High-purity high-toughness ultrahigh-strength steel pipe and method for manufacturing the same

Abstract

The application provides a high-purity high-toughness ultrahigh-strength steel pipe and a manufacturing method thereof, and relates to the technical field of steel materials. In the manufacturing method, a continuous casting pipe blank is directly pierced or forged into a pipe blank and then pierced, and then a reasonable heat treatment process is performed to obtain the high-purity high-toughness ultrahigh-strength steel pipe. In the process of manufacturing the steel material, the electric remelting is not needed, the time and cost consumed by the electric remelting are greatly reduced, the process flow is shortened, the production efficiency is greatly improved, and the production demand of large batches and fast rhythm is met. The application also provides a high-purity high-toughness ultrahigh-strength steel pipe, which is obtained by the above manufacturing method. On the basis of the specific chemical composition of the steel material in the application, the specific process treatment is combined, so that the steel pipe has the properties of high purity, high toughness and ultrahigh strength, and meets the demand of the downstream user market.

Description

Technical Field

[0001] This invention relates to the field of steel technology, and in particular to a high-purity, high-toughness, ultra-high-strength steel pipe and its manufacturing method. Background Technology

[0002] High-toughness and ultra-high-strength steel pipes, as the name suggests, refer to steel pipes that possess both high toughness and ultra-high strength. These materials are commonly used in the aerospace field, such as in key components of aircraft, rockets, and spacecraft, as well as in the defense industry, such as in the manufacture of weapons and equipment like aerospace missiles.

[0003] Currently, the metallurgical technology commonly used for high-toughness and ultra-high-strength steel pipes involves vacuum induction smelting of masterbatch, followed by vacuum arc remelting into ingots, forging of the ingots into bars of the required specifications, and further rolling of the forged bars into steel pipes of the required specifications using a steel pipe rolling mill. Alternatively, an electric furnace + LF refining + vacuum treatment + die casting masterbatch is used, followed by electroslag remelting into electroslag ingots, forging of the electroslag ingots into bars of the required specifications, and further rolling of the forged bars into pipes of the required specifications using a steel pipe rolling mill. These metallurgical technologies involve long processes, high costs, and low production efficiency, making them unsuitable for rapid, mass production. In response to the modular and modular requirements of aerospace and defense industries, the low-cost, large-scale production of aviation munitions, and the need to support sustained large-scale operations, higher requirements are placed on the purity, toughness, and ultra-high strength properties of high-toughness and ultra-high-strength steel pipes. Therefore, it is necessary to develop a low-cost, large-scale, systematic, energy-saving, short-process, and fast-paced production method that also meets the performance requirements of low P, low S, low O, low N, high purity, high toughness, and high strength to satisfy the needs of downstream user markets.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a high-purity, high-toughness, ultra-high-strength steel pipe and its manufacturing method, in order to solve the defects of existing metallurgical technology, such as high P, S, O, and N content in steel composition, long steel preparation process, high energy consumption, high process cost, low production efficiency, and inability to adapt to large-scale, fast-paced production.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] The primary objective of this invention is to provide a method for manufacturing high-purity, high-toughness, and ultra-high-strength steel pipes, comprising the following steps:

[0008] (a) Provide continuously cast tube blanks obtained by smelting and continuous casting;

[0009] (b) The continuously cast billet is heated and then directly rolled to obtain a steel pipe;

[0010] Alternatively, the continuously cast tube blank is heated and forged to obtain a forged tube blank, which is then annealed and directly rolled into a steel pipe.

[0011] (c) The steel pipe obtained in step (b) is subjected to normalizing and tempering treatment to obtain high-purity, high-toughness, and ultra-high-strength steel pipe.

[0012] Furthermore, based on the above-mentioned technical solution of the present invention, in step (a), the smelting includes primary refining, refining and vacuum treatment of the raw materials according to the composition of high-purity, high-toughness and ultra-high-strength steel pipes.

[0013] Furthermore, based on the above technical solution of the present invention, in step (a), an electric furnace or converter is used for primary refining, the tapping temperature is ≥1600℃, and the P content of the tapping steel is ≤0.005%.

[0014] And / or, in step (a), the refining is LF refining, the refining endpoint S content is ≤0.0010%, the endpoint temperature is 1595℃~1635℃, and the total refining time is ≥45min;

[0015] And / or, in step (a), the vacuum treatment time is ≥25 min, the treatment time for vacuum ≤0.5 Torr is ≥20 min, and argon soft blowing is used at the same time, with a soft blowing time of ≥15 min;

[0016] And / or, in step (a), during the continuous casting process, the molten steel in the tundish is superheated to 20°C to 35°C, and the constant temperature casting speed is 0.30 m / min to 0.43 m / min.

[0017] Furthermore, based on the above-mentioned technical solution of the present invention, in step (a), the high-purity, high-toughness, ultra-high-strength steel pipe comprises the following components in the following mass fractions: C: 0.25%–0.35%, Si: 1.00%–1.40%, Mn: 0.80%–1.10%, Cr: 1.00%–1.40%, Ni: 0%–0.50%, Mo: 0%–0.10%, W: 0%–0.10%, Nb: 0%–0.04%, Al: 0%–0.050%, P: ≤0.015%, S: ≤0.010%, O: ≤0.0010%, N: ≤0.0060%, with the remainder being iron and unavoidable impurities.

[0018] Furthermore, based on the above-mentioned technical solution of the present invention, in step (b), the heating temperature of the continuously cast billet during heat treatment is 1160℃-1280℃, the holding time is ≥2.5h; and / or, the minimum tapping frequency is ≥60S / piece.

[0019] Furthermore, based on the above-mentioned technical solution of the present invention, in step (b), the forging is a combined forging, including fast forging and radial forging.

[0020] Furthermore, based on the above technical solution of the present invention, in step (b), the initial forging temperature of the rapid forging is ≥950℃ and the final forging temperature is ≥800℃; preferably, an octagonal intermediate billet of 300mm to 360mm is obtained after rapid forging.

[0021] And / or, the initial forging temperature of the radial forging is ≥900℃ and the final forging temperature is ≥800℃;

[0022] And / or, when the temperature of the intermediate billet obtained after rapid forging is <900℃, the intermediate billet is reheated in the furnace before the radial forging is performed. The reheating temperature is 1180℃~1220℃ and the holding time is 1h~1.5h.

[0023] Furthermore, based on the above technical solution of the present invention, in step (b), the annealing temperature of the forged tube blank is 660℃~680℃, and the holding time is 20h~25h.

[0024] And / or, in step (b), the tube rolling includes piercing, tube rolling and diameter reduction.

[0025] Furthermore, based on the above technical solution of the present invention, in step (c), the normalizing temperature is 900℃~960℃, the holding time is ≥1h, and the furnace is air-cooled.

[0026] And / or, the tempering temperature is 660℃~700℃, the holding time is 6h~10h, and the furnace is air-cooled after removal.

[0027] The second objective of this invention is to provide a high-purity, high-toughness, ultra-high-strength steel pipe, which is manufactured using the above-mentioned method for producing high-purity, high-toughness, ultra-high-strength steel pipes.

[0028] The high-purity, high-toughness, ultra-high-strength steel pipe has a tensile strength ≥1700MPa, a yield strength ≥1400MPa, a yield-to-tensile ratio ≤0.86, an impact energy ≥70J, and a fracture toughness ≥90MPa*m. 1 / 2 .

[0029] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0030] (1) This invention provides a method for manufacturing high-purity, high-toughness, and ultra-high-strength steel pipes. In this method, the continuously cast billet is directly threaded into a pipe without electroslag remelting or is forged into a billet and then threaded into a pipe. After a reasonable heat treatment process, high-purity, high-toughness, and ultra-high-strength steel pipes are obtained. Electroslag remelting is not required in the steel preparation process, which greatly reduces the time and cost of electroslag remelting, shortens the process flow, greatly improves production efficiency, and meets the needs of large-scale, fast-paced production.

[0031] (2) This invention provides a high-purity, high-toughness, and ultra-high-strength steel pipe, which is manufactured by the above-described method. Based on the specific chemical composition of the steel of this invention, combined with specific process treatment, the steel pipe has high purity, high toughness, and ultra-high strength properties, meeting the needs of downstream market users. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0033] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0034] According to a first aspect of the present invention, a method for manufacturing a high-purity, high-toughness, ultra-high-strength steel pipe is provided, comprising the following steps:

[0035] (a) Provide continuously cast tube blanks obtained by smelting and continuous casting;

[0036] (b) The continuously cast billet is heated and then directly rolled to obtain a steel pipe;

[0037] Alternatively, the continuously cast tube blank is heated and forged to obtain a forged tube blank, which is then annealed and directly rolled into a steel pipe.

[0038] (c) The steel pipe obtained in step (b) is subjected to normalizing and tempering treatment to obtain high-purity, high-toughness, and ultra-high-strength steel pipe.

[0039] Specifically, this invention involves directly piercing and rolling the continuously cast tube billet obtained through smelting and continuous casting without electroslag remelting (hot piercing rolling), followed by normalizing and tempering heat treatment, to obtain high-purity, high-toughness, and ultra-high-strength steel pipes. Alternatively, the continuously cast tube billet can be heated and forged without electroslag remelting to obtain a forged tube billet. After annealing, the forged tube billet is directly pierced and rolled into pipes, followed by normalizing and tempering heat treatment, to obtain high-purity, high-toughness, and ultra-high-strength steel pipes.

[0040] Using the manufacturing method of this invention, a single continuous casting cycle can continuously cast over 600 tons of billets in just 6-7 hours, significantly improving production efficiency. Furthermore, the process is shorter and the cost is lower. In contrast, the traditional process of vacuum induction casting + vacuum consumable ingots or ingot casting masterbatch + electroslag remelting forging into bars, followed by rolling the forged billets into tubes, produces only 1-5 consumable ingots or electroslag ingot masterbatch per batch. Smelting over 600 tons of ingot masterbatch requires several months to over a year. Therefore, compared to traditional metallurgical processes, the manufacturing method of this invention increases production efficiency by more than 100 times. Meanwhile, in this preparation method, the continuously cast billet is directly threaded into a tube or forged into a billet before the electroslag remelting step, which greatly reduces the time and cost of electroslag remelting. At the same time, since the smelting process of this invention can obtain steel with high purity, even if the electroslag remelting step is omitted later, it will not have a significant impact on the purity and performance of the steel. The inclusions of the obtained steel pipe were tested and found to have a good purity level, with inclusions of type A and type B being ≤1.0 and inclusions of type C and type D being ≤0.5.

[0041] As an optional embodiment of the present invention, in step (a), smelting includes primary refining, refining and vacuum treatment of the raw materials according to the composition of high-purity, high-toughness and ultra-high-strength steel pipes.

[0042] As an optional embodiment of the present invention, in step (a), an electric furnace or converter is used for primary smelting, the hot charge ratio of molten iron is ≥80%, the sulfur in the molten iron is removed to S≤0.015% by KR treatment, the phosphorus is removed by high-activity and high-basicity (basicity R: 3.5~4.0) slag during the smelting process, the tapping temperature is ≥1600℃, and the phosphorus content in the tapped steel is ≤0.005%.

[0043] Using a higher proportion of hot-charged molten iron results in lower levels of residual and harmful elements (As, Sn, Pb, Sb, Bi) in the molten steel, leading to purer steel. It also results in higher thermal energy utilization and greater energy savings.

[0044] As an optional embodiment of the present invention, in step (a), the refining is LF refining, the S content at the refining endpoint is ≤0.0010%, the endpoint temperature is 1595~1635℃ (e.g., 1595℃, 1600℃, 1605℃, 1610℃, 1615℃, 1620℃, 1625℃, 1630℃ or 1635℃, etc.), and the total refining time is ≥45min.

[0045] As an optional embodiment of the present invention, in step (a), the vacuum treatment time is ≥25 min, the treatment time for vacuum ≤0.5 Torr is ≥20 min, and argon gas soft blowing is used for ≥15 min.

[0046] By specifically defining the smelting process in step (a), the molten steel obtained from the smelting process has a low content of P, S, O (O≤10ppm), and N (N≤40ppm), which can achieve a high purity. This makes it possible to skip the electroslag remelting step and directly heat-roll or forge the continuously cast billet in subsequent steps.

[0047] As an optional embodiment of the present invention, in step (a), during the continuous casting process, the superheat of the molten steel in the tundish is 20-35°C (e.g., 20°C, 25°C, 30°C, 32°C or 35°C, etc.), and the constant temperature casting speed is 0.30-0.43 m / min (e.g., 0.30 m / min, 0.32 m / min, 0.35 m / min, 0.38 m / min, 0.40 m / min or 0.43 m / min, etc.).

[0048] As an optional embodiment of the present invention, the high-purity, high-toughness, ultra-high-strength steel pipe comprises the following components by mass fraction: C: 0.25%–0.35%, Si: 1.00%–1.40%, Mn: 0.80%–1.10%, Cr: 1.00%–1.40%, Ni: 0%–0.50%, Mo: 0%–0.10%, W: 0%–0.10%, Nb: 0%–0.04%, Al: 0%–0.050%, P: ≤0.015%, S: ≤0.010%, O: ≤0.0010%, N: ≤0.0060%, with the remainder being iron and unavoidable impurities.

[0049] As a preferred embodiment of the present invention, the high-purity, high-toughness, ultra-high-strength steel pipe comprises the following components by mass fraction: C: 0.29%–0.33%, Si: 1.10%–1.40%, Mn: 0.80%–1.10%, Cr: 1.10%–1.40%, Ni: 0%–0.30%, Mo: 0%–0.10%, W: 0%–0.10%, Nb: 0%–0.04%, Al: 0%–0.050%, P: 0%–0.008%, S: 0%–0.002%, O: 0–0.0010%, N: 0–0.0050%, with the remainder being iron and unavoidable impurities.

[0050] The typical but non-limiting mass fractions of C are 0.29%, 0.30%, 0.31%, 0.32%, or 0.33%, etc.; the typical but non-limiting mass fractions of Si are 1.10%, 1.15%, 1.20%, 1.25%, 1.30%, 1.35%, or 1.40%, etc.; the typical but non-limiting mass fractions of Mn are 0.80%, 0.85%, 0.9%, 0.95%, 1.00%, 1.05%, or 1.10%, etc.; the typical but non-limiting mass fractions of Cr are 1.10%, 1.15%, 1.20%, 1.25%, 1.30%, 1.35%, or 1.40%, etc.; and the typical but non-limiting mass fractions of Ni are... The typical but non-restrictive mass fractions of the following are: 0%, 0.10%, 0.12%, 0.15%, 0.18%, 0.20%, 0.22%, 0.25%, 0.28%, or 0.30%; Mo is typically, but not restrictively, at 0%, 0.02%, 0.05%, 0.08%, or 0.10%; W is typically, but not restrictively, at 0%, 0.02%, 0.05%, 0.08%, or 0.10%; Nb is typically, but not restrictively, at 0%, 0.01%, 0.02%, or 0.04%; Al is typically, but not restrictively, at 0%, 0.01%, 0.02%, 0.04%, or 0.05%.

[0051] By limiting the components of high-purity, high-toughness, and ultra-high-strength steel pipes, the high toughness and ultra-high strength properties of the steel are made more stable, with a smaller fluctuation range, resulting in better overall performance.

[0052] As an optional embodiment of the present invention, in step (b), the heating temperature of the continuously cast billet is 1160℃-1220℃ (for example, 1160℃, 1165℃, 1170℃, 1175℃, 1180℃, 1185℃, 1190℃, 1195℃, 1200℃, 1205℃, 1210℃, 1215℃ or 1220℃, etc.), and the holding time is ≥2.5h.

[0053] As an optional embodiment of the present invention, in step (b), the forging is a combined forging, including fast forging and radial forging.

[0054] As an optional embodiment of the present invention, in step (b), the initial forging temperature of the fast forging is ≥950℃ and the final forging temperature is ≥800℃; preferably, an octagonal intermediate billet of 300-360mm is obtained after fast forging.

[0055] As an optional embodiment of the present invention, in step (b), the initial forging temperature of radial forging is ≥900℃ and the final forging temperature is ≥800℃.

[0056] As an optional embodiment of the present invention, in step (b), when the temperature of the intermediate billet obtained after rapid forging is <900℃, the intermediate billet is reheated in the furnace before radial forging. The reheating temperature is 1180℃-1220℃ and the holding time is 1h-1.5h.

[0057] As an optional embodiment of the present invention, in step (b), the annealing temperature of the forged tube blank is 660℃-680℃ (e.g., 660℃, 665℃, 670℃, 675℃ or 680℃, etc.), and the holding time is 20h-25h (e.g., 20h, 21h, 22h, 23h, 24h or 25h, etc.).

[0058] As an optional embodiment of the present invention, in step (b), the tube rolling includes heat treatment, piercing treatment, tube rolling treatment and diameter reduction treatment, wherein the heat treatment has a soaking temperature of 1230 to 1280°C and a heating time of 240 to 720 min; and / or, the minimum tapping frequency is ≥60 s / piece.

[0059] As an optional embodiment of the present invention, step (b) includes the following steps:

[0060] Heat treatment: The forged tube blank is heated to 1250℃ and held for 4 hours in a Φ40m ring furnace to obtain the heated tube blank.

[0061] Piercing Process: A conical piercing mill is preferably used to pierce the heated billet, resulting in a pierced rough tube. This ensures dimensional uniformity and increases the range of sizes of steel pipes that can be produced from the billet. The rolling angle is 15°, and the feed angle is 5–15° (e.g., any value from 5°, 6°, 7°, 8°, 9°, 10°, 11°, 12°, 13°, 14°, 15°, or any range between two). Rolling at these angles eliminates tangential and torsional deformation during the rolling process and improves the inner surface quality of the steel pipe. By controlling these angles, the interfacial thickness difference of the pierced rough tube is less than 5mm (e.g., any value from 5mm, 4mm, 3mm, 2mm, 1mm, or any range between two).

[0062] Rolling Process: The pierced rough tube is preferably rolled using an Assel rolling mill to obtain a rolled steel tube (rough tube). To improve the dimensional accuracy and surface quality of the steel tube, the total reduction rate of the rolling mill should not exceed 30% (e.g., any value among 30%, 25%, 20%, 15%, and 10%, or any range between two), while using a feed angle ≤11° (e.g., any value among 11°, 8°, 6°, 5°, and 4°, or any range between two), and a rolling angle ≤5° (e.g., any value among 5°, 4°, 3°, 2°, and 1°, or any range between two). Reduction Process: A ten-stand two-roll micro-tension reduction mill is preferably used to reduce the diameter of the rolled steel tube to obtain a steel tube.

[0063] As an optional embodiment of the present invention, in step (c), the normalizing temperature is 900-960℃, the holding time is ≥1h, and the furnace is air-cooled; the tempering temperature is 660-700℃, the holding time is 6-10h, and the furnace is air-cooled.

[0064] Typical but non-limiting normalizing temperatures are 900℃, 910℃, 920℃, 930℃, 940℃, 945℃, 950℃, 955℃, or 960℃, etc., and typical but non-limiting holding times are 1h, 1.5h, 2h, 2.5h, or 3h, etc. Typical but non-limiting tempering temperatures are 660℃, 665℃, 670℃, 675℃, 680℃, 685℃, 690℃, 695℃, or 700℃, etc., and typical but non-limiting holding times are 6h, 7h, 8h, 9h, or 10h, etc.

[0065] According to a second aspect of the present invention, a high-purity, high-toughness, ultra-high-strength steel pipe is also provided, which is manufactured by the above-described method for manufacturing high-purity, high-toughness, ultra-high-strength steel pipe.

[0066] Based on the specific chemical composition of this invention, combined with specific processes (such as piercing and rolling of the tube by a conical piercing mill and an Assel rolling mill, and full deformation by diameter reduction, as well as matching reasonable heat treatment processes), the steel pipe material has high purity, high toughness and ultra-high strength properties.

[0067] The high strength and high toughness performance of the final forged bars and steel pipes prepared by the present invention meet the performance technical requirements of vacuum induction + vacuum self-consumption or ingot casting masterbatch + electroslag remelting smelting.

[0068] As an optional embodiment of the present invention, the high-purity, high-toughness, ultra-high-strength steel pipe has a tensile strength ≥1700MPa, a yield strength ≥1400MPa, a yield-to-tensile ratio ≤0.86, an impact energy ≥70J, and a fracture toughness ≥90MPa*m. 1 / 2 .

[0069] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0070] Example 1

[0071] This embodiment provides a method for manufacturing high-purity, high-toughness, and ultra-high-strength steel pipes, including the following steps:

[0072] (a) Continuously cast tube blanks (continuously cast round tube blanks) obtained by smelting and continuous casting;

[0073] Primary refining: The molten iron treated with KR desulfurization (S content of 0.030%) is added to the electric furnace / converter for primary refining. The P content of the steel produced from the primary refining is 0.005%, and the tapping temperature is 1650℃. Lime, deoxidizer, refining slag and alloy are added with the steel stream. The deoxidizer is Al ferroin / ingot, the refining slag is finished bagged refining slag, and the alloy is ferrosilicon, silicon manganese alloy and ferrochrome. The amounts of lime, deoxidizer, refining slag and alloy are 400Kg, 240Kg, 400Kg and 3500Kg, respectively.

[0074] LF refining: The molten steel that has been initially refined in the electric furnace is transferred to the LF refining furnace for refining. The N content is 0.051%, the final S content is 0.0006%, the final pit opening temperature is 1605℃, and the total refining time is 55min.

[0075] RH vacuum treatment: The vacuum treatment time is 25 min, and the high vacuum treatment time is 20 min for ≤133 Pa; at the same time, argon gas soft blowing is used for 20 min.

[0076] Continuous casting: The standard is a superheat of 20-30°C for molten steel in the tundish. The casting speed is 0.37 m / min. The continuous casting process involves casting 5 heats of steel, about 600 tons, in one round. The diameter of the continuous casting round billet is 460 mm. The billet is cut to length.

[0077] (b) The continuously cast tube billet is first heated and then forged to obtain a forged tube billet. The forged tube billet is then annealed and then directly rolled to obtain a steel pipe.

[0078] Among them, the heat treatment is carried out at a temperature of 1220℃ for 3.5 hours.

[0079] Combined forging: Combined forging of fast forging and radial forging is adopted. The initial forging temperature of fast forging is 1030℃ and the final forging temperature is 960℃. The fast forging produces an octagonal intermediate billet of 330mm. The intermediate billet is then radially forged into a product. The final forging temperature is 820℃. The diameter of the forged bar is 330mm, resulting in a forged tube blank.

[0080] Annealing: Heat at 670℃ for 20 hours.

[0081] Pipe rolling includes: heat treatment, piercing treatment, pipe rolling treatment, and diameter reduction treatment;

[0082] Among them, heat treatment: the heat-treated forged tube blank is heated to 1250℃ and held for 4 hours in a Φ40m ring furnace to obtain the heated tube blank;

[0083] Perforation process: The heated tube blank is perforated using a vertical conical perforation machine with a rolling angle of 15° and a feeding angle of 10° to obtain the perforated rough tube.

[0084] Rolling process: The rough tube after piercing is rolled using an Assel rolling mill with a rolling angle of 4.5° and a feed angle of 5.5° to obtain rolled steel tube (rough tube);

[0085] Diameter reduction process: The above-mentioned rolled steel pipe is reduced in diameter using a two-roll micro-tension reducing mill to obtain a reduced diameter steel pipe with an outer diameter of 345mm, a wall thickness of 40mm, and an inner diameter of 265mm.

[0086] (c) The reduced-diameter steel pipe obtained in step (b) is subjected to normalizing and tempering treatment to obtain high-purity, high-toughness, and ultra-high-strength steel pipe.

[0087] Among them, normalizing treatment: heat at 950℃ for 1 hour, then air cool after being removed from the furnace;

[0088] Tempering treatment: Heat at 680℃ for 6 hours, then air cool after removal from the furnace.

[0089] The high-purity, high-toughness, and ultra-high-strength steel pipe obtained in this embodiment has the following chemical composition by mass fraction: C: 0.29%, Si: 1.34%, Mn: 1.01%, Cr: 1.26%, Ni: 0.28%, Mo: 0.08%, W: 0.09%, Nb: 0.015%, Al: 0.030%, P: 0.008%, S: 0.0008%, O: 5.4ppm, N: 31ppm, with the remainder being iron and unavoidable impurities.

[0090] Example 2

[0091] This embodiment provides a method for manufacturing high-purity, high-toughness, and ultra-high-strength steel pipes. Except that the continuous casting billet in step (b) of Embodiment 1 is not subjected to heat treatment and combined forging, but is directly rolled through the tube. The specific process steps and process parameters of the tube rolling, as well as steps (a) and (c), are the same as in Embodiment 1.

[0092] The high-purity, high-toughness, and ultra-high-strength steel pipe obtained in this embodiment has the following chemical composition by mass fraction: C: 0.277%, Si: 1.30%, Mn: 1.02%, Cr: 1.27%, Ni: 0.27%, Mo: 0.09%, W: 0.09%, Nb: 0.02%, Al: 0.028%, P: 0.007%, S: 0.0009%, O: 4.8ppm, N: 28ppm, with the remainder being iron and unavoidable impurities.

[0093] Example 3

[0094] This embodiment provides a method for manufacturing high-purity, high-toughness, and ultra-high-strength steel pipes, including the following steps:

[0095] (a) Continuously cast tube blanks (continuously cast round tube blanks) obtained by smelting and continuous casting;

[0096] Primary refining: The molten iron treated with KR desulfurization (S content of 0.030%) is added to the electric furnace / converter for primary refining. The P content of the steel produced from the primary refining is 0.005%, and the tapping temperature is 1640℃. Lime, deoxidizer, refining slag and alloy are added with the steel stream. The deoxidizer is Al ferroin / ingot, the refining slag is finished bagged refining slag, and the alloy is ferrosilicon, silicon manganese alloy and ferrochrome. The amounts of lime, deoxidizer, refining slag and alloy are 400Kg, 240Kg, 400Kg and 3500Kg, respectively.

[0097] LF refining: The molten steel that has been initially refined in the electric furnace is transferred to the LF refining furnace for refining. The N content is 0.040%, the final S content is 0.0007%, the final pit opening temperature is 1610℃, and the total refining time is 50min.

[0098] RH vacuum treatment: The vacuum treatment time is 25 min, and the high vacuum treatment time is 20 min for ≤133 Pa; at the same time, argon gas soft blowing is used for 20 min.

[0099] Continuous casting: The standard is a superheat of 20-30°C for molten steel in the tundish. The casting speed is 0.35m / min. The continuous casting process involves casting 5 heats of steel, about 600 tons, in one round. The diameter of the continuous casting round billet is 460mm. The billet is cut to length.

[0100] (b) The continuously cast tube billet is first heated and then forged to obtain a forged tube billet. The forged tube billet is then annealed and then directly rolled to obtain a steel pipe.

[0101] Among them, the heat treatment is carried out at a temperature of 1250℃ for 3.0 hours.

[0102] Combined forging: Combined forging of fast forging and radial forging is adopted. The initial forging temperature of fast forging is 1050℃ and the final forging temperature is 930℃. The fast forging produces an octagonal intermediate billet of 330mm. The intermediate billet is then radially forged into a product. The final forging temperature is 810℃. The diameter of the forged bar is 330mm, resulting in a forged tube blank.

[0103] Annealing: Heat at 660℃ for 24 hours.

[0104] Pipe rolling includes: heat treatment, piercing treatment, pipe rolling treatment, and diameter reduction treatment;

[0105] Among them, heat treatment: the heat-treated forged tube blank is heated to 1250℃ and held for 4 hours in a Φ40m ring furnace to obtain the heated tube blank;

[0106] Perforation process: The heated tube blank is perforated using a vertical conical perforation machine with a rolling angle of 15° and a feeding angle of 12° to obtain the perforated rough tube;

[0107] Rolling process: The rough tube after piercing is rolled using an Assel rolling mill with a rolling angle of 4.5° and a feed angle of 5.5° to obtain rolled steel tube (rough tube);

[0108] Diameter reduction process: The above-mentioned rolled steel pipe is reduced in diameter using a two-roll micro-tension reducing mill to obtain a reduced diameter steel pipe with an outer diameter of 345mm, a wall thickness of 40mm, and an inner diameter of 265mm.

[0109] (c) The reduced-diameter steel pipe obtained in step (b) is subjected to normalizing and tempering treatment to obtain high-purity, high-toughness, and ultra-high-strength steel pipe.

[0110] Among them, the normalizing treatment is carried out by heating at 940℃ for 1.5 hours and then air cooling after being removed from the furnace.

[0111] Tempering treatment: Heat at 660℃ for 10 hours, then air cool after removal from the furnace.

[0112] The high-purity, high-toughness, and ultra-high-strength steel pipe obtained in this embodiment has the following chemical composition by mass fraction: C: 0.279%, Si: 1.30%, Mn: 1.00%, Cr: 1.27%, Ni: 0.28%, Mo: 0.09%, W: 0.09%, Nb: 0.02%, Al: 0.032%, P: 0.007%, S: 0.0008%, O: 5.4ppm, N: 31ppm, with the remainder being iron and unavoidable impurities.

[0113] Example 4

[0114] This embodiment provides a method for manufacturing high-purity, high-toughness, and ultra-high-strength steel pipes. Except that the continuous casting billet in step (b) of embodiment 3 is not subjected to heat treatment and combined forging, but is directly rolled through the tube. The specific process steps and process parameters of the tube rolling, as well as steps (a) and (c), are the same as in embodiment 3.

[0115] The high-purity, high-toughness, and ultra-high-strength steel pipe obtained in this embodiment has the following chemical composition by mass fraction: C: 0.277%, Si: 1.31%, Mn: 1.03%, Cr: 1.27%, Ni: 0.27%, Mo: 0.09%, W: 0.09%, Nb: 0.015%, Al: 0.028%, P: 0.008%, S: 0.0009%, O: 5.1ppm, N: 36ppm, with the remainder being iron and unavoidable impurities.

[0116] Comparative Example 1

[0117] This comparative example provides a method for manufacturing high-toughness, ultra-high-strength steel pipes, including the following steps:

[0118] (a) Providing electrode blanks obtained by VIM (vacuum induction) smelting;

[0119] Raw material preparation: Alloy and raw steel are added to the vacuum induction furnace;

[0120] Vacuum induction smelting: high-temperature refining at 1590℃ with a vacuum degree of 0.05Pa during the refining period; casting a 6-ton electrode rod with a diameter of 570 at a low temperature of 1563℃, cooling in the mold after casting, and then hot-heat annealing after demolding.

[0121] (b) The electrode blank is subjected to VAR (vacuum arc remelting) to obtain a steel ingot;

[0122] Vacuum self-consumption smelting: 6T round ingot (diameter 640mm): 0.01Pa vacuum smelting, the melting rate of the self-consumption process is 60Kg / h, the weight of the capping electrode is 280Kg, and it is red-heat annealed after demolding.

[0123] (c) The steel ingot is first heated and then forged to obtain a forged tube blank. The forged tube blank is then annealed and then directly rolled to obtain a steel pipe. The specific steps and process parameters are the same as those in step (b) of Example 1.

[0124] (d) The steel pipe obtained in step (c) is subjected to normalizing and tempering treatment. The specific steps and process parameters are the same as those in step (c) of Example 1, to obtain high-toughness and ultra-high-strength steel pipe.

[0125] The high-toughness, ultra-high-strength steel pipe prepared in this comparative example has the following chemical composition by mass fraction:

[0126] C: 0.28%, Si: 1.29%, Mn: 1.03%, Cr: 1.33%, Ni: 0.262%, Mo: 0.09%, W: 0.101%, Nb: 0.019%, Al: 0.032%, P: 0.008%, S: 0.0015%, O: 11ppm, N: 60ppm, with the remainder being iron and unavoidable impurities.

[0127] To further verify the technical effects of the above embodiments and comparative examples, the following experimental examples are provided.

[0128] Experimental Example 1

[0129] The purity of the pipes provided in the various embodiments and comparative examples of the present invention was tested according to the GB10561A method, and the specific results are shown in Table 1.

[0130] Table 1

[0131]

[0132] As can be seen from the data in Table 1 above, the pipes provided in each embodiment of the present invention have high purity. Their purity level is basically equivalent to, or even slightly higher than, the purity level of the pipes prepared by the conventional preparation method in Comparative Example 1.

[0133] Experiment Example 2

[0134] The pipes provided in the embodiments and comparative examples of this invention were subjected to oil quenching at 890℃ and air tempering at 230℃ in actual production by downstream customers, and then samples were taken to test their relevant properties. Specifically, tensile strength, yield strength, elongation, and reduction of area Z were tested according to GB / T 228.1, impact absorption energy KU2 was tested according to GB / T 229, and fracture toughness was tested according to GB / T 4161. Specific results are shown in Table 2.

[0135] Table 2

[0136]

[0137] As can be seen from the data in Table 2, the mechanical properties of the low-P, low-S, low-O, low-N high-toughness ultra-high-strength steel pipe were tested. The results showed that the tensile strength Rm of the high-purity, high-toughness ultra-high-strength steel pipe produced by this invention is 1731–1767 MPa, and the yield strength Rp is… 0.2 Impact strength: 1446–1471 MPa; elongation after fracture (A): 11–12.5%; reduction of area (Z): 50–52%; impact energy (KU2): 83–102 J; fracture toughness (KIC): 114–124 MPa. 1 / 2The yield strength ratio is 0.82-0.84. Compared with Comparative Example 1, the overall performance of each embodiment is excellent, while the impact toughness and fracture toughness are significantly improved. Furthermore, since the preparation methods of each embodiment do not involve electroslag remelting, the time and cost of electroslag remelting are greatly reduced, resulting in a significant increase in production efficiency and a substantial reduction in production costs, achieving the goal of cost reduction and efficiency improvement.

[0138] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for manufacturing high-purity, high-toughness, and ultra-high-strength steel pipes, characterized in that, The method comprises the following steps: (a) providing a continuous casting pipe blank prepared by smelting and continuous casting; (b) heating the continuous casting pipe blank and then directly performing piercing rolling to obtain a steel pipe; or, heating and forging the continuous casting pipe blank to prepare a forged pipe blank, annealing the forged pipe blank, and then directly performing piercing rolling to obtain a steel pipe; (c) performing normalizing treatment and tempering treatment on the steel pipe obtained in step (b) to prepare a high-purity high-toughness ultra-high-strength steel pipe; In step (a), the high-purity high-toughness ultra-high-strength steel pipe comprises the following components in mass fraction: C: 0.25% to 0.35%, Si: 1.00% to 1.40%, Mn: 0.80% to 1.10%, Cr: 1.00% to 1.40%, Ni: 0% to 0.30%, Mo: 0% to 0.10%, W: 0% to 0.10%, Nb: 0% to 0.04%, Al: 0% to 0.050%, P: ≤0.015%, S: ≤0.010%, O: ≤0.0010%, N: ≤0.0060%, and the rest is iron and inevitable impurities; In step (b), the piercing rolling comprises heating treatment, piercing treatment, pipe rolling treatment and reducing treatment, wherein the soaking temperature of the heating treatment is 1230 to 1280℃, and the heating time is 240 to 720 min; In step (b), the forging is combined forging, comprising fast forging and radial forging; The initial forging temperature of the fast forging is ≥950℃, and the final forging temperature is ≥800℃; The initial forging temperature of the radial forging is ≥900℃, and the final forging temperature is ≥800℃; When the temperature of the intermediate blank obtained after the fast forging is <900℃, the intermediate blank is reheated before the radial forging, the reheating temperature is 1180 to 1220℃, and the holding time is 1 to 1.5 h; The high-purity high-toughness ultrahigh-strength steel pipe has a tensile strength of ≥ 1700 MPa, a yield strength of ≥ 1400 MPa, a yield ratio of ≤ 0.86, an impact energy of ≥ 83 J, and a fracture toughness of ≥ 90 MPa*m 1 / 2 .

2. The method of producing a high-purity high-toughness ultra-high-strength steel pipe according to claim 1, characterized by In step (a), the smelting comprises primary refining, refining and vacuum treatment of raw materials according to the components of the high-purity high-toughness ultra-high-strength steel pipe.

3. The method of producing a high-purity high-toughness ultra-high-strength steel pipe according to claim 2, characterized by In step (a), the primary refining is performed by using an electric furnace or a converter, the tapping temperature is ≥1600℃, and the P content in the tapping is ≤0.005%; And / or, in step (a), the refining is LF refining, the S content at the end of the refining is ≤0.0010%, the end temperature is 1595 to 1635℃, and the total refining time is ≥45 min; And / or, in step (a), the vacuum treatment time is ≥25 min, the treatment time under a vacuum of ≤0.5 Torr is ≥20 min, and argon soft blowing is simultaneously performed, and the soft blowing time is ≥15 min; And / or, in step (a), during the continuous casting, the superheat of the molten steel in the tundish is 20 to 35℃, and the constant temperature pulling speed is 0.30 to 0.43 m / min.

4. The method of producing a high-purity high-toughness ultra-high-strength steel pipe according to claim 2, characterized by In step (a), the primary refining is performed by using an electric furnace or a converter, the high-iron hot charging ratio is ≥80%, the S in the molten iron is removed to S ≤0.015% by KR treatment, the smelting process adopts a slag with a basicity R of 3.5 to 4.0 to remove P, the tapping temperature is ≥1600℃, and the P content in the tapping is ≤0.005%.

5. The method of producing a high-purity high-toughness ultra-high-strength steel pipe material according to claim 1, characterized by In step (b), the minimum tapping frequency of the continuous casting pipe blank during the heating treatment is ≥60 S / branch.

6. The method of producing a high-purity high-toughness ultra-high-strength steel pipe according to claim 1, characterized by In step (b), the octagonal intermediate blank with a length of 300mm-360mm is obtained after the fast forging.

7. The method of producing a high-purity high-toughness ultra-high-strength steel pipe according to claim 1, characterized by In step (b), the temperature for annealing the forged pipe blank is 660-680℃, and the holding time is 20-25h.

8. The method of producing a high-purity high-toughness ultra-high-strength steel pipe according to claim 1, characterized by In step (c), the normalizing temperature is 900-960℃, the holding time is ≥1h, and the blank is discharged and air-cooled. And / or, the tempering temperature is 660-700℃, the holding time is 6-10h, and the blank is discharged and air-cooled.

9. A high-purity high-toughness ultra-high-strength steel pipe material, characterized by comprising, in mass %, The high-purity high-toughness ultra-high-strength steel pipe material is manufactured by the method according to any one of claims 1-8.

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