Non-tempered steel production process

Abstract

The invention relates to the technical field of material smelting, and discloses a non-conditioned steel production process which comprises the following steps: firstly, smelting a steel billet, adding a deoxidizing agent, alloy elements and slag charge into molten steel, processing raw material steel into the steel billet meeting the requirement, and then processing the steel billet into a hollow pipe, the grain structure of a steel pipe is refined through online normalizing treatment, the steel pipe is fed into a reducing mill after a steel pipe frame is heated, the steel pipe is subjected to plastic deformation when passing through a plurality of rollers, the size and shape of the steel pipe are changed, the steel pipe enters a straightening machine through a conveying system, and the six-roller straightening machine applies roller pressure; a steel pipe is forced to be subjected to a series of bending deformation and adjustment in a straightening machine, parts with poor quality at the two ends of the steel pipe are cut off through an end cutter, finally, whether cracks, air holes and other defects exist in the steel pipe or on the surface of the steel pipe or not is checked through ultrasonic wave, eddy current or magnetic powder detection and other means, and meanwhile manual or mechanical surface inspection is conducted.

Description

Technical Field

[0001] The present invention relates to the technical field of material smelting, and particularly to a production process for non-adjustable steel. Background Art

[0002] The seamless steel pipe used for hydraulic cylinders has high strength, high toughness and good anti-fatigue characteristics, and can withstand high pressure and heavy load working environments. Its material undergoes precise proportioning and strict heat treatment processes to ensure that the steel pipe has excellent tensile resistance, impact resistance and wear resistance. The seamless structure eliminates weld defects, improves the overall sealing performance and durability, and is suitable for the conduction of high-pressure oil in hydraulic systems. At the same time, the surface quality of this steel pipe is excellent, and the inner wall is precisely processed to reduce frictional resistance, ensuring the smoothness and efficiency of the hydraulic cylinder during operation.

[0003] However, in the actual production process of the above seamless steel pipe, the requirements for inclusions, internal quality and surface quality of the steel billet are relatively strict, and the existing process research lacks a perfect deoxidation and dehydrogenation system and a reasonable refining and continuous casting process, making it difficult for the product quality to meet the requirements for manufacturing seamless steel pipes. In view of this, we propose a production process for non-adjustable steel. Summary of the Invention

[0004] The purpose of the present invention is to provide a production process for non-adjustable steel to solve the problems raised in the above background art.

[0005] To achieve the above purpose, the present invention provides the following technical solution: A production process for non-adjustable steel, including the following steps:

[0006] S1. Melting of the steel billet;

[0007] S2. Processing the steel billet into a hollow pipe;

[0008] S3. Online normalizing treatment;

[0009] S4. Reheating and reducing the pipe diameter;

[0010] S5. Natural cooling of the steel pipe and straightening the steel pipe;

[0011] S6. Non-destructive testing and inspection of the pipe body surface;

[0012] S7. Packaging and warehousing.

[0013] Preferably, the process of steel billet melting includes steelmaking, refining, vacuum degassing, and solidification forming. The C content in the raw material steel used for melting is 0.2% - 0.22%, the Si content is 0.21% - 0.27%, the Mn content is 1.56% - 1.66%, the P content should not be higher than 0.013%, the S content is lower than 0.006%, the Al content is 0.021% - 0.035%, and the V content is 0.10% - 0.15%. In the steelmaking process, a converter is used to convert molten iron into molten steel. When about 1 / 4 of the molten steel is tapped, deoxidizers, alloying elements, and slag materials are added to the molten steel to remove the dissolved oxygen in the molten steel, reduce the oxidability of the molten steel, and improve the quality of the steel. Manganese, vanadium, chromium, etc. are added to adjust the chemical composition of the steel to meet the performance requirements. The temperature of the molten steel is not lower than 1650°C to ensure the fluidity during tapping and the process requirements of subsequent processes. The C content in the molten steel is greater than 0.075% to ensure that the strength and hardness of the steel meet the design requirements. The P content is less than 0.01%. Phosphorus is a harmful element that will reduce the toughness and corrosion resistance of the steel. During the process of pouring the molten steel into the ladle, a slag stopper is used to prevent the slag in the converter from flowing into the ladle. The slag contains high oxides and impurities, and entering the molten steel will reduce the purity of the steel and affect its performance. After the molten steel enters the ladle, argon is blown through the bottom of the ladle to make the chemical composition evenly distributed, avoid segregation, help inclusions float to the surface of the molten steel, improve the purity of the molten steel, reduce the oxidation of the molten steel at the same time, and stabilize the temperature of the molten steel.

[0014] Preferably, the refining uses an LF furnace to heat the molten steel by electric arc. The power-on time of the LF furnace is greater than 25 minutes to adjust the temperature and provide heat support for subsequent chemical composition adjustment. During the refining process, argon is blown through the bottom of the ladle, and the argon blowing time should be greater than 45 minutes to remove inclusions and dissolved gases in the molten steel, quickly form "white slag", and maintain it for at least 25 minutes. The white slag contains a high alkalinity and calcium oxide, which can absorb oxides and impurities in the molten steel, improve the deoxidation efficiency, reduce the oxygen content in the molten steel, and ensure the purity of the steel. Alloying is added to adjust the composition of the molten steel, considering the composition changes in the VD furnace and continuous casting process. During the degassing treatment in a vacuum environment, element burning loss will occur, such as the oxidation consumption of aluminum and manganese. During the continuous casting process, carbon growth may occur, and the molten steel absorbs carbon from carbonaceous materials, so the composition needs to be adjusted in advance. Before the molten steel leaves the station, calcium treatment is carried out by feeding Ca wire. If the Ca wire fed in the starting pouring furnace is 90 - 100 m, the Ca wire fed in the continuous pouring furnace should be 60 - 110 m. The calcium treatment converts oxide inclusions, such as Al 2 O 3 into spherical inclusions, reduce the adverse effects on the performance of the steel, improve the plasticity and toughness of the steel, and reduce the risk of hot working cracking.

[0015] Preferably, the vacuum degassing is carried out using a VD furnace and an RH furnace. In the VD furnace, the molten steel is heated for at least 45 minutes. The VD furnace removes gases such as hydrogen, nitrogen, and oxygen in the molten steel through vacuum degassing, improving the purity of the molten steel. This process requires a certain amount of time to ensure complete gas removal. After the atmosphere re-enters the VD furnace, the composition of the molten steel cannot be adjusted anymore. After breaking the vacuum, the gas content in the molten steel is easily disturbed, and adjusting the composition at this time will cause unstable refining effects. In the RH furnace, the molten steel is heated for at least 40 minutes. The RH furnace further removes the gases in the molten steel and refines the molten steel to ensure the quality of the steel. After the RH furnace is evacuated, the composition of the molten steel cannot be adjusted anymore. In a vacuum state, adjusting the composition, such as adding alloying elements, will interfere with the gas removal and dissolution processes, affecting the purity and stability of the molten steel. During the operation of the VD furnace or RH furnace, the vacuum pumping pressure needs to be reduced to below 60 Pa and maintained for at least 15 minutes. After the vacuum treatment is completed, soft blowing is carried out using argon for at least 20 minutes. Before the molten steel is tapped, the hydrogen content is measured to make H less than 1.43 ppm. After the molten steel leaves the VD furnace or RH furnace, the ladle temperature when the molten steel leaves the station and the superheat of the tapping furnace are controlled within 32 °C. After the molten steel passes through the tundish, the superheat when it enters the continuous casting furnace is controlled within 22 °C.

[0016] Preferably, the solidification and forming include molten steel pouring, mold solidification, billet withdrawal and cooling. During the molten steel pouring process, the superheat of the molten steel in the tapping furnace and continuous casting furnace is controlled at 14 °C ± 1 °C. The surface of the molten steel is covered with protective slag, and slag from the tundish is strictly prohibited. Low-carbon steel series protective slag is used to control the liquid level fluctuation in the mold. When the fluctuation exceeds the range of ±6 mm, the billet will be scrapped. The billet uses a mold type of 280×280 mm or 350×430 mm. At least 2 macro samples are taken for each casting to conduct internal quality inspections. For the 280×280 mm square billet, it is sent to the rolling mill for processing by hot delivery and hot charging methods. If it is not hot delivered and hot charged, the billet should be placed in a special pit for slow cooling.

[0017] Preferably, before processing the steel billet, the steel billet is heated to 1100 °C - 1200 °C. The steel billet processing includes piercing and tube rolling. The piercing is carried out using a two-roll piercing mill. Pressure is applied to the heated steel billet through two inclined rotating rolls to form a cavity in its central part, and it is initially formed into a mandrel tube. Then, a tube rolling mill is used to roll the mandrel tube in multiple passes, gradually reducing the wall thickness and outer diameter to make it close to the design dimensions.

[0018] Preferably, for the online normalizing treatment, the grain structure of the steel pipe is refined by uniformly heating at a high temperature and then naturally cooling.

[0019] Preferably, the diameter reduction is achieved by adjusting the tensile force in real time with a micro-tension reducing mill, applying a very small tensile force to the steel pipe to control its deformation, and further reducing the diameter of the steel pipe to the precise size. During the diameter reduction process, the steel pipe undergoes plastic deformation when passing through multiple rolls, changing its size and shape while improving the surface quality.

[0020] Preferably, the straightening of the steel pipe is carried out using a six-roll straightening device. The steel pipe enters the straightening machine through the conveying system. The six-roll straightening machine applies roller pressure to force the steel pipe to undergo a series of bending deformations and adjustments inside the straightening machine, eliminating the bending caused by uneven cooling or processing stress of the steel pipe and restoring its straightness. Subsequently, a cutting machine is used to cut off the parts with poor quality at both ends of the steel pipe, and the steel pipe is cut into the appropriate finished length.

[0021] Preferably, the non-destructive testing and inspection of the pipe body surface are carried out by means such as ultrasonic, eddy current or magnetic particle testing to check whether there are defects such as cracks and pores inside and on the surface of the steel pipe, and at the same time, manual or mechanical surface inspection is carried out.

[0022] Compared with the prior art, the present invention provides a non-adjustable steel production process, which has the following beneficial effects:

[0023] 1. In this non-adjustable steel production process, by considering the composition changes in the VD furnace and continuous casting process during the refining process, during the degassing treatment in a vacuum environment, element burn-off will occur, such as the oxidation consumption of aluminum and manganese. Carbon growth may occur during the continuous casting process, and the molten steel absorbs the carbon of the carbonaceous material. Alloy is added to adjust the composition of the molten steel, and the composition is adjusted in advance to ensure that the finished steel pipe meets the requirements for manufacturing hydraulic cylinders. During the melting process of the steel billet, the slag is strictly controlled, and the protective slag covers the surface of the molten steel. The entire casting process requires protecting the molten steel from direct contact with air to prevent oxidation and the introduction of other impurities, and avoiding the entry of slag into the mold to avoid affecting the quality of the cast billet.

[0024] 2. In this non-adjustable steel production process, the steel billet is first preliminarily formed into a hollow billet using a two-roll piercing mill, and then a rolling mill is used to perform multiple passes of rolling on the hollow billet, gradually reducing the wall thickness and outer diameter to be close to the design size. Finally, the tensile force is adjusted in real time with a micro-tension reducing mill, applying a very small tensile force to the steel pipe to control its deformation, and further reducing the diameter of the steel pipe to the precise size.

[0025] 3. In this non-adjustable steel production process, the steel pipe enters the straightening machine through the conveying system. The six-roll straightening machine applies roller pressure, and after being processed by the six-roll straightening machine, the bending of the steel pipe is gradually eliminated, and its straightness is gradually restored. At this time, there is no obvious wavy deformation on the surface of the steel pipe, and the straightness meets the technical standards. The surface of the straightened steel pipe is also smoother, and its shape is closer to the ideal state. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the process of the present invention;

[0027] Figure 2 This is a schematic diagram of the steel billet melting process of the present invention. Specific embodiments

[0028] As Figure 1 - Figure 2 shown, the present invention provides a technical solution:

[0029] A production process for non-adjustable steel, comprising the following steps:

[0030] S1. Steel billet melting;

[0031] S2. Processing the steel billet into a hollow tube;

[0032] S3. Online normalizing treatment;

[0033] S4. Reheating and reducing the pipe diameter;

[0034] S5. Natural cooling of the steel pipe and straightening the steel pipe;

[0035] S6. Nondestructive testing and inspection of the pipe body surface;

[0036] S7. Packaging and warehousing.

[0037] Among them, the process of steel billet melting includes steelmaking, refining, vacuum degassing and solidification forming. The C content in the raw material steel used for melting is 0.2% - 0.22%, the Si content is 0.21% - 0.27%, the Mn content is 1.56% - 1.66%, the P content should not be higher than 0.013%, the S content is lower than 0.006%, the Al content is 0.021% - 0.035%, and the V content is 0.10% - 0.15%. In steelmaking, a converter is used to convert molten iron into molten steel. When about 1 / 4 of the molten steel is tapped from the converter, deoxidizers, alloying elements and slag materials are added to the molten steel to remove the dissolved oxygen in the molten steel, reduce the oxidability of the molten steel, and improve the quality of the steel. Manganese, vanadium, chromium, etc. are added to adjust the chemical composition of the steel to meet the performance requirements. The temperature of the molten steel is not lower than 1650 °C to ensure the fluidity during tapping and the process requirements of subsequent processes. The C content in the molten steel is greater than 0.075% to ensure that the strength and hardness of the steel meet the design requirements. The P content is less than 0.01%. Phosphorus is a harmful element that will reduce the toughness and corrosion resistance of the steel. During the process of pouring the molten steel into the ladle, a slag stopper is used to prevent the furnace slag in the converter from flowing into the ladle. The furnace slag contains high oxides and impurities, and entering the molten steel will reduce the purity of the steel and affect the performance. After the molten steel enters the ladle, argon is blown through the bottom of the ladle to make the chemical composition evenly distributed, avoid segregation, help inclusions float to the surface of the molten steel, improve the purity of the molten steel, and at the same time reduce the oxidation of the molten steel and stabilize the temperature of the molten steel.

[0038] Among them, refining uses an LF furnace to heat the molten steel by electric arc. The power-on time of the LF furnace is greater than 25 minutes, which adjusts the temperature and provides heat support for subsequent chemical composition adjustment. During the refining process, argon is blown into the molten steel through the bottom of the ladle. The argon blowing time should be greater than 45 minutes to remove inclusions and dissolved gases in the molten steel, quickly form "white slag", and maintain it for at least 25 minutes. The white slag has a high alkalinity and calcium oxide, which can absorb oxides and impurities in the molten steel, improve the deoxidation efficiency, reduce the oxygen content in the molten steel, ensure the purity of the steel, add alloys to adjust the composition of the molten steel, and consider the composition changes in the VD furnace and continuous casting process. During the degassing treatment in a vacuum environment, element burning losses will occur, such as the oxidation consumption of aluminum and manganese. Carbon growth may occur during the continuous casting process, and the molten steel absorbs carbon from carbonaceous materials, so the composition needs to be adjusted in advance. Before the molten steel leaves the station, calcium treatment is carried out by feeding Ca wire. If the Ca wire fed into the starting casting furnace is 90 - 100 m, the Ca wire fed into the continuous casting furnace should be 60 - 110 m. The calcium treatment converts oxide inclusions, such as Al 2 O 3 into spherical inclusions, reducing the adverse effects on the properties of the steel, improving the plasticity and toughness of the steel, and reducing the risk of hot working cracking.

[0039] Among them, vacuum degassing uses a VD furnace and an RH furnace. In the VD furnace, the molten steel is heated for at least 45 minutes. The VD furnace removes gases such as hydrogen, nitrogen, and oxygen in the molten steel through vacuum degassing, improving the purity of the molten steel. This process requires a certain amount of time to ensure complete gas removal. After the atmosphere re-enters the VD furnace, the composition of the molten steel cannot be adjusted again. After breaking the vacuum, the gas content of the molten steel is easily disturbed, and adjusting the composition at this time will lead to unstable refining effects. In the RH furnace, the molten steel is heated for at least 40 minutes. The RH furnace further removes gases in the molten steel and refines the molten steel to ensure the quality of the steel. After the RH furnace is evacuated, the composition of the molten steel cannot be adjusted again. In a vacuum state, adjusting the composition, such as adding alloying elements, will interfere with the gas removal and dissolution processes, affecting the purity and stability of the molten steel. During the operation of the VD furnace or RH furnace, the vacuum pumping pressure needs to be reduced to below 60 Pa and maintained for at least 15 minutes. After the vacuum treatment is completed, soft blowing is carried out with argon for at least 20 minutes. Before the molten steel is tapped, the hydrogen content is measured to make H less than 1.43 ppm. Excessive hydrogen content will cause hydrogen embrittlement in the steel, affecting the toughness and crack resistance of the steel. After the molten steel leaves the VD furnace or RH furnace, the upper platform temperature of the molten steel when it leaves the station and the superheat of the starting casting furnace are controlled within 32 °C. After the molten steel passes through the tundish, the superheat when it enters the continuous casting furnace is controlled within 22 °C.

[0040] Among them, solidification forming includes molten steel pouring, mold solidification, billet drawing and cooling. During the molten steel pouring process, the superheat of the molten steel in the starting furnace and continuous casting furnace is controlled at 14°C ± 1°C. A protective slag is used to cover the surface of the molten steel. The entire pouring process needs to protect the molten steel from direct contact with air to prevent oxidation and the introduction of other impurities. It is strictly prohibited for slag to flow from the tundish to avoid slag entering the mold and affecting the quality of the billet. A low-carbon steel series protective slag is used to reduce the change in the carbon content in the molten steel and prevent the formation of inclusions and impurities in the molten steel. The liquid level in the mold is controlled. When the fluctuation exceeds the range of ±6 mm, the billet will be rejected. If the liquid level fluctuation exceeds the range of ±6 mm, it indicates that the molten steel has uneven flow or temperature change during solidification, which may lead to quality problems of the billet, such as segregation and cracks. The billet uses a mold type of 280×280 mm or 350×430 mm. At least 2 macro samples are taken for each casting to conduct internal quality inspection. A macro microscope is used to check the internal microstructure of the billet. For the 280×280 mm square billet, it is sent to the rolling mill for processing by the hot delivery and hot charging method to maintain the temperature of the billet, reduce the cooling rate, and avoid cracks and dimensional instability. If it is not hot delivered and hot charged, the billet should be placed in a special pit for slow cooling.

[0041] Among them, before steel billet processing, the steel billet is heated to 1100°C - 1200°C. Steel billet processing includes piercing and tube rolling. Piercing uses a two-roll piercing mill. Pressure is applied to the heated steel billet through two inclined rotating rolls to form a cavity in its central part and initially form a rough tube. Then, a tube rolling mill is used to perform multiple passes of rolling on the rough tube, gradually reducing the wall thickness and outer diameter to make it close to the design size.

[0042] Among them, online normalizing treatment is carried out by heating uniformly at high temperature and then natural cooling. The grain structure of the steel tube is refined. The finer the grains, the better the strength, hardness and toughness of the steel tube usually are. It can evenly release the internal stress of the steel tube, thus avoiding deformation or cracks during subsequent processing or use.

[0043] Among them, reducing the tube diameter is achieved by the micro-tension reducing mill to adjust the tension in real time, applying a very small tensile force to the steel tube to control the deformation of the steel tube and further reducing the diameter of the steel tube to the precise size. During the reducing process, the steel tube undergoes plastic deformation when passing through multiple rolls, changing the size and shape of the steel tube and improving the surface quality at the same time. Through uniform micro-tension control, uneven phenomena such as local overstretching or local defects can be avoided during the deformation of the steel tube.

[0044] Among them, the straightening of the steel pipe adopts a six-roll straightening device. The steel pipe enters the straightening machine through the conveying system. The six-roll straightening machine applies roller pressure to force the steel pipe to undergo a series of bending deformations and adjustments in the straightening machine, eliminating the bending of the steel pipe caused by uneven cooling or processing stress and restoring its straightness. Subsequently, a cutting machine is used to cut off the parts with poor quality at both ends of the steel pipe, and the steel pipe is cut into a suitable finished length.

[0045] Among them, non-destructive testing and inspection of the pipe body surface use means such as ultrasonic, eddy current or magnetic particle testing to check whether there are defects such as cracks and pores inside and on the surface of the steel pipe, and at the same time, manual or mechanical surface inspection is carried out.

[0046] In an embodiment of the present invention, first, the steel billet is melted, deoxidizers, alloying elements and slag materials are added to the molten steel, and the raw steel is processed into a steel billet that meets the requirements. Then, the steel billet is processed into a hollow pipe. The grain structure of the steel pipe is refined through on-line normalizing treatment. After heating the steel pipe frame, the steel pipe is sent into a reducing mill. When the steel pipe passes through multiple rolls, plastic deformation occurs, changing the size and shape of the steel pipe and improving the surface quality at the same time. The steel pipe enters the straightening machine through the conveying system. The six-roll straightening machine applies roller pressure to force the steel pipe to undergo a series of bending deformations and adjustments in the straightening machine. A cutting machine is used to cut off the parts with poor quality at both ends of the steel pipe, and the steel pipe is cut into a suitable finished length. Finally, means such as ultrasonic, eddy current or magnetic particle testing are used to check whether there are defects such as cracks and pores inside and on the surface of the steel pipe, and at the same time, manual or mechanical surface inspection is carried out.

[0047] During the refining process, considering the composition changes in the VD furnace and continuous casting process, during the degassing treatment in a vacuum environment, element burn-off will occur, such as the oxidation consumption of aluminum and manganese. Carbon growth may occur during the continuous casting process, and the molten steel absorbs the carbon of the carbonaceous material. Alloys are added to adjust the composition of the molten steel, and the composition is adjusted in advance to ensure that the finished steel pipe meets the requirements for manufacturing hydraulic cylinders.

[0048] During the melting process of the steel billet, the slag is strictly controlled. During the process of pouring the molten steel into the ladle, a slag stopper is used to prevent the slag in the converter from flowing into the ladle. During the pouring process of the molten steel, a protective slag is used to cover the surface of the molten steel. The entire casting process needs to protect the molten steel from direct contact with air to prevent oxidation and the introduction of other impurities, avoid the entry of slag into the mold, and avoid affecting the quality of the casting billet. A low-carbon steel series protective slag is used to reduce the change of carbon content in the molten steel and prevent the formation of inclusions and impurities in the molten steel, ensuring the purity of the molten steel while preventing oxidation and the introduction of other impurities.

[0049] In order to improve the precision of steel pipes, a two-roll piercing mill is first used to preliminarily form the billet into a hollow bloom, and then a rolling mill is used to perform multiple passes of rolling on the hollow bloom to gradually reduce the wall thickness and outer diameter, making it close to the design size. Finally, a stretch reducing mill is used to adjust the tension in real time, applying a very small tensile force to the steel pipe to control its deformation and further reducing the diameter of the steel pipe to the precise size.

[0050] In addition, in order to make the surface of the steel pipe smoother and thus improve the tight fit degree of the hydraulic cylinder, the steel pipe is fed into a straightening machine through a conveying system. The six-roll straightening machine applies roller pressure. After being processed by the six-roll straightening machine, the bending of the steel pipe is gradually eliminated, and it gradually returns to straightness. At this time, there is no obvious wavy deformation on the surface of the steel pipe, and the straightness meets the technical standards. The surface of the straightened steel pipe is also smoother and closer to the ideal shape.

[0051] In the present invention, during use, first, the billet is melted to obtain a billet that meets the requirements. After sizing and cutting, the billet is reheated through a heating furnace, processed into a hollow bloom by a two-roll piercing mill, and then processed into a steel pipe by a rolling mill. Subsequently, the grain structure of the steel pipe is refined through online normalizing treatment. Then, the steel pipe is sent into a heating furnace for heating, and the diameter of the steel pipe is further reduced to the precise size by a stretch reducing mill. After natural cooling, it is straightened by a six-roll straightening machine. The poor-quality parts at both ends of the steel pipe are cut off by a cutting machine, and the steel pipe is cut into the appropriate finished length. After non-destructive testing and inspection of the pipe body surface, it is packaged and stored in the warehouse.

[0052] The above has generally described the present invention in detail, but based on the present invention, some modifications or improvements can be made, which are obvious to those of ordinary skill in the art. Therefore, modifications or improvements made without departing from the spirit and idea of the present invention are within the protection scope of the present invention.

Claims

1. A non-adjustable steel production process, characterized in that: The steps include: S1, billet smelting; S2, the steel billet is processed into a hollow tube; S3, online normalization processing; S4, reheating to reduce the pipe diameter; S5, the steel pipe is naturally cooled and straightened; S6, non-destructive testing and pipe surface inspection; S7, packaging and storage.

2. A non-adjustable steel production process according to claim 1, characterized in that: The process of smelting the steel billet includes steelmaking, refining, vacuum degassing and solidification molding. The C content of the raw steel used for smelting is 0.2%-0.22%, the Si content is 0.21%-0.27%, the Mn content is 1.56%-1.66%, the P content should not be higher than 0.013%, the S content is lower than 0.006%, the Al content is 0.021%-0.035%, and the V content is 0.10%-0.15%. The steelmaking adopts a converter to convert molten iron into molten steel. When the output of the molten steel is about 1 / 4, a deoxidizer, alloy elements and slag are added to the molten steel. The temperature of the molten steel is not lower than 1650°C, the C content in the molten steel is greater than 0.075%, and the P content is less than 0.01%. In the process of pouring the molten steel into the ladle, a slag stopper is used to prevent the slag in the converter from flowing into the ladle. After the molten steel enters the ladle, argon gas is blown into the bottom of the ladle.

3. A non-adjustable steel production process according to claim 2, characterized in that: The refining uses an LF furnace to heat the molten steel through an electric arc. The LF furnace is powered on for more than 25 minutes. During the refining process, argon is blown through the bottom of the ladle for more than 45 minutes to quickly form "white slag" which is maintained for at least 25 minutes. Alloys are added to adjust the composition of the molten steel. Before the molten steel leaves the station, calcification treatment is performed by feeding Ca wire. The Ca wire fed into the open-cast furnace is 90-100m, and the continuous casting furnace should be fed with 60-110m.

4. A non-adjustable steel production process according to claim 2, characterized in that: The vacuum degassing adopts a VD furnace and a RH furnace. The molten steel is heated for at least 45 minutes in the VD furnace. After the atmosphere re-enters the VD furnace, the composition of the molten steel cannot be adjusted. The molten steel is heated for at least 40 minutes in the RH furnace. After the RH furnace is vacuumized, the composition of the molten steel cannot be adjusted. During the operation of the VD furnace or the RH furnace, the vacuum pressure needs to be reduced to below 60Pa for at least 15 minutes. After the vacuum treatment is completed, argon is used for soft blowing for at least 20 minutes. Before the molten steel is discharged from the furnace, the hydrogen content is measured to make H less than 1.43ppm. After the molten steel leaves the VD furnace or the RH furnace, the upper stage temperature of the molten steel when it leaves the station and the superheat of the pouring furnace are controlled within 32°C. After the molten steel passes through the tundish, the superheat when it enters the continuous casting furnace is controlled within 22°C.

5. A non-adjustable steel production process according to claim 2, characterized in that: The solidification forming includes molten steel pouring, crystallizer solidification, billet pulling and cooling. During the molten steel casting process, the superheat of the molten steel in the molten steel pouring furnace and the continuous pouring furnace is controlled at 14°C±1°C, and protective slag is used to cover the surface of the molten steel. It is strictly prohibited to put slag in large bags. Low-carbon steel series protective slag is used to control the fluctuation of the crystallizer liquid level. When the fluctuation range exceeds ±6mm, the billet will be picked out and scrapped. The billet adopts a casting machine billet mold of 280×280mm or 350×430mm. At least 2 low-magnification samples are taken for each pouring for internal quality inspection. The 280×280mm square billet is sent to the rolling unit for processing by hot delivery and hot loading. If hot delivery and hot loading are not performed, the billet should be placed in a special pit for slow cooling.

6. A non-adjustable steel production process according to claim 1, characterized in that: The steel billet is heated to 1100°C to 1200°C before processing. The steel billet processing includes punching and tube rolling. The punching adopts a two-roller puncher, and pressure is applied to the heated steel billet through two inclined rotating rollers to form a cavity in its center part, which is initially formed into a rough tube. Then, a tube rolling machine is used to roll the rough tube for multiple times to gradually reduce the tube wall thickness and outer diameter to make it close to the designed size.

7. A non-adjustable steel production process according to claim 1, characterized in that: The online normalizing treatment refines the grain structure of the steel pipe by uniformly heating at a high temperature and then naturally cooling it.

8. The non-adjustable steel production process according to claim 1, characterized in that: The pipe diameter reduction is achieved by adjusting the tension in real time through a micro-tension reducer, applying a very small tensile force to the steel pipe, controlling the deformation of the steel pipe, and further reducing the diameter of the steel pipe to a precise size. During the diameter reduction process, the steel pipe undergoes plastic deformation when passing through multiple rollers, changing the size and shape of the steel pipe while improving the surface quality.

9. A non-adjustable steel production process according to claim 1, characterized in that: The straightening steel pipe adopts a six-roller straightening device. The steel pipe enters the straightening machine through a conveying system. The six-roller straightening machine applies roller pressure to force the steel pipe to undergo a series of bending deformations and adjustments in the straightening machine, thereby eliminating the bending of the steel pipe caused by uneven cooling or processing stress, and restoring its straightness. Subsequently, a head cutting machine is used to cut off the parts with poor quality at both ends of the steel pipe and cut the steel pipe into a suitable finished product length.

10. The non-adjustable steel production process according to claim 1, characterized in that: The non-destructive testing and pipe surface inspection use ultrasonic, eddy current or magnetic particle testing to check whether there are defects such as cracks and pores inside and on the surface of the steel pipe, and perform manual or mechanical surface inspection at the same time.

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