Oversized hot-rolled H-shaped steel for bridge and production method thereof

Abstract

The invention provides oversized hot-rolled H-shaped steel for bridges and a production method of the oversized hot-rolled H-shaped steel. The oversized hot-rolled H-shaped steel comprises the following components in percentage by weight: 0.14-0.20% of H-shaped steel, 0.15-0.50% of Si, 1.25-1.60% of Mn, less than or equal to 0.015% of P, less than or equal to 0.005% of S, 0.040-0.010% of V and the balance of Fe and inevitable impurities. And 3.7% < = 8.75 * C + Mn + 15 * V < = 4.2%, the height H of the produced H-shaped steel is 1000-1158 mm, the thickness t1 of a web plate is 20-36 mm, and the thickness t2 of a flange is 30-65 mm. The yield strength of the product is larger than or equal to 360 MPa, the tensile strength is larger than or equal to 500 MPa, the ductility is larger than or equal to 26%, KV2 is larger than or equal to 170 J under the condition of-20 DEG C, and the flaw detection grade meets the I-grade requirement in GB / T 2970. And no Nb element is added, so that the cost is low.

Description

Technical Field

[0001] The invention belongs to the technical field of hot-rolled H-shaped steel production, and specifically relates to an ultra-large-size hot-rolled H-shaped steel for bridges and a production method thereof. Background Art

[0002] H-shaped steel used in the bridge field is very difficult to produce by hot rolling due to its large cross-sectional size and small thickness, especially the large height size and small thickness of the web. Currently, welding is the main method. The strength and toughness requirements of H-shaped steel used in the bridge field are relatively high. Its strength is usually not less than 355MPa, and its toughness is not less than D grade. The thickness difference between the web and flange of H-shaped steel used in the bridge field is large, and the existing hot-rolled H-shaped steel production technology is difficult to achieve production. H-shaped steel used in the bridge field has high quality requirements and requires flaw detection. At present, the maximum H value of super-large H-shaped steel in China is 1172mm, the web thickness is 42mm, and the flange thickness is 72mm. The flaw detection can usually only meet the requirements of Level III in GB / T 2970.

[0003] The Chinese patent with publication number CN115532820A published on December 30, 2022, discloses a method for producing large-size H-shaped steel using medium-size profiled blanks. The production process includes profiled blank BD rolling, multi-pass continuous rolling, and cooling, wherein: profiled blank BD rolling adopts waist expansion rolling; multi-pass continuous rolling adopts XH rolling method; segmented cooling is adopted; natural cooling is adopted in the first third of the total cooling time, and the cooling rate is 12-14°C / min; strong wind cooling is adopted in the last two-thirds of the total cooling time, and the cooling rate is 25-30°C / min. It can be used with medium-size common profiled blanks, reducing the difficulty and cost of preliminary operations, and can achieve high dimensional accuracy control. However, the H value of the H-shaped steel produced by it is less than 1000mm. This patent provides the difficulties in producing super-large H-shaped steels above 1000mm.

[0004] The Chinese patent with publication number CN118127412A published on June 4, 2024, discloses a low-temperature hot-rolled H-beam and a preparation method thereof. The chemical composition of the low-temperature 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; among which As+Sn+Zn+Ca+Mg+S≤0.03, and the rest is iron Fe and unavoidable impurities. Through online organization control and microalloying process design, combined with the characteristics of H-beam reciprocating rolling, the industrialized production of large-scale high-strength and tough H-beam products is achieved to meet the requirements of transverse impact toughness. However, the addition of Nb is costly and not conducive to economical production.

[0005] The Chinese patent with the publication number CN110438397A published on November 12, 2019 discloses a large-section aluminum-containing hot-rolled H-beam and a preparation method thereof, wherein the chemical composition of the hot-rolled H-beam includes, by weight percentage: 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%, and the rest is iron and trace impurities. The preparation method includes hot metal pre-desulfurization, converter smelting, LF refining, near-net-shape profiled blank continuous casting and rolling. The present invention achieves the effects of fine grain strengthening and dispersion strengthening by using vanadium-titanium composite microalloying and aluminum elements at the same time, thereby improving the comprehensive mechanical properties of large-section H-beam. The production process adopts the non-balanced full-protection continuous casting process of the single-point flange of the profiled blank, strictly controls the cleanliness of the molten steel, reduces the nozzle nodules, has low inclusion content, and has stable low-temperature impact performance and high qualified rate of the rolled material. However, the Al content of the H-beam involved is relatively high, which makes it easier to crack for the production of profiled blanks. High Al will further increase the incidence of crack launch tubes, and the crack incidence will be higher as the size of the profiled blank increases. Therefore, this method is not suitable for the production of oversized H-beams.

[0006] Therefore, it is necessary to provide a production method for ultra-large hot-rolled H-shaped steel for bridges with larger H value and thinner web. Summary of the invention

[0007] The object of the present invention is to provide an ultra-large hot-rolled H-shaped steel for bridges and a production method thereof. Through component design, the H-shaped steel produced has 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 of greater than 170 J at -20°C, and a flaw detection grade that meets the Grade I requirement in GB / T 2970.

[0008] The specific technical solutions of the present invention are as follows:

[0009] An ultra-large hot-rolled H-shaped steel for bridges, comprising the following components in percentage by mass:

[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%, and the rest are Fe and unavoidable impurities.

[0011] The composition of the super-large hot-rolled H-shaped steel for bridges also meets the following requirements:

[0012] 3.7%≤8.75×C+Mn+15×V≤4.2%, ensuring the contents of the three strengthening elements C, Mn and V, and taking into account the orders of magnitude difference in the strengthening degree and added content of the three strengthening elements. At the same time, the hot-rolled H-shaped steel for bridges is large in size and rolling pressure. When designing the composition system, elements with relatively high deformation resistance under high temperature conditions should be avoided. Under the above ideas, based on multiple test data, the coefficients and ranges of the three strengthening elements are determined. This scheme can effectively ensure the strength and toughness of the H-shaped steel, and at the same time has high economy.

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

[0014] The yield strength of the super-large hot-rolled H-shaped steel for bridges is ≥360MPa, the tensile strength is ≥500MPa, the elongation is ≥26%, KV2 is ≥170J at -20°C, and the flaw detection grade meets the requirements of Grade I in GB / T 2970.

[0015] The present invention provides a method for producing super-large hot-rolled H-shaped steel for bridges, comprising the following process flow:

[0016] Continuous casting of special-shaped billets → heating in heating furnace → billet rolling → universal front controlled cooling → universal section rolling → air cooling after rolling.

[0017] Furthermore, before the continuous casting of the profiled billet, the process of molten iron pretreatment → converter smelting → argon blowing refining → LF refining is carried out. The molten iron pretreatment, converter smelting, argon blowing refining, and LF refining process can effectively improve the purity of the molten steel and lay a good foundation for the flaw detection requirements of H-beams. The main chemical elements of the molten steel are controlled at the following levels, namely C: 0.14-0.20%, Mn: 1.25-1.60%, V: 0.040%-0.100%. It is the composition of the molten steel in the middle package to ensure strength and toughness.

[0018] During the heating process of the heating furnace, the heating temperature of the special-shaped blank should be controlled at 1250-1280°C and kept warm for 220-280 minutes. In this temperature range, the second phase particles can be evenly melted in the austenite. At the same time, the metal deformation is easier in this temperature range, which is conducive to the rolling process. This temperature range and heating time range can avoid excessive austenite grains and ensure the strength and toughness of the H-shaped steel.

[0019] The billet is descaled by high-pressure water after being taken out of the furnace, and then enters the two-roller blanking mill → vertical universal rolling mill with controlled cooling function → two-roller reversible blanking mill for rolling.

[0020] During the slab rolling process, the slab rolling temperature is controlled at 1200-1230°C.

[0021] The universal section rolling has a universal section rolling temperature controlled at 1150-1200° C. In this temperature range, the deformation resistance is small and the rolling pressure is small, which is conducive to the rolling process.

[0022] The universal section is rolled, and during the rolling of the universal section, the elongation ratio of the web and the flange is controlled between 1.1 and 1.3 to ensure the deformation coordination of the web and the flange.

[0023] During the universal rolling, the flange cooling device is turned on to cool the flange, the cooling rate is controlled at 20-30°C / s, the surface temperature of the flange is controlled at 900-950°C after water cooling, the pass compression ratio of the flange during compression deformation is not less than 40%, and the compression amount in the thickness direction of the flange accounts for 40%-60% of the total compression amount during rolling in the vertical universal rolling mill. This solution promotes the deformation penetration of the flange core, improves the defects of the flange core, and improves the flaw detection pass rate of H-beam.

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

[0025] After rolling by the vertical universal mill, the steel is rolled by the conventional universal mill. During rolling by the mill, the total deformation of the flange is controlled at 40% to 60%, and the difference between the elongation of the web and the flange is controlled below 5%. After rolling, the steel is put on the cooling bed, and the subsequent process is carried out according to the existing conventional process.

[0026] Compared with the prior art, the present invention ensures the contents of three strengthening elements, C, Mn and V, by 3.7%≤8.75×C+Mn+15×V≤4.2% through composition design and process control. At the same time, the hot-rolled H-shaped steel for bridges has large size specifications and large rolling pressure. When designing the composition system, elements with relatively high deformation resistance under high temperature should be avoided. The present invention determines the coefficients and ranges of the three strengthening elements. The scheme can effectively ensure the strength and toughness of the H-shaped steel, and has high economy. The height H of the H-shaped steel produced by the present invention is 1000-1158mm, the web thickness t1 is 20-36mm, and the flange thickness t2 is 30-65mm. The product yield strength is ≥360MPa, the tensile strength is ≥500MPa, the elongation is ≥26%, KV2 is ≥170J under -20℃, and the flaw detection grade meets the requirements of Grade I in GB / T 2970. No Nb element is added, and the cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The metallographic structure of Example 1;

[0028] Figure 2 The metallographic structure of Example 2;

[0029] Figure 3 The metallographic structure of Example 3;

[0030] Figure 4 The metallographic structure of Example 4;

[0031] Figure 5 The metallographic structure of Example 5;

[0032] Figure 6 The metallographic structure of Example 6;

[0033] Figure 7 The metallographic structure of Example 7;

[0034] Figure 8 The metallographic structure of Example 8;

[0035] Fig. 9 The metallographic structure of comparative example 1;

[0036] Fig.10 This is the metallographic structure of Comparative Example 2;

[0037] Fig.11 This is the metallographic structure of Comparative Example 3;

[0038] Fig.12 This is the metallographic structure of Comparative Example 4. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] Example 1-Example 8

[0041] An ultra-large hot-rolled H-shaped steel for bridges includes the following mass percentage components: Fe and inevitable impurities as shown in Table 1. The balance not shown in Table 1 is Fe and inevitable impurities.

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

[0043]

[0044] The method for producing H-beam described in Example 1 includes the following process flow:

[0045] Hot metal pretreatment → converter smelting → argon blowing refining → LF refining → continuous casting of special-shaped billets → heating in heating furnace → billet rolling → universal pre-controlled cooling → universal section rolling → air cooling after rolling. Mainly in accordance with the following process control:

[0046] During the heating process of the heating furnace, the heating temperature should be controlled at 1270° C. and kept warm for 250 minutes.

[0047] The billet is descaled by high-pressure water after being taken out of the furnace, and then enters the two-roller blanking mill → vertical universal rolling mill with controlled cooling function → two-roller reversible blanking mill for rolling.

[0048] During the slab rolling, the slab rolling temperature is controlled at 1220°C;

[0049] The universal section rolling, the universal section rolling temperature is controlled at 1180°C;

[0050] The universal section is rolled, and during the rolling of the universal section, the elongation ratio of the web and the flange is controlled between 1.1 and 1.3 to ensure the deformation coordination of the web and the flange.

[0051] During the universal rolling, the flange cooling device is turned on to cool the flange, the cooling rate is controlled at 25°C / s, the flange surface temperature is controlled at 930°C after water cooling, the pass compression ratio of the flange during compression deformation is not less than 40%, and the compression amount in the flange thickness direction during rolling on the vertical universal rolling mill accounts for 40% to 60% of the total compression amount.

[0052] After rolling by the vertical universal rolling mill, the conventional universal rolling unit is used for rolling. During rolling by the unit, the total deformation of the flange is controlled at 40% to 60%, and the difference in elongation between the web and the flange is controlled below 5%.

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

[0054] Example 2-Example 8 are produced according to the same method as Example 1, except that the rolling parameters of Example 2-Example 8 are different according to the size specifications.

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

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

[0057]

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

[0059] Comparative Example 1-Comparative Example 4

[0060] An ultra-large hot-rolled H-shaped steel for bridges includes the following mass percentage components: Fe and inevitable impurities as shown in Table 1. The balance not shown in Table 4 is Fe and inevitable impurities.

[0061] Table 4 Comparative Example Chemical Composition (wt%)

[0062] Specifications (H×B×t1×t2) C Si Mn P S V 8.75C+Mn+15V Comparative Example 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 method of the H-beam described in Comparative Examples 1 to 4 is carried out as described in Example 1, except that the rolling parameters of Examples 2 to 8 are different according to the size specifications.

[0064] The performance of the H-beams produced in each comparative example 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 the above Examples 1 to 8 and Comparative Examples 1 to 4 are as follows: Figure 1-Figure 12 shown.

[0068] The grain sizes of Examples 1 to 8 are all above Grade 8.0. Example 6, in which the pearlite content is less than 20%, has a high V content, and the second phase particles play a strengthening role, making its strength greater than 360 MPa.

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

[0070] In the metallographic structure of Comparative Example 2, the pearlite content accounts for more than 20%, and the grain size has no obvious difference, but due to its low Mn content, 8.75C+Mn+15V is less than 3.7%, and the strength is less than 360MPa;

[0071] In the metallographic structure of Comparative Example 3, the pearlite content accounts for more than 20%, and the grain size has no obvious difference, but 8.75C+Mn+15V is less than 3.7%, and the V content is only 0.02%. The strengthening effect of the second phase particles is limited, resulting in a strength lower than 360MPa. At the same time, its S content reaches 0.030%, resulting in its nondestructive testing not meeting the requirements and insufficient toughness;

[0072] In the metallographic structure of Comparative Example 4, the pearlite content accounts for more than 20%, there is no obvious difference in grain size, the V content meets the requirements, and 8.75C+Mn+15V>3.7%, but its S content reaches 0.028%, resulting in its toughness and flaw detection not meeting the requirements.

[0073] The underlined data do not meet the requirements of the present invention.

[0074] The description of the above embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and 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 present invention should be within the protection scope of the present invention.

Claims

1. An ultra-large hot-rolled H-beam for bridges, characterized in that: The super-large hot-rolled H-shaped steel for bridges includes the following mass percentage components: 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%, and the rest are Fe and unavoidable impurities. The height H of the super-large hot-rolled H-shaped steel for bridges is 1000-1158 mm, the web thickness t1 is 20-36 mm, and the flange thickness t2 is 30-65 mm.

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

3. The super-large hot-rolled H-beam for bridges according to claim 1 or 2, characterized in that: The composition of the super-large hot-rolled H-shaped steel for bridges also meets the following requirements: 3.7%≤8.75×C+Mn+15×V≤4.2%.

4. The super-large hot-rolled H-beam for bridges according to any one of claims 1 to 3, characterized in that: The yield strength of the super-large hot-rolled H-shaped steel for bridges is ≥360MPa, the tensile strength is ≥500MPa, the elongation is ≥26%, KV2 is ≥170J at -20°C, and the flaw detection grade meets the requirements of Grade I in GB / T 2970.

5. A method for producing super-large hot-rolled H-shaped steel for bridges according to any one of claims 1 to 4, characterized in that: The production method comprises the following process flow: Continuous casting of special-shaped billets → heating in heating furnace → billet rolling → universal front controlled cooling → universal section rolling → air cooling after rolling.

6. The production method according to claim 5, characterized in that The heating furnace is heated, and the heating temperature should be controlled at 1250-1280° C. and kept warm for 220-280 minutes.

7. The production method according to claim 5, characterized in that: During the slab rolling process, the slab rolling temperature is controlled at 1200-1230°C.

8. The production method according to claim 5, characterized in that: The universal section rolling is carried out at a temperature controlled at 1150-1200°C.

9. The production method according to claim 5, characterized in that: The universal section is rolled, and during the universal section rolling, the elongation ratio of the web and the flange is controlled between 1.1 and 1.

3.

10. The production method according to claim 5, characterized in that: The flange is cooled during the universal rolling process, and the cooling rate is controlled at 20-30°C / s. The surface temperature of the flange is controlled at 900-950°C after water cooling, and the pass compression ratio of the flange during compression deformation is not less than 40%.

Images