring the temperature in the impact area of the tundish to be about 1350 °C.

[0025] (2) Argon protection atmosphere in the tundish: After the tundish baking is completed, two of the three argon blowing pipes are respectively inserted into the argon passage of the steel receiving hole of the tundish, and one argon blowing pipe is inserted into the argon passage of the temperature measuring hole of the tundish, and argon is opened for pre-blowing argon operation, and the pre-blowing argon time is 40 seconds.

[0026] (3) Control of molten steel superheat: For high-tonnage starting casting of the tundish, control the ladle inlet temperature of continuous casting to be 1588 °C, and control the molten steel superheat at the initial stage of starting casting to be 33 °C.

[0027] (4) Ladle starting pouring: After hanging the ladle protection sleeve, open the argon protection pouring valve, control the argon flow rate at 97 L / min, open the sliding gate of the ladle to start pouring. After the molten steel flows out normally, lower the ladle arm to the low position; when the molten steel in the tundish reaches 15 tons, close the pre-blowing argon valve, take out the pre-blowing argon pipe, and gradually add about 30 bags of covering agent and 3 bags of carbonized rice husk. When the molten steel in the tundish reaches 30 tons, the addition is completed.

[0028] (5) Tundish starting pouring: When the molten steel in the tundish reaches 35 tons, open the stopper rod, moderately open the flow, control the crystallizer liquid level to the set level, and then switch the control of the stopper rod from manual to automatic; control the starting casting speed at 0.2 m / min, gradually increase the casting speed to the target casting speed of 0.85 m / min according to the temperature-casting speed regime. After confirming normal and no sticking, switch to automatic control. Control the argon flow rate between the tundish crystallizer nozzle slide plates at 3 L / min, and control the back pressure between the plates at 0.2 bar; The time from ladle starting pouring to tundish starting pouring is 3.5 minutes.

[0029] (6) After the tundish starting pouring, the molten steel is poured into the crystallizer for cooling and solidification to obtain a continuous casting billet. The first billet, the first + 1 billet, and the first + 2 billets are cut off and taken offline for slow cooling and surface quality inspection.

[0030] (7) The continuous casting billet is rolled into a steel plate with a thickness of 30 mm according to the set process parameters. Ultrasonic flaw detection is carried out on the whole plate of the steel plate using the SY / T6423.3_U2 (2013) Standard for Nondestructive Testing Methods of Steel Pipes in the Petroleum and Natural Gas Industry. The flaw detection qualification rate meeting the standard reaches more than 99.3%.

[0031] Example 2 A tundish starting pouring process for reducing inclusions in the molten steel of pipeline steel. The working capacity of the tundish used is 45 tons, and the working liquid level height is 1250 mm. It includes the following steps: (1) Cleaning and baking inside the tundish: Before baking the tundish, use a high-power vacuum cleaner for sufficient cleaning; Bake according to the method of first small fire and then large fire. Bake with a small fire (≤400°C) for 1 hour, with a medium fire (400°C - 800°C) for 0.5 hour, and with a large fire (≥1000°C) for 1 hour. Measure the temperature in the impact area of the tundish to be about 1200°C.

[0032] (2) Argon protection atmosphere inside the tundish: After the tundish baking is completed, insert two of the three argon blowing pipes into the argon passage of the steel receiving hole of the tundish respectively, and insert one argon blowing pipe into the argon passage of the temperature measuring hole of the tundish. Open the argon for pre-blowing argon operation, and the pre-blowing argon time is 30 seconds.

[0033] (3) Control of molten steel superheat: For high-tonnage starting pouring of the tundish, control the temperature of the continuous casting ladle entering the station at 1583°C, and control the molten steel superheat at the initial stage of starting pouring at 25°C.

[0034] (4)Ladle starting pouring: After hanging the ladle protection sleeve, open the argon protection pouring valve, control the argon flow rate at 90 L / min, open the sliding gate of the ladle to start pouring. After the molten steel flows out normally, lower the large ladle arm to the low position; when the molten steel in the tundish reaches 15 tons, close the pre-blowing argon valve, take out the pre-blowing argon pipe, and gradually add about 28 bags of covering agent and 3 bags of carbonized rice husk. When the molten steel in the tundish reaches 30 tons, the addition is completed.

[0035] (5)Tundish starting pouring: When the molten steel in the tundish reaches 35 tons, open the stopper rod, moderately open the flow, control the crystallizer liquid level to the set level, and then change the control of the stopper rod from manual to automatic; control the starting casting speed at 0.1 m / min, gradually increase the casting speed to the target casting speed of 0.80 m / min according to the temperature-casting speed regime. After confirming normal and no sticking, switch to automatic control. Control the argon flow rate between the tundish crystallizer nozzle slide plates at 3 L / min, and control the back pressure between the plates at 0.15 bar; The time from ladle starting pouring to tundish starting pouring is 3.4 minutes.

[0036] (6)After the tundish starting pouring, the molten steel is injected into the crystallizer for cooling and solidification to obtain a continuous casting billet. The first three continuous casting billets, namely the starting billet, the starting + 1 billet, and the starting + 2 billet, are cut off and taken offline for slow cooling and surface quality inspection.

[0037] (7)The continuous casting billet is rolled into a steel plate with a thickness of 30 mm according to the set process parameters. The whole plate of the steel plate is inspected by ultrasonic flaw detection using the SY / T6423.3_U2 (2013) Standard for Nondestructive Testing Methods of Steel Tubes in the Petroleum and Natural Gas Industry. The flaw detection qualification rate meeting the standard reaches over 99.2%.

[0038] Example 3 A tundish starting pouring process for reducing inclusions in the molten steel of pipeline steel. The working capacity of the tundish used is 45 tons, and the working liquid level height is 1250 mm. The process includes the following steps: (1)Cleaning and baking inside the tundish: Before baking the tundish, use a high-power vacuum cleaner for thorough cleaning; Bake it in the order of first small fire then large fire. Bake with a small fire (≤400 °C) for 2 hours, medium fire (400 °C - 800 °C) for 1.5 hours, and large fire (≥1000 °C) for 3 hours. Measure the temperature in the impact area of the tundish to be about 1300 °C.

[0039] (2)Argon protection atmosphere inside the tundish: After the tundish baking is completed, insert two of the three argon blowing pipes into the argon passage of the molten steel receiving hole of the tundish respectively, and insert one argon blowing pipe into the argon passage of the temperature measuring hole of the tundish. Open the argon for pre-blowing argon operation, and the pre-blowing argon time is 35 seconds.

[0040] (3)Control of molten steel superheat: For high-tonnage starting pouring of the tundish, control the temperature of the continuous casting ladle entering the station at 1590 °C, and control the molten steel superheat at the initial stage of starting pouring at 35 °C.

[0041] (4)Ladle starting pouring: After hanging the ladle protection sleeve, open the argon protection pouring valve, control the argon flow rate at 100 L / min, open the sliding nozzle of the ladle for starting pouring. After the molten steel flows out normally, lower the ladle arm to the low position; when the molten steel in the tundish reaches 15 tons, close the pre-blowing argon valve, take out the pre-blowing argon pipe, and gradually add about 28 bags of covering agent and 3 bags of carbonized rice husk. When the molten steel in the tundish reaches 30 tons, the addition is completed.

[0042] (5)Tundish starting pouring: When the molten steel volume in the tundish reaches 35 tons, open the stopper rod, moderately open the flow, control the mold liquid level to the set level, and then switch the control of the stopper rod from manual to automatic; control the starting casting speed at 0.2 m / min, gradually increase the casting speed to the target casting speed of 0.90 m / min according to the temperature-casting speed regime. After confirming normal and no sticking, switch to automatic control. Control the argon flow rate between the tundish mold nozzle slide plates at 10 L / min, and the back pressure between the plates at 0.25 bar; the time from ladle starting pouring to tundish starting pouring is 3.5 minutes.

[0043] (6)After the tundish starting pouring, the molten steel is injected into the mold for cooling and solidification to obtain a continuous casting billet. The first billet, the first + 1 billet, and the first + 2 billets of the starting pouring are cut and taken offline for slow cooling and surface quality inspection.

[0044] (7)The continuous casting billet is rolled into a steel plate with a thickness of 35 mm according to the set process parameters. The whole plate of the steel plate is inspected by ultrasonic flaw detection using the SY / T6423.3_U2 (2013) Standard for Nondestructive Testing Methods of Steel Pipes in the Petroleum and Natural Gas Industry. The flaw detection qualification rate meeting the standard is over 99.3%.

[0045] Example 3 A tundish starting pouring process for reducing inclusions in the molten steel of pipeline steel. The working capacity of the tundish used is 45 tons, and the working liquid level height is 1240 mm. It includes the following steps: (1)Cleaning and baking inside the tundish: Before baking the tundish, use a high-power vacuum cleaner for thorough cleaning; bake it in the order of first low fire then high fire. Bake at low fire (≤400 °C) for 1.3 hours, at medium fire (400 °C - 800 °C) for 1.2 hours, and at high fire (≥1000 °C) for 2.3 hours. Measure the temperature in the impact area of the tundish to be about 1300 °C.

[0046] (2)Argon protection atmosphere inside the tundish: After the tundish baking is completed, insert two of the three argon blowing pipes into the argon passage of the molten steel receiving hole of the tundish respectively, and insert one argon blowing pipe into the argon passage of the temperature measuring hole of the tundish. Open the argon for pre-blowing argon operation, and the pre-blowing argon time is 38 seconds.

[0047] (3)Superheat control of molten steel: When starting casting with a high-tonnage tundish, control the temperature of the ladle entering the continuous casting station at 1582 °C, and control the superheat of the molten steel at the initial stage of casting at 38 °C.

[0048] (4)Ladle pouring: After hanging the ladle protection sleeve, open the argon protection pouring valve, control the argon flow rate at 93 L / min, open the sliding gate of the ladle for pouring. After the molten steel flows out normally, lower the ladle arm to the low position; when the molten steel in the tundish reaches 15 tons, close the pre-blowing argon valve, remove the pre-blowing argon pipe, and gradually add about 28 bags of covering agent and 3 bags of carbonized rice husk. When the molten steel in the tundish reaches 30 tons, the addition ends.

[0049] (5)Tundish pouring: When the molten steel in the tundish reaches 35 tons, open the stopper rod and moderately open the flow. After controlling the liquid level in the mold to the set liquid level, switch the control of the stopper rod from manual to automatic; control the starting casting speed at 0.1 m / min, and gradually increase the casting speed to the target casting speed of 0.82 m / min according to the temperature-casting speed regime. After confirming normal and no sticking, switch to automatic control. Control the argon flow rate between the tundish mold nozzle slide plates at 10 L / min, and control the back pressure between the plates at 0.23 bar; The time from ladle pouring to tundish pouring is 3.6 minutes.

[0050] (6)After tundish pouring, the molten steel is injected into the mold for cooling and solidification to obtain a continuous casting billet. The first billet, the first + 1 billet, and the first + 2 billets are cut off and sent offline for slow cooling and surface quality inspection.

[0051] (7)The continuous casting billet is rolled into a steel plate with a thickness of 35 mm according to the set process parameters. Ultrasonic flaw detection is carried out on the entire plate of the steel plate using the SY / T6423.3_U2 (2013) Standard for Nondestructive Testing Methods of Steel Pipes in the Petroleum and Natural Gas Industry. The flaw detection qualification rate meeting the standard reaches over 99.1%.

[0052] Example 4 A tundish pouring process for reducing inclusions in the molten steel of pipeline steel. The working capacity of the tundish used is 40 tons, and the working liquid level height is 1200 mm. It includes the following steps: (1)Cleaning and baking of the tundish: Before baking the tundish, use a high-power vacuum cleaner for thorough cleaning; Bake according to the method of first small fire then large fire. Bake with a small fire (≤400 °C) for 1.1 hours, medium fire (400 °C - 800 °C) for 1.3 hours, and large fire (≥1000 °C) for 2.7 hours. Measure the temperature in the impact zone of the tundish at about 1300 °C.

[0053] (2)Argon protection atmosphere in the tundish: After the tundish baking is completed, insert two of the three argon blowing pipes into the argon passage of the molten steel receiving hole in the tundish respectively, and insert one argon blowing pipe into the argon passage of the temperature measuring hole in the tundish. Open the argon for pre-blowing argon operation, and the pre-blowing argon time is 36 seconds.

[0054] (3)Control of molten steel superheat: When pouring at high tonnage in the tundish, control the temperature of the continuous casting ladle entering the station at 1588 °C, and control the superheat of the molten steel at the initial stage of pouring at 30 °C.

[0055] (4)Ladle pouring: After hanging the ladle protection sleeve, open the argon protection pouring valve, control the argon flow rate at 99 L / min, open the sliding nozzle of the ladle for pouring. After the molten steel flows out normally, lower the ladle arm to the low position; when the molten steel in the tundish reaches 15 tons, close the pre-blowing argon valve, take out the pre-blowing argon pipe, and gradually add about 28 bags of covering agent and 3 bags of carbonized rice husk. When the molten steel in the tundish reaches 30 tons, the addition is completed.

[0056] (5)Tundish pouring: When the molten steel in the tundish reaches 35 tons, open the stopper rod, open the flow moderately. After controlling the liquid level in the mold to the set liquid level, switch the control of the stopper rod from manual to automatic; control the starting casting speed at 0.2 m / min, gradually increase the casting speed to the target casting speed of 0.86 m / min according to the temperature-casting speed regime. After confirming normal and no sticking, switch to automatic control. Control the argon flow rate between the tundish mold nozzle and the slide plate at 6.0 L / min, and control the back pressure between the plates at 0.21 bar; The time from ladle pouring to tundish pouring is 3.5 minutes.

[0057] (6)After tundish pouring, the molten steel is injected into the mold for cooling and solidification to obtain a slab. The first slab, the first + 1 slab, and the first + 2 slabs among the corresponding poured slabs are cut and taken offline for slow cooling and surface quality inspection.

[0058] (7)The slab is rolled into a steel plate with a thickness of 30 mm according to the set process parameters. The whole plate of the steel plate is inspected by ultrasonic flaw detection using the SY / T6423.3_U2 (2013) Standard for Nondestructive Testing Methods of Steel Pipes in the Petroleum and Natural Gas Industry. The flaw detection qualification rate meeting the standard reaches over 99.4%.

[0059] Example 5 A tundish pouring process for reducing inclusions in molten steel of pipeline steel. The working capacity of the tundish used is 40 tons, and the working liquid level height is 1200 mm. It includes the following steps: (1)Cleaning and baking in the tundish: Before baking the tundish, use a high-power vacuum cleaner for thorough cleaning; Bake according to the method of first small fire and then large fire. Bake with a small fire (≤400 °C) for 1.6 hours, with a medium fire (400 °C - 800 °C) for 1.5 hours, and with a large fire (≥1000 °C) for 3.0 hours. Measure the temperature in the impact zone of the tundish at about 1300 °C.

[0060] (2)Argon protection atmosphere in the tundish: After the tundish baking is completed, insert two of the three argon blowing pipes into the argon passage of the molten steel receiving hole in the tundish, and insert one argon blowing pipe into the argon passage of the temperature measuring hole in the tundish. Open the argon for pre-blowing argon operation, and the pre-blowing argon time is 40 seconds.

[0061] (3)Control of molten steel superheat: When starting casting with a high-tonnage tundish, control the temperature of the continuous casting ladle entering the station at 1590 °C, and control the superheat of the molten steel at the initial stage of casting to be 30 °C.

[0062] (4)Ladle pouring: After hanging the ladle protection sleeve, open the argon protection pouring valve, control the argon flow rate at 90 L / min, open the sliding nozzle of the ladle for pouring. After the molten steel flows out normally, lower the ladle arm to the low position; when the molten steel in the tundish reaches 15 tons, close the pre-blowing argon valve, remove the pre-blowing argon pipe, and gradually add about 25 bags of covering agent and 3 bags of carbonized rice husk. When the molten steel in the tundish reaches 30 tons, the addition is completed.

[0063] (5)Tundish pouring: When the molten steel volume in the tundish reaches 35 tons, open the stopper rod and moderately open the flow. After controlling the mold liquid level to the set level, switch the control of the stopper rod from manual to automatic; control the starting casting speed at 0.1 m / min, and gradually increase the casting speed to the target casting speed of 0.85 m / min according to the temperature-casting speed regime. After confirming normal and no sticking, switch to automatic control. Control the argon flow rate between the tundish mold nozzle slide plates at 4.0 L / min, and the back pressure between the plates at 0.21 bar; the time from ladle pouring to tundish pouring is 3.55 minutes.

[0064] (6)After the tundish pouring, the molten steel is injected into the mold for cooling and solidification to obtain a slab. The first three slabs, namely the first slab, the first + 1 slab, and the first + 2 slab, are cut and taken offline for slow cooling and surface quality inspection after casting.

[0065] (7)The slab is rolled into a 30-mm-thick steel plate according to the set process parameters. Ultrasonic flaw detection is carried out on the entire plate of the steel plate using the SY / T6423.3_U2 (2013) Standard for Nondestructive Testing Methods for Steel Pipes in the Petroleum and Natural Gas Industry. The flaw detection qualification rate meeting the standard reaches more than 99.1%.

[0066] Example 6 A tundish pouring process for reducing inclusions in the molten steel of pipeline steel. The working capacity of the tundish used is 40 tons, and the working liquid level height is 1230 mm. It includes the following steps: (1)Cleaning and baking in the tundish: Before baking the tundish, use a high-power vacuum cleaner for thorough cleaning; bake it in the order of small fire first and then large fire. Bake with a small fire (≤400 °C) for 1.5 hours, with a medium fire (400 °C - 800 °C) for 1.5 hours, and with a large fire (≥1000 °C) for 2.8 hours. Measure the temperature in the impact zone of the tundish to be about 1300 °C.

[0067] (2)Argon protection atmosphere in the tundish: After the tundish baking is completed, insert two of the three argon blowing pipes into the argon passage of the ladle receiving hole in the tundish, and insert one argon blowing pipe into the argon passage of the tundish temperature measuring hole. Open the argon for pre-blowing operation, and the pre-blowing time is 38 seconds.

[0068] (3)Control of molten steel superheat: When starting casting with a high-tonnage tundish, control the temperature of the continuous casting ladle entering the station at 1580 °C, and control the superheat of the molten steel at the initial stage of casting at 35 °C.

[0069] (4)Ladle casting: After hanging the ladle protection sleeve, open the argon protection casting valve, control the argon flow rate at 95 L / min, open the sliding nozzle of the ladle for casting. After the molten steel flows out normally, lower the ladle arm to the low position; when the molten steel in the tundish reaches 15 tons, close the pre-blowing argon valve, remove the pre-blowing argon pipe, and gradually add about 25 bags of covering agent and 3 bags of carbonized rice husk. When the molten steel in the tundish reaches 30 tons, the addition is completed.

[0070] (5)Tundish casting: When the molten steel volume in the tundish reaches 35 tons, open the stopper rod, moderately open the flow, and after controlling the mold liquid level to the set level, switch the control of the stopper rod from manual to automatic; control the starting casting speed at 0.1 m / min, and gradually increase the casting speed to the target casting speed of 0.85 m / min according to the temperature-casting speed regime. After confirming normal and no sticking, switch to automatic control. Control the argon flow rate between the tundish mold nozzle slide plates at 5.0 L / min, and control the back pressure between the plates at 0.12 bar; the time from ladle casting to tundish casting is 3.45 minutes.

[0071] (6)After tundish casting, the molten steel is injected into the mold for cooling and solidification to obtain a slab. The first three slabs, namely the starting slab, the first + 1 slab, and the first + 2 slab, are cut off and taken offline for slow cooling and surface quality inspection.

[0072] (7)The slab is rolled into a steel plate with a thickness of 30 mm according to the set process parameters, and ultrasonic flaw detection is carried out on the entire plate of the steel plate using the SY / T6423.3_U2 (2013) Standard for Nondestructive Testing Methods of Steel Pipes in the Petroleum and Natural Gas Industry. The flaw detection qualification rate meeting the standard reaches over 99.0%.

[0073] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, those of ordinary skill in the art can make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions should all be within the scope covered by the present invention / Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention.

Claims

1. A tundish pouring process for reducing inclusions in molten steel of pipeline steel, characterized in that: Including: Control the superheat of molten steel in the ladle to be 25°C to 35°C, control the ladle inlet temperature to be 1580°C to 1590°C, and start pouring the ladle under argon protection. When the mass of molten steel in the tundish is 15 tons, add tundish covering agent and carbonized rice husk to the tundish in sequence. When the mass of molten steel in the tundish reaches 30 tons, the addition is completed. When the mass of molten steel in the tundish is 35 tons, open the stopper rod, and pour the tundish into the mold.

2. The tundish casting process for reducing inclusions in the molten steel of pipeline steel as claimed in claim 1, characterized in that, Pre-treat the tundish before pouring the ladle. The pre-treatment includes cleaning and baking the inside of the tundish.

3. The tundish pouring process for reducing inclusions in molten steel of pipeline steel according to claim 2, characterized in that: The baking treatment includes baking the inside of the tundish until the temperature of the tundish impact zone ≥ 1200°C.

4. The tundish casting process for reducing inclusions in pipeline steel molten steel according to claim 3, characterized in that, The baking treatment adopts a three-stage baking process, including baking for 1 - 2 hours at a temperature ≤ 400°C, baking for 0.5 - 1.5 hours at a temperature of 400°C - 800°C, and baking for 1 - 3 hours at a temperature ≥ 1000°C, and baking until the temperature of the tundish impact zone ≥ 1200°C.

5. The tundish casting process for reducing inclusions in pipeline steel molten steel according to claim 2, characterized in that, After the pre-treatment of the tundish, perform pre-blowing argon treatment. The pre-blowing argon treatment includes inserting two argon blowing pipes into the argon passage of the steel-receiving hole of the tundish respectively, inserting one argon blowing pipe into the argon passage of the temperature-measuring hole of the tundish, opening the argon valve to pre-blow argon, and the pre-blowing time is 30 seconds to 40 seconds.

6. The tundish casting process for reducing inclusions in pipeline steel molten steel according to claim 1, characterized in that, The flow rate of argon during ladle pouring is controlled at 90 L / min to 100 L / min.

7. The tundish casting process for reducing inclusions in pipeline steel molten steel as described in claim 1, characterized in that, The control mode of the stopper rod is that when the liquid level in the mold rises to the set liquid level, the control of the stopper rod is changed from manual to automatic control.

8. The tundish pouring process for reducing inclusions in molten steel of pipeline steel according to claim 1, characterized in that: The starting drawing speed after pouring the tundish into the mold is 0.1 m / min to 0.2 m / min, and then the drawing speed is gradually increased to 0.8 m / min to 0.9 m / min according to the temperature-drawing speed regime.

9. The tundish pouring process for reducing inclusions in molten steel of pipeline steel according to claim 1, characterized in that: The argon flow rate between the tundish mold nozzle slide plates is controlled at 3 L / min to 10 L / min, and the back pressure between the plates ≥ 0.1 bar.

10. The tundish casting process for reducing inclusions in the molten steel of pipeline steel as described in claim 1, characterized in that, Including the following steps: (1). Bake the inside of the tundish until the temperature of the tundish impact zone ≥ 1,200°C; (2). After baking the inside of the tundish, pre-blow argon into the tundish, and the pre-blowing time is 30 seconds to 40 seconds; (3). Control the superheat of molten steel in the ladle to be 25°C to 35°C, and control the ladle inlet temperature to be 1580°C to 1590°C; (4). Start pouring the ladle under argon protection. When the mass of molten steel in the tundish is 15 tons, close the pre-blowing argon valve, add tundish covering agent and carbonized rice husk to the tundish in sequence. When the mass of molten steel in the tundish reaches 30 tons, the addition is completed; (5). When the mass of molten steel in the tundish is 35 tons, open the stopper rod, pour the tundish into the mold. The control mode of the stopper rod is that when the liquid level in the mold rises to the set liquid level, the control of the stopper rod is changed from manual to automatic control. The starting drawing speed after pouring the tundish into the mold is 0.1 m / min to 0.2 m / min, and then the drawing speed is gradually increased to 0.8 m / min to 0.9 m / min according to the temperature-drawing speed regime.