A method for manufacturing a continuously cast slab for a full protection cast crude oil storage tank vessel steel

Abstract

The present application relates to the technical field of steel, and in particular, relates to a manufacturing method of a continuous casting slab for a full protection casting crude oil storage tank container steel. The process of the open casting process protection casting - ladle injection tundish protection casting - tundish full protection casting - crystallizer protection casting - crystallizer full protection casting is adopted, the secondary oxidation of molten steel is effectively reduced, the center segregation of the cast slab is finally controlled below the B class 1.0 level, the center porosity is controlled below the 1.0 level, the H element content in the continuous casting slab after smelting is controlled to be 1.0-3.0 ppm, the O element content is controlled to be 10-30 ppm, the N element content is controlled to be 15-25 ppm, the grade of various inclusions in the steel plate is controlled to be below the 1.0 level, and the number of inclusions in the unit area is 4.5-5.5 pieces / mm 2 .

Description

Technical Field

[0001] This invention relates to the field of steel technology, and more particularly to a method for manufacturing a continuously cast slab for a fully protected cast crude oil storage tank container. Background Technology

[0002] As an indispensable storage device in the petroleum industry, the safety and durability of crude oil storage tanks directly affect the stability of energy supply and the effectiveness of environmental protection. Therefore, the steel used to manufacture crude oil storage tanks must meet extremely high performance and quality requirements to ensure long-term stable operation under extreme environmental conditions.

[0003] However, traditional smelting processes face numerous challenges in producing steel that meets these stringent standards. First, secondary oxidation of the molten steel during smelting is difficult to avoid, increasing the content of harmful impurities and reducing the steel's purity and overall performance. Second, traditional processes have limited precision in controlling chemical composition, resulting in poor chemical stability of the steel, making it difficult to meet the stringent requirements for material homogeneity and reliability in crude oil storage tanks. Furthermore, fluctuations in temperature control, cooling rate, and solidification conditions during smelting often affect the internal quality of the cast billet, leading to defects such as shrinkage cavities, cracks, and segregation, further weakening the steel's mechanical properties and corrosion resistance, thus failing to ensure that the final product fully meets the stringent standards for crude oil storage tanks. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned problems and deficiencies and provide a method for manufacturing a continuously cast slab for a fully protected crude oil storage tank container.

[0005] This invention employs a process of tundish-tundish protected casting followed by tundish-crystallizer ...

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] This invention provides a method for manufacturing a continuously cast slab for a fully protected cast crude oil storage tank, the method comprising the following steps:

[0008] (1) Smelting:

[0009] The hot charging temperature of the converter smelting furnace charge is 1150-1200℃, with a net holding time of 3-6 minutes. The RH inlet temperature is 1590-1620℃, and the RH oxygen blowing rate is 45-65 m³ / h.3 / h, with a circulating oxygen blowing time of 20-30min, effectively preventing secondary oxidation of the molten steel; the smelting process involves fully protected casting, specifically including:

[0010] a. Protection during the casting process: Before casting begins, insert a 90° bent argon tube into the temperature sampling holes on both sides of the tundish. By forming argon convection to replace the air in the tundish, the argon pressure is controlled at 0.1-0.3 MPa. Through the above optimization measures, the total oxygen content in the tundish before casting begins is reduced to 45-55 ppm, and the nitrogen increase in the tundish during the first casting cycle is reduced to 1.5-2.5 ppm, showing a significant improvement effect.

[0011] b. Steel ladle injection into the tundish for protective casting: The argon flow rate is controlled at 110-130 NL / min, and the clamping pressure of the robotic arm is controlled at 140-150 kPa. Through the above optimization measures, the standard deviation of the argon flow rate is 9.0-11 NL / min, and the fluctuation of the argon flow rate is significantly improved. Under the condition of avoiding the leakage of molten steel, the argon protection effect at the interface is guaranteed, and the immersion casting rate is increased to 90-95%, which is conducive to avoiding secondary oxidation of molten steel during the casting process.

[0012] c. Full protection casting of tundish: Argon is continuously purged into the tundish to replace the air in the tundish. During the casting process, the tundish is in a high argon environment, which can prevent the air from entering. The argon pressure is controlled at 0.3-0.5MPa. Through the above optimization measures, the total oxygen content in the tundish is reduced to 35-45ppm.

[0013] d. Tundish injection crystallizer protection casting: A covering agent is added to the tundish to reduce heat loss of molten steel, isolate air, reduce secondary oxidation of molten steel, and absorb inclusions floating in molten steel;

[0014] e. Full protection casting in the crystallizer: Violent turbulence of the liquid surface in the crystallizer causes slag entrapment and exposed molten steel, resulting in secondary oxidation, which seriously affects the quality of the cast billet. This invention mainly optimizes the two aspects of argon blowing by the stopper rod and the immersion depth of the nozzle: Argon blowing by the stopper rod is beneficial for the floating of inclusions and the improvement of nozzle blockage. The argon flow rate of the stopper rod is controlled at 4-5L / min and the immersion depth is 180-190mm. The appropriate immersion depth of the nozzle will greatly improve the melting effect of the protective slag, accelerate the floating of inclusions, and improve the purity of the steel.

[0015] (2) Continuous casting: Secondary cooling water temperature is 30-35℃, pouring temperature is 1530-1550℃, and casting speed is 0.9-1.0 m·min. -1 The electromagnetic stirring process parameters are: stirring frequency 10-15Hz, stirring current 100-150A;

[0016] (3) Slow cooling: After smelting, the continuous casting billet is put into the slow cooling pit for slow cooling. The slow cooling temperature is controlled at 300-400℃ and the holding time is 12-24h.

[0017] In the above technical solution, further, in step (1), the size of the furnace charge is 50-100mm.

[0018] In the above technical solution, further, in step (1), an asbestos gasket is provided at the long nozzle of the ladle and the bottom nozzle of the steel ladle, and the asbestos gasket is preheated at a temperature of 300-350℃ to increase its expansion and reduce the interface gap between the long nozzle and the sliding nozzle of the ladle.

[0019] In the above technical solution, further, in step (1), a pressure stabilizing valve is installed on the argon pipeline of the long water inlet to stabilize the argon flow rate during the pouring process and avoid unstable flow caused by argon pressure fluctuations.

[0020] In the above technical solution, further, in step (1), the protrusion at the contact point between the robotic arm support ring and the long sprue is a T-shaped structure. The T-shaped structure increases the contact area, thereby enhancing the bonding force between the robotic arm support ring and the long sprue, which helps to reduce loosening or displacement caused by vibration or external force, and improves the stability of the overall structure.

[0021] In the above technical solution, further, in step (1), in order to keep the slag system in the liquid phase region, the mold protective slag is composed of the following components by mass percentage: CaO 30%-45%, Al2O3 25%-40%, MnO 0-10%, SiO2 5%-20%, with the balance being unavoidable impurities; the thickness of the slag film is 0.1-1.5mm, to ensure that the inclusions are fully floated and removed, and to prevent the generation of linear defects in the billet.

[0022] In the above technical solution, further, in step (1), the covering agent is composed of the following components by mass percentage: calcium aluminate: 70%-90%, magnesia: 0.1%-20%, binder: 0.1%-10%, additive: 0.1%-5%, calcium carbonate: 0%-25%, and quartz sand: 0%-5%.

[0023] In the above technical solution, the composition of the continuously cast slab obtained is as follows by weight percentage: C: 0.090%-0.115%, Si: 0.25%-0.35%, Mn: 1.45%-1.60%, P≤0.015%, S≤0.003%, Nb: 0.015%-0.035%, Ti: 0.015%-0.030%, V: 0.025%-0.045%, Ni: 0.17%-0.23%, Mo: 0.06%-0.12%, Alt: 0.015%-0.045%, with the remainder being Fe and unavoidable impurities.

[0024] The beneficial effects of this invention are as follows:

[0025] This invention employs a process of protected casting during the initial casting stage, followed by protected casting into the tundish, then fully protected casting into the tundish, then protected casting into the crystallizer, and finally fully protected casting into the crystallizer. During the initial casting, middle casting, and later casting stages, the fully protected casting process effectively reduces secondary oxidation of the molten steel. Ultimately, it controls the center segregation of the billet to below grade B 1.0 and center porosity to below grade 1.0. After smelting, the H content in the continuously cast billet is controlled at 1.0-3.0 ppm, the O content at 10-30 ppm, and the N content at 15-25 ppm. Non-metallic inclusions in the steel plate, including type A (sulfides), type B (alumina), type C (silicates), type D (spherical oxides), and type DS (single-particle spherical inclusions), are all controlled to below grade 1.0, with the number of inclusions per unit area being 4.5-5.5 per mm. 2 . Attached Figure Description

[0026] Figure 1 This is a low-magnification photograph of the continuously cast billet from Example 1. Detailed Implementation

[0027] The following examples are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0028] Examples 1-6

[0029] The chemical composition of the continuously cast slabs in Examples 1-6 of this invention is shown in Table 1.

[0030] Table 1. Chemical composition (wt%) of the continuously cast slabs in Examples 1-6 of the present invention.

[0031] Example C Si Mn P S V Nb Ti Ni Mo Alt 1 0.096 0.26 1.49 0.010 0.003 0.025 0.016 0.017 0.18 0.07 0.027 2 0.092 0.29 1.47 0.012 0.002 0.031 0.031 0.022 0.19 0.10 0.033 3 0.114 0.24 1.54 0.011 0.003 0.033 0.023 0.025 0.21 0.11 0.045 4 0.108 0.26 1.52 0.008 0.002 0.029 0.028 0.018 0.20 0.08 0.049 5 0.100 0.25 1.56 0.007 0.001 0.040 0.020 0.030 0.21 0.09 0.030 6 0.110 0.30 1.51 0.006 0.001 0.036 0.034 0.020 0.22 0.11 0.026

[0032] Table 2. Smelting process parameters for continuous casting slabs in Examples 1-6 of the present invention.

[0033]

[0034]

[0035] Table 3. Casting process parameters for examples 1-6 of the present invention: initial casting, ladle injection into the tundish, and tundish process protection.

[0036]

[0037] Table 4. Tundish injection into crystallizer and fully protected casting process parameters for Examples 1-6 of the present invention.

[0038]

[0039]

[0040] Table 5. Composition ratio of crystallizer protective slag in Examples 1-6 of the present invention.

[0041]

[0042] Table 6 Continuous casting process parameters of Examples 1-6 of the present invention

[0043]

[0044] Table 7 Low-magnification evaluation grades and gas element contents of continuously cast slabs in Examples 1-6 of the present invention

[0045]

[0046]

[0047] Table 8 Non-metallic inclusions in continuous casting slabs of Examples 1-6 of the present invention

[0048]

[0049] 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 method of manufacturing a continuously cast slab for a full-protective cast crude oil storage tank vessel steel, characterized by, The method comprises the following steps: (1) smelting: The hot charging temperature of converter smelting furnace charge is 1150-1200℃, the net holding time is 3-6min, the RH inlet temperature is 1590-1620℃, the RH oxygen blowing amount is 45-65m 3 / h, the circulating oxygen blowing time is 20-30min, and the smelting process is fully protected pouring, specifically including: a, open pouring process protection pouring: control argon pressure 0.1-0.3 MPa; b, ladle injection tundish protection pouring: control argon flow 110-130 NL / min, control the top pressure of manipulator 140-150 KPa; c, tundish full protection pouring: continue to blow argon in tundish, control argon pressure 0.3-0.5 MPa; d, tundish injection crystallizer protection pouring: tundish adds covering agent; e, crystallizer full protection pouring: stopper blowing argon is beneficial to inclusion floating and improving nozzle blockage, control stopper argon flow 4-5 L / min, immersion depth 180-190 mm; (2) Continuous casting: secondary cooling water temperature is 30-35℃, pouring temperature is 1530-1550℃, and the pulling speed is 0.9-1.0 m / min -1 , and the electromagnetic stirring process parameters are: stirring frequency is 10-15 Hz, and stirring current is 100-150 A; (3) slow cooling: after completing smelting, continuous casting billet enters slow cooling pit slow cooling, slow cooling temperature 300-400 DEG C, holding time 12-24 h; The composition of the continuous casting slab is as follows in terms of percentage by weight: C: 0.090%-0.115%, Si: 0.25%-0.35%, Mn: 1.45%-1.60%, P≤0.015%, S≤0.003%, Nb: 0.015%-0.035%, Ti: 0.015%-0.030%, V: 0.025%-0.045%, Ni: 0.17%-0.23%, Mo: 0.06%-0.12%, Alt: 0.015%-0.045%, and the rest is Fe and inevitable impurities.

2. The production method according to claim 1, characterized by In step (1), the charge size is 50-100 mm.

3. The production method according to claim 1, characterized by In step (1), the large ladle long nozzle and the ladle lower nozzle are provided with asbestos gaskets, and the asbestos gaskets are preheated, and the preheating temperature is 300-350 DEG C.

4. The production method according to claim 1, characterized by The crystallizer protection slag is composed of the following components in terms of percentage by mass: CaO 30%-45%, Al2O3 25%-40%, MnO 0-10%, SiO2 5%-20%, and the balance is inevitable impurities; the thickness of the slag film is 0.1-1.5 mm.

5. The production method according to claim 1, wherein In step (1), the covering agent is composed of the following components in terms of percentage by mass: calcium aluminate: 70%-90%, magnesia: 0.1%-20%, binder: 0.1%-10%, additive: 0.1%-5%, calcium carbonate: 0%-25%, and quartz sand: 0%-5%.

Images