A 355mpa grade ultra-thin hot-rolled h-beam with z-direction performance and a production method thereof

Abstract

The application provides a 355MPa grade super-thin hot-rolled H-shaped steel with Z-direction performance and a production method thereof, and the composition is as follows: C: 0.07-0.20%, Si: 0.20-0.55%, Mn: 1.20-1.55%, P≤0.010%, S≤0.005%, Nb: 0.030-0.050%, V: 0.020-0.060%, Ti: 0.010-0.020%, N≤0.0060%, Als: 0.008-0.045%, H≤0.0005%, and the rest is Fe and inevitable impurities. By means of chemical composition control, rapid cooling before universal rolling, and segmented cooling after rolling, the super-thick hot-rolled H-shaped steel with excellent comprehensive mechanical properties is obtained by using the combined effects of microstructure, precipitation, solid solution and fine-grain strengthening.

Description

Technical Field

[0001] This invention belongs to the field of H-beams, specifically relating to an ultra-large thin-gauge hot-rolled H-beam with Z-direction properties of 355MPa and its production method. Background Technology

[0002] With the increasing number of large bridges and high-rise buildings constructed both domestically and internationally, the demand for heavy hot-rolled H-beams will show a year-on-year upward trend. Considering the construction and safety of large and high-rise buildings, higher requirements are placed on the materials used. For hot-rolled H-beams, not only must they meet the strength requirements, but they must also have Z-direction properties.

[0003] So-called "Z-direction performance steel," also known as anti-lamellar tear steel, belongs to a type of low-alloy high-strength structural steel. This type of steel is typically made from a certain grade of low-alloy high-strength structural steel through special smelting and various processing techniques, resulting in a section reduction rate of over 15% in the thickness direction (Z-direction). According to standard GB / T5313, the Z-direction performance of steel with a thickness of 15mm-400mm can be tested. However, for ultra-large hot-rolled H-beams, limitations in rolling equipment capacity and roll pass shape prevent the achievement of low-temperature, high-reduction rolling. Currently, temperature-controlled rolling is commonly used, resulting in poor grain refinement and microstructure homogenization. This makes improving its Z-direction performance extremely difficult, and existing steelmaking, continuous casting, and rolling processes cannot guarantee that the product's Z-direction performance meets requirements. Therefore, improving the Z-direction performance of hot-rolled H-beams, especially ultra-large thin-gauge ones, is a major technical challenge, urgently requiring the development of new technical routes and key technologies to improve the Z-direction performance of thick, heavy hot-rolled H-beams.

[0004] Patent CN103334051A, published on October 2, 2013, discloses "A hot-rolled H-beam for construction with Z-directional properties and its production method." The chemical composition, by weight percentage, is: 0.06–0.18% C, 0.10%–0.25% Si, 0.90%–1.60% Mn, 0.008–0.020% P, ≤0.010% S, ≤0.10% V, ≤0.060% Nb, ≤0.030% Ti, and the balance being iron and unavoidable impurities. The process route is: hot metal pretreatment—converter refining—LF refining—continuous casting—heating—controlled rolling—cooling—slow cooling—straightening. The Z-direction performance of the structural steel produced in this paper reaches 40.81%, which meets the current technical requirements. However, this paper can only meet the requirements for hot-rolled H-beams with a flange thickness ≤ 40 mm, and cannot meet the mechanical and Z-direction performance requirements for sections with a cross-sectional height W ≥ 700 mm and a flange thickness ≤ 60 mm.

[0005] Patent CN108642390A, published on October 12, 2018, discloses "A high-strength thick steel plate with a thickness direction property Z of 35-50% and its production method." The process route is: steelmaking-continuous casting-heating-rough rolling-finish rolling-quenching-tempering-air cooling to room temperature. The chemical composition, by weight percentage, is: C: 0.10-0.18%, Si: 0.10-0.40%, Mn: 1.20%-1.60%, P≤0.010%, S≤0.005%, Cr: 0.10%-0.50%, Mo: 0.45-0.75%, Ni: 0.05-0.20%, Nb+Ti+V sum 0.040-0.06%, B: 0.0008-0.0020%, H≤2ppm. This method produces high-strength steel with an elongation A ≥ 15% and a thickness-direction property Z value of 35–50%, along with its production method. However, due to the characteristics of H-beam sections, the temperature difference between the flanges and web is significant during rolling and post-rolling processes, reaching up to 15°C. Therefore, the rolling method for thick plates cannot meet the performance requirements of H-beams.

[0006] Patent CN102618782A, published on August 1, 2012, discloses "A Large-Size Z-Oriented H-Beam and Its Preparation Method." This invention mainly achieves the composition design and production of large-size Z-oriented H-beams by reducing sulfur content, adding V microalloying, and not using Al for deoxidation. However, the special-shaped billet specification of this patent is 555×440×90mm, corresponding to the production of H300×300mm series hot-rolled H-beams, which cannot meet the production needs of ultra-large thin-size H-beams.

[0007] Patent CN114058948A, published on February 18, 2022, discloses "A Large-Size Z-Oriented Hot-Rolled H-Beam and Its Production Method." The chemical composition by mass percentage includes: C: 0.06%–0.18%, Si: 0.15%–0.40%, Mn: 1.20%–1.60%, P≤0.025%, S≤0.025%, Nb: 0.020%–0.050%, V: 0.010%–0.020%, with the remainder being Fe and unavoidable impurities, totaling 100% by mass. This invention also discloses a production method for large-size Z-oriented hot-rolled H-beams. This invention successfully developed large-size Z-direction hot-rolled H-beams by controlling the steelmaking process, including converter smelting, LF refining, continuous casting of special-shaped billets, and slow cooling of billet stacking. The continuous casting billet size is H730mm×370mm×90mm, and H-beams with a height greater than 730mm cannot be produced.

[0008] The patent published on March 21, 2023, with publication number CN115821154A, discloses "An ultra-thick hot-rolled H-beam with good Z-direction properties and its production method", with C: 0.15-0.18%, Si: 0.30-0.50%, Mn: 0.7-1.0%, P: ≤0.020%, S: ≤0.010%, Nb: 0.030-0.050%, Ti: 0.010-0.020%, N≤0.005%, and the remainder being Fe and unavoidable impurities. Compared with existing technologies, this invention obtains products with a thickness direction (Z direction) section reduction rate that meets the Z35 requirement specified in standard GB / T5313 through corresponding smelting and rolling processes. The flange thickness of the product ranges from 80mm to 140mm, while meeting the yield strength of 390MPa and having good low-temperature impact toughness at 20℃. According to the patent, it mainly meets the yield strength of 390MPa and is a heavy hot-rolled H-beam with a thickness of 80-140mm. There are no publicly reported methods for manufacturing ultra-large thin H-beams.

[0009] Patent CN116516246A, published on August 1, 2023, discloses "A Q460DE Grade Z-Directional Performance Hot-Rolled H-Beam and its Production Method." The H-beam has a carbon equivalent (CEV) of 0.36–0.41% and a weld crack sensitivity index (Pcm) of 0.18–0.23%. The flange thickness is 50–120 mm. At 1 / 6 of the flange width and 1 / 4 of the flange thickness, the size of the Nb(CN) second-phase particles is less than 60 nm, and the size of the V(CN) second-phase particles is less than 30 nm. The microstructure consists of ferrite and pearlite. The production method is as follows: hot metal pretreatment → alloy baking → converter smelting → LF refining → continuous casting → hot charging → furnace heating → high-pressure water descaling → billet mill rolling → universal mill rolling → air cooling on a cooling bed. This invention can obtain 50–120 mm thick Q460DE heavy-duty hot-rolled H-beams with excellent weldability. According to the patent, it mainly focuses on heavy hot-rolled H-beams with a yield strength of 460MPa and a thickness of 50-120mm. There are no publicly reported methods for manufacturing ultra-large and thin H-beams. Summary of the Invention

[0010] This invention provides a 355MPa grade ultra-large thin-gauge hot-rolled H-beam with Z-direction properties and its production method. Through composition design and microstructure control during the rolling process, the Z-direction properties of the web and flange of the ultra-large (1172mm≥W≥700mm) thin-gauge (flange thickness≤60mm) hot-rolled H-beam are achieved to be greater than 15%.

[0011] The specific technical solution of this invention is as follows:

[0012] An ultra-large, thin-gauge hot-rolled H-beam with Z-axis properties and a strength of 355 MPa, comprising the following components by weight percentage:

[0013] C: 0.07-0.20%, Si: 0.20-0.55%, Mn: 1.20-1.55%, P≤0.010%, S≤0.005%, Nb: 0.030-0.050%, V: 0.020-0.060%; Ti: 0.010-0.020%, N≤0.0060%, Als: 0.008-0.045%, H≤0.0005%, with the remainder being Fe and unavoidable impurities.

[0014] The composition of the 355MPa grade ultra-large thin-gauge hot-rolled H-beam with Z-direction properties satisfies CEV≤0.42; CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15;

[0015] The composition of the 355MPa grade ultra-large thin-gauge hot-rolled H-beam with Z-axis properties satisfies Pl=Pcm+H / 60+L / 7000≤0.30; where H is the hydrogen content in the steel composition, in %, and L is the total length of the unit inclusions, in μm / mm. 2 When calculating, simply substitute the value before the unit into the formula.

[0016] When using the above formulas, simply substitute the numerical value before the unit into the formula.

[0017] The aforementioned 355MPa grade ultra-large thin-gauge hot-rolled H-beam with Z-direction properties has a section height W ≥ 700mm and a flange thickness ≤ 60mm.

[0018] The 355MPa grade ultra-large thin-gauge hot-rolled H-beam with Z-direction properties has a flange thickness of 15-60mm. The room temperature microstructure of the flange and web in the same cross section, measured by area percentage at a standard sampling position 1 / 6 width from the end, is pearlite and ferrite, or pearlite and bainite; pearlite accounts for 10-25%, and the remaining microstructure is ferrite or bainite.

[0019] The grain size grades of the 355MPa grade ultra-large thin-gauge hot-rolled H-beams with Z-direction properties are 8.0–11.0 and 9.5–12.0 at the standard sampling positions of the flange and web, respectively; at the standard sampling positions of the flange, the size of the Nb(CN) and (Nb,Ti)Nb(CN) second-phase particles is less than 45nm, and the size of the V(CN) second-phase particles is less than 15mm.

[0020] Among them, at the standard sampling location of the flange of the steel product: the total volume fraction of Nb(CN) and (Nb,Ti)Nb(CN) second phase particles with a size of 20-40nm accounts for 0.03-0.0675% of the second phase particles, and the volume fraction of V(CN) second phase particles with a size ≤15nm accounts for 0.06-0.10% of the second phase particles.

[0021] The aforementioned 355MPa grade ultra-large thin-gauge hot-rolled H-beams with Z-direction properties have a yield strength Reh ≥ 355MPa, elongation A ≥ 17%, impact performance KV2 ≥ 27J, flange Z-direction properties ≥ 15%, and web Z-direction properties ≥ 15%; preferably, flange Z-direction properties ≥ 38% and web Z-direction properties ≥ 33%.

[0022] The chemical composition of this invention adopts the Nb-V-Ti microalloying and composition design concept. Considering production costs, in order to obtain a sufficiently fine-grained structure and adequate carbonitride precipitation, the contents of elements such as Ti, Nb, Als, P, and S must be strictly controlled. The contents of each component are controlled as follows:

[0023] C: 0.07-0.20%. As a basic element in steel, C plays a very important role in improving the strength of steel. In order to obtain higher strength and reduce the difficulty of decarbonization in steelmaking, the lower limit is set at 0.07%. Excessive C content will seriously deteriorate the plasticity, toughness and weld crack sensitivity index Pcm of steel, and reduce the weldability of H-beams. The upper limit is set at 0.20%, and the preferred content range is 0.07-0.12%.

[0024] Si: 0.20-0.55%. An appropriate amount of Si can play a strong solid solution strengthening role. Si is also an important reducing and deoxidizing element in the steelmaking process. In order to obtain higher strength, the lower limit is set at 0.20%, but the Si content should not be too high. Studies have shown that excessive Si content will accelerate high-temperature delamination, reduce toughness and resistance to lamellar tearing, and easily generate red iron oxide scale on the surface of steel, affecting the surface quality of the product. The upper limit is set at 0.55%, and the preferred content range is 0.20-0.30%.

[0025] Mn: 1.20-1.55%. Mn is a strengthening element in steel, which can improve the strength and hardenability of steel. In order to ensure the strength of steel, the lower limit is set at 1.20%. However, the Mn content cannot be too high. If it is too high, it will significantly increase the feasibility of billet segregation and have an adverse effect on the formability of steel. The upper limit is set at 1.55%, and the preferred content range is 1.25-1.40%.

[0026] P and S, as impurity elements, adversely affect the plasticity, toughness, and weldability of steel. P is a solidification segregation element, easily causing weld cracks and reduced toughness. S forms MnS during the center segregation process of solidification segregation, causing weld cracks, reduced toughness, and resistance to lamellar tearing. Therefore, they should be strictly controlled. Considering the difficulty of steelmaking control, in actual production, P should be controlled ≤0.0100%, and S ≤0.005%.

[0027] Nb: 0.030-0.050%. As a strong carbide-forming element, Nb forms Nb(C,N) dispersion compounds with C and N elements, which are distributed in the steel matrix and play a role in precipitation strengthening, while also improving toughness. The addition of Nb can inhibit austenite recrystallization during rolling, expand the non-recrystallization temperature range of austenite, and the cumulative deformation formed under subsequent low temperature and high pressure can elongate the austenite grains, forming a large number of deformation bands and dislocations at the grain boundaries. In the subsequent phase transformation process, it provides a large number of nucleation sites and refines the grains.

[0028] Nitrogen (N) content is set at ≤0.0060%. N is a forming element of Nb carbides, contributing to finer microstructure and precipitation strengthening. N is also a major element in the formation of TiN and AlN, and a key element controlling the size of TiN and AlN precipitates. Coarse TiN and AlN particles reduce low-temperature toughness, cause surface cracks in continuous casting, and contribute to strain aging in steel. Therefore, the upper limit for N content is set at 0.0060%.

[0029] Ti: 0.010-0.020%. Ti is the main element forming TiN. TiN is a high-temperature stable compound. By pinning austenite grains in the high-temperature region, TiN hinders austenite grain growth, thereby refining austenite grains during heating and rolling. To achieve this effect, the lower limit of Ti content is set at 0.010%. When the Ti content is too high, it will combine with excess N elements in the molten steel and grow rapidly. The large TiN particles will not have a grain-refining effect in the steel, but will instead become the source of cracks in the steel. Therefore, the upper limit of Ti is set at 0.020%, and the preferred Ti content range is 0.012-0.018%.

[0030] Als (Al₂S): 0.008-0.045%. Al is a strong deoxidizing element, commonly used in molten steel to reduce oxygen content, thereby reducing the number and size of inclusions and obtaining pure steel. Too low an Al content will result in excessive numbers and sizes of inclusions, leading to reduced impact resistance and yield strength, among other mechanical properties. Therefore, the lower limit for Als is set at 0.008%. However, Al is also a strong nitride-forming element, forming AlN. Appropriate amounts of AlN can refine grains and improve impact toughness. However, AlN tends to aggregate and grow in molten steel, increasing the crack sensitivity of continuously cast irregularly shaped billets and making surface cracks more likely. Simultaneously, excessive Al in steel competes with N, reducing the precipitation of second-phase particles such as V(C,N) and Nb(C,N), weakening the effects of V and Nb. Therefore, the upper limit for Al in steel is set at 0.045%, and the preferred Al content range is 0.008-0.012%.

[0031] V: 0.020-0.060%. As a strong carbide-forming element, V, together with C and N, forms V(C, N) dispersion compounds that are distributed in the steel matrix and play a role in precipitation strengthening. This is mainly achieved by acting as a ferrite phase deformation nucleus during the austenite-to-ferrite phase transformation, refining ferrite grains, and precipitating after the phase transformation to achieve precipitation strengthening. To improve strength, the lower limit is set at 0.020%. On the other hand, when the V content is greater than 0.060%, there will be too much N in the steel. When it combines with TiN, the precipitates will be coarse and damage toughness. Considering both the comprehensive mechanical properties of the product and production cost factors, the upper limit is set at 0.060%.

[0032] Hydrogen (H): The harmful effects of hydrogen in steel are mainly manifested in causing serious defects such as hydrogen embrittlement, white spots, point segregation, and static fatigue fracture. It reduces the plasticity of steel, increases its brittleness, and can cause sudden brittle fracture of steel structures or components under stress below their ultimate strength. Therefore, the H content should be controlled at H ≤ 0.0005%.

[0033] In order to intuitively evaluate the Z-direction properties of anti-lamellar tear steel, this invention uses the regression fitting formula Pl=Pcm+H / 60+L / 7000≤0.30 based on experimental data, where Pcm=C+Si / 30+(Mn+Cu+Cr).

[0034] / 20+Ni / 60+Mo / 15+V / 10+5B, where H is the hydrogen content in the steel composition, in %; L is the total length of inclusions per unit (μm / mm). 2The smaller the Pl value, the better the Z-axis performance. Chemical composition, H content, and inclusion length are key factors. Therefore, this invention uses a low-carbon composition design. To control inclusion length, the Mns inclusions require spheroidization treatment. To ensure the spheroidization effect of the Mns inclusions, the Ca / S ratio must be ≥0.3%. Simultaneously, the H content of the steel grade is less than 0.0005% to avoid white spots appearing during the final stretching process, which would reduce Z-axis performance.

[0035] This invention provides a method for producing ultra-large thin-gauge hot-rolled H-beams with Z-direction properties of 355MPa grade. The method includes: continuous casting - H-beam mill rolling - post-rolling air cooling.

[0036] In the aforementioned continuous casting, during the casting of irregular-shaped billets on the continuous casting machine, the working speed is 0.65-0.80 m / min, ensuring a primary cooling crystallization water flow rate of 200-250 m³ / min. 3 / h, the specific water volume for secondary cooling is 0.50-0.55l / kg.

[0037] Simultaneously, after continuous casting is completed, slow cooling is carried out by stacking, with a cooling rate of 50℃ / h.

[0038] The H-beam rolling process includes: after continuous casting and slow cooling, the shaped billet is heated and then rough rolled on a BD1 mill, with the rough rolling temperature controlled at 1100-1200℃ and the final rolling temperature ≥980℃; ensuring that the cumulative deformation rate of the web in the rough rolling section is 25-50% and the cumulative deformation rate of the flange is 15-30%.

[0039] The H-beam rolling mill employs a three-stage "relaxation-temperature control-deformation" coupled rolling process in the universal roughing zone. High-intensity cooling between rolling passes creates a significant temperature gradient along the thickness of the workpiece, making it more difficult for the surface metal to deform under the same rolling load conditions. This promotes deformation penetration into the core. In the first stage of rolling, the temperature is 960-1000℃, the speed is ≤2.0m / s, and the flange ultra-fast cooling device is activated, with a flange surface cooling rate of 5-10℃ / s and a temperature difference of 100-200℃ between the flange surface and the core. This enhances the thickness-direction deformation penetration to refine the austenite structure in the core. In the second stage, the temperature is 930-960℃, the speed is ≤3.0m / s, and the flange ultra-fast cooling device is activated, with a flange surface cooling rate of 3-7℃ / s and a temperature difference of 100-150℃ between the flange surface and the core. To refine the austenite microstructure in the core, deformation penetration in the thickness direction is improved. Simultaneously, temperature control is implemented after rolling in this stage to ensure the outer flange temperature is ≤930℃. In the third stage rolling range, the temperature is 850-930℃, the speed is ≤1.5m / s, and the flange ultra-fast cooling device is activated, with a surface cooling rate of 2-5℃ / s and a temperature difference of 50-100℃ between the flange surface and the core. Through repeated phase transformation coupled deformation, the surface austenite grains are refined, ultimately achieving a refined, homogenized, and approximately identical distortion state of austenite grains throughout the entire thickness of the microstructure. Refined and homogenized austenite grains are key to suppressing the formation of coarsening microstructure in the flange core.

[0040] Meanwhile, in order to reduce the temperature difference between the flange and the web, reduce the rolling pressure of the mill, and improve the surface quality of the finished product, the mill cooling water opening is 60%, and the cooling water pressure of the universal horizontal roll is 0.5-1MPa. This ensures that the temperature difference between the flange and the web is within the range of 80-120℃, and utilizes strain accumulation to provide the strain energy storage and nucleation sites required for subsequent phase transformation and precipitation.

[0041] After rolling, the rolled part is cooled to 200-300℃ at a cooling rate of 0.25-0.5℃ / s, and then air-cooled to room temperature in a cooling bed to ensure the precipitation of bainitic phase transformation, the dispersion of MC-type secondary carbide particles, and the solid solution of some alloying elements, thereby obtaining good strength and toughness indicators and Z-direction properties.

[0042] Compared with existing technologies, this invention utilizes controlled chemical composition and selective flange cooling to achieve a microstructure of pearlite and ferrite, or pearlite and bainite; the pearlite content is 10-25%, with the remaining microstructure being ferrite or bainite. By controlling the pearlite content, grain size, and bainite content, and through the combined effects of microstructure, precipitation, solid solution, and fine grain strengthening, ultra-large thin-gauge hot-rolled H-beams with excellent comprehensive mechanical properties are obtained. Attached Figure Description

[0043] Figure 1 This is a Z-axis SEM scanning electron microscope image of Example 4;

[0044] Figure 2 This is a Z-axis scanning electron microscope image of Comparative Example 1;

[0045] Figure 3 Metallographic image of Example 1;

[0046] Figure 4 This is a scanning electron microscope (SEM) image of Example 1;

[0047] Figure 5 The white spots are from the stretching in Comparative Example 2;

[0048] Figure 6 This is a TiN particle detection image for Comparative Example 4. Detailed Implementation

[0049] 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.

[0050] Examples 1-8

[0051] An ultra-large thin-gauge hot-rolled H-beam with Z-direction properties of 355MPa grade comprises the following mass percentage composition as shown in Table 1. The balance not shown in Table 1 is Fe and unavoidable impurities.

[0052] Comparative Examples 1-4

[0053] A hot-rolled H-beam comprises the following composition by weight percentage as shown in Table 1, where the balance not shown in Table 1 is Fe and unavoidable impurities.

[0054] Table 1. Chemical composition and weight percentage (%) of each example and comparative example.

[0055]

[0056]

[0057] The above embodiments and comparative examples were produced according to the following method: continuous casting - H-beam rolling mill rolling - post-rolling air cooling.

[0058] After being smelted as clean steel, the billet is continuously cast. Its chemical composition must be strictly controlled according to the above regulations. During the billet casting stage, a constant casting speed of 0.65-0.80 m / min is selected to ensure a primary cooling crystallization water flow rate of 200-250 m³ / min.3 The secondary cooling water volume is 0.50-0.55 L / kg. Simultaneously, after continuous casting, slow cooling is performed on the stacked material at a rate of 50 °C / h.

[0059] After slow cooling following continuous casting, the shaped billet is heated and then rough rolled on the BD1 mill. The rough rolling temperature is controlled at 1100-1200℃, and the final rolling temperature is ≥980℃. The cumulative deformation rate of the web in the rough rolling section is guaranteed to be 25-50%, and the cumulative deformation rate of the flange is 15-30%.

[0060] The universal roughing zone employs a three-stage "relaxation-temperature control-deformation" coupled rolling process. High-intensity cooling between rolling passes creates a large temperature gradient in the thickness direction of the workpiece, making it more difficult for the surface metal to deform under the same rolling load conditions. This promotes deformation penetration into the core. In the first stage of rolling, the temperature is 960-1000℃, the speed is ≤2.0m / s, and the flange ultra-fast cooling device is activated, with a flange surface cooling rate of 5-10℃ / s and a temperature difference of 100-200℃ between the flange surface and the core. This improves the deformation penetration in the thickness direction to refine the austenite structure in the core.

[0061] In the second stage of rolling, the temperature is 930-960℃, the speed is ≤3.0m / s, the flange ultra-fast cooling device is activated, the flange surface cooling rate is 3-7℃ / s, and the temperature difference between the flange surface and the core is 100-150℃. This improves the deformation penetration in the thickness direction to refine the austenite structure in the core.

[0062] In the third stage of rolling, the temperature is 850-930℃, the speed is ≤1.5m / s, and the flange ultra-fast cooling device is activated, with a flange surface cooling rate of 2-5℃ / s and a temperature difference of 50-100℃ between the flange surface and the core. Through repeated phase transformation coupled deformation, the surface austenite grains are refined, ultimately achieving a refined, homogenized, and approximately identical distortion state of austenite grains throughout the entire thickness of the microstructure. Refined and homogenized austenite grains are key to suppressing the formation of coarsening microstructure in the flange core.

[0063] Meanwhile, in order to reduce the temperature difference between the flange and the web, reduce the rolling pressure of the mill, and improve the surface quality of the finished product, the mill cooling water opening is 60%, and the cooling water pressure of the universal horizontal roll is 0.5-1MPa. This ensures that the temperature difference between the flange and the web is within the range of 80-120℃, and utilizes strain accumulation to provide the strain energy storage and nucleation sites required for subsequent phase transformation and precipitation.

[0064] The rolled workpiece is cooled to 200-300℃ at a cooling rate of 0.25-0.5℃ / s, and then air-cooled to room temperature on a cooling bed.

[0065] The parameters for each embodiment and comparative example are shown in Table 2.

[0066] Table 2. Main process parameters for each embodiment and comparative example (temperature unit: °C)

[0067]

[0068]

[0069] The product performance of the H-beams produced in the above embodiments and comparative examples was sampled according to the standard "GB / T 2975-2018 Sampling location and specimen preparation for mechanical property testing of steel and steel products" and tested according to the standards "GB / T 228.1 Metallic materials - tensile testing - Part 1: Room temperature test method" and "YB / T 4831 Method for hot-rolled H-beams with properties in the thickness direction". The results are shown in Table 3.

[0070] Table 3 Performance of each embodiment and comparative example product

[0071]

[0072] The poor Z-axis properties are mainly due to inclusions, especially MnS inclusions, as shown in Comparative Example 1. The low yield strength is caused by an unreasonable design of the C, Mn, Nb, and V composition, as shown in Comparative Example 3. The low Z-axis properties in Comparative Example 2 are mainly due to the high H content of the steel, which causes H aggregation during the Z-axis tensile test, leading to hydrogen embrittlement and white spots at the fracture site of the tensile specimen. Figure 5 As shown in the figure. In Comparative Example 4, the main issue is the higher N content. At high temperatures, N reacts with Ti to form coarse TiN particles, affecting the final Z-axis properties of the product, such as... Figure 6 As shown.

[0073] The data underlined above do 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 ultra-large, thin-gauge hot-rolled H-beam with Z-axis properties and a strength of 355 MPa, characterized in that, The 355MPa grade ultra-large thin-gauge hot-rolled H-beams with Z-axis properties comprise the following composition by weight percentage: C: 0.07-0.20%, Si: 0.20-0.55%, Mn: 1.20-1.55%, P≤0.010%, S≤0.005%, Nb: 0.030-0.050%, V: 0.020-0.060%; Ti: 0.010-0.020%, N≤0.0060%, Als: 0.008-0.045%, H≤0.0005%, with the remainder being Fe and unavoidable impurities; The composition of the 355MPa grade ultra-large thin-gauge hot-rolled H-beam with Z-axis properties satisfies Pl=Pcm+H / 60+L / 7000≤0.30, where H is the hydrogen content in the steel composition (%) and L is the total length of inclusions per unit (μm / mm). 2 ; The aforementioned 355MPa grade ultra-large thin-gauge hot-rolled H-beam with Z-direction properties has a section height W ≥ 700mm and a flange thickness ≤ 60mm. The microstructure of the 355MPa grade ultra-large thin-gauge hot-rolled H-beam with Z-direction properties is pearlite and ferrite, or pearlite and bainite; the pearlite accounts for 10~25%, and the remaining microstructure is ferrite or bainite. The ferrite grain size grades of the 355MPa grade ultra-large thin-gauge hot-rolled H-beams with Z-axis properties are 8.0-11.0 and 9.5-12.0 in the flange and web, respectively; the size of Nb(CN) and (Nb,Ti)Nb(CN) second-phase particles is less than 45nm, and the size of V(CN) second-phase particles is less than 15mm; the total volume fraction of Nb(CN) and (Nb,Ti)Nb(CN) second-phase particles with a size of 20-40nm accounts for 0.03-0.0675%, and the volume fraction of V(CN) second-phase particles with a size ≤15nm is 0.06-0.10%. The 355MPa grade ultra-large thin-gauge hot-rolled H-beam with Z-direction properties has a yield strength Reh≥355MPa, elongation A≥17%, impact performance: KV2≥27J, and flange Z-direction performance≥15%.

2. The 355MPa grade ultra-large thin-gauge hot-rolled H-beam with Z-direction properties according to claim 1, characterized in that, The composition of the 355MPa grade ultra-large thin-gauge hot-rolled H-beam with Z-direction properties satisfies CEV≤0.

42.

3. A method for producing ultra-large, thin-gauge hot-rolled H-beams with Z-axis properties of 55MPa grade as described in claim 1 or 2, characterized in that, The production method includes rough rolling and universal rough rolling followed by post-rolling cooling.

4. The production method according to claim 3, characterized in that, The roughing temperature is 1100-1200℃, and the final rolling temperature is ≥980℃; the cumulative deformation rate of the web in the roughing section is guaranteed to be 25-50%, and the cumulative deformation rate of the flange is 15-30%.

5. The production method according to claim 3, characterized in that, The universal roughing zone is a three-stage rolling mill. In the first stage, the temperature is 960-1000℃, the speed is ≤2.0m / s, the flange surface cooling rate is 5-10℃ / s, and the temperature difference between the flange surface and the core is 100-200℃. In the second stage, the temperature is 930-960℃, the speed is ≤3.0m / s, the flange surface cooling rate is 3-7℃ / s, and the temperature difference between the flange surface and the core is 200-300℃. In the third stage, the temperature is 850-930℃, the speed is ≤1.5m / s, the flange surface cooling rate is 2-5℃ / s, and the temperature difference between the flange surface and the core is 50-100℃.

6. The production method according to claim 3, characterized in that, The rolled workpiece is cooled to 200-300℃ at a cooling rate of 0.25-0.5℃ / s.

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