A high-plasticity, toughness, and fatigue-resistant X65-grade catenary riser steel plate and its production method

Abstract

This invention relates to a high-ductility, high-toughness, fatigue-resistant X65 grade steel plate for catenary risers and its production method. The chemical composition of the steel plate, by weight percentage, is: C: 0.040%–0.060%, Si: 0.10%–0.20%, Mn: 1.50%–1.65%, P≤0.015%, S≤0.0015%, Cr≥0.10%, Cr+Ni: 0.22%–0.33%, Cu: ≤0.20%, Nb: 0.030%–0.050%, Ti: 0.010%–0.025%, Al The alloy composition is 0.026%–0.050%, with the balance being Fe and unavoidable impurities. Using inexpensive elements such as C, Mn, Cr, and Cu, supplemented with trace amounts of Nb and Ni, and employing appropriate heating, rolling, and cooling processes, a fine-grained polygonal ferrite + acicular ferrite microstructure is obtained. The alloy addition is low, resulting in low alloy cost. The steel plate exhibits a transverse yield strength of 476–540 MPa and a tensile strength of 540–640 MPa, achieving X65 strength level. The steel plate has an impact energy ≥350 J at -30℃, a CTOD ≥1.0 mm at -10℃, and a strength of 10... 7 The fatigue strength after each cycle is ≥350MPa, the longitudinal elongation after fracture of the steel plate is 57%~68%, and the uniform elongation is ≥12%, which meets the technical requirements for manufacturing X65 grade deep-water steel catenary risers.

Description

Technical Field

[0001] This invention relates to the field of metal material production technology, and in particular to a high-ductility, high-toughness, fatigue-resistant X65 grade steel plate for catenary risers and its production method. Background Technology

[0002] With the development of offshore oil and gas engineering, riser systems have become key equipment connecting offshore platforms and subsea oil and gas drilling and production. Steel catenary risers are a type of riser widely used in deepwater oil and gas development projects. They have great adaptability to the movement of floating bodies and represent the technological development direction of deep-sea platform risers. The high-pressure and low-temperature environment of the deep sea requires steel catenary risers to have a good match between crush resistance and high strength and toughness. In addition, apart from the bottom of the platform and the seabed wellhead, there are no fixed supports in other parts of the riser. Therefore, the impact of the floating body movement of the offshore platform and the vortex-induced vibration in the high-velocity deep-water area on the steel catenary riser cannot be ignored. The floating body movement of the platform will cause overall traction and tension in the longitudinal direction of the steel pipe, which requires the steel catenary riser to have excellent plasticity; while vortex-induced vibration will cause periodic reciprocating motion of the steel pipe, which requires the steel catenary riser to also have excellent fatigue resistance.

[0003] Patent application number 202010620828.2 discloses an extra-thick-walled X70 grade marine acid-resistant pipeline steel and its preparation method. Its chemical composition is: C: 0.03%-0.05%, Si: 0.10%-0.30%, Mn: 1.0%-1.3%, P≤0.010%, S≤0.003%, Cr: 0.2%-0.3%, Mo: 0.10%-0.20%, Ni: 0.2%-0.4%, Nb: 0. 0.04%-0.07%, V: 0.03%-0.05%, Ti: 0.01%-0.02%, Al: 0.01%-0.045%, with the remainder being Fe and unavoidable impurity elements; its chemical composition contains V and Mo elements, and also has a high Ni content, which is significantly different from the composition design scheme of this patent, and the alloy cost is high. In addition, the elongation (elongation after fracture) of the steel A50mm does not exceed 35%, and the fatigue resistance of the steel is not mentioned.

[0004] Patent application number 201410677813.4 discloses extra-thick, high-strength, high-toughness subsea pipeline steel for ultra-deep-sea applications and its manufacturing method. Its chemical composition is: C: 0.020%-0.050%, Si: ≤0.10%, Mn: 1.00%-1.50%, P≤0.010%, S≤0.0010%, Cu: 0.10%-0.30%, Cr: 0.10%-0.25%, Ni: 0.31%-0.50%, Mo: ≤0.15%, Nb: 0.030%-0.065%, V: 0.015%-0.040%, T... i: 0.010%-0.025%, Al: 0.010%-0.050%, N: ≤0.008%, balance being Fe and unavoidable impurities; compared with this patent, its chemical composition contains 0.31%-0.50% Ni and 0.015%-0.040% V, not only is the composition design different, but the Ni content is also high. At the same time, Ni and V are both expensive alloying elements, resulting in high alloy costs. In addition, the heat treatment temperature of the steel plate described in this patent is ≤1100℃ and the final cooling temperature is less than 300℃, which is different from the production process of the steel plate in this patent. Furthermore, it does not mention the fatigue resistance of the steel.

[0005] Patent application number 202111179082.7 discloses a weldable, high-strength, high-toughness, low-yield-strength-ratio pipeline steel and its preparation method. Its chemical composition is as follows: C: 0.03%-0.06%, Si: 0.15%-0.25%, Mn: 1.60%-1.80%, P≤0.015%, S≤0.004%, Nb: 0.05%-0.06%, Ti: 0.008%-0.020%, Mo: 0.10%-0.20%, Al: 0.02%-0.04%, Cu: 0.10%-0.20%, Cr: 0.15%-0.25%, with the balance being iron and other unavoidable impurities. Its chemical composition contains 0.10%-0.20% Mo, which is different from the composition design scheme of this patent. In addition, the microstructure of the steel plate is ferrite + granular bainite, which is significantly different from the microstructure design of this patent, and there is no mention of the fatigue resistance of the steel.

[0006] Patent application number 202111192650.7 discloses corrosion-resistant and fatigue-resistant underwater oil and gas production pipeline steel and its production method. Its chemical composition is as follows: C: 0.030%-0.055%, Si: 0.26%-0.40%, Mn: 1.10%-1.18%, P≤0.010%, S≤0.0015%, Nb: 0.035%-0.060%, Ti: 0.012%-0.025%, V: 0.01%-0.04%, Ni: 0.10%-0.19%, Cu: 0.16%-0.25%, Ni / Cu≥0.7, Mo: 0.1 0%-0.19%, Cr: <0.25%, Al: 0.010%-0.025%, Ca: 0.0015%-0.0050%, Ca / S≥1.6, N: 0.0010%-0.0040%, H≤0.00015%, O≤0.0020%, with the balance being Fe and unavoidable impurities; compared with this patent, its chemical composition contains 0.10%-0.19% Mo, 0.16%-0.25% Cu and 0.01%-0.04% V. Not only is the composition design different, but Mo and V are both expensive alloying elements, resulting in high alloy costs.

[0007] Patent application number 202111194029.4 discloses heat-resistant and fatigue-resistant precipitation-strengthened pipeline steel and its production method. Its chemical composition is: C: 0.040%-0.060%, Si: 0.26%-0.45%, Mn: 1.50%-1.69%, P≤0.012%, S≤0.002%, Nb: 0.04%-0.07%, Ti: 0.012%-0.025%, Mo: 0.16%-0.29%, V: 0.01%-0.04%, Cr: 0.16%-0.30%, Ni <0.15%, Cu<0.15%, Al: 0.010%-0.025%, Ca: 0.0015-0.0045%, Ca / S≥1.6, Nb: 0.0010%-0.0045%, H≤0.00015%, O≤0.0020%, the remainder being Fe and unavoidable impurities; compared with this patent, its chemical composition contains 0.16%-0.29% Mo and 0.01%-0.04% V elements. Not only is the composition design scheme different, but Mo and V are both expensive alloying elements, resulting in high alloy costs.

[0008] In summary, the main problems in the production of high-toughness catenary riser steel plates are as follows.

[0009] 1) The plasticity of steel is not high, and the elongation after fracture is less than 30%;

[0010] 2) The fatigue resistance of steel was not mentioned, and no specific scheme was designed to improve the fatigue resistance of steel;

[0011] 3) The alloy content is high, with the addition of precious alloying elements such as Mo and V, which increases the cost of the alloy. Summary of the Invention

[0012] This invention provides a high-ductility, high-toughness, and fatigue-resistant X65 grade steel plate for catenary risers and its production method. It involves low alloy addition, resulting in low alloy cost. Furthermore, targeted microstructure design enhances the steel plate's plasticity and fatigue resistance, leading to a steel plate with excellent strength-toughness balance and superior fatigue resistance. The steel plate exhibits excellent comprehensive mechanical properties, with a transverse yield strength of 476–540 MPa and a tensile strength of 540–640 MPa, reaching the X65 grade. The steel plate also demonstrates an impact energy ≥350 J at -30℃, a CTOD ≥1.0 mm at -10℃, and a 10 7 The fatigue strength after each cycle is ≥350MPa, the longitudinal elongation after fracture of the steel plate is 57%~68%, the uniform elongation is ≥12%, and all properties meet the technical requirements for manufacturing X65 grade deep-water steel catenary risers.

[0013] To achieve the above objectives, the present invention employs the following technical solution:

[0014] A high-ductility, high-toughness, fatigue-resistant X65 grade steel plate for catenary risers, wherein the chemical composition of the steel plate by weight percentage is: C: 0.040%–0.060%, Si: 0.10%–0.20%, Mn: 1.50%–1.65%, P≤0.015%, S≤0.0015%, Cr≥0.10%, Cr+Ni: 0.22%–0.33%, Cu: ≤0.20%, Nb: 0.030%–0.050%, Ti: 0.010%–0.025%, Al: 0.026%–0.050%, with the balance being Fe and unavoidable impurities.

[0015] A method for producing high-ductility, high-toughness, fatigue-resistant X65 grade steel plate for catenary risers includes smelting, continuous casting, heating, rolling, and accelerated cooling, wherein:

[0016] (1) Smelting: Converter smelting and ladle refining are adopted. The RH vacuum treatment time is ≥25min. After the RH treatment, Ca treatment and micro-titanium treatment are carried out. The net circulation time is ≥10min.

[0017] (2) Continuous casting: control the superheat to 20-45℃ and control the continuous casting billet pulling speed to 0.6-1.1m / min;

[0018] (3) Heating: The temperature of the high-temperature heating section is 1200~1240℃, and the temperature of the soaking section is 1160~1200℃;

[0019] (4) Rolling: Rough rolling is carried out in two stages. The rolling temperature at the beginning of the second stage is 1080-1100℃, and the single-pass reduction rate of the last two passes before the end of rolling is ≥14%. The rolling temperature at the beginning of the finishing stage is 855-885℃, the single-pass reduction rate of the first three passes of finishing rolling is ≥13%, and the finishing rolling temperature is 785-815℃.

[0020] (5) Accelerated cooling: Air cooling and water cooling are used for the initial cooling. The starting temperature for water cooling of the steel plate is 765-785℃, the cooling rate is 20-28℃ / s, and the final cooling temperature is 380-440℃.

[0021] Furthermore, the continuous casting process employs dynamic light reduction and electromagnetic stirring at the end of billet solidification, with a light reduction of 5–8 mm.

[0022] Furthermore, the time for the high-temperature heating section + the heat spread section is not less than 120 minutes, and the time for the heat spread section is not less than 50 minutes.

[0023] Furthermore, the microstructure control target obtained by the water-cooled accelerated cooling is fine-grained polygonal ferrite + acicular ferrite, with the volume fraction of polygonal ferrite being 40% to 60% and the average grain size being ≤8μm.

[0024] Furthermore, the thickness of the intermediate billet in the finishing rolling stage is 2.8 to 3.5t, where t is the thickness of the finished steel plate and t is 25 to 40 mm.

[0025] Furthermore, the total mass percentage of alloying elements in the steel plate does not exceed 2.5%.

[0026] Furthermore, the steel plate has a transverse yield strength of 476–540 MPa, a tensile strength of 540–640 MPa, and a strength reaching the X65 grade; the steel plate has an impact energy of ≥350 J at -30℃, a CTOD of ≥1.0 mm at -10℃, and a strength of 10 7 Cycle fatigue strength ≥350MPa, longitudinal elongation after fracture of steel plate 57%~68%, uniform elongation ≥12%.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1) This invention uses inexpensive elements such as C, Mn, Cr, and Cu, along with trace amounts of Nb and Ni elements. Through the interaction between these elements, and with appropriate heating, rolling, and cooling processes, a microstructure of fine-grained polygonal ferrite + acicular ferrite is finally obtained.

[0029] 2) The total content of alloying elements in this invention does not exceed 2.5%, which not only results in low alloy addition and low alloy cost, but also allows for targeted microstructure design to improve the plasticity and fatigue resistance of the steel plate. The microstructure type is significantly different from the existing X65 grade pipeline steel ferrite + granular bainite microstructure, which can ensure that the produced steel plate has good strength and toughness matching and excellent fatigue resistance.

[0030] 3) The steel plate possesses excellent comprehensive mechanical properties. Its transverse yield strength is 476–540 MPa, and its tensile strength is 540–640 MPa, reaching the X65 strength grade. The steel plate has an impact energy ≥350 J at -30℃, a CTOD ≥1.0 mm at -10℃, and a 10 7 The fatigue strength after each cycle is ≥350MPa, the longitudinal elongation after fracture of the steel plate is 57%~68%, the uniform elongation is ≥12%, and all properties meet the technical requirements for manufacturing X65 grade deep-water steel catenary risers. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of a typical metallographic structure according to an embodiment of the present invention. Detailed Implementation

[0032] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0033] This invention discloses a high-ductility, fatigue-resistant X65 grade steel plate for catenary risers. The chemical composition of the steel plate, by weight percentage, is as follows: C: 0.040%–0.060%, Si: 0.10%–0.20%, Mn: 1.50%–1.65%, P≤0.015%, S≤0.0015%, Cr≥0.10%, Cr+Ni: 0.22%–0.33%, Cu: ≤0.20%, Nb: 0.030%–0.050%, Ti: 0.010%–0.025%, Al: 0.026%–0.050%, with the balance being Fe and unavoidable impurities.

[0034] The rationale for the composition design of this invention is as follows:

[0035] C: The most basic and economical strengthening element in steel. Controlling the appropriate C content can not only ensure the strength of the steel plate, but also prevent the steel plate from segregating in the center and improve the corrosion resistance of the steel. Therefore, the range of C controlled in this invention is 0.040% to 0.060%.

[0036] Si: It can improve the strength of steel plates through solid solution strengthening and has the effect of improving the hardenability and corrosion resistance of materials. Among the alloying elements, Si is abundant and relatively inexpensive. Adding an appropriate amount of Si to steel can also inhibit the precipitation of cementite. At the same time, Si will accumulate around carbides, hindering the growth of carbides and promoting the carbides to become smaller and dispersed in the matrix, which is beneficial to improving strength. However, a high Si content makes steel prone to graphitization, which makes the steel brittle, reduces plasticity, and deteriorates toughness. Therefore, the Si content in this invention is controlled at 0.10% to 0.20%.

[0037] Mn is a common strengthening element in steel. It can be dissolved in large quantities in the Fe matrix to improve strength through solid solution strengthening. Manganese can reduce the critical cooling rate of steel, greatly improve hardenability, and significantly reduce the brittle transition temperature of steel, improve impact toughness, and refine the microstructure of steel. It is an important strengthening and toughening element. However, if the Mn content is too high, it is easy to form segregation in steel, which has an adverse effect on the plasticity, toughness and corrosion resistance of steel. Therefore, the present invention controls the Mn range to be 1.50% to 1.65%.

[0038] Cr and Ni can improve the hardenability of steel, enhance the cooling effect of thick-walled steel plates, improve the uniformity of microstructure in the thickness direction, and compensate for the strength loss caused by low C and low Mn content in steel plates. Cr alloys are inexpensive and can not only replace precious metal elements such as Mo and V that play a strengthening role to reduce alloy costs, but also, under similar content conditions, have a less strong inhibitory effect on ferrite transformation than Mo, and can more stably control the formation of polygonal ferrite in steel plates. However, high Cr content can make the hardenability of steel too high, forming too much hardened microstructure, which deteriorates the toughness and fatigue resistance of the steel plate. Ni can improve the strength of steel, lower the critical cooling temperature, delay the pearlite transformation, and is beneficial to microstructure control and grain refinement, improving low-temperature toughness and fatigue resistance. However, Ni is expensive and should not be added in excess. Therefore, this invention controls Cr ≥ 0.10%, and the range of Cr + Ni is 0.22% to 0.33%.

[0039] Cu can improve the strength of steel, compensate for the strength loss caused by low carbon content, and also increase the stability of austenite, improve the hardenability of steel plates, and improve the cooling effect of thick-walled steel plates. However, excessive Cu content can easily cause steel plates to become brittle and reduce toughness. Therefore, this invention controls the Cu content to not exceed 0.20%.

[0040] Nb: Grain refining element. When heated, undissolved Nb carbon and nitride particles are distributed on the austenite grain boundaries, which can hinder the growth of austenite grains in steel during heating. It can effectively delay the recrystallization of deformed austenite, prevent austenite grain growth, refine ferrite grains, improve the impact toughness of steel and reduce its brittle transition temperature. Therefore, the present invention controls the range of Nb to be 0.030% to 0.050%.

[0041] Ti is a strong solid nitrogen element. Adding trace amounts of Ti to Al steel can significantly reduce the corrosion rate. Ti can preferentially combine with N in the steel, reducing the amount of AlN in the steel and improving weldability. However, when the Ti content exceeds a certain value, TiN particles will coarsen, causing low-temperature toughness to deteriorate. Therefore, the present invention selects a Ti content of 0.010% to 0.025%.

[0042] Al: It is usually used as a deoxidizer in steel. If the aluminum content is too low, the deoxidation will be insufficient and easily oxidized elements such as Ti will form oxides. If the aluminum content is too high, the alumina inclusions will increase and the cleanliness of the steel will be reduced. Therefore, the present invention controls the range of Al to be 0.026% to 0.050%.

[0043] P and S: As impurity elements, phosphorus and sulfur significantly deteriorate the toughness, plasticity and weldability of steel, so their content in steel should be reduced as much as possible. Therefore, in this invention, the content of P and S is required to be controlled at P≤0.015% and S≤0.0015%, respectively.

[0044] A production method for high-ductility, high-toughness, and fatigue-resistant X65 grade steel plate for catenary risers includes smelting, continuous casting, heating, rolling, and accelerated cooling. Its purpose is to effectively improve the microstructure and grain size of the steel plate while obtaining ideal internal quality and reducing harmful elements and impurities. It relies on the process to refine and control the microstructure composition, ensuring the steel plate's excellent strength, toughness, and fatigue resistance.

[0045] (1) Smelting: The steelmaking process route of converter smelting and ladle refining is adopted. The RH vacuum treatment time is ≥25min. After the RH treatment, Ca treatment and micro-titanium treatment are carried out. The net circulation time is ≥10min, which effectively removes the gas in the molten steel and changes the morphology of non-metallic inclusions. At the same time, the inclusions and other impurities are fully floated to the surface, improving the cleanliness of the molten steel.

[0046] (2) Continuous casting: Controlling the superheat to 20-45℃ during continuous casting can maintain the fluidity of molten steel, continue to promote the floating of inclusions, and effectively control the size and quantity of inclusions in the steel. Dynamic light reduction and electromagnetic stirring at the end of billet solidification are adopted. The light reduction is 5-8mm, and the continuous casting billet pulling speed is controlled at 0.6-1.1m / min. Maintaining a constant pulling speed can reduce center segregation. By controlling inclusions and center segregation, the internal quality of the slab is improved, and the toughness and fatigue resistance of the steel are enhanced.

[0047] (3) Heating: A multi-stage stepped temperature heating method is adopted. The temperature of the high-temperature heating section is 1200~1240℃, the temperature of the soaking section is 1160~1200℃, the time of the high-temperature heating section + soaking section is not less than 120min, and the time of the soaking section is not less than 50min. The heating process is designed to ensure the solid solution of Mn, Cr, Ni, Cu and Nb elements so that they can play a role in the subsequent rolling and accelerated cooling. At the same time, it effectively controls the growth of austenite grains. The heating time can ensure the heating effect and temperature uniformity.

[0048] (4) Rolling: Steel plates are produced in medium and heavy plate mills. Rough rolling is carried out in two stages. The rolling temperature at the beginning of the second stage is 1080-1100℃. The single-pass reduction rate of the last two passes before the end of rolling is ≥14%, so that the original austenite grains are fully broken and refined. The thickness of the intermediate billet in the finishing rolling stage is 2.8-3.5t, where t is the thickness of the finished steel plate and t is 25-40mm. The starting rolling temperature of the finishing rolling stage is 855-885℃. The single-pass reduction rate of the first three passes of finishing rolling is ≥13%, and the final rolling temperature is 785-815℃. The design of the finishing rolling process can ensure that the austenite is fully flattened and deformed and accumulates deformation energy. On the other hand, it can promote the precipitation of fine Nb precipitates, pin grain boundaries and dislocations, increase nucleation sites, and further refine the grains.

[0049] (5) Accelerated Cooling: After rolling, the steel plate is air-cooled for a waiting period. The waiting time is aimed at ensuring the starting temperature of the water-cooled accelerated cooling is 765-785℃. The cooling rate of the water-cooled accelerated cooling is 20-28℃ / s, and the final cooling temperature is 380-440℃. The microstructure control target obtained by air cooling and water-cooled accelerated cooling is fine-grained polygonal ferrite + acicular ferrite, where the volume fraction of polygonal ferrite is 40%-60%, and the average grain size is ≤8μm. Compared with the existing X65 grade pipeline steel ferrite + granular bainite microstructure, the fine-grained polygonal ferrite in the final microstructure can play a good role in coordinating strain and improving the plasticity of the steel. The steel plate has a high strength and can effectively resist the traction and tension of the steel pipe caused by the movement of the floating body. Moreover, its internal dislocation density is not high, which can reduce the stress concentration caused by the periodic reciprocating deformation of the material, effectively resist fatigue crack initiation, and can also effectively absorb the energy of the crack after it is initiated and continues to propagate, thus hindering the further propagation of the crack and improving the crack arrest performance. The movable dislocation slip in the acicular ferrite and the irregular interlacing distribution of the acicular ferrite laths can not only improve the strength of the steel plate, but also, together with the polygonal ferrite, play a strong role in hindering the propagation of fatigue cracks, causing the fatigue crack to frequently turn, slowing down the fatigue crack propagation rate, and thus improving the fatigue resistance of the steel plate.

[0050] Furthermore, the total content of alloying elements in this invention does not exceed 2.5%, the steel plate has a transverse yield strength of 476-540 MPa, a tensile strength of 540-640 MPa, and a strength reaching X65 level; the steel plate has an impact energy of ≥350 J at -30℃, a CTOD of ≥1.0 mm at -10℃, and a strength of 10 7 Cycle fatigue strength ≥350MPa, longitudinal elongation after fracture of steel plate 57%~68%, uniform elongation ≥12%.

[0051] The following embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments. Unless otherwise specified, the methods used in the following embodiments are conventional methods.

[0052]

Example

[0053] The steel plate of the present invention is obtained by smelting according to the chemical composition range designed according to the present invention, and the chemical composition is shown in Table 1. The molten steel obtained is continuously cast-heated-rolled-accelerated cooled. The heating, rolling and cooling processes are shown in Tables 2-4.

[0054] Table 1. Chemical composition (wt%) of the steel in the embodiments of the present invention.

[0055] serial number C Si Mn P S Nb Cu Ni Cr Al Mo V Ti Example 1 0.057 0.12 1.53 0.010 0.0010 0.037 0.10 0 0.25 0.037 — — 0.021 Example 2 0.054 0.18 1.55 0.013 0.0015 0.040 0.12 0.08 0.14 0.050 — — 0.016 Example 3 0.060 0.14 1.50 0.015 0.0012 0.031 0 0.1 0.18 0.046 — — 0.012 Example 4 0.049 0.10 1.62 0.008 0.0007 0.045 0.20 0.15 0.12 0.031 — — 0.019 Example 5 0.052 0.17 1.60 0.007 0.0008 0.042 0.16 0.15 0.15 0.026 — — 0.025 Example 6 0.046 0.20 1.57 0.012 0.0014 0.034 0.04 0.2 0.1 0.034 — — 0.015 Example 7 0.050 0.15 1.59 0.009 0.0009 0.036 0.15 0.18 0.14 0.043 — — 0.010 Example 8 0.055 0.11 1.52 0.011 0.0011 0.039 0.02 0.17 0.11 0.048 — — 0.023 Example 9 0.043 0.16 1.65 0.014 0.0013 0.047 0.18 0.16 0.17 0.040 — — 0.018 Example 10 0.040 0.13 1.63 0.012 0.0010 0.050 0.07 0.13 0.2 0.028 — — 0.011 Comparative Example 1 0.046 0.15 1.18 0.013 0.0010 0.04 — 0.20 0.16 0.034 0.20 0.05 0.011 Comparative Example 2 0.021 0.10 1.45 0.010 0.0007 0.059 0.10 0.43 0.25 0.023 0.15 0.040 0.014 Comparative Example 3 0.05 0.20 1.70 ＜0.01 ＜0.003 0.05 0.15 — 0.20 0.020 0.15 — 0.01 Comparative Example 4 0.036 0.38 1.27 0.007 0.0011 0.051 0.18 0.14 0.13 0.020 0.17 0.02 0.019 Comparative Example 5 0.055 0.42 1.50 0.008 0.0016 0.066 0 0 0.22 0.018 0.25 0.01 0.016

[0056] Table 2. Steel smelting process in the embodiments of the present invention.

[0057]

[0058]

[0059] Table 3. Steel slab heating process in the embodiments of the present invention.

[0060]

[0061] Table 4. Rolling and accelerated cooling processes of steel in the embodiments of the present invention.

[0062]

[0063]

[0064] The mechanical properties and microstructure of the steel in the embodiments of the present invention were tested, and the results are shown in Tables 5-6. Figure 1 The tissue images show the tissue characteristics in Table 6.

[0065] Table 5 Tensile properties of steels in the embodiments of the present invention

[0066]

[0067] Table 6. Toughness, fatigue resistance, and microstructure characteristics of the steel in the embodiments of the present invention.

[0068]

[0069]

Claims

1. A high-ductility, high-toughness, fatigue-resistant X65 grade steel plate for catenary risers, characterized in that, The chemical composition of the steel plate, by weight percentage, is as follows: C: 0.040%~0.060%, Si: 0.10%~0.20%, Mn: 1.50%~1.65%, P≤0.015%, S≤0.0015%, Cr≥0.10%, Cr+Ni: 0.22%~0.33%, Cu: ≤0.20%, Nb: 0.030%~0.050%, Ti: 0.011%~0.025%, Al: 0.026%~0.050%, with the balance being Fe and unavoidable impurities; The method for producing the steel plate includes smelting, continuous casting, heating, rolling, and accelerated cooling, wherein: (1) Smelting: Converter smelting and ladle refining are adopted. The RH vacuum treatment time is ≥25min. After the RH treatment, Ca treatment and micro-titanium treatment are carried out. The net circulation time is ≥10min. (2) Continuous casting: control the superheat to 26-45℃ and control the continuous casting billet pulling speed to 0.6-1.1m / min; (3) Heating: The temperature of the high-temperature heating section is 1200~1240℃, and the temperature of the soaking section is 1160~1200℃; (4) Rolling: Rough rolling is carried out in two stages. The rolling temperature at the beginning of the second stage is 1080-1100℃, and the single-pass reduction rate of the last two passes before the end of rolling is ≥14%. The rolling temperature at the beginning of the finishing stage is 855-885℃, the single-pass reduction rate of the first three passes of finishing rolling is ≥13%, and the finishing rolling temperature is 785-815℃. (5) Accelerated cooling: Air cooling and water cooling are used for the initial cooling. The starting temperature of water cooling for the steel plate is 765-785℃, the cooling rate of water cooling is 20-28℃ / s, and the final cooling temperature is 395-440℃.

2. The high-ductility, high-toughness, fatigue-resistant X65 grade steel plate for catenary risers according to claim 1, characterized in that, The continuous casting process employs dynamic light reduction and electromagnetic stirring at the end of billet solidification, with a light reduction of 5–8 mm.

3. The high-ductility, high-toughness, fatigue-resistant X65 grade steel plate for catenary risers according to claim 1, characterized in that, The time for the high-temperature heating section plus the heat spread section shall not be less than 120 minutes, and the time for the heat spread section shall not be less than 50 minutes.

4. The high-ductility, high-toughness, fatigue-resistant X65 grade steel plate for catenary risers according to claim 1, characterized in that, The microstructure control target obtained by the water-cooled accelerated cooling is fine-grained polygonal ferrite + acicular ferrite, with the volume fraction of polygonal ferrite ranging from 44% to 60% and the average grain size from 6.3 to 8 μm.

5. The high-ductility, high-toughness, fatigue-resistant X65 grade steel plate for catenary risers according to claim 1, characterized in that, The thickness of the intermediate billet in the finishing rolling stage is 2.8 to 3.5t, where t is the thickness of the finished steel plate, which is 25 to 40 mm.

6. The high-ductility, high-toughness, fatigue-resistant X65 grade steel plate for catenary risers according to claim 1, characterized in that, The total mass percentage of alloying elements in the steel plate does not exceed 2.5%.

7. The high-ductility, high-toughness, fatigue-resistant X65 grade steel plate for catenary risers according to claim 1, characterized in that, The steel plate has a transverse yield strength of 476–540 MPa and a tensile strength of 540–640 MPa, reaching the X65 strength grade; the steel plate has an impact energy of ≥350 J at -30℃ and a CTOD of ≥1.0 mm at -10℃. 7 Cycle fatigue strength ≥350MPa, longitudinal elongation after fracture of steel plate 57%~68%, uniform elongation ≥12%.

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