A wide and thick steel plate for high-performance marine oil and gas production riser and a method for manufacturing the same

Abstract

The application discloses a wide and thick steel plate for high-performance offshore oil and gas exploitation stand pipes and a preparation method thereof. The steel plate comprises the following components: C: 0.025%-0.060%, Si: 0.20%-0.50%, Mn: 0.80%-1.40%, Nb: 0.010%-0.035%, V: 0.080%, Ti: 0.005%-0.020%, Ni: 0.01%-0.10%, Mo: 0.15%, Cr: 0.10%-0.40%, Cu: 0.15%, Zr: 0.025%, Al: 0.005%-0.025%, N: 0.0040%-0.010%, Ca: 0.0015%-0.0040%, Ca / S: 1.6, P: 0.010%, S: 0.002%, H: 0.00015%, O: 0.0018%, and the balance of iron and inevitable impurities.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of materials and metallurgy, and more particularly to a wide and thick steel plate for high-performance marine oil and gas exploitation riser and a preparation method thereof. BACKGROUND

[0002] With the increasing demand for energy from human economic and social activities, the demand for oil and gas continues to increase, and only relying on land oil and gas resources cannot meet the corresponding demand, so the development of marine oil and gas resources is increasingly valued. According to the analysis of international authoritative agencies, marine oil and gas resources account for about 63% of the global recoverable oil and gas reserves in the future, of which deep-sea oil and gas resources 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 oil and gas development, especially deep-sea oil and gas development.

[0003] The riser system is a connecting channel between the offshore oil and gas platform and the underwater production system, and plays a crucial role in marine oil and gas development. Steel catenary riser has gradually become the preferred form of riser for marine oil and gas development due to its simple structure, economy and other advantages. The riser serves in the marine environment for a long time, has low service temperature, is subjected to complex loads generated by sea currents, surges, platform movements, seabed movements and fluid movements in the pipe, and is also subjected to corrosion of seawater and internal conveying medium for a long time; at the same time, the riser may face a large deformation during laying, especially during deep-sea laying, so the marine riser 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 researches on steel catenary riser at home and abroad, and some patents and literatures are found through retrieval, but there are obvious differences in the components, production methods, properties and microstructure design described in the contents of the patents and literatures and the technical solutions of the present application. Patent EP17833981A discloses 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, has high alloy cost, low weldability, and needs to be produced by quenching and tempering process, which has many manufacturing processes. Patent CN110106439A discloses an X65-grade marine riser steel plate, which uses high Nb and Ni in the composition, has high cost, and has ferrite structure, which has insufficient strain resistance and fracture strength. Patent CN116555670A discloses a marine riser steel, which has high alloy content, and requires that the cumulative deformation of the last 2-3 passes of rough rolling is greater than 50%, which is difficult to realize industrialization for wide and thick steel plates and requires high equipment capacity. Patent CN114763593A discloses a marine engineering steel, which is designed with high Ni and Cr and is rolled and quenched and tempered, which has high cost and long manufacturing cycle.

[0005] In summary, the prior art has deficiencies in the research on the wide-thick steel plate for high-performance offshore oil and gas production riser, especially the wide-thick steel plate for offshore oil and gas production riser with comprehensive technical characteristics of high strength, low-temperature toughness, high fatigue performance, corrosion resistance, strain resistance and good welding performance and the production technology thereof. SUMMARY

[0006] The present application aims to overcome the above-mentioned defects in the prior art, solve the problem of matching the comprehensive technical characteristics of high strength, high toughness, high fatigue performance, corrosion resistance, strain resistance and good welding performance of the wide-thick steel plate for high-performance offshore oil and gas production riser, break the traditional high-Nb and high-alloy design idea of the product, and provide a wide-thick steel plate for high-performance offshore oil and gas production riser with thickness ≥ 25 mm, high strength, high toughness, high fatigue performance, good corrosion resistance, strain resistance and welding performance, and a preparation method thereof, which is suitable for manufacturing high-performance offshore oil and gas production straight-welded riser.

[0007] To achieve the above-mentioned object, the technical scheme of the present application is as follows:

[0008] A wide-thick steel plate for high-performance offshore oil and gas production riser, characterized by comprising the following components in weight percentage: C: 0.025%-0.060%, Si: 0.20%-0.50%, Mn: 0.80%-1.40%, Nb: 0.010%-0.035%, V≤0.080%, Ti: 0.005%-0.020%, Ni: 0.01%-0.10%, Mo<0.15%, Cr: 0.10%-0.40%, Cu<0.15%, Zr≤0.025%, Al: 0.005%-0.025%, N: 0.0040%-0.010%, Ca: 0.0015%-0.0040%, Ca / S≥1.6, P≤0.010%, S≤0.002%, H≤0.00015%, O≤0.0018%, and (Nb+V): 0.030%-0.105%, Ti / N≤2.5, ((Cr / 1.8)+Mo)≥0.15%, and the balance being iron and unavoidable impurities.

[0009] This invention also discloses a method for preparing high-performance thick steel plates for offshore oil and gas extraction risers as described above, characterized by comprising: converter smelting, ladle refining, continuous casting, heating, rolling, and cooling processes; in the rolling process, the heated continuous casting billet is sequentially subjected to roughing and finishing rolling; the roughing rolling includes a first roughing rolling stage, intermediate cooling, and a second roughing rolling stage; the initial roughing rolling temperature is 1070℃~1130℃, and the final roughing rolling temperature is 980℃~1030℃; the last 2 to 3 passes of the first roughing rolling stage, and the intermediate cooling... Both the roughing and roughing stages employ rapid spray water cooling. The initial temperature of the roughing stage is <1050℃, with a total deformation rate ≥30%, and a deformation rate ≥15% per pass, increasing progressively. The roughing rolling speed is 1.0m / s to 1.8m / s. After roughing, the intermediate billet is rapidly cooled to 860℃ to 920℃, then allowed to warm to the finishing rolling start temperature of 800℃ to 860℃. The finishing rolling finish temperature is 740℃ to 780℃, with a deformation rate of 60% to 80% during the finishing stage. The total deformation rate below 800℃ is ≥15%.

[0010] Implementing the embodiments of the present invention will have the following beneficial effects:

[0011] (1) The composition of this invention employs a low Nb, Mo, and Mn design to promote the polygonal ferrite phase transformation before accelerated cooling, ensuring its proportion in the microstructure, and simultaneously improving alloy economy. Strength is enhanced and the yield strength ratio is controlled through the composite control of Mo and Cr. The composite addition of Nb, V, and N, along with the control of Al and Ti, provides favorable conditions for the precipitation of Nb and V carbonitrides, promoting grain refinement and the formation of fine precipitates, exerting a hydrogen trapping effect, and achieving beneficial influences on strengthening, phase transformation, microstructure, steel plate properties, and post-weld performance, thereby improving strength, corrosion resistance, and weldability. Inclusions are controlled by adding elements such as Zr and Ca, reducing their adverse effects on fatigue performance. In addition, by reducing the content of P, S, H and O and controlling the quality of continuously cast billets, the toughness, corrosion resistance and fatigue resistance are improved; coupled with the production processes such as smelting, heating, rolling and cooling that match the alloy composition, the problem of matching the comprehensive technical characteristics of high strength, high toughness, high fatigue performance, corrosion resistance, strain resistance and good weldability of wide and thick steel plates for high-performance marine oil and gas extraction risers is solved.

[0012] (2) Based on the composition design of this invention, the production methods of low temperature heating, high temperature gradient deformation of thick section in rough rolling + low temperature rolling, rapid cooling of intermediate billet after rough rolling, low temperature deformation in fine rolling and multi-stage water cooling were adopted to obtain a microstructure of polygonal ferrite + lath bainite, which may also include a small amount of granular bainite and fine precipitates dispersedly. The proportion of each phase, the size and distribution of precipitates are ideally controlled, which plays an important role in obtaining good comprehensive performance of steel plates.

[0013] (3) The high-performance offshore oil and gas extraction riser of this invention has a thickness ≥25mm, a transverse yield strength of 430-530MPa, a transverse tensile strength of 570-660MPa, a transverse yield-to-tensile ratio <0.79, a transverse impact energy average of ≥250J at -60℃, a transverse DWTT shear area ≥85% at -40℃, and a weld heat-affected zone transverse impact energy average of ≥200J at -20℃; a longitudinal yield strength of 400-500MPa, a longitudinal tensile strength of 550-640MPa, a longitudinal uniform elongation UEL ≥12%, a longitudinal yield-to-tensile ratio <0.78, and a longitudinal strain hardening index ≥0.12. 7 The cycle fatigue strength is ≥300MPa, and the resistance to HIC corrosion meets the requirements of CLR≤15%, CTR≤5%, and CSR≤2% after 96 hours of corrosion with NACE standard A solution. The resistance to SSCC corrosion meets the requirements of no fracture after 720 hours of immersion in saturated H2S solution under 72% stress loading and no visible cracks under 10x magnification. The manufactured marine risers meet the requirements of X60 and X65 grades. Attached Figure Description

[0014] Figure 1 This is a microstructure diagram of the steel plate in Embodiment 2 of the present invention.

[0015] Figure 2 This is a morphological diagram of the precipitated phase structure of the steel plate in Example 4 of the present invention. Detailed Implementation

[0016] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0017] I. Chemical composition and mechanical properties

[0018] This invention discloses a high-performance thick steel plate for offshore oil and gas extraction risers, comprising the following components by weight percentage: C: 0.025%–0.060%, Si: 0.20%–0.50%, Mn: 0.80%–1.40%, Nb: 0.010%–0.035%, V≤0.080%, Ti: 0.005%–0.020%, Ni: 0.01%–0.10%, Mo<0.15%, Cr: 0.10%–0.40%, Cu<0.15%, Zn<0.020%, Ni<0.01%–0.10%, Mo<0.15%, Cr<0.10%–0.40%, Cu<0.15%, Zn<0.020%, Ni<0.020%, Mo<0.020%, Nb ... r≤0.025%, Al: 0.005%~0.025%, N: 0.0040%~0.010%, Ca: 0.0015%~0.0040%, Ca / S≥1.6, P≤0.010%, S≤0.002%, H≤0.00015%, O≤0.0018%, and (Nb+V): 0.030%~0.105%, Ti / N≤2.5, ((Cr / 1.8)+Mo)≥0.15%, with the balance being iron and unavoidable impurities.

[0019] In one specific embodiment, the steel plate CE IIW The CEP is 0.31% to 0.38%. cm It ranges from 0.13% to 0.16%, of which CE IIW =C+Mn / 6+(Cr+Mo) / 5+(Ni+Cu) / 15;

[0020] CE Pcm =C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B.

[0021] Specifically, the mechanism of action of each alloy component in the steel of this invention is as follows:

[0022] Carbon (C) is a fundamental element for enhancing strength, exerting its effects through both alloy carbide precipitation and interstitial solid solution. In addition to utilizing C's solid solution strengthening properties, this invention focuses on leveraging C's ability to form fine precipitates with Nb and V during medium-temperature rolling and warming of steel plates. This promotes the formation of fine precipitates, thereby increasing nucleation sites, refining the microstructure, increasing hydrogen traps, and reducing hydrogen embrittlement tendency. Simultaneously, C significantly improves hardenability and tensile strength, and is also beneficial for controlling the yield strength ratio. However, excessive carbon content is detrimental to plasticity, toughness, weldability, and corrosion resistance; therefore, the C content in this invention is controlled at 0.025%–0.060%.

[0023] Si can improve hardenability and strength, and increase strain hardening rate. At the same time, in order to reduce the influence of Al on nitrogen formation, this invention utilizes Si to partially replace Al as a deoxidizer. However, excessive Si content will increase the M / A ratio in the microstructure and reduce toughness and plasticity. Therefore, the suitable range of Si content in this invention is 0.20% to 0.50%.

[0024] Mn can effectively improve strength and hardenability. At the same time, Mn can also lower the phase transformation temperature, which is beneficial to grain refinement. Moreover, Mn is inexpensive and can improve the economic efficiency of products. However, excessive manganese content can easily induce segregation, leading to a decrease in corrosion resistance and fatigue resistance. In this invention, the Mn content is controlled at 0.80% to 1.40%.

[0025] Nb has a grain-refining effect, which can improve strength and toughness. It can also form fine Nb(CN) precipitates under appropriate processes, playing a role in precipitation strengthening and hydrogen trapping. However, if the Nb content is too high, on the one hand, the heating temperature of the continuously cast billet needs to be increased to ensure the solid solution effect, which increases energy consumption. Moreover, 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 precipitate phase when Nb+V composite addition is used in this invention. Therefore, the Nb content is controlled at 0.010% to 0.035%.

[0026] V has solid solution and precipitation effects, and has a strong tendency to combine with C and N. It can combine with C and N to form fine precipitates during rolling and cooling, which can refine grains, reduce aging sensitivity, and increase hydrogen trapping. Moreover, V can promote ferrite nucleation during austenite phase transformation, which is beneficial to obtaining polygonal ferrite and can also improve the uniformity of microstructure in the thickness section of steel plate. In addition, it can inhibit the formation of coarse structure during welding and improve the toughness and hardness of welded joints. However, excessive V content is detrimental to toughness and weldability. Therefore, V in this invention does not exceed 0.080%.

[0027] The present invention further sets the total content of Nb and V within the range of 0.030% to 0.105%, which is beneficial to ensure that the precipitates are fine and dispersed and to prevent the precipitates from growing excessively; at the same time, it is beneficial to control the microstructure and alloy cost.

[0028] N: In this invention, N forms fine precipitates with Nb, Ti, and V, which play a role in strengthening, refining grains, and hydrogen trapping, thereby improving toughness and corrosion resistance. However, excessive N content will deteriorate toughness and may also lead to defects in steel plates. Its content should be controlled between 0.0040% and 0.010%.

[0029] Ti readily forms Ti(CN) precipitates with high solution temperatures, inhibiting austenite grain growth under high-temperature conditions. Simultaneously, Ti can refine the weld microstructure and improve the toughness of the heat-affected zone after welding. Furthermore, it has an oxygen-fixing effect. However, excessively high Ti and Ti / N ratios can increase precipitate size and inhibit the formation of Nb and V-containing precipitates. In this invention, the Ti content is controlled at 0.005%–0.020%, and the Ti / N ratio is ≤2.5.

[0030] 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 embrittlement and improve corrosion resistance; however, Ni is expensive, and adding too much is not economical; therefore, the Ni content in this invention is controlled at 0.01% to 0.10%.

[0031] Mo can improve hardenability, promote microstructure transformation at medium and low temperatures, and has a certain grain-refining effect, effectively reducing the phase transformation temperature; however, Mo can inhibit the formation of polygonal ferrite and also lead to increased costs. Therefore, this invention controls the Mo content to below 0.15%.

[0032] Cr can increase hardenability and tensile strength, but it has a weaker inhibitory effect on the transformation of austenite to polygonal ferrite, which is beneficial for increasing the "hardness difference" between the soft and hard phases in the microstructure and for controlling strain and yield strength ratio. Moreover, Cr, as an inexpensive element, can replace expensive alloying elements such as Mo, Ni, and Cu, effectively reducing costs. However, excessive Cr content will increase the sensitivity to welding cracks. Therefore, this invention controls the Cr content at 0.10% to 0.40%, and satisfies ((Cr / 1.8) + Mo) ≥ 0.15%, which can ensure hardenability and strengthening effect, compensate for the strength loss caused by low Mn and Ni content, and at the same time, facilitate phase transformation and microstructure control, and improve strain performance.

[0033] Cu improves hardenability, increases the proportion of hard phase structure and hardness, and improves tensile strength. At the same time, it is beneficial to corrosion resistance. However, excessive Cu content is detrimental to toughness. In this invention, the Cu content is controlled at <0.15%.

[0034] Zr is a strong deoxidizing element. This invention utilizes Zr oxides formed by the combination of Zr and oxygen. These oxides have a small density difference with molten steel, facilitating dispersed distribution. Simultaneously, the Zr oxides in molten steel carry an electric charge and possess a certain degree of conductivity, making them less prone to aggregation and growth. This promotes the fine and dispersed distribution of Zr oxides within the steel, fostering phase deformation nuclei, refining grains, and improving performance. Furthermore, Zr can refine the microstructure of the weld heat-affected zone, improving toughness. Moreover, the interaction between Zr and oxygen reduces the interaction between V and oxygen, promoting the precipitation and formation of VN. However, excessively high Zr content leads to decreased toughness; therefore, in this invention, Zr ≤ 0.025%.

[0035] Al has a strong affinity for O and N and is a deoxygenating element. However, excessive Al content will promote the increase of Al-containing inclusions and the decrease of free N, affecting the formation of NbN and VN. In this invention, the Al content should be controlled between 0.005% and 0.025%.

[0036] Ca and Ca / S can promote the modification and spheroidization of inclusions, effectively improving corrosion resistance and toughness. Therefore, the Ca content of this invention is 0.0015% to 0.0040%, and the Ca / S ratio is ≥1.6.

[0037] In this invention, P and S are considered harmful impurity elements. P can reduce toughness, and this invention sets P ≤ 0.010%. Increased S content promotes the formation and growth of inclusions, disrupts the continuity of the matrix, and leads to decreased fatigue and corrosion resistance. Therefore, S ≤ 0.002%.

[0038] Increased H and O content leads to decreased toughness, increased inclusions, and affects corrosion resistance and fatigue performance. Therefore, this invention controls H ≤ 0.00015% and O ≤ 0.0018%.

[0039] This invention CE IIW Controlled within 0.31% to 0.38%, CE Pcm By controlling the content at 0.13% to 0.16%, the strength and toughness requirements of the steel plate can be met, while also reducing the tendency for welding cracks, thus giving the steel plate good weldability.

[0040] In one specific embodiment, the microstructure of the steel plate is polygonal ferrite and bainite; the bainite includes lath bainite and granular bainite; the volume percentage of polygonal ferrite is 25% to 75%, and the average grain diameter is 5.0 μm to 10 μm; the steel plate contains fine carbonitrides with a particle size of 5 nm to 20 nm that are dispersedly distributed.

[0041] In one specific embodiment, the thickness of the steel plate is ≥25mm; the transverse yield strength of the steel plate is 430MPa~530MPa, the transverse tensile strength is 570MPa~660MPa, the transverse yield-to-tensile ratio is <0.79, the average transverse impact energy at -60℃ is ≥250J, the transverse DWTT shear area at -40℃ is ≥85%, and the average transverse impact energy at -20℃ in the weld heat-affected zone is ≥200J; the longitudinal yield strength is 400MPa~500MPa, the longitudinal tensile strength is 550MPa~640MPa, the longitudinal uniform elongation (UEL) is ≥12%, the longitudinal yield-to-tensile ratio is <0.78, and the longitudinal strain hardening index is ≥0.12. 7 The cycle fatigue strength is ≥300MPa, and the resistance to HIC corrosion meets the requirements of CLR≤15%, CTR≤5%, and CSR≤2% after 96 hours of corrosion with NACE standard A solution. The resistance to SSCC corrosion meets the requirements of no fracture after 720 hours of immersion in saturated H2S solution under 72% stress loading and no visible cracks under 10x magnification.

[0042] II. Production Process Technology

[0043] The present invention also discloses a method for preparing high-performance thick steel plates for marine oil and gas extraction risers as described in any embodiment of the present invention, comprising: converter smelting, ladle refining, continuous casting process, heating process, rolling process and cooling process.

[0044] Furthermore, the specific steps include:

[0045] S1. In converter smelting, the converter tapping temperature is ≤1640℃, C≤0.040%, slag is blocked during tapping, and the slag layer thickness is ≤35mm; lime and fluorite are added in a 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%.

[0046] S2. In the ladle refining process, after the molten steel obtained from converter smelting is refined and deoxidized, Ti, Zr and V are added in sequence to adjust the composition of the molten steel.

[0047] S3. In the continuous casting process, the refining time of molten steel before continuous casting is ≥10min; the superheating temperature of the continuously cast billet is 10℃~40℃; the residence time of molten steel in the tundish during casting is ≥350s; the dynamic light reduction of the billet is ≥4mm; the continuous casting adopts a constant casting speed of 0.6m / min~1.5m / min; the center segregation of the continuously cast billet is ≤C0.5 grade; the center porosity is ≤0.5 grade; and the inclusions of Class A, Class B, Class C and Class D are controlled within Grade 1.

[0048] Specifically, low-carbon, low-temperature converter tapping and slag-blocking can effectively control the carbon content of the final product, ensure dephosphorization, and reduce phosphorus and sulfur reversion; white slag formation and control of FeO+MnO in the slag can ensure the slag's reducing capacity, 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 pre-casting slag calming, casting superheat, and tundish dwell time can homogenize the slag temperature and effectively promote the flotation and removal of inclusions; dynamic light reduction and continuous casting billet casting speed control can effectively improve billet quality and reduce defects such as cracks and segregation; the control of center segregation, center porosity, and inclusions is an effective guarantee for the quality of continuous casting billets and the performance of steel plates.

[0049] S4. In the heating process, the continuously cast billet adopts a multi-stage heating method including preheating, heating, and homogenization, with a total heating time of 1.0 min / mm to 1.8 min / mm and a furnace exit temperature of 1100℃ to 1170℃. Specifically, the multi-stage heating of the continuously cast billet and the control of the total heating time are beneficial to improving heating efficiency and uniformity. Since the Nb content in this invention is low, low-temperature heating at the furnace exit can meet the element solution requirements. At the same time, it can effectively reduce the austenite grain size and is more conducive to reducing the rough rolling temperature and the rolling time in the rough rolling stage, thus achieving efficient low-temperature rolling.

[0050] S5. In the rolling process, the heated continuously cast billet is sequentially subjected to roughing and finishing rolling. Roughing includes roughing stage one, intermediate cooling, and roughing stage two. The initial roughing temperature is 1070℃~1130℃, and the final roughing temperature is 980℃~1030℃. The last two to three passes of roughing stage one, intermediate cooling, and roughing stage two all use rapid spray water cooling. The starting temperature of roughing stage two is <1050℃, the total deformation rate is ≥30%, the deformation rate per pass is ≥15% and increases progressively, and the roughing rolling speed is 1.0m / s~1.8m / s. After roughing, the intermediate billet is rapidly cooled to 860℃~920℃, and then heated to the finishing rolling starting temperature of 800℃~860℃. The finishing rolling temperature is 740℃~780℃, the deformation rate in the finishing stage is 60%~80%, and the total deformation rate below 800℃ is ≥15%.

[0051] S6. In the cooling process, the pre-straightened rolled steel plate undergoes two-stage cooling. The initial water cooling temperature is 690℃~740℃, and the final water cooling temperature is 100℃~250℃. There are a total of 15 sets of water cooling manifolds. During water cooling, the water flow rate of the first 5 to 7 sets of upper manifolds is 350L / m. 2 *min~550L / m 2 *min, the remaining upper manifold water flow is 150L / m 2 *min~330L / m 2 *min.

[0052] Specifically, the roughing process of this invention focuses on low-temperature rolling combined with high temperature gradient deformation of the thickness section. Because the low Nb and V-containing design of this invention lowers the austenite recrystallization temperature, the low-temperature rolling in the roughing stage promotes austenite grain recrystallization and effectively inhibits grain growth. Multi-stage rapid cooling significantly increases the temperature gradient of the thickness section, and the low-temperature, low-speed rolling in the second stage of roughing promotes the penetration of rolling deformation towards the center of the billet thickness, refining the microstructure near the thickness center and improving the uniformity of the steel plate's microstructure. The progressively increasing deformation rate in the second stage of roughing promotes sufficient austenite recrystallization. The deformation rate in the finishing rolling stage ensures the deformation and flattening of austenite in the non-recrystallized region; rapid cooling of the intermediate billet after rough rolling can quickly reduce the temperature and effectively inhibit austenite growth; the use of low-temperature rolling and low-temperature deformation rate control in the finishing rolling stage is beneficial to the formation of substructures and the accumulation of deformation energy in the microstructure; on the other hand, it can promote the formation of ferrite induced by a small amount of deformation, improve plasticity, toughness and strain; it can also provide good thermodynamic and kinetic conditions for the precipitation of Nb(CN) and V(CN), thereby playing a role in grain refinement, pinning, and promoting phase deformation nucleation; pre-straightening of the rolled steel plate is beneficial to improving the uniformity of water cooling and ensuring the shape of the steel plate; the initial water cooling temperature control can ensure the formation of a partially polygonal ferrite soft phase structure before accelerated 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 a fast initial cooling and a slow final cooling can increase the cooling rate of the high-temperature section and inhibit high-temperature phase transformation, while the smaller cooling water volume in the low-temperature section can reduce internal stress and improve the shape of the plate after cooling.

[0053] The following are specific embodiments.

[0054] Examples 1-8

[0055] The chemical composition of the steel in Examples 1-8 of this invention is shown in Table 1. The smelting and refining processes of Examples 1-8 of this invention are shown in Table 2. The continuous casting process of Examples 1-8 of this invention is shown in Table 3. The heating and rough rolling processes of Examples 1-8 of this invention are shown in Table 4. The finishing rolling and cooling processes of Examples 1-8 of this invention are shown in Table 5. The microstructure of Examples 1-8 of this invention is shown in Table 6. The mechanical properties of the steel plates in Examples 1-8 of this invention are shown in Table 7. The corrosion resistance of Examples 1-8 of this invention is shown in Table 8. The microstructure morphology of the steel plate in Example 2 of this invention is shown in Table 8. Figure 1 The morphology of the precipitated phase in the steel plate of Example 4 of this invention is shown below. Figure 2 .

[0056] Table 1. Chemical composition (%) of the steel in Examples 1-8 of the present invention

[0057] Example C Si Mn Nb V Nb+V Ti Ti / N Ni Mo Cr Mo+Cr / 1.8 1 0.049 0.27 1.08 0.029 0.057 0.086 0.013 2.50 0.06 0.09 0.37 0.30 2 0.051 0.34 1.32 0.033 0 0.033 0.016 2.46 0.09 0.05 0.22 0.17 3 0.031 0.42 1.37 0.018 0.075 0.093 0.009 1.23 0.05 0.13 0.19 0.24 4 0.057 0.37 0.96 0.032 0.072 0.104 0.012 1.71 0.09 0.12 0.28 0.28 5 0.038 0.28 1.26 0.025 0.043 0.068 0.01 1.61 0.08 0 0.36 0.20 6 0.043 0.33 1.21 0.015 0.062 0.077 0.011 2.29 0.07 0.08 0.31 0.25 7 0.036 0.47 1.18 0.021 0.058 0.079 0.013 2.36 0.06 0.09 0.28 0.25 8 0.041 0.36 1.28 0.026 0.065 0.091 0.015 2.46 0.10 0 0.34 0.19 Example Cu Zr Al N Ca Ca / S P S H O CE IIW ]]> CE Pcm ]]> 1 0 0.011 0.009 0.0052 0.0025 2.08 0.006 0.0012 0.00010 0.0011 0.336 0.143 2 0 0.020 0.018 0.0065 0.0031 3.10 0.008 0.0010 0.00012 0.0015 0.331 0.144 3 0.09 0.016 0.011 0.0073 0.0018 2.00 0.006 0.0009 0.00013 0.0010 0.348 0.145 4 0.12 0 0.023 0.0070 0.0033 3.30 0.005 0.0010 0.00009 0.0011 0.325 0.154 5 0.13 0.022 0.008 0.0062 0.0027 1.93 0.009 0.0014 0.00010 0.0014 0.343 0.140 6 0.07 0.015 0.012 0.0048 0.0030 2.73 0.008 0.0011 0.00015 0.0012 0.344 0.146 7 0.05 0.012 0.009 0.0055 0.0032 2.13 0.005 0.0015 0.00012 0.0010 0.326 0.140 8 0.10 0.019 0.021 0.0061 0.0027 2.45 0.007 0.0011 0.00010 0.0012 0.349 0.147

[0058] Table 2 Smelting and refining processes of Examples 1-8 of the present invention

[0059] Example Tapping temperature / °C Smelting tapping C content / % Top slag lime / fluorite FeO + MnO in slag weight percentage / % 1 1625 0.032 4.5 0.88 2 1621 0.035 4.2 0.93 3 1633 0.022 4.6 0.70 4 1617 0.039 4.2 0.77 5 1635 0.027 4.3 0.84 6 1630 0.030 4.8 0.80 7 1637 0.021 4.1 0.85 8 1631 0.031 4.6 0.91

[0060] Table 3 Continuous casting process of Examples 1-8 of the present invention

[0061]

[0062] Table 4 Heating and roughing processes of Examples 1-8 of the present invention

[0063]

[0064]

[0065] Table 5. Finishing and cooling processes of Examples 1-8 of the present invention.

[0066]

[0067] Table 6. Microstructure of Examples 1-8 of the present invention

[0068] Example Polygonal ferrite volume percentage / % Average grain size / pm 1 32 8.4 2 57 7.2 3 68 7.9 4 56 8.2 5 43 8.9 6 62 7.1 7 38 7.5 8 49 7.0

[0069] Table 7 Mechanical properties of steel plates from Examples 1-8 of the present invention

[0070]

[0071]

[0072] Note: The tensile specimen is a full-thickness rectangular specimen with a parallel test section width of 38.1 mm; the impact specimen dimensions are 10*55*55 mm.

[0073] Table 8 Corrosion resistance of Examples 1-8 of the present invention

[0074]

[0075] Based on the above results, the thickness of the high-performance offshore oil and gas extraction riser steel plate of this invention is ≥25mm. The composition employs a low Nb, Mo, and Mn design to promote the polygonal ferrite phase transformation before accelerated cooling, ensuring its proportion in the microstructure and improving alloy economy. Strength is enhanced and the yield strength ratio is controlled through the composite control of Mo and Cr. The combined addition of Nb, V, and N, along with the control of Al and Ti, promotes grain refinement and the formation of fine precipitates, exerting a hydrogen trapping effect and achieving beneficial effects on strengthening, phase transformation, microstructure, steel plate properties, and post-weld performance, thereby improving strength, corrosion resistance, and weldability. The addition of elements such as Zr and Ca controls inclusions, reducing their adverse effects on fatigue performance. In addition, by reducing the content of P, S, H and O and controlling the quality of continuous casting billets, the toughness, corrosion resistance and fatigue resistance are improved; coupled with the smelting, heating, rolling and cooling processes that match the alloy composition, the steel plate obtains comprehensive technical characteristics such as high strength, high toughness, high fatigue performance, as well as good corrosion resistance, strain resistance and weldability, and ideal microstructure, which meet the requirements for manufacturing high-performance marine oil and gas extraction risers.

[0076] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A wide and thick steel plate for high performance offshore oil and gas production riser, characterized by, The steel plate comprises the following components by weight percentage: C: 0.025%-0.060%, Si: 0.20%-0.50%, Mn: 0.80%-1.40%, Nb: 0.010%-0.018%, V: 0.043%-0.075%, Ti: 0.005%-0.020%, Ni: 0.01%-0.07%, Mo: <0.15%, Cr: 0.10%-0.40%, Cu: <0.15%, Zr: 0.015%-0.025%, Al: 0.005%-0.025%, N: 0.0048%-0.010%, Ca: 0.0015%-0.0040%, Ca / S: ≥1.6, P: ≤0.010%, S: ≤0.002%, H: ≤0.00015%, O: ≤0.0018%, and (Nb+V): 0.077%-0.093%, Ti / N: ≤2.5, ((Cr / 1.8)+Mo): ≥0.15%, and the balance being iron and inevitable impurities; The thickness of the steel plate is greater than or equal to 25 mm; the transverse yield strength of the steel plate is 430 MPa to 530 MPa, the transverse tensile strength is 570 MPa to 660 MPa, the transverse yield strength ratio is less than 0.79, the average transverse impact energy at -60 DEG C is greater than or equal to 250 J, the transverse DWTT shear area at -40 DEG C is greater than or equal to 85%, the average transverse impact energy of the welding heat affected zone at -20 DEG C is greater than or equal to 200 J; the longitudinal yield strength is 400 MPa to 500 MPa, the longitudinal tensile strength is 550 MPa to 640 MPa, the longitudinal uniform elongation U EL is greater than or equal to 12%, the longitudinal yield strength ratio is less than 0.78, the longitudinal strain hardening index is greater than or equal to 0.12, the 10 7 times fatigue strength is greater than or equal to 300 MPa, the HIC corrosion resistance satisfies CLR less than or equal to 15%, CTR less than or equal to 5% and CSR less than or equal to 2% after corrosion in NACE standard A solution for 96 hours, the SSCC corrosion resistance satisfies no fracture and no visible cracks under 10 times magnification after immersion in saturated H2S solution for 720 hours under 72% stress loading.

2. The wide and thick steel plate for high-performance offshore oil and gas production risers according to claim 1, characterized by, The steel sheet CE IIW is 0.31% to 0.38%, CE Pcm is 0.13% to 0.16%, wherein, CE IIW = C + Mn / 6 + (Cr + Mo) / 5 + (Ni + Cu) / 15; CE Pcm = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15 + V / 10 + 5B.

3. The wide and thick steel plate for high performance offshore oil and gas production riser according to claim 1, characterized by, The microstructure of the steel plate is polygonal ferrite and bainite; The bainite comprises lath bainite and granular bainite; The volume percentage of the polygonal ferrite is 25%-75%, and the average grain diameter is 5.0-10 μm; The steel plate contains fine carbonitride with a particle size of 5-20 nm dispersedly distributed therein.

4. A method of manufacturing a wide and thick steel plate for a high performance offshore oil and gas production riser according to any one of claims 1 to 3, characterized in that, The steel plate comprises: converter smelting, secondary refining, continuous casting process, heating process, rolling process and cooling process; In the rolling process, the heated continuous casting billet is sequentially subjected to rough rolling and finish rolling; the rough rolling comprises rough rolling stage one, intermediate cooling and rough rolling stage two; the rough rolling starting temperature is 1070-1130 °C, and the rough rolling final temperature is 980-1030 °C; the last 2-3 passes of the rough rolling stage one, the intermediate cooling and the rough rolling stage two all adopt rapid spray water cooling; the rough rolling stage two starting temperature is <1050 °C, the total deformation rate is ≥30%, the deformation rate of each pass is ≥15% and increases from pass to pass, and the rough rolling speed is 1.0-1.8 m / s; after the rough rolling, the intermediate warm-up billet is rapidly cooled to 860-920 °C, and then is warmed up to the finish rolling starting temperature of 800-860 °C, the finish rolling final temperature is 740-780 °C, the deformation rate in the finish rolling stage is 60%-80%, and the total deformation rate below 800 °C is ≥15%.

5. The preparation method according to claim 4, characterized in that, In the converter smelting, the converter tapping temperature is ≤1640 °C, C is ≤0.040%, the slag is blocked during tapping, and the slag layer thickness is ≤35 mm; lime and fluorite are added in a ratio of 4 / 1-5 / 1 to form top slag, and the weight percentage of FeO+MnO in the slag is controlled to be ≤1%.

6. The preparation method according to claim 4, characterized in that, In the secondary refining, after the molten steel obtained by the converter smelting is refined and deoxidized, Ti, Zr and V are sequentially added to adjust the composition of the molten steel.

7. The preparation method according to claim 4, characterized in that, In the continuous casting process, the static time of molten steel after refining and before continuous casting is greater than or equal to 10 min; the overheat of the continuous casting billet is 10-40 DEG C, the residence time of molten steel in the tundish during casting is greater than or equal to 350 s, and the dynamic soft reduction amount of the billet is greater than or equal to 4 mm; the continuous casting adopts constant speed, the speed is 0.6-1.5 m / min, the center segregation of the continuous casting billet is less than or equal to C0.5 level, the center porosity is less than or equal to 0.5 level, and the A, B, C and D type inclusions are controlled to be less than or equal to 1 level.

8. The preparation method according to claim 4, characterized in that, In the heating process, the total heating time is 1.0-1.8 min / mm, and the discharge temperature is 1100-1170 DEG C.

9. The preparation method according to claim 4, characterized in that, In the cooling process, the rolled steel plate is pre-straightened and then cooled in two stages, the initial water cooling temperature is 690-740 DEG C, the final water cooling temperature is 100-250 DEG C, there are 15 groups of water cooling headers, the water flow of the first 5-7 groups of upper headers is 350 L / m 2 *min-550 L / m 2 *min, the water flow of the rest of the upper headers is 150 L / m 2 *min-330 L / m 2 *min.

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