Smelting and continuous casting method of H-shaped steel with yield strength of 420 MPa for bridge structure

Abstract

The invention discloses a smelting and continuous casting method of H-shaped steel with the yield strength of 420 MPa for a bridge structure. The smelting process of the steel comprises the steps of converter smelting, LF refining, beam blank continuous casting and casting blank stacking and slow cooling. The H-shaped steel comprises the following chemical components in percentage by mass: 0.07%-0.11% of C, 0.25%-0.35% of Si, 1.50%-1.70% of Mn, less than or equal to 0.025% of P, less than or equal to 0.025% of S, 0.035%-0.045% of Nb, 0.08%-0.10% of V and the balance of Fe and inevitable impurities, and the total mass fraction is 100%. By optimizing the chemical components and the steelmaking process, the H-shaped steel has excellent low-temperature impact toughness while maintaining the yield strength of 420 MPa, particularly has good toughness performance at-40 DEG C, and meets the requirements of a bridge structure for high strength and high toughness of steel.

Description

Technical Field

[0001] The invention belongs to the technical field of smelting and continuous casting, and in particular relates to a smelting and continuous casting method for H-shaped steel with a yield strength of 420 MPa for a bridge structure. Background Art

[0002] With the rapid development of my country's economy, my country's transportation construction has developed rapidly, driving a new round of large-scale road and bridge construction, thereby driving the demand for bridge steel. In 2021, my country's steel structure output reached 90 million tons, accounting for 8.5% of the total steel output, and it has increased year by year. With the leapfrog development of my country's railway construction, most of the newly built high-speed railways are replaced by bridges, of which 80% are prestressed reinforced concrete bridges, and there is great potential for replacement with steel bridges. In the future, the tensile strength level of steel used in my country's railway bridges will mainly remain in the range of 500-600MPa, but will pursue specific indicators that are more excellent, such as low yield ratio and corrosion resistance. In the future, my country's bridge steel will have a broader prospect.

[0003] Announcement No. CN 117339995 B introduces a rolling method for H-beams with a grade of 400MPa for bridge structures, including the steps of molten iron pretreatment, converter refining, refining, continuous casting, heating of ingots, high-pressure water dephosphorization, rolling, cooling and straightening, and introduces the structure and working principle of its rolling device. This patent introduces a smelting and continuous casting method for H-beams with a yield strength of 420MPa for bridge structures, including specific chemical composition and converter smelting, LF refining, continuous casting of special-shaped ingots, slow cooling of ingot stacking, etc. The H-beams involved in this patent have a higher yield strength, and the chemical composition and steelmaking process are introduced in detail, which has a deeper research and innovation in improving the performance of steel.

[0004] Publication No. CN 117840210 A introduces a rolling production method for high-strength and high-toughness H-shaped steel for bridge structures. This patent introduces a smelting and continuous casting method for H-shaped steel for bridge structures with a yield strength of 420MPa. The H-shaped steel involved in this patent describes various process control details of the steelmaking process, and the description of related processes is more detailed and comprehensive.

[0005] Publication No. CN 117684072 A introduces a smelting and continuous casting method for hot-rolled H-beam for bridge structure. This patent introduces a smelting and continuous casting method for H-beam for bridge structure with a yield strength of 420MPa, including specific chemical composition and converter smelting, LF refining, special-shaped billet continuous casting, billet stacking slow cooling and other processes. The H-beam involved in this patent has unique control over the chemical composition and various process parameters in the steelmaking process, and provides a production method for H-beam under different performance indicators and application scenarios. Summary of the invention

[0006] The purpose of the present invention is to provide a smelting and continuous casting method for H-shaped steel for bridge structures with a yield strength of 420MPa. By optimizing the chemical composition and steelmaking process, the H-shaped steel has excellent low-temperature impact toughness while maintaining a yield strength of 420MPa, especially still has good toughness performance at -40°C, meeting the high strength and high toughness requirements of bridge structures for steel.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] The present invention discloses a smelting and continuous casting method for H-shaped steel for bridge structure with a yield strength of 420 MPa. The steel smelting process comprises: converter smelting, LF refining, continuous casting of special-shaped billets, and slow cooling of billet stacking.

[0009] The converter uses low-sulfur hot metal, top and bottom double blowing, and controls the final slag basicity to 2.0-3.8. The steel tapping slag is blocked, and aluminum-manganese-iron deoxidation alloying is used in the steel tapping process;

[0010] Refining white slag operation, using calcium carbide, silicon calcium barium, aluminum particles to adjust the slag, before leaving the station to make white slag, after entering the station to take the initial sample to determine the oxygen content ≤ 20ppm; the whole process of bottom blowing argon, soft blowing time is not less than 15min, refining cycle is not less than 25min;

[0011] The continuous casting adopts a full-protection pouring process, using a large ladle with a long nozzle and a sealing ring; the tundish uses a plugger to pour molten steel, controls the billet pulling speed, avoids nozzle blockage, and controls the superheat at 15-30°C; the billet pulling speed is 0.7-1.0m / min, and the smelted molten steel is poured into special-shaped billets, which are stacked and slowly cooled for 24 hours;

[0012] The chemical components of the H-shaped steel include by weight percentage: C 0.07% to 0.11%, Si 0.25% to 0.35%, Mn 1.50% to 1.70%, P≤0.025%, S≤0.025%, Nb 0.035% to 0.045%, V 0.08% to 0.10%, and the rest are Fe and unavoidable impurities, with a total weight fraction of 100%.

[0013] Furthermore, the cross-sectional dimensions of the continuous casting billet are H555mm×440mm×105mm.

[0014] Furthermore, the chemical composition of the H-beam includes by weight percentage: C 0.07%, Si 0.28%, Mn 1.57%, P 0.014%, S 0.004%, Nb 0.039%, V 0.092%, and the rest is Fe and unavoidable impurities, with a total weight fraction of 100%.

[0015] Furthermore, the chemical composition of the H-beam includes by weight percentage: C 0.08%, Si 0.31%, Mn 1.62%, P 0.012%, S 0.005%, Nb 0.041%, V 0.093%, and the rest is Fe and unavoidable impurities, with a total weight fraction of 100%.

[0016] Furthermore, the chemical composition of the H-beam includes by weight percentage: C 0.07%, Si 0.32%, Mn 1.65%, P 0.011%, S 0.004%, Nb 0.036%, V 0.091%, and the rest is Fe and unavoidable impurities, with a total weight fraction of 100%.

[0017] Furthermore, the chemical composition of the H-beam includes by weight percentage: C 0.08%, Si 0.30%, Mn 1.60%, P 0.013%, S 0.005%, Nb 0.039%, V 0.094%, and the rest is Fe and unavoidable impurities, with a total weight fraction of 100%.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are:

[0019] (1) By optimizing the chemical composition and steelmaking process, the H-shaped steel has excellent low-temperature impact toughness while maintaining a yield strength of 420 MPa, especially at -40°C, which meets the high strength and high toughness requirements of bridge structures for steel.

[0020] (2) The present invention adopts a reasonably controlled carbon equivalent (less than 0.34), which effectively improves the welding performance of H-shaped steel and reduces quality problems such as cracks that may occur during the welding process. It is suitable for welding applications in complex bridge structures and ensures the integrity and reliability of the structure.

[0021] (3) By adopting the slow cooling and full-protection pouring process of the continuous casting billet, the defect rate on the surface and inside of the billet is significantly reduced, and the surface crack rate of the billet is less than 2%, which improves the overall quality and surface finish of the final H-beam and ensures the stability of product performance after rolling. DETAILED DESCRIPTION

[0022] Embodiment 1:

[0023] The present invention provides a method for producing H-shaped steel for bridge structure with a yield strength of 420 MPa. The production process is carried out according to the following steps:

[0024] The converter uses low-sulfur molten iron, top and bottom double blowing, and controls the final slag basicity to 2.65. Slag is blocked during steel tapping, and aluminum-manganese-iron deoxidation and alloying are used in the steel tapping process.

[0025] Refining white slag operation, using calcium carbide, silicon calcium barium, aluminum particles to adjust the slag, before leaving the station to achieve white slag, after entering the station to take the initial sample to determine the oxygen content ≤ 20ppm. Bottom argon blowing is carried out throughout the process, the soft blowing time is 15.17min, and the refining cycle is 26.12min.

[0026] The continuous casting adopts a full protection pouring process, using a large ladle with a long nozzle and a sealing ring. The tundish uses a plugger to pour molten steel, control the billet pulling speed, avoid nozzle blockage, and control the superheat at 26.87℃; the billet pulling speed is 0.87m / min, and the smelted molten steel is poured into special-shaped billets, which are stacked and slowly cooled for 24 hours.

[0027] Example 2-4: Except for some specific process parameters that are different from those in Example 1, the rest of Example 2-4 is exactly the same as Example 1. See Table 4 for specific process parameters.

[0028] Table 4 Process parameters of each embodiment

[0029]

[0030]

[0031] Scale 1:

[0032] Comparative Example 1 is different from Example 1 except that the C content is increased, the Nb and V contents are reduced, and stacking and slow cooling are not performed. The rest is exactly the same as Example 1. In this comparative example, C is 0.13%, Nb is 0.015%, and V is 0.055%.

[0033] Comparative Example 2:

[0034] Comparative Example 2 is completely the same as Example 1 except that the Si content is reduced and the Mn, Nb and V contents are reduced. In this comparative example, Si is 0.20%, Mn is 1.75%, Nb is 0.055% and V is 0.12%.

[0035] Comparative Example 3:

[0036] Comparative Example 3 is completely the same as Example 1 except that the Si and V contents are increased, which is different from Example 1. The Si content in this comparative example is 0.50% and the V content is 0.11%.

[0037] Comparative Example 4:

[0038] Comparative Example 4 is completely the same as Example 1 except that stacking and slow cooling are not performed, which is different from Example 1.

[0039] Table 1 shows the chemical composition of various steel grades, and Tables 2, 3 and 4 further illustrate the present invention in conjunction with the embodiments.

[0040] Table 1 Chemical composition of each example (mass percentage / %)

[0041]

[0042] Table 2 Non-metallic inclusions and austenite grain size of each example

[0043]

[0044] Table 4 Mechanical properties of H-beam after rolling in each example

[0045]

[0046]

[0047] Through the comparison of multiple comparative examples with the embodiments: the lower carbon content of the present invention, the precise balance of silicon, niobium and vanadium, improves weldability, toughness and strength. Stacked slow cooling avoids internal stress and defects, improves the quality of steel, and has obvious advantages over the rapid cooling method. The combination of alloy composition and slow cooling process is not obvious because traditional methods tend to have faster production speeds but compromise mechanical properties. These examples demonstrate the superiority of alloy composition and process in mechanical properties, especially low temperature toughness and weldability. The combination of alloy composition and cooling control produces a steel product with excellent performance.

[0048] It can be seen from the above embodiments and comparative examples that:

[0049] (1) In Comparative Example 1, the higher carbon content reduces weldability and increases brittleness, especially at low temperatures. The composition also limits the balance of strength and toughness, because the higher carbon content increases yield strength but reduces impact toughness; the lower niobium and vanadium contents reduce the contribution of microalloying to toughness. Niobium and vanadium precipitates can improve grain refinement and improve toughness through precipitation strengthening; the refined grain structure obtained by slow cooling cannot be achieved without stacking slow cooling.

[0050] (2) In Comparative Example 2, the lower silicon content reduces the efficiency of deoxidation during steelmaking, weakens the steel matrix, and reduces the overall strength; the higher niobium and vanadium contents increase the cost, but the improvement in mechanical properties is not significant, which is lower than the effect that can be achieved through a more balanced composition; the higher manganese content will aggravate the segregation problem during casting, affecting toughness and uniformity.

[0051] (3) In Comparative Example 3, the higher silicon content increases the risk of silicon-induced toughness reduction at low temperatures, affecting low-temperature performance; the higher vanadium content leads to an increase in carbon equivalent, increasing the possibility of weldability problems.

[0052] (4) In Comparative Example 4, the lack of stacking and slow cooling resulted in a thermal gradient, which led to internal stress and promoted the generation of microcracks, reducing the toughness and ductility of the steel.

[0053] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A smelting and continuous casting method for H-shaped steel for bridge structure with a yield strength of 420 MPa, characterized in that: The steel smelting process is: converter smelting, LF refining, continuous casting of profiled billets, and slow cooling of billet stacking; The converter uses low-sulfur hot metal, top and bottom double blowing, and controls the final slag basicity to 2.0-3.

8. The steel tapping slag is blocked, and aluminum-manganese-iron deoxidation alloying is used in the steel tapping process; Refining white slag operation, using calcium carbide, silicon calcium barium, aluminum particles to adjust the slag, before leaving the station to make white slag, after entering the station to take the initial sample to determine the oxygen content ≤ 20ppm; the whole process of bottom blowing argon, soft blowing time is not less than 15min, refining cycle is not less than 25min; The continuous casting adopts a full-protection pouring process, using a large ladle with a long nozzle and a sealing ring; the tundish uses a plugger to pour molten steel, controls the billet pulling speed, avoids nozzle blockage, and controls the superheat at 15-30°C; the billet pulling speed is 0.7-1.0m / min, and the smelted molten steel is poured into special-shaped billets, which are stacked and slowly cooled for 24 hours; The chemical components of the H-shaped steel include by weight percentage: C 0.07% to 0.11%, Si 0.25% to 0.35%, Mn 1.50% to 1.70%, P≤0.025%, S≤0.025%, Nb 0.035% to 0.045%, V 0.08% to 0.10%, and the rest are Fe and unavoidable impurities, with a total weight fraction of 100%.

2. The smelting and continuous casting method of H-shaped steel for bridge structure with a yield strength of 420 MPa according to claim 1 is characterized in that: The cross-sectional dimensions of the continuous casting billet are H555mm×440mm×105mm.

3. The smelting and continuous casting method of H-shaped steel for bridge structure with a yield strength of 420 MPa according to claim 1, characterized in that: The chemical components of the H-shaped steel include by weight percentage: C 0.07%, Si 0.28%, Mn 1.57%, P 0.014%, S 0.004%, Nb 0.039%, V 0.092%, and the rest are Fe and unavoidable impurities, with a total weight fraction of 100%.

4. The smelting and continuous casting method of H-shaped steel for bridge structure with a yield strength of 420 MPa according to claim 1, characterized in that: The chemical components of the H-shaped steel include by weight percentage: C 0.08%, Si 0.31%, Mn 1.62%, P 0.012%, S 0.005%, Nb 0.041%, V 0.093%, and the rest are Fe and unavoidable impurities, with a total weight fraction of 100%.

5. The smelting and continuous casting method of H-shaped steel for bridge structure with a yield strength of 420 MPa according to claim 1, characterized in that: The chemical components of the H-shaped steel include by weight percentage: C 0.07%, Si 0.32%, Mn 1.65%, P 0.011%, S 0.004%, Nb 0.036%, V 0.091%, and the rest are Fe and unavoidable impurities, with a total weight fraction of 100%.

6. The smelting and continuous casting method of H-shaped steel for bridge structure with a yield strength of 420 MPa according to claim 1, characterized in that: The chemical components of the H-shaped steel include by weight percentage: C 0.08%, Si 0.30%, Mn 1.60%, P 0.013%, S 0.005%, Nb 0.039%, V 0.094%, and the rest are Fe and unavoidable impurities, with a total weight fraction of 100%.

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