Method for manufacturing hot-rolled h-shaped steel for tank dome

Abstract

The application discloses a manufacturing method of hot-rolled H-shaped steel for a storage tank dome, and a smelting process is as follows: blast furnace molten iron, molten iron pretreatment, converter smelting, LF refining, VD vacuum treatment and special-shaped blank continuous casting; the mass percentage of the chemical components includes C 0.06%-0.14%, Si 0.25%-0.45%, Mn 1.35%-1.50%, P<=0.02%, S<=0.020%, V 0.03%-0.09%, Nb 0.015%-0.035%, and the rest is Fe and impurities, and the total mass percentage is 100%. The H-shaped steel prepared by the method has high yield strength and tensile strength, and good impact toughness.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, and in particular relates to a method for manufacturing hot-rolled H-beams for storage tank domes. Background Technology

[0002] Large and super-large storage tanks are trending towards larger volumes, lighter structures, and industrialized construction. As a key load-bearing structure, the tank dome faces multiple technical requirements, including large spans, high load-bearing capacity, low-temperature adaptability, earthquake and wind resistance, and rapid construction. Traditional tank domes are mostly assembled using angle steel, channel steel, and other profiles, which suffer from low cross-sectional stress efficiency, large component splicing volume, high welding residual stress, insufficient overall stiffness, and difficulty in controlling installation accuracy. These methods can no longer meet the structural safety and engineering construction needs of super-large storage tank domes.

[0003] With advancements in high-performance structural steel manufacturing and steel structure engineering technologies, Q355NE hot-rolled H-beams, with their superior cross-sectional mechanical properties, high bending and torsional stiffness, high dimensional accuracy, and excellent construction and assembly characteristics, have gradually become the core material for storage tank dome shells, trusses, ring beams, and support systems. The use of high-strength, high-toughness hot-rolled H-beams effectively reduces steel consumption, shortens construction cycles, and improves long-term structural reliability. They are suitable for complex working conditions such as low temperatures, outdoor exposure, and heavy loads, providing crucial material support and technical assurance for the upgrading and large-scale application of large storage tank dome structures. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a method for manufacturing hot-rolled H-beams for tank domes.

[0005] To solve the aforementioned technical problem, the present invention adopts the following technical solution:

[0006] This invention discloses a method for manufacturing hot-rolled H-beams for storage tank domes, comprising the following smelting process: blast furnace molten iron → molten iron pretreatment → converter smelting → LF refining → VD vacuum treatment → continuous casting of shaped billets; characterized in that:

[0007] During the converter smelting process, the total oxygen supply time at the converter endpoint is controlled to be less than 15 minutes, and the cumulative total oxygen content is less than 4000 mg / L. 3 Ensure one-time drawing, final C > 0.02%, final temperature > 1620℃, control the slag amount in the converter to be less than 30mm, and use aluminum-iron deoxidation in the converter tapping process;

[0008] During the LF refining process, desulfurization, composition fine-tuning, and temperature increase are carried out according to the composition and temperature of the converter steel. Phosphorus iron is added in the later stage of refining to ensure that the composition of the steel meets the internal control requirements. The LF refining heating time is less than 50 minutes, and silicon-calcium-barium aluminum-free deoxidation is used to produce white slag. The LF off-site temperature is controlled at 1680-1690℃.

[0009] During the VD vacuum treatment process, the deep vacuum time is ≥12min, the deep vacuum degree target is <0.1KPa, the weak stirring time after breaking the vacuum is ≥20min, the silicon-calcium wire is fed in, the soft blowing time is ≥20min, and the temperature after VD is controlled at 1595-1605℃.

[0010] During the continuous casting of the irregular billet, protective pouring is used throughout. Argon blowing is used to control the connection between the ladle and the long nozzle. The lower nozzle is controlled with an asbestos bowl. The nozzle insertion depth is 75-85mm. Weak cooling is used for the secondary cooling. The secondary cooling water volume is 0.85-0.95L / kg. The superheat is ≤35℃. The melting point of the protective slag is 1237℃, the density is 0.85-0.95g / ml, and the viscosity is 8.90 Poise. Constant casting speed is used, with the casting machine speed controlled at 0.9-1.3m / min. The ingot pressure on the first straightening machine is 150-160bar, and the ingot pressure on the second to sixth straightening machines is 60-70bar. The billet is stacked and slowly cooled for more than 48 hours.

[0011] Its chemical composition by mass percentage includes: C 0.06%~0.14%, Si 0.25%~0.45%, Mn 1.35%~1.50%, P≤0.02%, S≤0.020%, V 0.03%~0.09%, Nb 0.015%~0.035%, with the remainder being Fe and impurities, totaling 100% by mass.

[0012] Furthermore, 50-60 kg / furnace of vanadium-nitrogen alloy is added during the later stages of refining.

[0013] Furthermore, 55 kg / furnace of vanadium-nitrogen alloy is added during the later stages of refining; this furnace is a 100t furnace.

[0014] Furthermore, the cross-sectional dimensions of the continuously cast billet are 555×440×105mm.

[0015] Furthermore, the mass percentage of its chemical composition includes: C 0.06%, Si 0.30%, Mn 1.36%, P 0.012%, S 0.015%, V 0.056%, Nb 0.018%, with the remainder being Fe and impurities, totaling 100% by mass.

[0016] Furthermore, the chemical composition by mass percentage includes: C 0.08%, Si 0.27%, Mn 1.35%, P 0.0117%, S 0.017%, V 0.059%, Nb 0.03%, with the remainder being Fe and impurities, totaling 100% by mass.

[0017] Furthermore, the mass percentage of its chemical composition includes: C 0.10%, Si 0.33%, Mn 1.36%, P 0.0111%, S 0.015%, V 0.057%, Nb 0.023%, with the remainder being Fe and impurities, totaling 100% by mass.

[0018] Furthermore, the chemical composition by mass percentage includes: C 0.11%, Si 0.25%, Mn 1.45%, P 0.0090%, S 0.015%, V 0.033%, Nb 0.025%, with the remainder being Fe and impurities, totaling 100% by mass.

[0019] The functions of each element are as follows:

[0020] C: C is the most effective element for improving the strength of steel. Increasing the C content can improve the tensile strength and yield strength of steel, but the elongation and impact toughness will decrease. In order to ensure that the low-temperature normalized rolled H-beams obtain good comprehensive performance, the C content of the steel in this invention is designed to be 0.06-0.14%.

[0021] Mn: Mn is an important strengthening and toughening element with low cost. As the manganese content increases, the strength of the steel significantly improves, enhancing its processing performance, while the ductile-brittle transition temperature remains almost unchanged. However, excessively high manganese content inhibits ferrite transformation, affecting the yield strength of the steel and hindering the control of the yield-to-tensile ratio. The Mn content of the steel in this invention is designed to be 1.35-1.50%.

[0022] Si: Si can improve the strength of steel. By increasing the Si element, the strength of steel can be improved to a certain extent. However, as the mass percentage of Si increases further, it is easy to cause the formation of martensite structure in the steel. Therefore, the mass percentage of Si in the normalized H-beam for marine engineering and its production method described in this invention is controlled at 0.25-0.45%.

[0023] V: In steel, V can play a role in precipitation strengthening, grain refinement strengthening, and grain boundary strengthening, and can lower the ductile-brittle transition temperature. V carbonitrides can effectively refine ferrite grains. In low-temperature steel, a small amount of V refines the grains and increases toughness. The V content of the steel in this invention is designed to be 0.03% to 0.09%.

[0024] P: P has a strong effect on solid solution strengthening and cold work hardening in steel. While P acts on ferrite, increasing the strength and hardness of steel, its greatest drawback is severe segregation, increasing temper brittleness, and significantly increasing the plasticity and toughness of the steel. This leads to a phenomenon known as "cold brittleness," where the steel is prone to cracking during cold working. Therefore, the P content of the steel in this invention is designed to be ≤0.020%.

[0025] S: S is a hot brittleness and machinability element. It is known that machinability improves with increasing mass percentage of sulfur, but hot workability deteriorates with increasing sulfur content. Therefore, in the preparation method of normalized rolled low alloy structural steel described in this invention, the mass percentage of S is limited to S≤0.015%.

[0026] Nb: Adding trace amounts of Nb alloying element to steel strongly inhibits austenite grain growth, making it easier to obtain a fine-grained structure. Niobium produces significant grain refinement and moderate precipitation strengthening during controlled rolling. The Nb content of the steel in this invention is designed to be 0.015%–0.035%.

[0027] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0028] The H-beams prepared by this invention not only have high yield and tensile strength, but also excellent impact toughness. Detailed Implementation

[0029] The smelting process of hot-rolled H-beams for storage tank domes is as follows: blast furnace molten iron → molten iron pretreatment → converter smelting → LF refining → VD vacuum treatment → continuous casting of shaped billets.

[0030] Pre-treated desulfurized molten iron is used: [S] < 0.030% entering the converter; molten iron temperature ≥ 1250℃. Re-blowing converter smelting is employed, controlling the final slag basicity to 3.0. Final C ≥ 0.02%, final temperature ≥ 1610℃, final deoxidation using Al deoxidation. Alloy copper and nickel are added with scrap steel. Quicklime is added during tapping. Refining white slag operation is performed. Ar blowing is carried out throughout the refining process. Desulfurization, composition fine-tuning, and temperature increase operations are performed according to the converter steel composition and temperature. In the later stages of refining, 55 kg / furnace of vanadium-nitrogen alloy is added; if the vanadium content is insufficient, ferrovanadium is used to supplement it, and the composition is fine-tuned. At the end of refining, 150 m of silicon-calcium wire is fed, ensuring a soft blowing time ≥ 20 min; the molten steel must not be exposed during soft blowing.

[0031] Protective casting is used throughout the process. Liquidus temperature TL = 1511℃; superheat ≤ 35℃. A weak cooling regime is adopted. Constant casting speed of 0.9-1.2 m / min is used. After cutting, the continuously cast billet is promptly removed from the line and stacked for slow cooling, with the top cover mold placed underneath. The slow cooling time is greater than or equal to 48 hours.

[0032] The cross-sectional dimensions of the continuously cast billet are 555×440×105mm.

[0033] The surface quality of the continuously cast billet of the hot-rolled H-beams used for the tank dome was inspected, and the internal quality was tested by hot acid at low magnification.

[0034] No obvious surface or internal quality defects were found during the inspection, and the quality of the cast billet was good. Tables 1, 2, 3, and 4 further illustrate the invention with reference to examples.

[0035] Table 1 Chemical composition of each example (mass percentage / %)

[0036] Example 1 0.06 0.30 1.36 0.0120 0.015 0.056 0.018 Example 2 0.08 0.27 1.35 0.0117 0.017 0.059 0.03 Example 3 0.10 0.33 1.36 0.0111 0.015 0.057 0.023 Example 4 0.11 0.25 1.45 0.0090 0.015 0.033 0.025

[0037] Table 2. Casting speed and superheat control for each example.

[0038] Example 1 33 0.9 Example 2 34 0.9 Example 3 30 1.0 Example 4 31 0.9

[0039] Table 3. Surface temperature of billet entering the straightening machine for each example.

[0040] Example 1 873 959 913 Example 2 877 962 926 Example 3 881 966 917 Example 4 876 950 931

[0041] Table 4 Mechanical properties of rolled H-beams in various examples

[0042] Example 1 433.7 579.4 25.44 intact 188.0 Example 2 438.4 567.2 27.03 intact 169.6 Example 3 426.5 554.3 26.04 intact 171.0 Example 4 459.1 563.1 24.88 intact 153

[0043] As can be seen from Table 4, this H-beam not only has high yield and tensile strength, but also excellent impact toughness.

[0044] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for manufacturing hot-rolled H-beams for storage tank domes, comprising the following smelting process: blast furnace molten iron → molten iron pretreatment → converter smelting → LF refining → VD vacuum treatment → continuous casting of shaped billets; characterized in that: During the converter smelting process, the total oxygen supply time at the converter endpoint is controlled to be less than 15 minutes, and the cumulative total oxygen content is less than 4000 mg / L. 3 Ensure one-time drawing, final C > 0.02%, final temperature > 1620℃, control the slag amount in the converter to be less than 30mm, and use aluminum-iron deoxidation in the converter tapping process; During the LF refining process, desulfurization, composition fine-tuning, and temperature increase are carried out according to the composition and temperature of the converter steel. Phosphorus iron is added in the later stage of refining to ensure that the composition of the steel meets the internal control requirements. The LF refining heating time is less than 50 minutes, and silicon-calcium-barium aluminum-free deoxidation is used to produce white slag. The LF off-site temperature is controlled at 1680-1690℃. During the VD vacuum treatment process, the deep vacuum time is ≥12min, the deep vacuum degree target is <0.1KPa, the weak stirring time after breaking the vacuum is ≥20min, the silicon-calcium wire is fed in, the soft blowing time is ≥20min, and the temperature after VD is controlled at 1595-1605℃. During the continuous casting of the irregular billet, protective pouring is used throughout. Argon blowing is used to control the connection between the ladle and the long nozzle. The lower nozzle is controlled with an asbestos bowl. The nozzle insertion depth is 75-85mm. Weak cooling is used for the secondary cooling. The secondary cooling water volume is 0.85-0.95L / kg. The superheat is ≤35℃. The melting point of the protective slag is 1237℃, the density is 0.85-0.95g / ml, and the viscosity is 8.90 Poise. Constant casting speed is used, with the casting machine speed controlled at 0.9-1.3m / min. The ingot pressure on the first straightening machine is 150-160bar, and the ingot pressure on the second to sixth straightening machines is 60-70bar. The billet is stacked and slowly cooled for more than 48 hours. Its chemical composition by mass percentage includes: C 0.06%~0.14%, Si 0.25%~0.45%, Mn 1.35%~1.50%, P≤0.02%, S≤0.020%, V 0.03%~0.09%, Nb 0.015%~0.035%, with the remainder being Fe and impurities, totaling 100% by mass.

2. The method for manufacturing hot-rolled H-beams for tank domes according to claim 1, characterized in that: Add 50-60 kg / furnace of vanadium-nitrogen alloy during the later stages of refining.

3. The method for manufacturing hot-rolled H-beams for tank domes according to claim 1 or 2, characterized in that: 55 kg / furnace of vanadium-nitrogen alloy is added during the later stage of refining.

4. The method for manufacturing hot-rolled H-beams for tank domes according to claim 1, characterized in that: The cross-sectional dimensions of the continuously cast billet are 555×440×105mm.

5. The method for manufacturing hot-rolled H-beams for tank domes according to claim 1, characterized in that: Its chemical composition by mass percentage includes: C 0.06%, Si 0.30%, Mn 1.36%, P 0.012%, S 0.015%, V 0.056%, Nb 0.018%, with the remainder being Fe and impurities, totaling 100% by mass.

6. The method for manufacturing hot-rolled H-beams for tank domes according to claim 1, characterized in that: Its chemical composition by mass percentage includes: C 0.08%, Si 0.27%, Mn 1.35%, P 0.0117%, S 0.017%, V 0.059%, Nb 0.03%, with the remainder being Fe and impurities, totaling 100% by mass.

7. The method for manufacturing hot-rolled H-beams for tank domes according to claim 1, characterized in that: Its chemical composition by mass percentage includes: C 0.10%, Si 0.33%, Mn 1.36%, P 0.0111%, S 0.015%, V 0.057%, Nb 0.023%, with the remainder being Fe and impurities, totaling 100% by mass.

8. The method for manufacturing hot-rolled H-beams for tank domes according to claim 1, characterized in that: Its chemical composition by mass percentage includes: C 0.11%, Si 0.25%, Mn 1.45%, P 0.0090%, S 0.015%, V 0.033%, Nb 0.025%, with the remainder being Fe and impurities, totaling 100% by mass.