Seamless steel tube as well as preparation method and application thereof

Abstract

The invention provides a seamless steel tube as well as a preparation method and application thereof. The seamless steel tube comprises the following chemical components in percentage by weight: 0.16-0.26% of C, 0.20-0.35% of Si, 1.20-1.50% of Mn, 0.40-0.60% of Cr, 0.010-0.030% of Ti, 0.020-0.030% of Nb, less than or equal to 0.05% of Mo, less than or equal to 0.05% of V, less than or equal to 0.05% of Al, less than or equal to 0.005% of Ca, less than or equal to 0.010% of N, less than or equal to 0.005% of S, less than or equal to 0.015% of P, less than or equal to 0.15% of Cu, less than or equal to 0.25% of Ni, less than or equal to 0.0020% of O, less than or equal to 0.0002% of H, less than or equal to 0.015% of As, less than or equal to The metallographic structure comprises tempered sorbite and austenite, the volume content of the austenite is smaller than or equal to 5%, and the grain size is larger than or equal to 7 grades. According to the seamless steel pipe material, specific raw material components cooperate with one another, a sorbite structure with low dislocation density and a high-density nano-sized precipitated phase (austenite) are obtained, and the sorbite structure and the high-density nano-sized precipitated phase supplement one another, so that the seamless steel pipe material has high strength, high toughness, high collapse resistance and excellent high-temperature resistance at the same time.

Description

Technical Field

[0001] The present invention relates to the field of metallurgy technology, and in particular to a seamless steel pipe and a preparation method and application thereof. Background Art

[0002] At present, seamless steel pipes are widely used in 110KSI-140KSI perforating gun barrels and 140V casing.

[0003] (I) For perforating gun barrels

[0004] Perforation is an extremely important technology in oil exploration and development system engineering, and is one of the important means to improve the recovery rate of oil and gas wells. In the perforation operation, the perforating gun barrel acts as a bullet holder to position the perforation direction, protect the perforating pyrotechnic device from being soaked by the fluid in the well, withstand the pressure, reduce the damage to the downhole casing during the perforation operation, and protect the oil layer casing during the explosion. Due to its harsh working conditions, the gun barrel is not only affected by medium corrosion, well temperature and pressure, but also by the high pressure and huge shock wave generated when the perforating bullet is fired. Therefore, the quality, strength and toughness of the perforating gun barrel are very strict.

[0005] The requirements for perforating gun barrels are not only strong pressure resistance, but also the ability to withstand the high pressure environment generated by deep wells and perforating bullets, and strong resistance to expansion and deformation, effectively preventing the occurrence of well jamming. In addition, in addition to the strength requirements of the perforating gun barrel, it is also expected to reduce the wall thickness of the gun body and improve the perforation quality. Therefore, the perforating gun barrel must have high toughness while requiring high strength, because the high-strength perforating gun barrel is not tough enough, especially when the lateral impact toughness is low, it will lead to high burrs in the perforation holes and even cracks in the gun body, causing accidents such as well jamming. As the depth of the well increases, the strength of the casing used is higher, so the required perforating explosion force is also greater, and the strength requirements of the perforating gun barrel itself are also higher. There are not many studies on ultra-deep well perforating equipment in China, and the selection of materials is also concentrated on conventional low-alloy steels such as 32CrMo4 and 35CrMo, mainly by increasing the wall thickness of the perforating gun barrel to improve the anti-extrusion strength of the steel pipe.

[0006] For example, CN 107841681 B provides a method for manufacturing a perforating gun, which mainly adopts a sub-temperature quenching method between AC1 and AC3 temperatures to obtain the perforating gun steel pipe material. The method has complex control for large-scale production on site and poor process stability. CN108118251A patent provides a method for manufacturing a high-strength perforating gun. The Mo content designed in this patent is 0.3-0.7%, which is costly. The performance of the steel pipe manufactured according to this method cannot simultaneously meet the room temperature yield strength>965MPa, tensile strength≥1034Mpa and 0℃ full-size (10×10mm) V-notch transverse (T) impact energy≥80J requirements. Patent CN201510234477.0 discloses a high-grade perforating gun barrel and forming method, with low carbon content and Mo content of about 1.0, containing alloy elements such as W, expensive, very easy to bend after water quenching at 880-920℃, and extremely difficult to produce. CN108251747A provides a steel pipe for a crane boom and a manufacturing method thereof. The steel pipe composition includes, by weight percentage, 0.11-0.15% C, 0.28-0.76% Si, 0.92-1.20% Cr, 1.10-1.20% Mn, 0.50-0.60% Mo, 0.056-0.12% V, 0.039-0.12% Nb, 0.565-1.23% W, 0.34-1.32% Ni and 0-0.005% N. The patent has a high W content, contains more Ni and Nb, and has more alloy elements. The alloy elements interact and interfere with each other more, and the performance of the final product is uncontrollable. At the same time, due to the high alloy content, the material manufacturing cost of the patent is high.

[0007] (ii) For 140V bushing

[0008] Ultra-deep well oil casing has significant economic benefits and market application prospects. The construction of ultra-deep wells not only requires oil casing to have higher strength, but also puts forward higher requirements for toughness and corrosion resistance. The requirements for 140v casing are not only high strength, but also high toughness, high anti-collapse performance and excellent high temperature resistance. In the development of new steel grades, the focus is on solving the contradiction between high strength and high toughness, and the contradiction between performance and production cost.

[0009] In summary, in the oil exploration and development system engineering, for seamless steel pipes used in perforating gun barrels and 140V casings, it is difficult to obtain seamless steel pipes with excellent comprehensive performance (such as high strength, high toughness, high collapse resistance and excellent high temperature resistance) at a low cost in the existing technology. Therefore, it is necessary to provide a seamless steel pipe that can have the above excellent performance at a lower cost. Summary of the invention

[0010] The main purpose of the present invention is to provide a seamless steel pipe and a preparation method and application thereof, so as to solve the problem that the prior art cannot obtain seamless steel pipes with excellent comprehensive performance (such as high strength, high toughness, high anti-collapse performance and excellent high temperature resistance) under low cost requirements.

[0011] In order to achieve the above object, according to one aspect of the present invention, a seamless steel pipe is provided. The chemical composition of the seamless steel pipe includes, by weight percentage: C: 0.16-0.26%, Si: 0.20-0.35%, Mn: 1.20-1.50%, Cr: 0.40-0.60%, Ti: 0.010-0.030%, Nb: 0.020-0.030%, Mo≤0.05%, V≤0.05%, Al≤0.05%, Ca≤0.005%, N≤0.010%, S≤0. 005%, P≤0.015%, Cu≤0.15%, Ni≤0.25%, O≤0.0020%, H≤0.0002, As≤0.015%, Sn≤0.010%, Pb≤0.010%, Sb≤0.010%, Bi≤0.010%, and the sum of As, Sn, Pb, Sb and Bi is ≤0.30%, and the balance is iron and unavoidable impurities; wherein, the metallographic structure of the seamless steel pipe includes tempered troostite and austenite, the volume content of austenite is ≤5%, and the grain size of the seamless smooth pipe is ≥7 levels.

[0012] Furthermore, the chemical composition of the seamless steel pipe includes, by weight percentage: C: 0.18-0.21%, Si: 0.24-0.28%, Mn: 1.27-1.30%, Cr: 0.46-0.50%, Ti: 0.010-0.030%, Nb: 0.021-0.029%, Mo≤0.04%, V≤0.02%, Al≤0.03%, Ca≤0.005%, N≤ 0.010%, S≤0.003%, P≤0.012%, Cu≤0.15%, Ni≤0.110%, O≤0.0020%, H≤0.0002%, As≤0.015%, Sn≤0.010%, Pb≤0.010%, Sb≤0.010%, Bi≤0.010%, and the sum of As, Sn, Pb, Sb and Bi ≤0.30%, the balance being iron and unavoidable impurities.

[0013] Furthermore, the volume content of austenite is ≤3%; and / or the grain size of the seamless steel pipe is >7 grades.

[0014] In order to achieve the above-mentioned purpose, according to the second aspect of the present invention, a method for preparing the above-mentioned seamless steel pipe is provided, and the preparation method comprises: step S1, smelting and casting the raw materials in sequence to obtain a cast tube billet; step S2, rolling the cast tube billet to obtain a rolled tube billet; step S3, quenching, tempering and hot straightening the rolled tube billet in sequence to obtain a seamless steel pipe.

[0015] Furthermore, in step S1, the smelting method includes at least one of vacuum induction smelting, electric arc furnace smelting or converter smelting.

[0016] Furthermore, in step S2, during the rolling process, the rolling ratio is ≥3, preferably 5-10.

[0017] Furthermore, the rolling includes initial rolling and final rolling, the temperature of the initial rolling is 1100-1500°C, and the temperature of the final rolling is 805-950°C.

[0018] Furthermore, step S3, quenching comprises: firstly subjecting the rolled tube blank to a heat preservation treatment at 860-924°C for 30-90 minutes, and then cooling it to 15-50°C.

[0019] Furthermore, the cooling rate is 40-80°C / s.

[0020] Furthermore, in step S3, the tempering treatment temperature is 600-700° C., and the tempering treatment time is 40-100 min.

[0021] Furthermore, the treatment temperature of the heat straightening is 500-550°C.

[0022] According to the third aspect of the present application, a 110KSI-140KSI perforating gun barrel is provided, and the pipe material of the perforating gun barrel is the seamless steel pipe material provided in the first aspect, or the seamless steel pipe material obtained by the preparation method provided in the second aspect. According to the fourth aspect of the present application, a 140V casing is provided, and the pipe material of the casing is the seamless steel pipe material provided in the first aspect, or the seamless steel pipe material obtained by the preparation method provided in the second aspect.

[0023] By applying the technical solution of the present application, the present application obtains a troostite structure with a lower dislocation density and a high-density nano-sized precipitation phase (austenite) through the synergy of specific raw material components. The two complement each other to enable the seamless steel pipe to have high strength, high toughness, high anti-collapse performance and excellent high temperature resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0025] Figure 1 The SEM image of the metallographic structure of the seamless steel pipe provided in Example 3 of the present application is shown. DETAILED DESCRIPTION

[0026] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0027] As analyzed in the background technology of this application, in the oil exploration and development system engineering, for seamless steel tubes used in perforating gun barrels and 140V sleeves, it is difficult for the existing technology to produce seamless steel tubes with excellent comprehensive performance (such as high strength, high toughness, high collapse resistance and excellent high temperature resistance) at a low cost. In order to solve these problems, this application provides a seamless steel tube and its preparation method and application.

[0028] In a first typical embodiment of the present application, a seamless steel pipe is provided, wherein the chemical composition of the seamless steel pipe comprises, by weight percentage: C: 0.16-0.26%, Si: 0.20-0.35%, Mn: 1.20-1.50%, Cr: 0.40-0.60%, Ti: 0.010-0.030%, Nb: 0.020-0.030%, Mo≤0.05%, V≤0.05%, Al≤0.05%, S≤0.00 5%, P≤0.015%, Cu≤0.15%, Ni≤0.25%, As≤0.015%, Sn≤0.010%, Pb≤0.010%, Sb≤0.010%, Bi≤0.010%, and the sum of As, Sn, Pb, Sb and Bi is ≤0.30%, and the balance is iron and unavoidable impurities; wherein, the metallographic structure of the seamless steel pipe includes tempered troostite and austenite, the volume content of austenite is ≤5%, and the grain size of the seamless steel pipe is ≥7 grades.

[0029] The present application obtains a troostite structure with a lower dislocation density and a high-density nano-sized precipitation phase (austenite) through the synergy of specific raw material components. The two complement each other to make the seamless steel pipe have high strength, high toughness, high collapse resistance and excellent high temperature resistance.

[0030] The seamless steel pipe provided in this application has the following excellent effects:

[0031] (1) Yield strength at room temperature ≥965MPa, tensile strength ≥1034MPa; full-size (10×10mm) V-notch impact energy at 0℃ transverse (T) ≥80J, longitudinal (L) ≥100J.

[0032] (2) When the temperature rises to 400°C, the strength decreases by no more than 15%, and it can be used in an environment with a maximum temperature of 250°C.

[0033] (3) When the perforating gun is subsequently used, the expansion of the tube body after perforation is ≤4.5 mm, which can ensure that the tube body does not crack during perforation.

[0034] In order to further illustrate the beneficial effects of the present invention, the main elements in the above seamless steel pipe are described as follows:

[0035] In terms of weight percentage, the C content is controlled at 0.16-0.26%, the Mn content is controlled at 1.20-1.50%, and the Cr content is controlled at 0.40-0.60%, and the high-cost Mo is removed. The reasonable combination of carbonitrides formed by C, Mn, and Cr within this range not only effectively improves the toughness of seamless steel pipes, but also enables the material to obtain higher strength properties under the condition of subsequent higher tempering temperature. At the same time, the Nb content in the above-mentioned components of the present application is 0.020-0.030wt%, the Ni content is ≤0.25wt%, and the content of Nb and Ni is very low. At the same time, a reasonable formula of a small amount of C, Cr, and Mn elements is used to prepare high-performance seamless steel pipes at low cost, and the material manufacturing cost is low. The C content is controlled at 0.16-0.26wt%. Based on this, while ensuring the high strength performance of the material, the sensitivity of water quenching cracking can also be reduced. Si: solid dissolves in ferrite to increase the yield strength of steel, but at the same time it loses plasticity and toughness. In order to cooperate with other elements to make the material have both high strength and high toughness, the Si content is 0.20-0.35% by weight. Mn: It is mainly dissolved in ferrite to strengthen the steel and is used to improve the hardenability of steel. However, if the content is too high, the segregation will be serious, which will have a greater impact on the lateral impact of the material. In order to cooperate with other elements to make the material have excellent hardenability and less impact from lateral impact, the Mn content is controlled at 1.20-1.50% by weight. Cr: It is an element that can strongly improve the hardenability and a strong carbide-forming element. It precipitates carbides during tempering to improve the strength of steel, which is beneficial to improve the high temperature strength and anti-collapse performance of the material. However, if the content is too high, coarse M will precipitate. 23C6 carbide loses its beneficial effect. In order to balance the high temperature strength and anti-collapse performance of the material, the Cr content is controlled at 0.40-0.60% by weight. V: A strong carbonitride forming element. Vanadium carbonitride is finely dispersed and precipitated in ferrite, which can further achieve the effect of precipitation strengthening during the tempering process. It can effectively pin the movement of dislocations and delay the process of crushing instability, thereby effectively improving the high temperature strength and anti-collapse performance of the material. However, V carbides are easy to precipitate when tempered at a temperature higher than 500°C. Therefore, under the current conventional tempering temperature conditions, in order to give full play to the role of V, the V content is controlled at ≤0.05% by weight. Al: A traditional deoxidation and nitrogen fixing element. The AlN formed can refine the austenite grains, which is beneficial to delay the crushing instability process. By weight, Al≤0.05%. Ca: It can purify molten steel, promote the spheroidization of MnS, and improve the anti-extrusion performance of the material. However, when the content is too high, it is easy to form coarse non-metallic inclusions. Therefore, in order to balance the comprehensive performance of the material, Ca is ≤0.005% by weight.

[0036] Typically but not limiting, in the seamless steel pipe provided in the present application, by weight percentage, the C content is 0.16%, 0.18%, 0.22%, 0.24%, 0.26% or a range consisting of any two values; the Si content is 0.20%, 0.22%, 0.25%, 0.28%, 0.30%, 0.32%, 0.35% or a range consisting of any two values; the Mn content is 1.20%, 1.25%, 1.30%, 1.35%, 1.40%, 1.45%, 1.50% or a range consisting of any two numerical values; the Cr content is 0.40%, 0.45%, 0.50%, 0.55%, 0.60% or a range consisting of any two numerical values; the Ti content is 0.010%, 0.015%, 0.018%, 0.020%, 0.025%, 0.030% or a range consisting of any two numerical values; the Nb content is 0.020%, 0.022%, 0.025%, 0.028%, 0.030% or a range consisting of any two numerical values.

[0037] In order to further balance the manufacturing cost, rigidity and high temperature resistance of the seamless steel pipe, in some preferred embodiments, the chemical composition of the seamless steel pipe includes, by weight percentage: C: 0.18-0.21%, Si: 0.24-0.28%, Mn: 1.27-1.30%, Cr: 0.46-0.50%, Ti: 0.10-0.030%, Nb: 0.021-0.029%, Mo≤0.04%, V≤0.02%, Al≤0.03%, Ca≤0.05%, N≤0.010%, S≤0.003%, P≤0.012%, Cu≤0.15%, Ni≤0.110%, O≤0.0020%, H≤0.0002%, As≤0.15%, Sn≤0.010%, Pb≤0.010%, Sb≤0.010%, Bi≤0.010%, and the balance is iron and unavoidable impurities.

[0038] In order to further improve the strength, toughness, collapse resistance and high temperature resistance of the seamless steel pipe, in some embodiments, the volume content of austenite is ≤3%. In other embodiments, the grain size of the seamless steel pipe is greater than grade 7.

[0039] In a second typical embodiment of the present application, a method for preparing the above-mentioned seamless steel pipe is also provided, and the preparation method comprises: step S1, smelting and casting the raw materials in sequence to obtain a cast tube billet; step S2, rolling the cast tube billet to obtain a rolled tube billet; step S3, quenching, tempering and heat straightening the rolled tube billet in sequence to obtain a seamless steel pipe.

[0040] The present application adopts a specific raw material design and sequentially performs smelting, casting, rolling, quenching, tempering and heat straightening, so that tempered troostite and austenite are generated inside the seamless steel pipe, and the volume content of austenite is ≤5%, and the grain size is ≥7, thereby making the seamless steel pipe have high strength, high toughness, high collapse resistance and excellent high temperature resistance.

[0041] This application does not specifically limit the smelting method, and the smelting methods commonly used in the art can be applied to this application. In order to further improve the comprehensive performance of seamless steel pipes, in some preferred embodiments, the above-mentioned smelting method includes but is not limited to one of vacuum induction smelting, electric arc furnace smelting or converter smelting. It is further explained that when the converter smelting method is adopted, the raw materials are firstly smelted in an electric furnace, then refined outside the furnace, and then calcium treated, and then vacuum degassing is performed. This is well known to those skilled in the art and will not be elaborated here.

[0042] The present application does not make any special limitation on the casting method, and the commonly used casting methods in the field can be applied to the present application. In order to further improve the comprehensive performance of seamless steel pipes, in some preferred embodiments, the present application casts or continuously casts (such as arc continuous casting) the material after smelting to obtain a cast tube billet, and then cools and finishes the cast tube billet for standby use.

[0043] The present application does not specifically limit the method of rolling the cast tube blank. The rolling methods commonly used in the field can be applied to the present application. In order to further optimize the organizational properties of seamless steel pipes, in some preferred embodiments, rolling includes: inspection and grinding of the cast tube blank → sawing and cutting → ring furnace heating → conical roller perforation → tube rolling → online normalization → stepping furnace reheating → sizing → cooling on a cooling bed, wherein online normalization is to refine the hot-rolled grains, and other methods can also be used to make the hot-rolled grain size ≥ 7 levels, and the grains are uniform. Online normalization: also known as online normalizing process, usually refers to using an online heating furnace to reheat the steel to a temperature above the Ac3 or Acm line, keeping it warm for a period of time, so that the structure of the steel is transformed into austenite, and then air-cooled, and sometimes blowing or spray cooling can be used as needed to transform the supercooled austenite structure into pearlite. The cooling rate for normalizing is faster than the cooling rate of conventional normalizing, so the pearlite structure obtained is also correspondingly fine.

[0044] In order to further promote the uniformity of the metallographic structure of the material, in some preferred embodiments, the rolling ratio (definition: the ratio of the cross-sectional areas of the workpiece before and after rolling deformation, steel tube rolling ratio = casting tube cross-sectional area / rolling tube cross-sectional area) during the rolling process is greater than 3, preferably 5-10. The rolling ratio is 3, 4, 5, 6, 7, 8, 9, 10 or a range of any two values.

[0045] In order to further improve the mechanical properties of the seamless steel pipe, in some preferred embodiments, the rolling process includes initial rolling and final rolling, the initial rolling temperature is controlled to be 1100-1150°C, and the final rolling temperature is controlled to be 805-950°C.

[0046] Typically but not limiting, the initial rolling temperature is 1100°C, 1120°C, 1130°C, 1140°C, 1150°C or a range consisting of any two values; the final rolling temperature is 805°C, 820°C, 830°C, 850°C, 880°C, 900°C, 920°C, 950°C or a range consisting of any two values.

[0047] In order to further balance the toughness and strength properties of seamless steel pipes, the present application sequentially quenches, tempers and heat straightens the rolled tube blanks to obtain seamless steel pipes. Based on the composition of seamless steel pipes, the present application further optimizes the quenching and tempering heat treatment process, and effectively controls the composition of the metallographic structure in the seamless steel pipe through the quenching and tempering heat treatment process, thereby reducing the dislocation density, and greatly improving the toughness of the seamless steel pipe while making it have high strength. Preferably, the treatment temperature of heat straightening is 500-550°C, such as 500°C, 510°C, 520°C, 530°C, 540°C, 550°C or a range of any two values.

[0048] In some preferred embodiments, quenching includes first subjecting the rolled tube blank to a temperature of 860-924°C (such as 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 924°C, etc.) for 30-90 minutes (such as 30 minutes, 40 minutes, 50 minutes, 80 minutes, 90 minutes, etc.), and then cooling the material to 15-50°C (such as 15°C, 20°C, 30°C, 35°C, 40°C, 45°C, 50°C, etc.) by internal pouring and external spraying. In order to facilitate obtaining more than 95% tempered troostite in the seamless steel pipe, in some preferred embodiments, the cooling medium used in the internal pouring and external spraying method is water. Preferably, during the cooling process, the cooling rate of the material is 40-80°C / s (such as 40°C / s, 50°C / s, 60°C / s, 70°C / s, 80°C / s, etc.).

[0049] In a preferred embodiment, the tempering treatment temperature is 600-700°C, and the holding time is 40-100 minutes. Depending on the chemical composition of the raw materials, the amount of carbonitride precipitation phase generated during the tempering process of the heat treatment will be affected by different temperature conditions. In order to meet the high strength and toughness requirements, the tempering temperature of the heat treatment is also adjusted accordingly. In order to make the seamless steel pipe have excellent toughness and strength properties at the same time, tempering at 600-700°C can make carbon fully react with elements such as Mn, Cr, and V to form corresponding carbides to play a full precipitation strengthening role. By combining sub-temperature quenching with low-temperature tempering, the dislocation density at low carbon content is reduced, and the martensitic plate structure after tempering is restored, combined with widening and polygonization, so that the large-angle grain boundaries (≥15 degrees) increase, the energy required for crack propagation during the impact process increases, and the impact performance increases.

[0050] Typically but not limiting, the tempering treatment temperature is 460°C, 480°C, 500°C, 520°C, 550°C, 580°C, 600°C or a range consisting of any two values; the tempering holding treatment time is 40min, 50min, 60min, 80min, 100min or a range consisting of any two values.

[0051] In the third typical embodiment of the present application, a 110KSI-140KSI perforating gun barrel is also provided. The tube material of the perforating gun barrel is the seamless steel tube provided in the above-mentioned first typical embodiment or the seamless steel tube obtained by the preparation method provided in the above-mentioned second typical embodiment.

[0052] Based on the same analysis as above, the 110KSI-140KSI perforating gun barrel provided in this application adopts a seamless steel pipe with a troostite structure with a low dislocation density and a high-density nano-sized precipitation phase (austenite) as the pipe material, so that it can have high strength, high toughness, high anti-collapse performance and excellent high temperature resistance at a relatively low cost, and can ensure that the pipe does not crack during perforation.

[0053] In the fourth typical embodiment of the present application, a 140V bushing is also provided, the tube material of the bushing is the seamless steel tube provided in the above-mentioned first typical embodiment or the seamless steel tube obtained by the preparation method provided in the above-mentioned second typical embodiment.

[0054] Based on the same analysis as above, the 140V bushing provided in this application adopts a seamless steel pipe with a troostite structure with low dislocation density and a high-density nano-sized precipitation phase (austenite) as the pipe material, so that it can have high strength, high toughness, high anti-collapse performance and excellent high temperature resistance at a relatively low cost.

[0055] In order to further illustrate the beneficial effects of the present application, the beneficial effects of the present application will be further illustrated below in combination with embodiments and comparative examples.

[0056] Example

[0057] According to the ingredient formula in Table 1, 12 embodiments A1-A12 and 9 comparative examples B1-B9 were obtained, as shown in Table 1 below.

[0058] The seamless steel pipe provided in the above embodiment is prepared according to the following steps:

[0059] (1) The raw materials are prepared according to the chemical composition designed in Table 1, and the raw materials are subjected to electric furnace smelting, external furnace refining, vacuum degassing and arc continuous casting to obtain a casting tube blank.

[0060] The raw materials for batching include high-quality molten iron, pipe heads, pure materials, high-quality scrap steel, ferroalloys and the like. The amount of high-quality molten iron added is ≥50%, wherein high-quality molten iron, pipe heads, pure materials, and high-quality scrap steel mainly refer to materials with less five harmful elements and inclusions compared with similar raw and auxiliary materials. Among them, in high-quality molten iron, P≤0.015%, S≤0.005%, As≤0.015%, Sn≤0.010%, and Pb≤0.010%. Pipe heads, pure materials (pure materials refer to pure scrap steel bulk materials, such as pipe blanks, pipe heads, rails, wires, steel plates or various scraps, which are clean and free of rust, oil stains, and coatings), and high-quality scrap steel, the harmful elements requirements are as follows: As+Sn+Pb+Sb+Bi≤0.030%.

[0061] (2) The cast tube billet is rolled to obtain a rolled tube billet, wherein the rolling ratio is as shown in Table 2.

[0062] The rolling process includes initial rolling and final rolling. The temperatures of initial rolling and final rolling are shown in Table 2.

[0063] (3) The rolled tube is quenched, tempered and hot straightened in sequence to obtain a seamless steel tube.

[0064] The quenching includes: firstly subjecting the rolled tube blank to a heat preservation treatment at a quenching temperature, and then cooling the material to 25°C; the quenching temperature, the heat preservation time and the material cooling rate are shown in Table 2.

[0065] The annealing temperature and holding time are shown in Table 2.

[0066] The treatment temperature of heat straightening is shown in Table 2.

[0067] Table 1

[0068]

[0069] Table 2

[0070]

[0071]

[0072] Performance Characterization

[0073] (1) The metallographic structure and grain size of the seamless steel pipes provided in the above embodiments and comparative examples were observed by SEM. The results are shown in Table 3 below.

[0074] Table 3

[0075]

[0076]

[0077] Figure 1The SEM image of the seamless steel pipe provided in Example 3 is as follows: Figure 1 It can be seen that the fiber structure of the seamless steel pipe provided in Example 3 is 99.05v% tempered troostite+0.15v% retained austenite, and the grain size is level 9.

[0078] (2) The mechanical properties of the materials are tested according to GB / T 228 tensile test for metal materials, the transverse impact energy of the materials is tested according to GB / T 229 Charpy pendulum impact test method for metal materials, and the collapse strength is calculated according to SY / T6328 Performance calculation of casing, tubing, drill pipe and line pipe in the petroleum and natural gas industry. The formula in clause 3.1.2 of API 5C3 standard is

[0079]

[0080] A=3.297

[0081] B=0.0971

[0082] C=3751

[0083] The specifications of the produced steel pipe are ∮89mm*10mm (89mm represents the diameter of the steel pipe, 10mm represents the wall thickness of the steel pipe), and the results are shown in Table 4.

[0084] Table 4

[0085]

[0086]

[0087] From the above description, it can be seen that the above-mentioned embodiments of the present invention achieve the following technical effects: the present application obtains a troostite structure with a lower dislocation density and a high-density nano-sized precipitation phase (austenite) through the synergy of specific raw material components. The two complement each other to make the seamless steel pipe have high strength, high toughness, high anti-collapse performance and excellent high temperature resistance.

[0088] 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 seamless steel pipe, characterized in that: The chemical composition of seamless steel pipes, by weight percentage, includes: C: 0.16-0.26%, Si: 0.20-0.35%, Mn: 1.20-1.50%, Cr: 0.40-0.60%, Ti: 0.010-0.030%, Nb: 0.020-0.030%, Mo≤0.05%, V≤0.05%, Al≤0.05%, Ca≤0.005%, N≤0.010%, S≤0.005%, P≤0.015%, Cu≤0.15%, Ni≤0.25%, O≤0.0020%, H≤0.0002, As≤0.015%, Sn≤0.010%, Pb≤0.010%, Sb≤0.010%, Bi≤0.010%, and the sum of As, Sn, Pb, Sb and Bi is ≤0.30%, and the balance is iron and unavoidable impurities; The metallographic structure of the seamless steel pipe includes tempered troostite and austenite, the volume content of the austenite is ≤5%, and the grain size of the seamless steel pipe is ≥7 levels.

2. The seamless steel pipe according to claim 1, characterized in that: The chemical composition of the seamless steel pipe includes, by weight percentage: C: 0.18-0.21%, Si: 0.24-0.28%, Mn: 1.27-1.30%, Cr: 0.46-0.50%, Ti: 0.010-0.030%, Nb: 0.021-0.029%, Mo≤0.04%, V≤0.02%, Al≤0.03%, Ca≤0.005%, N≤0 .010%, S≤0.003%, P≤0.012%, Cu≤0.15%, Ni≤0.110%, O≤0.0020%, H≤0.0002%, As≤0.015%, Sn≤0.010%, Pb≤0.010%, Sb≤0.010%, Bi≤0.010%, and the sum of As, Sn, Pb, Sb and Bi ≤0.30%, the balance is iron and unavoidable impurities.

3. The seamless steel pipe according to claim 1, characterized in that: The volume content of austenite is ≤3%; And / or, the grain size of the seamless steel pipe is greater than grade 7.

4. A method for preparing a seamless steel pipe according to any one of claims 1 to 3, characterized in that: The preparation method comprises: Step S1, smelting and casting the raw materials in sequence to obtain a casting tube blank; Step S2, rolling the cast tube blank to obtain a rolled tube blank; Step S3, quenching, tempering and hot straightening the rolled tube in sequence to obtain the seamless steel tube.

5. The preparation method according to claim 4, characterized in that: In the step S1, the smelting method includes at least one of vacuum induction smelting, electric arc furnace smelting or converter smelting.

6. The preparation method according to claim 4, characterized in that: In step S2, during the rolling process, the rolling ratio is ≥3, preferably 5-10; And or, the rolling includes initial rolling and final rolling, the temperature of the initial rolling is 1100-1150°C, and the temperature of the final rolling is 805-950°C.

7. The preparation method according to claim 4, characterized in that: The quenching in step S3 includes: firstly subjecting the rolled tube blank to a heat preservation treatment at 860-924°C for 30-90 minutes, and then cooling it to 15-50°C; Preferably, the cooling speed is 40-80°C / s.

8. The preparation method according to claim 4, characterized in that: In step S3, the tempering treatment temperature is 600-700° C., and the tempering treatment time is 40-100 min; And / or, the heat straightening treatment temperature is 500-550°C.

9. A 110KSI-140KSI perforating gun barrel, characterized in that: The tube material of the perforating gun barrel is the seamless steel tube material according to any one of claims 1 to 3, or the seamless steel tube material obtained by the preparation method according to any one of claims 4 to 8.

10. A 140V bushing, characterized in that: The pipe material of the 140V casing is the seamless steel pipe material described in any one of claims 1 to 3, or the seamless steel pipe material prepared by the preparation method described in any one of claims 4 to 8.

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