A smelting and continuous casting method of hot-rolled H-shaped steel for bridge structure with excellent comprehensive mechanical properties

Abstract

The application discloses a smelting and continuous casting method of hot-rolled H-shaped steel for bridge structure with excellent comprehensive mechanical properties, which controls the composition of the continuous casting molten steel as follows: C 0.14-0.16%, Si 0.35-0.40%, Mn 1.20-1.25%, P≤0.030%, S≤0.015%, V 0.05-0.07%, Nb 0.030-0.040%, Cr 0.30-0.35%, Cu 0.1-0.2%, Ni 0.1%-0.2%, and the rest is Fe and inevitable impurities, and controls the final slag basicity in the combined blown converter smelting process as 2.4-2.6, controls the appropriate slab web, flange and R angle temperature and the pulling speed in the shaped blank continuous casting process, so that the hot-rolled H-shaped steel for bridge structure with excellent comprehensive mechanical properties can be obtained, and the hot-rolled H-shaped steel is more beneficial to the construction of railway bridges in high-cold regions.

Description

Technical Field

[0001] This invention belongs to the field of smelting and continuous casting technology, specifically relating to a smelting and continuous casting method for hot-rolled H-beams used in bridge structures with excellent comprehensive mechanical properties. Background Technology

[0002] With the increasing construction of high-speed railways in cold regions, the market demand for hot-rolled H-beams for low-temperature resistant bridge structures is growing. Therefore, developing hot-rolled H-beams for bridge structures with excellent comprehensive mechanical properties, including high strength and high low-temperature toughness, is of profound significance for railway construction in cold regions and also plays a crucial role in improving the economic benefits for enterprises.

[0003] Patent document CN115505823A (hereinafter referred to as Document 1) discloses a continuous casting method for smelting Q420 grade hot-rolled H-beams for bridge structures. This method controls the superheat to ≤30℃ in the shaped billet continuous casting process, employs a weak cooling regime, and before entering the straightening machine, controls the target temperature of the billet web to 835-845℃, the target temperature of the billet flange to 785-795℃, and the R-angle temperature to 870-880℃. A constant casting speed of 0.8m / min-0.9m / min is also used. This yields Q420 grade hot-rolled H-beams for bridge structures with the following mechanical properties: yield strength ≥450MPa, tensile strength ≥650MPa, yield-to-tensile ratio ≤0.70, elongation A ≥24%, impact energy at -40℃ ≥170J, and corrosion rate ≤41% relative to Q345B, exhibiting superior comprehensive mechanical properties. Because high-speed rails laid in cold regions are often in extremely harsh working environments, in addition to gravity loads, they must also be affected by wind loads, wave loads, river loads, ice loads, seismic loads, etc. Therefore, in order to ensure the safety of the rails, in addition to having excellent strength properties, the rails also need to have higher low-temperature toughness properties. Summary of the Invention

[0004] To address the problems existing in the prior art, one aspect of the present invention provides a smelting and continuous casting method for hot-rolled H-beams used in bridge structures with excellent comprehensive mechanical properties, comprising the following processes: smelting in a combined blowing converter, LF refining, continuous casting of shaped billets, and slow cooling of billet stacking; wherein:

[0005] In the aforementioned combined blowing converter smelting process, the final slag basicity is controlled to be 2.4-2.6;

[0006] In the LF refining process, the composition of the molten steel supplied for continuous casting is controlled as follows: C 0.14-0.16%, Si 0.35-0.40%, Mn 1.20-1.25%, P≤0.030%, S≤0.015%, V 0.05-0.07%, Nb 0.030-0.040%, Cr 0.30-0.35%, Cu 0.1-0.2%, Ni 0.1%-0.2%, with the remainder being Fe and unavoidable impurities.

[0007] In the aforementioned continuous casting process for irregularly shaped billets, protective casting is employed throughout, with a superheat of 25-30℃ and a weak cooling regime. Before entering the straightening machine, the target temperature for the billet web is 850-860℃, the target temperature for the billet flange is 820-840℃, and the R-angle temperature is 870-880℃. Constant casting speed is used, controlled at 0.3-0.5 m / min.

[0008] The mechanical properties of the hot-rolled H-beams for bridge structures with excellent comprehensive mechanical properties meet the following requirements: yield strength ≥ 480 MPa, tensile strength ≥ 630 MPa, elongation A ≥ 24.5%, and impact energy at -40℃ ≥ 200 J.

[0009] In some embodiments, the mechanical properties of the hot-rolled H-beams for bridge structures with excellent comprehensive mechanical properties meet the following requirements: yield strength ≥ 486 MPa, tensile strength ≥ 634 MPa, elongation A ≥ 24.5%, and impact energy at -40℃ ≥ 201 J.

[0010] In some embodiments, in the LF refining process, the composition of the molten steel supplied for continuous casting is controlled as follows: C 0.14-0.16%, Si 0.35-0.40%, Mn 1.21-1.25%, P≤0.025%, S≤0.015%, V 0.05-0.07%, Nb 0.0320-0.039%, Cr 0.30-0.35%, Cu 0.11-0.18%, Ni 0.11%-0.19%, with the remainder being Fe and unavoidable impurities.

[0011] In some embodiments, in the combined blowing converter smelting process, the endpoint control targets are C≥0.06%, P≤0.020%, T≥1640℃, SiMn and MnFe deoxidation alloying is adopted, Al deoxidation is adopted for final deoxidation, lime is added during the tapping process, and slag is blocked during tapping.

[0012] In some embodiments, the LF refining process involves Ar blowing throughout. Desulfurization, composition fine-tuning, and heating are performed based on the converter steel composition and temperature. After desulfurization, S ≤ 0.015%, and the composition content is C 0.14-0.16%, Si 0.35-0.40%, Mn 1.20-1.25%, P ≤ 0.030%, S ≤ 0.015%. After heating, the temperature T ≥ 1640℃. In the later stages of refining, ferrovanadium, ferroniobium, copper plates, nickel plates, and ferrochrome are added. After addition, the composition is maintained at V 0.05-0.07%, Nb 0.030-0.040%, Cr 0.30-0.35%, Cu 0.1-0.2%, and Ni 0.1%-0.2%, with a soft blowing time greater than 10 minutes.

[0013] In the slow cooling process of the billet stacking, the slow cooling time is greater than 48 hours.

[0014] Another aspect of the present invention provides a hot-rolled H-beam for bridge structures with excellent comprehensive mechanical properties, which is obtained by rolling a continuously cast billet obtained by the above-mentioned smelting and continuous casting method.

[0015] In some embodiments, the cross-sectional dimensions of the continuously cast billet are H555mm×440mm×105mm.

[0016] In some embodiments, the mechanical properties of the hot-rolled H-beams used in the bridge structure meet the following requirements: yield strength ≥ 480 MPa, tensile strength ≥ 630 MPa, elongation A ≥ 24.5%, and impact energy at -40℃ ≥ 200 J.

[0017] In some embodiments, the mechanical properties of the hot-rolled H-beams used in the bridge structure meet the following requirements: yield strength ≥ 486 MPa, tensile strength ≥ 634 MPa, elongation A ≥ 24.5%, and impact energy at -40℃ ≥ 201 J.

[0018] The smelting and continuous casting method for hot-rolled H-beams for bridge structures with excellent comprehensive mechanical properties, based on the above technical solutions, mainly achieves this by optimizing and controlling the final slag basicity, the composition of the molten steel supplied for continuous casting, the target temperatures of the web, flanges, and radius of the billet in the shaped billet continuous casting process, and the casting speed. This allows for the production of hot-rolled H-beams for bridge structures with excellent comprehensive mechanical properties, meeting the following requirements: yield strength ≥ 480 MPa, tensile strength ≥ 630 MPa, elongation A ≥ 24.5%, and impact energy at -40℃ ≥ 200 J. The strength and plasticity of this hot-rolled H-beam for bridge structures are basically equivalent to those in Reference 1. However, the low-temperature toughness of the hot-rolled H-beam for bridge structures produced by this invention is significantly better than that of the hot-rolled H-beam produced in Reference 1. Therefore, the hot-rolled H-beam for bridge structures with excellent comprehensive mechanical properties provided by this invention is more suitable for constructing bridges and railways in cold regions. Detailed Implementation

[0019] The present invention aims to provide a smelting and continuous casting method for hot-rolled H-beams for bridge structures with excellent comprehensive mechanical properties, and to provide hot-rolled H-beams for bridge structures with excellent comprehensive mechanical properties obtained by the smelting and continuous casting method.

[0020] The smelting and continuous casting method for hot-rolled H-beams for bridge structures with excellent comprehensive mechanical properties provided by this invention includes the following processes: smelting in a combined blowing converter, LF refining, continuous casting of shaped billets, and slow cooling of billet stacking, wherein:

[0021] In the aforementioned combined blowing converter smelting process, the final slag basicity is controlled at 2.4-2.6, the final control target is C≥0.06%, P≤0.020%, T≥1640℃, SiMn and MnFe deoxidation alloying is adopted, Al deoxidation is adopted for final deoxidation, and quicklime is added during the tapping process to prevent slag from being removed during tapping.

[0022] In the LF refining process, Ar blowing is performed throughout. Desulfurization, composition fine-tuning, and temperature increase are conducted based on the converter steel composition and temperature. After desulfurization, S ≤ 0.015%, and the composition content is C 0.14-0.16%, Si 0.35-0.40%, Mn 1.20-1.25%, P ≤ 0.030%, S ≤ 0.015%. After temperature increase, T ≥ 1640℃. In the later stages of refining, ferrovanadium, ferroniobium, copper plates, nickel plates, and ferrochrome are added. After addition, the composition is maintained at V 0.05-0.07%, Nb 0.030-0.040%, Cr 0.30-0.35%, Cu 0.1-0.2%, and Ni 0.1%-0.2%, with a soft blowing time greater than 10 minutes. In other words, in the LF refining process, the composition of the continuously cast steel is controlled as follows: C 0.14-0.16%, Si 0.35-0.40%, Mn 1.20-1.25%, P≤0.030%, S≤0.015%, V 0.05-0.07%, Nb 0.030-0.040%, Cr 0.30-0.35%, Cu 0.1-0.2%, Ni 0.1%-0.2%, with the remainder being Fe and unavoidable impurities;

[0023] In the aforementioned shaped billet continuous casting process, protective casting is used throughout, with a superheat of 25-30℃ and a weak cooling regime. Before entering the straightening machine, the target temperature of the billet web is 850-860℃, the target temperature of the billet flange is 820-840℃, and the R-angle temperature is 870-880℃. Constant casting speed is used, with the casting speed controlled at 0.3-0.5m / min. The cross-sectional dimensions of the continuously cast billet can be H555mm×440mm×105mm.

[0024] In the slow cooling process of the billet stacking, the slow cooling time is greater than 48 hours.

[0025] The continuously cast billet obtained by the above smelting and continuous casting method can be rolled according to the rolling method disclosed in patent document CN108754327A (hereinafter referred to as document 2) to obtain the hot-rolled H-beam for bridge structure with excellent comprehensive mechanical properties of the present invention.

[0026] The present invention will be described in detail below through specific embodiments. These embodiments are intended to help understand the present invention and are not intended to limit the scope of the present invention.

[0027] Example 1:

[0028] This embodiment aims to produce a hot-rolled H-beam for bridge structures with excellent comprehensive mechanical properties. Its chemical composition is shown in Table 1 below. The specific production method includes the following processes: smelting in a combined blowing converter, LF refining, continuous casting of shaped billets and slow cooling of billet stacks, heating of shaped billets, rolling, and air cooling after rolling. The heating, rolling, and air cooling processes of shaped billets are carried out according to the operation in Reference 2 above. The control parameters of the continuous casting process of shaped billets are shown in Table 2 below. The surface quality of the continuously cast billets is inspected, and the internal quality is tested by hot acid low-magnification inspection. The quality of the H-beam billets is also monitored. No obvious surface or internal quality defects of the billets are found. The billet quality is good, and the surface crack rate of the billets is less than 1%. All properties of the rolled H-beams meet the standard requirements, as shown in Table 3 below.

[0029] Examples 2-4

[0030] Examples 2-4 were performed following the procedures of Example 1, with the only differences being the chemical composition of the hot-rolled H-beams for bridge structures with excellent comprehensive mechanical properties and the parameter control in the continuous casting process of the special-shaped billet, as shown in Tables 1 and 2 below. The mechanical properties and corrosion resistance of the hot-rolled H-beams for bridge structures with excellent comprehensive mechanical properties obtained after rolling in Examples 2-4 were tested, and the test results are shown in Table 3 below.

[0031] Comparative Example 1

[0032] Comparative Example 1 was performed following the same procedure as Example 1, except for the parameter control in the continuous casting process of the shaped billet, as shown in Tables 1 and 2 below. The mechanical properties and corrosion resistance of the hot-rolled H-beams obtained after rolling in Comparative Example 1 were tested, and the test results are shown in Table 3 below.

[0033] Table 1: Chemical composition (wt%) of hot-rolled H-beams in various examples

[0034] Example C Si Mn P S V Nb Cr Cu Ni Example 1 0.14 0.35 1.25 0.020 0.015 0.05 0.033 0.35 0.11 0.12 Example 2 0.15 0.40 1.21 0.021 0.008 0.07 0.034 0.32 0.13 0.11 Example 3 0.16 0.38 1.25 0.024 0.010 0.06 0.039 0.33 0.14 0.15 Example 4 0.14 0.37 1.23 0.015 0.012 0.07 0.032 0.30 0.18 0.19 Comparative Example 1 0.14 0.35 1.25 0.020 0.015 0.05 0.033 0.35 0.11 0.12

[0035] Table 2: Continuous casting process parameters for irregular billets in each example

[0036] Example Superheat (°C) Pulling speed (m / min) Flange tip (°C) R angle (°C) Web (°C) Example 1 28 0.35 820 875 850 Example 2 25 0.45 825 870 855 Example 3 27 0.50 835 880 857 Example 4 26 0.30 840 875 860 Comparative Example 1 28 0.85 790 875 840

[0037] Table 3: Mechanical properties of hot-rolled H-beams in various examples

[0038]

[0039] As shown in Tables 1-3 above, the hot-rolled H-beams for bridge structures produced in Examples 1-4 all possess excellent comprehensive mechanical properties, meeting the following requirements: yield strength ≥ 480 MPa, tensile strength ≥ 630 MPa, elongation A ≥ 24.5%, and impact energy at -40℃ ≥ 200 J. In contrast, although Comparative Example 1 used the same molten steel composition for continuous casting as Example 1, it controlled lower target temperatures for the web and flanges of the billet in the shaped billet continuous casting process. The resulting hot-rolled H-beams showed a significant decrease in yield strength and low-temperature toughness.

[0040] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A smelting and continuous casting method of hot-rolled H-shaped steel for bridge structure with excellent comprehensive mechanical properties, comprising the following processes: Combined blowing converter smelting, LF refining, continuous casting of special-shaped billets, and slow cooling of billet stacking; among which: In the aforementioned combined blowing converter smelting process, the final slag basicity is controlled to be 2.4-2.6; In the LF refining process, the composition of the molten steel supplied for continuous casting is controlled as follows: C 0.14-0.16%, Si 0.35-0.40%, Mn 1.20-1.25%, P≤0.030%, S≤0.015%, V 0.05-0.07%, Nb 0.030-0.040%, Cr 0.30-0.35%, Cu 0.1-0.2%, Ni 0.1%-0.2%, with the remainder being Fe and unavoidable impurities; In the LF refining process, Ar blowing is performed throughout. Desulfurization, composition fine-tuning, and temperature increase are carried out according to the composition and temperature of the converter steel. After desulfurization, S ≤ 0.015%, and the composition content is C 0.14-0.16%, Si 0.35-0.40%, Mn 1.20-1.25%, P ≤ 0.030%, S ≤ 0.015%. After temperature increase, T ≥ 1640℃. In the later stage of refining, ferrovanadium, ferroniobium, copper plate, nickel plate, and ferrochrome are added. After addition, V 0.05-0.07%, Nb 0.030-0.040%, Cr 0.30-0.35%, Cu 0.1-0.2%, and Ni 0.1%-0.2% are ensured, and the soft blowing time is greater than 10 minutes. In the aforementioned continuous casting process for irregularly shaped billets, protective casting is employed throughout, with a superheat of 25-30℃ and a weak cooling regime. Before entering the straightening machine, the target temperature for the billet web is 850-860℃, the target temperature for the billet flange is 820-840℃, and the R-angle temperature is 870-880℃. Constant casting speed is used, controlled at 0.3-0.5 m / min. In the aforementioned billet stacking slow cooling process, the slow cooling time is greater than 48 hours; The mechanical properties of the hot-rolled H-beams for bridge structures with excellent comprehensive mechanical properties meet the following requirements: yield strength ≥ 480 MPa, tensile strength ≥ 630 MPa, elongation A ≥ 24.5%, and impact energy at -40℃ ≥ 200 J.

2. The smelting and continuous casting method according to claim 1, wherein the mechanical properties of the hot-rolled H-beam for bridge structures with excellent comprehensive mechanical properties meet the following requirements: yield strength ≥ 486 MPa, tensile strength ≥ 634 MPa, elongation A ≥ 24.5%, and impact energy at -40℃ ≥ 201 J.

3. The smelting and continuous casting method according to claim 1 or 2, wherein in the LF refining process, the composition of the molten steel supplied for continuous casting is controlled as follows: C 0.14-0.16%, Si 0.35-0.40%, Mn 1.21-1.25%, P≤0.025%, S≤0.015%, V 0.05-0.07%, Nb 0.0320-0.039%, Cr 0.30-0.35%, Cu 0.11-0.18%, Ni 0.11%-0.19%, with the remainder being Fe and unavoidable impurities.

4. The smelting and continuous casting method according to claim 1 or 2, wherein in the combined blowing converter smelting process, the endpoint control targets are C≥0.06%, P≤0.020%, T≥1640℃, SiMn and MnFe deoxidation alloying is adopted, Al deoxidation is adopted for final deoxidation, quicklime is added during the tapping process, and slag is blocked during tapping.

5. A hot-rolled H-beam for bridge structures with excellent comprehensive mechanical properties, which is obtained by rolling a continuously cast billet obtained by the smelting and continuous casting method according to any one of claims 1-4.

6. The hot-rolled H-beam for bridge structures according to claim 5, wherein the cross-sectional dimensions of the continuously cast billet are H555mm×440mm×105mm.

7. The hot-rolled H-beam for bridge structures according to claim 5 or 6, wherein its mechanical properties meet the following requirements: yield strength ≥ 480 MPa, tensile strength ≥ 630 MPa, elongation A ≥ 24.5%, and impact energy at -40℃ ≥ 200 J.

8. The hot-rolled H-beam for bridge structures according to claim 5 or 6, wherein its mechanical properties meet the following requirements: yield strength ≥ 486 MPa, tensile strength ≥ 634 MPa, elongation A ≥ 24.5%, and impact energy at -40℃ ≥ 201 J.

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