Low-cost ti microalloyed 600mpa grade hot-rolled steel strip and method of manufacture and use thereof

Abstract

The application discloses a low-cost Ti micro-alloyed 600MPa-grade hot-rolled steel strip and a preparation method and application thereof, and chemical component contents of the hot-rolled steel strip are as follows: C: 0.10%; Si: 0.10-0.20%; Mn: 0.80; P: 0.015%; S: 0.008%; Ti: 0.07-0.09%; Als: 0.015-0.035%; and the rest is Fe and inevitable inclusions. Through reasonable component design and process optimization, the application realizes precipitation strengthening of the Ti micro-alloyed steel by adopting a three-stage controlled cooling process of ultra-fast cooling-air cooling-ultra-fast cooling after rolling, and considers low-temperature coiling phase change strengthening, so that the low-cost 600MPa-grade Ti micro-alloyed high-strength steel with excellent comprehensive performance is obtained. The application is used for manufacturing of photovoltaic supports, can significantly reduce the cost, improve the strength, realize light weight, reduce carbon emission and realize green manufacturing of products.

Description

Technical Field

[0001] This invention belongs to the field of hot-rolled high-strength steel production technology, specifically relating to a low-cost Ti microalloyed 600MPa grade hot-rolled steel strip, its preparation method, and its application. Background Technology

[0002] Photovoltaic (PV) mounting systems are specialized structures designed for placing, installing, and securing solar panels in a solar photovoltaic (PV) power generation system. These systems require robust, reliable, and highly weather-resistant structures capable of withstanding atmospheric corrosion, wind loads, and other external effects. Driven by domestic and international policies promoting environmental protection and energy conservation, reducing carbon emissions, achieving truly clean energy, high strength and lightweight construction, thinner zinc coatings, and the development of new weather-resistant steel materials for PV mounting systems have become inevitable trends. This also places increasingly higher demands on the overall performance of the steel used in PV mounting systems.

[0003] In recent years, Ti microalloyed hot-rolled high-strength steel has been widely used in photovoltaic brackets, automobiles, construction, railway vehicles, and other fields, becoming an important raw material for achieving lightweight design and manufacturing in these industries. Ti possesses excellent grain refinement and precipitation strengthening properties, primarily precipitating as fine Ti (C, N) particles, which can significantly improve the overall performance of steel. However, the process window for Ti carbonitride precipitates, especially interphase precipitation, is relatively narrow, making precise control during rolling difficult. Therefore, obtaining a higher volume fraction of nanoprecipitates in the subsequently cooled ferrite is crucial for improving steel strength and reducing costs.

[0004] Currently, domestic photovoltaic (PV) mounting systems mainly use Q235 / Q345B grade high-strength steel with batch hot-dip galvanizing to achieve robust, reliable structures and strong weather resistance. However, for the design and optimization of PV mounting systems' structure, components, nodes, and material selection, 600MPa grade high-strength steel is being used to replace Q235 / Q345B, resulting in a weight reduction rate of 25-35% after verification. Therefore, developing 600MPa and higher grade PV mounting steel is of great significance for promoting lightweighting in the PV industry, reducing carbon emissions, and achieving clean energy.

[0005] Chinese Patent CN 108277441 A discloses a 600MPa grade Ti microalloyed hot-rolled duplex steel plate and its preparation method. Specifically, the chemical composition of the duplex steel plate, by mass percentage, is: C: 0.04–0.08%, Si: 0.05–0.15%, Mn: 0.90–1.10%, S: ≤0.013%, P: ≤0.020%, Als: 0.02–0.05%, Ti: 0.03–0.05%, with the balance being Fe and unavoidable impurities. The preparation method of the duplex steel plate is as follows: 1) Heating the steel billet to 1200–1240℃ and holding at that temperature for 1.5–2.5 hours; 2) Rough rolling the heated steel billet; 3) Finish rolling the intermediate billet; 4) Performing a three-stage cooling process of water-air-water cooling on the strip. The patent uses 0.9-1.1% Mn in its chemical composition, which is relatively expensive. The strip is cooled in three stages: water-cooling-air-water-cooling. The target microstructure is a dual-phase microstructure of ferrite and martensite. The yield strength of the product is only 362-395 MPa, which is relatively low.

[0006] Chinese patent CN 110616301 A discloses a production method for improving the precipitation strengthening effect of Ti microalloyed hot-rolled high-strength steel online. Specifically, it discloses: molten steel with added Ti microalloying element is cast into a billet or ingot; after heating, it undergoes rough rolling, finish rolling, laminar flow cooling, and coiling to obtain a hot-rolled coil; after uncoiling, an insulation cover is placed on the line, and the coil moves along a conveyor chain into a steel coil warehouse; after reaching the required online insulation time, it is removed from the insulation cover and air-cooled to room temperature. This process requires an additional insulation cover, involves numerous steps, and has a long process time, significantly increasing costs.

[0007] It is evident that existing research on Ti microalloyed hot-rolled high-strength steel mainly focuses on how to achieve ferrite + bainite or ferrite + martensite dual-phase high-strength steel to reduce costs. However, these steels have relatively poor formability. Alternatively, additional equipment such as adding insulation covers can be used to promote precipitation strengthening, but this involves more steps and a longer process time, significantly increasing costs. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a low-cost Ti microalloyed 600MPa grade hot-rolled steel strip and its preparation method. Through reasonable composition design and process optimization, a three-stage controlled cooling process of ultra-fast cooling-air cooling-ultra-fast cooling is adopted after rolling to achieve precipitation strengthening of Ti microalloyed steel while taking into account low-temperature coiling phase transformation strengthening, resulting in a low-cost 600MPa grade Ti microalloyed high-strength steel with excellent comprehensive performance.

[0009] The present invention also provides the application of the aforementioned low-cost Ti microalloyed 600MPa grade hot-rolled steel strip as steel for photovoltaic brackets. The Ti microalloyed steel obtained by the present invention is mainly used in the manufacture of photovoltaic brackets, which can significantly reduce costs, improve strength, achieve lightweighting, reduce carbon emissions, truly achieve clean energy, and realize green manufacturing of products.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A low-cost Ti microalloyed 600MPa grade hot-rolled steel strip has the following chemical composition by weight percentage: C: ≤0.10%; Si: 0.10~0.20%; Mn: ≤0.80%; P: ≤0.015%; S: ≤0.008%; Ti: 0.07~0.09%; Als: 0.015~0.035%; with the remainder being Fe and unavoidable inclusions.

[0012] The design principle of the alloying elements and their mass percentages for a low-cost Ti microalloyed 600MPa grade hot-rolled steel strip of this invention is as follows: The chemical composition of this invention adopts a design concept of low C + appropriate Si + appropriate Mn + high Ti content, and strictly controls the content of impurity elements such as P and S. C: ≤0.10%. As a basic element in steel, C plays a very important role in improving the strength of steel. In order to obtain high strength, a certain amount of C must be ensured. However, too high a C content will deteriorate the welding performance. At the same time, it is difficult to obtain the required amount of ferrite during the cooling process after hot rolling, resulting in poor plasticity of the steel. In addition, the low C design is conducive to hot charging and hot delivery in steel mills, improving production speed, reducing costs, and reducing environmental pollution. Si: 0.10~0.20%. Adding an appropriate amount of Si element can not only play a solid solution strengthening effect to increase the strength of steel, but also help prevent stored wet rust or white rust, improve the quality of subsequent galvanizing coating, and reduce the phenomenon of incomplete coating. Mn: ≤0.80%. Mn can significantly improve strength, but excessive Mn content easily causes center segregation, which is not conducive to the uniform distribution of steel strip microstructure and properties. Moreover, it is difficult to form the required amount of ferrite after rolling, which adversely affects the formability of the steel. In addition, the increase in Mn content will also increase the alloy cost, which is not conducive to low-cost design. P and S, as impurity elements, will adversely affect the formability and weldability of steel and should be strictly controlled. The lower their content, the better. Therefore, P and S are controlled at P≤0.015% and S≤0.008%. Al is the main deoxidizing element in steel and can significantly reduce the O content in steel. Therefore, Al is controlled at 0.015~0.035%. Ti: 0.07-0.09%. In this invention, Ti mainly plays three roles: first, it combines with N element to form TiN, which plays a role in nitrogen fixation; second, it refines austenite grains and also refines the ferrite and pearlite that are eventually transformed; and third, it ensures that nano-level Ti precipitates are uniformly and abundantly precipitated during the air cooling stage of the three-stage controlled cooling process of ultra-fast cooling-air cooling-ultra-fast cooling, thereby fully improving the strength of the material. This achieves precipitation strengthening of Ti microalloyed steel while taking into account low-temperature coiling phase transformation strengthening, thus ensuring that the material has excellent comprehensive performance under the premise of low cost.

[0013] The microstructure of the low-cost Ti microalloyed 600MPa grade hot-rolled steel strip is ferrite + pearlite + Ti precipitates.

[0014] The microstructure of the low-cost Ti microalloyed 600MPa grade hot-rolled steel strip contains 70%-80% ferrite, 19%-29% pearlite, and ≥0.4% precipitates.

[0015] The low-cost Ti microalloyed 600MPa grade hot-rolled steel strip has a yield strength ≥600MPa, tensile strength ≥680MPa, elongation A50 ≥25%, cold bending performance of 180°, and D=a qualified, exhibiting high strength and good formability.

[0016] The production method of low-cost Ti microalloyed 600MPa grade hot-rolled steel strip provided by the present invention includes the following steps: converter smelting, refining, continuous casting, heating, rolling, cooling and coiling.

[0017] In the cooling process, a three-stage controlled cooling process of ultra-fast cooling-air cooling-ultra-fast cooling is adopted. After rolling, the first stage of water cooling of the steel plate adopts ultra-fast cooling at a cooling rate of ≥100℃ / s to 640-660℃ and then air cooling. The second stage of air cooling is 15-25s. The third stage of water cooling adopts ultra-fast cooling at a cooling rate of ≥100℃ / s to 570-610℃ for coiling. After coiling, it is air cooled to room temperature.

[0018] The preferred cooling rate for stage I water cooling is 100–150 °C / s; the preferred cooling rate for stage III water cooling is 100–150 °C / s.

[0019] The nitrogen content in the final steel composition after refining is ≤50ppm.

[0020] During the heating process, the heating temperature is 1250±20℃, and the total time spent in the furnace is ≥160min.

[0021] In the rolling process, a two-stage controlled rolling process is adopted, with a cumulative reduction rate of ≥70% in roughing and ≥80% in finishing; the initial rolling temperature of roughing is 1130~1180℃, and the final rolling temperature of finishing is 860~900℃; the crown is controlled at 40±20μm, the wedge is controlled at 0±20μm, and the flatness is controlled at -50I~+50I.

[0022] In the low-cost Ti microalloyed 600MPa grade hot-rolled steel strip production method provided by this invention, the final rolling temperature is controlled at 860-900℃ in the hot rolling process design. A lower final rolling temperature is beneficial for refining the original austenite grain size and for rapidly entering the ferrite transformation region after final rolling to obtain a ferrite microstructure. A three-stage controlled cooling process is adopted after rolling: Stage I water cooling of the post-rolled steel plate uses ultra-rapid cooling at a rate ≥100℃ / s to 640-660℃ followed by air cooling. The purpose is to allow the material to quickly enter the ferrite phase transformation region and refine the ferrite grains. The ultra-rapid cooling technology allows sufficient time for subsequent air cooling. Stage II air cooling lasts 15-25s, the purpose of which is to homogenize the temperature of the steel plate and promote the uniform and sufficient precipitation of nano-level Ti precipitates. To achieve the goal of improving precipitation strengthening effect; the third stage water cooling adopts ultra-fast cooling at a cooling rate of ≥100℃ / s to cool to 570-610℃ for coiling, and then air cooling to room temperature. The purpose is to rapidly transform the untransformed austenite structure into pearlite structure, so that the steel plate structure is ferrite + pearlite + a large amount of Ti precipitates, realizing precipitation strengthening of Ti microalloyed steel while taking into account low-temperature coiling phase transformation strengthening, thereby ensuring that the material has excellent comprehensive performance under the premise of low cost.

[0023] The hot-rolled steel sheet produced using the technical solution of this invention has a microstructure consisting of ferrite + pearlite + a large amount of Ti precipitates, wherein the volume of ferrite is 70%-80%, the volume of pearlite is 19%-29%, the volume of precipitates is ≥0.4%, the yield strength of the product is ≥600MPa, the tensile strength is ≥680MPa, the elongation A50 is ≥25%, the cold bending performance is 180°, and D=a is qualified, exhibiting high strength and good formability. Attached Figure Description

[0024] Figure 1 The image shows the metallographic structure of the hot-rolled steel strip in Example 1.

[0025] Figure 2 This is a TEM image of the hot-rolled steel strip in Example 1, from which a large amount of Ti precipitates can be seen;

[0026] Figure 3 The image shows the metallographic structure of the hot-rolled steel strip in Example 2;

[0027] Figure 4 This is a TEM image of the hot-rolled steel strip in Example 2, from which a large amount of Ti precipitates can be seen;

[0028] Figure 5 The image shows the metallographic structure of the hot-rolled steel strip in Example 3.

[0029] Figure 6 This is a TEM image of the hot-rolled steel strip in Example 3, from which a large amount of Ti precipitates can be seen;

[0030] Figure 7 The image shows the metallographic structure of the hot-rolled steel strip in Example 4.

[0031] Figure 8 This is a TEM image of the hot-rolled steel strip in Example 4, from which a large amount of Ti precipitates can be seen;

[0032] Figure 9 The metallographic structure of the hot-rolled steel strip in Comparative Example 1 is shown.

[0033] Figure 10 The image shows the metallographic structure of the hot-rolled steel strip in Comparative Example 2. Detailed Implementation

[0034] This invention provides a low-cost Ti microalloyed 600MPa grade hot-rolled steel strip with the following chemical composition by weight percentage: C: ≤0.10%; Si: 0.10-0.20%; Mn: ≤0.80%; P: ≤0.015%; S: ≤0.008%; Ti: 0.07-0.09%; Als: 0.015-0.035%; the remainder being Fe and unavoidable inclusions.

[0035] The production method of the low-cost Ti microalloyed 600MPa grade hot-rolled steel strip includes the following steps: converter smelting, refining, continuous casting, heating, rolling, cooling and coiling.

[0036] The nitrogen content in the final steel composition after refining is ≤50ppm.

[0037] During the heating process, the heating temperature is 1250±20℃, and the total time spent in the furnace is ≥160min.

[0038] In the rolling process, a two-stage controlled rolling process is adopted, with a cumulative reduction rate of ≥70% in roughing and ≥80% in finishing; the initial rolling temperature of roughing is 1130~1180℃, and the final rolling temperature of finishing is 860~900℃; the crown is controlled at 40±20μm, the wedge is controlled at 0±20μm, and the flatness is controlled at -50I~+50I.

[0039] In the cooling process, a three-stage controlled cooling process of ultra-fast cooling-air cooling-ultra-fast cooling is adopted. After rolling, the first stage of water cooling of the steel plate adopts ultra-fast cooling at a cooling rate of ≥100℃ / s to 640-660℃ and then air cooling. The second stage of air cooling is 15-25s. The third stage of water cooling adopts ultra-fast cooling at a cooling rate of ≥100℃ / s to 570-610℃ for coiling. After coiling, it is air cooled to room temperature.

[0040] The present invention will now be described in detail with reference to the embodiments.

[0041] The composition and weight percentage of the hot-rolled steel strip in each embodiment and comparative example are shown in Table 1.

[0042] Table 1

[0043] serial number C Si Mn P S Als Ti N Example 1 0.077 0.156 0.678 0.0125 0.0041 0.0323 0.0853 0.0017 Example 2 0.082 0.163 0.689 0.0098 0.0010 0.0331 0.0833 0.0020 Example 3 0.076 0.147 0.699 0.0138 0.0014 0.0305 0.0819 0.0019 Example 4 0.081 0.155 0.653 0.0098 0.0023 0.0275 0.0767 0.0021 Comparative Example 1 0.171 0.202 1.205 0.0152 0.0035 0.0401 0.1071 0.0037 Comparative Example 2 0.080 0.164 0.704 0.0146 0.0027 0.0299 0.0912 0.0017

[0044] The production process parameters of the hot-rolled steel strip in each embodiment and comparative example are shown in Table 2.

[0045] Table 2

[0046]

[0047]

[0048] The properties of the hot-rolled steel strips in each embodiment and comparative example are shown in Table 3.

[0049] Table 3

[0050]

[0051]

[0052] As can be seen from Table 3, the microstructure of the hot-rolled steel sheet produced by the method of the present invention is ferrite + pearlite + a large amount of Ti precipitates, wherein the volume of ferrite is 70%-80%, the volume of pearlite is 19%-29%, the volume of precipitates is ≥0.4%, the yield strength of the product is ≥600MPa, the tensile strength is ≥680MPa, the elongation A50 is ≥25%, the cold bending performance is 180°, and D=a is qualified, exhibiting high strength and good formability.

[0053] The above detailed description of a low-cost Ti microalloyed 600MPa grade hot-rolled steel strip, its preparation method, and its application, with reference to the embodiments, is illustrative rather than limiting. Several embodiments can be listed within the defined scope. Therefore, variations and modifications without departing from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A low-cost Ti microalloyed 600MPa grade hot-rolled steel strip, characterized in that, Its chemical composition by weight percentage is: C: ≤0.10%; Si: 0.147~0.20%; Mn: ≤0.80%; P: ≤0.015%; S: ≤0.008%; Ti: 0.07~0.09%; Als: 0.015~0.035%; the remainder is Fe and unavoidable inclusions; The microstructure of the low-cost Ti microalloyed 600MPa grade hot-rolled steel strip is ferrite + pearlite + Ti precipitates, with ferrite volume of 70%-80%, pearlite volume of 19%-29%, and precipitate volume of ≥0.4%. The production method of the low-cost Ti microalloyed 600MPa grade hot-rolled steel strip includes the following steps: converter smelting, refining, continuous casting, heating, rolling, cooling and coiling; The low-cost Ti microalloyed 600MPa grade hot-rolled steel strip is cooled by a three-stage controlled cooling process of ultra-fast cooling-air cooling-ultra-fast cooling after hot rolling. The first stage of water cooling of the rolled steel plate uses ultra-fast cooling at a cooling rate of ≥100℃ / s to 640-660℃, followed by air cooling. The second stage is air cooling for 15~25s. The third stage of water cooling uses ultra-fast cooling at a cooling rate of ≥100℃ / s to 570-610℃ before coiling. After coiling, it is air-cooled to room temperature.

2. The low-cost Ti microalloyed 600MPa grade hot-rolled steel strip according to claim 1, characterized in that, The low-cost Ti microalloyed 600MPa grade hot-rolled steel strip has a yield strength ≥600MPa, tensile strength ≥680MPa, elongation A50 ≥25%, cold bending performance 180°, and D=a is qualified.

3. The method for producing low-cost Ti microalloyed 600MPa grade hot-rolled steel strip as described in claim 1 or 2, characterized in that, The production method includes the following steps: converter smelting, refining, continuous casting, heating, rolling, cooling and coiling.

4. The production method according to claim 3, characterized in that, The nitrogen content in the final steel composition after refining is ≤50ppm.

5. The production method according to claim 3, characterized in that, During the heating process, the heating temperature is 1250±20℃, and the total time spent in the furnace is ≥160min.

6. The production method according to claim 3, characterized in that, In the rolling process, a two-stage controlled rolling process is adopted, with a cumulative reduction rate of ≥70% in roughing and ≥80% in finishing; the initial rolling temperature of roughing is 1130~1180℃, and the final rolling temperature of finishing is 860~900℃; the crown is controlled at 40±20μm, the wedge is controlled at 0±20μm, and the flatness is controlled at -50I~+50I.

7. Application of the low-cost Ti microalloyed 600MPa grade hot-rolled steel strip as described in claim 1 or 2 as steel for photovoltaic brackets.

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