Pressure vessel steel plate for large heat input welding 150 thousand cubic large 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 high heat input welding of a 150,000-cube large 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 percent to 0.100 percent of C, 0.20 percent to 0.30 percent of Si, 1.45 percent to 1.60 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.003 percent of S, 0.030 percent to 0.050 percent of Nb, 0.020 percent to 0.050 percent of Ti, 0.040 percent to 0.060 percent of V, 0.50 percent to 0.60 percent of Ni, 0.10 percent to 0.30 percent of Cr, 0.15 percent to 0.25 percent of Mo, 0.10 percent to 0.18 percent of Cu, 0.020 percent to 0.050 percent of Alt, 0.006 percent to 0.008 percent of N and the balance of Fe and inevitable impurities. According to the method, the technological means of nickel molybdenum chromium-niobium vanadium titanium microalloying, continuous casting billet smelting, controlled rolling and controlled cooling and thermal refining are adopted, so that the product has good obdurability matching, welding performance and a flat and straight plate shape, the toughness of a steel plate welding heat affected zone is improved, and the welding heat input is improved to 200 KJ / cm.

Description

Technical Field

[0001] The present invention relates to the field of steel technology, and in particular to a pressure vessel steel plate for high-energy line welding of a 150,000 cubic meter large crude oil storage tank and a manufacturing method thereof. Background Art

[0002] With the implementation of my country's energy strategy and the increase in demand for oil reserves, crude oil storage tanks are developing in the direction of large-scale. Large crude oil storage tanks have higher requirements on the performance of steel, especially in welding technology, which needs to be able to withstand higher line energy input. During high-line energy welding, the welding heat affected zone is large and welding cracks are prone to occur. The development of steel for crude oil storage tanks suitable for high-line energy welding technology needs to have lower welding crack sensitivity to ensure the quality of the welded joints.

[0003] At present, crude oil storage tank steel plates produced by traditional smelting methods will have a significant decrease in toughness in the HAZ of the welding heat affected zone due to the severe coarsening of austenite grains and the formation of brittle hard phase structure in the grains after high-energy line welding heat cycles, and often cannot meet the minimum requirements of impact toughness. Therefore, the development of crude oil storage tank steel suitable for high-energy line welding technology is one of the technological innovations in the field of steel manufacturing, which can not only improve the technical level of my country's steel manufacturing, but also promote technological progress and industrial upgrading in related industries. Summary of the invention

[0004] The purpose of the present invention is to overcome the above problems and shortcomings and to provide a pressure vessel steel plate for large crude oil storage tanks with 150,000 cubic meters of high heat input welding 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 and tempering treatment, so that the product has good strength-toughness matching, welding performance and flat plate shape. By strictly controlling the addition order of alloy elements, fine dispersed inclusions are formed in the molten steel, the toughness of the heat-affected zone of the steel plate welding is improved, and the welding heat input is increased to 200KJ / cm. After simulated post-weld heat treatment, it still has a low yield strength ratio and good strength-toughness matching.

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

[0007] On one hand, the present invention provides a pressure vessel steel plate for welding a 150,000 cubic large crude oil storage tank with high heat input, and 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 ≤ 0.015%, 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%, 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. Therefore, the present invention requires that the C content in the steel be controlled at 0.070% to 0.100%.

[0011] (2) Si: Si is a common solid solution strengthening alloy 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 steel. Therefore, the Si content of the present invention is controlled at 0.20% to 0.30%.

[0012] (3) Mn: Mn 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. Mn is easy to combine with S to form MnS, which will reduce the material's resistance to hydrogen-induced cracking. At the same time, too high Mn content will reduce the activity of carbon. Therefore, the Mn content in steel is required to be 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, deteriorates cold bending performance, and is particularly sensitive to radiation embrittlement. Therefore, the P content in steel is required to be as low as possible, and the present invention requires it to be less than 0.015%.

[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 present invention requires that the S content in the steel should be limited to less than 0.003%.

[0015] (6) V: V is a microalloying element. Microalloying V in steel can form fine second-phase particles, which play a role in pinning grain boundaries and precipitation strengthening. It can effectively refine grains and greatly improve the comprehensive mechanical properties of steel, such as strength, toughness, ductility and thermal fatigue resistance. Therefore, the range of V added to steel is 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 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 Ti2O3 particles, which can serve as the heterogeneous nucleation core of needle-shaped pearlite during the 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 present invention requires that the Ti content in the steel be controlled to 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 present invention requires that the Alt content in the steel be 0.020% to 0.0050%.

[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 then changes the substructure of the matrix organization, thereby improving the toughness of steel, especially low-temperature toughness. However, excessive Ni content in medium carbon steel will increase the phase transition temperature. Therefore, the Ni content is controlled at 0.50% to 0.60%.

[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, and the refined carbides pin dislocations, greatly improving the strength and toughness of the steel. Therefore, the present invention requires that the Mo content in the steel be controlled to 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 present invention requires that the Cu content in the steel be controlled to be 0.10% to 0.18%.

[0022] (13) Cr: Chromium is an element that stabilizes carbides. Adding chromium reduces the dissolution rate of carbides. Therefore, when using a hot deformation microstructure refinement process, even if the heating temperature is increased or the heating time is extended, the eutectoid transformation can still be avoided and a refined microstructure can be obtained. Chromium can also inhibit the graphitization of ultra-high carbon steel containing silicon and aluminum, increase the hardenability of steel and have a secondary hardening effect. It can improve the hardness and wear resistance of high carbon steel without making the steel brittle, thereby increasing fatigue life. Therefore, the present invention requires that the Cr content in the steel be controlled to 0.10% to 0.30%.

[0023] (14) N: N can combine with Ti to form a large number of dispersed fine TiN, which can serve as the heterogeneous nucleation core of acicular ferrite during the solidification of the structure, thereby refining the structure and improving the welding performance. Therefore, the present invention requires that the N content in the steel be controlled to 0.006% to 0.008%.

[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, the thickness of the finished steel plate is 10mm≤<30mm, the tensile strength of the finished steel plate at 1 / 4 of the thickness in the delivery state is 760-790MPa, the yield strength is 640-670MPa, the elongation after fracture is 19-22%, the yield strength ratio is 0.83-0.86, the impact energy at -50℃ is 160-230J, the side expansion value LE is 1.1-1.9mm, the welding line energy is 190-200KJ / cm, the impact energy at -50℃ of the heat affected zone after welding is 110-190J, and the side expansion value LE after welding is 1.0-1.9mm;

[0026] 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 740~790MPa, the yield strength is 620~660MPa, the elongation after fracture is 20~23%, the yield strength ratio is 0.82~0.85, the impact energy at -50℃ is 160~250J, the side expansion value LE is 1.2~1.5mm, the welding line energy is 190-200KJ / cm, the impact energy of the heat affected zone at -50℃ after welding is 140~200J, and the side expansion value LE after welding is 1.3~1.7mm.

[0027] 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 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] 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 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 invention provides a method for manufacturing the above steel plate, comprising the following steps:

[0030] (1) Continuous casting smelting:

[0031] The oxide metallurgical technology is adopted. The oxygen content before converter deoxidation is 700-1000ppm. Ferrosilicon 75# alloy and aluminum particles are added to the converter for deoxidation. After entering the LF furnace for heating, ferrotitanium is added for deoxidation when the oxygen content is 30-50ppm. When the oxygen content in the molten steel reaches 8-10ppm, slag making and composition adjustment are carried out. The RH inlet temperature is 1590-1620℃, and the RH oxygen blowing volume is 5-25m 3 / h, circulating oxygen blowing time 5 ~ 10min, effectively preventing secondary oxidation of molten steel, RH furnace vacuum to 0.4 ~ 0.5tor, continuous casting full protection pouring, continuous casting billet thickness 250 ~ 300mm;

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

[0033] 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 1030-1060℃, and after rough rolling, the intermediate billet roller reciprocates and swings to air cool to 905-935℃ for continuous multi-pass finishing rolling. The finishing rolling final rolling temperature is 835-875℃. After finishing rolling, the roller is stationary for 40-90s to relax. After relaxation, pre-straightening is carried out, and then ACC laminar cooling is carried out. The start cooling temperature is 780-830℃, 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 100-200℃, the number of ACC headers is 10-12 groups, the roller speed is 1.2-1.4m / s, and the water volume is 240-260m 3 / h, water temperature 14 ~ 20 ℃, at the same time, during ACC laminar cooling, the head and tail of the pre-straightened steel plate are shielded and controlled. After ACC laminar cooling, the temperature difference between the head and tail of the steel plate is less than 20 ℃, and the unevenness of the steel plate is ≤ 8mm / m;

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

[0035] The quenching temperature is 920-940°C, the heating rate is 0.5-1.5min / mm, the net insulation is 20-60min, and after the insulation is completed, it is water-cooled to room temperature. The tempering temperature is 650-670°C, the heating rate is 1.5-2.5min / mm, and the net insulation is 30-110min. After the insulation is completed, it is air-cooled to room temperature and then straightened. The unevenness of the finished steel plate after cold straightening is ≤5mm / m.

[0036] 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;

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

[0038] The amount of aluminum particles added is 0.03-0.08 kg / ton of steel; during the converter smelting process, only a small amount of aluminum particles is used for deoxidation in the slag, and a large amount of aluminum deoxidizer is not used;

[0039] In the LF furnace, the amount of ferrotitanium added is 0.8 to 1 kg per ton of steel.

[0040] In the above technical solution, further, in step (1), in order to make the slag system in the liquid phase, the crystallizer protection slag is composed of the following components in weight percentage: CaO 40% to 55%, Al2O3 1% to 5%, MnO 0 to 10%, SiO2 30% to 40%, and the balance is inevitable impurities. The thickness of the slag film is 0.1 to 1.5 mm, which ensures that the inclusions are fully floated and removed to prevent the generation of linear defects in the ingot.

[0041] 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 it comes off the line. The slow cooling temperature is 300-400℃ and the holding time is 12-24h.

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

[0043] The continuous casting whole process protective pouring adopts two-stage protective pouring, i.e. protective pouring from ladle to tundish + protective pouring from tundish to crystallizer; among which:

[0044] The protective pouring method from ladle to tundish is as follows: a. Adding covering agent to the tundish to reduce the heat loss of molten steel, isolate air, reduce the secondary oxidation of molten steel, and absorb the inclusions floating from the molten steel;

[0045] 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.

[0046] The liquid protection method is adopted for protective pouring from the tundish to the crystallizer. A nozzle ring is installed at the bottom of the tundish to spray liquid nitrogen around 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), 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 the continuous casting billet thickness * (0.9-1.2) min·mm -1 ; 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.

[0048] In the above technical solution, further, in step (2), rolling is carried out in a double-stand rolling mill, and longitudinal-transverse rolling or full longitudinal rolling is adopted in the rough rolling stage, with a reduction rate of 15% to 25% in each pass, and a reduction rate of the rough rolling pass is greater than 15%, so that it is greater than the critical deformation rate to avoid the generation of mixed crystals, repeated deformation and repeated recrystallization of austenite grains; the thickness of the intermediate billet is 3 to 4 times the thickness of the finished steel plate;

[0049] Full longitudinal rolling is adopted in the finishing rolling stage. The austenite is fully flattened and elongated along the rolling direction. The reduction rate of each pass is 5% to 15%, and the reduction rate of the finishing pass is less than 15%, which is conducive to plate shape control. After rolling in the unrecrystallized zone of austenite, a large number of deformation bands and dislocations are formed in the deformed austenite grains, which increases the phase deformation nucleus position and phase transformation driving force.

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

[0051] The shielding control principle is: the temperature of the head and tail of the steel plate is close to that of the body, reducing the number of cooling header groups put into use for shielding control and shortening the flow adjustment time;

[0052] The shielding control parameters are: shielding flow rate is 5% to 10%, the head shielding position is 800 to 900 mm away from the plate head, and the tail shielding position is 100 to 200 mm away from the plate tail; through the use of the ACC head and tail shielding function, while reducing the temperature difference between the head and tail of the steel plate and the body, the temperature of the online quenching steel plate is uniform in the length direction and has a good plate shape, meeting the plate shape requirements of the steel plate entering the furnace.

[0053] 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 +1.5mm, the roller gap correction range is ~1.5 to +0.5mm and the load reduction range is +0.5 to +1.0mm, 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.

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

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

[0056] 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.

[0057] 2. Adopting "oxide metallurgy" technology, by strictly controlling the order of adding alloy elements, fine dispersed inclusions are formed in molten steel to improve the toughness of the heat affected zone of steel plate welding. The grade of various inclusions in the delivered steel plate is controlled below grade 1.0, and the density of TiN particles with a size of 0.01 to 0.3 μm is 2.0 to 2.9*10 6 Pieces / 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 Pieces / mm 2 There are no TiN particles larger than 0.5 μm; the density of Ti2O3 particles with a size of 0.5 to 5 μm is 2300 to 2400 particles / mm 2 ; The density of Ti2O3 particles with a size of 0.01 to 0.5 μm is 5300 to 5400 particles / mm 2 The surface density of inclusions with a size of 0.2 to 0.5 μm in steel is 3200 to 3300 per mm 2 The surface density of inclusions with a size of 0.5 to 1.0 μm in steel is 1500 to 1600 per mm 2 The surface density of inclusions with a size of 2.5 to 6.0 μm in steel is 40 to 60 per mm 2 .

[0058] 3. By optimizing the protective pouring, slag system ratio and RH circulation process, the inclusion content in the steel is reduced, the low-power quality of the continuous casting billet is improved, and the foundation is laid for improving the qualified rate of flaw detection and reducing the tensile delamination rate. The center segregation (grade) is ≤C1.0, and the center porosity is ≤0.5.

[0059] 4. The controlled rolling and controlled cooling process is adopted to obtain products with fully uniform and refined structure and good straightness. The unevenness after cold straightening is ≤5mm / m.

[0060] 5. Through relaxation treatment and quenching and tempering heat treatment, the microstructure of the finished steel plate is made into 20% to 30% ferrite + 70% to 80% tempered bainite two phases, the second phase is dispersedly distributed, the organization is uniform, and the strength and toughness of the product are well matched. By reasonably adjusting the ratio of ferrite and tempered bainite organizations, it is ensured that the product has good mechanical properties and a low yield strength ratio in the mold welding state. The steel plates of the delivery state and the simulated post-weld heat treatment state of the present invention have good strength and toughness matching, and the yield strength and tensile strength fluctuation range are both within 50MPa, and the yield strength ratio is 0.85 to 0.90.

[0061] In summary, the pressure vessel steel plate product of the present invention has good process performance and mechanical properties, the deviation of the mechanical properties of the head and tail of the steel plate is small, and the performance uniformity of the whole plate is good. It is widely used in key areas such as national strategic crude oil reserves and local crude oil commercial storage projects. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0063] 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.

[0064] Examples 1-7

[0065] The chemical compositions of the steel plates of Examples 1-7 of the present invention are shown in Table 1.

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

[0067] Example 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 for continuous casting smelting of Examples 1-7 of the present invention

[0069]

[0070] Table 3 Chemical composition, slag film thickness and casting process parameters of the mold protection slag of Examples 1-7 of the present invention

[0071]

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

[0073]

[0074]

[0075] Table 5 Heating process parameters of continuous casting slabs in Examples 1-7 of the present invention

[0076]

[0077] Table 6 Process parameters of steel plate rolling and relaxation treatment in Examples 1-7 of the present invention

[0078]

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

[0080] 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

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

[0082]

[0083] Table 9 Tempering heat treatment process parameters of steel plates in Examples 1-7 of the present invention

[0084]

[0085]

[0086] Table 10 Comprehensive mechanical properties of steel plates in delivery state in Examples 1-7 of the present invention

[0087]

[0088]

[0089] 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 11.

[0090] Table 11 Test results of flaw detection performance of steel plates in delivery state of Examples 1-7 of the present invention

[0091]

[0092]

[0093] Table 12 Non-metallic inclusions in the steel plates of Examples 1-7 of the present invention as delivered

[0094]

[0095] Table 13 Density and size of titanium compounds and inclusions in the steel plates of Examples 1-7 of the present invention as delivered

[0096]

[0097] It can be seen from Table 13 that the level of various inclusions in the delivered steel plate is controlled below level 1.0, and the density of TiN particles with a size of 0.01 to 0.3 μm is 2.0 to 2.9*10 6 Pieces / 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 Pieces / mm 2 There are no TiN particles larger than 0.5 μm; the density of Ti2O3 particles with a size of 0.5 to 5 μm is 2300 to 2400 particles / mm 2 ; The density of Ti2O3 particles with a size of 0.01 to 0.5 μm is 5300 to 5400 particles / mm 2 The surface density of inclusions with a size of 0.2 to 0.5 μm in steel is 3200 to 3300 per mm 2 The surface density of inclusions with a size of 0.5 to 1.0 μm in steel is 1500 to 1600 per mm 2 The surface density of inclusions with a size of 2.5 to 6.0 μm in steel is 40 to 60 per mm 2 .

[0098] 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 570-590°C, net heat preservation 60-210min, heating rate 2-8°C / min above 300°C, no need to control the heating rate before heating to 300°C; cooling rate 2-10°C / min below 300°C, 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 simulated post-weld heat treated steel plates are shown in Table 15.

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

[0100] Example Die soldering temperature ℃ Net insulation time min Heating rate above 300℃℃ / min Cooling rate below 300℃℃ / 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 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 is composed of 20% to 30% acicular ferrite and 70% to 80% tempered bainite.

[0105] 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 high-energy-line welding pressure vessel steel plate for a 150,000 cubic large crude oil storage tank, 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%, and the rest is Fe and unavoidable impurities.

2. The high-heat-input welding pressure vessel steel plate for 150,000 cubic large crude oil storage tank according to claim 1 is characterized in that: 10mm≤The thickness of the finished steel plate is <30mm, the tensile strength of the finished steel plate in the transverse direction at 1 / 4 of the thickness in the delivery state is 760~790MPa, the yield strength is 640~670MPa, the elongation after fracture is 19%~22%, the yield strength ratio is 0.83~0.86, the impact energy at -50℃ is 160~230J, the side expansion value LE is 1.1~1.9mm, the welding line energy is 190-200KJ / cm, the impact energy at -50℃ of the heat affected zone after welding is 110~190J, and the side expansion value LE after welding is 1.0~1.9mm; 30mm≤The thickness of the finished steel plate is ≤50mm, the transverse tensile strength of the finished steel plate at 1 / 4 and 1 / 2 of the thickness in the delivery state is 740~790MPa, the yield strength is 620~660MPa, the elongation after fracture is 20%~23%, the yield strength ratio is 0.82~0.85, the impact energy at -50℃ is 160~250J, the side expansion value LE is 1.2~1.5mm, the welding line energy is 190-200KJ / cm, the impact energy at -50℃ of the heat affected zone after welding is 140~200J, and the side expansion value LE after welding is 1.3~1.7mm; 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 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; 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 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.

3. A method for manufacturing the steel plate according to any one of claims 1 to 2, characterized in that: The following steps are involved: (1) Continuous casting smelting: The oxide metallurgical technology is adopted. The oxygen content before converter deoxidation is 700-1000ppm. Ferrosilicon 75# alloy and aluminum particles are added to the converter for deoxidation. After entering the LF furnace for heating, ferrotitanium is added for deoxidation when the oxygen content is 30-50ppm. When the oxygen content in the molten steel reaches 8-10ppm, slag making and composition adjustment are carried out. The RH inlet temperature is 1590-1620℃, and the RH oxygen blowing volume is 5-25m 3 / h, circulating oxygen blowing time 5-10min, RH furnace vacuum to 0.4-0.5tor, protection pouring from ladle to tundish, continuous casting billet thickness 250-300mm; (2) Controlled rolling and controlled cooling: 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 1030-1060℃, the intermediate billet after rough rolling is air-cooled to 905-935℃ for continuous multi-pass finishing rolling, the finishing rolling final rolling temperature is 835-875℃, the roller is stationary for 40-90s after finishing rolling, and relaxation treatment is carried out. After relaxation treatment, pre-straightening is carried out, and then ACC laminar cooling is carried out. The start cooling temperature is 780-830℃, 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 100-200℃, the number of ACC headers is 10-12 groups, the roller speed is 1.2-1.4m / s, and the water volume is 240-260m 3 / h, water temperature 14 ~ 20 ℃, at the same time, during ACC laminar cooling, the head and tail of the pre-straightened steel plate are shielded and controlled. After ACC laminar cooling, the temperature difference between the head and tail of the steel plate is less than 20 ℃, and the unevenness of the steel plate is ≤ 8mm / m; (3) Quenching and tempering heat treatment: The quenching temperature is 920-940℃, the heating rate is 0.5-1.5min / mm, the net heat preservation is 20-60min, and after the heat preservation is completed, it is water-cooled to room temperature. The tempering temperature is 650-670℃, the heating rate is 1.5-2.5min / mm, the net heat preservation is 30-110min, and after the heat preservation is completed, it is air-cooled to room temperature; Straightening: The unevenness of the finished steel plate after straightening is ≤5mm / m.

4. The manufacturing method according to claim 3, 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 min; The addition amount of ferrosilicon 75# alloy is 4-5kg / ton of steel. Ferrosilicon 75# alloy is a ferrosilicon alloy with a silicon content of 75%. The addition amount of aluminum particles is 0.8-1kg / ton of steel. In the LF furnace, the amount of ferrotitanium added is 0.8 to 1 kg per ton of steel.

5. The manufacturing method according to claim 3, 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 coming off the 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 protection slag is composed of the following components in weight percentage: CaO 40% to 55%, Al2O3 1% to 5%, MnO0 to 10%, SiO2 30% to 40%, and the remainder is inevitable impurities. The thickness of the slag film is 0.1 to 1.5 mm.

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

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

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

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

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