Ni-containing low-temperature steel seamless steel pipe, method for manufacturing the same, and use thereof

Abstract

The application provides a Ni-containing low-temperature seamless steel pipe and a preparation method and application thereof. The preparation method comprises the following steps in sequence: preparing raw materials according to the composition of the Ni-containing low-temperature seamless steel pipe and obtaining a pipe blank; performing heat treatment on the pipe blank to obtain a heat-treated pipe blank; performing the following processes on the heat-treated pipe blank in sequence: piercing treatment, first pipe rolling treatment and sizing treatment, to obtain a sized steel pipe; performing quenching treatment on the sized steel pipe to obtain a quenched steel pipe; performing the following processes on the quenched steel pipe in sequence: second pipe rolling treatment and hot expansion annealing treatment, to obtain the Ni-containing low-temperature seamless steel pipe; the second pipe rolling treatment is performed at 200 DEG C to 250 DEG C; and the hot expansion annealing treatment is performed at 450 DEG C to 550 DEG C. The application overcomes the collapse deformation problem of large-diameter thin-wall steel pipes caused by self-weight, solves the problems of low strength and poor size precision in the traditional process, and achieves the purpose of combining high strength and excellent low-temperature impact toughness.

Description

Technical Field

[0001] This invention relates to the field of steel pipe technology, and more specifically, to a Ni-containing low-temperature steel seamless pipe, its preparation method, and its application. Background Technology

[0002] The long-distance, large-scale storage and transportation of cryogenic liquid gases such as liquefied natural gas (LNG) and liquefied petroleum gas (LPG) is currently a critical link in the energy supply chain. As the core infrastructure carrying these cryogenic media, cryogenic pipelines not only need to withstand internal high pressure but also require long-term stable operation in extremely cold environments. Furthermore, some transported media contain corrosive components such as hydrogen sulfide, which places stringent requirements on the corrosion resistance of the pipe materials. At the same time, to reduce the cost of constructing long-distance pipelines and improve transportation efficiency, the engineering community generally favors large-diameter, thin-walled pipe designs, thereby significantly reducing material usage and overall cost while meeting mechanical performance requirements.

[0003] In terms of material selection, nickel-containing cryogenic steel is widely used in the manufacture of such high-pressure cryogenic pipelines due to its excellent low-temperature toughness and good weldability. The traditional production process for seamless cryogenic steel pipes typically follows a sequence of "billet smelting - heating - piercing - continuous rolling - sizing - cooling - heat treatment (normalizing or quenching and tempering) - finishing." This process is mature in the production of small- and medium-diameter or medium-walled steel pipes, but it has revealed many insurmountable technical bottlenecks when facing the current market demand for large-diameter, thin-walled, high-strength, and high-toughness steel pipes.

[0004] First, in the production of large-diameter thin-walled steel pipes using traditional hot rolling processes, the large outer diameter and relatively thin wall thickness, coupled with the complex stress state during rolling, easily lead to dimensional accuracy problems such as uneven wall thickness and excessive ellipticity. More seriously, during subsequent heat treatment, the inconsistent cooling rates inside and outside the pipe wall, along with deformation caused by its own weight, often result in significant dimensional deformation, bending, or even collapse, leading to extremely low yields and making it difficult to meet the high dimensional accuracy requirements for on-site butt welding. Second, the strength of low-temperature steel pipes produced by traditional processes is generally low. To achieve the load-bearing capacity required for high-pressure transmission, the wall thickness must be increased, directly offsetting the cost advantages of thinner walls. To achieve high strength and high toughness, traditional processes often require complex alloy composition adjustments or multiple heat treatments, which not only increases production costs but may also lead to decreased weldability and increased difficulty in on-site construction. Furthermore, existing technologies often struggle to simultaneously achieve excellent low-temperature toughness while pursuing high strength. While simple cold working or high-temperature normalizing can improve strength, it can easily lead to coarse grains or residual stress concentration, thus deteriorating impact toughness at -70°C. Furthermore, for thin-walled pipes with extremely high diameter-to-thickness ratios, if the traditional hot expansion process is not properly sequenced with the quenching process, the steel pipe is highly susceptible to plastic deformation, surface damage, or deterioration of ovality under its own weight. This severely affects the appearance quality and geometric stability of the pipe, and may even cause the pipe to fail non-destructive testing and be deemed scrap.

[0005] Therefore, how to provide a large-diameter thin-walled seamless steel pipe with high outer diameter accuracy, good surface quality, high strength and excellent low-temperature toughness, and its preparation method, is one of the technical problems that need to be solved in this field. Summary of the Invention

[0006] The main objective of this invention is to provide a Ni-containing low-temperature steel seamless pipe, its preparation method, and its application, so as to solve the problem that seamless steel pipes in the prior art are difficult to simultaneously achieve large diameter, thin wall, high outer diameter accuracy, high strength, and excellent low-temperature toughness.

[0007] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a Ni-containing low-temperature steel seamless pipe, comprising the following steps in sequence: Step S1, preparing raw materials according to the composition of the Ni-containing low-temperature steel seamless pipe and obtaining a pipe blank; the Ni-containing low-temperature steel seamless pipe includes 0.31 wt.% to 0.79 wt.% Ni by weight percentage; Step S2, heat-treating the pipe blank to obtain a heat-treated pipe blank; Step S3, subjecting the heat-treated pipe blank to a piercing process, a first rolling process, and a sizing process in sequence to obtain a sizing steel pipe; Step S4, subjecting the sizing steel pipe to a quenching process to obtain a quenched steel pipe; Step S5, subjecting the quenched steel pipe to a second rolling process and a hot expansion annealing process in sequence to obtain the Ni-containing low-temperature steel seamless pipe; the second rolling process is performed at 200°C to 250°C; the hot expansion annealing process is performed at 450°C to 550°C.

[0008] Further, in step S5, the second rolling process is carried out at 220℃~240℃; the total deformation of the second rolling process is 55%~70%; and / or, the hot expansion annealing process is carried out at 490℃~500℃; the steel pipe advancing speed of the hot expansion annealing process is 130mm / min~200mm / min, and the diameter expansion rate is 3%~10%.

[0009] Further, in step S4, the holding temperature for quenching is 810℃~900℃; and / or, the wall thickness of the sizing steel pipe is denoted as D, where the unit of D is mm; the holding time for quenching is denoted as T, where the unit of T is min; the values ​​of D and T satisfy: T = (1.0~1.3)×D.

[0010] Further, in step S3, the ratio of the outer diameter of the Ni-containing low-temperature steel seamless pipe to the outer diameter of the sizing steel pipe is 1:(0.75~0.99); and / or, the rotational speed of the guide disc of the piercing mill used for piercing is 1.52m / s~2.57m / s, the rolling speed is 0.53m / s~3.25m / s, and the piercing process is carried out at 1100℃~1150℃; and / or, the first rolling process is carried out at 960℃~1000℃; and / or, the sizing process is carried out at 900℃~950℃.

[0011] Furthermore, in step S2, the heat treatment includes a first stage of heat treatment, a second stage of heat treatment, a third stage of heat treatment, and a fourth stage of heat treatment, each performed sequentially for 30 min to 40 min; the temperature of the heat-treated tube blank is 1190℃ to 1200℃.

[0012] Furthermore, step S2 includes the following sequential processes: preheating the tube blank at a temperature of 100℃~300℃ for 1h~4h; performing a first-stage heating treatment on the tube blank to bring its temperature to 400℃~1000℃; performing a second-stage heating treatment on the tube blank to bring its temperature to 900℃~1150℃; performing a third-stage heating treatment on the tube blank to bring its temperature to 1160℃~1190℃; performing a fourth-stage heating treatment on the tube blank to bring its temperature to 1190℃~1200℃; and performing a homogenization treatment on the tube blank at a temperature of 1190℃~1200℃ for 30min~40min to obtain a heat-treated tube blank.

[0013] Furthermore, by weight percentage, Ni-containing low-temperature seamless steel pipes include 0.04wt.%~0.10wt.% C, 0.1wt.%~0.17wt.% Si, 1.11wt.%~1.48wt.% Mn, 0~0.005wt.% S, 0~0.01wt.% P, 0.31wt.%~0.79wt.% Ni, 0~0.2wt.% Cr, 0~0.10wt.% Mo, 0.01wt.%~0.1wt.% Ti, 0.010wt.%~0.05wt.% Nb, 0.015wt.%~0.045wt.% Al, 0.18wt.%~0.25wt.% V, with the remainder being Fe and unavoidable impurities.

[0014] The second aspect of the present invention provides a seamless steel pipe containing Ni low-temperature steel, which is prepared by the above-described preparation method; the outer diameter of the seamless steel pipe containing Ni low-temperature steel is denoted as R1, and the wall thickness of the seamless steel pipe containing Ni low-temperature steel is denoted as R2, the units of R1 and R2 are both mm; R1 / R2≥40.

[0015] Furthermore, the outer diameter of the Ni-containing low-temperature steel seamless pipe is 325mm~845mm; and / or, at -70±5℃, the full-size impact value of the Ni-containing low-temperature steel seamless pipe is ≥54J.

[0016] A third aspect of the present invention provides an application of the above-mentioned Ni-containing low-temperature steel seamless steel pipe as a storage or transportation pipeline in the petroleum or chemical industry.

[0017] By applying the technical solution of this invention, a high-hardness martensitic structure is obtained by quenching a sizing steel pipe. The quenched steel pipe is then subjected to a second rolling process below the recrystallization temperature of 200℃~250℃ to refine the grains and improve the strength. A hot expansion annealing process is then performed at 450℃~550℃ to eliminate residual stress, achieve dimensional stabilization, and precipitate carbides to improve low-temperature toughness. This achieves the goal of overcoming the problem of collapse and deformation of large-diameter thin-walled steel pipes due to their own weight, solving the problems of low strength and poor dimensional accuracy in traditional processes, and balancing high strength and excellent low-temperature impact toughness. As a result, a large-diameter thin-walled high-strength and high-toughness seamless steel pipe with high outer diameter dimensional accuracy, good surface quality, high yield strength, and excellent low-temperature impact toughness is produced. Attached Figure Description

[0018] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0019] Figure 1 The metallographic structure diagram of the Ni-containing low-temperature steel seamless steel pipe obtained in Example 1 of the present invention, namely steel pipe 1;

[0020] Figure 2 The image shows the metallographic structure of the steel pipe obtained in Comparative Example 1 of this invention, namely steel pipe 2. Detailed Implementation

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0022] As described in the background section, existing seamless steel pipes suffer from the problem of not being able to simultaneously achieve large diameter, thin wall, high outer diameter accuracy, high strength, and excellent low-temperature toughness. To address the aforementioned technical problems, the first aspect of this invention provides a method for preparing a Ni-containing low-temperature steel seamless pipe, comprising the following steps: Step S1, preparing raw materials according to the composition of the Ni-containing low-temperature steel seamless pipe and obtaining a pipe blank; the Ni-containing low-temperature steel seamless pipe includes 0.31 wt.% to 0.79 wt.% Ni by weight percentage; Step S2, heat-treating the pipe blank to obtain a heat-treated pipe blank; Step S3, subjecting the heat-treated pipe blank to a piercing process, a first rolling process, and a sizing process sequentially to obtain a sizing steel pipe; Step S4, subjecting the sizing steel pipe to a quenching process to obtain a quenched steel pipe; Step S5, subjecting the quenched steel pipe to a second rolling process and a hot expansion annealing process sequentially to obtain the Ni-containing low-temperature steel seamless pipe; the second rolling process is performed at 200°C to 250°C; the hot expansion annealing process is performed at 450°C to 550°C.

[0023] The preparation method provided by this invention, through specific process sequence and parameter control, synergistically achieves a comprehensive improvement in the strength, toughness, and dimensional accuracy of large-diameter, thin-walled, Ni-containing low-temperature seamless steel pipes. Specifically:

[0024] First, after obtaining the sizing steel pipe, the quenching treatment in step S4 rapidly transforms the austenite in the sizing steel pipe into martensite. This phase transformation process provides the steel pipe with extremely high matrix strength through solid solution strengthening and a sharp increase in dislocation density, which is a prerequisite for achieving high strength indicators. Subsequently, the second rolling treatment in step S5 is carried out in the range of 200℃~250℃, which is lower than the material's recrystallization temperature. This temperature range allows the metastable martensite structure to be refined to the nanometer or submicron level during plastic deformation through dynamic recovery and deformation-induced phase transformation mechanisms. At the same time, it introduces high-density dislocations and substructures, further significantly improving the material's work hardening ability and tensile strength, thus solving the problem of insufficient strength in traditional hot-rolled pipes.

[0025] Secondly, the hot expansion annealing treatment (450℃~550℃) immediately following the second rolling process works by achieving the final dimensional shaping of the large-diameter thin-walled tube through thermal expansion. Simultaneously, within this specific temperature range, martensite decomposes, precipitating fine carbides, and the refined grains recrystallize into equiaxed grains, thus eliminating the work hardening and internal stress caused by the second rolling. This process not only restores the material's plasticity but, more importantly, significantly improves low-temperature impact toughness through grain refinement and dispersed carbide precipitation, overcoming the contradiction that high strength is usually accompanied by a decrease in toughness.

[0026] Finally, the specific process sequence of "quenching-low temperature large deformation rolling-hot expansion annealing" solves the problem of mechanical stability in the forming process of large-diameter thin-walled steel pipes. The traditional process of hot expansion followed by quenching is prone to collapse due to its own weight. However, this solution, after obtaining high strength through quenching, further solidifies the grain structure by low temperature rolling, and finally performs mild dimensional correction and microstructure stabilization through hot expansion annealing. This ensures the geometric dimensional stability of the steel pipe under its own weight (high roundness, no collapse), and achieves a perfect match between high strength and high toughness through grain refinement and microstructure control. Thus, a large-diameter thin-walled seamless steel pipe with excellent mechanical properties and dimensional accuracy that meets the requirements is produced.

[0027] In general, existing technologies that employ a hot-expansion followed by quenching and tempering process for steel pipes can lead to problems such as collapse, dents, and blown-out defects due to the weight of the pipes, affecting the geometric dimensions and surface quality of large-diameter thin-walled seamless steel pipes and ultimately failing to meet usage requirements. Furthermore, for long-distance pipelines, this process only achieves the material's inherent strength and cannot achieve further breakthroughs. This invention, by quenching the steel pipe after the first rolling (hot rolling) followed by warm rolling and hot expansion annealing, not only solves the problem of forming large-diameter thin-walled seamless steel pipes but also produces large-diameter thin-walled seamless steel pipes with higher strength while maintaining low-temperature toughness at -70℃, exhibiting excellent overall performance. In particular, when this large-diameter thin-walled seamless steel pipe is used to manufacture large-diameter, thin-walled nickel-containing low-temperature seamless steel pipes with large outer diameters and high diameter-to-thickness ratios, it achieves high dimensional accuracy, good surface quality, high strength, and good low-temperature toughness; it can replace or even outperform welded pipes of the same grade. This also enables the mass production of this high-strength, high-toughness, large-diameter thin-walled seamless steel pipe.

[0028] As mentioned earlier, the purpose of low-temperature rolling (warm rolling, i.e., the second tube rolling process) is to refine the grain size of the martensite structure below the recrystallization temperature during low-temperature rolling, obtaining an ultra-fine grain structure, thereby significantly improving the strength of the material. Since the lath martensite structure after quenching has high strength, to ensure a smoother grain refinement rolling process, it is preferable to perform the second tube rolling process at 220℃~240℃, thus more effectively balancing the deformation amount and grain refinement effect, ultimately obtaining a seamless steel pipe with superior overall performance. To further enhance its mechanical strength, the total deformation amount of the above-mentioned second tube rolling process is preferably 55%~70%, thereby further refining the grains and increasing the strength of the resulting steel pipe.

[0029] Furthermore, the purpose of the aforementioned hot expansion annealing is to obtain seamless steel pipes with large outer diameters and thin walls, while simultaneously improving the low-temperature impact toughness of the material. The temperature and speed of the hot expansion process affect the uniformity of the outer diameter and wall thickness of the large-diameter thin-walled seamless steel pipe. If the hot expansion speed is too fast, it can easily lead to uneven wall thickness in the resulting large-diameter thin-walled seamless steel pipe; conversely, if the hot expansion speed is too slow, it will increase energy consumption and reduce strength, thus deteriorating the mechanical properties of the large-diameter thin-walled seamless steel pipe. Based on this, by further optimizing the hot expansion annealing treatment to be carried out at 490℃~500℃, the mechanical properties and wall thickness uniformity of the resulting steel pipe are further improved. Simultaneously, the preferred steel pipe feeding speed for the hot expansion annealing treatment is 130mm / min~200mm / min (more preferably 150mm / min~170mm / min), with an expansion rate of 3%~10%, thereby promoting more uniform heating of the steel pipe in the hot expansion mold, resulting in more consistent wall temperature and deformation rate, and thus more effectively improving the uniformity of the outer diameter and wall thickness. At the same time, the specific propulsion speed also allows the tail of the steel pipe to quickly enter the cooling stage after leaving the heating zone, thereby further refining the grains and better maintaining the dimensional accuracy after thermal expansion.

[0030] Furthermore, in practical applications, the hot expansion annealing process also includes cooling, straightening, and finishing the resulting steel pipe. The water ring cooling method used to cool the seamless steel pipe helps to achieve a more uniform and refined microstructure in the large-diameter thin-walled seamless steel pipe. The straightening and finishing processes further eliminate any bends in the large-diameter thin-walled seamless steel pipe, resulting in a high-strength, high-toughness large-diameter thin-walled seamless steel pipe that is as perfect as possible.

[0031] In the above preparation method, the purpose of quenching is to transform supercooled austenite into martensite, thereby helping to improve the strength of the obtained seamless steel pipe. The quenching temperature affects the efficiency and degree of transformation of austenite into martensite or bainite. Therefore, in order to optimize the quenching effect, the holding temperature for quenching in step S4 is preferably 810℃~900℃, more preferably 860℃~880℃. In addition, if the quenching time is too long, the surface quality of the large-diameter thin-walled seamless steel pipe will deteriorate and the low-temperature impact will worsen; if the quenching time is too short, the microstructure of the large-diameter thin-walled seamless steel pipe will not be completely transformed. Therefore, it is preferable to control the holding time for quenching according to the wall thickness coefficient of 1.0min / mm~1.3min / mm, that is: let the wall thickness of the sizing steel pipe be D, where D is in mm; let the holding time for quenching be T, where T is in min; the values ​​of D and T satisfy: T = (1.0~1.3)×D. Optimizing the quenching time using the above method can significantly improve the strength and low-temperature impact toughness of the resulting Ni-containing low-temperature steel seamless pipe. In practical applications, the wall thickness of the sized steel pipe is 6.55mm~20.00mm.

[0032] To better control the piercing and sizing processes and obtain more uniform and regular sizing steel pipes, in step S3 above, preferably: the ratio of the outer diameter of the Ni-containing low-temperature steel seamless pipe to the outer diameter of the sizing steel pipe is 1:(0.75~0.99); and / or, the rotational speed of the piercing mill guide disc used for piercing is 1.52m / s~2.57m / s, the rolling speed is 0.53m / s~3.25m / s, and the piercing process is carried out at 1100℃~1150℃; and / or, the first rolling process is carried out at 960℃~1000℃; and / or, the sizing process is carried out at 900℃~950℃.

[0033] In step S2, preferably, the heat treatment includes a first stage of heat treatment, a second stage of heat treatment, a third stage of heat treatment, and a fourth stage of heat treatment, each lasting 30 to 40 minutes independently; the temperature of the heat-treated tube blank is 1190℃ to 1200℃. Based on this preferred scheme, by controlling thermal stress and improving the uniformity of the microstructure through stepped heating, the resulting heat-treated tube blank has better plasticity, thereby making the subsequent piercing, rolling, and heat treatment processes more stable, and ultimately obtaining a large-diameter thin-walled seamless steel pipe with a more uniform microstructure and better mechanical properties.

[0034] Furthermore, step S2 preferably includes the following sequential processes: preheating the tube blank at a temperature of 100℃~300℃ for 1h~4h; performing a first-stage heating treatment on the tube blank to reach a temperature of 400℃~1000℃; performing a second-stage heating treatment on the tube blank to reach a temperature of 900℃~1150℃; performing a third-stage heating treatment on the tube blank to reach a temperature of 1160℃~1190℃; performing a fourth-stage heating treatment on the tube blank to reach a temperature of 1190℃~1200℃; and performing a homogenization treatment on the tube blank at a temperature of 1190℃~1200℃ for 30min~40min, thereby obtaining a heat-treated tube blank. The preheating treatment is performed at 100℃~300℃ for 1h~4h, effectively removing moisture and volatiles from the surface of the tube blank and initially reducing the temperature difference between the inside and outside of the tube blank, thus reducing thermal stress during subsequent high-temperature heating. Subsequently, the tube blank is heated to 400℃~1000℃ (more preferably 500℃~600℃) in the first stage, 900℃~1150℃ (more preferably 900℃~1100℃) in the second stage, 1160℃~1190℃ (more preferably 1160℃~1180℃) in the third stage, and 1190℃~1200℃ (more preferably 1193℃~1198℃) in the fourth stage. This stepped heating strategy allows the tube blank temperature to rise gradually, with each stage of temperature increase undergoing sufficient heat conduction balance, further improving the temperature uniformity of the tube blank cross-section. Finally, a soaking heat treatment is performed at 1190℃~1200℃ for 30min~40min, allowing the austenite grains to grow to a suitable size and become homogenized, and the carbon and alloying elements to dissolve completely, thus more thoroughly eliminating compositional segregation. In summary, based on this preferred heat treatment mechanism, the resulting heat-treated tube blank has better internal microstructure uniformity, finer austenite grains, and superior thermoplasticity. This further improves the success rate of subsequent piercing and rolling, and also further enhances the strength and low-temperature toughness of the final steel pipe.

[0035] Furthermore, by weight percentage, the aforementioned Ni-containing low-temperature seamless steel pipe of the present invention preferably comprises 0.04 wt.% to 0.10 wt.% C, 0.1 wt.% to 0.17 wt.% Si, 1.11 wt.% to 1.48 wt.% Mn, 0 to 0.005 wt.% S, 0 to 0.01 wt.% P, 0.31 wt.% to 0.79 wt.% Ni, 0 to 0.2 wt.% Cr, 0 to 0.10 wt.% Mo, 0.01 wt.% to 0.1 wt.% Ti, 0.010 wt.% to 0.05 wt.% Nb, 0.015 wt.% to 0.045 wt.% Al, 0.18 wt.% to 0.25 wt.% V, with the remainder being Fe and unavoidable impurities. In addition to the basic carbon steel components Fe, C, Si, and Mn, the above-mentioned steel pipe composition mainly contains a high amount of Ni. Ni is an austenite stabilizing element, which is particularly crucial for the stability of 09MnNiD seamless steel pipes at low temperatures. Ni's ability to lower the ductile-brittle transition temperature is second only to N, making it the best metallic element for this purpose. Ni also helps improve the hardenability and strength of 09MnNiD seamless steel pipes, while simultaneously enhancing their low-temperature plasticity. Mn is an austenite stabilizing element and also a matrix strengthening element, capable of improving the strength of 09MnNiD seamless steel pipes through precipitation strengthening. Mn also improves the hardenability of the material; too low an Mn content results in insufficient strength, while too high a Mn content affects the toughness of the 09MnNiD seamless steel pipe. Furthermore, the presence of Si and Mn in a certain proportion in large-diameter, thin-walled 09MnNiD seamless steel pipes helps to inhibit their segregation. Si is a deoxidizing element in steelmaking, which is crucial for reducing the content of harmful elements in 09MnNiD seamless steel pipes. Si can also improve strength. In addition to inhibiting Mn segregation when present in a certain proportion with Mn in 09MnNiD seamless steel pipes, Si can also inhibit P segregation at grain boundaries. C can improve strength through interstitial solid solution, but excessive C is detrimental to the low-temperature toughness of the weld heat-affected zone. Therefore, the lower the C content, the better, while ensuring strength. Al is also an excellent deoxidizing element, which can work with Si to remove oxygen from the billet. The synergistic effect of the two elements improves the deoxidation effect and effectively prevents inclusions from appearing in clumps, thereby reducing the toughness of the seamless steel pipe and causing surface defects. The Al in this application is total aluminum content, including acid-fused aluminum and alumina. Cr works synergistically with Mn to improve the hardenability of 09MnNiD seamless steel pipes and prevent or slow down the precipitation and aggregation of carbides during tempering, thus improving the tempering stability of 09MnNiD seamless steel pipes.V (Volume) can refine grains, preventing the austenite grains in the billet from growing too coarse during the heating stage. This allows for further grain refinement of the 09MnNiD seamless steel pipe during subsequent rolling, improving its strength and toughness. S (Saturate) readily forms MnS precipitates with Mn, while P (Polymerase) tends to segregate at grain boundaries, reducing their resistance to crack propagation. Therefore, both S and P reduce the low-temperature toughness of the 09MnNiD seamless steel pipe. Controlling the S and P content within the aforementioned ranges reduces their intergranular brittleness tendency, thus mitigating their detrimental effects on the low-temperature toughness of the high-strength, high-toughness 09MnNiD seamless steel pipe. By strictly controlling the content of each chemical component in the billet and ensuring a reasonable ratio between them, the resulting 09MnNiD seamless steel pipe possesses excellent mechanical properties and good low-temperature toughness and strength.

[0036] A second aspect of this invention provides a seamless Ni-containing low-temperature steel pipe, which is prepared by the above-described method. The outer diameter of the seamless Ni-containing low-temperature steel pipe is denoted as R1, and the wall thickness as R2, where both R1 and R2 are in mm; R1 / R2 ≥ 40. The resulting seamless Ni-containing low-temperature steel pipe not only possesses excellent dimensional accuracy but also maintains high strength and high low-temperature toughness. The diameter-to-thickness ratio ≥ 40 signifies reduced steel consumption, lowering pipe material and manufacturing costs, with particularly significant material-saving effects for long-distance pipelines. Furthermore, the thin-walled structure allows the pipe to withstand higher internal pressure under the same pressure, or to have a higher safety margin under the same internal pressure, improving the pipe's pressure-bearing efficiency. In addition, the large diameter means a larger flow cross-sectional area, improving the medium's transport efficiency and reducing pumping energy consumption. It should be noted that due to the complex metallographic changes during the preparation process, and the limitations of the alloy material field and existing testing and characterization methods, it is difficult to comprehensively and quantitatively characterize the complex microstructure and metallographic features of the obtained Ni-containing low-temperature steel seamless pipe. However, the performance test results have already shown that the Ni-containing low-temperature steel seamless pipe obtained by this invention possesses higher mechanical properties, especially superior low-temperature toughness.

[0037] Furthermore, in this invention, the aforementioned R1 / R2 (i.e., diameter-to-thickness ratio) can specifically be 60~65 (in practice, it can be 60, 61, 62, 63, 64, 65, or any range of values ​​formed by any two of the aforementioned points).

[0038] In several preferred embodiments, the outer diameter of the aforementioned Ni-containing low-temperature steel seamless pipe is 325mm to 845mm. Within this size range, the steel pipe can effectively balance manufacturing difficulty and transportation efficiency, meeting the needs of long-distance main pipelines. Furthermore, at -70±5℃, the full-size impact value of the aforementioned Ni-containing low-temperature steel seamless pipe is preferably ≥54J (specifically 80J~185J), meaning that the steel pipe still possesses extremely high fracture toughness in extremely cold environments and can effectively resist low-temperature brittle fracture.

[0039] A third aspect of this invention provides an application of the aforementioned Ni-containing low-temperature steel seamless pipe as a storage or transportation pipeline in the petroleum or chemical industries. The aforementioned Ni-containing low-temperature steel seamless pipe possesses excellent low-temperature toughness, high strength, corrosion resistance, and dimensional accuracy. As a storage pipeline, its high dimensional accuracy and surface quality ensure reliable sealing and prevent leakage of low-temperature media; as a transportation pipeline, its high strength allows for thinner walls, reducing construction costs, while its excellent -70°C low-temperature impact toughness ensures structural integrity under extreme climates or accident conditions, preventing catastrophic brittle fracture.

[0040] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0041] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0042] Example 1

[0043] Preparation of a Ni-containing low-temperature seamless steel pipe:

[0044] (1) By weight percentage, the steel pipe comprises 0.06 wt.% C, 0.13 wt.% Si, 1.35 wt.% Mn, 0.003 wt.% S, 0.007 wt.% P, 0.53 wt.% Ni, 0.12 wt.% Cr, 0.04 wt.% Mo, 0.03 wt.% Ti, 0.025 wt.% Nb, 0.035 wt.% Al, and 0.22 wt.% V, with the remainder being Fe and unavoidable impurities. The raw materials are prepared according to the above composition and continuously cast into a billet.

[0045] (2) The above-mentioned tube blank is heated in a ring furnace: the tube blank is first preheated at 200℃ for 1.5h, and then the first stage of heating treatment is carried out to bring the temperature of the tube blank to 550℃; after the second stage of heating treatment, the temperature of the tube blank reaches 900℃; after the third stage of heating treatment, the temperature of the tube blank reaches 1160℃; after the fourth stage of heating treatment, the temperature of the tube blank reaches 1195℃. The time for the first stage of heating treatment, the second stage of heating treatment, the third stage of heating treatment, the fourth stage of heating treatment, and the soaking treatment can each be 30~40 minutes independently.

[0046] (3) The rotational speed of the piercing mill guide plate during piercing is 2.02 m / s, the rolling speed is 1.53 m / s, and the temperature is 1120℃. The temperature during tube rolling is 980℃, and the temperature during sizing is 930℃. Following this, the heated tube blank is pierced, rolled, and sizing is performed to obtain a sizing steel pipe. The outer diameter of the resulting sizing steel pipe is 325 mm, which is 3 / 4 times the target outer diameter (i.e., the ratio of the target outer diameter to the outer diameter of the sizing steel pipe is 1:0.75).

[0047] (4) The sizing steel pipe is quenched at 870℃. The quenching holding time is controlled according to the wall thickness coefficient of 1.1min / mm, specifically 19min (the wall thickness of the sizing steel pipe is 17.27mm).

[0048] (5) Then, the steel pipe is thinned by warm rolling at 230℃, and after multiple passes of warm rolling, the total deformation reaches 60%. The warm-rolled steel pipe is then hot-expanded and annealed at 495℃. The feed rate of the hot-expanded steel pipe is 160mm / min, and the diameter expansion rate is 6.5%. A cooling water ring is added 1 meter at the end of the hot expansion to water-cool the steel pipe at a cooling rate of 60℃ / s. Diameter expansion rate = (diameter after hot expansion - diameter before hot expansion) / diameter before hot expansion × 100%.

[0049] Finally, a large-diameter thin-walled seamless steel pipe was obtained, with an outer diameter of 610 mm and a wall thickness of 9.53 mm. The obtained large-diameter thin-walled 09MnNiD seamless steel pipe underwent straightening, dimensional and surface quality inspection, and was packaged and stored. This pipe is designated as steel pipe 1. The metallographic structure of steel pipe 1 is shown below. Figure 1 As shown, Figure 1 The steel pipe 1 shows that it has a tempered sorbite structure.

[0050] Example 2

[0051] The only difference between this embodiment and embodiment 1 is that in step (5), the temperature of the warm rolling thinning is changed to 200°C.

[0052] Example 3

[0053] The only difference between this embodiment and embodiment 1 is that in step (5), the temperature of the warm rolling thinning is changed to 250°C.

[0054] Example 4

[0055] The only difference between this embodiment and embodiment 1 is that in step (5), the temperature of the thermal expansion annealing is changed to 450°C.

[0056] Example 5

[0057] The only difference between this embodiment and embodiment 1 is that in step (5), the temperature of the thermal expansion annealing is changed to 550°C.

[0058] Example 6

[0059] The only difference between this embodiment and embodiment 1 is that in step (5), the pushing speed of the hot-expanded annealed steel pipe is changed to 130 mm / min.

[0060] Example 7

[0061] The only difference between this embodiment and embodiment 1 is that in step (5), the pushing speed of the hot-expanded annealed steel pipe is changed to 200 mm / min.

[0062] Example 8

[0063] The only difference between this embodiment and embodiment 1 is that in step (4), the quenching holding temperature is changed to 810℃, and the holding time is controlled according to the wall thickness coefficient of 0.8min / mm, specifically 14min.

[0064] Example 9

[0065] The only difference between this embodiment and embodiment 1 is that in step (4), the quenching holding temperature is changed to 900℃, and the holding time is controlled according to the wall thickness coefficient of 1.5 min / mm, specifically 26 min.

[0066] Example 10

[0067] The only difference between this embodiment and embodiment 1 is that in step (2), the third stage of heating treatment is not performed.

[0068] Example 11

[0069] The difference between this embodiment and embodiment 1 lies only in step (2), specifically:

[0070] (2) The above-mentioned tube blank is heated in a ring furnace: the tube blank is first preheated at 100℃ for 4 hours, and then the first stage of heating treatment is carried out to bring the temperature of the tube blank to 400℃; after the second stage of heating treatment, the temperature of the tube blank reaches 800℃; after the third stage of heating treatment, the temperature of the tube blank reaches 1150℃; after the fourth stage of heating treatment, the temperature of the tube blank reaches 1200℃. The time for the first stage of heating treatment, the second stage of heating treatment, the third stage of heating treatment, the fourth stage of heating treatment, and the soaking treatment can each be 30~40 minutes independently.

[0071] Example 12

[0072] The difference between this embodiment and embodiment 1 lies only in step (2), specifically:

[0073] (2) The above-mentioned tube blank is heated in a ring furnace: the tube blank is first preheated at 300℃ for 1 hour, and then the first stage of heating treatment is carried out to bring the temperature of the tube blank to 1000℃; after the second stage of heating treatment, the temperature of the tube blank reaches 1150℃; after the third stage of heating treatment, the temperature of the tube blank reaches 1190℃; after the fourth stage of heating treatment, the temperature of the tube blank reaches 1190℃. The time for the first stage of heating treatment, the second stage of heating treatment, the third stage of heating treatment, the fourth stage of heating treatment, and the soaking treatment can each be 30~40 minutes independently.

[0074] Comparative Example 1

[0075] The only difference between this comparative example and Example 1 is that step (5) was not performed; instead, the steel pipe obtained after quenching was tempered at 495°C. The resulting steel pipe is designated as steel pipe 2, and its metallographic structure is shown in the figure below. Figure 2 As shown.

[0076] Comparative Example 2

[0077] The only difference between this comparative example and Example 1 is that in step (5), the temperature of the warm rolling thinning is changed to 180°C.

[0078] Comparative Example 3

[0079] The only difference between this comparative example and Example 1 is that in step (5), the temperature of the warm rolling thinning is changed to 280°C.

[0080] Comparative Example 4

[0081] The only difference between this comparative example and Example 1 is that in step (5), the temperature of the thermal expansion annealing is changed to 400°C.

[0082] Comparative Example 5

[0083] The only difference between this comparative example and Example 1 is that in step (5), the temperature of the thermal expansion annealing is changed to 600°C.

[0084] The specifications, outer diameter deviation, and wall thickness accuracy of the steel pipe samples obtained in each embodiment and comparative example are shown in Table 1.

[0085] Table 1

[0086]

[0087] Test methods

[0088] R p0.2: This is the specified plastic elongation strength, which is tested according to GB / T228.1 "Metallic materials - Tensile testing - Part 1: Tensile testing at room temperature".

[0089] R m: It is the tensile strength, which is tested according to GB / T228.1 "Metallic materials - Tensile testing - Part 1: Tensile testing at room temperature".

[0090] A Elongation is measured according to GB / T228.1 "Metallic materials - Tensile testing - Part 1: Tensile testing at room temperature".

[0091] Full-size impact value at -70℃: Tested according to GB / T229 "Metallic materials - Tensile testing - Part 1: Tensile testing at room temperature".

[0092] The steel pipe samples obtained from each embodiment and comparative example were subjected to the above tests, and the results are shown in Table 2.

[0093] Table 2

[0094]

[0095] As can be seen from the above description, compared with the various comparative examples, the above embodiments of the present invention have achieved the goal of overcoming the problem of collapse and deformation of large-diameter thin-walled steel pipes due to their own weight, solving the problems of low strength and poor dimensional accuracy of traditional processes, and taking into account both high strength and excellent low-temperature impact toughness, thereby producing large-diameter thin-walled high-strength and high-toughness seamless steel pipes with high outer diameter dimensional accuracy, good surface quality, high yield strength and excellent low-temperature impact toughness.

[0096] Specifically, in each embodiment:

[0097] Comparing Examples 2 and 3 with Example 1, it can be seen that by further optimizing the temperature of warm rolling thinning in step S5, the deformation amount and grain refinement effect can be more effectively balanced, and a seamless steel pipe with better overall performance can be obtained.

[0098] Comparing Examples 4 and 5 with Example 1, it can be seen that by further optimizing the temperature of the hot expansion annealing in step S5, the mechanical properties and wall thickness uniformity of the obtained steel pipe can be further improved.

[0099] Comparing Examples 6 and 7 with Example 1, it can be seen that by further optimizing the steel pipe pushing speed in step S5 during hot expansion annealing, the steel pipe can be heated more evenly in the hot expansion mold, and the wall temperature and deformation rate are more consistent, thereby more effectively improving the uniformity of outer diameter and wall thickness.

[0100] Comparing Examples 8 and 9 with Example 1, it can be seen that by further optimizing the quenching temperature and time in step S4, the quenching effect can be further optimized, and the strength and low-temperature impact toughness of the obtained Ni-containing low-temperature steel seamless pipe can be significantly improved.

[0101] Comparing Examples 10 to 12 with Example 1, it can be seen that by further optimizing the heat treatment conditions in step S2, the obtained heat-treated tube blank can have better plasticity, thereby making the subsequent piercing, rolling and heat treatment processes more stable, and finally obtaining a large-diameter thin-walled seamless steel pipe with more uniform structure and better mechanical properties.

[0102] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0103] 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 preparing a Ni-containing low-temperature seamless steel pipe, characterized in that, Including the following: Step S1: Prepare raw materials and obtain tube blanks according to the composition of the Ni-containing low-temperature steel seamless steel pipe; the Ni-containing low-temperature steel seamless steel pipe contains 0.31wt.%~0.79wt.% Ni by weight percentage. Step S2: The tube blank is heat-treated to obtain a heat-treated tube blank; Step S3: The heat-treated tube blank is sequentially subjected to piercing treatment, first rolling treatment and sizing treatment to obtain a sizing steel pipe; Step S4: The sizing steel pipe is quenched to obtain a quenched steel pipe; Step S5: The quenched steel pipe is subjected to a second rolling process and a hot expansion annealing process in sequence to obtain the Ni-containing low-temperature steel seamless pipe; the second rolling process is carried out at 200℃~250℃; the hot expansion annealing process is carried out at 450℃~550℃.

2. The method for preparing Ni-containing low-temperature seamless steel pipe according to claim 1, characterized in that, In step S5 The second rolling process is performed at 220°C to 240°C; the total deformation of the second rolling process is 55% to 70%; and / or, The hot expansion annealing treatment is carried out at 490℃~500℃; the steel pipe advancing speed of the hot expansion annealing treatment is 130mm / min~200mm / min, and the diameter expansion rate is 3%~10%.

3. The method for preparing Ni-containing low-temperature seamless steel pipe according to claim 1, characterized in that, In step S4 The holding temperature for the quenching treatment is 810℃~900℃; and / or, Let D be the wall thickness of the sizing steel pipe, and let the unit of D be mm; let T be the holding time of the quenching treatment, and let the unit of T be min; the values ​​of D and T satisfy: T = (1.0~1.3) × D.

4. The method for preparing Ni-containing low-temperature seamless steel pipe according to any one of claims 1 to 3, characterized in that, In step S3 The ratio of the outer diameter of the Ni-containing low-temperature steel seamless pipe to the outer diameter of the sized steel pipe is 1:(0.75~0.99); and / or, The piercing mill guide plate used in the piercing process rotates at a speed of 1.52 m / s to 2.57 m / s, and the rolling speed is 0.53 m / s to 3.25 m / s, and the piercing process is carried out at 1100℃ to 1150℃; and / or, The first rolling process is performed at 960°C to 1000°C; and / or, The sizing process is carried out at 900℃~950℃.

5. The method for preparing Ni-containing low-temperature seamless steel pipe according to any one of claims 1 to 3, characterized in that, In step S2 The heat treatment includes a first stage of heat treatment, a second stage of heat treatment, a third stage of heat treatment, and a fourth stage of heat treatment, each performed sequentially and independently for 30 min to 40 min. The temperature of the heat-treated tube blank is 1190℃~1200℃.

6. The method for preparing Ni-containing low-temperature seamless steel pipe according to claim 5, characterized in that, Step S2 includes the following steps performed sequentially: The tube blank is preheated at a temperature of 100℃~300℃ for 1h~4h; The tube blank is subjected to the first stage of heating treatment to bring its temperature to 400℃~1000℃; The tube blank is subjected to a second stage of heating treatment to bring its temperature to 900℃~1150℃; The tube blank is subjected to the third stage of heating treatment to bring its temperature to 1160℃~1190℃; The tube blank is subjected to the fourth stage of heating treatment to bring its temperature to 1190℃~1200℃; The tube blank is subjected to a homogenization heat treatment at a temperature of 1190℃~1200℃ for 30min~40min to obtain the heat-treated tube blank.

7. The method for preparing Ni-containing low-temperature seamless steel pipe according to any one of claims 1 to 3, characterized in that, By weight percentage, the Ni-containing low-temperature seamless steel pipe comprises 0.04wt.%~0.10wt.% C, 0.1wt.%~0.17wt.% Si, 1.11wt.%~1.48wt.% Mn, 0~0.005wt.% S, 0~0.01wt.% P, 0.31wt.%~0.79wt.% Ni, 0~0.2wt.% Cr, 0~0.10wt.% Mo, 0.01wt.%~0.1wt.% Ti, 0.010wt.%~0.05wt.% Nb, 0.015wt.%~0.045wt.% Al, and 0.18wt.%~0.25wt.% V, with the remainder being Fe and unavoidable impurities.

8. A seamless steel pipe containing Ni at low temperature, characterized in that, The Ni-containing low-temperature steel seamless steel pipe is prepared by the preparation method of the Ni-containing low-temperature steel seamless steel pipe according to any one of claims 1 to 7; the outer diameter of the Ni-containing low-temperature steel seamless steel pipe is denoted as R1, the wall thickness of the Ni-containing low-temperature steel seamless steel pipe is denoted as R2, and the units of R1 and R2 are both mm; R1 / R2≥40.

9. The seamless steel pipe containing Ni at low temperatures according to claim 8, characterized in that, The outer diameter of the Ni-containing low-temperature steel seamless pipe is 325mm~845mm; and / or, At -70±5℃, the full-size impact value of the Ni-containing low-temperature steel seamless pipe is ≥54J.

10. The application of the Ni-containing low-temperature steel seamless pipe as described in claim 8 or 9 as a storage or transportation pipeline in the petroleum or chemical industry.

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