Wide and thick steel plate for 550MPa-grade corrosion-resistant and anti-fatigue marine tendon pipe and production method of wide and thick steel plate

Abstract

The invention discloses a wide and thick steel plate for a 550MPa-grade corrosion-resistant anti-fatigue ocean tendon pipe and a production method of the wide and thick steel plate, the component design of the wide and thick steel plate enables CEIIW to be controlled to be 0.33-0.37% and CEPcm to be controlled to be 0.13-0.17%, the low-Nb and Mo-free design is adopted, the phase change temperature is increased, polygonal ferrite phase change is promoted, the tensile strength of the steel plate is improved, and the tensile strength of the steel plate is improved. The production methods of low-temperature heating, rough rolling multi-stage thickness section high-temperature gradient deformation and low-temperature rolling, intermediate temperature-waiting blank rapid cooling after rough rolling is finished, finish rolling low-temperature deformation, multi-stage water cooling and the like are combined to obtain a microstructure of granular bainite and polygonal ferrite, and the average deformation austenite height does not exceed 18 microns; the proportion, the size and the distribution of each phase are ideally controlled, and an important role is played for obtaining good comprehensive performance of the steel plate; the problem of matching of comprehensive technical characteristics such as high strength, high toughness, corrosion resistance, fatigue resistance and easy welding of the wide and thick steel plate for the ocean tendon pipe is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of low-alloy steel, and particularly relates to a wide and thick steel plate for marine tendon pipes with a yield strength of 550 MPa, a wall thickness of ≥30 mm, high toughness, corrosion resistance, fatigue resistance, and weldability, and a production method thereof, which is suitable for manufacturing high-performance marine platform tendon pipes; specifically, it is a wide and thick steel plate for marine tendon pipes with 550 MPa corrosion resistance and fatigue resistance and a production method thereof. Background Art

[0002] With the continuous increase in the demand for oil and natural gas, the development of marine oil and gas resources has attracted increasing attention. According to the analysis of international authoritative institutions, in the future global recoverable oil and gas reserves, marine oil and gas resources will account for about 63%, of which deep-sea oil and gas resources will account for 43%; the development of marine oil and gas resources has become the main economic growth point of the oil and gas industry. Therefore, there is an urgent need to develop key equipment and materials for marine, especially deep-sea oil and gas development.

[0003] Tendon pipes are the core components of marine platforms such as TLPs, which are used to connect the upper floating body of the platform and the subsea anchoring system. They are applied in water depths exceeding 1500 meters, with severe service conditions, and are subjected to the combined action of high water depth external pressure, fixed loads, marine environmental loads, working condition loads, and hydrostatic loads. They will also be corroded under marine and working conditions for a long time. Therefore, it is required that marine tendon pipes must have comprehensive properties such as high strength, high toughness, corrosion resistance, fatigue resistance, and weldability.

[0004] There have been some similar studies on the steel for marine tendon pipes in the prior art, but there are still some technical defect problems to be solved; for example, Patent CN109720514A, "A Tendon for a Tension Leg Floating Wind Turbine Platform", provides a structure and design of a telescopic tension tendon, but it does not involve the material for tendon pipes. Patent CN110106439A, "X65 Hot-Rolled Steel Plate for Marine Risers and Its Preparation Method", provides an X65-grade steel plate for marine risers, with relatively high Nb and Ni contents in the composition, resulting in high production and manufacturing costs. Patent CN116555670A, "A Steel for Anti-Fatigue Marine Risers and Its Preparation Method", provides a steel for marine risers, also with relatively high alloy contents, and requires the cumulative deformation in the last 2 - 3 passes of rough rolling to be greater than 50%. For wide and thick steel plates, it is difficult to achieve industrially and requires high equipment capabilities. Patent CN114763593A, "Steel for Marine Engineering with High Humid Heat Atmospheric Corrosion Resistance and Its Manufacturing Method", provides a steel for marine engineering, with a design of high Ni and Cr contents and a rolling + quenching and tempering process, resulting in high production costs and long manufacturing cycles. Patent CN113075064A, "Full-Size Fatigue Test Method for Welded Joints of Tension Leg Platform Tension Tendons", provides a fatigue test method for welded joints of tension tendons, but it does not involve the tendon pipe material itself.

[0005] In summary, the existing technology has deficiencies in the research on wide and thick steel plates for marine tendons, especially high-performance steel for marine platform tendons with comprehensive technical characteristics such as thick wall, high toughness, corrosion resistance, fatigue resistance, and weldability, and urgent improvement is needed. Summary of the Invention

[0006] In order to overcome the defects of the above-mentioned existing technology and solve the problem of matching comprehensive technical characteristics such as thick wall, high toughness, corrosion resistance, fatigue resistance, and weldability of wide and thick steel plates for marine tendons, the present invention provides a wide and thick steel plate for marine tendons with 550 MPa grade corrosion resistance and fatigue resistance and its production method to meet the technical requirements of high-performance steel for marine platform tendons.

[0007] In order to achieve the above-mentioned invention purpose, the present invention provides a wide and thick steel plate for marine tendons with 550 MPa grade corrosion resistance and fatigue resistance. The chemical composition of the wide and thick steel plate in weight percentage is: C: 0.040% - 0.070%, Si: 0.20% - 0.45%, Mn: 1.20% - 1.50%, Nb: 0.010% - 0.035%, Ti: 0.008% - 0.025%, Ti / N ≥ 3.42, Cr: 0.15% - 0.40%, Ni < 0.10%, Cu < 0.10%, (Cr + Ni + Cu): 0.20% - 0.50%, RE: 0.002% - 0.006%, Al: 0.020% - 0.045%, Ca: 0.0015% - 0.0045%, Ca / S ≥ 1.6, N: 0.002% - 0.007%, P ≤ 0.010%, S ≤ 0.002%, H ≤ 0.00015%, O ≤ 0.0012%, and the balance is iron and unavoidable impurities.

[0008] The CE of the wide and thick steel plate for marine tendons with 550 MPa grade corrosion resistance and fatigue resistance IIW is controlled within 0.33% - 0.37%, and CE Pcm is controlled within 0.13% - 0.17%;

[0009] Among them, CE IIW = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15;

[0010] CE Pcm = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15 + V / 10 + 5B; where each element symbol represents the weight percentage of the corresponding element.

[0011] The thickness of the above-mentioned 550 MPa grade corrosion-resistant and fatigue-resistant marine tendon steel plate is ≥ 30 mm. In the composition, a low-Nb and Mo-free design is adopted to increase the phase transformation temperature, promote the transformation of polygonal ferrite, and ensure its proportion in the microstructure. At the same time, the alloy economy is improved. Make full use of RE to play roles such as solid solution and interfacial segregation, improve strength, refine grains, reduce interfacial energy, and improve corrosion resistance. Moreover, it acts together with Ca to purify the molten steel and modify and disperse inclusions, reducing the adverse effects of inclusions on fatigue performance. By adding a small amount of Ni and Cu, the strength and toughness and corrosion resistance are improved. Use inexpensive Cr and Mn elements to ensure strength and improve the economy of the product. In addition, by reducing the contents of P, S, H, and O and controlling the quality of continuous casting billets, etc., the toughness, corrosion resistance, and fatigue resistance are improved; combined with production processes such as smelting, heating, rolling, and cooling that match the alloy composition, the steel plate obtains comprehensive technical characteristics such as high strength, high toughness, corrosion resistance, fatigue resistance, and weldability, as well as an ideal microstructure.

[0012] Reasons for the composition design of the present invention:

[0013] C is a basic element for increasing strength, with obvious effects on improving hardenability and tensile strength, and is also beneficial to the control of the yield ratio; however, too high carbon is adverse to plasticity, toughness, weldability, corrosion resistance, etc.; in the present invention, C is controlled at 0.040% - 0.070%.

[0014] Si can improve hardenability and strength. At the same time, too high Si content will increase M / A in the microstructure, reducing toughness and plasticity. In the present invention, its suitable range is 0.20% - 0.45%.

[0015] Mn can effectively improve strength and hardenability. At the same time, Mn can also reduce the phase transformation temperature, which is beneficial to grain refinement; moreover, the Mn element is inexpensive and can improve the economy of the product; but too high manganese content is prone to induce segregation, resulting in a reduction in corrosion resistance and fatigue resistance, etc. In the present invention, the Mn content is controlled at 1.20% - 1.50%.

[0016] Nb has a grain refinement effect, can improve strength and toughness, and can also form fine Nb(C, N) precipitates under appropriate processes to play the role of precipitation strengthening; however, too high Nb content, on the one hand, requires increasing the heating temperature of the continuous casting billet to ensure the solid solution effect, increasing energy consumption, and will inhibit the transformation of austenite to polygonal ferrite, increasing the control difficulty of polygonal ferrite in the microstructure; therefore, the Nb content is controlled at 0.010% - 0.035%.

[0017] Ti has a nitrogen-fixing effect, easily forms precipitation phases of Ti(C, N) with a relatively high solution temperature, inhibits the grain growth of austenite under high-temperature conditions; at the same time, Ti can also refine the welding structure, improve the toughness of the heat-affected zone after welding, and has the effect of fixing oxygen; however, too high Ti content will increase the size of the precipitates and reduce the beneficial effects. In the present invention, the Ti content is controlled at 0.008% - 0.025%, and Ti / N ≥ 3.42.

[0018] Cr can increase hardenability, improve the tensile strength, has a weak inhibition on the transformation from austenite to polygonal ferrite, is beneficial to increasing the "hardness difference" between soft / hard phases in the microstructure, and is beneficial to the control of the yield ratio; moreover, as an inexpensive element, Cr can replace precious alloy elements such as Mo, Ni, and Cu, effectively reducing the cost; however, too high Cr content will increase the sensitivity to welding cracks. Therefore, in the present invention, the Cr content is controlled at 0.15% - 0.40%.

[0019] Ni has a solution strengthening effect, is beneficial to improving toughness; can reduce the critical cooling rate and delay the pearlite transformation; can also reduce Cu brittleness and improve corrosion resistance; however, Ni has a relatively high price, and adding too much is not beneficial to economy; therefore, in the present invention, the Ni content is controlled below 0.10%.

[0020] Cu increases hardenability, increases the proportion and hardness of the hard phase structure, improves the tensile strength, and is also beneficial to corrosion resistance at the same time. However, too high Cu content is not beneficial to toughness. In the present invention, the Cu content is controlled below 0.10%.

[0021] (Cr + Ni + Cu) being controlled at 0.20% - 0.50% can ensure hardenability and strengthening effect, and at the same time, is beneficial to phase transformation and microstructure control.

[0022] RE: In the present invention, the RE element can effectively inhibit the diffusion of elements such as C, control phase transformation, and promote the transformation of medium-temperature structures; it is beneficial to increasing strength under solution conditions; when segregating at interfaces such as grain boundaries and phase boundaries, it will reduce the interface energy and corrosion sensitivity; it can also improve the density of the rust layer and reduce the corrosion rate. In addition, during the smelting process, it is beneficial to reduce, disperse, and spheroidize inclusions, improve the quality of the continuous casting billet, and reduce the adverse effects of inclusions on fatigue performance. In the present invention, RE is controlled at 0.002% - 0.006%.

[0023] Al has a strong affinity with O and N and is a deoxidizing element. However, too high Al content will promote the increase of inclusions. In the present invention, the Al content is controlled at 0.020% - 0.045%.

[0024] Ca and Ca / S can promote the modification and spheroidization of inclusions, effectively improve corrosion resistance, toughness, and fatigue performance. In the present invention, the Ca content is controlled at 0.0015% - 0.0045%, and Ca / S ≥ 1.6.

[0025] N can form fine precipitates with Nb and Ti to play the role of strengthening, fine grain and hydrogen trap, but too high N content deteriorates toughness and may also cause steel plate defects. In the present invention, the N content is controlled at 0.002% to 0.007%.

[0026] P and S are harmful impurity elements in the present invention; P will lead to reduced toughness, and the present invention controls P to ≤0.010%; an increase in S content will promote the formation and growth of inclusions, destroy the continuity of the matrix, and lead to a decrease in fatigue and corrosion resistance, so S≤0.002%.

[0027] Increased H and O contents will lead to decreased toughness and increased inclusions, affecting corrosion resistance, fatigue performance, etc. Therefore, the present invention controls H≤0.00015% and O≤0.0012%.

[0028] CE design of the composition of the wide and thick steel plate for 550MPa corrosion-resistant and fatigue-resistant marine tendon tubes in this technical solution IIW Controlled at 0.33% to 0.37%, CE Pcm Controlling it within 0.13% to 0.17% can not only meet the strength and toughness requirements of the steel plate, but also reduce the tendency of welding cracking, making the steel plate have good weldability.

[0029] A method for producing the above-mentioned 550MPa grade corrosion-resistant and fatigue-resistant wide and thick steel plate for marine tendon tubes, the production method comprising the following process steps: converter smelting, refining outside the furnace, continuous casting, rolling and cooling;

[0030] Among them, the converter tapping temperature is ≤1650℃, C≤0.045%;

[0031] After refining and deoxidation, Ti is added first, and then RE is added; the cooling time of molten steel before loading on the machine is ≥10min, the pouring superheat of continuous casting billet is 10℃~40℃, the average residence time of molten steel in the tundish during pouring is ≥360s, and the dynamic soft reduction of the casting billet is ≥4mm;

[0032] The continuous casting billet adopts multi-stage heating of preheating, heating and soaking, with a total heating time of 1.0-1.8min / mm and a furnace temperature of 1120℃-1170℃;

[0033] Rough rolling includes three stages: rough rolling stage 1, intermediate cooling, and rough rolling stage 2. The rough rolling start temperature is 1070℃~1130℃, and the rough rolling final temperature is 970℃~1030℃.

[0034] The deformation rate in the finishing rolling stage is 60% to 75%, the starting temperature of the finishing rolling is 800°C to 850°C, and the final rolling temperature of the finishing rolling is 750°C to 790°C;

[0035] The rolled steel plate is pre-straightened and then cooled in two stages.

[0036] In the above technical solution, further, for slag splashing tapping of the converter, the thickness of the slag layer is ≤ 35 mm, lime and fluorite are added to make the top slag according to the mass ratio of 4 / 1 to 5 / 1, and the weight percentage of FeO + MnO in the slag is controlled to be ≤ 1%.

[0037] Further, continuous casting is carried out at a constant casting speed, the casting speed control range is 0.6 - 1.2 m / min, the center segregation of the continuous casting billet is ≤ C0.5 grade, the center porosity is ≤ 0.5 grade, and the inclusions of types A / B / C / D are controlled within grade 1.

[0038] Low-carbon, low-temperature, and slag splashing tapping of the converter can effectively control the carbon content of the final product, ensure the dephosphorization effect, and reduce rephosphorization and resulfurization; making white slag and controlling FeO + MnO in the slag can ensure the reduction ability of the slag, fully desulfurize, reduce inclusions, and improve cleanliness; the addition sequence of Ti and RE after refining deoxidation can more effectively improve the recovery rate and efficiency of the corresponding elements; the control of the steel water's tranquility before being fed into the machine, the pouring superheat, and the residence time in the tundish can homogenize the steel water temperature, effectively promote the floating and removal of inclusions; the dynamic soft reduction and the control of the continuous casting billet casting speed can effectively improve the quality of the casting billet, reduce defects such as cracks and segregation. The control of center segregation, center porosity, and inclusions is an effective guarantee for the quality of the continuous casting billet and the performance of the steel plate.

[0039] In the above technical solution, further, the continuous casting billet is heated in multiple stages including preheating, heating, and soaking, the total heating time is 1.1 - 1.7 min / mm, and the tapping temperature is 1130°C - 1160°C. The multi-stage heating of the continuous casting billet and the control of the total heating time are beneficial to improving the heating efficiency and uniformity; since the Nb content in the present invention is low, low-temperature heating and tapping can meet the need for element solution, and at the same time, it can effectively reduce the austenite grain size, and is more conducive to reducing the rough rolling temperature and reducing the rolling time in the rough rolling stage, realizing high-efficiency low-temperature rolling.

[0040] In the above technical solution, further, in the three stages of the first roughing stage, intermediate cooling, and the second roughing stage of rough rolling, the last 2-3 passes of the first roughing stage, intermediate cooling, and the second roughing stage all adopt rapid spray water cooling; the starting temperature of the second roughing stage is below 1050 °C, the total deformation rate is ≥30%, the deformation rate of each pass is ≥15% and increases gradually from pass to pass, and the rough rolling speed is 1.0 m / s - 1.8 m / s. The rough rolling of this technical solution mainly adopts the process of low-temperature rolling + high temperature gradient deformation of the thickness section. Due to the low Nb content in the component design of the present invention, the austenite recrystallization temperature is reduced; therefore, low-temperature rolling and other methods are adopted in the rough rolling stage to recrystallize austenite grains and effectively inhibit grain growth; through multi-stage rapid cooling, the temperature gradient of the thickness section is significantly increased, and the low-temperature and low-speed rolling in the second roughing stage is combined to promote the penetration of rolling deformation into the center of the slab thickness, refine the structure near the center of the thickness, and improve the uniformity of the steel plate structure performance; the gradually increasing deformation rate in the second roughing stage can promote the full recrystallization of austenite.

[0041] In the above technical solution, further, the deformation rate in the finishing rolling stage is 60% - 70%. After rough rolling, the intermediate waiting billet is rapidly cooled to 850 °C - 900 °C, and the average cooling speed is ≥2 °C / s. Then, it is waited until the starting temperature of finishing rolling. The starting temperature of finishing rolling is 800 °C - 850 °C, the final rolling temperature of finishing rolling is 750 °C - 790 °C. After the rolled steel plate is pre-straightened, it is cooled in two stages. The starting water cooling temperature is 720 °C - 760 °C, and the ending water cooling temperature is 300 °C - 450 °C. During water cooling, the water volume of the first 5 - 7 groups of upper headers is 350 - 550 L / m 2 ·min, and the water volume of the remaining upper headers is 150 - 300 L / m 2 ·min. The deformation rate in the finishing rolling stage can ensure the deformation and flattening of austenite in the non-recrystallized zone; the rapid cooling of the intermediate waiting billet after rough rolling can quickly reduce the temperature to 30 °C - 60 °C higher than the starting temperature of finishing rolling, effectively inhibiting the growth of austenite; the low-temperature rolling in the finishing rolling stage is beneficial to the formation of substructures in the microstructure and the accumulation of deformation energy, promoting phase transformation nucleation and refining grains; the pre-straightening of the rolled steel plate is beneficial to improving the cooling uniformity of water cooling and ensuring the shape of the steel plate; the control of the starting water cooling temperature can ensure the formation of part of the polygonal ferrite soft phase structure before accelerating water cooling; the use of a lower final cooling temperature can promote the formation of a high-hardness structure mainly composed of granular bainite; the use of a segmented water cooling process with fast cooling at the front and slow cooling at the back can, on the one hand, increase the cooling speed in the high-temperature section and inhibit high-temperature phase transformation; at the same time, the smaller cooling water volume in the low-temperature section can reduce the internal stress and improve the shape of the steel plate after cooling.

[0042] The wide and thick steel plate for corrosion-resistant and fatigue-resistant marine tendon pipes with a strength level of 550 MPa prepared by the above production method has a microstructure of granular bainite + polygonal ferrite, wherein the volume percentage of polygonal ferrite is 10% - 60%, and the average height of deformed austenite does not exceed 18 μm. The steel plate has comprehensive technical characteristics such as high strength, high toughness, corrosion resistance, fatigue resistance, and easy weldability, and can meet the requirements for manufacturing high-performance marine platform tendon pipes.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] ① In the composition of the present invention, a design with low Nb and no Mo is adopted to increase the phase transformation temperature, promote the phase transformation of polygonal ferrite, and ensure its proportion in the microstructure. At the same time, the alloy economy is improved. The full use of RE plays roles such as solid solution and interfacial segregation, improves strength, refines grains, reduces the interfacial energy, and improves corrosion resistance. Moreover, it acts together with Ca to purify the molten steel and modify and disperse inclusions, reducing the adverse effects of inclusions on fatigue performance. By adding a small amount of Ni and Cu, the strength and toughness and corrosion resistance are improved; the use of inexpensive Cr and Mn elements ensures strength and improves the economy of the product. In addition, by reducing the contents of P, S, H, and O and controlling the quality of continuous casting billets, etc., the toughness, corrosion resistance, and fatigue resistance are improved; the production processes such as smelting, heating, rolling, and cooling that match the alloy composition solve the problem of matching the comprehensive technical characteristics such as high strength, high toughness, corrosion resistance, fatigue resistance, and easy weldability of the wide and thick steel plate for marine tendon pipes.

[0045] ② On the basis of the composition design of the present invention, production methods such as low-temperature heating, multi-stage high-temperature gradient deformation of the thickness section in rough rolling + low-temperature rolling, rapid cooling of the intermediate waiting billet after rough rolling, low-temperature deformation in finish rolling, and multi-stage water cooling are adopted to obtain a microstructure of granular bainite + polygonal ferrite, and the average height of deformed austenite does not exceed 18 μm. The proportion, size, and distribution of each phase are ideally controlled, which plays an important role in obtaining good comprehensive properties of the steel plate.

[0046] ③ The thickness of the wide and thick steel plate for corrosion-resistant and fatigue-resistant marine tendon pipes with a strength level of 550 MPa according to the present invention is ≥ 30 mm, the transverse yield strength can reach 470 - 540 MPa, the transverse tensile strength reaches 580 - 650 MPa, the transverse yield ratio < 0.89, the average value of the transverse impact energy at -60 °C ≥ 250 J, the average value of the transverse impact energy in the heat-affected zone of welding at -20 °C ≥ 200 J, the transverse CTOD at -20 °C ≥ 0.7 mm, the transverse DWTT shear area at -20 °C ≥ 85%; the longitudinal yield strength can reach 450 - 530 MPa, the longitudinal tensile strength reaches 560 - 630 MPa, the longitudinal yield ratio < 0.89, 7 The fatigue strength for 10 2The S solution immersion does not cause fracture and there are no visible cracks under 10 - fold magnification; the fabricated marine tendon pipes meet the requirements of 550 MPa grade. Brief Description of the Drawings

[0047] Figure 1 It is the microstructure diagram of the wide and thick steel plate for 550 MPa grade corrosion - resistant and fatigue - resistant marine tendon pipes prepared in Example 1. Detailed Description of the Invention

[0048] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited in any way. To avoid repetition, in the following embodiments, the raw materials are all commercially available products unless otherwise specified, and the methods used are all conventional methods unless otherwise specified.

[0049] For the wide and thick steel plate for 550 MPa grade corrosion - resistant and fatigue - resistant marine tendon pipes, the chemical composition of the wide and thick steel plate by weight percentage is: C: 0.040% - 0.070%, Si: 0.20% - 0.45%, Mn: 1.20% - 1.50%, Nb: 0.010% - 0.035%, Ti: 0.008% - 0.025%, Ti / N≥3.42, Cr: 0.15% - 0.40%, Ni<0.10%, Cu<0.10%, (Cr + Ni + Cu): 0.20% - 0.50%, RE: 0.002% - 0.006%, Al: 0.020% - 0.045%, Ca: 0.0015% - 0.0045%, Ca / S≥1.6, N: 0.002% - 0.007%, P≤0.010%, S≤0.002%, H≤0.00015%, O≤0.0012%, and the balance is iron and unavoidable impurities.

[0050] The CE of the wide and thick steel plate for 550 MPa grade corrosion - resistant and fatigue - resistant marine tendon pipes IIW is controlled within 0.33% - 0.37%, and CE Pcm is controlled within 0.13% - 0.17%.

[0051] Among them, CE IIW = C + Mn / 6+(Cr + Mo + V) / 5+(Ni + Cu) / 15;

[0052] CE Pcm = C + Si / 30+(Mn + Cu + Cr) / 20+Ni / 60+Mo / 15+V / 10+5B; where each element symbol represents the weight percentage of the corresponding element.

[0053] A production method of the wide and thick steel plate for 550 MPa grade corrosion - resistant and fatigue - resistant marine tendon pipes as described above, the production method includes the following technological steps: converter smelting, secondary refining, continuous casting, rolling, and cooling, etc.

[0054] Among them, the tapping temperature of the converter is ≤1650°C, and C is ≤0.045%;

[0055] After refining and deoxidation, Ti is added first, and then RE is added; the ladle calming time before the molten steel is fed into the machine is ≥10 minutes, the casting superheat of the continuous casting billet is 10°C to 40°C, the average residence time of the molten steel in the tundish during casting is ≥360 s, and the dynamic soft reduction of the billet is ≥4 mm;

[0056] The continuous casting billet is heated in multiple stages of preheating, heating, and soaking, with a total heating time of 1.0 to 1.8 min / mm and an outlet temperature of 1120°C to 1170°C;

[0057] Rough rolling includes three stages: rough rolling stage 1, intermediate cooling, and rough rolling stage 2. The rough rolling starting temperature is 1070°C to 1130°C, and the rough rolling finishing temperature is 970°C to 1030°C. Among them, in the last 2 - 3 passes of rough rolling stage 1, intermediate cooling, and rough rolling stage 2, rapid spray water cooling is used;

[0058] The deformation rate in the finish rolling stage is 60% to 75%. After rough rolling, the intermediate waiting billet is rapidly cooled to 850°C to 900°C, with an average cooling rate of ≥2°C / s. The finish rolling starting temperature is 800°C to 850°C, and the finish rolling finishing temperature is 750°C to 790°C;

[0059] After pre - straightening the rolled steel plate, two - stage cooling is carried out.

[0060] For those not described in the following examples, they are the same as the description content of the above - mentioned specific implementation manners.

[0061] Example

[0062] 550 MPa - grade corrosion - resistant and fatigue - resistant marine tendon steel plates with wide and thick cross - sections and their production methods. The chemical compositions of the wide and thick steel plates in Examples 1 to 8 are shown in Table 1.

[0063] Table 1 Chemical compositions of the wide and thick steel plates in Examples 1 to 8 wt%

[0064]

[0065]

[0066] The smelting and refining process parameters of the production methods of the wide and thick steel plates in Examples 1 to 8 are shown in Table 2. The tapping temperature of the converter is ≤1650°C, and C is ≤0.045%; slag - tapping is carried out, the thickness of the slag layer is ≤35 mm, lime and fluorite are added to make the top - slag in a mass ratio of 4 / 1 to 5 / 1, and the weight percentage of FeO + MnO in the slag is controlled to be ≤1%.

[0067] Table 2 Smelting and refining process parameters of Examples 1 to 8

[0068]

[0069] For the continuous casting process parameters of the production methods of heavy and wide steel plates in Examples 1 to 8, as shown in Table 3, the ladle calming time before the molten steel is fed into the machine is ≥10 min, the superheat of the continuous casting billet during pouring is 10°C to 40°C, the average residence time of the molten steel in the tundish during pouring is ≥360 s, and the dynamic soft reduction of the billet is ≥4 mm; continuous casting is carried out at a constant casting speed, and the casting speed control range is 0.6 to 1.2 m / min. The center segregation of the continuous casting billet is ≤ Grade C0.5, the center porosity is ≤ Grade 0.5, and the inclusions of types A / B / C / D are controlled within Grade 1.

[0070] Table 3 Continuous casting process parameters of Examples 1 to 8

[0071]

[0072]

[0073] For the heating and rough rolling process control parameters of the continuous casting billets of the production methods of heavy and wide steel plates in Examples 1 to 8, see Table 4. The continuous casting billets are heated in multiple stages of preheating, heating, and soaking, with a total heating time of 1.0 to 1.8 min / mm and an out-of-furnace temperature of 1120°C to 1170°C; the rough rolling starting temperature is 1070°C to 1130°C, and the rough rolling finishing temperature is 970°C to 1030°C; the starting temperature of the second stage of rough rolling is below 1050°C, the total reduction rate is ≥30%, the reduction rate of each pass is ≥15% and increases gradually, and the rough rolling speed is 1.0 m / s to 1.8 m / s.

[0074] Table 4 Heating and rough rolling process parameters of the continuous casting billets of Examples 1 to 8

[0075]

[0076] For the finish rolling and cooling process parameters of the production methods of heavy and wide steel plates in Examples 1 to 8, see Table 5. The reduction rate in the finish rolling stage is 60% to 75%. After rough rolling, the intermediate waiting-temperature billet is quickly cooled to 850°C to 900°C, with an average cooling rate of ≥2°C / s. Then, it is waited at temperature until the finish rolling starting temperature. The finish rolling starting temperature is 800°C to 850°C, the finish rolling finishing temperature is 750°C to 790°C. After the rolled steel plate is pre-straightened, it is cooled in two stages. The starting water cooling temperature is 720°C to 760°C, the water cooling ending temperature is 300°C to 450°C. During water cooling, the water volume of the first 5 to 7 groups of upper headers is 350 to 550 L / m 2 ·min, and the water volume of the remaining upper headers is 150 to 300 L / m 2 ·min.

[0077] Table 5 Finish rolling and cooling process of the examples

[0078]

[0079] The statistical results of the microstructure of the 550 MPa grade corrosion-resistant and fatigue-resistant marine tendon steel plates with wide and thick thickness prepared in Examples 1 to 8 are shown in Table 6. The microstructure is granular bainite + polygonal ferrite (such as Figure 1 the microstructure of the product prepared in Example 1 shown), among which, the volume percentage of polygonal ferrite is 10% - 60%, and the average height of deformed austenite does not exceed 18 μm.

[0080] Table 6 Statistical results of the microstructure of Examples 1 to 8

[0081] Example Volume percentage of polygonal ferrite / % Average height of deformed austenite / μm 1 18 13.8 2 52 14.5 3 21 14.0 4 47 13.7 5 15 13.1 6 50 13.6 7 36 12.8 8 24 13.5

[0082] The mechanical property test results of the 550 MPa grade corrosion-resistant and fatigue-resistant marine tendon steel plates with wide and thick thickness prepared in Examples 1 to 8 are shown in Table 7. The thickness ≥ 30 mm, the transverse yield strength can reach 470 - 540 MPa, the transverse tensile strength reaches 580 - 650 MPa, the transverse yield ratio < 0.89, the average - 60 °C transverse impact energy ≥ 250 J, the average - 20 °C transverse impact energy in the heat affected zone of welding ≥ 200 J, - 20 °C transverse CTOD ≥ 0.7 mm, - 20 °C transverse DWTT shear area ≥ 85%; the longitudinal yield strength can reach 450 - 530 MPa, the longitudinal tensile strength reaches 560 - 630 MPa, the longitudinal yield ratio < 0.89, 10 7 cycle fatigue strength ≥ 310 MPa.

[0083] Table 7 Mechanical property test results of the products prepared in Examples 1 to 8

[0084]

[0085] The corrosion resistance test results of the 550 MPa grade corrosion-resistant and fatigue-resistant marine tendon steel plates with wide and thick thickness prepared in Examples 1 to 8 are shown in Table 8. The anti-SSCC corrosion performance meets the requirements that no fracture occurs after being soaked in saturated H 2 S solution for 720 h under 72% stress loading condition and no visible cracks are observed under 10-fold magnification.

[0086] Table 8 Corrosion resistance test results of the products prepared in Examples 1 to 8

[0087]

[0088] It can be illustrated by Examples 1 to 8 that the present invention adopts a low Nb and Mo-free composition design, raises the phase transformation temperature, promotes the phase transformation of polygonal ferrite, and obtains a microstructure of granular bainite + polygonal ferrite by matching a specific production method. The average height of deformed austenite does not exceed 18 μm, and the proportion, size and distribution of each phase are ideally controlled, which plays an important role in the steel plate obtaining good comprehensive properties.

[0089] For any person skilled in the art, without departing from the scope of the technical solution of the present invention, many possible changes and modifications can be made to the technical solution of the present invention by using the technical content disclosed above, or it can be modified into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. 550MPa grade corrosion-resistant and fatigue-resistant wide and thick steel plate for marine tendon tubes, characterized by: The chemical composition weight percentage of the wide and thick steel plate is C: 0.040% to 0.070%, Si: 0.20% to 0.45%, Mn: 1.20% to 1.50%, Nb: 0.010% to 0.035%, Ti: 0.008% to 0.025%, Ti / N≥3.42, Cr: 0.15% to 0.40%, Ni<0.10%, Cu<0.10%, (Cr+Ni +Cu): 0.20% ~ 0.50%, RE: 0.002% ~ 0.006%, Al: 0.020% ~ 0.045%, Ca: 0.0015% ~ 0.0045%, Ca / S ≥ 1.6, N: 0.002% ~ 0.007%, P ≤ 0.010%, S ≤ 0.002%, H ≤ 0.00015%, O ≤ 0.0012%, the balance is iron and unavoidable impurities.

2. The 550MPa grade corrosion-resistant and fatigue-resistant wide and thick steel plate for marine tendon tubes according to claim 1 is characterized in that: The wide and thick steel plate CE for marine tendon tube IIW Controlled at 0.33% to 0.37%, CE Pcm Controlled at 0.13% to 0.17%; Among them, CE IIW =C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15; CE Pcm =C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B; wherein the symbol of each element represents the weight percentage of the corresponding element.

3. The 550MPa grade corrosion-resistant and fatigue-resistant wide and thick steel plate for marine tendon tubes according to claim 1 is characterized in that: The thickness of the wide and thick steel plate is ≥30mm, the transverse yield strength is 470-540MPa, the transverse tensile strength is 580-650MPa, the transverse yield strength ratio is <0.89, the average transverse impact energy at -60°C is ≥250J, the average transverse impact energy at -20°C of the welding heat affected zone is ≥200J, the transverse CTOD at -20°C is ≥0.7mm, and the transverse DWTT shear area at -20°C is ≥85%; the longitudinal yield strength is 450-530MPa, the longitudinal tensile strength is 560-630MPa, the longitudinal yield strength ratio is <0.89, 10 7 The cyclic fatigue strength is ≥310MPa; the SSCC corrosion resistance meets the requirements of no fracture after 720h immersion in saturated H2S solution under 72% stress loading conditions and no visible cracks under 10x magnification observation.

4. The 550MPa grade corrosion-resistant and fatigue-resistant wide and thick steel plate for marine tendon tubes according to claim 1 is characterized in that: The microstructure of the wide and thick steel plate is granular bainite+polygonal ferrite, wherein the volume percentage of the polygonal ferrite is 10% to 60%, and the height of the deformed austenite does not exceed 18 μm on average.

5. A method for producing a 550MPa grade corrosion-resistant and fatigue-resistant wide and thick steel plate for marine tendon tubes as claimed in any one of claims 1 to 4, characterized in that: The production method comprises the following process steps: converter smelting, refining outside the furnace, continuous casting, rolling and cooling; Among them, the converter tapping temperature is ≤1650℃, C≤0.045%; After refining and deoxidation, Ti is added first, and then RE is added; the cooling time of molten steel before loading on the machine is ≥10min, the pouring superheat of continuous casting billet is 10℃~40℃, the average residence time of molten steel in the tundish during pouring is ≥360s, and the dynamic soft reduction of the casting billet is ≥4mm; The continuous casting billet adopts multi-stage heating of preheating, heating and soaking, with a total heating time of 1.0-1.8min / mm and a furnace temperature of 1120℃-1170℃; Rough rolling includes three stages: rough rolling stage 1, intermediate cooling and rough rolling stage 2. The starting temperature of rough rolling is 1070℃~1130℃, and the final temperature of rough rolling is 970℃~1030℃. The last 2~3 passes of rough rolling stage 1, intermediate cooling and rough rolling stage 2 are all cooled by rapid spray water. The deformation rate in the finishing rolling stage is 60% to 75%. After the rough rolling is completed, the intermediate warm billet is quickly cooled to 850°C to 900°C, with an average cooling rate of ≥2°C / s. Then, the billet is heated to the finishing rolling start temperature, the finishing rolling start temperature is 800°C to 850°C, and the finishing rolling final rolling temperature is 750°C to 790°C. The rolled steel plate is pre-straightened and then cooled in two stages.

6. The production method according to claim 5, characterized in that The converter is slag-blocking for tapping, with a slag layer thickness of ≤35mm. Lime and fluorite are added in a mass ratio of 4 / 1 to 5 / 1 to form top slag, and the weight percentage of FeO+MnO in the slag is controlled to be ≤1%.

7. The production method according to claim 5, characterized in that: The continuous casting adopts a constant pulling speed, the pulling speed control range is 0.6-1.2 m / min, the center segregation of the continuous casting billet is ≤C0.5 level, the center looseness is ≤0.5 level, and A / B / C / D type inclusions are controlled within 1 level.

8. The production method according to claim 5, characterized in that: The starting temperature of the second stage of rough rolling is below 1050° C., the total deformation rate is ≥30%, the deformation rate of each pass is ≥15% and increases gradually, and the rough rolling speed is 1.0-1.8 m / s.

9. The production method according to claim 5, characterized in that: The water cooling temperature at the start of the two-stage cooling is 720°C to 760°C, and the water cooling end temperature is 300°C to 450°C; the water volume of the first 5 to 7 groups of upper headers during water cooling is 350 to 550 L / m 2 ·min, the water volume of other upper headers is 150~300L / m 2 ·min.

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