A high-plasticity, toughness, and fatigue-resistant X60 grade catenary riser steel plate and its production method

Abstract

The present invention relates to a high-plasticity, toughness and fatigue-resistant X60 grade catenary riser steel plate and a production method thereof. The chemical composition of the steel plate is as follows by weight: C: 0.060% to 0.080%, Si: 0.10% to 0.20%, Mn: 1.30% to 1.45%, P≤0.015%, S≤0.0015%, Cr: 0.10% to 0.21%, Nb: 0.010% to 0.030%, Ti: 0.010% to 0.025%, Al: 0.026% to 0.050%, and the balance is Fe and inevitable impurities; using cheap elements such as C, Mn, Cr and trace amounts of Nb, through the interaction between the elements, and with appropriate heating, rolling and cooling processes, the final structure type of polygonal ferrite + acicular ferrite is obtained. The total content of alloy elements does not exceed 2%, the amount of alloy added is small, the alloy cost is low, the transverse yield strength of the steel plate is 415~475MPa, the tensile strength is 520~600MPa, and the strength reaches X60 level; the impact energy of the steel plate at -30℃ is ≥350J, the CTOD at -10℃ is ≥1.2mm, 10 7 The cyclic fatigue strength is ≥340MPa, the longitudinal elongation of the steel plate is 57% to 68%, and the uniform elongation is ≥13%.

Description

Technical Field

[0001] The present invention relates to the technical field of metal material production, and in particular to a high-plasticity, toughness, and fatigue-resistant X60-grade catenary riser steel plate and a production method thereof. Background Art

[0002] With the development of offshore oil and gas projects, the riser system has become a key equipment connecting the offshore platform with submarine oil and gas drilling and production. The steel catenary riser is a type of riser widely used in deepwater oil and gas development projects. It has great adaptability to the movement of the floating body and represents the technical development direction of the deep-sea platform riser. The high-pressure and low-temperature environment of the deep sea requires the steel catenary riser to have a good match between anti-crushing and high-strength and toughness. In addition, except for the bottom of the platform and the submarine wellhead, there is no fixed support in other parts of the riser. Therefore, the influence of the floating body movement of the offshore platform and the vortex-induced vibration in the deep-water high-velocity sea area on the steel catenary riser cannot be ignored. The floating body movement of the platform will cause overall traction and stretching in the longitudinal direction of the steel pipe, which requires the steel catenary riser to have excellent plasticity; and the vortex-induced vibration will cause periodic reciprocating motion to the steel pipe, which requires the steel catenary riser to have excellent fatigue resistance.

[0003] Patent application number 202010620828.2 discloses an extra-thick-wall 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. 04%-0.07%, V: 0.03%-0.05%, Ti: 0.01%-0.02%, Al: 0.01%-0.045%, and the rest are Fe and inevitable impurity elements; its chemical composition contains V and Mo elements, and the content of Ni element is high, which is significantly different from the composition design scheme of this patent, and the alloy cost is relatively high. In addition, the elongation (elongation after fracture) A50mm of the steel does not exceed 35%, and there is no mention of the fatigue resistance of the steel.

[0004] Patent application number 201410677813.4 discloses a super-thick, high-strength, high-toughness submarine pipeline steel for ultra-deep sea use and a manufacturing method thereof, wherein the chemical composition is as follows: 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%, and the balance is Fe and inevitable 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 high. At the same time, Ni and V are both precious alloy elements, and the alloy cost is high. In addition, the soaking temperature of the steel plate described in this patent is ≤1100°C, and the final cooling temperature is less than 300°C, which is different from the production process of the steel plate of this patent. In addition, there is no mention of the fatigue resistance of the steel.

[0005] Patent application number 202111179082.7 discloses an easy-to-weld, high-strength, toughness, low-yield ratio pipeline steel and its preparation method. Its chemical composition is: 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%, and the remainder is iron and other unavoidable impurities; its chemical composition contains 0.10%-0.20% of Mo element, 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. In addition, 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 and transportation pipeline steel and its production method, the chemical composition of which is: 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%, the balance being Fe and unavoidable impurities; compared with the present patent, its chemical composition contains 0.10%-0.19% of Mo, 0.16%-0.25% of Cu and 0.01%-0.04% of V. Not only is the composition design different, but Mo and V are both precious alloy elements, and the alloy cost is high.

[0007] Patent application number 202111194029.4 discloses heat-resistant and fatigue-resistant precipitation-strengthened pipeline steel and its production method, whose 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%, and the rest are Fe and inevitable impurities; compared with this patent, its chemical composition contains 0.16%-0.29% Mo and 0.01%-0.04% V elements, not only the composition design is different, but Mo and V are both precious alloy elements, and the alloy cost is high.

[0008] In summary, the current production of high-toughness steel plates for catenary risers mainly has the following problems.

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

[0010] 2) There is no mention of the fatigue resistance of steel, and no special design is made to improve the fatigue resistance of steel;

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

[0012] The present invention provides a high-plasticity, toughness and fatigue-resistant X60 grade catenary riser steel plate and its production method. The alloy addition amount is small, the alloy cost is low, and a targeted microstructure design is carried out to improve the plasticity and fatigue resistance of the steel plate. The produced steel plate has good strength and toughness matching and excellent fatigue resistance. The steel plate has excellent comprehensive mechanical properties, the transverse yield strength of the steel plate is 415-475MPa, the tensile strength is 520-600MPa, and the strength reaches X60 level; the steel plate has an impact energy of ≥350J at -30℃, CTOD ≥1.2mm at -10℃, and 10 7 The cyclic fatigue strength is ≥340MPa, the longitudinal elongation of the steel plate is 57% to 68%, and the uniform elongation is ≥13%. All performances meet the technical requirements for manufacturing X60-level deep-water steel catenary risers.

[0013] In order to achieve the above object, the present invention adopts the following technical solutions:

[0014] A high-plasticity, toughness, and fatigue-resistant X60-grade catenary riser steel plate has the following chemical compositions by weight: C: 0.060% to 0.080%, Si: 0.10% to 0.20%, Mn: 1.30% to 1.45%, P≤0.015%, S≤0.0015%, Cr: 0.10% to 0.21%, Nb: 0.010% to 0.030%, Ti: 0.010% to 0.025%, Al: 0.026% to 0.050%, and the balance being Fe and unavoidable impurities.

[0015] A method for producing high-plasticity, toughness, and fatigue-resistant X60 grade catenary riser steel plates, comprising smelting, continuous casting, heating, rolling, and accelerated cooling, wherein:

[0016] (1) Smelting: converter smelting and refining outside the furnace are adopted, RH vacuum treatment time is ≥25min, Ca treatment and micro-titanium treatment are carried out after RH treatment, and the net cycle time is ≥10min;

[0017] (2) Continuous casting: Control the superheat at 20-45°C, use dynamic soft reduction and electromagnetic stirring at the end of solidification of the ingot, and the soft reduction is 5-8 mm;

[0018] (3) Heating: A multi-stage stepped temperature heating method is adopted, wherein the high temperature heating section is at 1210-1250°C and the soaking section is at 1180-1220°C;

[0019] (4) Rolling: The reduction ratio of the last two passes of the rough rolling stage is ≥14%; the starting rolling temperature of the finishing rolling stage is 890-920°C, the reduction ratio of the first three passes of the finishing rolling is ≥13%, and the final rolling temperature is 820-850°C;

[0020] (5) Accelerated cooling: The starting cooling temperature of the steel plate for water-cooled accelerated cooling is 800-820°C, the cooling rate of water-cooled accelerated cooling is 10-18°C / s, and the final cooling temperature is 380-440°C.

[0021] Furthermore, during the continuous casting, the pulling speed of the continuous casting billet is controlled to be 0.6 to 1.1 m / min, and the pulling speed is kept constant.

[0022] Furthermore, the duration of the high-temperature heating section + soaking section is not less than 120 minutes, and the soaking section is not less than 50 minutes.

[0023] Furthermore, the microstructure control target obtained by the air cooling and water cooling accelerated cooling is polygonal ferrite + acicular ferrite, the volume fraction of the polygonal ferrite is 60% to 80%, and the average grain size is ≤10μm.

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

[0025] Furthermore, the total mass percentage of alloy elements in the steel plate does not exceed 2%.

[0026] Furthermore, the transverse yield strength of the steel plate is 415~475MPa, the tensile strength is 520~600MPa, and the strength reaches X60 level; the impact energy of the steel plate at -30℃ is ≥350J, the CTOD at -10℃ is ≥1.2mm, and the 7 The cyclic fatigue strength is ≥340MPa, the longitudinal elongation of the steel plate is 57% to 68%, and the uniform elongation is ≥13%.

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

[0028] 1) The present invention uses cheap elements such as C, Mn, Cr and a trace amount of Nb. Through the interaction between the elements and suitable heating, rolling and cooling processes, a polygonal ferrite + acicular ferrite structure is finally obtained;

[0029] 2) The total content of alloying elements in the present invention does not exceed 2%, which not only reduces the amount of alloy added and the alloy cost, but also provides a targeted microstructure design to improve the plasticity and fatigue resistance of the steel plate. The microstructure type is significantly different from the ferrite + pearlite structure of existing X60-grade pipeline steel, ensuring that the produced steel plate has a good balance of strength and toughness and excellent fatigue resistance.

[0030] 3) The steel plate has excellent comprehensive mechanical properties, with a transverse yield strength of 415-475 MPa, a tensile strength of 520-600 MPa, and a strength of X60 level; the steel plate has an impact energy of ≥350J at -30℃, a CTOD of ≥1.2mm at -10℃, and a 7 The cyclic fatigue strength is ≥340MPa, the longitudinal elongation of the steel plate is 57% to 68%, and the uniform elongation is ≥13%. All performances meet the technical requirements for manufacturing X60-level deep-water steel catenary risers. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of a typical metallographic structure of the embodiment of the present invention. DETAILED DESCRIPTION

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

[0033] The present invention discloses a high-plasticity, toughness and fatigue-resistant X60 grade catenary riser steel plate. The chemical composition of the steel plate is as follows by weight: C: 0.060%-0.080%, Si: 0.10%-0.20%, Mn: 1.30%-1.45%, P≤0.015%, S≤0.0015%, Cr: 0.10%-0.21%, Nb: 0.010%-0.030%, Ti: 0.010%-0.025%, Al: 0.026%-0.050%, and the balance is Fe and unavoidable impurities.

[0034] The composition design reasons of the present invention are 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 central segregation of the steel plate and improve the corrosion resistance of the steel. Therefore, the present invention controls the C content in the range of 0.060% to 0.080%.

[0036] Si: can improve the strength of steel plates through solid solution strengthening, and has the effect of improving the hardenability and corrosion resistance of the material. Among all alloying elements, Si is abundant in resources and relatively inexpensive. Adding an appropriate amount of Si to steel can also inhibit the precipitation of cementite. At the same time, Si will be enriched around carbides, hindering the growth of carbides, causing carbides to become small and dispersed in the matrix, which is beneficial to improving strength. However, a higher content of Si tends to graphitize steel, making the steel brittle, reducing plasticity, and worsening toughness. Therefore, the Si content of the present invention is controlled at 0.10% to 0.20%.

[0037] Mn: It is a common strengthening element in steel and can be dissolved in the Fe matrix in large quantities 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 the steel, which has an adverse effect on the plasticity, toughness and corrosion resistance of the steel. Therefore, the present invention controls the Mn range to 1.30% to 1.45%.

[0038] Cr: It can improve the hardenability of steel, enhance the cooling effect of thick-walled steel plates, improve the uniformity of the structure in the thickness direction, and compensate for the strength loss of the steel plates due to low C and low Mn. The price of Cr alloys is not high. It can not only replace precious metal elements such as Mo and V that have a strengthening effect, thereby reducing the alloy cost, but also has a less strong inhibitory effect on ferrite transformation than Mo under conditions of similar content. It can more stably control the formation of polygonal ferrite in the steel plates. However, a higher Cr content will make the hardenability of steel too high, form excessive hardenable structure, and deteriorate the toughness and fatigue resistance of the steel plates. Therefore, the present invention controls the Cr range to 0.10% to 0.21%.

[0039] Nb: A grain-refining element. Undissolved Nb carbon and nitride particles are distributed on the austenite grain boundaries during heating, hindering austenite grain growth during heating. This effectively delays the recrystallization of deformed austenite, prevents austenite grain growth, refines ferrite grains, improves the impact toughness of steel, and lowers its brittle transition temperature. Therefore, the present invention controls the Nb content within a range of 0.010% to 0.030%.

[0040] Ti: is a strong nitrogen-fixing element. Adding a trace amount of Ti to Al-containing steel can significantly reduce the corrosion rate. Ti can preferentially combine with nitrogen in the steel, reducing the amount of AlN in the steel and improving weldability. However, when the Ti content exceeds a certain value, the TiN particles will coarsen, causing the low-temperature toughness to deteriorate. Therefore, the Ti content in the present invention is selected to be 0.010% to 0.025%.

[0041] Al: Usually used as a deoxidizer in steel. If the aluminum content is too low, deoxidation is insufficient and easily oxidized elements such as Ti will form oxides. If the aluminum content is too high, aluminum oxide inclusions will increase, reducing the cleanliness of the steel. Therefore, the present invention controls the range of Al to 0.026% to 0.050%.

[0042] 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, the present invention requires that the P and S contents be controlled within the range of P≤0.015% and S≤0.0015%, respectively.

[0043] A production method for high-ductility, toughness, and fatigue-resistant X60-grade catenary riser steel plate includes smelting, continuous casting, heating, rolling, and accelerated cooling. The method aims to achieve ideal internal quality, reduce harmful elements and impurities, and effectively improve the steel plate's microstructure and grain size. Appropriate processes are used to refine and control the microstructure, ensuring the steel plate's excellent combined strength, toughness, and fatigue resistance. The method comprises:

[0044] (1) Smelting: The steelmaking process route of converter smelting and refining outside the furnace is adopted. The RH vacuum treatment time is ≥25min. After the RH treatment, Ca treatment and micro-titanium treatment are carried out. The net cycle time is ≥10min. This can effectively remove the gas in the molten steel and change the morphology of non-metallic inclusions. At the same time, impurities such as inclusions can be fully floated to improve the cleanliness of the molten steel.

[0045] (2) Continuous casting: During the continuous casting process, the superheat is controlled at 20-45°C to maintain the fluidity of the molten steel, continue to promote the floating of inclusions, and effectively control the size and number of inclusions in the steel. Dynamic light reduction and electromagnetic stirring at the end of solidification of the billet are used, with a light reduction of 5-8 mm. The continuous casting billet drawing speed is controlled at 0.6-1.1 m / min and kept constant. This 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.

[0046] (3) Heating: A multi-stage stepped temperature heating method is adopted, with the high-temperature heating section at 1210-1250°C, the soaking section at 1180-1220°C, the high-temperature heating section + soaking section time not less than 120 min, and the soaking section time not less than 50 min. The design of the heating process is mainly to ensure the solid solution of Mn, Cr, and Nb elements so that they can play a role in subsequent rolling and accelerated cooling, and at the same time, effectively control the growth of austenite grains; the heating time can ensure the heating effect and temperature uniformity.

[0047] (4) Rolling: Steel plates are produced by two-stage rolling in medium and thick plate mills. The single-pass reduction rate of the last two passes in the rough rolling stage 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, t is 25~40mm, the starting rolling temperature in the finishing rolling stage is 890~920℃, the single-pass reduction rate of the first three passes in the finishing rolling is ≥13%, and the final rolling temperature is 820~850℃. The design of the finishing rolling process can ensure that the austenite is fully flattened and deformed and accumulates deformation energy, and on the other hand, it can promote the induction precipitation of fine Nb precipitates, pinning grain boundaries and dislocations, increasing nucleation sites, and further refining grains.

[0048] (5) Accelerated cooling: After the steel plate is rolled, it is air-cooled to hold the temperature. The holding time is aimed at ensuring that the starting cooling temperature of the steel plate for water-cooled accelerated cooling is 800-820°C. The cooling rate of water-cooled accelerated cooling is 10-18°C / s, and the final cooling temperature is 380-440°C. The microstructure control target obtained by air-cooled holding and water-cooled accelerated cooling is polygonal ferrite + acicular ferrite, where the volume fraction of polygonal ferrite is 60%-80%, and the average grain size is ≤10μm. Compared with the existing X60 grade pipeline steel ferrite + pearlite structure, the fine-grained polygonal ferrite in the final structure can play a good role in coordinating strain and improve the plasticity of the steel. It can effectively cope with the traction and stretching of steel pipes caused by the movement of floating bodies; and 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 cracking, and at the same time effectively absorb the energy that continues to expand after the crack starts, hinder the further expansion of the crack, and improve the crack arrest performance; the movable dislocation slip in the acicular ferrite and the irregular staggered distribution of acicular ferrite laths can not only improve the strength of the steel plate, but also, together with the polygonal ferrite, have a strong hindering effect on the propagation of fatigue cracks, causing fatigue cracks to frequently turn, slowing down the fatigue crack growth rate, and thereby improving the fatigue resistance of the steel plate.

[0049] Furthermore, the total content of alloying elements in the present invention does not exceed 2%, the transverse yield strength of the steel plate is 415-475MPa, the tensile strength is 520-600MPa, and the strength reaches X60 level; the steel plate has an impact energy of ≥350J at -30℃, CTOD ≥1.2mm at -10℃, and 10 7 The cyclic fatigue strength is ≥340MPa, the longitudinal elongation of the steel plate is 57% to 68%, and the uniform elongation is ≥13%.

[0050] The following examples are implemented under the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operating processes, but the scope of protection of the present invention is not limited to the following examples. The methods used in the following examples are conventional methods unless otherwise specified.

[0051] [Example]

[0052] Smelting is carried out according to the chemical composition range designed by the present invention. The chemical composition is shown in Table 1. The obtained molten steel is subjected to continuous casting-heating-rolling-accelerated cooling to obtain the steel plate of the present invention. The heating, rolling and cooling processes are shown in Tables 2-4.

[0053] Table 1 Chemical composition of steel according to the present invention (wt%)

[0054]

[0055] Table 2 Smelting process of steel according to the present invention

[0056]

[0057]

[0058] Table 3 Slab heating process of steel according to the present invention

[0059] serial number Continuous casting slab thickness / mm High temperature section heating temperature / ℃ Soaking section temperature / ℃ High temperature heating section + soaking section time / min Soaking time / min Example 1 250 1222 1194 148 74 Example 2 250 1212 1180 152 88 Example 3 250 1238 1206 120 57 Example 4 300 1250 1212 133 65 Example 5 300 1243 1220 125 52 Example 6 300 1210 1188 143 79 Example 7 300 1233 1197 139 68 Example 8 300 1226 1215 122 60 Comparative Example 1 230 1200 1150-1180 60-100 — Comparative Example 2 — — 1085 — — Comparative Example 3 — — — — — Comparative Example 4 — — 1180 Soaking section 0.5min / mm Soaking section 0.5min / mm Comparative Example 5 — — 1193 Soaking section 0.5min / mm Soaking section 0.5min / mm

[0060] Table 4 Rolling and accelerated cooling process of steel according to the present invention

[0061]

[0062] The mechanical properties and microstructure characteristics of the steel in the embodiment of the present invention were tested, and the results are shown in Table 5-6. Figure 1 The tissue characteristics in Table 6 can be seen in the tissue pictures.

[0063] Table 5 Tensile properties of steel according to the present invention

[0064]

[0065]

[0066] Table 6 Toughness, fatigue resistance and microstructure characteristics of the steel according to the present invention

[0067]

Claims

1. A high-ductility, fatigue-resistant X60 grade steel plate for catenary risers, characterized in that: The chemical composition of the steel plate is as follows by weight: C: 0.060%-0.080%, Si: 0.10%-0.20%, Mn: 1.30%-1.45%, P≤0.015%, S≤0.0015%, Cr: 0.10%-0.21%, Nb: 0.010%-0.030%, Ti: 0.010%-0.025%, Al: 0.026%-0.050%, and the balance is Fe and unavoidable impurities; The production method of the high-plasticity, toughness and fatigue-resistant X60 grade catenary riser steel plate comprises smelting, continuous casting, heating, rolling and accelerated cooling, wherein: (1) Smelting: converter smelting and refining outside the furnace are adopted, RH vacuum treatment time is ≥25min, Ca treatment and micro-titanium treatment are carried out after RH treatment, and the net cycle time is ≥10min; (2) Continuous casting: Control the superheat at 20-45°C, use dynamic soft reduction and electromagnetic stirring at the end of solidification of the billet, and the soft reduction is 5-8 mm; (3) Heating: A multi-stage stepped temperature heating method is adopted, wherein the high temperature heating section temperature is 1210-1250°C, and the soaking section temperature is 1180-1220°C; (4) Rolling: The single pass reduction rate of the last two passes in the rough rolling stage is ≥14%; the starting rolling temperature in the finishing rolling stage is 890-920℃, the single pass reduction rate of the first three passes in the finishing rolling is ≥13%, and the final rolling temperature is 820-850℃; (5) Accelerated cooling: The starting cooling temperature of the steel plate for water-cooled accelerated cooling is 800-820°C, the cooling rate of water-cooled accelerated cooling is 10-18°C / s, and the final cooling temperature is 380-440°C.

2. The high plasticity, toughness and fatigue-resistant X60 grade catenary riser steel plate according to claim 1, characterized in that: During the continuous casting, the continuous casting billet pulling speed is controlled at 0.6-1.1 m / min to keep the pulling speed constant.

3. The high plasticity, toughness and fatigue-resistant X60 grade catenary riser steel plate according to claim 1, characterized in that: The time of the high temperature heating section + soaking section is not less than 120 minutes, and the time of the soaking section is not less than 50 minutes.

4. The high plasticity, toughness and fatigue-resistant X60 grade catenary riser steel plate according to claim 1, characterized in that: The microstructure control target obtained by the water-cooling accelerated cooling is polygonal ferrite + acicular ferrite, the volume fraction of the polygonal ferrite is 60% to 80%, and the average grain size is ≤10 μm.

5. The high plasticity, toughness and fatigue-resistant X60 grade catenary riser steel plate according to claim 1, characterized in that: The thickness of the intermediate billet in the finishing rolling stage is 2.8 to 3.5 t, wherein t is the thickness of the finished steel plate, which is 25 to 40 mm.

6. The high plasticity, toughness and fatigue-resistant X60 grade catenary riser steel plate according to claim 1, characterized in that: The total mass percentage of alloy elements in the steel plate does not exceed 2%.

7. The high plasticity, toughness and fatigue-resistant X60 grade catenary riser steel plate according to claim 1, characterized in that: The transverse yield strength of the steel plate is 415-475MPa, the tensile strength is 520-600MPa, and the strength reaches X60 level; the steel plate has an impact energy of ≥350J at -30℃, CTOD ≥1.2mm at -10℃, and a 7 The cyclic fatigue strength is ≥340MPa, the longitudinal elongation of the steel plate is 57% to 68%, and the uniform elongation is ≥13%.

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