Wide and thick steel plate for 700MPa-grade corrosion-resistant 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 700MPa-grade corrosion-resistant anti-fatigue marine tendon pipe and a production method of the wide and thick steel plate. According to the component design of the wide and thick steel plate, CEIIW is controlled to be 0.41-0.47%, CEPcm is controlled to be 0.16-0.20%, low-Nb and low-Mo design is adopted, the phase change temperature is increased, and phase change of polygonal ferrite is promoted; rE solid solution, interface segregation and other effects are fully utilized to improve the strength and corrosion resistance, and the RE and Ca act together to purify molten steel and modify and disperse inclusions. On the basis of component design, 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 other methods are adopted to obtain a microstructure of lath bainite, granular bainite and polygonal ferrite, and the proportion, size and distribution control of all phases is ideal; the method plays an important role in obtaining good comprehensive performance of the steel plate.

Description

Technical Field

[0001] The present invention belongs to the technical field of low alloy steel, and in particular relates to a 700MPa grade thick-walled, high-toughness, corrosion-resistant, fatigue-resistant, easy-to-weld wide and thick steel plate for marine tendon tubes with a thickness of ≥30mm and a production method thereof, which is suitable for making high-performance marine platform tendon tubes; specifically, a 700MPa grade corrosion-resistant and fatigue-resistant wide and thick steel plate for marine tendon tubes and a production method thereof. Background Art

[0002] As the demand for oil and natural gas continues to increase, the development of marine oil and gas resources has received increasing attention. According to analysis by international authoritative organizations, marine oil and gas resources will account for about 63% of the world's recoverable oil and gas reserves in the future, 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, it is urgent to develop key equipment and materials for marine, especially deep-sea oil and gas development.

[0003] Tendon tubes are core components of TLP and other offshore platforms, used to connect the upper buoy of the platform and the seabed anchoring system. The maximum water depth of application exceeds 1,500 meters. The service conditions are harsh, and they are subjected to the coupling of high-depth external pressure, fixed loads, marine environmental loads, operating loads and fluid static loads. They are also subject to long-term corrosion under marine and operating conditions. Therefore, the marine tendon tubes must have comprehensive properties such as high strength, high toughness, corrosion resistance, fatigue resistance and easy welding.

[0004] There have been some similar studies on steel for marine tendon tubes in the prior art, but the relevant technologies still have defects. For example, patent CN109720514A "Tendons for tension leg floating wind power platform" provides a structure and design of telescopic tension tendons, but it does not involve tendon tube materials. Patent CN110106439A "X65 hot-rolled steel plate for marine risers and preparation method thereof" provides an X65-grade marine riser steel plate, which uses a high content of Nb and Ni in the composition, resulting in high production and manufacturing costs. Patent CN116555670A "A fatigue-resistant marine riser steel and preparation method thereof" provides a marine riser steel, which also has a high alloy content, and requires the cumulative deformation of the last 2 to 3 passes of rough rolling to be greater than 50%. For wide and thick steel plates, industrialization is difficult to achieve and requires high equipment capabilities. Patent CN114763593 A "Marine engineering steel with high humidity and heat atmospheric corrosion resistance and its manufacturing method" provides a marine engineering steel, which adopts high Ni and Cr content design and rolling + tempering process, with high production cost and long manufacturing cycle. Patent CN113075064A "A full-scale fatigue test method for tension leg platform tension tendon welded joint" provides a fatigue test method for tension tendon welded joint, but it does not involve the tendon tube material itself.

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

[0006] In order to overcome the defects of the above-mentioned existing technology and solve the problem of matching the 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 700MPa-class corrosion-resistant and fatigue-resistant marine tendons 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 700MPa-class corrosion-resistant and fatigue-resistant marine tendons. The chemical composition of the wide and thick steel plate by weight percentage is: C: 0.035% - 0.065%, Si: 0.20% - 0.45%, Mn: 1.65% - 1.80%, Nb: 0.010% - 0.035%, Ti: 0.008% - 0.025%, Ti / N ≥ 3.42, Ni: 0.01% - 0.20%, Cu: 0.01% - 0.20%, Cr: 0.20% - 0.50%, Mo: 0.01% - 0.15%, (Cr + Ni + Cu + Mo): 0.40% - 0.85%, RE: 0.003% - 0.007%, Al: 0.020% - 0.045%, Ca: 0.0015% - 0.0040%, 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 inevitable impurities.

[0008] The CE of the wide and thick steel plate for 700MPa-class corrosion-resistant and fatigue-resistant marine tendons IIW is controlled within 0.41% - 0.47%, and CE Pcm is controlled within 0.16% - 0.20%;

[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 heavy plate for 700MPa corrosion-resistant and fatigue-resistant marine tendon pipes is ≥30mm. In the composition, low Nb and low Mo designs are adopted to increase the phase transformation temperature, promote the transformation of polygonal ferrite, ensure its proportion in the microstructure, and improve the alloy economy. Make full use of RE to play roles such as solid solution and interfacial segregation, increase strength, refine grains, reduce interfacial energy, and improve corrosion resistance. Moreover, it works together with Ca to play the roles of purifying molten steel and modifying and dispersing 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, and its effects of improving hardenability and tensile strength are obvious, and it is also beneficial to the control of the yield ratio; however, too high carbon content is adverse to plasticity, toughness, weldability, corrosion resistance, etc.; in the present invention, the C content is controlled at 0.035% - 0.065%.

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

[0015] Mn can effectively increase 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 1.65% - 1.80%.

[0016] Nb has a grain refinement effect, can increase strength and toughness, and can also form fine Nb(C, N) precipitates under appropriate processes to play precipitation strengthening; but 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 the effect of fixing nitrogen, and it is easy to form precipitation phases of Ti(C, N) with a relatively high solution temperature, which inhibits the grain growth of austenite under high-temperature conditions; at the same time, Ti can also refine the welding structure and improve the toughness of the heat-affected zone after welding; moreover, it has the effect of fixing oxygen; however, if the Ti content is too high, the size of the precipitates will increase and the beneficial effects will decrease. In the present invention, the Ti content is controlled at 0.008% - 0.025%, and Ti / N ≥ 3.42.

[0018] Ni has a solution strengthening effect, which is beneficial to improving toughness; it can reduce the critical cooling rate and delay the pearlite transformation; it can also reduce Cu brittleness and improve corrosion resistance; however, the price of Ni is relatively high, and adding too much is not beneficial to economy; therefore, in the present invention, the Ni content is controlled at 0.01% - 0.20%.

[0019] Cu improves hardenability, increases the proportion and hardness of the hard phase structure, and improves the tensile strength. At the same time, it is beneficial to corrosion resistance, but too high a Cu content is not beneficial to toughness. In the present invention, the Cu content is controlled at 0.01% - 0.20%.

[0020] Cr can increase hardenability and improve the tensile strength. It has a weak inhibition on the transformation of austenite to polygonal ferrite, which is beneficial to increasing the "hardness difference" between the 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 a Cr content will increase the sensitivity to welding cracks. Therefore, in the present invention, the Cr content is controlled at 0.20% - 0.50%.

[0021] Mo can improve hardenability, promote the transformation of medium and low-temperature structures, has a certain grain refinement effect, and can effectively reduce the phase transformation temperature; however, Mo will inhibit the formation of polygonal ferrite and also lead to an increase in cost. Therefore, in the present invention, the Mo content is controlled at 0.01% - 0.15%.

[0022] (Cr + Ni + Cu + Mo) is controlled at 0.40% - 0.85%, which can ensure hardenability and strengthening effects, and is beneficial to phase transformation and microstructure control.

[0023] 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 the reduction, dispersion, and spheroidization of inclusions, improving the quality of the continuous casting billet and reducing the adverse effects of inclusions on fatigue performance. In the present invention, the RE content is controlled at 0.003% - 0.007%.

[0024] Al has a strong affinity with O and N and is a deoxidizing element. However, too high an Al content will promote the increase of inclusions. In the present invention, the Al content is controlled within a range of 0.020% to 0.045%.

[0025] Ca and Ca / S can promote inclusion modification and spheroidization, effectively improving corrosion resistance, toughness and fatigue resistance. The Ca content of the present invention is controlled at 0.0015% to 0.0040%, and Ca / S is ≥1.6.

[0026] 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%.

[0027] 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 is controlled to ≤0.002%.

[0028] 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%.

[0029] CE design of the composition of the wide and thick steel plate for 700MPa corrosion-resistant and fatigue-resistant marine tendon tubes in this technical solution IIW Controlled at 0.41%~0.47%, CE Pcm Controlling it within 0.16% to 0.20% 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.

[0030] A method for producing the above-mentioned 700MPa 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;

[0031] Among them, the converter tapping temperature is ≤1640℃, C≤0.040%;

[0032] 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;

[0033] 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℃-1180℃;

[0034] The rough rolling process includes three stages: the first stage of rough rolling, intermediate cooling, and the second stage of rough rolling. The starting rolling temperature for rough rolling is 1090°C to 1150°C, and the final rolling temperature for rough rolling is 970°C to 1030°C;

[0035] The deformation rate in the finish rolling stage is 60% to 80%. The starting rolling temperature for finish rolling is 800°C to 850°C, and the final rolling temperature for finish rolling is 750°C to 790°C;

[0036] After pre-straightening the rolled steel plate, two-stage cooling is carried out.

[0037] In the above technical solution, further, during tapping from the converter with slag blocking, the thickness of the slag layer is ≤ 35 mm. Lime and fluorite are added to make the top slag according to a mass ratio of 4 / 1 to 5 / 1, and the weight percentage of FeO + MnO in the slag is controlled to be ≤ 1%.

[0038] Further, 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 central segregation of the continuous casting billet is ≤ C0.5 level, the central porosity is ≤ 0.5 level, and the control of A / B / C / D type inclusions is within level 1.

[0039] Low-carbon, low-temperature tapping from the converter with slag blocking 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 pre-sedimentation before being fed into the rolling mill, pouring superheat, and residence time in the tundish can equalize the steel water temperature, effectively promote the floating and removal of inclusions; the control of dynamic soft reduction and the casting speed of the continuous casting billet can effectively improve the quality of the casting billet, reduce defects such as cracks and segregation. The control of central segregation, central porosity, and inclusions is an effective guarantee for the quality of the continuous casting billet and the performance of the steel plate.

[0040] 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 1.2 to 1.6 min / mm, and the furnace outlet temperature is 1140°C to 1170°C. The control of the continuous casting billet's multi-stage heating and the total heating time is beneficial to improving the heating efficiency and uniformity; due to the low Nb content in the present invention, low-temperature heating and furnace outlet can meet the need for element solid solution, effectively reduce the austenite grain size, and is more conducive to reducing the rough rolling temperature, shortening the rolling time in the rough rolling stage, and realizing high-efficiency low-temperature rolling.

[0041] In the above technical solution, further, in the three stages of the first rough rolling stage, intermediate cooling, and the second rough rolling stage of rough rolling, the last 2-3 passes of the first rough rolling stage, intermediate cooling, and the second rough rolling stage all adopt rapid spray water cooling; the starting temperature of the second rough rolling 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 key of rough rolling in this technical solution adopts the process of low-temperature rolling + high temperature gradient deformation of the thickness section. Due to the low Nb content 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 rough rolling stage is combined to promote the penetration of rolling deformation to the thickness center of the slab, refine the structure near the thickness center, and improve the uniformity of the steel plate structure performance; adopting a gradually increasing deformation rate in the second rough rolling stage can promote the full recrystallization of austenite.

[0042] In the above technical solution, further, the deformation rate in the finish rolling stage is 65% - 75%. After rough rolling, the intermediate waiting billet is rapidly cooled to 860 °C - 900 °C, and the average cooling speed is ≥ 2 °C / s, and then it is waited until the start rolling temperature of finish rolling. The start rolling temperature of finish rolling is 800 °C - 850 °C, the finish rolling temperature of finish rolling is 750 °C - 790 °C. After the rolled steel plate is pre-straightened, two-stage cooling is carried out. The starting water cooling temperature is 720 °C - 760 °C, the ending water cooling temperature is 250 °C - 350 °C. When water cooling, the water volume of the first 5 - 7 groups of upper headers is 400 - 550 L / m 2 ·min, and the water volume of the remaining upper headers is 200 - 350 L / m 2 ·min. The deformation rate in the finish 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 - 70 °C higher than the start rolling temperature of finish rolling, effectively inhibiting the growth of austenite; adopting low-temperature rolling in the finish 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; pre-straightening the rolled steel plate is beneficial to improving the cooling uniformity of water cooling and ensuring the shape of the steel plate; controlling the starting water cooling temperature can ensure the formation of some polygonal ferrite soft phase structures before accelerating water cooling; adopting a lower final cooling temperature can promote the formation of high-hardness structures mainly composed of granular bainite and acicular ferrite; adopting the segmented water cooling process with fast first and slow later 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.

[0043] The wide and thick steel plate for 700 MPa - grade corrosion - resistant and fatigue - resistant marine tendon pipes prepared by the above production method has a microstructure of lath bainite + granular bainite + polygonal ferrite. Among them, the volume percentage of polygonal ferrite is 5% - 50%, 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, meeting the requirements for manufacturing high - performance marine platform tendon pipes.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0045] ① In the composition of the present invention, low - Nb and low - Mo designs are adopted to increase the phase transformation temperature, promote the phase transformation of polygonal ferrite, ensure its proportion in the microstructure, and at the same time improve the alloy economy. Make full use of RE to play roles such as solid solution and interfacial segregation, increase strength, refine grains, reduce interfacial energy, and improve corrosion resistance. Moreover, jointly with Ca, it plays a role in purifying molten steel and modifying and dispersing 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 problem of matching 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 is solved.

[0046] ② Based on the composition design of the present invention, production methods such as low - temperature heating, multi - stage thickness - section high - temperature - gradient deformation in rough rolling + low - temperature rolling, rapid cooling of the intermediate waiting - temperature billet after rough rolling, low - temperature deformation in finish rolling, and multi - stage water cooling are adopted to obtain a microstructure of lath bainite + granular bainite + polygonal ferrite, with the average height of deformed austenite not exceeding 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.

[0047] ③ The thickness of the wide and thick steel plate for 700 MPa - grade corrosion - resistant and fatigue - resistant marine tendon pipes described in the present invention is ≥ 30 mm. The transverse yield strength can reach 530 - 620 MPa, the transverse tensile strength reaches 720 - 770 MPa, the transverse yield - strength ratio < 0.85, the average - value of - 60 °C transverse impact energy ≥ 270 J, the average - value of - 20 °C transverse impact energy in the heat - affected zone of welding ≥ 200 J, - 20 °C transverse CTOD ≥ 0.7 mm, and the - 20 °C transverse DWTT shear area ≥ 85%; the longitudinal yield strength can reach 510 - 590 MPa, the longitudinal tensile strength reaches 700 - 760 MPa, the longitudinal yield - strength ratio < 0.83, 10 7The weekly fatigue strength is ≥370 MPa; the anti-SSCC corrosion performance meets the requirement that no fracture occurs after being immersed in a saturated H2S solution for 720 hours under 72% stress loading conditions, and no visible cracks are observed under 10-fold magnification; the fabricated marine tendon pipe meets the 700 MPa grade requirement. Description of the Drawings

[0048] Figure 1 It is the microstructure diagram of the wide and thick steel plate for 700 MPa grade corrosion-resistant and fatigue-resistant marine tendon pipes prepared in Example 1. Detailed Embodiments

[0049] 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, raw materials are commercially available products unless otherwise specified, and the methods used are conventional methods unless otherwise specified. The tensile specimen for the mechanical properties of the fabricated product is a full-thickness rectangular specimen, and the width of the parallel test section is 38.1 mm; the size of the impact specimen is 10*55*55 mm.

[0050] For the wide and thick steel plate for 700 MPa grade corrosion-resistant and fatigue-resistant marine tendon pipes, the chemical composition of the wide and thick steel plate is by weight percentage: C: 0.035% - 0.065%, Si: 0.20% - 0.45%, Mn: 1.65% - 1.80%, Nb: 0.010% - 0.035%, Ti: 0.008% - 0.025%, Ti / N ≥ 3.42, Ni: 0.01% - 0.20%, Cu: 0.01% - 0.20%, Cr: 0.20% - 0.50%, Mo: 0.01% - 0.15%, (Cr + Ni + Cu + Mo): 0.40% - 0.85%, RE: 0.003% - 0.007%, Al: 0.020% - 0.045%, Ca: 0.0015% - 0.0040%, 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.

[0051] The CE of the wide and thick steel plate for 700 MPa grade corrosion-resistant and fatigue-resistant marine tendon pipes IIW is controlled within 0.41% - 0.47%, and the CE Pcm is controlled within 0.16% - 0.20%.

[0052] Among them, CE IIW = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15;

[0053] CE Pcm= C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15 + V / 10 + 5B; where the symbols of each element represent the weight percentage of the corresponding element.

[0054] A production method of a wide and thick steel plate for 700MPa grade corrosion-resistant and fatigue-resistant marine tendon pipes, the production method comprising the following process steps: converter smelting, secondary refining, continuous casting, rolling and cooling, etc.;

[0055] Among them, the tapping temperature of the converter ≤ 1640°C, C ≤ 0.040%;

[0056] After refining and deoxidation, Ti is added first, and then RE; the holding time before the molten steel is fed into the machine ≥ 10 min, the superheat of the continuous casting billet during casting is 10°C - 40°C, the average residence time of the molten steel in the tundish during casting ≥ 360 s, and the dynamic soft reduction of the billet ≥ 4 mm;

[0057] The continuous casting billet is heated in multiple stages of preheating, heating, and soaking, with a total heating time of 1.0 - 1.8 min / mm and an out-of-furnace temperature of 1120°C - 1180°C;

[0058] The rough rolling includes three stages: rough rolling stage 1, intermediate cooling, and rough rolling stage 2. The rough rolling starting temperature is 1090°C - 1150°C, and the rough rolling finishing temperature is 970°C - 1030°C. Among them, the last 2 - 3 passes of rough rolling stage 1, intermediate cooling, and rough rolling stage 2 all use rapid spray water cooling;

[0059] The deformation rate in the finish rolling stage is 60% - 80%. After the rough rolling is completed, the intermediate waiting billet is quickly cooled to 860°C - 900°C, with an average cooling rate ≥ 2°C / s. Then, it is held at the finish rolling starting temperature. The finish rolling starting temperature is 800°C - 850°C, and the finish rolling finishing temperature is 750°C - 790°C;

[0060] After the rolled steel plate is pre-straightened, it is cooled in two stages.

[0061] For those not described in the following examples, they are the same as the description content of the above specific implementation manners.

[0062] Example

[0063] A wide and thick steel plate for 700MPa grade corrosion-resistant and fatigue-resistant marine tendon pipes and its production method. The chemical compositions of the wide and thick steel plates in Examples 1 - 8 are shown in Table 1.

[0064] Table 1 Chemical composition table of wide and thick steel plates in Examples 1 - 8 wt%

[0065]

[0066]

[0067] For the smelting and refining process parameters of the production methods of heavy and wide steel plates in Examples 1 to 8, as shown in Table 2, the tapping temperature of the converter is ≤1640 °C, and C is ≤0.040%; slag tapping is carried out during tapping, the thickness of the slag layer is ≤35 mm, lime and fluorite are added in a mass ratio of 4 / 1 to 5 / 1 to make the top slag, and the weight percentage of FeO + MnO in the slag is controlled to be ≤1%.

[0068] Table 2 Smelting and refining process parameters of Examples 1 to 8

[0069]

[0070] 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 standing time before the molten steel is fed into the machine is ≥10 min, the superheat of the continuous casting billet during casting 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; continuous casting adopts 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 ≤0.5 grade, and the control of A / B / C / D type inclusions is within Grade 1.

[0071] Table 3 Continuous casting process parameters of Examples 1 to 8

[0072]

[0073] For the control parameters of the heating and rough rolling of the continuous casting billets in 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 including 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 1180 °C; the rough rolling starting temperature is 1090 °C to 1150 °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 deformation rate is ≥30%, the deformation 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 continuous casting billets in Examples 1 to 8

[0075]

[0076] For the finishing rolling and cooling process parameters of the production methods of heavy and wide steel plates in Examples 1 to 8, see Table 5. The deformation rate in the finishing rolling stage is 60% to 80%. After rough rolling, the intermediate waiting billet is quickly cooled to 860 °C to 900 °C, and the average cooling speed is ≥2 °C / s. Then, it is waited until the finishing rolling starting temperature. The finishing rolling starting temperature is 800 °C to 850 °C, the finishing 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 end temperature is 250 °C to 350 °C, and the water volume of the first 5 to 7 groups of upper headers during water cooling is 400 to 550 L / m2 ·min, and the water volume of the remaining upper header is 200 - 350 L / m 2 ·min.

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

[0078]

[0079] The statistical results of the microstructure of the heavy plate for 700 MPa - grade corrosion - resistant and fatigue - resistant marine tendon pipes prepared in Examples 1 - 8 are shown in Table 6. The microstructure of the heavy plate is lath bainite + granular bainite + polygonal ferrite (such as the microstructure of the product prepared in Example 1 shown Figure 1 ). Among them, the volume percentage of polygonal ferrite is 5% - 50%, and the average height of deformed austenite does not exceed 18 μm.

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

[0081] Embodiment Volume percentage of polygonal ferrite / % Average height of deformed austenite / μm 1 18 12.9 2 30 13.6 3 26 12.7 4 36 13.9 5 12 13.1 6 42 14.0 7 45 12.5 8 28 13.3

[0082] The mechanical property test results of the heavy plate for 700 MPa - grade corrosion - resistant and fatigue - resistant marine tendon pipes prepared in Examples 1 - 8 are shown in Table 7. The thickness of the heavy plate is ≥30 mm, the transverse yield strength is 530 - 620 MPa, the transverse tensile strength is 720 - 770 MPa, the transverse yield ratio is <0.85, the average value of transverse impact energy at - 60 °C is ≥270 J, the average value of transverse impact energy in the heat - affected zone of welding at - 20 °C is ≥200 J, the transverse CTOD at - 20 °C is ≥0.7 mm, and the transverse DWTT shear area at - 20 °C is ≥85%; the longitudinal yield strength is 510 - 590 MPa, the longitudinal tensile strength is 700 - 760 MPa, the longitudinal yield ratio is <0.83, and the fatigue strength after 10 7 cycle times is ≥370 MPa.

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

[0084]

[0085] The corrosion - resistance test results of the heavy plate for 700 MPa - grade corrosion - resistant and fatigue - resistant marine tendon pipes prepared in Examples 1 - 8 are shown in Table 8. The anti - SSCC corrosion performance meets the requirements that no fracture occurs after being soaked in a saturated H2S solution for 720 hours under a 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 - 8

[0087]

[0088]

[0089] Examples 1 to 8 can illustrate that: in the components of the present invention, a design with low Nb and low Mo is adopted to increase the phase transformation temperature, promote the transformation of polygonal ferrite, ensure its proportion in the microstructure, and improve the alloy economy at the same time; make full use of RE to play roles such as solid solution and interfacial segregation, increase strength, refine grains, reduce the interfacial energy, improve corrosion resistance, and jointly act with Ca to play the roles of purifying molten steel and modifying and dispersing 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. On the basis of the composition design, production methods such as low-temperature heating, multi-stage thickness-section high-temperature gradient deformation + low-temperature rolling in rough 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 lath bainite + granular bainite + polygonal ferrite. 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 obtaining good comprehensive properties of the steel plate.

[0090] 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 modified into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still be within the scope of protection of the technical solution of the present invention.

Claims

1. 700MPa 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: 0.035% to 0.065%, Si: 0.20% to 0.45%, Mn: 1.65% to 1.80%, Nb: 0.010% to 0.035%, Ti: 0.008% to 0.025%, Ti / N ≥ 3.42, Ni: 0.01% to 0.20%, Cu: 0.01% to 0.20%, Cr: 0.20% to 0.50%, Mo: 0.01% to 0.15%, (Cr+Ni+Cu+Mo): 0.40%~0.85%, RE: 0.003%~0.007%, Al: 0.020%~0.045%, Ca: 0.0015%~0.0040%, 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 700MPa 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 0.41%~0.47%, CE Pcm Controlled at 0.16% to 0.20%; 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 700MPa 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 530-620MPa, the transverse tensile strength is 720-770MPa, the transverse yield strength ratio is <0.85, the average transverse impact energy at -60°C is ≥270J, 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 510-590MPa, the longitudinal tensile strength is 700-760MPa, the longitudinal yield strength ratio is <0.83, 10 7 The cyclic fatigue strength is ≥370MPa; the SSCC corrosion resistance meets the requirements of no fracture after 720 hours of immersion in saturated H2S solution under 72% stress loading conditions and no visible cracks under 10 times magnification observation.

4. The 700MPa 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 lath bainite+granular bainite+polygonal ferrite, wherein the volume percentage of polygonal ferrite is 5% to 50%, and the average height of deformed austenite does not exceed 18 μm.

5. A method for producing a 700MPa 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 ≤1640℃, C≤0.040%; 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℃-1180℃; Rough rolling includes three stages: rough rolling stage 1, intermediate cooling and rough rolling stage 2. The starting temperature of rough rolling is 1090℃~1150℃, 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 80%. After the rough rolling is completed, the intermediate warm billet is quickly cooled to 860°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 250°C to 350°C; the water volume of the first 5 to 7 groups of upper headers during water cooling is 400 to 550 L / m 2 ·min, the water volume of other upper headers is 200~350L / m 2 ·min.

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