A large heat input welding 150,000 cubic large crude oil storage tank pressure vessel steel plate and its manufacturing method

Abstract

The present application relates to the technical field of steel, and in particular, relates to a large-line-energy welding 150,000 cubic large crude oil storage tank pressure vessel steel plate and a manufacturing method thereof.The chemical components of the steel plate are as follows in terms of percentage by weight: C: 0.070%-0.100%, Si: 0.20%-0.30%, Mn: 1.45%-1.60%, P: 0.015% or less, S: 0.003% or less, Nb: 0.030%-0.050%, Ti: 0.020%-0.050%, V: 0.040%-0.060%, Ni: 0.50%-0.60%, Cr: 0.10%-0.30%, Mo: 0.15%-0.25%, Cu: 0.10%-0.18%, Alt: 0.020%-0.050%, N: 0.006%-0.008%, and the rest is Fe and inevitable impurities.The present application adopts the process means of nickel-molybdenum-chromium-niobium-vanadium-titanium micro-alloying + continuous casting billet smelting + controlled rolling and controlled cooling + quenching and tempering treatment, so that the product has good strength and toughness matching, welding performance and flat plate shape, improves the toughness of the steel plate welding heat affected zone, and increases the welding heat input to 200 KJ / cm.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel, in particular, especially relates to a pressure vessel steel plate for 150,000 cubic large-scale crude oil storage tank with large heat input welding and a manufacturing method thereof. BACKGROUND

[0002] With the implementation of China's energy strategy and the increasing demand for oil reserves, crude oil storage tanks are developing towards large-scale. The performance of steel for large-scale crude oil storage tanks is required to be higher, especially in the welding process, which needs to withstand higher heat input. In the large heat input welding process, the heat affected zone is large, which is easy to produce welding cracks. The development of crude oil storage tank steel suitable for large heat input welding process needs to have lower welding crack sensitivity to ensure the quality of the welded joint.

[0003] At present, the crude oil storage tank steel plate produced by the traditional smelting method will have a large decrease in toughness of the heat affected zone (HAZ) after large heat input welding due to the serious coarsening of austenite grains and the formation of brittle and hard phase microstructure in the grains, which often cannot meet the minimum requirement of impact toughness. Therefore, the development of crude oil storage tank steel suitable for large heat input welding process is one of the technical innovations in the field of steel manufacturing, which not only can improve the technical level of steel manufacturing in China, but also can promote the technical progress and industrial upgrading of related industries. SUMMARY

[0004] The purpose of the present application is to overcome the above problems and deficiencies, and to provide a pressure vessel steel plate for 150,000 cubic large-scale crude oil storage tank with large heat input welding and a manufacturing method thereof.

[0005] The present application adopts the process means of nickel-molybdenum-chromium-niobium-vanadium-titanium micro-alloying + continuous casting billet smelting + controlled rolling and controlled cooling + quenching and tempering treatment, so that the product has good strength and toughness matching, welding performance and flat plate shape. By strictly controlling the addition sequence of alloying elements, fine and dispersed inclusions are formed in the molten steel, the toughness of the steel plate welding heat affected zone is improved, and the welding heat input is increased to 200 KJ / cm. After simulating post-weld heat treatment, it still has low yield ratio and good strength and toughness matching.

[0006] In order to achieve the above purpose, the technical scheme of the present application is as follows:

[0007] In one aspect, the present application provides a pressure vessel steel plate for 150,000 cubic large-scale crude oil storage tank with large heat input welding, the chemical composition of the steel plate is as follows in terms of weight percentage:

[0008] C: 0.070% to 0.100%, Si: 0.20% to 0.30%, Mn: 1.45% to 1.60%, P ≤ 0.015%, S ≤ 0.003%, Nb: 0.030% to 0.050%, Ti: 0.020% to 0.050%, V: 0.040% to 0.060%, Ni: 0.50% to 0.60%, Cr: 0.10% to 0.30%, Mo: 0.15% to 0.25%, Cu: 0.10% to 0.18%, Alt: 0.020% to 0.050%, N: 0.006% to 0.008%, and the rest is Fe and inevitable impurities.

[0009] The above component design is as follows:

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

[0011] (2) Si: Si is a common solid solution strengthening alloying element in steel, which is necessary for the strength and toughness of the steel, hardenability and ensuring the deoxidization of the steel. However, high content of Si will also result in the decrease of the toughness of the steel. Therefore, the content of Si in the present application is controlled in 0.20% to 0.30%.

[0012] (3) Mn: Mn element can strengthen pearlite in the steel through solid solution strengthening, and C-Mn strengthening is also the main way to improve the strength of low carbon steel. However, too high content of Mn will increase the production cost, and Mn element is easy to combine with S element to form MnS, which reduces the hydrogen-induced cracking resistance of the material, and too high content of Mn will also reduce the activity of carbon element. Therefore, the content of Mn in the steel is required to be controlled in 1.45% to 1.60%.

[0013] (4) P: P is a harmful element in steel, which increases the cold brittleness of the steel, makes the welding performance worse, reduces the plasticity, makes the cold bending performance worse, and P is also particularly sensitive to irradiation embrittlement. Therefore, the lower the content of P in the steel is, the better, and the content of P in the present application is required to be lower than 0.015%.

[0014] (5) S: Sulfur is a harmful element under normal circumstances, and S is easy to form brittle sulfide with alloying elements in the steel, which makes the steel produce thermal brittleness, reduces the ductility and toughness of the steel, and S also has the tendency to accelerate irradiation embrittlement. Therefore, the content of S in the steel is required to be limited below 0.003% in the present application.

[0015] (6) V: V is a micro-alloying element. Micro-alloying of V in the steel can form fine second phase particles, which can pin grain boundaries and provide precipitation strengthening, and can effectively refine the grains, greatly improve the comprehensive mechanical properties of the steel, such as strength, toughness, ductility and thermal fatigue resistance. Therefore, the range of V added in the steel is 0.040% to 0.060%.

[0016] (7) Nb: Nb is a strong carbide-forming element. In the steel, Nb forms NbC phase with large dispersion and good high-temperature stability, which provides precipitation strengthening. Through multi-stage rolling, the grains can be effectively refined, the toughness reduction caused by precipitation strengthening can be improved, and thus the steel plate can obtain high strength and high toughness. In addition, in the steel with Nb-Mo composite addition, Mo can also be segregated on the interface of the NbC matrix, which prevents the coarsening of NbC particles, and thus greatly improves the high-temperature strength of the steel. Therefore, the content of Nb is controlled to be 0.030% to 0.050%.

[0017] (8) Ti: Adding an appropriate amount of Ti can form a large number of fine TiN or Ti2O3 particles dispersedly distributed, which can act as heterogeneous nucleation core for acicular pearlite during solidification of the structure, thereby refining the structure and inhibiting the coarsening of austenite grains. The high-melting-point inclusions formed by Ti can also refine the intracrystalline structure and obtain good HAZ toughness. Therefore, the content of Ti in the steel is controlled to be 0.020% to 0.050%.

[0018] (9) Al: Adding a small amount of Al element in the steel can effectively refine the austenite grains, thereby refining the ferrite grains and the structure and improving the impact toughness of the steel. However, Al has the disadvantage of affecting the hot working performance, welding performance and cutting performance of the steel. Therefore, the content of Al in the steel is controlled to be 0.020% to 0.0050%.

[0019] (10) Ni: Ni is a solid solution strengthening element in the steel, which can improve the strength of the steel. Ni can reduce the resistance to dislocation movement of the steel, relax the stress, and thus change the substructure of the matrix structure, thereby improving the toughness of the steel, especially the low-temperature toughness. However, too high Ni content in the medium carbon steel can increase the phase transition temperature. Therefore, the content of Ni is controlled to be 0.50% to 0.60%.

[0020] (11) Mo: Mo mainly relies on solid solution strengthening and grain boundary strengthening to improve the strength of the steel. Secondly, Mo increases the stability of undercooled austenite, which makes the austenite to pearlite transformation curve move to the right, and the pearlite structure obtained after phase transition is finer. In addition, Ti and Mo combine to precipitate a large amount of nanometer-sized Ti-Mo(CN) carbides in the steel, which can pin dislocations and greatly improve the strength and toughness of the steel. Therefore, the content of Mo in the steel is controlled to be 0.15% to 0.25%.

[0021] (12) Cu: The outstanding role of Cu in the steel is to improve the corrosion resistance of plain low alloy steel, and also to improve the strength and yield ratio of the steel, and has no adverse effect on the welding performance. Meanwhile, its effect is similar to that of nickel, and can play a role in nickel saving and cost reduction. However, when the content is high, copper brittleness occurs during hot deformation processing. Therefore, the content of Cu in the steel is controlled to be 0.10% to 0.18% in the present application.

[0022] (13) Cr: Chromium is an element that stabilizes carbide, and the addition of chromium reduces the dissolution rate of carbide. Therefore, when a hot deformation organization refining process is used, even if the heating temperature is increased or the heating time is prolonged, the eutectoid transformation can still be avoided to obtain a refined organization; chromium can also inhibit the graphitization of silicon and aluminum containing ultra-high carbon steel, increase the hardenability of the steel and have the effect of secondary hardening, which can improve the hardness and wear resistance of high carbon steel without making the steel brittle, and improve the fatigue life. Therefore, the content of Cr in the steel is controlled to be 0.10% to 0.30% in the present application.

[0023] (14) N: N can combine with Ti to form a large number of fine TiN dispersedly distributed, which can act as heterogeneous nucleation core for acicular ferrite during organization solidification, thereby refining the organization and improving the welding performance. Therefore, the content of N in the steel is controlled to be 0.006% to 0.008% in the present application.

[0024] In the above technical solution, further, the thickness of the finished steel plate is 10 to 50 mm.

[0025] In the above technical solution, further, 10 mm≤ the thickness of the finished steel plate <30 mm, the tensile strength of the finished steel plate at the delivery state at the thickness 1 / 4 is 760 to 790 MPa, the yield strength is 640 to 670 MPa, the elongation after fracture is 19 to 22%, the yield ratio is 0.83 to 0.86, the impact energy at -50°C is 160 to 230 J, the lateral expansion value LE is 1.1 to 1.9 mm, the welding line energy is 190-200 KJ / cm, the impact energy at -50°C of the heat affected zone after welding is 110 to 190 J, and the lateral expansion value LE after welding is 1.0 to 1.9 mm.

[0026] 30 mm≤ the thickness of the finished steel plate ≤50 mm, the tensile strength of the finished steel plate at the delivery state at the thickness 1 / 4 and 1 / 2 is 740 to 790 MPa, the yield strength is 620 to 660 MPa, the elongation after fracture is 20 to 23%, the yield ratio is 0.82 to 0.85, the impact energy at -50°C is 160 to 250 J, the lateral expansion value LE is 1.2 to 1.5 mm, the welding line energy is 190-200 KJ / cm, the impact energy at -50°C of the heat affected zone after welding is 140 to 200 J, and the lateral expansion value LE after welding is 1.3 to 1.7 mm.

[0027] In the technical solution, further, 10mm≤thickness of the finished steel plate<30mm, the tensile strength of the finished steel plate in the simulated post-weld heat treatment state at the 1 / 4 thickness in the transverse direction is 750-780MPa, the yield strength is 630-660MPa, the elongation after fracture is 19-22%, the yield strength ratio is 0.83-0.86, the impact energy at-50℃ is 160-230J, and the lateral expansion value LE is 1.0-2.0mm;

[0028] 30mm≤thickness of the finished steel plate≤50mm, the tensile strength of the finished steel plate in the simulated post-weld heat treatment state at the 1 / 4 and 1 / 2 thicknesses in the transverse direction is 750-780MPa, the yield strength is 630-660MPa, the elongation after fracture is 20-24%, the yield strength ratio is 0.83-0.85, the impact energy at-50℃ is 220-250J, and the lateral expansion value LE is 1.3-1.7mm.

[0029] Another aspect of the present application provides a manufacturing method of the above steel plate, comprising the following steps:

[0030] (1) Continuous casting billet smelting:

[0031] The oxide metallurgy technology is adopted, the oxygen content is 700-1000ppm before the converter deoxidization, the silicon iron 75# alloy and aluminum particles are added for deoxidization in the converter, the titanium iron is added for deoxidization when the oxygen content is 30-50ppm after the LF furnace temperature rising, the slagging and composition adjustment are performed when the oxygen content in the molten steel is 8-10ppm, the RH enters the station at the temperature of 1590-1620℃, the RH oxygen blowing amount is 5-25m 3 / h, the circulating oxygen blowing time is 5-10min, the effective secondary oxidation of the molten steel is prevented, the RH furnace is vacuumized to 0.4-0.5tor, the continuous casting is protected pouring in the whole process, and the continuous casting billet thickness is 250-300mm;

[0032] (2) Controlled rolling and controlled cooling:

[0033] After the continuous casting billet heating, rough rolling and blooming are performed, the rough rolling and blooming temperature is 1100-1130℃, the rough rolling final rolling temperature is 1030-1060℃, the intermediate billet roller back and forth swing air cooling is performed after the rough rolling, the temperature is waited to 905-935℃, the continuous multi-pass finishing rolling is performed, the finishing rolling final rolling temperature is 835-875℃, the roller is static waiting for 40-90s after the finishing rolling, the relaxation treatment is performed, the pre-straightening is performed after the relaxation treatment, then the ACC laminar cooling is performed, the open cooling temperature is 780-830℃, the austenite grain is stored with more stored energy, the cooling speed is 15-25℃ / s water cooling, the steel plate red temperature is 100-200℃, the ACC header number is 10-12 groups, the roller speed is 1.2-1.4m / s, and the water amount is 240-260m 3h, water temperature 14-20℃, at the same time, the head and tail of the pre-straightened steel plate are shielded and controlled in the ACC laminar cooling, the temperature difference of the redness of the head and tail of the steel plate after the ACC laminar cooling is less than 20℃, and the unevenness of the steel plate is less than or equal to 8mm / m;

[0034] (3) Quenching and tempering heat treatment:

[0035] The quenching temperature is 920-940℃, the heating rate is 0.5-1.5min / mm, the net holding time is 20-60min, after the holding, the water cooling is performed to room temperature, the tempering temperature is 650-670℃, the heating rate is 1.5-2.5min / mm, the net holding time is 30-110min, after the holding, the air cooling is performed to room temperature, and then the straightening is performed, and the unevenness of the finished steel plate after the cold straightening is less than or equal to 5mm / m.

[0036] In the step (1), in the converter smelting, the charge size is 50-100mm, and the charge hot charging temperature is 1150-1200℃.

[0037] The adding amount of the ferrosilicon 75# alloy is 4-5kg / ton of steel, and the ferrosilicon 75# alloy is a ferrosilicon alloy with a silicon content of 75%.

[0038] The adding amount of the aluminum particle is 0.03-0.08kg / ton of steel, and only a small amount of aluminum particle is used for slag deoxidization in the converter smelting process.

[0039] In the LF furnace, the adding amount of the ferrotitanium is 0.8-1kg / ton of steel.

[0040] In the step (1), in order to make the slag system in the liquid phase zone, the crystallizer protective slag is composed of the following components in weight percentage: CaO 40%-55%, Al2O3 1%-5%, MnO 0-10%, SiO2 30%-40%, and the balance is inevitable impurities, the thickness of the slag film is 0.1-1.5mm, the sufficient floating removal of the inclusions is ensured, and the generation of linear defects in the cast blank is prevented.

[0041] In the step (1), the pouring temperature is 1530-1550℃, and the pulling speed is 0.9-1.0m·min -1 The billet is cooled in the slow cooling pit after being discharged, the slow cooling temperature is 300-400℃, and the holding time is 12-24h.

[0042] The content of H element in the continuous casting billet is 1.0-2.0ppm, and the content of O element is 10-20ppm.

[0043] The continuous casting full-range protection casting adopts two-stage protection casting, i.e. ladle to tundish protection casting + tundish to crystallizer protection casting; wherein:

[0044] The ladle to tundish protection casting method is: a, adding covering agent in the tundish, which is used to reduce the heat loss of the molten steel, isolate air, reduce the secondary oxidation of the molten steel, and absorb the inclusions floating from the molten steel;

[0045] b, the protection casting adopts the protection sleeve method, the molten steel in the ladle flows into the tundish through a long refractory protection pipe, argon is introduced at the connection between the long nozzle protection pipe and the wide mouth of the ladle to form a positive pressure to prevent air from entering;

[0046] The tundish to crystallizer protection casting adopts the liquid protection method, a nozzle ring is installed at the bottom of the tundish, liquid nitrogen is sprayed to the surrounding of the molten steel and the liquid surface of the crystallizer to form a nitrogen curtain to prevent secondary oxidation.

[0047] In the above technical solution, further, in step (2), heating adopts four-stage heating mode, heating I section temperature is 600-650℃, heating II section temperature is 1000-1050℃, heating III section temperature is 1170-1210℃, soaking section temperature is 1150-1190℃, soaking section time is 30-40min, and total heating time is continuous casting billet thickness*(0.9-1.2)min·mm -1 ; The appropriate heating system effectively controls the original austenite grain size and ensures the full solid solution of alloy elements, and ensures the good final performance of the product.

[0048] In the above technical solution, further, in step (2), rolling is carried out on the double-rack rolling mill, longitudinal-horizontal rolling or full longitudinal rolling is adopted in the rough rolling stage, and the pass reduction rate is 15%-25%; the rough rolling pass reduction rate is greater than 15%, so that it is greater than the critical deformation rate, and mixed crystal is avoided, and austenite grains are repeatedly deformed and recrystallized; the intermediate billet thickness is 3-4 times the thickness of the finished steel plate.

[0049] Full longitudinal rolling is adopted in the finish rolling stage, the austenite is fully flattened and elongated along the rolling direction, the pass reduction rate is 5%-15%, and the finish rolling pass reduction rate is less than 15%, so as to facilitate plate shape control; after rolling through the austenite non-recrystallization zone, a large number of deformation bands and dislocations are formed in the deformed austenite grains, and the phase nucleation position and phase change driving force are increased.

[0050] In the above technical solution, further, in step (2), in the ACC laminar cooling, the head and tail of the steel plate are shielded and controlled according to the water-out plate shape of the steel plate;

[0051] The shielding control principle is that the temperature of the head and tail of the steel plate is close to that of the body, the number of cooling header groups for shielding control is reduced, and the flow adjustment time is shortened;

[0052] The shielding control parameters are: the shielding flow is 5% to 10%, the head shielding position is 800 to 900 mm away from the head of the plate, and the tail shielding position is 100 to 200 mm away from the tail of the plate; through the use of the ACC head and tail shielding function, the temperature difference between the head and tail of the steel plate and the body is reduced, the temperature in the length direction of the on-line quenched steel plate is uniform, and good plate shape is obtained, thereby meeting the requirements of the plate shape of the steel plate entering the furnace.

[0053] In the technical scheme, further, in step (2), in the pre-straightening process, according to the thickness of the finished steel plate, the roll gap setting parameters of the pre-straightening machine system are adjusted and controlled: the inclination correction range is 0 to +1.5 mm, the roll gap correction range is -1.5 to +0.5 mm, and the strip load press-down range is +0.5 to +1.0 mm, so that the steel plate after pre-straightening is flat and can smoothly enter the ACC area, avoiding a series of problems such as temperature unevenness, plate shape buckling and the like caused by local water accumulation, asymmetric cooling, uneven cooling and the like during water cooling.

[0054] In the technical scheme, further, in step (3), the straightening speed is 60 to 80 r / min.

[0055] The beneficial effects of the present application are:

[0056] 1. Nb-V-Ti-Ni-Mo-Cr microalloying is adopted to control the expected transformation of the organizational structure and lay the foundation for the strength and toughness of the steel plate.

[0057] 2. The "oxide metallurgy" technology is adopted to form fine and dispersed inclusions in the molten steel by strictly controlling the addition sequence of alloying elements, thereby improving the toughness of the steel plate in the welding heat affected zone. The grade of various inclusions in the delivered steel plate is controlled to be below 1.0, the density of TiN particles with a size of 0.01 to 0.3 μm is 2.0 to 2.9*10 6 mm 2 ; the density of TiN particles with a size of 0.3 to 0.5 μm is 1.0 to 1.9*10 4 mm 2 , there is no TiN particle with a size greater than 0.5 μm; the density of Ti2O3 particles with a size of 0.5 to 5 μm is 2300 to 2400 mm 2 ; the density of Ti2O3 particles with a size of 0.01 to 0.5 μm is 5300 to 5400 mm 2 ; the surface density of inclusions with a size of 0.2 to 0.5 μm in the steel is 3200 to 3300 mm 2 ; the surface density of inclusions with a size of 0.5 to 1.0 μm in the steel is 1500 to 1600 mm 2 ; and the surface density of inclusions with a size of 2.5 to 6.0 μm in the steel is 40 to 60 mm 2 .

[0058] 3. By optimizing the protection casting, slag ratio and RH cycle process, the inclusion content in the steel is reduced, the macrostructure quality of the continuous casting billet is improved, the basis for improving the flaw detection qualified rate and reducing the tensile layering rate is laid, the center segregation (level) is ≤C1.0 level, and the center porosity is ≤0.5 level.

[0059] 4. The controlled rolling and controlled cooling process is used, the product with fully refined and uniform structure and good flatness is obtained, and the unevenness after cold straightening is ≤5mm / m.

[0060] 5. By relaxation treatment and quenching and tempering heat treatment, the microstructure of the finished steel plate is 20%-30% ferrite + 70%-80% tempered bainite two-phase, the second phase is dispersedly distributed, the structure is uniform, the product has good strength and toughness matching, the proportion of ferrite and tempered bainite structure is reasonably adjusted, the mechanical properties of the product in the as-welded state are good, and the yield strength and tensile strength fluctuation range are within 50MPa, and the yield strength ratio is 0.85-0.90.

[0061] In summary, the pressure vessel steel plate product of the present application has good process performance and mechanical properties, the mechanical property deviation of the steel plate head and tail is small, the uniformity of the through plate performance is good, and is widely applied to key fields such as national strategic crude oil reserves and local crude oil storage projects. BRIEF DESCRIPTION OF DRAWINGS

[0062] Figure 1 The metallographic structure of the steel plate in the quenched and tempered state of Example 1. DETAILED DESCRIPTION

[0063] The following examples can make those skilled in the art more fully understand the present application, but do not limit the present application in any way.

[0064] Examples 1-7

[0065] The chemical composition of the steel plate of Examples 1-7 of the present application is shown in Table 1.

[0066] Table 1 Chemical composition (wt%) of the steel plate of Examples 1-7 of the present application

[0067] Examples C Si Mn P S V Nb Ti Ni Cr Mo Cu N Alt 1 0.076 0.26 1.49 0.010 0.003 0.045 0.036 0.027 0.60 0.11 0.17 0.11 0.0061 0.027 2 0.092 0.29 1.47 0.012 0.002 0.051 0.031 0.032 0.58 0.18 0.20 0.13 0.0068 0.033 3 0.074 0.24 1.54 0.011 0.003 0.043 0.043 0.045 0.53 0.21 0.21 0.16 0.0066 0.045 4 0.088 0.26 1.52 0.008 0.002 0.059 0.048 0.028 0.54 0.26 0.18 0.14 0.0071 0.039 5 0.100 0.25 1.56 0.007 0.001 0.040 0.040 0.030 0.51 0.14 0.19 0.15 0.0078 0.030 6 0.098 0.30 1.51 0.006 0.001 0.056 0.034 0.049 0.52 0.28 0.24 0.17 0.0075 0.026 7 0.090 0.25 1.50 0.012 0.002 0.050 0.040 0.020 0.55 0.20 0.20 0.15 0.0079 0.040

[0068] Table 2 Main process parameters of the continuous casting billet smelting of Examples 1-7 of the present application

[0069]

[0070] Table 3 Chemical composition, slag film thickness and pouring process parameters of the mold powder of Examples 1-7 of the present application

[0071]

[0072] Table 4 Macroscopic evaluation grade of continuous casting billets of Examples 1-7 of the present application and gas element content of the continuous casting billets

[0073]

[0074]

[0075] Table 5 Heating process parameters of continuous casting billets of Examples 1-7 of the present application

[0076]

[0077] Table 6 Rolling and relaxation treatment process parameters of steel plates of Examples 1-7 of the present application

[0078]

[0079] Table 7 Pre-straightening process parameters of steel plates of Examples 1-7 of the present application

[0080] Examples Sag correction / mm Roll gap correction / mm Strip load reduction / 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

[0081] Table 8 ACC laminar cooling process parameters of steel plates of Examples 1-7 of the present application

[0082]

[0083] Table 9 Quenching and tempering heat treatment process parameters of steel plates of Examples 1-7 of the present application

[0084]

[0085]

[0086] Table 10 Comprehensive mechanical properties of steel plates of Examples 1-7 of the present application in as-delivered state

[0087]

[0088]

[0089] The whole steel plate was subjected to ultrasonic testing according to the provisions of NB / T 47013.3, the scanning mode was: the probe was scanned in parallel lines perpendicular to and parallel to the rolling direction of the steel plate with a spacing of 190-200 mm, 100% scanning should be performed within the range of 40-50 mm on both sides of the steel plate bevel predetermined line, and the defect evaluation was qualified according to the T1 level of NB / T 47013.3, the qualified rate was 100%. The flaw detection performance test results are shown in Table 11.

[0090] Table 11 Flaw detection performance test results of steel plates of Examples 1-7 of the present application in as-delivered state

[0091]

[0092]

[0093] Table 12 Non-metallic inclusions in delivery condition of steel sheets of Examples 1-7 of the present application

[0094]

[0095] Table 13 Density and size of titanium compounds and inclusions in delivery condition of steel sheets of Examples 1-7 of the present application

[0096]

[0097] As can be seen from Table 13, the grade of each type of inclusions in the delivery condition steel sheets is controlled to be below 1.0, the density of TiN particles with a size of 0.01-0.3 μm is 2.0-2.9*10 6 mm 2 ; the density of TiN particles with a size of 0.3-0.5 μm is 1.0-1.9*10 4 mm 2 , and there is no TiN particle with a size greater than 0.5 μm; the density of Ti2O3 particles with a size of 0.5-5 μm is 2300-2400 mm 2 ; the density of Ti2O3 particles with a size of 0.01-0.5 μm is 5300-5400 mm 2 ; the surface density of inclusions with a size of 0.2-0.5 μm in the steel is 3200-3300 mm 2 ; the surface density of inclusions with a size of 0.5-1.0 μm in the steel is 1500-1600 mm 2 ; and the surface density of inclusions with a size of 2.5-6.0 μm in the steel is 40-60 mm 2 .

[0098] The samples of Examples 1-7 were subjected to simulated post-weld heat treatment, and the simulated post-weld heat treatment regime was as follows: temperature 570-590°C, net holding time 60-210 min, heating rate above 300°C 2-8°C / min, and no need to control the heating rate before heating to 300°C; cooling rate below 300°C 2-10°C / min, and natural cooling after cooling to 300°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 steel sheets in the simulated post-weld heat treatment condition are shown in Table 15.

[0099] Table 14 Main process parameters of simulated post-weld heat treatment of the steel of Examples 1-7 of the present application

[0100] Examples Die welding temperature °C Net soaking time min Ramp up rate above 300°C °C / min Ramp down rate below 300°C °C / min 1 575 62 3 3 2 579 82 4 6 3 580 100 5 7 4 582 188 6 5 5 588 208 7 9 6 585 153 7 9 7 579 198 6 8

[0101] Table 15 Comprehensive mechanical properties of steel plates in the mold-welded state in Examples 1-7 of the present invention

[0102]

[0103]

[0104] like Figure 1 As shown, the metallographic structure of the steel plate consists of 20%–30% acicular ferrite and 70%–80% tempered bainite.

[0105] To illustrate the present invention, the present invention has been appropriately and sufficiently described above through embodiments. The above embodiments are only for illustrating the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., should be included within the protection scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. A pressure vessel steel plate for a large crude oil storage tank with a capacity of 150,000 cubic meters, welded using high heat input, characterized in that: Its chemical composition by weight percentage is as follows: C: 0.070%~0.100%, Si: 0.20%~0.30%, Mn: 1.45%~1.60%, P≤0.015%, S≤0.003%, Nb: 0.030%~0.050%, Ti: 0.020%~0.050%, V: 0.040%~0.060%, Ni: 0.50%~0.60%, Cr: 0.10%~0.30%, Mo: 0.15%~0.25%, Cu: 0.10%~0.18%, Alt: 0.020%~0.050%, N: 0.006%~0.008%, with the remainder being Fe and unavoidable impurities; Its manufacturing method includes the following steps: (1) Continuous casting billet smelting: Using oxide metallurgy technology, the oxygen content before converter deoxidation is 700~1000 ppm. Ferrosilicon 75# alloy and aluminum granules are added to the converter for deoxidation. After heating in the LF furnace, when the oxygen content reaches 30~50 ppm, ferrotitanium is added for further deoxidation. When the oxygen content in the molten steel reaches 8~10 ppm, slagging and composition adjustment are performed. The RH inlet temperature is 1590~1620℃, and the RH oxygen blowing rate is 5~25 m³ / h. 3 / h, circulating oxygen blowing time 5~10min, RH furnace vacuumed to 0.4~0.5tor, ladle to tundish protective casting, continuous casting billet thickness 250~300mm; (2) Controlled rolling and controlled cooling: After heating, the continuously cast billet undergoes rough rolling at a starting temperature of 1100-1130℃ and a finishing temperature of 1030-1060℃. Following rough rolling, the intermediate billet is air-cooled to 905-935℃ before being subjected to continuous multi-pass finishing rolling at a finishing temperature of 835-875℃. After finishing rolling, the billet is allowed to rest on the roller table for 40-90 seconds for relaxation treatment. Following relaxation, pre-straightening is performed, followed by ACC laminar flow cooling at an starting temperature of 780-830℃ to preserve a significant amount of stored energy in the austenite grains. The cooling rate is 15-25℃ / s. Water cooling is used, with 10-12 ACC manifolds, a roll speed of 1.2-1.4 m / s, and a water flow rate of 240-260 m³ / s. 3 / h, water temperature 14~20℃, and at the same time, during ACC laminar flow cooling, the head and tail of the pre-straightened steel plate are shielded and controlled, the steel plate reddening temperature is 100~200℃, the reddening temperature difference between the head and tail of the steel plate after ACC laminar flow cooling is less than 20℃, and the flatness of the steel plate is ≤8mm / m. (3) Tempering heat treatment: The quenching temperature is 920~940℃, the heating rate is 0.5~1.5min / mm, the net holding time is 20~60min, after the holding time is completed, the water is cooled to room temperature. The tempering temperature is 650~670℃, the heating rate is 1.5~2.5min / mm, the net holding time is 30~110min, after the holding time is completed, the air is cooled to room temperature. (4) Straightening: The flatness of the finished steel plate after straightening is ≤5mm / m.

2. The high heat input welding method for pressure vessel steel plates used in large crude oil storage tanks with a capacity of 150,000 cubic meters, as described in claim 1, is characterized in that... For finished steel plates with a thickness of 10mm or less and a thickness of less than 30mm, the tensile strength at 1 / 4 of the thickness in the delivery state of the finished steel plate is 760~790MPa, the yield strength is 640~670MPa, the elongation after fracture is 19%~22%, the yield ratio is 0.83~0.86, the impact energy at -50℃ is 160~230J, the lateral expansion value LE is 1.1~1.9mm, the welding heat input energy is 190-200KJ / cm, the impact energy at -50℃ in the heat-affected zone after welding is 110~190J, and the lateral expansion value LE after welding is 1.0~1.9mm. For finished steel plates with a thickness of 30mm or less and 50mm or less, the tensile strength in the transverse direction at 1 / 4 and 1 / 2 of the thickness in the delivery state of the finished steel plate is 740~790MPa, the yield strength is 620~660MPa, the elongation after fracture is 20%~23%, the yield ratio is 0.82~0.85, the impact energy at -50℃ is 160~250J, the lateral expansion value LE is 1.2~1.5mm, the welding heat input energy is 190-200KJ / cm, the impact energy at -50℃ in the heat-affected zone after welding is 140~200J, and the lateral expansion value LE after welding is 1.3~1.7mm. For finished steel plates with a thickness of 10mm or less and a thickness of less than 30mm, the tensile strength at 1 / 4 of the thickness of the finished steel plate in the simulated post-weld heat-treated state is 750~780MPa, the yield strength is 630~660MPa, the elongation after fracture is 19%~22%, the yield ratio is 0.83~0.86, the impact energy at -50℃ is 160~230J, and the lateral expansion value LE is 1.0~2.0mm. The thickness of the finished steel plate is 30mm≤50mm. The tensile strength of the finished steel plate at 1 / 4 and 1 / 2 of the thickness in the transverse direction at the simulated post-weld heat-treated state is 750~780MPa, the yield strength is 630~660MPa, the elongation after fracture is 20%~24%, the yield ratio is 0.83~0.85, the impact energy at -50℃ is 220~250J, and the lateral expansion value LE is 1.3~1.7mm.

3. A method for manufacturing the steel plate according to any one of claims 1-2, characterized in that, Includes the following steps: (1) Continuous casting billet smelting: Using oxide metallurgy technology, the oxygen content before converter deoxidation is 700~1000 ppm. Ferrosilicon 75# alloy and aluminum granules are added to the converter for deoxidation. After heating in the LF furnace, when the oxygen content reaches 30~50 ppm, ferrotitanium is added for further deoxidation. When the oxygen content in the molten steel reaches 8~10 ppm, slagging and composition adjustment are performed. The RH inlet temperature is 1590~1620℃, and the RH oxygen blowing rate is 5~25 m³ / h. 3 / h, circulating oxygen blowing time 5~10min, RH furnace vacuumed to 0.4~0.5tor, ladle to tundish protective casting, continuous casting billet thickness 250~300mm; (2) Controlled rolling and controlled cooling: After heating, the continuously cast billet undergoes rough rolling at a starting temperature of 1100-1130℃ and a finishing temperature of 1030-1060℃. Following rough rolling, the intermediate billet is air-cooled to 905-935℃ before being subjected to continuous multi-pass finishing rolling at a finishing temperature of 835-875℃. After finishing rolling, the billet is allowed to rest on the roller table for 40-90 seconds for relaxation treatment. Following relaxation, pre-straightening is performed, followed by ACC laminar flow cooling at an starting temperature of 780-830℃ to preserve a significant amount of stored energy in the austenite grains. The cooling rate is 15-25℃ / s. Water cooling is used, with 10-12 ACC manifolds, a roll speed of 1.2-1.4 m / s, and a water flow rate of 240-260 m³ / s. 3 / h, water temperature 14~20℃, and at the same time, during ACC laminar flow cooling, the head and tail of the pre-straightened steel plate are shielded and controlled, the steel plate reddening temperature is 100~200℃, the reddening temperature difference between the head and tail of the steel plate after ACC laminar flow cooling is less than 20℃, and the flatness of the steel plate is ≤8mm / m. (3) Tempering heat treatment: The quenching temperature is 920~940℃, the heating rate is 0.5~1.5min / mm, the net holding time is 20~60min, after the holding time is completed, the water is cooled to room temperature. The tempering temperature is 650~670℃, the heating rate is 1.5~2.5min / mm, the net holding time is 30~110min, after the holding time is completed, the air is cooled to room temperature. (4) Straightening: The flatness of the finished steel plate after straightening is ≤5mm / m.

4. The manufacturing method according to claim 3, characterized in that, In step (1), the furnace charge size in the converter is 50~100mm, the furnace charge hot charging temperature is 1150~1200℃, and the net heat preservation time is 3~6min; The amount of ferrosilicon 75# alloy added is 4~5 kg / ton of steel. Ferrosilicon 75# alloy is a ferrosilicon alloy with a silicon content of 75%. The amount of aluminum particles added is 0.8~1 kg / ton of steel. In the LF furnace, the amount of ferrotitanium added is 0.8~1 kg / ton of steel.

5. The manufacturing method according to claim 3, characterized in that, In step (1), the pouring temperature is 1530~1550℃ and the casting speed is 0.9~1.0 m·min. -1 The steel billet is placed in a slow cooling pit after it leaves the production line. The slow cooling temperature is 300~400℃ and the holding time is 12~24h.

6. The manufacturing method according to claim 3, characterized in that, In step (1), the mold protective slag is composed of the following components by weight percentage: CaO 40%~55%, Al2O3 1%~5%, MnO 0~10%, SiO2 30%~40%, with the balance being unavoidable impurities, and the thickness of the slag film is 0.1~1.5mm.

7. The manufacturing method according to claim 3, characterized in that, In step (2), a four-stage heating method is adopted. The temperature of heating stage I is 600~650℃, the temperature of heating stage II is 1000~1050℃, the temperature of heating stage III is 1170~1210℃, the temperature of the soaking stage is 1150~1190℃, the soaking stage time is 30~40min, and the total heating time is the thickness of the continuously cast billet × (0.9~1.2) min·mm. -1 .

8. The manufacturing method according to claim 3, characterized in that, In step (2), the roughing stage adopts longitudinal-transverse rolling or full longitudinal rolling, with a reduction rate of 15% to 25% per pass; the thickness of the intermediate billet is 3 to 4 times the thickness of the finished steel plate; the finishing stage adopts full longitudinal rolling, with a reduction rate of 5% to 15% per pass.

9. The manufacturing method according to claim 3, characterized in that, In step (2), the shielding control parameters are: shielding flow rate is 5%~10%, the head shielding position is 800~900mm away from the head of the board, and the tail shielding position is 100~200mm away from the tail of the board; In the pre-straightening process, the roll gap setting parameters of the pre-straightening machine system are: tilt correction range of 0~+1.5mm, roll gap correction range of -1.5~+0.5mm, and load reduction range of +0.5~+1.0mm.

10. The manufacturing method according to claim 3, characterized in that, In step (4), the straightening speed is 60~80 r / min.

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