High-purity high-toughness ultrahigh-strength steel pipe and manufacturing method thereof

Abstract

The invention provides a high-purity, high-toughness and ultrahigh-strength steel pipe material and a manufacturing method thereof, and relates to the technical field of steel materials. According to the preparation method, a continuous casting pipe blank is not subjected to an electroslag remelting step and is directly subjected to pipe penetration or is forged into a pipe blank and then is subjected to pipe penetration, and then the high-purity, high-toughness and ultrahigh-strength steel pipe is prepared through a reasonable heat treatment process; in the steel preparation process, electroslag remelting is not needed, the time and cost consumed by electroslag remelting are greatly reduced, the technological process is shortened, the production efficiency is greatly improved, and the large-batch and fast-paced production requirement is met. The invention further provides the high-purity, high-toughness and ultrahigh-strength steel pipe which is manufactured through the manufacturing method. On the basis of the specific chemical composition of the steel, specific process treatment is combined, so that the steel pipe has high purity, high toughness and ultrahigh strength, and the requirements of downstream user markets are met.

Description

Technical Field

[0001] The present invention relates to the technical field of steel materials, and in particular to a high-purity, high-toughness and ultra-high-strength steel pipe and a manufacturing method thereof. Background Art

[0002] High-toughness and ultra-high-strength steel pipes, as the name implies, are steel pipes that have both high toughness and ultra-high strength. Such materials are usually used in the aerospace field, such as aircraft, rockets, spacecraft and other key components, as well as in the defense and military field, such as the manufacture of weapons and equipment such as aviation missiles.

[0003] At present, the metallurgical technology commonly used for high-toughness ultra-high-strength steel pipes is vacuum induction smelting of masterbatch, and then vacuum consumable smelting into ingots, and the ingots are forged into bars of the required specifications, and the forged bars are further rolled into steel pipes of the required specifications through steel pipe units; or, electric furnace + LF refining + vacuum treatment + die casting masterbatch, and then electroslag remelting into electroslag ingots, and the electroslag ingots are forged into bars of the required specifications, and the forged bars are further rolled into pipes of the required specifications through steel pipe units. The above metallurgical technology has a long process flow, high process cost, low production efficiency, and cannot adapt to fast-paced batch production. In view of the modular combination of aerospace and national defense military industry, low-cost large-scale production of aviation ammunition projects, and the support of sustained large-scale operations, higher requirements are also put forward for the purity, high toughness and ultra-high strength performance of high-toughness ultra-high-strength steel pipes. Therefore, it is necessary to develop a low-cost, large-scale, systematic, energy-saving, short-process, fast-paced production method that can meet the performance requirements of low P, low S, low O, low N, high purity, high toughness and high strength to meet the needs of the downstream user market.

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

[0005] The purpose of the present invention is to provide a high-purity, high-toughness, ultra-high-strength steel pipe and a manufacturing method thereof, so as to solve the defects existing in the existing metallurgical technology, such as high P, S, O, and N contents in the 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] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The first object of the present invention is to provide a method for manufacturing a high-purity, high-toughness, ultra-high-strength steel pipe, comprising the following steps:

[0008] (a) providing a continuous casting tube blank obtained by smelting and continuous casting;

[0009] (b) heating the continuous casting tube billet and then directly performing tube rolling to obtain a steel tube;

[0010] Alternatively, the continuous casting tube blank is heated and forged to obtain a forged tube blank, the forged tube blank is annealed, and then directly subjected to tube rolling to obtain a steel pipe;

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

[0012] Furthermore, based on the above 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 the high-purity, high-toughness and ultra-high-strength steel pipe.

[0013] Further, on the basis of the above technical solution of the present invention, in step (a), an electric furnace or a converter is used for primary smelting, the tapping temperature is ≥1600°C, and the P content of the tapped steel is ≤0.005%;

[0014] And / or, in step (a), the refining is LF refining, the S content at the refining end point is ≤0.0010%, the end point temperature is 1595°C to 1635°C, and the total refining time is ≥45min;

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

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

[0017] Further, on the basis of the above technical solution of the present invention, in step (a), the high-purity, high-toughness and ultra-high-strength steel pipe includes 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 0.50%, 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 are iron and unavoidable impurities.

[0018] Furthermore, based on the above technical solution of the present invention, in step (b), the heating temperature of the continuous casting tube billet during heat treatment is 1160°C-1280°C, and the insulation time is ≥2.5h; and / or the minimum steel tapping frequency is ≥60S / piece.

[0019] Further, based on the above technical solution of the present invention, in step (b), the forging is combined forging, including rapid forging and radial forging.

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

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

[0022] And / or, when the temperature of the intermediate billet obtained after rapid forging is less than 900°C, the intermediate billet is first returned to the furnace for heating before the radial forging, and the heating temperature is 1180°C to 1220°C, and the holding time is 1h to 1.5h.

[0023] Further, on the basis of the above technical solution of the present invention, in step (b), the temperature of annealing the forged tube blank is 660° C. to 680° C., and the holding time is 20 h to 25 h;

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

[0025] Further, on the basis of the above technical solution of the present invention, in step (c), the normalizing temperature is 900°C to 960°C, the holding time is ≥1h, and the furnace is air-cooled;

[0026] And / or, the tempering temperature is 660°C to 700°C, the holding time is 6h to 10h, and the steel is air-cooled after being taken out of the furnace.

[0027] The second object of the present invention is to provide a high-purity, high-toughness, ultra-high-strength steel pipe, which is manufactured by the above-mentioned method for manufacturing the high-purity, high-toughness, ultra-high-strength steel pipe;

[0028] The tensile strength of the high-purity, high-toughness and ultra-high-strength steel pipe is ≥1700MPa, the yield strength is ≥1400MPa, the yield strength ratio is ≤0.86, the impact energy is ≥70J, and the fracture toughness is ≥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) The present invention provides a method for manufacturing high-purity, high-toughness, and ultra-high-strength steel pipes. In the preparation method, the continuous casting tube blank is directly inserted into the tube or forged into the tube blank and then inserted into the tube without the electroslag remelting step, and then subjected to a reasonable heat treatment process to obtain high-purity, high-toughness, and ultra-high-strength steel pipes. In the steel preparation process, there is no need to perform electroslag remelting, 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) The present invention provides a high-purity, high-toughness, ultra-high-strength steel pipe material, which is produced by the above-mentioned manufacturing method. Based on the specific chemical composition of the steel material of the present invention, combined with specific process treatment, the steel pipe material has high purity, high toughness and ultra-high strength performance, meeting the needs of downstream market users. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention. The process parameters of the following embodiments that do not specify specific conditions are usually based on conventional conditions.

[0033] The endpoints and any values ​​of the ranges disclosed in the present 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in the present invention.

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

[0035] (a) providing a continuous casting tube blank obtained by smelting and continuous casting;

[0036] (b) heating the continuous casting tube billet and then directly performing tube rolling to obtain a steel tube;

[0037] Alternatively, the continuous casting tube blank is heated and forged to obtain a forged tube blank, the forged tube blank is annealed, and then directly subjected to tube rolling to obtain a steel pipe;

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

[0039] Specifically, the present invention directly performs tube-piercing and rolling (hot tube-piercing and tube-rolling) on ​​the continuous casting tube blank obtained by smelting and continuous casting without electroslag remelting, and performs normalizing and tempering heat treatment, so as to obtain a high-purity, high-toughness, ultra-high-strength steel tube. Alternatively, the continuous casting tube blank is heated and forged without electroslag remelting to obtain a forged tube blank, and the forged tube blank is directly rolled into a tube after annealing, and normalizing and tempering heat treatment is performed to obtain a high-purity, high-toughness, ultra-high-strength steel tube.

[0040] By adopting the manufacturing method of the present invention, it only takes 6-7 hours to continuously cast more than 600 tons of continuous casting billets in one continuous casting round, which greatly improves production efficiency, shortens the process flow, and reduces process costs. In contrast, the traditional vacuum induction + vacuum consumable or die casting masterbatch + electroslag remelting ingot forging into rods, and the forged billets are then rolled into pipes. In the smelting process, only 1-5 consumable ingots or electroslag ingot masterbatch are produced in one furnace batch. It takes several months to more than a year to complete the smelting of more than 600 tons of ingot masterbatch. Therefore, compared with the traditional metallurgical process, the production efficiency of the manufacturing method of the present invention is increased by more than 100 times. At the same time, in the preparation method, the continuous casting tube blank is directly inserted into the tube or forged into the tube blank without the electroslag remelting step, which greatly reduces the time and cost consumed by the electroslag remelting. At the same time, since the smelting process steps of the present invention can obtain molten steel with high purity, even if the electroslag remelting step is omitted in the later stage, it will not have a significant impact on the purity and performance of the steel. The inclusions of the prepared steel pipe are tested and it is found that it has a good purity level. The inclusions of Class A and Class B are both ≤1.0 level, and the inclusions of Class C and Class D are both ≤0.5 level.

[0041] As an optional embodiment 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 the high-purity, high-toughness and ultra-high-strength steel pipe.

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

[0043] The use of a higher hot-charging ratio of molten iron can reduce the residual and five harmful elements (As, Sn, Pb, Sb, Bi) in the molten steel, making the steel purer, with higher thermal energy utilization and more energy-saving.

[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°C (for example, 1595°C, 1600°C, 1605°C, 1610°C, 1615°C, 1620°C, 1625°C, 1630°C or 1635°C, 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 vacuum treatment time of ≤0.5 Torr is ≥20 min, and argon soft blowing is used at the same time, and the soft blowing time is ≥15 min.

[0046] By specifically limiting the smelting process of step (a), the molten steel obtained by smelting has lower P, S, O (O≤10ppm) and N (N≤40ppm) contents and can achieve higher purity, making it possible to omit the electroslag remelting step in the subsequent continuous casting tube billet and directly carry out hot rolling or forging.

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

[0048] As an optional embodiment of the present invention, the high-purity, high-toughness and ultra-high-strength steel pipe includes 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 0.50%, 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 unavoidable impurities.

[0049] As a preferred embodiment of the present invention, the high-purity, high-toughness and ultra-high-strength steel pipe includes the following components in mass fraction: C: 0.29% to 0.33%, Si: 1.10% to 1.40%, Mn: 0.80% to 1.10%, Cr: 1.10% 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% to 0.008%, S: 0% to 0.002%, O: 0-0.0010%, N: 0-0.0050%, and the rest is iron and unavoidable impurities.

[0050] Among them, the typical but non-limiting mass fraction of C is 0.29%, 0.30%, 0.31%, 0.32% or 0.33%, etc.; the typical but non-limiting mass fraction of Si is 1.10%, 1.15%, 1.20%, 1.25%, 1.30%, 1.35% or 1.40%, etc.; the typical but non-limiting mass fraction of Mn is 0.80%, 0.85%, 0.9%, 0.95%, 1.00%, 1.05% or 1.10%, etc.; the typical but non-limiting mass fraction of Cr is 1.10%, 1.15%, 1.20%, 1.25%, 1.30%, 1.35% or 1.40%, etc.; the typical but non-limiting mass fraction of Ni is The typical but non-limiting mass fraction of Mo is 0%, 0.10%, 0.12%, 0.15%, 0.18%, 0.20%, 0.22%, 0.25%, 0.28% or 0.30%, etc.; the typical but non-limiting mass fraction of Mo is 0%, 0.02%, 0.05%, 0.08% or 0.10%, etc.; the typical but non-limiting mass fraction of W is 0%, 0.02%, 0.05%, 0.08% or 0.10%, etc.; the typical but non-limiting mass fraction of Nb is 0%, 0.01%, 0.02% or 0.04%, etc.; the typical but non-limiting mass fraction of Al is 0%, 0.01%, 0.02%, 0.04% or 0.05%, etc.

[0051] By limiting the various components of high-purity, high-toughness and ultra-high-strength steel pipes, the high toughness and ultra-high strength performance of the steel are made more stable, the fluctuation range is small, and the overall performance is better.

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

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

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

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

[0056] As an optional embodiment of the present invention, in step (b), when the temperature of the intermediate billet obtained after rapid forging is less than 900°C, the intermediate billet is first returned to the furnace for heating before radial forging, and the heating temperature is 1180°C-1220°C and the holding time is 1h-1.5h.

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

[0058] As an optional embodiment of the present invention, in step (b), tube rolling includes heating treatment, perforation treatment, tube rolling treatment and diameter reducing treatment, wherein the soaking temperature of the heating treatment is 1230-1280°C, the heating time is 240-720min; and / or the minimum steel tapping frequency is ≥60S / piece.

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

[0060] Heating treatment: the forged tube billet is placed in a Φ40m annular furnace at a heating temperature of 1250°C for 4 hours to obtain a heated tube billet.

[0061] Perforation treatment: It is preferred to use a conical perforator to perforate the heated tube blank to obtain a perforated rough tube. While ensuring the uniformity of size, the size range of the steel tube that can be produced from the blank can also be increased. Among them, the rolling angle is 15°, and the feeding angle is 5-15° (for example: any value among 5°, 6°, 7°, 8°, 9°, 10°, 11°, 12°, 13°, 14°, 15° or any range between two); the above-mentioned angles are used for rolling to eliminate tangential deformation and torsional deformation during the rolling process and to improve the inner surface quality of the steel tube. By controlling the above-mentioned angles, the interface thickness difference of the rough tube after the perforation is achieved to be less than 5mm (for example: any value among 5mm, 4mm, 3mm, 2mm, 1mm or any range between two).

[0062] Pipe rolling treatment: preferably, the Assel pipe rolling mill is used to roll the above-mentioned perforated rough pipe to obtain a rolled steel pipe (rough pipe). In order to improve the dimensional accuracy and surface quality of the steel pipe, the total diameter reduction rate of the pipe rolling mill does not exceed 30% (for example, any value among 30%, 25%, 20%, 15%, 10% or any range between two), and at the same time, a feed angle of ≤11° (for example, any value among 11°, 8°, 6°, 5°, 4° or any range between two), and a rolling angle of ≤5° (for example, any value among 5°, 4°, 3°, 2°, 1° or any range between two). Diameter reduction treatment: preferably, a ten-stand two-roller micro-tension reducing mill is used to reduce the diameter of the rolled steel pipe to obtain a steel pipe.

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

[0064] Typical but non-limiting normalizing temperatures are 900°C, 910°C, 920°C, 930°C, 940°C, 945°C, 950°C, 955°C or 960°C, 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°C, 665°C, 670°C, 675°C, 680°C, 685°C, 690°C, 695°C or 700°C, 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, there is also provided a high-purity, high-toughness, ultra-high-strength steel pipe, which is manufactured by the above-mentioned method for manufacturing the high-purity, high-toughness, ultra-high-strength steel pipe.

[0066] On the basis of the specific chemical composition of the present invention, combined with specific processes (such as piercing and rolling by a conical piercer + Assel tube rolling mill and sufficient deformation by reducing the diameter and matching a reasonable heat treatment process), the steel pipe material has high purity, high toughness and ultra-high strength performance.

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

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

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

[0070] Example 1

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

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

[0073] Primary refining: adding the molten iron (S content of 0.030%) treated by KR desulfurization to an electric furnace / converter for primary refining, the P content of the primary refining steel is 0.005%, and the tapping temperature is 1650°C; adding lime, deoxidizer, refining slag and alloy along with the steel flow, the deoxidizer is Al iron / ingot, the refining slag is the finished bagged refining slag, the alloy is ferrosilicon, silicon-manganese alloy and ferrochrome, the amount of lime, deoxidizer, refining slag and alloy is 400Kg, 240Kg, 400Kg and 3500Kg respectively;

[0074] LF refining: The molten steel 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 pitting temperature is 1605℃, and the total refining time is 55min.

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

[0076] Continuous casting: With the molten steel in the tundish superheated at 20-30℃ as the standard, the casting speed is 0.37m / min and the continuous casting is carried out at a uniform speed. In one round of continuous casting, 5 furnaces of steel, about 600 tons, are continuously cast to form continuous casting billets. The diameter of the continuous casting round billet is 460mm, and the billets are cut to a fixed length.

[0077] (b) firstly subjecting the continuous casting tube blank to a heating treatment, and then subjecting the continuous casting tube blank to a combined forging to obtain a forged tube blank, and then subjecting the forged tube blank to an annealing treatment, and then directly subjecting the forged tube blank to a tube rolling to obtain a steel tube;

[0078] Among them, heating treatment: heating temperature is 1220℃, keeping temperature for 3.5h;

[0079] Combined forging: The combined forging of fast forging and radial forging is adopted. The initial forging temperature of fast forging is 1030℃, the final forging temperature is 960℃, the fast forging is used to open a 330mm octagonal intermediate billet, the intermediate billet is then radially forged into material, the final forging temperature is 820℃, the diameter of the forged bar is 330 round, and the forged tube billet is obtained;

[0080] Annealing treatment: heat at 670℃ for 20h.

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

[0082] Wherein, heating treatment: the heat-treated forged tube billet is placed in a Φ40m annular furnace and kept at a heating temperature of 1250°C for 4 hours to obtain a heated tube billet;

[0083] Perforation treatment: a vertical conical perforator is used to perforate the heated tube blank, with a rolling angle of 15° and a feeding angle of 10° to obtain a perforated rough tube;

[0084] Pipe rolling treatment: the rough pipe after perforation is rolled by an Assel pipe rolling mill, the rolling angle is 4.5°, the feeding angle is 5.5°, and the rolled steel pipe (rough pipe) is obtained;

[0085] Reducing treatment: The rolled steel pipe is reduced in diameter by a two-roller micro-tension reducing mill to obtain a reduced-diameter steel pipe with an outer diameter of 345 mm, a wall thickness of 40 mm, and an inner diameter of 265 mm.

[0086] (c) normalizing and tempering the reduced-diameter steel pipe obtained in step (b) to obtain a high-purity, high-toughness, ultra-high-strength steel pipe;

[0087] Among them, normalizing treatment: heat at 950℃, keep warm for 1h, and air cool after leaving the furnace;

[0088] Tempering treatment: heat at 680℃ for 6h, then air cool after being taken out of the furnace.

[0089] The high-purity, high-toughness and ultra-high-strength steel pipe prepared in this embodiment includes the following chemical components 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, and the rest is iron and unavoidable impurities.

[0090] Example 2

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

[0092] The high-purity, high-toughness and ultra-high-strength steel pipe prepared in this embodiment includes the following chemical components 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, and the rest is iron and unavoidable impurities.

[0093] Example 3

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

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

[0096] Primary refining: adding the molten iron (S content of 0.030%) treated by KR desulfurization to an electric furnace / converter for primary refining, the P content of the primary refining steel is 0.005%, and the tapping temperature is 1640°C; adding lime, deoxidizer, refining slag and alloy along with the steel flow, the deoxidizer is Al iron / ingot, the refining slag is the finished bagged refining slag, the alloy is ferrosilicon, silicon-manganese alloy and ferrochrome, and the amount of lime, deoxidizer, refining slag and alloy is 400Kg, 240Kg, 400Kg and 3500Kg respectively;

[0097] LF refining: The molten steel 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 pitting temperature is 1610℃, and the total refining time is 50min.

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

[0099] Continuous casting: With the molten steel in the tundish superheated at 20-30℃ as the standard, the casting speed is 0.35m / min and the continuous casting is carried out at a uniform speed. In one round of continuous casting, 5 furnaces of steel, about 600 tons, are continuously cast to form continuous casting billets. The diameter of the continuous casting round billet is 460mm, and the billets are cut to a fixed length.

[0100] (b) firstly subjecting the continuous casting tube blank to a heating treatment, and then subjecting the continuous casting tube blank to a combined forging to obtain a forged tube blank, and then subjecting the forged tube blank to an annealing treatment, and then directly subjecting the forged tube blank to a tube rolling to obtain a steel tube;

[0101] Among them, heating treatment: heating temperature is 1250℃, and heat preservation is 3.0h;

[0102] Combined forging: The combined forging of fast forging and radial forging is adopted. The initial forging temperature of fast forging is 1050℃, the final forging temperature is 930℃, the fast forging is used to open a 330mm octagonal intermediate billet, the intermediate billet is then radially forged into material, the final forging temperature is 810℃, the diameter of the forged bar is 330 round, and the forged tube billet is obtained;

[0103] Annealing treatment: heat at 660℃ for 24h.

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

[0105] Among them, heating treatment: the heat-treated forged tube billet is placed in a Φ40m annular furnace and kept at a heating temperature of 1250°C for 4 hours to obtain a heated tube billet;

[0106] Perforation treatment: a vertical conical perforator is used to perforate the heated tube blank, with a rolling angle of 15° and a feeding angle of 12° to obtain a perforated rough tube;

[0107] Pipe rolling treatment: the rough pipe after perforation is rolled by an Assel pipe rolling mill, the rolling angle is 4.5°, the feeding angle is 5.5°, and the rolled steel pipe (rough pipe) is obtained;

[0108] Reducing treatment: The rolled steel pipe is reduced in diameter by a two-roller micro-tension reducing mill to obtain a reduced-diameter steel pipe with an outer diameter of 345 mm, a wall thickness of 40 mm, and an inner diameter of 265 mm.

[0109] (c) normalizing and tempering the reduced-diameter steel pipe obtained in step (b) to obtain a high-purity, high-toughness, ultra-high-strength steel pipe;

[0110] Among them, normalizing treatment: heat at 940℃, keep warm for 1.5h, and air cool after leaving the furnace;

[0111] Tempering treatment: heat at 660℃ for 10h, then air cool after removing from the furnace.

[0112] The high-purity, high-toughness and ultra-high-strength steel pipe prepared in this embodiment includes the following chemical components 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, and the rest is iron and unavoidable impurities.

[0113] Example 4

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

[0115] The high-purity, high-toughness and ultra-high-strength steel pipe prepared in this embodiment includes the following chemical components 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, and the rest is iron and unavoidable impurities.

[0116] Comparative Example 1

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

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

[0119] Raw material batching: alloy and raw steel are added into vacuum induction furnace;

[0120] Vacuum induction smelting: 1590℃ high temperature refining, vacuum degree of 0.05Pa during refining; 1563℃ low temperature casting of a 6-ton electrode rod of Φ570, mold cooling after casting, and hot annealing after demoulding.

[0121] (b) subjecting the electrode blank to VAR (vacuum automatic refining) smelting to obtain a steel ingot;

[0122] Vacuum consumable smelting: 6T round ingot (diameter 640mm): 0.01Pa vacuum smelting, consumable process melting rate is 60Kg / h, capping electrode weight is 280Kg, and red annealing is performed after demoulding.

[0123] (c) The steel ingot is first subjected to a heating treatment, and then subjected to a combined forging to obtain a forged tube blank, and then the forged tube blank is subjected to an annealing treatment, and then directly subjected to tube rolling to obtain a steel tube; the specific steps and process parameters are the same as those of step (b) of Example 1.

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

[0125] The high-toughness ultra-high-strength steel pipe prepared in this comparative example includes the following chemical components 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, and the rest are iron and unavoidable impurities.

[0127] In order to further verify the technical effects of the above embodiments and comparative examples, the following experimental examples are specially designed.

[0128] Experimental Example 1

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

[0130] Table 1

[0131]

[0132] It can be seen from the data in Table 1 above that the pipes provided in each embodiment of the present invention have a relatively high purity, and their purity levels are substantially equivalent to the purity level of the pipes prepared by the traditional preparation method in Comparative Example 1, or even slightly higher than the purity level of the pipes in Comparative Example 1.

[0133] Experimental Example 2

[0134] The pipes provided in the embodiments and comparative examples of the present invention are subjected to 890°C oil quenching and 230°C air tempering treatment in the actual production of downstream customers, and then samples are taken to test their relevant properties. Among them, the tensile strength, yield strength, elongation, and cross-sectional shrinkage Z are tested in accordance with GB / T 228.1, the impact absorption energy KU2 is tested in accordance with GB / T 229, and the fracture toughness is tested in accordance with GB / T 4161. The specific results are shown in Table 2.

[0135] Table 2

[0136]

[0137] From the data in Table 2, it can be seen that the mechanical properties of the low P, low S, low O, low N high toughness ultra-high strength steel pipe were tested. After testing, it was found that the tensile strength Rm of the high purity, high toughness, ultra-high strength steel pipe prepared by the present invention is 1731-1767 MPa, and the yield strength Rp 0.2 : 1446~1471MPa, elongation after fracture A: 11~12.5%, section shrinkage Z: 50~52%, impact absorption energy KU2: 83~102J, fracture toughness KIC: 114~124MPa.m 1 / 2, the yield strength ratio is 0.82-0.84. Compared with comparative example 1, the comprehensive performance of each embodiment is maintained on the basis of excellent impact toughness and fracture toughness greatly improved. At the same time, since the preparation method of each embodiment does not require the electroslag remelting step, the time and cost of electroslag remelting are greatly reduced, so that the production efficiency is greatly improved, the production cost is significantly reduced, and the purpose of reducing costs and increasing efficiency is achieved.

[0138] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for manufacturing a high-purity, high-toughness, ultra-high-strength steel pipe, characterized in that: The steps include: (a) providing a continuous casting tube blank obtained by smelting and continuous casting; (b) heating the continuous casting tube billet and then directly performing tube rolling to obtain a steel tube; Alternatively, the continuous casting tube blank is heated and forged to obtain a forged tube blank, the forged tube blank is annealed, and then directly subjected to tube rolling to obtain a steel pipe; (c) normalizing and tempering the steel pipe obtained in step (b) to obtain a high-purity, high-toughness, ultra-high-strength steel pipe.

2. The method for manufacturing a high-purity, high-toughness, ultra-high-strength steel pipe according to claim 1, characterized in that: In step (a), the smelting includes primary refining, refining and vacuum treatment of the raw materials according to the composition of the high-purity, high-toughness and ultra-high-strength steel pipe.

3. The method for manufacturing a high-purity, high-toughness, ultra-high-strength steel pipe according to claim 2, characterized in that: In step (a), an electric furnace or a converter is used for primary smelting, the tapping temperature is ≥1600°C, and the P content of the tapped steel is ≤0.005%; preferably, an electric furnace or a converter is used for primary smelting, a high iron water hot charging ratio is ≥80%, the molten iron S is removed by KR treatment to S≤0.015%, the smelting process uses a slag with a basicity R of 3.5 to 4.0 to remove P, the tapping temperature is ≥1600°C, and the P content of the tapped steel is ≤0.005%; And / or, in step (a), the refining is LF refining, the S content at the refining end point is ≤0.0010%, the end point temperature is 1595°C to 1635°C, and the total refining time is ≥45min; And / or, in step (a), the vacuum treatment time is ≥25 min, the vacuum treatment time is ≥20 min when the vacuum is ≤0.5 Torr, and argon soft blowing is used at the same time, and the soft blowing time is ≥15 min; And / or, in step (a), during the continuous casting process, the superheat of the molten steel in the tundish is 20°C to 35°C, and the constant temperature casting speed is 0.30m / min-0.43m / min.

4. The method for manufacturing a high-purity, high-toughness, ultra-high-strength steel pipe according to claim 1, characterized in that: In step (a), the high-purity, high-toughness and 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 0.50%, 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 unavoidable impurities.

5. The method for manufacturing a high-purity, high-toughness, ultra-high-strength steel pipe according to claim 1, characterized in that: In step (b), the heating temperature of the continuous casting billet during the heating treatment is 1160° C.-1280° C., and the holding time is ≥2.5 h; and / or the minimum steel tapping frequency is ≥60S / piece.

6. The method for manufacturing a high-purity, high-toughness, ultra-high-strength steel pipe according to claim 1, characterized in that: In step (b), the forging is combined forging, including rapid forging and radial forging.

7. The method for manufacturing a high-purity, high-toughness, ultra-high-strength steel pipe according to claim 6, characterized in that: In step (b), the initial forging temperature of the rapid forging is ≥950°C, and the final forging temperature is ≥800°C; preferably, an octagonal intermediate billet of 300 mm to 360 mm is obtained after the rapid forging; And / or, the initial forging temperature of the radial forging is ≥900°C, and the final forging temperature is ≥800°C; And / or, when the temperature of the intermediate billet obtained after rapid forging is less than 900°C, the intermediate billet is first returned to the furnace for heating before the radial forging, and the heating temperature is 1180°C to 1220°C, and the holding time is 1h to 1.5h.

8. The method for manufacturing a high-purity, high-toughness, ultra-high-strength steel pipe according to claim 1, characterized in that: In step (b), the temperature of annealing the forged tube blank is 660° C. to 680° C., and the holding time is 20 h to 25 h; And / or, in step (b), the tube piercing and rolling includes a piercing process, a tube rolling process and a diameter reducing process.

9. The method for manufacturing a high-purity, high-toughness, ultra-high-strength steel pipe according to claim 1, characterized in that: In step (c), the normalizing temperature is 900°C to 960°C, the holding time is ≥1h, and the product is air-cooled after being taken out of the furnace; And / or, the tempering temperature is 660°C to 700°C, the holding time is 6h to 10h, and the steel is air-cooled after being taken out of the furnace.

10. A high-purity, high-toughness, ultra-high-strength steel pipe, characterized in that: It is produced by the method for producing a high-purity, high-toughness, ultra-high-strength steel pipe according to any one of claims 1 to 9; The tensile strength of the high-purity, high-toughness and ultra-high-strength steel pipe is ≥1700MPa, the yield strength is ≥1400MPa, the yield strength ratio is ≤0.86, the impact energy is ≥70J, and the fracture toughness is ≥90MPa*m 1 / 2 .

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