A seamless niobium-vanadium-titanium microalloyed steel pipe and its preparation method

Abstract

This invention discloses a niobium-vanadium-titanium microalloyed seamless steel pipe and its preparation method, belonging to the technical field of seamless steel pipes. The method includes the following steps: S1. Heating, piercing, rolling, and sizing the niobium-vanadium-titanium microalloyed steel pipe to obtain a billet; S2. Annealing and heat-treating the billet to obtain a heat-treated steel pipe; S3. Spraying a coating onto the surface of the heat-treated steel pipe to obtain the niobium-vanadium-titanium microalloyed seamless steel pipe. The niobium-vanadium-titanium microalloyed seamless steel pipe of this invention possesses excellent mechanical properties, meeting the requirements of high-strength operating environments; the surface of the niobium-vanadium-titanium microalloyed seamless steel pipe is corrosion-resistant, making it suitable for high-strength, highly corrosive environments.

Description

Technical Field

[0001] This invention belongs to the field of seamless steel pipe technology, specifically a niobium vanadium titanium microalloyed seamless steel pipe and its preparation method. Background Technology

[0002] In the industrial sector, seamless steel pipes are widely used as an important structural and transportation material in many industries such as petroleum, chemical, power, and machinery manufacturing. With the continuous development of industrial technology, the performance requirements for seamless steel pipes are also increasing. They not only need to have high strength, toughness, and corrosion resistance, but also good fatigue performance and dimensional accuracy.

[0003] Currently, seamless steel pipes on the market have some shortcomings in their production process. Regarding heat treatment, some traditional methods struggle to achieve a good balance between strength and toughness, limiting the performance of the steel pipes under certain complex working conditions. In terms of coating protection, traditional single-coating systems often fail to simultaneously meet the requirements of high adhesion, high wear resistance, and high corrosion resistance, resulting in a short coating lifespan and requiring frequent maintenance and replacement, thus increasing operating costs. Summary of the Invention

[0004] To overcome the aforementioned technical problems, this invention provides a niobium-vanadium-titanium microalloyed seamless steel pipe and its preparation method. The niobium-vanadium-titanium microalloyed seamless steel pipe prepared by this invention possesses excellent mechanical properties, meeting the requirements of high-intensity operating environments; its surface is corrosion-resistant, making it suitable for high-intensity, highly corrosive environments.

[0005] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0006] This invention discloses a method for preparing niobium-vanadium-titanium microalloyed seamless steel pipe, comprising the following steps:

[0007] S1. Niobium-vanadium-titanium microalloyed tube blanks are obtained by heating, piercing, rolling and sizing.

[0008] S2. After annealing and heat treatment of the tube blank, heat-treated steel pipe is obtained;

[0009] S3. By spraying a coating onto the surface of the heat-treated steel pipe, a seamless niobium-vanadium-titanium microalloyed steel pipe can be obtained.

[0010] According to some embodiments of the present invention, the niobium vanadium titanium microalloy comprises the following chemical composition by mass fraction: C: 0.12-0.18%, Si: 0.20-0.40%, Mn: 1.20-1.50%, P≤0.015%, S≤0.002%, Nb: 0.02-0.06%, V: 0.04-0.08%, Ti: 0.01-0.03%, with the balance being Fe and unavoidable impurities.

[0011] According to some embodiments of the present invention, the heating is performed at 1200~1300°C for 60~90 minutes; preferably, the heating is performed at 1220~1280°C for 70~80 minutes.

[0012] According to some embodiments of the present invention, the oxygen content in the heating furnace during heating is 0.3~0.5 vol%, preferably 0.35~0.45 vol%; when heating steel, trace amounts of oxygen can inhibit excessive carburization or decarburization; in addition, trace amounts of oxygen react with iron and alloying elements on the surface of the steel pipe to form a very thin oxide film, which can prevent further oxidation of the internal metal.

[0013] According to some embodiments of the present invention, the temperature of the perforation head is 800~900°C, preferably 830~870°C.

[0014] According to some embodiments of the present invention, the perforation speed is 1~2 m / s, preferably 1.4~1.8 m / s.

[0015] According to some embodiments of the present invention, the deformation amount per pass of the rolling mill is 10-20%, and the total deformation amount of the rolling mill is controlled at 30-50%.

[0016] According to some embodiments of the present invention, the surface roughness after rolling is ≥0.8μm, preferably 1.2~2μm.

[0017] According to some embodiments of the present invention, the sizing temperature is 850~950°C, preferably 880~920°C.

[0018] According to some embodiments of the present invention, the annealing involves lowering the temperature to 650-700°C, holding for 90-120 minutes, and then furnace cooling to 300-350°C; preferably, the annealing involves lowering the temperature to 680-700°C, holding for 100-120 minutes, and then furnace cooling to 300-320°C. This annealing temperature allows the grains inside the steel to recrystallize, enabling broken grains to re-nucleate and grow, thereby eliminating work hardening and internal stress generated by previous processing (such as pipe rolling and sizing); furnace cooling avoids the generation of new internal stresses from rapid cooling, and also prevents the precipitation of certain alloying elements to form harmful phases that could affect the subsequent heat treatment effect.

[0019] According to some embodiments of the present invention, the furnace atmosphere during annealing is nitrogen.

[0020] According to some embodiments of the present invention, the heat treatment method is quenching-partitioning.

[0021] According to some embodiments of the present invention, the heat treatment further includes a straightening process.

[0022] According to some embodiments of the present invention, the quenching is performed by heating to 750~800℃ and holding for 30~60 minutes, followed by water mist cooling, wherein the pressure of the water mist is 0.3~0.5MPa. This temperature range is higher than the austenitizing temperature of the steel, which enables the steel to completely transform into a uniform austenitic structure. For steel containing microalloying elements such as niobium, vanadium, and titanium, this temperature can ensure that the microalloyed carbonitrides are fully dissolved into the austenite, thereby improving the alloying degree of the austenite and preparing for subsequent cooling to form martensite.

[0023] According to some embodiments of the present invention, the component is heated to 180-220°C at a heating rate of 5-10°C / min and held for 60-90 min; preferably, the component is heated to 200-220°C at a heating rate of 8-10°C / min and held for 70-80 min. This temperature range is conducive to the diffusion of carbon from martensite to retained austenite, improving the stability of retained austenite. Simultaneously, some martensite decomposes into tempered martensite, improving the toughness of the steel.

[0024] According to some embodiments of the present invention, the atmosphere during the partitioning is a mixture of 5-10 vol% H2 and the balance N2; preferably, the atmosphere during the partitioning is a mixture of 6-9 vol% H2 and the balance N2; the reducing properties of hydrogen eliminate surface oxidation interference, and nitrogen prevents new oxidation from occurring. When carbon diffuses from martensite to retained austenite at high temperatures, there is no oxidation hindrance, the diffusion is more complete, and the stability of retained austenite is significantly improved; at the same time, the mixed gas atmosphere is stable, avoiding interference from harmful gases on the microstructure transformation.

[0025] According to some embodiments of the present invention, the fractionation process is followed by air cooling to room temperature.

[0026] According to some embodiments of the present invention, the coating is divided into a base coat and a top coat;

[0027] According to some embodiments of the present invention, the undercoat is nickel-chromium alloy powder; the topcoat is fluorocarbon paint.

[0028] According to some embodiments of the present invention, the chemical composition of the nickel-chromium alloy powder, by mass fraction, is: 14~19% Cr, 2.5~4.5% B, 3.3~5.0% Si, 4.5~8.0% Fe, 0.3~1.0% C and balance Ni;

[0029] According to some embodiments of the present invention, the underlying coating is applied by flame spraying.

[0030] According to some embodiments of the present invention, the surface coating is applied by spraying.

[0031] The present invention also discloses a niobium-vanadium-titanium microalloyed seamless steel pipe, which is prepared by the aforementioned preparation method.

[0032] According to some embodiments of the present invention, the yield strength of the niobium vanadium titanium microalloyed seamless steel pipe is 550~600MPa.

[0033] According to some embodiments of the present invention, the tensile strength of the niobium vanadium titanium microalloyed seamless steel pipe is 600~700MPa.

[0034] According to some embodiments of the present invention, the elongation of the niobium vanadium titanium microalloyed seamless steel tube is ≥22%.

[0035] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0036] Compared with the prior art, the beneficial effects of the present invention are:

[0037] 1. The preparation process of this invention precisely controls the key parameters of heating, annealing, and heat treatment to ensure uniform steel pipe microstructure and stable performance. Controlling the oxygen content during heating maintains a stable heating temperature and avoids surface damage caused by excessive oxidation, while also inhibiting excessive carburization or decarburization, laying a good foundation for subsequent processing. The annealing process utilizes the principle of recrystallization to eliminate internal stress generated during processes such as pipe rolling, resulting in refined and uniform grains, preparing the microstructure for quenching. In the quenching-partitioning heat treatment process, a suitable quenching temperature ensures complete austenitization of the steel, while the mixed gas atmosphere at the partitioning temperature promotes carbon diffusion from martensite to retained austenite, significantly improving the stability of retained austenite and achieving a balance between strength and toughness.

[0038] 2. In terms of mechanical properties, the yield strength of the niobium vanadium titanium microalloyed seamless steel pipe prepared by the present invention is 550~600MPa, and can reach 555~585MPa in some preferred embodiments; the tensile strength of the niobium vanadium titanium microalloyed seamless steel pipe is 600~700MPa, and can reach 630~670MPa in some preferred embodiments; the elongation of the niobium vanadium titanium microalloyed seamless steel pipe is ≥21%, and can reach ≥22% in some preferred embodiments.

[0039] 3. In terms of surface properties, the niobium vanadium titanium microalloy seamless steel pipe of the present invention has good corrosion resistance and wear resistance, and can be widely used in highly corrosive fields such as petroleum and chemical industries. Detailed Implementation

[0040] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[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] The "range" disclosed in this invention is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be combined arbitrarily; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for specific parameters, it is understood that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this invention, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed herein; "0-5" is merely a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer greater than or equal to 2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0043] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0044] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0045] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0046] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0047] Unless otherwise specified, the term "or" is inclusive in this invention. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0048] The raw material information used in the following examples is as follows:

[0049] The composition of nickel-chromium alloy powder by mass fraction is: 17.5% Ni, 3.7% B, 3.3% Si, 4.6% Fe, 0.82% C and balance Ni and unavoidable impurities;

[0050] The fluorocarbon paint was purchased from Zoge Coatings FC1200 fluorocarbon metallic paint, which has a fluorine content of 22%.

[0051] This includes, but is not limited to, the models from the above manufacturers.

[0052] Example 1

[0053] The preparation method of the niobium vanadium titanium microalloyed seamless steel tube in this embodiment is as follows:

[0054] S1. Raw material preparation: Prepare niobium vanadium titanium microalloyed steel with the following chemical composition: C: 0.134%, Si: 0.25%, Mn: 1.42%, P: 0.011%, S: 0.002%, Nb: 0.045%, V: 0.061%, Ti: 0.018%, with the balance being Fe and unavoidable impurities.

[0055] Heating: The niobium-vanadium-titanium microalloyed steel is placed in a heating furnace and heated to 1200℃ in an atmosphere with an oxygen content of 0.4 vol%, and held at this temperature for 65 minutes.

[0056] Piercing: The heated steel is pierced, with the mandrel temperature controlled at 850℃ and the piercing speed at 1.3m / s, to obtain a tube.

[0057] Tube rolling: The tube is rolled using a tube rolling mill. The deformation in each pass is controlled at 12-14%, and the total deformation is controlled at 37%. The surface roughness of the steel pipe after rolling reaches 1.5μm.

[0058] Sizing: The rolled steel pipe is sizing, and the sizing temperature is controlled at 900℃ to obtain a tube blank.

[0059] S2. Annealing: The sized tube blank is placed in an annealing furnace, and high-purity nitrogen (purity ≥99.9%) is introduced into the furnace as a protective atmosphere to cool the tube blank to 680℃ and hold it at this temperature for 100 minutes, and then cool it down to 320℃ with the furnace.

[0060] Quenching: Take out the annealed tube blank, heat it to 800℃ and hold it for 50 minutes, and then quench it by water mist cooling. The water mist pressure is controlled at 0.40MPa and the temperature is cooled to 160℃.

[0061] Preparation: The quenched steel pipe is placed in a furnace, and a mixture of 8.5 vol% H2 and the balance N2 is introduced as a protective atmosphere. The temperature is increased to 200℃ at a rate of 8℃ / min, and held at this temperature for 70 minutes. Then it is air-cooled to room temperature to complete the heat treatment and obtain the heat-treated steel pipe.

[0062] Straightening: A multi-roller straightener is used to straighten the heat-treated steel pipe. The straightening pressure is controlled at 6~9MPa to ensure that the straightness error of the steel pipe is ≤1mm / m.

[0063] S3. Undercoat spraying: Using arc spraying, nickel-chromium alloy powder is applied to the surface of the straightened steel pipe by flame spraying (1050℃) to form an undercoat.

[0064] Surface coating spraying: After the base coat has dried, fluorocarbon paint is applied to the surface of the base coat by spraying to form a surface coating, thus obtaining the niobium vanadium titanium microalloy seamless steel pipe.

[0065] Example 2

[0066] The difference between this embodiment and Embodiment 1 is as follows:

[0067] S1 heating: The niobium vanadium titanium microalloyed steel is placed in a heating furnace and heated to 1250℃ in an atmosphere with an oxygen content of 0.45 vol%, and held at this temperature for 75 min.

[0068] All other steps and parameters are the same as in Example 1.

[0069] Example 3

[0070] The difference between this embodiment and Embodiment 2 is as follows:

[0071] In S1, the temperature of the piercing control head is 900℃, and the piercing speed is 1.8m / s;

[0072] All other steps and parameters are the same as in Example 1.

[0073] Example 4

[0074] The difference between this embodiment and Embodiment 1 is as follows:

[0075] During the heating process of S1, the temperature was raised to 1230℃ in an atmosphere with an oxygen content of 0.3 vol%, and held at this temperature for 70 minutes.

[0076] Rolling: The deformation amount per pass is controlled at 14~15%, and the total deformation amount is controlled at 40%. The surface roughness of the steel pipe after rolling reaches 1.2μm.

[0077] The sizing temperature is 850℃;

[0078] The other raw materials, steps and parameters are the same as in Example 1.

[0079] Example 5

[0080] The difference between this embodiment and Embodiment 1 is as follows:

[0081] During the S2 annealing process, the billet is cooled to 610℃ and held at this temperature for 100 minutes, and then cooled to 300℃ in the furnace.

[0082] All other steps and parameters are the same as in Example 1.

[0083] Example 6

[0084] The difference between this embodiment and Embodiment 1 is as follows:

[0085] During the S2 quenching process, the annealed tube blank is taken out, heated to 750℃ and held for 60 minutes;

[0086] Partitioning: The quenched steel pipe is placed in a furnace, and a mixed gas of 7.2% H2 and the balance N2 is introduced as the atmosphere. The temperature is increased to 220°C at a heating rate of 5°C / min. The temperature is held at this temperature for 60 minutes, and then air-cooled to room temperature to complete the heat treatment and obtain the heat-treated steel pipe.

[0087] All other steps and parameters are the same as in Example 1.

[0088] Comparative Example 1

[0089] The difference between this comparative example and Example 1 is as follows:

[0090] The heat treatment in this comparative example does not include quenching, that is, the fractionation process is carried out directly after annealing.

[0091] The other raw materials, steps and parameters are the same as in Example 1.

[0092] Comparative Example 2

[0093] The difference between this comparative example and Example 1 is as follows:

[0094] The heat treatment in this comparative example does not include the fractionation process; that is, only quenching is performed after annealing.

[0095] The other raw materials, steps and parameters are the same as in Example 1.

[0096] Comparative Example 3

[0097] The difference between this comparative example and Example 2 is as follows:

[0098] The niobium-vanadium-titanium microalloyed seamless steel pipe in this comparative example was not coated with paint, i.e., it did not include step S3.

[0099] All other steps and parameters are the same as in Example 1.

[0100] Test Example 1—Mechanical Property Test

[0101] The mechanical properties of the niobium-vanadium-titanium microalloyed seamless steel pipes prepared in the above embodiments and comparative examples were tested, and the test results are shown in Table 1.

[0102]

[0103] Test Example 2—Coating Performance Test

[0104] The corrosion resistance and wear resistance of the niobium vanadium titanium microalloyed seamless steel pipes prepared in Example 2 and Comparative Example 3 were tested, and the test results are shown in Table 2.

[0105] The corrosion resistance test shall be conducted in accordance with GB / T 10125-2021; sodium chloride shall be dissolved in distilled water to prepare a solution with a concentration of 50±5 g / L and a pH value between 6.7 and 7.0. The test temperature shall be 35±2℃ and the test time shall be 800 h.

[0106] The wear resistance test is conducted in accordance with GB / T 1768-2006; the load is 500g, the number of revolutions is 1000 revolutions, and the wear stroke is 4.7±0.1mm per revolution.

[0107]

[0108] Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this invention can be purchased commercially or prepared using existing methods. The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this invention. It should be understood that the above descriptions are merely specific embodiments of this invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for preparing a niobium-vanadium-titanium microalloyed seamless steel pipe, characterized in that, Includes the following steps: S1. Niobium-vanadium-titanium microalloyed tube blanks are obtained by heating, piercing, rolling and sizing. Heating is performed at 1200~1300℃ for 60~90 minutes, with the oxygen content in the furnace being 0.3~0.5 vol% during heating. The temperature of the piercing head is 800~900℃, and the piercing speed is 1~2m / s; S2. After annealing, heat treatment and straightening the tube blank, heat-treated steel pipe is obtained; Annealing involves cooling to 650-700℃ in a nitrogen atmosphere and holding for 90-120 minutes, then cooling in the furnace to 300-350℃. The heat treatment method is quenching-partitioning. Quenching involves heating to 750~800℃ and holding for 30~60min, followed by water mist cooling, with the water mist pressure being 0.3~0.5MPa. Partitioning involves heating to 180~220℃ in a mixed gas atmosphere of 5~10 vol% H2 and balance N2 at a heating rate of 5~10℃ / min, holding for 60~90min, and then air cooling to room temperature. S3. Spray a coating onto the surface of the heat-treated steel pipe. The coating consists of a base coat and a top coat. The base coat is nickel-chromium alloy powder, and the top coat is fluorocarbon paint. This will produce a niobium-vanadium-titanium microalloy seamless steel pipe. The chemical composition of the nickel-chromium alloy powder, by mass fraction, is: 14~19% Cr, 2.5~4.5% B, 3.3~5.0% Si, 4.5~8.0% Fe, 0.3~1.0% C and balance Ni; The elongation of the niobium-vanadium-titanium microalloyed seamless steel pipe is ≥22%.

2. The method for preparing niobium-vanadium-titanium microalloyed seamless steel pipe as described in claim 1, characterized in that, The niobium-vanadium-titanium microalloy comprises the following chemical composition by mass fraction: C: 0.12-0.18%, Si: 0.20-0.40%, Mn: 1.20-1.50%, P≤0.015%, S≤0.002%, Nb: 0.02-0.06%, V: 0.04-0.08%, Ti: 0.01-0.03%, with the balance being Fe and unavoidable impurities.

3. The method for preparing niobium-vanadium-titanium microalloyed seamless steel pipe as described in claim 1, characterized in that, The heating process involves holding the temperature at 1220~1280℃ for 70~80 minutes. The oxygen content in the heating furnace during heating is 0.35~0.45 vol%; The temperature of the perforation head is 830~870℃; The perforation speed is 1.4~1.8m / s.

4. The method for preparing niobium-vanadium-titanium microalloyed seamless steel pipe as described in claim 1, characterized in that, The deformation amount per pass of the tube rolling is 10-20%, and the total deformation amount of the tube rolling is controlled at 30-50%. The surface roughness of the rolled tube is ≥0.8μm; The sizing temperature is between 850 and 950°C.

5. The method for preparing the niobium-vanadium-titanium microalloyed seamless steel pipe as described in claim 1, characterized in that, The surface roughness of the rolled tube is 1.2~2μm; The sizing temperature is 880~920℃.

6. The method for preparing niobium-vanadium-titanium microalloyed seamless steel pipe as described in claim 1, characterized in that, The annealing process involves lowering the temperature to 680-700℃, holding it at that temperature for 100-120 minutes, and then cooling it in the furnace to 300-320℃.

7. The method for preparing the niobium-vanadium-titanium microalloyed seamless steel pipe as described in claim 6, characterized in that, The mixture is heated to 200-220°C at a heating rate of 8-10°C / min and held for 70-80 minutes. The atmosphere during the distribution is a mixture of 5-8 vol% H2 and the balance N2.

8. A niobium-vanadium-titanium microalloyed seamless steel pipe, characterized in that, It is prepared by the method for preparing niobium vanadium titanium microalloyed seamless steel tube as described in any one of claims 1 to 7.

9. The niobium-vanadium-titanium microalloyed seamless steel pipe as described in claim 8, characterized in that, The yield strength of the niobium-vanadium-titanium microalloyed seamless steel pipe is 550~600MPa; The tensile strength of the niobium-vanadium-titanium microalloyed seamless steel pipe is 600~700MPa.

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