Wide and thick steel plate for 700MPa-grade high-performance marine riser and production method thereof

Abstract

The invention discloses a wide and thick steel plate for a 700MPa-grade high-performance marine riser 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 0.39%-0.47%, and CEPcm is controlled to be 0.16%-0.20%; phase transformation of polygonal ferrite before accelerated cooling is promoted through the design of low Nb, Mo and Mn; the beneficial effects on strengthening, phase change, microstructure, steel plate performance and post-welding performance are achieved through Mo and Cr compound control, Nb, V and N compound adding and the like. On the basis of component design, 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 adopted to obtain polygonal ferrite and batten bainite, and a microstructure of a small amount of granular bainite can also be included; the average height of deformed austenite does not exceed 15 microns, and the proportion of each phase and the size and distribution of precipitated phases are ideal to control.

Description

Technical Field

[0001] The present invention belongs to the technical field of low alloy steel, and in particular relates to a 700MPa grade steel plate for offshore oil and gas production riser with a thickness of ≥25mm, high toughness, high fatigue resistance, corrosion resistance, strain resistance and good welding performance, and a production method thereof, which is suitable for manufacturing high-performance offshore oil and gas production straight seam welded risers; specifically, a 700MPa grade wide and thick steel plate for high-performance offshore risers and a production method thereof. Background Art

[0002] With the growth of energy demand in human economic and social activities, the demand for oil and natural gas continues to increase. Relying solely on land oil and gas resources can no longer meet the corresponding demand. Therefore, the development of marine oil and gas resources has received increasing attention. According to the analysis of 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] The riser system is the connection channel between the offshore oil and gas platform and the underwater production system, and plays a vital role in marine oil and gas development. Steel marine risers have gradually become the preferred riser form for marine oil and gas development due to their simple structure and high economy. Risers serve in the marine environment for a long time, with low service temperature. They are subject to complex loads generated by ocean currents, surges, platform movement, seabed movement and fluid movement in the pipe. They are also corroded by seawater and internal conveying media for a long time. At the same time, risers may face large deformation during service, especially in deep-sea service. Therefore, marine risers must have comprehensive properties such as high strength, low-temperature toughness, high fatigue performance, corrosion resistance, strain resistance and good welding performance.

[0004] There are some related studies on marine riser steel at home and abroad, but the related technologies still have defects. For example, patent EP17833981 A "HIGH STRENGTH SEAMLESS STEEL PIPE AND RISER" provides a high-strength seamless steel pipe and riser, which is designed with high C (0.10% to 0.18%), high Ni, Mo, and Cu alloys. The alloy cost is high, the weldability is low, and the tempering process is required. There are many manufacturing processes. Patent CN110106439 A "X65 hot-rolled steel plate for marine risers and its preparation method" provides an X65 grade marine riser steel plate, which contains high Nb and Ni in the composition, has high cost, uses ferrite structure, and has insufficient strain resistance and fracture strength. Patent CN116555670 A "Anti-fatigue marine riser steel and its preparation method" 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 capacity. 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.

[0005] In summary, the existing technology is still insufficient in the research on high-performance wide and thick steel plates for marine risers, especially high-performance wide and thick steel plates for marine risers with comprehensive technical characteristics such as high strength, low-temperature toughness, high fatigue performance, corrosion resistance, strain resistance and good welding performance and their production technology, and improvement is urgently needed. Summary of the invention

[0006] In order to overcome the defects of the above-mentioned prior art, solve the problem of matching the comprehensive technical characteristics of high strength, high toughness, high fatigue resistance, corrosion resistance, strain resistance and good welding performance of wide and thick steel plates for high-performance marine risers, and break the traditional component design concept of the product, the present invention provides a 700MPa grade high-performance wide and thick steel plate for marine risers and a production method thereof, so as to meet the technical requirements of high-performance marine riser steel.

[0007] In order to achieve the above-mentioned invention object, the present invention provides a 700MPa high-performance wide and thick steel plate for marine risers, wherein the chemical composition weight percentage of the wide and thick steel plate is C: 0.025% to 0.055%, Si: 0.20% to 0.50%, Mn: 1.30% to 1.65%, Nb: 0.015% to 0.035%, V: 0.05% to 0.12%, (Nb+V): 0.075% to 0.14%, Ti: 0.005% to 0.020%, Ti / N≤2.5, Ni: 0.0 1%~0.15%, Mo<0.15%, Cr: 0.16%~0.50%, (Mo+Cr / 1.8)≥0.20%, Cu<0.20%, Zr≤0.025%, Al: 0.005%~0.025%, N: 0.0050%~0.012%, Ca: 0.0015%~0.0040%, Ca / S≥1.6, P≤0.010%, S≤0.002%, H≤0.00015%, O≤0.0018%, the balance is iron and unavoidable impurities.

[0008] The 700MPa high performance wide and thick steel plate CE for offshore risers IIW Controlled at 0.39%~0.47%, CE Pcm Controlled at 0.16% to 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; wherein the symbol of each element represents the weight percentage of the corresponding element.

[0011] The thickness of the above-mentioned 700MPa-grade high-performance wide and thick steel plate for marine risers is ≥25mm, and the composition is designed with low Nb, Mo, and Mn to promote the phase transformation of polygonal ferrite before accelerated cooling, ensure its proportion in the microstructure, and improve the economy of the alloy. Through the composite control of Mo and Cr, the strength is improved and the yield strength ratio is controlled. By using the composite addition of V, Nb, and N and the control of Al and Ti, the grain refinement and fine precipitation formation are promoted, the hydrogen trap effect is exerted, and the strengthening, phase transformation, microstructure, steel plate performance and post-weld performance are achieved. The favorable effects, corrosion resistance and weldability are improved. By adding elements such as Zr and Ca to control inclusions, the adverse effects on fatigue performance are reduced. In addition, by reducing the P, S, H, O content and controlling the quality of continuous casting billets, the toughness, corrosion resistance and fatigue resistance are improved; with the smelting, heating, rolling and cooling production processes matching the alloy composition, the steel plate obtains comprehensive technical characteristics such as high strength, high toughness, high fatigue resistance, corrosion resistance, strain resistance and good welding performance, as well as an ideal microstructure.

[0012] Reasons for designing the ingredients of the present invention:

[0013] C is a basic element for improving strength, and it works in the form of alloy carbide precipitation and interstitial solid solution. In addition to utilizing C solid solution strengthening, the present invention focuses on the characteristics of C forming fine precipitation phases with Nb and V during medium-temperature rolling and waiting for temperature of steel plates, promoting the formation of fine precipitation, thereby increasing the nucleation position and refining the microstructure; increasing hydrogen traps and reducing hydrogen embrittlement tendency; at the same time, C has a significant effect on improving hardenability and tensile strength, and is also beneficial to the control of yield ratio; however, too high carbon content is not good for plasticity, toughness, weldability, corrosion resistance, etc.; in the present invention, the C content is controlled at 0.025% to 0.055%.

[0014] Si can improve hardenability and strength and increase strain hardening rate. At the same time, in order to reduce the influence of Al on the formation of nitrides, the present invention utilizes Si to partially replace Al to play the role of a deoxidizer; however, too high Si content will increase the M / A in the structure and reduce toughness and plasticity. The suitable content range of Si in the present invention is 0.20% to 0.50%.

[0015] Mn can effectively improve strength and hardenability, and can also reduce phase transition temperature, which is beneficial to grain refinement; and Mn is cheap and can improve the economy of the product; but too high manganese content can easily induce segregation, resulting in reduced corrosion resistance and fatigue resistance. In the present invention, the Mn content is controlled at 1.30% to 1.65%.

[0016] Nb has a grain-refining effect, can improve strength and toughness, and can also form fine Nb (C, N) precipitation under appropriate processes, playing the role of precipitation strengthening and hydrogen trap; however, if the Nb content is too high, on the one hand, it is necessary to increase the heating temperature of the continuous casting billet to ensure the solid solution effect, which increases energy consumption; and it will inhibit the transformation of austenite to polygonal ferrite, increasing the difficulty of controlling polygonal ferrite in the microstructure; at the same time, it will also inhibit the formation of V precipitation phase when Nb+V is added in combination. Therefore, the present invention controls the Nb content to 0.015% to 0.035%.

[0017] V has solid solution and precipitation effects, has a strong tendency to combine with C and N, can combine with C and N to form fine precipitation during rolling and cooling, and play the role of refining grains, reducing aging sensitivity, and increasing hydrogen traps; and V can promote ferrite nucleation during austenite transformation, which is beneficial to obtain polygonal ferrite and can improve the uniformity of microstructure of the thickness section of the steel plate; and it can also inhibit the formation of coarse structure during welding and improve the toughness and hardness of the welded joint; but too high V content is not good for toughness and weldability, so the V content in the present invention is controlled at 0.05% to 0.12%.

[0018] Controlling Nb+V within the range of 0.075% to 0.14% is beneficial to ensuring the fine dispersion of the precipitated phase and preventing the precipitated phase from growing excessively; at the same time, it is beneficial to controlling the microstructure and alloy cost.

[0019] Ti is easy to form Ti(C, N) precipitation phase with a higher solid 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; and it has the effect of fixing oxygen; but if Ti and Ti / N are too high, the size of the precipitate will increase, and the formation of precipitation phases containing Nb and V will be inhibited. In the present invention, the Ti content is controlled to 0.005% to 0.020%, and Ti / N≤2.5.

[0020] Ni has a solid 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; but Ni is relatively expensive, and adding too much is not economical; therefore, the Ni content of the present invention is controlled at 0.01% to 0.15%.

[0021] Mo can improve hardenability, promote low-temperature microstructure transformation, has a certain grain refining effect, and can effectively reduce the phase transition temperature; however, Mo will inhibit the formation of polygonal ferrite and also lead to increased costs. Therefore, the present invention controls the Mo content to below 0.15%.

[0022] Cr can increase hardenability and improve tensile strength, and has a weaker inhibition on the transformation of austenite to polygonal ferrite, which is beneficial to increase the "hardness difference" of the soft / hard phase in the microstructure and is beneficial to the control of strain and yield ratio; moreover, Cr, as a cheap element, 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 of welding cracks, so the present invention controls the Cr content within a range of 0.16% to 0.50%.

[0023] (Mo+Cr / 1.8)≥0.20% can ensure hardenability and strengthening effect, make up for the strength loss caused by low Mn and Ni content, and at the same time, is beneficial to phase transformation and microstructure control, and improves strain performance.

[0024] Cu improves hardenability, increases the hard phase structure ratio and hardness, improves tensile strength, and is beneficial to corrosion resistance. However, too high a Cu content is detrimental to toughness. In the present invention, the Cu content is controlled to be less than 0.20%.

[0025] Zr is a strong deoxidizing element. The present invention utilizes Zr oxide formed by the combination of Zr and oxygen. The density difference between Zr and molten steel is small, and it is easy to achieve dispersed distribution. At the same time, Zr oxide in molten steel carries electric charge and has a certain conductivity. It is not easy to aggregate and grow, which is conducive to the fine and dispersed distribution of Zr oxide in steel, promoting phase deformation nucleation, refining grains, and improving performance. At the same time, Zr can also refine the microstructure of the welding heat affected zone and improve toughness. Moreover, after Zr reacts with oxygen, it can reduce the effect of V and oxygen, and promote the precipitation and formation of VN. However, if the Zr content is too high, the toughness will decrease. Therefore, in the present invention, Zr is controlled to be ≤0.025%.

[0026] 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 Al-containing inclusions and the reduction of free N, affecting the formation of NbN and VN. In the present invention, the Al content is preferably controlled within a range of 0.005% to 0.025%.

[0027] N: The present invention utilizes N to form fine precipitates with Nb, Ti, and V to exert strengthening, grain refinement, and hydrogen trapping effects, thereby improving strength, toughness, and corrosion resistance. However, excessive N content deteriorates toughness and may also cause steel plate defects. The content is preferably controlled within a range of 0.0050% to 0.012%.

[0028] Ca and Ca / S can promote inclusion modification and spheroidization, effectively improving corrosion resistance and toughness. In the present invention, the Ca content is controlled to be 0.0015% to 0.0040%, and Ca / S is ≥1.6.

[0029] 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%.

[0030] 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≤0.0018%.

[0031] CE of the composition design of wide and thick steel plates for high-performance offshore risers in this technical solution IIW Controlled at 0.39%~0.47%, CE Pcm Controlling it within the range of 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.

[0032] A method for producing the above-mentioned 700MPa-grade high-performance wide and thick steel plate for marine risers, the production method comprising the following process steps: converter smelting, refining outside the furnace, continuous casting, rolling and cooling;

[0033] Among them, the converter tapping temperature is ≤1640℃, C≤0.040%;

[0034] After refining and deoxidation, Ti is added first, followed by Zr and V; 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;

[0035] The continuous casting billet adopts multi-stage heating of preheating, heating and soaking, with a total heating time of 1.1-1.8min / mm and a furnace temperature of 1120℃-1180℃;

[0036] Rough rolling includes three stages: rough rolling stage 1, intermediate cooling, and rough rolling stage 2. The rough rolling start temperature is 1060℃~1140℃, and the rough rolling final temperature is 980℃~1040℃.

[0037] The deformation rate in the finishing rolling stage is 60% to 80%, the starting temperature of finishing rolling is 790℃ to 850℃, the final temperature of finishing rolling is 730℃ to 770℃, and the total deformation rate below 800℃ is ≥25%;

[0038] The rolled steel plate is pre-straightened and then cooled in two stages.

[0039] In the above technical scheme, further, the converter is slag blocked for steel tapping, the slag layer thickness is ≤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%.

[0040] Furthermore, the continuous casting adopts a constant pulling speed, the pulling speed control range is 0.6 to 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 inclusions are controlled within 1 level.

[0041] Low-carbon, low-temperature and slag-blocking steelmaking in 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 reducing ability of the slag, fully desulfurize, reduce inclusions, and improve cleanliness; the order of adding Ti, Zr, and V after refining and deoxidation can more effectively improve the yield and efficiency of the corresponding elements; the control of sedation before molten steel is put on the machine, pouring superheat, and the residence time of the tundish can homogenize the temperature of the molten steel and effectively promote the floating and removal of inclusions; dynamic light reduction and control of continuous casting billet pulling speed can effectively improve the quality of the billet and reduce defects such as cracks and segregation. The control of center segregation, center looseness, and inclusions is an effective guarantee for the quality of continuous casting billets and the performance of steel plates.

[0042] In the above technical solution, the continuous casting billet is further heated by preheating, heating and soaking in multiple stages, with a total heating time of 1.2 to 1.6 min / mm and a furnace discharge temperature of 1150°C to 1170°C. The control of the multi-stage heating of the continuous casting billet and the total heating time is conducive to improving the heating efficiency and uniformity; since the Nb content in the present invention is low, the element solid solution requirement can be met by heating at low temperature out of the furnace, and at the same time, the austenite grain size can be effectively reduced, and it is more conducive to reducing the rough rolling temperature, reducing the rolling time in the rough rolling stage, and realizing efficient low-temperature rolling.

[0043] In the above technical scheme, further, in the three stages of rough rolling, namely, rough rolling stage 1, intermediate cooling and rough rolling stage 2, the last 2 to 3 passes of rough rolling stage 1, intermediate cooling and rough rolling stage 2 are all cooled by rapid spray water; the starting temperature of rough rolling stage 2 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 1.0m / s to 1.8m / s. The rough rolling of the technical solution mainly adopts the process of low temperature rolling + high temperature gradient deformation of the thickness section. Due to the low Nb and V-containing design of the present invention, the austenite recrystallization temperature is reduced; therefore, low temperature rolling is adopted in the rough rolling stage to recrystallize the austenite grains and effectively inhibit the 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 stage of rough rolling is combined to promote the rolling deformation to penetrate into the thickness center of the ingot, refine the structure near the thickness center, and improve the uniformity of the steel plate structure and performance; the deformation rate that increases step by step in the second stage of rough rolling can promote sufficient recrystallization of austenite.

[0044] In the above technical scheme, further, the deformation rate in the finishing rolling stage is 65% to 75%. After the rough rolling is completed, the intermediate warm billet is quickly cooled to 850℃ to 900℃, with an average cooling rate of ≥2℃ / s, and then warmed to the finishing rolling start temperature. The finishing rolling start temperature is 790℃ to 850℃, the finishing rolling final rolling temperature is 730℃ to 770℃, and the total deformation rate below 800℃ is ≥25%. After the steel plate is pre-straightened after rolling, it is cooled in two stages, with the starting water cooling temperature of 680℃ to 740℃ and the ending water cooling temperature of 100℃ to 200℃. The water volume of the first 5 to 7 groups of upper headers during water cooling is 350 to 550L / m 2 ·min, the water volume of other upper headers is 150~330L / 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 warm billet after rough rolling can quickly reduce the temperature and effectively inhibit the growth of austenite; the low-temperature rolling and low-temperature deformation rate control in the finishing rolling stage are used, on the one hand, which is conducive to the formation of substructures and the accumulation of deformation energy in the microstructure; on the other hand, it can promote the formation of a small amount of deformation-induced ferrite, improve plasticity and strain; it can also provide good thermodynamic and kinetic conditions for the precipitation of Nb (C / N) and V (C / N), thereby playing the role of fine grain, pinning, and promoting phase deformation nucleation; the pre-straightening of the steel plate after rolling is conducive to improving the uniformity of water cooling and ensuring the shape of the steel plate; the control of the initial water cooling temperature can ensure the formation of some polygonal ferrite soft phase structure before accelerating water cooling; the use of a low final cooling temperature can form a high-hardness structure dominated by bainite; the use of a segmented water cooling process with fast front and slow back can increase the cooling rate of the high-temperature section and inhibit high-temperature phase transformation. At the same time, the small amount of cooling water in the low-temperature section can reduce internal stress and improve the shape of the plate after cooling.

[0045] The 700MPa high-performance wide and thick steel plate for marine risers produced by the above production method has a microstructure of polygonal ferrite + lath bainite, and may also include a small amount of granular bainite, wherein the volume percentage of polygonal ferrite is 15% to 70% and there are a large number of dislocations in the polygonal ferrite crystals, which promotes the average height of deformed austenite not exceeding 15μm, and contains dispersed fine precipitations of 5 to 20nm in the matrix. The steel plate has comprehensive technical characteristics such as high strength, high toughness, high fatigue resistance, corrosion resistance, strain resistance and good welding performance, and can meet the requirements for manufacturing high-performance marine oil and gas production risers.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] ① The composition of the present invention adopts a low Nb, Mo, and Mn design to promote the polygonal ferrite phase transformation before accelerated cooling, ensure its proportion in the microstructure, and improve the economy of the alloy. Through the composite control of Mo and Cr, the strength is improved and the yield strength ratio is controlled. The composite addition of Nb, V, and N and the control of Al and Ti provide good conditions for the precipitation of Nb and V carbonitrides, promote grain refinement and fine precipitation formation, exert the hydrogen trap effect, achieve a favorable effect on strengthening, phase transformation, microstructure, steel plate performance and post-weld performance, and improve strength, corrosion resistance and weldability. By adding elements such as Zr and Ca to control inclusions, the adverse effect on fatigue performance is reduced. In addition, by reducing the P, S, H, O contents and controlling the quality of continuous casting ingots, the toughness, corrosion resistance and fatigue resistance are improved; and by using smelting, heating, rolling and cooling production processes that match the alloy composition, the difficult problem of matching the comprehensive technical characteristics of high strength, high toughness, high fatigue resistance, corrosion resistance, strain resistance and good welding performance of wide and thick steel plates for high-performance offshore oil and gas production risers is solved.

[0048] ② Based on the composition design of the present invention, a production method is adopted, including low-temperature heating, rough rolling multi-stage thickness section high temperature gradient deformation + low-temperature rolling, rapid cooling of the intermediate warm billet after the rough rolling, finishing rolling low-temperature deformation and multi-stage water cooling, to obtain a polygonal ferrite + lath bainite microstructure, which can also include a small amount of granular bainite and dispersed fine precipitation. The average height of the deformed austenite does not exceed 15μm, and the proportion of each phase, the size and distribution of the precipitate phase are ideally controlled, which plays an important role in obtaining good comprehensive performance of the steel plate.

[0049] ③ The 700MPa high-performance wide and thick steel plate for marine riser of the present invention has a thickness of ≥25mm, a transverse yield strength of 500-590MPa, a transverse tensile strength of 710-770MPa, a transverse yield strength ratio of <0.78, an average transverse impact energy of -60℃ ≥250J, a transverse DWTT shear area of ​​-40℃ ≥85%, and an average transverse impact energy of -20℃ welding heat affected zone ≥180J; the longitudinal yield strength can reach 470-560MPa, the longitudinal tensile strength reaches 700-760MPa, the longitudinal yield strength ratio is <0.77, the longitudinal uniform elongation UEL ≥12%, the longitudinal strain hardening index ≥0.12, 10 7 The cyclic fatigue strength is ≥350MPa, the HIC corrosion resistance meets the requirements of CLR≤15%, CTR≤5%, and CSR≤2% after 96 hours of NACE standard B solution corrosion, and 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; the manufactured marine riser meets the 700MPa grade requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 The microstructure diagram of the 700MPa high-performance wide and thick steel plate for marine riser prepared in Example 1;

[0051] Figure 2 This is a high-magnification morphology image of the polygonal ferrite of the 700MPa-grade high-performance wide and thick steel plate for marine risers prepared in Example 1. DETAILED DESCRIPTION

[0052] The present invention is further described below in conjunction with specific examples, but the present invention is not limited in any way. To avoid redundant description, the raw materials in the following examples are all commercially available products unless otherwise specified, and the methods used are all conventional methods unless otherwise specified. The tensile specimen for the mechanical properties test of the product is a full-thickness rectangular specimen with a parallel test section width of 38.1 mm; the impact specimen size is 10*55*55 mm.

[0053] 700MPa high-performance wide and thick steel plate for marine riser, the chemical composition weight percentage of the wide and thick steel plate is C: 0.025% to 0.055%, Si: 0.20% to 0.50%, Mn: 1.30% to 1.65%, Nb: 0.015% to 0.035%, V: 0.05% to 0.12%, (Nb+V): 0.075% to 0.14%, Ti: 0.005% to 0.020%, Ti / N≤2.5, Ni: 0.01% to 0.15%, Mo<0.15%, Cr: 0.16%~0.50%, (Mo+Cr / 1.8)≥0.20%, Cu<0.20%, Zr≤0.025%, Al: 0.005%~0.025%, N: 0.0050%~0.012%, Ca: 0.0015%~0.0040%, Ca / S≥1.6, P≤0.010%, S≤0.002%, H≤0.00015%, O≤0.0018%, and the balance is iron and unavoidable impurities.

[0054] The CE of the 700MPa high performance wide and thick steel plate for offshore risers IIW Controlled at 0.39%~0.47%, CE Pcm Controlled at 0.16% to 0.20%,

[0055] Among them, CE IIW =C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15;

[0056] 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.

[0057] A method for producing the above-mentioned 700MPa-grade high-performance wide and thick steel plate for marine risers, the production method comprising the following process steps: converter smelting, refining outside the furnace, continuous casting, rolling and cooling, etc.;

[0058] Among them, the converter tapping temperature is ≤1640℃, C≤0.040%;

[0059] After refining and deoxidation, Ti is added first, followed by Zr and V; 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;

[0060] The continuous casting billet adopts multi-stage heating of preheating, heating and soaking, with a total heating time of 1.1-1.8min / mm and a furnace temperature of 1120℃-1180℃;

[0061] Rough rolling includes three stages: rough rolling stage 1, intermediate cooling and rough rolling stage 2. The starting temperature of rough rolling is 1060℃~1140℃, and the final temperature of rough rolling is 980℃~1040℃. The last 2-3 passes of rough rolling stage 1, intermediate cooling and rough rolling stage 2 are all cooled by rapid spray water.

[0062] 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 850 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 790°C to 850°C, the finishing rolling final rolling temperature is 730°C to 770°C, and the total deformation rate below 800°C is ≥25%;

[0063] The rolled steel plate is pre-straightened and then cooled in two stages.

[0064] The matters not described in the following embodiments are the same as the description of the above specific implementation methods.

[0065] Example

[0066] 700MPa grade high performance wide and thick steel plates for marine risers and production method thereof. The chemical compositions of the wide and thick steel plates of Examples 1 to 8 are shown in Table 1.

[0067] Table 1 Chemical composition of wide and thick steel plates of Examples 1 to 8 wt%

[0068]

[0069]

[0070] The smelting and refining process parameters of the wide and thick steel plate production method of Examples 1 to 8 are shown in Table 2. The converter tapping temperature is ≤1640°C, C ≤0.040%; slag blocking is used for tapping, the slag layer thickness is ≤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%.

[0071] Table 2 Smelting and refining process parameters of Examples 1 to 8

[0072]

[0073] The continuous casting process parameters of the wide and thick steel plate production method of Examples 1 to 8 are shown in Table 3, the cooling time of the molten steel before loading on the machine is ≥10min, the pouring superheat of the continuous casting billet is 10℃~40℃, the average residence time of the molten steel in the tundish during pouring is ≥360s, and the dynamic light reduction of the casting billet is ≥4mm; the continuous casting adopts a constant pulling speed, the pulling speed control range is 0.6~1.2m / 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 level 1.

[0074] Table 3 Continuous casting process parameters of Examples 1 to 8

[0075]

[0076] The continuous casting slab heating and rough rolling process control parameters of the wide and thick steel plate production method of Examples 1 to 8 are shown in Table 4. The continuous casting slab adopts multi-stage heating of preheating, heating and soaking, with a total heating time of 1.1 to 1.8 min / mm and a furnace outlet temperature of 1120°C to 1180°C; the rough rolling start temperature is 1060°C to 1140°C, and the rough rolling final temperature is 980°C to 1040°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 from pass to pass, and the rough rolling speed is 1.0 m / s to 1.8 m / s.

[0077] Table 4 Continuous casting slab heating and rough rolling process parameters of Examples 1 to 8

[0078]

[0079]

[0080] The finishing rolling and cooling process parameters of the wide and thick steel plate production method of Examples 1 to 8 are shown in Table 5. 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 850°C to 900°C, with an average cooling rate of ≥2°C / s, and then warmed to the finishing rolling start temperature. The finishing rolling start temperature is 790°C to 850°C, the finishing rolling final rolling temperature is 730°C to 770°C, and the total deformation rate below 800°C is ≥25%; the steel plate is pre-straightened after rolling and then cooled in two stages, with the starting water cooling temperature of 680°C to 740°C and the ending water cooling temperature of 100°C to 200°C. The water volume of the first 5 to 7 groups of upper headers during water cooling is 350 to 550L / m 2 ·min, the water volume of other upper headers is 150~330L / m 2 ·min.

[0081] Table 5 Finishing rolling and cooling process of the embodiment

[0082]

[0083] The microstructure statistics of the 700 MPa high-performance wide and thick steel plates for marine risers prepared in Examples 1 to 8 are shown in Table 6. The microstructure of the wide and thick steel plates is polygonal ferrite + lath bainite, and also includes a small amount of granular bainite (such as Figure 1-2 As shown); wherein, the volume percentage of polygonal ferrite is 15% to 70%, the average height of deformed austenite does not exceed 15 μm, and the matrix contains dispersedly distributed fine precipitations of 5 to 20 nm.

[0084] Table 6 Microstructure statistics of products obtained in Examples 1 to 8

[0085]

[0086]

[0087] The mechanical properties test results of the 700MPa high-performance wide and thick steel plates for marine risers prepared in Examples 1 to 8 are shown in Table 7. The thickness of the wide and thick steel plates is ≥25mm, the transverse yield strength is 500-590MPa, the transverse tensile strength is 710-770MPa, the transverse yield strength ratio is <0.78, the average transverse impact energy at -60°C is ≥250J, the transverse DWTT shear area at -40°C is ≥85%, and the average transverse impact energy at -20°C of the welding heat affected zone is ≥180J; the longitudinal yield strength is 470-560MPa, the longitudinal tensile strength is 700-760MPa, the longitudinal yield strength ratio is <0.77, the longitudinal uniform elongation UEL is ≥12%, the longitudinal strain hardening index is ≥0.12, 10 7 Cyclic fatigue strength ≥350MPa.

[0088] Table 7 Mechanical properties test results of the products obtained in Examples 1 to 8

[0089]

[0090] The corrosion resistance test results of the 700MPa high-performance wide and thick steel plates for marine risers prepared in Examples 1 to 8 are shown in Table 8. The HIC corrosion resistance meets the requirements of CLR≤15%, CTR≤5%, and CSR≤2% after 96 hours of NACE standard B solution corrosion, and 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.

[0091] Table 8 Corrosion resistance test results of the products obtained in Examples 1 to 8

[0092]

[0093] Through Examples 1 to 8, it can be illustrated that: the present invention adopts a low Nb, Mo, and Mn component design to promote the polygonal ferrite phase transformation before accelerated cooling and ensure its proportion in the microstructure; through the composite control of Mo and Cr, the strength is improved and the yield strength ratio is controlled; the composite addition of Nb, V, and N and the control of Al and Ti provide good conditions for the precipitation of Nb and V carbonitrides, promote grain refinement and the formation of fine precipitation, exert the hydrogen trap effect, and achieve a favorable effect on strengthening, phase transformation, microstructure, steel plate performance and post-weld performance; by adding elements such as Zr and Ca to control inclusions, the adverse effect on fatigue performance is reduced. On the basis of composition design, polygonal ferrite + lath bainite is obtained by adopting production methods such as low-temperature heating, rough rolling multi-stage thickness section high temperature gradient deformation + low-temperature rolling, rapid cooling of the intermediate warm billet after the end of rough rolling, finishing rolling low-temperature deformation and multi-stage water cooling. The microstructure may also include a small amount of granular bainite and dispersed fine precipitation. The average height of deformed austenite does not exceed 15μm. The proportion of each phase, the size and distribution of the precipitate phase are ideally controlled, which plays an important role in obtaining good comprehensive performance of the steel plate.

[0094] For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or 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 should still fall within the scope of protection of the technical solution of the present invention.

Claims

1. 700MPa high performance wide and thick steel plate for offshore riser, characterized by: The chemical composition weight percentage of the wide and thick steel plate is C: 0.025% to 0.055%, Si: 0.20% to 0.50%, Mn: 1.30% to 1.65%, Nb: 0.015% to 0.035%, V: 0.05% to 0.12%, (Nb+V): 0.075% to 0.14%, Ti: 0.005% to 0.020%, Ti / N≤2.5, Ni: 0.01% to 0.15%, Mo<0.15%, C r: 0.16% ~ 0.50%, (Mo + Cr / 1.8) ≥ 0.20%, Cu < 0.20%, Zr ≤ 0.025%, Al: 0.005% ~ 0.025%, N: 0.0050% ~ 0.012%, Ca: 0.0015% ~ 0.0040%, Ca / S ≥ 1.6, P ≤ 0.010%, S ≤ 0.002%, H ≤ 0.00015%, O ≤ 0.0018%, the balance is iron and unavoidable impurities.

2. The 700MPa high-performance wide and thick steel plate for marine risers according to claim 1, characterized in that: The wide and thick steel plate CE for offshore riser IIW Controlled at 0.39%~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 high-performance wide and thick steel plate for marine riser according to claim 1, characterized in that: The thickness of the wide and thick steel plate is ≥25mm, the transverse yield strength is 500-590MPa, the transverse tensile strength is 710-770MPa, the transverse yield strength ratio is <0.78, the average transverse impact energy at -60°C is ≥250J, the transverse DWTT shear area at -40°C is ≥85%, and the average transverse impact energy at -20°C of the welding heat affected zone is ≥180J; the longitudinal yield strength is 470-560MPa, the longitudinal tensile strength is 700-760MPa, the longitudinal yield strength ratio is <0.77, the longitudinal uniform elongation UEL is ≥12%, the longitudinal strain hardening index is ≥0.12, 10 7 The cyclic fatigue strength is ≥350MPa, the HIC corrosion resistance meets the requirements of CLR≤15%, CTR≤5%, and CSR≤2% after 96 hours of NACE standard B solution corrosion, and 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 high-performance wide and thick steel plate for marine riser according to claim 1, characterized in that: The microstructure of the wide and thick steel plate is polygonal ferrite + lath bainite, and also includes a small amount of granular bainite; wherein the volume percentage of polygonal ferrite is 15% to 70%, the average height of deformed austenite does not exceed 15μm, and the matrix contains dispersedly distributed fine precipitations of 5 to 20nm.

5. A method for producing a 700MPa high-performance wide and thick steel plate for marine risers according to 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, followed by Zr and V; 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 1.1-1.8min / 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 1060℃~1140℃, and the final temperature of rough rolling is 980℃~1040℃. 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 850℃ to 900℃, with an average cooling rate of ≥2℃ / s. Then, it is heated to the finishing rolling start temperature, the finishing rolling start temperature is 790℃ to 850℃, the finishing rolling final rolling temperature is 730℃ to 770℃, and the total deformation rate below 800℃ is ≥25%; 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 680°C to 740°C, and the water cooling end temperature is 100°C to 200°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 150~330L / m 2 ·min.

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