Method for preparing 420 MPa hot-rolled H-shaped steel of different grades under same steel and iron components and hot-rolled H-shaped steel

Abstract

The invention discloses a method for preparing hot-rolled H-shaped steel of 420 MPa and different grades under the same steel and iron component and the hot-rolled H-shaped steel. The hot-rolled H-shaped steel comprises the following elements in percentage by mass: 0.12%-0.19% of C, 0.20%-0.50% of Si, 1.35%-1.60% of Mn, 0.010%-0.025% of V, 0.008%-0.020% of Nb, and the balance of H-shaped steel. The method comprises the following steps of converter smelting, argon blowing refining, special-shaped blank continuous casting, blank heating, cogging rolling, universal rolling and air cooling on a cooling bed after rolling. The 420MPa-grade high-strength B-grade, C-grade and D-grade hot-rolled H-shaped steel is prepared under the same steel and iron component by performing different control on the universal rolling process, meanwhile, the method is convenient for group production of blanks of a steel mill, and the production efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of hot-rolled H-beams, and particularly relates to a method for preparing hot-rolled H-beams with different grades of 420 MPa under the same steel composition and the hot-rolled H-beams. Background Art

[0002] Hot-rolled H-beams are steel materials with an H cross-section produced by a hot-rolling process. Its cross-sectional shape usually consists of two parallel flanges and a vertical web. This structural design endows it with excellent bending, compressive, and torsional resistance properties, while being relatively light in weight, facilitating transportation and installation.

[0003] Currently, its materials are mainly 235 MPa grade plain carbon steel and 355 MPa grade low alloy steel. For example, Chinese Patent CN103834860 A discloses a 235 MPa grade low-temperature resistant hot-rolled H-beam and its preparation method. The weight percentages of the chemical components of the 235 MPa grade low-temperature resistant hot-rolled H-beam are: C 0.08 - 0.16%, Si 0.10 - 0.30%, Mn 0.65 - 1.20%, P≤0.025%, S≤0.025%, Nb 0.015 - 0.035%, Ti 0.005 - 0.030%, and the rest are iron and trace impurities. The strength of the hot-rolled H-beams in this patent is relatively low.

[0004] Chinese Patent CN 118996258 A discloses a 355 MPa grade weather-resistant hot-rolled H-beam and its production method, with the composition: C: 0.07 - 0.12%, Si: 0.15 - 0.50%, Mn: 1.10 - 1.35%, P: ≤0.030%, S: ≤0.030%, Ni: 0.20 - 0.50%, Cr: 0.40 - 0.70%, Cu: 0.20 - 0.40%, V: 0.040 - 0.100%, Al: 0.003 - 0.010%, and the rest are Fe and trace residual elements. The strength of the hot-rolled H-beams in this patent is also relatively low.

[0005] With the requirements of lightweight design and extending the product service life, the development is moving from plain carbon steel to low alloy steel. Among them, the demand for grades B, C, and D of 420 MPa will gradually increase. Grade B steel has good impact resistance at normal temperature, grade C steel can still maintain good impact resistance at a lower temperature of 0 °C, and grade D steel can still have excellent impact resistance at an even lower temperature of -20 °C.

[0006] And usually, for grades B, C, and D of the same strength in hot-rolled H-beams, there are differences in chemical composition, which will cause difficulties in the production of steel mill billets and increase production costs during production. Summary of the Invention

[0007] To solve the above technical problems, the present invention provides a method for preparing hot-rolled H-beams with different grades of 420 MPa under the same steel composition. By adopting reasonable chemical compositions, heating systems and rolling processes, especially through strict heating temperatures, heating times, controlling the reduction amount between passes and selectively cooling and temperature controlling rolling between the universal mill stands, the performance uniformity of the whole cross-section of the rolled piece is improved. Utilizing the mechanisms of fine grain strengthening, precipitation strengthening, phase transformation strengthening and solid solution strengthening, hot-rolled H-beams of grades B, C and D with a yield strength of 420 MPa and excellent comprehensive mechanical properties are obtained. At the same time, this method is convenient for the steel mill to organize production of billets and improves production efficiency.

[0008] The present invention also provides a 420 MPa grade hot-rolled H-beam, which is produced by the method of the present invention, has grades B, C and / or D, and can meet the requirements of different low-temperature grades.

[0009] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0010] A method for preparing hot-rolled H-beams with different grades of 420 MPa under the same steel composition, the method comprising the following steps: converter smelting → argon blowing refining → special-shaped billet continuous casting → billet heating → blooming rolling → universal rolling → air cooling on the cooling bed after rolling;

[0011] In the universal rolling step, for the 420 MPa grade B hot-rolled H-beam, after rough rolling, it directly enters the universal rolling mill for rolling, and the remaining deformation of the billet is completed in this stage. The rolling temperature of the 3rd pass is controlled at 960 - 980 °C, and the finishing rolling temperature is controlled at 900 - 930 °C;

[0012] For the 420 MPa grade C hot-rolled H-beam, the selective control cooling device between the universal mill stands is turned on, the rolling temperature of the 3rd pass is controlled at 930 - 950 °C, and the finishing rolling temperature is controlled at 880 - 900 °C;

[0013] For the 420 MPa grade D hot-rolled H-beam, the selective control cooling device between the universal mill stands is turned on, the 3rd pass is controlled-rolled at 900 - 930 °C, and the finishing rolling temperature is controlled at 830 - 880 °C;

[0014] The hot-rolled H-beam comprises the following elements in mass percentages: C: 0.12% - 0.19%, Si: 0.20% - 0.50%, Mn: 1.35% - 1.60%, P: ≤0.035%, S: ≤0.035%, V: 0.010% - 0.025%, Nb: 0.008% - 0.020%, and the rest is Fe and inevitable impurities.

[0015] Further, in the universal rolling step, in the temperature range of 950°C < temperature ≤ 1000°C, the pass reduction rate is controlled at 12% - 18%; in the temperature range of 930°C < temperature ≤ 950°C, the pass reduction rate is controlled at 20% - 30%; in the temperature range of temperature ≤ 930°C, the pass reduction rate is controlled at 12% - 17%; the reduction rate of the blank in the universal rolling stage is controlled above 60%.

[0016] In the blank heating step, the profiled blank enters the heating furnace and is heated to 1220°C - 1260°C by the heating furnace, and the residence time in the furnace is 100 min - 130 min.

[0017] In the blooming rolling step, the rolling start temperature in the rough rolling stage is controlled at 1100°C - 1200°C, and the final rolling temperature is controlled above 1000°C.

[0018] In the blooming rolling step, in the temperature range of 1100°C < temperature ≤ 1200°C, the pass reduction rate is controlled at 10% - 15%; in the temperature range of 1050°C < temperature ≤ 1100°C, the pass reduction rate is controlled at 15% - 25%; in the temperature range of 1000°C ≤ temperature ≤ 1050°C, the pass reduction rate is controlled at 15% - 25%, and the total reduction rate of the blank is controlled above 50%.

[0019] The hot-rolled H-beam preferably comprises the following elements by mass percentage: C: 0.16% - 0.19%, Si: 0.25% - 0.50%, Mn: 1.40% - 1.60%, P: ≤0.025%, S: ≤0.020%, V: 0.015% - 0.025%, Nb: 0.010% - 0.020%, and the rest is Fe and unavoidable impurities.

[0020] The present invention also provides the 420 MPa grade hot-rolled H-beam produced by the above method. The hot-rolled H-beam is of 420 MPa grade B, 420 MPa grade C, and / or D grade.

[0021] The thickness of the hot-rolled H-beam is ≤ 40 mm, the metallographic structure is a duplex structure of ferrite + pearlite, and the ferrite grain size grade is above 8.0.

[0022] The yield strength of the hot-rolled H-beam is ≥ 420 MPa, the tensile strength is 520 MPa - 680 MPa, the elongation is ≥ 20%, the Charpy impact energy at room temperature of grade B is ≥ 120 J, the Charpy impact energy at 0°C of grade C is ≥ 80 J, and the Charpy impact energy at -20°C of grade D is ≥ 50 J.

[0023] Considering the production cost, the chemical composition of the present invention adopts the design concept of Nb-V complex microalloying composition. In order to obtain sufficient precipitation of V(C, N) to highlight the precipitation strengthening effect at low temperatures and good low-temperature impact values, the addition of V element is made by fully incorporating V-N alloy, and the contents of impurity elements such as P and S are strictly controlled. The content control of each component is as follows:

[0024] C: 0.12% - 0.19%. 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 at the same time reduce the difficulty of decarburization in steelmaking, the lower limit is set at 0.12%. If the C content is too high, the plasticity, toughness and weldability of the steel will be severely deteriorated, and the upper limit is set at 0.19%.

[0025] Si: 0.20% - 0.50%. An appropriate content of Si can play a strong solid solution strengthening role. Si is also an important reduction and deoxidation element in the steelmaking process. In order to obtain higher strength, the lower limit is set at 0.20%. However, the Si content cannot be too high. Research shows that too high Si content will accelerate high-temperature delamination, reduce toughness and resistance to lamellar tearing performance, and is prone to generate red scale on the surface of the steel, affecting the surface quality of the product. The upper limit is set at 0.50%.

[0026] Mn: 1.35% - 1.60%. As a strengthening element in steel, Mn can improve the strength and hardenability of steel. In order to ensure the strength of the steel, the lower limit is set at 1.35%. However, the Mn content cannot be too high, as too high Mn content will significantly increase the feasibility of slab segregation and have an adverse impact on the forming performance of the steel. The upper limit is set at 1.60%.

[0027] P and S, as impurity elements, will have an adverse impact on the plasticity, toughness and weldability of the steel and should be strictly controlled. Considering the difficulty of steelmaking control, in actual production, P: ≤0.035%, S: ≤0.035% are controlled.

[0028] V: 0.010% - 0.025%. As a strong carbide - forming element, V(C, N) dispersion compounds play a role in precipitation strengthening in steel. Precipitation strengthening is a method of enhancing the strength of materials by dispersing fine precipitates in the matrix. These precipitates can hinder the movement of grain boundaries and dislocations, thereby increasing the strength and hardness of the steel. The precipitation of V(C, N) mainly occurs during and after the phase transformation from austenite to ferrite. During this process, due to temperature changes and microstructure transformation, V(C, N) compounds precipitate and disperse in the steel matrix. This precipitation behavior makes the strengthening effect of the steel more significant. The addition of V can also affect the toughness level of the steel. By controlling the content of V and the distribution of precipitates, the toughness of the steel can be adjusted to a certain extent to meet the requirements of different engineering applications. To increase strength, the lower limit is set at 0.010%, and considering production cost factors while ensuring the comprehensive mechanical property index of the product, the upper limit is set at 0.025%, and the V element is added as total V - N.

[0029] Nb: 0.008% - 0.020%. The strengthening effect of niobium on steel is mainly grain refinement strengthening and dispersion strengthening. Grain refinement strengthening improves the strength and toughness of steel by refining the grain size of the steel. Dispersion strengthening hinders grain boundary slip and dislocation movement by dispersing fine precipitates in the steel, thereby increasing the strength of the steel. Niobium can form stable carbides and carbonitrides with carbon and nitrogen in the steel. These compounds play a role in dispersion strengthening in the steel because they can hinder the movement of grain boundaries and dislocations, thereby increasing the strength and hardness of the steel. Niobium can also achieve the dispersion distribution of precipitates by inducing precipitation and controlling the cooling rate. The dispersion distribution of precipitates has an important impact on the toughness level of the steel. By adjusting the distribution and quantity of precipitates, the toughness level of the steel can be adjusted within a wide range to meet different engineering requirements. Therefore, adding niobium can not only increase the strength of the steel, but also improve the toughness, high - temperature oxidation resistance and corrosion resistance of the steel, reduce the brittle transition temperature of the steel, and obtain good welding and forming properties. To increase strength, the lower limit is set at 0.008%, and considering production cost factors while ensuring the comprehensive mechanical property index of the product, the upper limit is set at 0.020%.

[0030] In the method for preparing hot - rolled H - beams with different grades of 420 MPa under the same steel composition provided by the present invention, to ensure the full solution of alloying elements, avoid over - burning and excessive coarsening of austenite grains, a relatively high heating temperature and a relatively long heating time are adopted during the heating of the profiled billet.

[0031] In the blooming rolling stage, since the blooming rolling stage is within the austenite recrystallization temperature range, the pass reduction must be greater than the upper limit of the critical recrystallization deformation amount to ensure complete recrystallization. The reduction rate control in different temperature ranges is to ensure that the austenite recrystallization percentage in each pass reaches more than 50%. Through large rolling deformations and repeated recrystallizations of austenite, the austenite grains are continuously refined, so that the ferrite grain size of the final product reaches grade 8.0 or above, meeting the comprehensive mechanical property requirements of the product.

[0032] The universal rolling stage is within the austenite non-recrystallization temperature range. Austenite recrystallization does not occur in this temperature range. The cumulative deformation formed by large reduction at low temperature can elongate the austenite grains, forming a large number of deformation bands and dislocations inside the grains. The increase in the grain boundary area improves the nucleation density of austenite, further refining the grain size and enhancing the strength of the steel and improving its toughness. A large number of crystallographic defects generated in the deformed austenite provide nucleation sites for ferrite phase transformation, resulting in the refinement of ferrite grains. At the same time, the elongated austenite, a large number of deformation bands and dislocation sites also provide a large number of landing points for the precipitation of carbide and nitride second-phase particles. The stored energy formed by large reduction at low temperature also provides sufficient kinetic energy for the precipitation of carbide and nitride second-phase particles. Adding Nb to the steel, for the steel containing these trace alloying elements, due to the increase in the recrystallization temperature and the expansion of the austenite non-recrystallization zone, it is beneficial to realize rolling in the non-recrystallization zone. It improves the strength of the steel by refining grains at high temperatures. The dissolved Nb plays a role of solute dragging on the growth of austenite grains, preventing the growth of austenite grains. At the same time, the undissolved Nb forms Nb(C, N) compounds with C and N elements, which can significantly pin the austenite grain boundaries, refine the austenite grains, and play a role in refining the final product structure. As a strong carbide-forming element, with the addition of 0.01% - 0.03% content of V alloying element, a large number of V(C, N) dispersed compounds are formed and distributed in the matrix in this stage, further improving the strength and toughness of the steel.

[0033] The selective controlled cooling device between the universal stands can more accurately control the temperature change of the rolled piece. Combining with the reduction designed in the rolling schedule, the set deformation amount is given to the H-beam in the corresponding temperature range to ensure the performance of the final product. After rolling, the H-beam is air-cooled on the cooling bed. In the universal rolling stage of the present invention, different controls are carried out for hot-rolled H-beams of different grades. Controlled rolling is carried out for hot-rolled H-beams of grades C and D in the 3rd pass of universal rolling.

[0034] Compared with the prior art, considering the cost and quality comprehensively, hot-rolled H-beams with a flange thickness ≤ 40 mm, yield strength of grade 420 MPa at levels B (room temperature), C (0 °C), and D (-20 °C) are prepared under the same steel composition. By adopting a reasonable and economical chemical composition ratio, controlling the reduction per pass, and controlling the rolling temperature in the universal mill section, the properties of the rolled piece are improved. Utilizing the mechanisms of fine grain strengthening, precipitation strengthening, and phase transformation strengthening, hot-rolled H-beams with a duplex structure of ferrite + pearlite and a ferrite grain size grade above 8.0 are obtained; the hot-rolled H-beams produced by this technical solution have a yield strength above 420 MPa, a tensile strength of 520 MPa - 680 MPa, an elongation ≥ 20%, a room temperature impact energy of ≥ 120 J for grade B, an impact energy of ≥ 80 J at 0 °C for grade C, and an impact energy of ≥ 50 J at -20 °C for grade D; meeting the requirements of high strength, good toughness, and excellent welding performance for H-beams. Description of the Drawings

[0035] Figure 1 It is the microstructure of the H-beam in Example 1, which is a duplex structure of ferrite + pearlite, and the grain size grade is 9.0; Figure 2 It is the microstructure of the H-beam in Example 2, which is a duplex structure of ferrite + pearlite, and the grain size grade is 9.0;

[0036] Figure 3 It is the microstructure of the H-beam in Example 3, which is a duplex structure of ferrite + pearlite, and the grain size grade is 9.5. Detailed Embodiments

[0037] A method for preparing hot-rolled H-beams with different grades of 420 MPa under the same steel composition provided by the present invention, the method includes the following steps: converter smelting → argon blowing refining → continuous casting of special-shaped billets → billet heating → blooming rolling → universal rolling → air cooling on the cooling bed after rolling;

[0038] Molten iron is sent to the converter for smelting, the tapping time ≥ 3 minutes. In the early stage of tapping, a carburizer is added according to the converter end carbon content for preliminary deoxidation;

[0039] During the smelting process, inert gas argon is blown at the bottom to remove the dissolved gases and suspended non-metallic inclusions in the steel grade, purify the molten steel, and then continuously cast it into billets;

[0040] In the billet heating step, the special-shaped billet enters the heating furnace and is heated to 1220 °C - 1260 °C by the heating furnace, and the residence time in the furnace is 100 min - 130 min;

[0041] In the blooming rolling step, the rolling start temperature in the rough rolling stage is controlled at 1100 °C - 1200 °C, and the final rolling temperature is controlled above 1000 °C;

[0042] In the blooming rolling step, in the temperature range of 1100°C < temperature ≤ 1200°C, the reduction per pass is controlled within 12% - 20%; in the temperature range of 1050°C < temperature ≤ 1100°C, the reduction per pass is controlled within 18% - 30%; in the temperature range of 1000°C ≤ temperature ≤ 1050°C, the reduction per pass is controlled within 20% - 25%, and the total reduction of the billet is controlled above 50%.

[0043] In the universal rolling step, for the 420 MPa grade B hot-rolled H-beams, there is no need to wait for temperature equalization. After rough rolling, it directly enters the universal rolling mill for rolling, and the remaining deformation of the billet is completed in this stage. The finishing temperature is controlled below 920°C;

[0044] For the 420 MPa grade C hot-rolled H-beams, the selective controlled cooling device between the universal stands is turned on. The third pass is controlled rolling at 920°C ≤ temperature ≤ 950°C, and the finishing temperature is controlled ≤ 900°C;

[0045] For the 420 MPa grade D hot-rolled H-beams, the selective controlled cooling device between the universal stands is turned on. The third pass is controlled rolling at 900°C ≤ temperature ≤ 930°C, and the finishing temperature is controlled ≤ 880°C;

[0046] In the universal rolling step, in the temperature range of 950°C < temperature ≤ 1000°C, the reduction per pass is controlled within 12% - 18%; in the temperature range of 930°C < temperature ≤ 950°C, the reduction per pass is controlled within 20% - 30%; in the temperature range of temperature ≤ 930°C, the reduction per pass is controlled within 12% - 17%; the reduction of the billet in the universal rolling stage is controlled above 60%.

[0047] The hot-rolled H-beams include the following elements by mass percentage: C: 0.12% - 0.19%, Si: 0.20% - 0.50%, Mn: 1.35% - 1.60%, P: ≤ 0.035%, S: ≤ 0.035%, V: 0.010% - 0.025%, Nb: 0.008% - 0.020%, and the rest is Fe and inevitable impurities.

[0048] The following is a detailed description of the present application in combination with embodiments.

[0049] The chemical compositions and weight percentages of the hot-rolled H-beams in each embodiment and comparative example are shown in Table 1.

[0050] Table 1

[0051]

[0052] The production process parameters of the hot-rolled H-beams in each embodiment and comparative example are shown in Table 2.

[0053] Table 2

[0054]

[0055]

[0056] The performance test results of the hot-rolled H-beams in each example and comparative example are shown in Table 3.

[0057] Table 3

[0058]

[0059] As can be seen from Table 3 for each example, in the rough rolling and universal rolling stages, applying a reduction amount within a given range within the appropriate temperature range given in the present invention, and performing controlled rolling in the 3rd pass of the universal section, it is possible to produce hot-rolled H-beams with mechanical property requirements for different grades of 420 MPa under one composition system.

[0060] Although the production processes and parameters of Comparative Examples 1 and 4 were controlled in accordance with the requirements of the present invention for B-grade hot-rolled H-beams, due to their inappropriate composition, it was impossible to produce B-grade hot-rolled H-beams that meet the requirements of this application.

[0061] Although the chemical composition content and composition of Comparative Examples 2 and 5 were controlled in accordance with the requirements of the present invention, due to the fact that their rolling processes were not controlled in accordance with the requirements of this application for C-grade hot-rolled H-beams, it was impossible to produce C-grade hot-rolled H-beams that meet the requirements of this application.

[0062] Although the chemical composition content and composition of Comparative Examples 3 and 6 were controlled in accordance with the requirements of the present invention, due to the fact that their rolling processes were not controlled in accordance with the requirements of this application for D-grade hot-rolled H-beams, it was impossible to produce D-grade hot-rolled H-beams that meet the requirements of this application.

[0063] The above detailed description of a method for preparing hot-rolled H-beams with different grades of 420 MPa under the same steel composition and the hot-rolled H-beams with reference to the examples is illustrative rather than restrictive. Several examples can be listed within the defined scope. Therefore, changes and modifications without departing from the general concept of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing hot-rolled H-beams with different grades of 420 MPa under the same steel composition, characterized in that, The method includes the following steps: converter smelting → argon blowing refining → continuous casting of profiled billets → billet heating → blooming rolling → universal rolling → air cooling on the cooling bed after rolling; In the universal rolling step, for the 420 MPa grade B hot-rolled H-beams, after rough rolling, it directly enters the universal rolling mill for rolling, and the remaining deformation of the billet is completed in this stage. The rolling temperature of the 3rd pass is controlled at 960 - 980 °C, and the finishing rolling temperature is controlled at 900 - 930 °C; For the 420 MPa grade C hot-rolled H-beams, the selective controlled cooling device between the universal stands is turned on, and the rolling temperature of the 3rd pass is controlled at 930 - 950 °C, and the finishing rolling temperature is controlled at 885 - 900 °C; For the 420 MPa grade D hot-rolled H-beams, the selective controlled cooling device between the universal stands is turned on, and the 3rd pass is controlled rolling at 900 - 930 °C, and the finishing rolling temperature is controlled at 830 - 880 °C; The hot-rolled H-beams include the following elements by mass percentage: C: 0.12% - 0.19%, Si: 0.20% - 0.50%, Mn: 1.35% - 1.60%, P: ≤0.035%, S: ≤0.035%, V: 0.010% - 0.025%, Nb: 0.008% - 0.020%, and the rest are Fe and unavoidable impurities.

2. The method for preparing hot-rolled H-beams with different grades of 420 MPa under the same steel composition according to claim 1, wherein, In the universal rolling step, in the temperature range of 950 °C < temperature ≤ 1000 °C, the pass reduction rate is controlled at 12% - 18%; in the temperature range of 930 °C < temperature ≤ 950 °C, the pass reduction rate is controlled at 20% - 30%; in the temperature range of temperature ≤ 930 °C, the pass reduction rate is controlled at 12% - 17%; the total reduction rate of the billet in the universal rolling stage is controlled at more than 60%.

3. The method for preparing hot-rolled H-beams with different grades of 420 MPa under the same steel composition according to claim 1 or 2, characterized in that, In the billet heating step, the profiled billet enters the heating furnace and is heated to 1220 °C - 1260 °C by the heating furnace, and the residence time in the furnace is 100 min - 130 min.

4. The method for preparing hot-rolled H-beams with different grades of 420 MPa under the same steel composition according to claim 1 or 2, characterized in that, In the blooming rolling step, the starting rolling temperature in the rough rolling stage is controlled at 1100 °C - 1200 °C, and the finishing rolling temperature is controlled above 1000 °C.

5. The method for preparing hot-rolled H-beams with different grades of 420 MPa under the same steel composition according to claim 1 or 2, characterized in that, In the blooming rolling step, in the temperature range of 1100 °C < temperature ≤ 1200 °C, the pass reduction rate is controlled at 10% - 15%; in the temperature range of 1050 °C < temperature ≤ 1100 °C, the pass reduction rate is controlled at 15% - 25%; in the temperature range of 1000 °C ≤ temperature ≤ 1050 °C, the pass reduction rate is controlled at 15% - 25%, and the total reduction rate of the billet is controlled at more than 50%.

6. The method for preparing hot-rolled H-beams with different grades of 420 MPa under the same steel composition according to claim 1 or 2, characterized in that, The hot-rolled H-beams include the following elements by mass percentage: C: 0.16% - 0.19%, Si: 0.25% - 0.50%, Mn: 1.40% - 1.60%, P: ≤0.025%, S: ≤0.020%, V: 0.015% - 0.025%, Nb: 0.010% - 0.020%, and the rest are Fe and unavoidable impurities.

7. The 420 MPa grade hot-rolled H-beam produced by the method according to any one of claims 1-6, characterized in that, The hot-rolled H-beams are of 420 MPa grade B, 420 MPa grade C, and / or D grade.

8. The hot-rolled H-beam with a yield strength of 420 MPa according to claim 7, characterized in that, The thickness of the hot-rolled H-beams ≤ 40 mm, and the metallographic structure is a duplex structure of ferrite + pearlite, and the ferrite grain size grade is above 8.

0.

9. The hot-rolled H-beam of 420 MPa grade according to claim 7, characterized in that, The yield strength of the hot-rolled H-beam is ≥ 420 MPa, the tensile strength is 520 MPa to 680 MPa, the elongation is ≥ 20%, the Charpy impact energy at room temperature for grade B is ≥ 120 J, the Charpy impact energy at 0 °C for grade C is ≥ 80 J, and the Charpy impact energy at -20 °C for grade D is ≥ 50 J.

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