An ultra-large specification hot-rolled h-shaped steel for bridges and a production method thereof

Abstract

The application provides a super-large-specification hot-rolled H-shaped steel for bridges and a production method thereof, and the composition is as follows: 0.14-0.20% of C, 0.15-0.50% of Si, 1.25-1.60% of Mn, 0.015% or less of P, 0.005% or less of S, 0.040%-0.010% of V, and the rest is Fe and inevitable impurities. The following conditions are also met: 3.7%<=8.75xC+Mn+15xV<=4.2%, the height H of the produced H-shaped steel is 1000-1158mm, the web thickness t1 is 20-36mm, and the flange thickness t2 is 30-65mm. The yield strength of the product is >=360MPa, the tensile strength is >=500MPa, the elongation rate is >=26%, the KV2 under the condition of-20 DEG C is >=170J, and the flaw detection level meets the I-grade requirement in GB / T 2970. No Nb element is added, and the cost is low.

Description

Technical Field

[0001] This invention belongs to the field of hot-rolled H-beam production technology, specifically relating to an ultra-large hot-rolled H-beam for bridges and its production method. Background Technology

[0002] H-beams used in bridge construction are extremely difficult to produce using hot rolling due to their large cross-sectional dimensions and small thickness, especially the large and thin web height. Currently, welding is the primary method. Bridge-grade H-beams require high strength and toughness, typically with a strength of at least 355 MPa and a toughness of at least Grade D. The significant difference in thickness between the web and flanges makes production difficult with existing hot-rolled H-beam technology. Furthermore, bridge-grade H-beams require flaw detection and have high quality standards. Currently, the largest H-value for extra-large H-beams in China is 1172 mm, with a web thickness of 42 mm and a flange thickness of 72 mm. Flaw detection typically only meets the Grade III requirements of GB / T 2970.

[0003] Chinese patent CN115532820A, published on December 30, 2022, discloses a method for producing large-size H-beams using medium-sized shaped billets. The production process includes shaped billet BD rolling, multi-pass continuous rolling, and cooling. Specifically, BD rolling employs widening rolling; multi-pass continuous rolling uses the XH rolling method; and segmented cooling is employed. The first third of the total cooling time uses natural cooling at a rate of 12–14 °C / min; the latter two-thirds of the total cooling time uses forced air cooling at a rate of 25–30 °C / min. This method can use the same shaped billets as medium-sized ones, reducing the difficulty and cost of initial operations and enabling high dimensional accuracy control. However, the H-beams produced using this method have an H-value below 1000 mm. This patent addresses the challenges of producing ultra-large H-beams exceeding 1000 mm in diameter.

[0004] Chinese Patent CN118127412A, published on June 4, 2024, discloses a low-temperature resistant hot-rolled H-beam and its preparation method. The chemical composition of the low-temperature resistant hot-rolled H-beam, by weight percentage, includes: C: 0.10–0.13; Si: ≤0.25; Mn: 0.8–1.0; V: 0.07–0.11; P ≤0.01; S ≤0.005; Nb: 0.005–0.015; Al: 0.008–0.015; N: 0.08–0.012; O ≤0.003; RE: 0.008–0.015; wherein As+Sn+Zn+Ca+Mg+S ≤0.03, and the remainder is iron (Fe) and unavoidable impurities. By employing online micro-alloying and micro-compounding processes, combined with the reciprocating rolling characteristics of H-beams, this technology enables the industrial production of large-size, high-strength, and high-toughness H-beams, meeting the requirements for transverse impact toughness. However, the addition of nitrogen (Nb) increases its cost, hindering economical production.

[0005] Chinese patent CN110438397A, published on November 12, 2019, discloses a large-section aluminum-containing hot-rolled H-beam and its preparation method. The chemical composition of the hot-rolled H-beam, by weight percentage, includes: C: 0.11–0.14%, Si: 0.18–0.25%, Mn: 1.40–1.50%, P≤0.025%, S≤0.008%, V: 0.040–0.050%, Ti: 0.012–0.02%, Al: 0.040–0.050%, with the remainder being iron and trace impurities. The preparation method includes pre-desulfurization of molten iron, converter smelting, LF refining, near-net-shape continuous casting of special-shaped billets, and rolling. This invention achieves fine-grain strengthening and dispersion strengthening effects through vanadium-titanium composite microalloying combined with aluminum, thereby improving the comprehensive mechanical properties of the large-section H-beam. The production process employs a single-point flange unbalanced fully protected continuous casting process for irregularly shaped billets, strictly controlling the cleanliness of the molten steel, reducing nozzle clogging, resulting in low inclusion content, stable low-temperature impact performance of the rolled product, and a high pass rate. However, the H-beams involved have a high Al content, which makes them more prone to cracking in the production of irregularly shaped billets. High Al content further increases the incidence of crack initiation tubes, and the cracking rate increases with the size of the irregularly shaped billet. Therefore, this method is not suitable for the production of ultra-large H-beams.

[0006] Therefore, there is a need to provide a production method for ultra-large hot-rolled H-beams for bridges with larger H-values ​​and thinner webs. Summary of the Invention

[0007] The purpose of this invention is to provide an ultra-large hot-rolled H-beam for bridges and its production method. Through composition design, the produced H-beam can have an H value of up to 1158 mm, a web thickness of less than 25 mm, a flange thickness of less than 65 mm, a yield strength of up to 360 MPa, a KV2 greater than 170 J at -20℃, and a flaw detection level that meets the Class I requirements of GB / T 2970.

[0008] The specific technical solution of this invention is as follows:

[0009] A type of extra-large hot-rolled H-beam for bridges, comprising the following components by weight percentage:

[0010] C: 0.14–0.20%, Si: 0.15–0.50%, Mn: 1.25–1.60%, P ≤ 0.015%, S ≤ 0.005%, V: 0.040%–0.100%, with the remainder being Fe and unavoidable impurities.

[0011] The composition of the extra-large hot-rolled H-beams used in the bridge also meets the following requirements:

[0012] The content of the three strengthening elements, C, Mn, and V, is 3.7% ≤ 8.75 × C + Mn + 15 × V ≤ 4.2%. Considering the order-of-magnitude differences in the strengthening degree and content of the three strengthening elements, and the large size and high rolling pressure of hot-rolled H-beams for bridges, the addition of elements with high deformation resistance at high temperatures should be avoided in the composition system design. Based on the above approach and multiple test data, the coefficients and ranges of the three strengthening elements were determined. This scheme can effectively ensure the strength and toughness of H-beams, while also being highly economical.

[0013] The aforementioned extra-large hot-rolled H-beams for bridges have a height H of 1000-1158 mm, a web thickness t1 of 20-36 mm, and a flange thickness t2 of 30-65 mm. Preferably, the height H of the aforementioned extra-large hot-rolled H-beams for bridges is 1088-1158 mm, the web thickness t1 is 20-25 mm, and the flange thickness t2 is 30-65 mm.

[0014] The aforementioned extra-large hot-rolled H-beams for bridges have a yield strength ≥360MPa, tensile strength ≥500MPa, elongation ≥26%, KV2 ≥170J at -20℃, and the flaw detection level meets the Class I requirements in GB / T 2970.

[0015] This invention provides a method for producing extra-large hot-rolled H-beams for bridges, comprising the following process flow:

[0016] Continuous casting of irregular billets → heating in a heating furnace → billet rolling → universal pre-cooling → universal section rolling → post-rolling air cooling.

[0017] Furthermore, before continuous casting of irregularly shaped billets, a process of hot metal pretreatment → converter smelting → argon blowing refining → LF refining is performed. This process effectively improves the purity of the molten steel, laying a solid foundation for the flaw detection requirements of H-beams. The main chemical elements in the molten steel are controlled at the following levels: C: 0.14–0.20%, Mn: 1.25–1.60%, V: 0.040%–0.100%. This is the composition of the tundish steel to ensure strength and toughness.

[0018] During the heating process of the furnace and the shaped billet, the heating temperature should be controlled at 1250-1280℃ and held for 220-280 minutes. In this temperature range, the second phase particles can be uniformly melted into the austenite. At the same time, the metal is easier to deform in this temperature range, which is conducive to the rolling process. This temperature range and heating time range can avoid the austenite grains from being too large, ensuring the strength and toughness of the H-beam.

[0019] After the billet exits the furnace, it undergoes high-pressure water descaling and enters a two-roll billet mill → a vertical universal mill with controlled cooling function → a two-roll reversible billet mill for rolling.

[0020] During the initial rolling process, the initial rolling temperature is controlled at 1200–1230℃.

[0021] The universal segment rolling process involves controlling the rolling temperature between 1150 and 1200°C. Within this temperature range, the deformation resistance is low, the rolling pressure is low, and this is beneficial for the rolling process.

[0022] During the universal segment rolling process, the ratio of the elongation of the web to the flange is controlled between 1.1 and 1.3 to ensure the deformation coordination between the web and the flange.

[0023] The universal rolling process involves activating the flange cooling device during universal rolling to cool the flanges at a rate controlled at 20–30°C / s. After water cooling, the flange surface temperature is controlled at 900–950°C. During flange compression deformation, the compression ratio per pass is not less than 40%, and in vertical universal rolling mills, the compression in the flange thickness direction accounts for 40%–60% of the total compression. This scheme promotes core deformation penetration, improves core defects, and increases the pass rate of H-beam flaw detection.

[0024] During universal rolling, the cooling device is turned on for the first 5 passes and turned off for subsequent passes.

[0025] After rolling on the vertical universal rolling mill, the product is rolled on a conventional universal mill unit. During this unit rolling, the total flange deformation is controlled between 40% and 60%, and the difference between the web and flange elongation is controlled below 5%. After rolling, the product is placed on a cooling bed, and subsequent processes are carried out according to existing conventional processes.

[0026] Compared with existing technologies, this invention, through composition design and process control, ensures the content of the three strengthening elements, C, Mn, and V, through 3.7% ≤ 8.75 × C + Mn + 15 × V ≤ 4.2%. Furthermore, since hot-rolled H-beams for bridges have large dimensions and high rolling pressure, elements with high deformation resistance at high temperatures should be avoided in the composition system design. This invention determines the coefficients and ranges of the three strengthening elements, effectively ensuring the strength and toughness of the H-beams while also being highly economical. The H-beams produced by this invention have a height H of 1000-1158 mm, a web thickness t1 of 20-36 mm, and a flange thickness t2 of 30-65 mm. The product has a yield strength ≥ 360 MPa, tensile strength ≥ 500 MPa, elongation ≥ 26%, KV2 ≥ 170 J at -20℃, and meets the Class I requirements of GB / T 2970 for flaw detection. Moreover, it does not contain Nb, resulting in low cost. Attached Figure Description

[0027] Figure 1 The metallographic structure is shown in Example 1;

[0028] Figure 2 The metallographic structure is shown in Example 2;

[0029] Figure 3 The metallographic structure is shown in Example 3;

[0030] Figure 4 The metallographic structure is shown in Example 4;

[0031] Figure 5 The metallographic structure is shown in Example 5;

[0032] Figure 6 The metallographic structure is shown in Example 6;

[0033] Figure 7 The metallographic structure is shown in Example 7;

[0034] Figure 8 The metallographic structure is shown in Example 8;

[0035] Figure 9 For comparative example 1, the metallographic structure is shown.

[0036] Figure 10 For comparative example 2, the metallographic structure is shown.

[0037] Figure 11 For comparative example 3, the metallographic structure is shown.

[0038] Figure 12 For comparative example 4, the metallographic structure is shown. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Examples 1-8

[0041] An extra-large hot-rolled H-beam for bridges comprises the following composition by weight percentage, as shown in Table 1, consisting of Fe and unavoidable impurities. Balances not shown in Table 1 are for Fe and unavoidable impurities.

[0042] Table 1 Chemical composition (wt%) of the examples

[0043]

[0044] The production method of H-beams described in Example 1 includes the following process flow:

[0045] Hot metal pretreatment → converter smelting → argon blowing refining → LF refining → continuous casting of shaped billets → heating furnace heating → billet rolling → universal pre-cooling → universal section rolling → post-rolling air cooling. The main process control follows these steps:

[0046] During the heating process of the furnace, the heating temperature should be controlled at 1270℃ and held for 250 minutes.

[0047] After the billet exits the furnace, it undergoes high-pressure water descaling and enters a two-roll billet mill → a vertical universal mill with controlled cooling function → a two-roll reversible billet mill for rolling.

[0048] During the initial rolling process, the initial rolling temperature is controlled at 1220℃.

[0049] The universal segment rolling process is carried out at a temperature controlled at 1180℃.

[0050] During the universal segment rolling process, the ratio of the elongation of the web to the flange is controlled between 1.1 and 1.3 to ensure the deformation coordination between the web and the flange.

[0051] During the universal rolling process, the flange cooling device is activated to cool the flange. The cooling rate is controlled at 25℃ / s. After water cooling, the surface temperature of the flange is controlled at 930℃. During flange compression deformation, the compression ratio per pass is not less than 40%, and during vertical universal rolling, the compression in the flange thickness direction accounts for 40% to 60% of the total compression.

[0052] After rolling in a vertical universal mill, the blades are rolled in a conventional universal mill. During rolling in this mill, the total flange deformation is controlled at 40% to 60%, and the difference between the web and flange elongation is controlled at less than 5%.

[0053] After rolling, the rolls are placed on a cooling bed and the subsequent processes are carried out according to existing conventional processes.

[0054] Examples 2-8 were produced using the same method as Example 1, except that the rolling parameters differed according to the size specifications.

[0055] The performance of the H-beams produced in each embodiment was tested, and the results are shown in Table 2 according to GB / T 1591.

[0056] Table 2 Mechanical properties of products in the examples

[0057]

[0058] The flaw detection results of Examples 1-8 above meet the Class I requirements of GB / T 2970 standard.

[0059] Comparative Examples 1-4

[0060] An extra-large hot-rolled H-beam for bridges comprises the following composition by weight percentage: as shown in Table 1, consisting of Fe and unavoidable impurities. The balance not shown in Table 4 consists of Fe and unavoidable impurities.

[0061] Table 4. Chemical composition (wt%) of comparative examples

[0062] 1158×415×36×65 0.14 0.28 1.30 0.013 0.002 0.05 3.28 Comparative Example 1 1108×402×22×40 0.18 0.24 1.15 0.012 0.003 0.062 3.66 Comparative Example 2 1100×460×20×36 0.20 0.32 1.56 0.025 0.030 0.02 3.61 Comparative Example 3 1088×460×20×30 0.17 0.25 1.32 0.017 0.028 0.072 3.89 Comparative Example 4

[0063] The production methods of H-beams described in Comparative Examples 1-4 are as described in Example 1, except that the rolling parameters in Examples 2-8 differ according to the size specifications.

[0064] The performance of H-beams produced in each proportion was tested, and the results are shown in Table 3.

[0065] Table 3 Mechanical properties of each comparative example

[0066]

[0067] The metallographic structures of Examples 1-8 and Comparative Examples 1-4 are as follows: Figures 1-12 As shown.

[0068] The grain size of Examples 1-8 is all above grade 8.0. Example 6, with a pearlite content of <20%, has a high V content, and the second-phase particles play a reinforcing role, resulting in a strength >360MPa.

[0069] In Comparative Example 1, the pearlite content was less than 20%, and the V content was only 0.05%. The strengthening effect of the second phase particles was limited, and its strength was less than 360 MPa and its toughness was insufficient.

[0070] In Comparative Example 2, the pearlite content in the metallographic structure is >20%, and the grain size is not significantly different. However, due to its low Mn content, 8.75C+Mn+15V <3.7%, and the strength is <360MPa.

[0071] In Comparative Example 3, the pearlite content in the metallographic structure is >20%, and the grain size is not significantly different. However, 8.75C+Mn+15V <3.7%, and the V content is only 0.02%. The strengthening effect of the second phase particles is limited, resulting in a strength of less than 360MPa. At the same time, its S content reaches 0.030%, which makes it unsuitable for flaw detection and has insufficient toughness.

[0072] In Comparative Example 4, the pearlite content in the metallographic structure is >20%, the grain size is not significantly different, the V content meets the requirements, and 8.75C+Mn+15V>3.7%, but its S content reaches 0.028%, which causes its toughness and flaw detection to not meet the requirements.

[0073] The underlined data represents data that does not meet the requirements of this invention.

[0074] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A type of extra-large hot-rolled H-beam for bridges, characterized in that, The extra-large hot-rolled H-beams for bridges comprise the following composition by weight percentage: C: 0.14~0.20%, Si: 0.15~0.50%, Mn: 1.25~1.60%, P≤0.015%, S≤0.005%, V: 0.040%~0.100%, with the remainder being Fe and unavoidable impurities; The height H of the extra-large hot-rolled H-beams used for bridges is 1000-1158mm, the web thickness t1 is 20-36mm, and the flange thickness t2 is 30-65mm. The composition of the extra-large hot-rolled H-beams used in the bridge also meets the following requirements: 3.7%≤8.75×C+Mn+15×V≤4.2%; The aforementioned extra-large hot-rolled H-beams for bridges have a yield strength ≥360MPa, tensile strength ≥500MPa, elongation ≥26%, KV2 ≥170J at -20℃, and the flaw detection level meets the Class I requirements in GB / T 2970.

2. The extra-large hot-rolled H-beam for bridges according to claim 1, characterized in that, The height H of the extra-large hot-rolled H-beams used for bridges is 1088-1158mm, the web thickness t1 is 20-25mm, and the flange thickness t2 is 30-65mm.

3. A method for producing extra-large hot-rolled H-beams for bridges as described in claim 1 or 2, characterized in that, The production method includes the following process flow: Continuous casting of irregular billets → heating in a heating furnace → billet rolling → universal pre-cooling → universal section rolling → post-rolling air cooling.

4. The production method according to claim 3, characterized in that, The heating furnace should be used to heat the furnace, and the heating temperature should be controlled at 1250~1280℃ for 220~280 minutes.

5. The production method according to claim 3, characterized in that, During the initial rolling process, the initial rolling temperature is controlled at 1200~1230℃.

6. The production method according to claim 3, characterized in that, The universal section rolling process is carried out at a temperature controlled between 1150 and 1200°C.

7. The production method according to claim 3, characterized in that, In the universal segment rolling process, the ratio of the elongation of the web to the flange is controlled between 1.1 and 1.

3.

8. The production method according to claim 3, characterized in that, The universal rolling process cools the flange at a rate of 20-30°C / s. After water cooling, the surface temperature of the flange is controlled at 900-950°C. During flange compression deformation, the compression ratio per pass is not less than 40%.

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