Pressure vessel steel plate for 720MPa-grade 16-200,000 cubic oversize crude oil storage tank and manufacturing method of pressure vessel steel plate

Abstract

The invention relates to the technical field of steel, in particular to a pressure vessel steel plate for a 720 MPa-grade 16-200 thousand cubic oversize crude oil storage tank and a manufacturing method of the pressure vessel steel plate. The steel plate comprises the following chemical components in percentage by weight: 0.070% to 0.100% of C, 0.20% to 0.30% of Si, 1.45% to 1.60% of Mn, less than or equal to 0.012% of P, less than or equal to 0.002% of S, 0.030% to 0.050% of Nb, 0.015% to 0.025% of Ti, 0.040% to 0.060% of V, 0.80% to 0.90% of Ni, 0.40% to 0.55% of Cr, 0.15% to 0.25% of Mo, 0.30% to 0.45% of Cu, 0.020% to 0.050% of Alt and the balance of Fe and inevitable impurities. A martensite, retained austenite and carbide three-phase microstructure is obtained through quenching-carbon distribution-tempering heat treatment, carbides are dispersed and distributed, the microstructure is uniform, and the product has the characteristics of high strength, high toughness and high plasticity and is widely applied to the key fields of national strategic crude oil reserve, local crude oil commercial storage projects and the like.

Description

Technical Field

[0001] The present invention relates to the field of steel technology, and in particular to a 720MPa grade 160,000-200,000 cubic meter extra-large crude oil storage tank pressure vessel steel plate and a manufacturing method thereof. Background Art

[0002] With the continuous growth of global energy demand, the demand for ultra-large crude oil storage tanks is increasing. At present, the manufacture of ultra-large crude oil storage tanks abroad mainly adopts steel plates with yield strength of 550Mpa and 620Mpa. Due to the limited yield strength of steel plates, in order to ensure the structural integrity and safety of storage tanks under complex working conditions, thicker steel plates have to be used, and the thickness usually reaches 60 to 80mm. This increase in thickness directly leads to the difficulty of engineering welding and manufacturing costs.

[0003] In addition, in the industrial production process of steel plates, improper protection pouring measures is another problem that needs to be solved urgently. If the molten steel is not effectively protected during the pouring process, secondary oxidation is very likely to occur. This will not only introduce a large number of non-metallic inclusions and reduce the purity of the steel, but also have an adverse effect on the mechanical properties and corrosion resistance of the steel plate. The decline in the purity of the steel will directly affect the service life and safety performance of the storage tank, and increase the cost of subsequent maintenance and replacement. Summary of the invention

[0004] The object of the present invention is to overcome the above problems and shortcomings and to provide a 720MPa grade 160,000-200,000 cubic meter extra-large crude oil storage tank pressure vessel steel plate and a manufacturing method thereof.

[0005] The present invention adopts the process of nickel-molybdenum-chromium-niobium-vanadium-titanium microalloying + continuous casting billet smelting + controlled rolling and controlled cooling + quenching-carbon distribution-tempering treatment, so that the product has high strength, high toughness and high plasticity, and at the same time the internal quality of the continuous casting billet and the purity of the steel are greatly improved, the deviation of the mechanical properties of the steel plate head and tail is small, and the uniformity of the plate performance is good. After the simulated post-weld heat treatment, it still has a low yield strength ratio and good strength and toughness matching.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] In one aspect, the present invention provides a 720MPa grade 160,000-200,000 cubic extra-large crude oil storage tank pressure vessel steel plate, the chemical composition of the steel plate is as follows by weight percentage:

[0008] C: 0.070% ~ 0.100%, Si: 0.20% ~ 0.30%, Mn: 1.45% ~ 1.60%, P ≤ 0.012%, S ≤ 0.002%, Nb: 0.030% ~ 0.050%, Ti: 0.015% ~ 0.025%, V: 0.040% ~ 0.060%, Ni: 0.80% ~ 0.90%, Cr: 0.40% ~ 0.55%, Mo: 0.15% ~ 0.25%, Cu: 0.30% ~ 0.45%, Alt: 0.020 ~ 0.050%, and the rest is Fe and unavoidable impurities.

[0009] The reasons for adopting the above components are as follows:

[0010] (1) C: C is the main component element of steel. The strength of steel mainly depends on the content of C in the steel. Too high C content will lead to poor toughness, plasticity and welding performance of the steel; low C content will lead to low strength and performance after simulated stress relief treatment. In order to ensure that the steel plate has good low-temperature impact toughness, strength and welding performance during use, the C content in the steel of the present invention is controlled to be 0.070% to 0.100%.

[0011] (2) Si: Si is a common solid solution strengthening alloying element in steel. It is essential for the toughness and hardenability of steel and even for ensuring the deoxidation of steel. However, a high content of Si will also lead to a decrease in the toughness of the steel. Therefore, the Si content in the steel of the present invention is controlled at 0.20% to 0.30%.

[0012] (3) Mn: The Mn element can strengthen pearlite in steel by solid solution strengthening. C-Mn strengthening is also the main way to improve the strength of low carbon steel. However, if the Mn content is too high, the production cost will be increased. The Mn element is easy to combine with the S element to form MnS, which reduces the material's resistance to hydrogen-induced cracking. At the same time, too high a Mn content will reduce the activity of the carbon element. Therefore, the Mn content in the steel of the present invention is controlled at 1.45% to 1.60%.

[0013] (4) P: Phosphorus is a harmful element in steel. It increases the cold brittleness of steel, deteriorates welding performance, reduces plasticity, and deteriorates cold bending performance. In addition, P is particularly sensitive to radiation embrittlement. Therefore, the P content in steel is required to be as low as possible. The present invention controls the P content to be less than 0.012%.

[0014] (5) S: S is usually a harmful element. S is usually easy to form brittle sulfides with alloy elements in steel, making the steel hot brittle and reducing the ductility and toughness of the steel. At the same time, S also tends to accelerate radiation embrittlement. Therefore, the S content in the steel of the present invention is controlled to be less than 0.002%.

[0015] (6) V: V is a microalloying element. Microalloying of V in steel can form fine second-phase particles, which play a role in pinning grain boundaries and precipitation strengthening. It can effectively refine the grains and greatly improve the comprehensive mechanical properties of the steel, such as strength, toughness, ductility and thermal fatigue resistance. The V content in the steel of the present invention is controlled at 0.040% to 0.060%.

[0016] (7) Nb: As a strong carbide-forming element, Nb forms a NbC phase with large dispersion and good high-temperature stability in steel, which plays a role in precipitation strengthening. Through multi-stage rolling, it can effectively refine the grains and improve the reduction of toughness caused by precipitation strengthening, so that the steel plate can obtain the comprehensive performance of high strength and high toughness. In addition, in the steel with Nb-Mo composite addition, Mo can also be segregated on the NbC matrix interface, preventing the coarsening of NbC particles, thereby greatly improving the high-temperature strength of the steel. Therefore, the Nb content in the steel of the present invention is controlled at 0.030% to 0.050%.

[0017] (8) Ti: Adding an appropriate amount of Ti can form a large number of dispersed fine TiN or Ti 2 O 3 Ti also has a deoxidizing effect, ensuring that B is not oxidized and nitrided. B can reduce the transformation temperature from austenite to pearlite phase, promote the formation of needle-shaped pearlite in the grains, and play a role in refining the grains. However, when w(Ti) ≥ 0.09%, the content of needle-shaped pearlite will be reduced, and the low-temperature toughness of the steel plate will be deteriorated. Therefore, the Ti content in the steel of the present invention is controlled to be 0.020% to 0.050%.

[0018] (9) Alt: Adding a small amount of Al to steel can effectively refine austenite grains, thereby refining ferrite grains and structure, and improving the impact toughness of steel. However, Al has the disadvantage of affecting the hot working performance, welding performance and cutting performance of steel. Therefore, the Alt content in the steel of the present invention is controlled at 0.015% to 0.045%.

[0019] (10) Ni: Ni is a solid solution strengthening element in steel that can improve the strength of steel. Ni reduces the resistance to dislocation movement in steel, relaxes stress, and further changes the substructure of the matrix structure, thereby improving the toughness of steel, especially low-temperature toughness. However, too high Ni content in medium carbon steel will increase the phase transition temperature. Therefore, the Ni content in the present invention is controlled at 0.80% to 0.90%.

[0020] (11) Mo: Mo mainly relies on solid solution strengthening and grain boundary strengthening to improve the strength of steel. Secondly, Mo increases the stability of supercooled austenite, shifts the austenite to pearlite transformation curve to the right, and obtains a finer pearlite structure after phase transformation. In addition, Ti and Mo combine to precipitate a large amount of nano-sized Ti-Mo (CN) carbides in the steel. The refined carbides pin dislocations, greatly improving the strength and toughness of the steel. Therefore, the Mo content in the steel of the present invention is controlled to be 0.15% to 0.25%.

[0021] (12) Cu: The prominent role of Cu in steel is to improve the corrosion resistance of ordinary carbon low alloy steel, and to increase the strength and yield strength ratio of steel, without adversely affecting the welding performance. At the same time, its role is similar to that of nickel, and it can play a certain role in saving nickel and reducing costs. However, when the content is high, it will cause copper brittleness during hot deformation processing. Therefore, the Cu content in the steel of the present invention is controlled to be 0.30% to 0.45%.

[0022] (13) Cr: Chromium is an element that stabilizes carbides. The main function of chromium in quenched and tempered steel is to improve hardenability, so that the steel has better comprehensive mechanical properties after quenching and tempering, and the strength, toughness and elongation are all improved. Chromium-containing carbides can also be formed in carburized steel, thereby improving the wear resistance of the material surface. Therefore, the Cr content in the steel of the present invention is controlled to be 0.40% to 0.55%.

[0023] In the above technical solution, further, the thickness of the finished steel plate is 10 to 50 mm.

[0024] In the above technical solution, further, the thickness of the finished steel plate is 10mm≤<30mm, the tensile strength of the finished steel plate in the transverse direction at 1 / 4 of the thickness in the delivery state is 860-890MPa, the yield strength is 740-770MPa, the elongation after fracture is 29%-32%, the yield strength ratio is 0.85-0.87, the impact energy at -70°C is 160-230J, the side expansion value LE is 1.1-1.9mm, the welding line energy is 140-150KJ / cm, the impact energy of the heat affected zone at -50°C after welding is 120-190J, and the side expansion value LE after welding is 1.0-2.0mm;

[0025] The thickness of the finished steel plate is 30mm≤≤50mm, the transverse tensile strength of the finished steel plate at 1 / 4 and 1 / 2 of the thickness in the delivery state is 840~890MPa, the yield strength is 720~760MPa, the elongation after fracture is 30%~33%, the yield strength ratio is 0.85~0.87, the impact energy at -70℃ is 160~250J, the side expansion value LE is 1.2~1.5mm, the welding line energy is 140~150KJ / cm, the impact energy of the heat affected zone at -50℃ after welding is 110~200J, and the side expansion value LE after welding is 1.3~1.7mm.

[0026] In the above technical solution, further, the thickness of the finished steel plate is 10mm≤<30mm, the tensile strength of the finished steel plate at 1 / 4 of the thickness after simulated post-weld heat treatment is 850-880MPa, the yield strength is 730-760MPa, the elongation after fracture is 29%-32%, the yield strength ratio is 0.85-0.87, the impact energy at -70℃ is 150-250J, and the lateral expansion value LE is 1.0-2.0mm;

[0027] The thickness of the finished steel plate is 30mm≤≤50mm. The transverse tensile strength of the finished steel plate at 1 / 4 and 1 / 2 of the thickness after simulated post-weld heat treatment is 850-880MPa, the yield strength is 730-760MPa, the elongation after fracture is 24%-33%, the yield strength ratio is 0.85-0.86, the impact energy at -70℃ is 190-270J, and the lateral expansion value LE is 1.3-1.7mm.

[0028] Another aspect of the present invention provides a method for manufacturing the above steel plate, comprising the following steps:

[0029] (1) Continuous casting smelting:

[0030] RH inlet temperature is 1590~1720℃, RH oxygen blowing volume is 5~25m 3 / h, circulating oxygen blowing time 30 ~ 40min, effectively preventing secondary oxidation of molten steel, and adopting two-step aluminum deoxidation method, that is, adding aluminum cake for pre-deoxidation during converter steelmaking + adding aluminum wire for deoxidation during LF furnace refining, continuous casting whole process protection casting, continuous casting billet thickness 250 ~ 300mm;

[0031] (2) Controlled rolling and controlled cooling:

[0032] After heating the continuous casting billet, rough rolling is carried out to open the billet. The rough rolling start temperature is 1100-1130℃, the rough rolling final rolling temperature is 980-1020℃, and after rough rolling, the intermediate billet roller table swings back and forth and air cools to 905-935℃ for continuous multi-pass finishing rolling. The finishing rolling final rolling temperature is 835-875℃. After finishing rolling, pre-straightening is carried out, followed by ACC laminar cooling. The start cooling temperature is 810-860℃, so that the austenite grains can retain more storage energy. The cooling rate is 15-25℃ / s water cooling, the steel plate red-return temperature is 650-720℃, the number of ACC headers is 10-12 groups, the roller speed is 1.2-1.4m / s, and the water volume is 270-290m 3 / h, water temperature 24 ~ 30 ℃, at the same time, the head and tail of the pre-straightened steel plate are shielded during ACC laminar cooling, so that the temperature difference between the head and tail of the steel plate is less than 20 ℃, the temperature uniformity of the steel plate is good, the unevenness of the steel plate after ACC is ≤ 8mm / m, the steel plate shape is straight, and the steel plate shape requirements for entering the furnace are met;

[0033] (3) Quenching-Carbon Distribution-Tempering Heat Treatment:

[0034] The quenching temperature is 850-870℃, the heating rate is 0.5-1.5min / mm, the net heat preservation is 20-80min, after the heat preservation, water cool to 100-120℃, the chamber furnace is kept for 10-20min, the tempering temperature is 420-440℃, the heating rate is 1.5-2.5min / mm, the net heat preservation is 30-130min, after the heat preservation, air cool to room temperature;

[0035] (4) Straightening:

[0036] The unevenness of the finished steel plate after straightening is ≤5mm / m.

[0037] In the above technical solution, further, in step (1), during converter smelting, the charge block size is 50-100 mm, the charge hot charging temperature is 1150-1200° C., and the net insulation time is 3-6 min;

[0038] The amount of aluminum cake added is 1 to 5 kg / ton of steel, and the amount of aluminum wire added is 1 to 5 kg / ton of steel.

[0039] In the above technical solution, further, in step (1), the mold protection slag is composed of the following components in weight percentage: CaO 35% to 50%, Al 2 O 3 30%~40%, MnO 0~10%, SiO 2 5% to 10%, the remainder is inevitable impurities, the thickness of the slag film is 0.1 to 1.5 mm, to ensure that the inclusions are fully floated and removed to prevent the occurrence of linear defects in the ingot.

[0040] In the above technical solution, further, in step (1), the pouring temperature is 1530-1550°C, the pulling speed is 0.9-1.0 m·min -1 The billet is put into the slow cooling pit for slow cooling after coming off the line. The slow cooling temperature is 300-400℃ and the holding time is 12-24h.

[0041] In the above technical solution, further, in step (1), the continuous casting full-process protective pouring adopts two-stage protective pouring, i.e., protective pouring from ladle to tundish + protective pouring from tundish to crystallizer; wherein:

[0042] The method of protective pouring from ladle to tundish is:

[0043] a. Add covering agent to the tundish to reduce heat loss of molten steel, isolate air, reduce secondary oxidation of molten steel, and absorb inclusions floating from the molten steel;

[0044] b. Protective pouring adopts the protective sleeve method, which allows the molten steel in the ladle to flow into the tundish through a longer refractory protective tube. Argon gas is introduced into the connection between the long water inlet protective tube and the ladle water outlet to maintain positive pressure and prevent air from entering.

[0045] The protective pouring method from the tundish to the crystallizer is: using the liquid protection method, a nozzle ring is installed at the bottom of the tundish, and liquid nitrogen is sprayed around the molten steel and the liquid surface of the crystallizer. The injection pressure of the liquid nitrogen is 0.5~2MPa, forming a nitrogen curtain to prevent secondary oxidation. The pressure range of the nitrogen curtain is 0.1~0.5MPa.

[0046] In the above technical solution, further, in step (2), the heating adopts a four-stage heating method, the heating stage I temperature is 600-650°C, the heating stage II temperature is 1000-1050°C, the heating stage III temperature is 1170-1210°C, the soaking stage temperature is 1150-1190°C, the soaking stage time is 30-40min, and the total heating time is H*(0.9-1.2)min·mm -1 , H is the continuous casting billet thickness, mm; the appropriate heating system effectively controls the original austenite grain size and ensures sufficient solid solution of alloy elements, ensuring good final performance of the product.

[0047] In the above technical scheme, further, in step (2), rolling is carried out in a double-stand rolling mill, the reduction rate of each rough rolling pass is 10% to 15%, the thickness of the intermediate billet is 3 to 4 times the thickness of the finished steel plate, and the reduction rate of each finishing rolling pass is 8% to 13% to the final finished product thickness; the deformation amount should be appropriately increased in the rough rolling stage to promote the plastic deformation and recrystallization process of the steel, and the deformation amount should be controlled in the finishing rolling stage to avoid excessive work hardening of the steel. By reasonably distributing the deformation amount, the microstructure of the steel is optimized, thereby reducing its yield strength ratio.

[0048] In the above technical solution, further, in step (2), during the pre-straightening process, according to the thickness of the finished steel plate, the roller gap setting parameters of the pre-straightening machine system are adjusted: the tilt correction range is 0 to +1.5 mm, the roller gap correction range is -1.5 to +0.5 mm and the load reduction range is +0.5 to +1.0 mm, so that the steel plate after pre-straightening is straight and can smoothly enter the ACC area, avoiding a series of problems such as uneven temperature and warping of the steel plate caused by local water accumulation, asymmetric cooling and uneven cooling during the water cooling process.

[0049] In the above technical solution, further, in step (3), the straightening speed is 150 to 200 r / min.

[0050] The beneficial effects of the present invention are:

[0051] 1. Use niobium, vanadium, titanium, nickel, molybdenum and chromium microalloying to control the expected transformation of the organizational structure and lay the foundation for the strength and toughness of the steel plate.

[0052] 2. During the smelting process of continuous casting billets, the inclusion content in the steel is reduced by optimizing the protective pouring, slag system ratio and RH circulation process, and the low-power quality of the continuous casting billets is improved, which lays the foundation for improving the qualified rate of flaw detection and reducing the tensile delamination rate. The smelting process adopts the oxygen control-aluminum control method to fully improve the purity of the steel, reduce the inclusion content in the steel, and control the component segregation. The central segregation (grade) is ≤C1.0, and the central looseness is ≤0.5. Non-metallic inclusions such as Class A (sulfide), Class B (alumina), Class C (silicate), Class D (spherical oxide) and Class DS (single-particle spherical) shall not be greater than Class 0.5.

[0053] 3. The controlled rolling and controlled cooling process is adopted to obtain products with fully uniform and refined structure and good flatness. The unevenness after cold straightening is ≤5mm / m.

[0054] 4. Through quenching-carbon distribution-tempering heat treatment, a three-phase microstructure of 20-40% martensite, 30-40% retained austenite and 30-40% carbide is obtained. The carbides are dispersed and the organization is uniform. At the same time, the product has the characteristics of high strength, high toughness and high plasticity. It is ensured that the product has good mechanical properties and low yield strength ratio in the mold welding state. The steel plates in the delivery state and the simulated post-weld heat treatment state have good strength and toughness matching. The fluctuation range of yield strength and tensile strength is within 50MPa, and the yield strength ratio is 0.85-0.87. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 This is a metallographic structure photograph of the steel plate in Example 1. DETAILED DESCRIPTION

[0056] The following examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0057] Examples 1-7

[0058] The chemical compositions of the steel plates of Examples 1-7 of the present invention are shown in Table 1.

[0059] Table 1 Chemical composition of steel plates of Examples 1-7 of the present invention (wt%)

[0060] Example C Si Mn P S V Nb Ti Ni Cr Mo Cu Alt 1 0.074 0.26 1.49 0.010 0.001 0.045 0.034 0.017 0.82 0.42 0.17 0.32 0.027 2 0.082 0.29 1.47 0.012 0.002 0.051 0.042 0.022 0.85 0.51 0.20 0.38 0.033 3 0.091 0.24 1.54 0.011 0.001 0.043 0.037 0.025 0.87 0.48 0.21 0.42 0.045 4 0.077 0.26 1.52 0.008 0.002 0.059 0.048 0.018 0.81 0.54 0.18 0.36 0.039 5 0.095 0.25 1.56 0.007 0.001 0.040 0.031 0.020 0.89 0.45 0.19 0.40 0.030 6 0.088 0.30 1.51 0.006 0.001 0.056 0.045 0.019 0.84 0.49 0.24 0.34 0.026 7 0.099 0.25 1.50 0.009 0.002 0.050 0.049 0.020 0.86 0.50 0.20 0.44 0.040

[0061] Table 2 Main process parameters for continuous casting smelting of Examples 1-7 of the present invention

[0062]

[0063] Table 3 Chemical composition and slag film thickness of the mold protection slag of Examples 1-7 of the present invention

[0064]

[0065]

[0066] Table 4 Liquid protection pouring and pouring process parameters of Examples 1-7 of the present invention

[0067]

[0068] Table 5 Macroscopic evaluation grade of continuous casting slabs and gas element content of casting slabs in Examples 1-7 of the present invention

[0069]

[0070]

[0071] Table 6 Heating process parameters of continuous casting slabs in Examples 1-7 of the present invention

[0072]

[0073] Table 7 Steel plate rolling process parameters of Examples 1-7 of the present invention

[0074]

[0075]

[0076] Table 8 Pre-straightening process parameters of steel plates in Examples 1-7 of the present invention

[0077] Example Tilt correction / mm Roll gap correction / mm Depression with load / mm 1 0.9 -1.4 0.6 2 1.0 -1.0 0.7 3 1.1 -0.6 0.9 4 1.2 0.1 0.8 5 1.3 0.2 0.6 6 1.4 0.4 0.9 7 1.0 -1.1 0.7

[0078] Table 9 ACC laminar cooling process parameters of steel plates in Examples 1-7 of the present invention

[0079]

[0080]

[0081] Table 10 Quenching-carbon distribution-tempering heat treatment process parameters of the steel of the present invention

[0082]

[0083] Table 11 Comprehensive mechanical properties of steel plates in delivery state in Examples 1-7 of the present invention

[0084]

[0085]

[0086] The whole steel plate is ultrasonically tested according to the provisions of NB / T 47013.3. The scanning method is: the probe is scanned with parallel lines perpendicular to and parallel to the rolling direction of the steel plate and with a spacing of 190-200mm. 100% scanning should be done within 40-50mm on both sides of the predetermined line of the steel plate groove. The defect assessment is qualified according to the T1 level specified in NB / T 47013.3, and the qualified rate is 100%. The flaw detection performance test results are shown in Table 14.

[0087] Table 12 Test results of flaw detection performance of steel plates in delivery state of Examples 1-7 of the present invention

[0088]

[0089]

[0090] Table 13 Non-metallic inclusions in the steel plates of Examples 1-7 of the present invention as delivered

[0091]

[0092] The samples of Examples 1-7 were subjected to simulated post-weld heat treatment tests, and the simulated post-weld heat treatment system was as follows: temperature 630-650°C, net heat preservation 40-240min, heating rate 2-8°C / min above 400°C, no need to control the heating rate before heating to 400°C; cooling rate 2-10°C / min below 400°C, natural cooling after cooling to 400°C, and air cooling to room temperature. The simulated post-weld heat treatment process parameters are shown in Table 14, and the mechanical properties of the simulated post-weld heat treated steel plates are shown in Table 15.

[0093] Table 14 Main process parameters of simulated post-weld heat treatment of steel in Example 1-7 of the present invention

[0094]

[0095]

[0096] Table 15 Comprehensive mechanical properties of steel plates in mold-welded state in Examples 1-7 of the present invention

[0097]

[0098] like Figure 1 As shown, the steel plate has a three-phase microstructure of 20-40% martensite, 30-40% retained austenite and 30-40% carbide. The carbides are dispersed and the structure is uniform.

[0099] In order to describe the present invention, the present invention is appropriately and fully illustrated by the examples in the above. The above implementation modes are only used to illustrate the present invention, but not to limit the present invention. Ordinary technicians in the relevant technical field can make various changes and modifications without departing from the spirit and scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made should be included in the protection scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. A 720MPa grade 160,000-200,000 cubic extra-large crude oil storage tank pressure vessel steel plate, characterized in that: The chemical composition of the steel plate is as follows by weight percentage: C: 0.070% ~ 0.100%, Si: 0.20% ~ 0.30%, Mn: 1.45% ~ 1.60%, P ≤ 0.012%, S ≤ 0.002%, Nb: 0.030% ~ 0.050%, Ti: 0.015% ~ 0.025%, V: 0.040% ~ 0.060%, Ni: 0.80% ~ 0.90%, Cr: 0.40% ~ 0.55%, Mo: 0.15% ~ 0.25%, Cu: 0.30% ~ 0.45%, Alt: 0.020 ~ 0.050%, and the rest is Fe and unavoidable impurities.

2. The 720MPa grade 160,000-200,000 cubic extra-large crude oil storage tank pressure vessel steel plate according to claim 1, characterized in that: The thickness of the finished steel plate is 10 to 50 mm.

3. The 720MPa grade 160,000-200,000 cubic extra-large crude oil storage tank pressure vessel steel plate according to claim 2, characterized in that: 10mm≤The thickness of the finished steel plate is <30mm, the transverse tensile strength of the finished steel plate at 1 / 4 of the thickness in the delivery state is 860~890MPa, the yield strength is 740~770MPa, the elongation after fracture is 29%~32%, the yield strength ratio is 0.85~0.87, the impact energy at -70℃ is 160~230J, the side expansion value LE is 1.1~1.9mm, the welding line energy is 140-150KJ / cm, the impact energy of the heat affected zone at -50℃ after welding is 120~190J, and the side expansion value LE after welding is 1.0~2.0mm; The thickness of the finished steel plate is 30mm≤≤50mm, the transverse tensile strength of the finished steel plate at 1 / 4 and 1 / 2 of the thickness in the delivery state is 840~890MPa, the yield strength is 720~760MPa, the elongation after fracture is 30%~33%, the yield strength ratio is 0.85~0.87, the impact energy at -70℃ is 160~250J, the side expansion value LE is 1.2~1.5mm, the welding line energy is 140~150KJ / cm, the impact energy of the heat affected zone at -50℃ after welding is 110~200J, and the side expansion value LE after welding is 1.3~1.7mm.

4. The 720MPa grade 160,000-200,000 cubic extra-large crude oil storage tank pressure vessel steel plate according to claim 2, characterized in that: 10mm≤The thickness of the finished steel plate is <30mm. The tensile strength of the finished steel plate at 1 / 4 of the thickness after simulated post-weld heat treatment is 850-880MPa, the yield strength is 730-760MPa, the elongation after fracture is 29%-32%, the yield strength ratio is 0.85-0.87, the impact energy at -70℃ is 150-250J, and the lateral expansion value LE is 1.0-2.0mm; The thickness of the finished steel plate is 30mm≤≤50mm. The transverse tensile strength of the finished steel plate at 1 / 4 and 1 / 2 of the thickness after simulated post-weld heat treatment is 850-880MPa, the yield strength is 730-760MPa, the elongation after fracture is 24%-33%, the yield strength ratio is 0.85-0.86, the impact energy at -70℃ is 190-270J, and the lateral expansion value LE is 1.3-1.7mm.

5. A method for manufacturing a 720MPa grade 160,000-200,000 cubic meter extra-large crude oil storage tank pressure vessel steel plate as claimed in any one of claims 1 to 4, characterized in that: The method comprises the following steps: (1) Continuous casting smelting: RH inlet temperature is 1590~1720℃, RH oxygen blowing volume is 5~25m 3 / h, the circulating oxygen blowing time is 30-40min, and the two-step aluminum addition method is used for deoxidation, that is, the aluminum cake is added for pre-deoxidation during the converter steelmaking process and the aluminum wire is added for deoxidation during the LF furnace refining process. The continuous casting is protected throughout the casting process, and the continuous casting billet thickness is 250-300mm; (2) Controlled rolling and controlled cooling: After heating the continuous casting billet, rough rolling is carried out to open the billet. The starting rolling temperature of rough rolling is 1100-1130℃, and the final rolling temperature of rough rolling is 980-1020℃. After rough rolling, the intermediate billet roller table swings back and forth and air cools until the temperature reaches 905-935℃ for continuous multi-pass finishing rolling. The final rolling temperature of finishing rolling is 835-875℃. After finishing rolling, pre-straightening is carried out, followed by ACC laminar cooling. The starting cooling temperature is 810-860℃, so that the austenite grains can retain more storage energy. The cooling rate is 15-25℃ / s water cooling, the steel plate red-returning temperature is 650-720℃, the number of ACC headers is 10-12 groups, the roller speed is 1.2-1.4m / s, and the water volume is 270-290m 3 / h, water temperature 24 ~ 30 ℃, at the same time, the head and tail of the pre-straightened steel plate are shielded during ACC laminar cooling, so that the temperature difference between the head and tail of the steel plate is less than 20 ℃, and the unevenness of the steel plate after ACC laminar cooling is ≤ 8mm / m; (3) Quenching-Carbon Distribution-Tempering Heat Treatment: The quenching temperature is 850-870℃, the heating rate is 0.5-1.5min / mm, the net heat preservation is 20-80min, after the heat preservation, water cool to 100-120℃, the chamber furnace is kept for 10-20min, the tempering temperature is 420-440℃, the heating rate is 1.5-2.5min / mm, the net heat preservation is 30-130min, after the heat preservation, air cool to room temperature; (4) Straightening: The unevenness of the finished steel plate after straightening is ≤5mm / m.

6. The manufacturing method according to claim 5, characterized in that: In step (1), during converter smelting, the charge block size is 50-100 mm, the charge hot charging temperature is 1150-1200°C, and the net insulation time is 3-6 minutes. The amount of aluminum cake added is 1 to 5 kg / ton of steel, and the amount of aluminum wire added is 1 to 5 kg / ton of steel.

7. The manufacturing method according to claim 5, characterized in that: In step (1), the pouring temperature is 1530-1550°C and the pulling speed is 0.9-1.0 m / min. -1 The billet is put into the slow cooling pit for slow cooling after it comes off the line. The slow cooling temperature is 300-400℃ and the holding time is 12-24h. The mold protection slag is composed of the following components in weight percentage: CaO 35%-50%, Al2O3 30%-40%, MnO0-10%, SiO2 5%-10%, and the balance is inevitable impurities. The thickness of the slag film is 0.1-1.5 mm.

8. The manufacturing method according to claim 5, characterized in that: In step (2), the heating adopts a four-stage heating method, with the temperature of heating stage I being 600-650°C, the temperature of heating stage II being 1000-1050°C, the temperature of heating stage III being 1170-1210°C, the temperature of the soaking stage being 1150-1190°C, the soaking stage time being 30-40 min, and the total heating time being H*(0.9-1.2) min·mm -1 , H is the continuous casting billet thickness, mm; The reduction rate of each rough rolling pass is 10% to 15%, the thickness of the intermediate billet is 3 to 4 times the thickness of the finished steel plate, and the reduction rate of each finishing rolling pass is 8% to 13% to the final finished product thickness.

9. The manufacturing method according to claim 5, characterized in that: In step (2), during the pre-straightening process, the pre-straightening machine system roll gap setting parameters are: the tilt correction range is 0 to +1.5 mm, the roll gap correction range is -1.5 to +0.5 mm, and the load reduction range is +0.5 to +1.0 mm.

10. The manufacturing method according to claim 5, characterized in that: In step (3), the straightening speed is 150-200 r / min.

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