High-plasticity anti-fatigue X65 seamless line pipe and manufacturing method thereof

Abstract

The invention discloses a high-plasticity anti-fatigue X65 seamless line pipe, which contains Fe and inevitable impurities, and further contains the following chemical elements in percentage by mass: 0.06 to 0.11 percent of C, 0.15 to 0.35 percent of Si, 1.41 to 1.65 percent of Mn, 0.01 to 0.10 percent of Cr, 0.07 to 0.20 percent of Mo, 0.01 to 0.04 percent of Nb, 0.03 to 0.08 percent of V, 0.010 to 0.025 percent of Ti, 0.001 to 0.004 percent of Ca, 0.02 to 0.04 percent of Alt and the balance of Fe. The high-plasticity anti-fatigue X65 seamless line pipe does not contain Cu and Ni. The invention further discloses a manufacturing method of the seamless line pipe. The manufacturing method comprises the steps that a pipe blank is manufactured; manufacturing the pipe blank into a steel pipe; quenching, wherein the quenching temperature is controlled to be 880-940 DEG C; tempering: controlling the tempering temperature to be 620-700 DEG C;

Description

Technical Field

[0001] The present invention relates to a steel pipe and a manufacturing method thereof, and particularly to a seamless pipeline pipe and a manufacturing method thereof. Background Art

[0002] In some application scenarios of pipeline pipes, high requirements are imposed on the plasticity of materials, especially for the uniform elongation index, which is crucial for the anti-local buckling and safe service of pipelines. For example, in the scenario of laying offshore pipeline pipes by the coiling method, the pipeline pipe materials will undergo different forms of strain such as tension and compression. Since new dislocations will be formed during the strain process, the strain aging problem will occur during long-term service, resulting in a decrease in plasticity, especially the uniform elongation index. Therefore, in order to meet the technical requirements of high-plasticity seamless pipeline pipes for the coiling method laying application scenario, new solutions for steel grades and processes are urgently needed.

[0003] For example: In the Chinese patent document with the publication number CN105543705A, the publication date of May 4, 2016, and the title "Manufacturing Method of Anti-Large-Strain and Anti-Corrosion Seamless Pipeline Pipe for R-Lay Laying in Marine Environment", a seamless pipeline pipe is disclosed. It adopts the design of seamless pipeline pipe with high C, low Mn, and high Cr. However, this composition design method is not beneficial to the anti-strain aging performance and is also not conducive to the uniform elongation after strain aging.

[0004] In the prior art, no solution is given to improve the performance of X65 seamless pipeline pipes after anti-strain aging, because it is impossible to ensure high performance of the total elongation and uniform elongation indexes after strain aging, and the insufficient plasticity after strain aging will correspondingly lead to insufficient fatigue performance after strain aging. Summary of the Invention

[0005] One of the purposes of the present invention is to provide a high-plasticity and anti-fatigue X65 seamless pipeline pipe, which can improve the anti-strain aging performance.

[0006] In order to achieve the above purpose, the present invention provides a high-plasticity and anti-fatigue X65 seamless pipeline pipe, which contains Fe and inevitable impurities. In addition, it also contains the following chemical elements in mass percentages:

[0007] C: 0.06 - 0.11%, Si: 0.15 - 0.35%, Mn: 1.41 - 1.65%, Cr: 0.01 - 0.10%, Mo: 0.07 - 0.20%, Nb: 0.01 - 0.04%, V: 0.03 - 0.08%, Ti: 0.010 - 0.025%, Ca: 0.001 - 0.004%, Alt: 0.020 - 0.040%;

[0008] The high-plasticity fatigue-resistant X65 seamless line pipe does not contain Cu and Ni.

[0009] Furthermore, in the high plasticity and fatigue-resistant X65 seamless pipeline described in the present invention, the mass percentage of each chemical element is:

[0010] C: 0.06~0.11%, Si: 0.15~0.35%, Mn: 1.41~1.65%, Cr: 0.01~0.10%, Mo: 0.07~0.20%, Nb: 0.01~0.04%, V: 0.03~0.08%, Ti: 0.010~0.025%, Ca: 0.001~0.004%, Alt: 0.020~0.040%; the balance is Fe and unavoidable impurities.

[0011] In the high plasticity and fatigue-resistant X65 seamless pipeline designed by the present invention, the seamless pipeline is designed with a lower C content, and at the same time, high Mn, high Mo, and Nb-Ti-V microalloying promote grain refinement, so that the material obtains good strength and toughness, and meets the X65 strength level. At the same time, the present invention also improves the strain aging resistance by adding and controlling the Ti content to achieve Ti solidification of N, thereby ensuring the plasticity level after strain aging, and avoiding excessive Ti addition to cause large-sized TiN particles in the steel, thereby adversely affecting plasticity, fatigue resistance, and low-temperature toughness. In addition, in the present invention, by controlling the Cr content, Cr and C are combined to form Cr carbides, and C is fully precipitated, thereby improving the strain aging resistance.

[0012] Specifically, in the high plasticity and fatigue-resistant X65 seamless line pipe of the present invention, the design principle of the chemical elements is as follows:

[0013] C: In the high-plasticity and fatigue-resistant X65 seamless pipeline described in the present invention, the C element is a strengthening element, which can improve the strength of steel through interstitial solid solution strengthening. Increasing the carbon content can greatly improve the hardenability of steel, reduce the amount of other precious alloys added, and reduce production costs, but the increase in C content is not good for the plasticity, toughness, weldability and strain aging resistance of steel. Therefore, the ultra-low C design is adopted in the high-plasticity and fatigue-resistant X65 seamless pipeline described in the present invention, and the mass percentage of the C element can be controlled between 0.06 and 0.11%.

[0014] Si: In the high-plasticity and anti-fatigue X65 seamless pipeline steel pipe of the present invention, Si is a solid-solution strengthening element and also a deoxidizing element in the steel. However, when the Si content is too high, it will have an adverse effect on the surface quality and welding performance. If the Si content exceeds 0.35%, the toughness may decrease. Therefore, in the high-plasticity and anti-fatigue X65 seamless pipeline steel pipe of the present invention, the mass percentage of the Si element can be controlled between 0.15 and 0.35%.

[0015] Mn: In the high-plasticity and anti-fatigue X65 seamless pipeline steel pipe of the present invention, the Mn element can improve the strength of the steel through solid-solution strengthening, and it is the most important and economical strengthening element in the steel to compensate for the strength loss caused by the decrease in the C content. Mn helps to obtain fine phase transformation products, and at the same time, by forming carbides with C to reduce the existence of solid-solution C, it can improve the anti-strain aging performance of the steel and the plasticity after strain aging. However, too much Mn element will also aggravate the center segregation. Therefore, in the high-plasticity and anti-fatigue X65 seamless pipeline steel pipe of the present invention, the mass percentage of the Mn element can be controlled between 1.41 and 1.65%.

[0016] Cr: In the high-plasticity and anti-fatigue X65 seamless pipeline steel pipe of the present invention, the Cr element has a certain solid-solution strengthening effect. Since Cr can effectively improve the hardenability of the steel and inhibit the formation of ferrite transformation, it is necessary to control the upper limit of Cr not to be too high. When the mass percentage of Cr is controlled at ≤0.10%, the excessive hardenability of the steel can be avoided. At the same time, Cr is a strong carbide-forming element. When the mass percentage of Cr is controlled at ≥0.01%, it can promote the precipitation of solid-solution carbon in the form of carbides, thereby improving the anti-strain aging performance and the plasticity after strain aging. Therefore, in the high-plasticity and anti-fatigue X65 seamless pipeline steel pipe of the present invention, the mass percentage of the Cr element can be controlled between 0.01 and 0.10%.

[0017] Mo: In the high-plasticity and anti-fatigue X65 seamless pipeline steel pipe of the present invention, Mo is a strong hardenability element, which can significantly delay the ferrite phase transformation and inhibit the formation of ferrite and pearlite; it can effectively promote the bainite transformation to strengthen the matrix, obtain a finer structure, and provide more nucleation sites for precipitation strengthening, enhancing the effect of precipitation strengthening. At the same time, Mo is a strong carbide-forming element, which can promote the precipitation of solid-solution carbon in the form of carbides, thereby improving the anti-strain aging performance and the plasticity after strain aging. A certain amount of Mo is obviously beneficial to the improvement of the material's tissue performance, but when the Mo content is too high, the plasticity of the steel will decrease. Therefore, in the high-plasticity and anti-fatigue X65 seamless pipeline steel pipe of the present invention, considering the high cost of Mo, the mass percentage of the Mo element can be controlled between 0.07 and 0.20%.

[0018] Nb: In the high-plasticity and anti-fatigue X65 seamless pipeline steel pipe described in the present invention, the Nb element is an important element for steel microalloying. During the hot rolling process at high temperature, the dissolved Nb precipitates by strain induction to form Nb carbonitrides, which pin the grain boundaries and inhibit the growth of deformed austenite, obtaining a fine austenite grain size. The dissolved Nb will precipitate dispersedly in the matrix as the second-phase particles NbC after quenching and tempering, playing the role of precipitation strengthening. At the same time, the Nb element can improve the anti-strain aging performance. Excessive Nb will lead to an increase in the anisotropy of the material, resulting in uneven performance and a decrease in plasticity and toughness. Therefore, in the high-plasticity and anti-fatigue X65 seamless pipeline steel pipe described in the present invention, the mass percentage of the Nb element can be controlled between 0.01% and 0.04%.

[0019] V: In the high-plasticity and anti-fatigue X65 seamless pipeline steel pipe described in the present invention, vanadium mainly exists in the form of carbides in the steel. Vanadium can refine the grain structure of the steel in the steel, increase the grain coarsening temperature of the steel, improve the strength of the steel through fine grain strengthening and precipitation strengthening, and can also improve the softening problem in the heat affected zone of welding and enhance the welding performance. However, too high a content of V will lead to a decrease in the toughness of the steel and an increase in the ductile-brittle transition temperature. Therefore, in the high-plasticity and anti-fatigue X65 seamless pipeline steel pipe described in the present invention, the mass percentage of the V element can be controlled between 0.03% and 0.08%.

[0020] Ti: In the high-plasticity and anti-fatigue X65 seamless pipeline steel pipe described in the present invention, the Ti element is a good deoxidizer and degasser and an effective element for fixing nitrogen and carbon. The undissolved carbonitrides of Ti can prevent the growth of austenite grains when the steel is heated. The TiN and TiC precipitated during rough rolling in the high-temperature austenite zone can effectively inhibit the growth of austenite grains, thus refining the grains. At the same time, it can also improve the anti-strain aging performance by fixing C and N. In addition, the precipitation during the welding process can also inhibit the growth of high-temperature grains, thus improving the welding performance. Therefore, in the high-plasticity and anti-fatigue X65 seamless pipeline steel pipe described in the present invention, the mass percentage of the Ti element can be controlled between 0.010% and 0.025%.

[0021] Ca: In the high-plasticity and anti-fatigue X65 seamless pipeline steel pipe described in the present invention, the morphology of sulfides can be controlled by Ca treatment, improving the anisotropy of the steel plate and enhancing the low-temperature toughness. However, too high a Ca content will easily lead to an increase in the amount and size of CaO inclusions in the steel. Therefore, in the high-plasticity and anti-fatigue X65 seamless pipeline steel pipe described in the present invention, the mass percentage of the Ca element can be controlled between 0.0010% and 0.0040%.

[0022] Alt: In the high-plasticity and anti-fatigue X65 seamless pipeline steel tube of the present invention, Alt refers to total aluminum, that is, the total content of aluminum. Al is used for deoxidizing the steel grade, and appropriate Al is also beneficial to refining the grains and improving the strength and toughness properties. However, if the Alt content is greater than 0.040%, coarse precipitates may be formed, thereby reducing the low-temperature toughness of the steel. Therefore, in the high-plasticity and anti-fatigue X65 seamless pipeline steel tube of the present invention, the mass percentage of Alt can be controlled between 0.020% and 0.040%.

[0023] Furthermore, in the high-plasticity and anti-fatigue X65 seamless pipeline steel tube of the present invention, the mass percentage content of each chemical element satisfies: (Nb + V + Ti) / 6 + (Mn + Cr + Mo) / 24 ≥ C.

[0024] The present invention controls (Nb + V + Ti) / 6 + (Mn + Cr + Mo) / 24 ≥ C to ensure that C can fully precipitate to form carbides or carbonitrides, reduce the content of solid-solution C, and further improve the anti-strain aging performance and the overall plasticity of the material.

[0025] Furthermore, in the high-plasticity and anti-fatigue X65 seamless pipeline steel tube of the present invention, CEpcm ≤ 0.215%, where:

[0026] CEpcm = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5B, and each element in the formula is substituted with its corresponding mass percentage content.

[0027] In the present invention, considering the hardenability and the cumulative value of elements, in order to avoid too high hardenability of the steel, it is also necessary to control CEpcm ≤ 0.215%. By controlling CEpcm, which is a key factor affecting hardenability, the hardenability of the material can be appropriately reduced. Combining with the quenching process of the present invention, it can promote the preferential formation of a small amount of ferrite during quenching, so that 1 - 8% of ferrite structure is formed in the structure, improve the anti-strain aging performance and the overall plasticity of the material.

[0028] Furthermore, in the high-plasticity and anti-fatigue X65 seamless pipeline steel tube of the present invention, it also contains 0 < B ≤ 0.0005 wt%.

[0029] In the present invention, the main function of the B element is to increase the hardenability and strength of the steel, thereby saving other relatively rare and precious metals. However, excessive B element will have a significant adverse effect on the low-temperature toughness of the material. Therefore, in the high-plasticity and anti-fatigue X65 seamless pipeline steel tube of the present invention, the mass percentage of the B element can be controlled between 0 < B ≤ 0.0005%.

[0030] Furthermore, in the high-plasticity anti-fatigue X65 seamless pipeline steel pipe of the present invention, among the inevitable impurities, P≤0.015%, S≤0.005%, N≤0.007%, H≤0.0002%, O≤0.003%.

[0031] In the high-plasticity anti-fatigue X65 seamless pipeline steel pipe of the present invention, P, S, N, H, and O are all inevitable impurities, and it is desirable that their contents are as low as possible. Among them:

[0032] Elements P and S are the main impurity elements in steel. Phosphorus easily causes cold brittleness of steel, and sulfur easily causes hot brittleness, resulting in unstable properties of steel. Especially as the S content increases, the MnS inclusions increase, significantly reducing the low-temperature toughness of the material. Therefore, in the high-plasticity anti-fatigue X65 seamless pipeline steel pipe of the present invention, the mass percentage of element S can be controlled at S≤0.005%, and the mass percentage of element P can be controlled at P≤0.015%

[0033] Too high contents of N, H, and O are not beneficial to the plasticity of the material. Therefore, in the high-plasticity anti-fatigue X65 seamless pipeline steel pipe of the present invention, the mass percentage of element N can be controlled at N≤0.0070%, the mass percentage of element H can be controlled at H≤0.0002%, and the mass percentage of element O can be controlled at O≤0.0030%.

[0034] Furthermore, in the high-plasticity anti-fatigue X65 seamless pipeline steel pipe of the present invention, its microstructure is tempered bainite + ferrite, and the volume percentage of ferrite is 1-8%.

[0035] Furthermore, in the high-plasticity anti-fatigue X65 seamless pipeline steel pipe of the present invention, its properties meet at least one of the following items:

[0036] Yield strength ≥ 450 MPa, tensile strength ≥ 535 MPa, yield ratio ≤ 0.90, -30°C impact energy KV8 ≥ 200 J, total elongation index ≥ 33%, uniform elongation ≥ 9%;

[0037] After undergoing tensile strain aging or compressive strain aging, it can meet: yield strength ≥ 450 MPa, tensile strength ≥ 535 MPa, total elongation index ≥ 30%, uniform elongation ≥ 6%;

[0038] After undergoing tensile strain aging or compressive strain aging, it can also meet: fatigue life under the fatigue condition of 300 MPa and stress ratio R = -1 ≥ 10 million times.

[0039] Accordingly, another object of the present invention is to provide a manufacturing method for a high-plasticity and anti-fatigue X65 seamless pipeline pipe. The high-plasticity and anti-fatigue X65 seamless pipeline pipe obtained by using this manufacturing method has high plasticity, high anti-fatigue performance, and high low-temperature toughness at the same time.

[0040] To achieve the above object, the present invention provides the above-mentioned manufacturing method for a high-plasticity and anti-fatigue X65 seamless pipeline pipe, which includes the steps:

[0041] (1) Prepare a tube blank;

[0042] (2) Make the tube blank into a steel pipe;

[0043] (3) Quenching: Control the quenching temperature to be 880 - 940 °C;

[0044] (4) Tempering: Control the tempering temperature to be 620 - 700 °C.

[0045] By controlling the quenching temperature in the present invention, the grains of Nb-Ti-V can be refined, and the austenite grain size in the initial state is small, so that it is more conducive to obtaining a small amount of ferrite structure during the quenching process. In addition, by controlling the tempering temperature in the present invention, C and N are promoted to precipitate fully in the form of carbides and nitrides, thereby improving the anti-strain aging performance.

[0046] The specific quenching temperature is controlled to be 880 - 940 °C because: when the quenching temperature is too high, the austenite grains coarsen and grow, and large-sized austenite grains are not conducive to the formation of a small amount of ferrite structure. When the quenching temperature is too low, the austenite grains are too small, resulting in too high a proportion of ferrite formed, and the strength cannot meet the requirements. Moreover, when the quenching temperature is too low, the hardenability of the material is insufficient, and the strength target of X65 cannot be achieved either.

[0047] The specific tempering temperature is controlled to be 620 - 700 °C because: when the tempering temperature is too high, a large amount of the bainite structure formed during quenching recovers and softens, and transforms into a ferrite form, resulting in the strength of the material not meeting the X65 target; when the tempering temperature is too low, carbon and nitrogen do not precipitate sufficiently in the form of precipitates, and will re-precipitate and pin new dislocations at dislocations during the subsequent strain aging process, resulting in a reduction in the plasticity index.

[0048] Furthermore, in step (3) of the manufacturing method for a high-plasticity and anti-fatigue X65 seamless pipeline pipe of the present invention, control the quenching heating time to be 0.3 - 1.2 h.

[0049] In a preferred embodiment, the quenching heating time is controlled to be 0.3 - 1.2 h because: when the quenching time is too long, the austenite grains coarsen and grow, and large-sized austenite grains are not conducive to the formation of a small amount of ferrite structure; when the quenching time is too short, the austenite grains are too fine, resulting in too high a proportion of ferrite formed, and the strength cannot meet the requirements; and when the quenching time is too short, the hardenability of the material is insufficient, which is also not conducive to achieving the strength target of X65.

[0050] Further, in step (4) of the manufacturing method of the high-plasticity anti-fatigue X65 seamless pipeline tube of the present invention, the tempering heating time is controlled to be 0.3 - 1.2 h.

[0051] In a preferred embodiment, the tempering heating time is controlled to be 0.3 - 1.2 h because: when the tempering time is too long, a large amount of the bainite structure formed during quenching recovers and softens, transforming into a ferrite morphology, which is not conducive to improving the strength of the material; when the tempering time is too short, carbon and nitrogen do not precipitate sufficiently in the form of precipitates, and will re-precipitate and pin new dislocations at dislocations during the subsequent strain aging process, resulting in a decrease in the plasticity index.

[0052] Compared with the prior art, the high-plasticity anti-fatigue X65 seamless pipeline tube and its manufacturing method of the present invention have the following advantages and beneficial effects:

[0053] The high-plasticity anti-fatigue X65 seamless pipeline tube of the present invention simultaneously has high plasticity, high anti-fatigue performance, and high low-temperature toughness.

[0054] In some embodiments, the performance of the high-plasticity anti-fatigue X65 seamless pipeline tube of the present invention meets: yield strength ≥ 450 MPa, tensile strength ≥ 535 MPa, yield ratio ≤ 0.90, -30°C impact energy KV8 ≥ 200 J, total elongation index ≥ 33%, uniform elongation ≥ 9%;

[0055] After undergoing tensile strain aging or compressive strain aging, it can meet: yield strength ≥ 450 MPa, tensile strength ≥ 535 MPa, total elongation index ≥ 30%, uniform elongation ≥ 6%; and the fatigue life under the fatigue condition of 300 MPa and stress ratio R = -1 (tension-compression) ≥ 10 million times. Specific Embodiments

[0056] The following will further explain and illustrate the high-plasticity anti-fatigue X65 seamless pipeline tube and its manufacturing method of the present invention in combination with specific examples. However, this explanation and illustration do not unduly limit the technical solution of the present invention.

[0057] Examples 1 - 9 and Comparative Examples 1 - 5

[0058] The high-plasticity anti-fatigue X65 seamless pipeline pipes of Examples 1-9 and the seamless pipeline pipes of Comparative Examples 1-5 were all prepared by the following steps:

[0059] (1) Smelt according to the chemical composition ratios shown in Tables 1-1 and 1-2 and prepare a pipe blank;

[0060] (2) Make the pipe blank into a steel pipe;

[0061] (3) Quenching: Control the quenching temperature at 880-940 °C and control the quenching heating time at 0.3-1.2 h;

[0062] (4) Tempering: Control the tempering temperature at 620-700 °C and control the tempering heating time at 0.3-1.2 h.

[0063] It should be noted that the high-plasticity anti-fatigue X65 seamless pipeline pipes of Examples 1-9 of the present invention were all prepared by the above steps, and their chemical compositions and related process parameters all meet the control requirements of the design specifications of the present invention. The seamless pipeline pipes of Comparative Examples 1-5 were also prepared by the above process flow, but the chemical compositions of the seamless pipeline pipes of Comparative Examples 1-3 do not meet the present invention, and the manufacturing process parameters of Comparative Examples 4-5 do not meet the present invention.

[0064] Tables 1-1 and 1-2 list the mass percentages of each chemical element in the high-plasticity anti-fatigue X65 seamless pipeline pipes of Examples 1-9 and the seamless pipeline pipes of Comparative Examples 1-5.

[0065] Table 1-1. (wt%, the balance is Fe and other unavoidable impurities except P, S, N, H, O)

[0066] Number C Si Mn Cr Mo Nb V Ti Ca Alt B Example 1 0.06 0.35 1.65 0.10 0.07 0.02 0.05 0.015 0.004 0.040 0.0005 Example 2 0.09 0.25 1.53 0.08 0.12 0.04 0.03 0.010 0.001 0.030 0.0003 Example 3 0.11 0.15 1.41 0.10 0.15 0.01 0.08 0.025 0.002 0.020 0.0002 Example 4 0.07 0.26 1.49 0.01 0.08 0.03 0.03 0.010 0.003 0.025 0.0004 Example 5 0.09 0.34 1.50 0.05 0.10 0.04 0.07 0.020 0.002 0.032 0.0004 Example 6 0.11 0.16 1.60 0.07 0.11 0.03 0.06 0.022 0.004 0.022 0.0003 Example 7 0.06 0.29 1.55 0.01 0.07 0.02 0.03 0.012 0.004 0.026 0.0005 Example 8 0.08 0.33 1.48 0.09 0.13 0.04 0.07 0.024 0.004 0.028 0.0004 Example 9 0.10 0.17 1.42 0.06 0.20 0.02 0.05 0.021 0.003 0.035 0.0003 Comparative Example 1 0.11 0.15 <![CDATA 1.32 > 0.08 0.07 0.01 0.05 0.015 0.002 0.020 0.0002 Comparative Example 2 0.11 0.15 1.42 0.08 <![CDATA 0.02 > 0.01 0.05 0.015 0.002 0.020 0.0002 Comparative Example 3 0.09 0.33 1.48 <![CDATA 0.15 > 0.13 0.04 0.07 0.024 0.004 0.028 0.0004 Comparative Example 4 0.11 0.15 1.41 0.10 0.15 0.01 0.08 0.025 0.002 0.020 0.0002 Comparative Example 5 0.11 0.15 1.41 0.10 0.15 0.01 0.08 0.025 0.002 0.020 0.0002

[0067] Table 1-2. (wt%, the balance is Fe and other unavoidable impurities except P, S, N, H, O)

[0068]

[0069] Table 2 lists the specific process parameters of the high-plasticity anti-fatigue X65 seamless pipeline pipes of Examples 1-9 and the seamless pipeline pipes of Comparative Examples 1-5.

[0070] Table 2.

[0071] Number Quenching Temperature (°C) Quenching Heating Time (h) Tempering Temperature (°C) Tempering Heating Time (h) Example 1 880 1.2 620 1.2 Example 2 910 0.8 660 0.8 Example 3 900 1.1 655 0.8 Example 4 925 0.5 690 0.4 Example 5 915 0.6 650 1.0 Example 6 905 1.1 640 0.9 Example 7 890 1.1 670 0.6 Example 8 885 1.2 635 0.7 Example 9 940 0.3 700 0.3 Comparative Example 1 900 1.1 655 0.8 Comparative Example 2 900 1.1 655 0.8 Comparative Example 3 900 1.1 655 0.8 Comparative Example 4 <![CDATA 860 > 1.2 620 1.2 Comparative Example 5 <![CDATA 980 > 0.3 700 0.3

[0072] Samples were taken from the finally prepared high-plasticity anti-fatigue X65 seamless pipeline pipes of Examples 1-9 and the seamless pipeline pipes of Comparative Examples 1-5 respectively, and the microstructures of the seamless pipeline pipe samples of each example and comparative example were observed and analyzed, and the results are listed in Table 3.

[0073] Table 3

[0074]

[0075]

[0076] As can be seen from Table 3 above, the main microstructure of the high-plasticity anti-fatigue X65 seamless pipeline pipe in Embodiments 1-9 of the present invention is tempered bainite + ferrite, and the volume percentage of ferrite in the microstructure is between 1% and 8%.

[0077] Samples were taken again from the high-plasticity anti-fatigue X65 seamless pipeline pipes in Embodiments 1-9 and the seamless pipeline pipes in Comparative Examples 1-5, and various performance tests were carried out on the seamless pipeline pipe samples of each embodiment and comparative example obtained based on the sampling before and after strain aging. The test results before strain aging are listed in Table 4, and the test results after 3% tensile or 3% compressive strain and 250°C / 1h strain aging are listed in Tables 5 and 6 respectively.

[0078] The relevant performance test methods are as follows:

[0079] Tensile test: Test according to ASTM E8 / E8M method;

[0080] Impact test: Test according to ASTM E23 method;

[0081] Tensile test after 3% tensile strain and 250°C / 1h: First, perform 3% tensile strain treatment, then heat-treat the specimen by the method of heat preservation at 250°C for 1h and air cooling, and then perform tensile test and impact test.

[0082] Tensile test after 3% compressive strain and 250°C / 1h: First, perform 3% tensile strain treatment, then heat-treat the specimen by the method of heat preservation at 250°C for 1h and air cooling, and then perform tensile test and impact test.

[0083] It should be noted that the -30°C impact energy KV8 was detected three times in Tables 4, 5 and 6.

[0084] Table 4

[0085]

[0086]

[0087] Table 5. Re-test of tensile and impact properties after 3% tensile strain + 250°C aging

[0088]

[0089] Table 6. Tensile and impact properties were tested again after 6.3% compressive strain and aging at 250°C

[0090]

[0091]

[0092] As can be seen from Table 4 above, in the present invention, compared with the seamless pipeline pipes of Comparative Examples 1-5, the high-plasticity anti-fatigue X65 seamless pipeline pipes of Examples 1-9 of the present invention have better performance. Their yield strength is between 483-512 MPa, the tensile strength is between 576-611 MPa, the yield ratio is less than or equal to 0.85, the total elongation is ≥36%, the uniform elongation is ≥12%, and the impact energy KV8 at -30°C is greater than 200 J.

[0093] As can be seen from Tables 5 and 6 above, after tensile strain aging or compressive strain aging, when compared with the seamless pipeline pipes of Comparative Examples 1-5, during the subsequent tensile test, the total elongation and uniform elongation of the high-plasticity anti-fatigue X65 seamless pipeline pipes of Examples 1-9 of the present invention did not decrease significantly.

[0094] In addition, for the high-plasticity anti-fatigue X65 seamless pipeline pipes of Examples 1-9 and the seamless pipeline pipes of Comparative Examples 1-5, after 3% tensile strain + aging at 250°C / 1 h (State 1) and after 3% compressive strain + aging at 250°C / 1 h (State 2), fatigue test samples were taken again. Fatigue life detection was carried out under the tensile-compressive fatigue conditions of 300 MPa and a stress ratio of R = -1, and the results were recorded in Table 7.

[0095] Table 7.

[0096]

[0097] As can be seen from Table 7 above, in the present invention, compared with the seamless pipeline pipes of Comparative Examples 1-5, the high-plasticity anti-fatigue X65 seamless pipeline pipes of Examples 1-9 of the present invention have better fatigue performance after tensile strain aging or compressive strain aging, and their fatigue life is greater than 10 million times.

[0098] It should be noted that the prior art part in the protection scope of the present invention is not limited to the embodiments given in this application document. All prior arts that do not conflict with the solution of the present invention, including but not limited to prior patent documents, prior published publications, prior public uses, etc., can be included in the protection scope of the present invention.

[0099] In addition, the combination modes of the technical features in this case are not limited to the combination modes recorded in the claims of this case or the combination modes recorded in the specific embodiments. All the technical features recorded in this case can be freely combined or joined in any way, unless contradictions occur among them.

[0100] It should also be noted that the specific embodiments listed above are only for this invention. Obviously, this invention is not limited to the above embodiments, and there are many similar variations. All the deformations directly derived or associated by those skilled in the art from the disclosed content of this invention shall fall within the protection scope of this invention.

Claims

1. A high-plasticity and anti-fatigue X65 seamless pipeline tube, which contains Fe and inevitable impurities, characterized in that, it also contains the following chemical elements in the following mass percentages: C: 0.06 - 0.11%, Si: 0.15 - 0.35%, Mn: 1.41 - 1.65%, Cr: 0.01 - 0.10%, Mo: 0.07 - 0.20%, Nb: 0.01 - 0.04%, V: 0.03 - 0.08%, Ti: 0.010 - 0.025%, Ca: 0.001 - 0.004%, Alt: 0.02 - 0.04%; the high-plasticity and anti-fatigue X65 seamless pipeline tube does not contain Cu and Ni.

2. The high-plasticity and anti-fatigue X65 seamless pipeline tube according to claim 1, characterized in that, the mass percentages of its various chemical elements are: C: 0.06 - 0.11%, Si: 0.15 - 0.35%, Mn: 1.41 - 1.65%, Cr: 0.01 - 0.10%, Mo: 0.07 - 0.20%, Nb: 0.01 - 0.04%, V: 0.03 - 0.08%, Ti: 0.010 - 0.025%, Ca: 0.001 - 0.004%, Alt: 0.02 - 0.04%; the balance is Fe and inevitable impurities.

3. The high-plasticity and anti-fatigue X65 seamless pipeline tube according to claim 1 or 2, characterized in that, the mass percentage contents of its various chemical elements satisfy: (Nb + V + Ti) / 6 + (Mn + Cr + Mo) / 24 ≥ C.

4. The high-plasticity and anti-fatigue X65 seamless pipeline tube according to claim 1 or 2, characterized in that, CEpcm ≤ 0.215%, where: CEpcm = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5B, and each element in the formula is substituted with its corresponding mass percentage content.

5. The high-plasticity and anti-fatigue X65 seamless pipeline tube according to claim 1 or 2, characterized in that, it also contains 0 < B ≤ 0.0005 wt%.

6. The high-plasticity and anti-fatigue X65 seamless pipeline tube according to claim 1 or 2, characterized in that, among the inevitable impurities, P ≤ 0.015%, S ≤ 0.005%, N ≤ 0.007%, H ≤ 0.0002%, O ≤ 0.003%.

7. The high-plasticity and anti-fatigue X65 seamless pipeline tube according to claim 1 or 2, characterized in that, its microstructure is tempered bainite + ferrite, and the volume percentage of ferrite is 1 - 8%.

8. The high-plasticity and anti-fatigue X65 seamless pipeline tube according to claim 1 or 2, characterized in that, its performance meets at least one of the following items: yield strength ≥ 450 MPa, tensile strength ≥ 535 MPa, yield ratio ≤ 0.90, -30°C impact energy KV8 ≥ 200 J, total elongation index ≥ 33%, uniform elongation ≥ 9%; After undergoing tensile strain aging or compressive strain aging, the following requirements can be met: yield strength ≥ 450 MPa, tensile strength ≥ 535 MPa, total elongation index ≥ 30%, and uniform elongation ≥ 6%. After undergoing tensile strain aging or compressive strain aging, the following can also be satisfied: fatigue life under the fatigue condition of 300 MPa and stress ratio R = -1 (tension-compression) ≥ 10 million cycles.

9. A manufacturing method of a high-plasticity and anti-fatigue X65 seamless pipeline tube as described in any one of claims 1-8, characterized in that, it includes the steps of: (1) Producing a tube blank; (2) Forming the tube blank into a steel pipe; (3) Quenching: controlling the quenching temperature to be 880 - 940 °C; (4) Tempering: controlling the tempering temperature to be 620 - 700 °C.

10. The manufacturing method as described in claim 9, characterized in that, in step (3), controlling the quenching heating time to be 0.3 - 1.2 h.

11. The manufacturing method as described in claim 9, characterized in that, in step (4), controlling the tempering heating time to be 0.3 - 1.2 h.

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