Low yield ratio heavy industrial atmosphere corrosion resistant bridge steel plate and production method thereof

Abstract

The application provides a low yield ratio heavy industrial atmospheric corrosion resistant bridge steel plate and a manufacturing method thereof. The steel plate comprises the following components in percentage by weight: C: 0.07% to 0.10%, Si: 0.10% to 0.30%, Mn: 0.60% to 1.00%, P: less than or equal to 0.010%, S: less than or equal to 0.003%, Nb: 0.02% to 0.04%, Ni: 0.15% to 0.35%, Cu: 0.10% to 0.40%, Mo: 0.20% to 0.50%, Cr: 1.50% to 2.40%, Ti: 0.01% to 0.030%, Sb: 0.03 to 0.10%, Al: 0.015% to 0.040%, and the balance of iron and inevitable impurities. The production method of the steel plate comprises the following steps: molten iron pretreatment, smelting, continuous casting, slab heating, rolling and straightening. The steel plate has the following properties: yield strength is greater than or equal to 345 MPa, tensile strength is greater than or equal to 510 MPa, elongation after fracture is greater than or equal to 30%, yield ratio is less than or equal to 0.75, thickness direction section shrinkage is greater than or equal to 70%, and low temperature impact energy at-40 DEG C is greater than or equal to 300 J. The annual corrosion rate of the steel plate in a simulated heavy industrial atmospheric environment is less than or equal to 0.05 mm / a, and the corrosion performance is 4 to 8 times higher than that of common Q345qE.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials, and in particular relates to a low yield strength ratio bridge steel plate resistant to heavy industrial atmospheric corrosion and its production method. Background Technology

[0002] Material corrosion is widespread in all sectors of socio-economic development. Accidents caused by corrosion are alarming and have a serious impact on socio-economic progress. Studies have found that corrosion costs in China account for approximately 3.4% of GDP. Metallic materials are frequently exposed to the atmosphere. Data shows that about 80% of metal components are used in atmospheric environments, and atmospheric corrosion accounts for more than half of the total metal corrosion loss. The direct and indirect economic losses are substantial, especially the corrosion of carbon steel by industrial atmospheres.

[0003] Due to my country's vast territory, spanning three major climate zones—temperate, subtropical, and tropical—and the significant differences in atmospheric environments, the influencing factors are complex. Furthermore, the interaction of various environmental factors affecting the corrosion of weather-resistant bridge steel leads to substantial differences in its corrosion development mechanisms and patterns. In some traditional industries, such as coal mining, steel, and petrochemical enterprises, the main air pollutants produced include asphalt fumes, hydrogen fluoride, dust, NOx, SO2, CO, H2S, and Cl2. Among these, the levels of SO2, particulate matter, fluorides, and Cl2 all exceed the corresponding standards, with SO2 levels being particularly high. This heavy industrial atmospheric environment has a more complex and severe impact on the corrosiveness of commonly used carbon steel.

[0004] With the booming development of the transportation industry, the requirements for the load-bearing capacity, seismic performance, and corrosion resistance of bridge structures are constantly increasing. Therefore, bridge structures must not only consider the basic mechanical properties of materials, but also their weldability and corrosion resistance, especially in heavy industrial atmospheric environments, to ensure the safety of the bridge throughout its life cycle.

[0005] Currently, existing bridge steel can meet most of the market demand in the bridge industry. However, the corrosion problem of weather-resistant bridge steel, especially bridge steel in the complex atmospheric environment of heavy industry, needs further research. A search revealed some patents and literature, but the contents described therein are significantly different from the technical solution of this invention in terms of composition, production method, performance, product category, etc.

[0006] Chinese invention patent application CN 109797342 A discloses a high-strength, high-toughness, atmospheric corrosion-resistant steel plate for steel structure fabrication and its manufacturing method. The elemental composition (wt%) is: C: 0.03–0.10%, Si: 0.30–0.50%, Mn: 1.10–1.50%, P < 0.010%, S < 0.003%, Cr: 0.45–0.70%, Cu: 0.25–0.40%, Ni: 0.30–0.40%, Alt: ≥ 0.030%. Ti: 0.006–0.030%, V: 0.040–0.080%, Mo: 0.02–0.08%, Ca: 0.0010–0.0030%, N: 0.0020–0.0080%, B: 0.0002–0.0030%, Ce: 0.001–0.010%, atmospheric corrosion resistance index I > 6.5, CEV < 0.54, Pcm < 0.27, balance being Fe and unavoidable impurities. This application employs a specific chemical composition design and steel plate tempering process to obtain a high-performance steel plate with a bainitic structure, suitable for use in steel structures such as bridges and high-rise buildings. However, the disadvantages of this patent application are that the steel plate does not have a low yield strength ratio, resulting in poor safety performance; the addition of rare elements such as Ca, B, and Ce makes smelting difficult and increases production costs; the excessively high carbon equivalent leads to poor weldability. A quenching and tempering treatment is required, making the process complex.

[0007] Chinese invention patent application number CN 10738538 A discloses a TMCP type bridge steel plate with a yield strength of 420MPa and its production method. The chemical composition and mass percentage of the steel plate are as follows: C: 0.07-0.09%, Si: 0.25-0.50%, Mn: 1.40-1.60%, P≤0.015%, S≤0.005%, Ni: 0.15-0.25%, Cr: 0.10-0.20%, Nb: 0.020-0.030%, Al: 0.030-0.050%, V: 0.030-0.040%, with the balance being Fe and unavoidable impurities. The production method includes smelting, continuous casting, heating, rolling, and cooling processes. The steel plate employs a low-C, Nb, V microalloying design in its chemical composition, supplemented with alloying elements such as Ni and Cr to ensure a balance between strength and toughness, resulting in a composite microstructure of bainitic and ferritic materials. The maximum thickness of the steel plate can reach 70 mm. However, a drawback of this patent application is its lack of resistance to industrial atmospheric corrosion.

[0008] Chinese invention patent application CN 106011658 A discloses a marine climate-resistant corrosion-resistant steel and its production method. Its chemical composition (by weight percentage) is: C: ≤0.06%, Si: ≤0.50%, Mn ≤1.50%, P ≤0.010%, S ≤0.005%, Ni: 3.0%–4.5%, Cu: 0.8%–2.0%, Al: 0.5%–1.0%, with the remainder being iron and unavoidable impurities. The manufacturing method includes conventional converter smelting, continuous casting into billets, heating the billets, hot rolling, coiling, and cooling to room temperature using a pre-cooling method. This improves the steel plate's resistance to corrosion in high-temperature, high-humidity, and high-salinity marine climates. However, this patent invention is limited to producing thin-gauge steel plates using hot continuous rolling. Furthermore, the steel plates produced by hot continuous rolling have relatively high internal stress, making them unsuitable for further manufacturing complex-shaped bridge components. In addition, this steel grade lacks low-temperature toughness and is unsuitable for use in railway-highway bridges.

[0009] Chinese Invention Patent Application No. CN 107177803 B discloses a paint-free high-strength bolt steel resistant to industrial atmospheric corrosion for bridge structures and its manufacturing method, belonging to the technical field of high-strength bolt steel for bridge structures. The weight percentages of its components are: C 0.16–0.45%, Si 0.01–2.2%, Mn 0.3–2.2%, P 0.001–0.024%, S 0.002–0.025%, B 0.0005–0.0100%, Ti 0.04–0.50%, V 0.01–0.20%, Al 0.001–0.10%, Cr 0.001–0.34%, Cu 0.2–0.5%, Ni 0.2–1.5%, with the balance being Fe and trace impurities. Suitable for producing bolts ranging from M16 to 30mm. After bolt manufacturing, the bolts undergo a tempering heat treatment process of oil quenching at 840-920℃ followed by tempering at 380-625℃ to achieve optimal strength and toughness. Advantages include excellent resistance to industrial atmospheric corrosion and low-temperature performance when used for connecting uncoated bridge structural plates and profiles. However, this patented invention is limited to the production of bridge bolts, contains a high amount of alloying elements such as C, Ni, and B, and involves complex processes. It lacks a low yield strength ratio and excellent ductility and toughness, making it unsuitable for bridge steel applications. Summary of the Invention

[0010] To address the shortcomings of existing technologies, the present invention aims to provide a low yield strength ratio bridge steel plate resistant to heavy industrial atmospheric corrosion and its production method. The product manufactured according to the chemical composition and production process requirements of the steel of this invention possesses high toughness, low yield strength ratio, high plasticity, and excellent resistance to heavy industrial atmospheric corrosion and weldability. The plate exhibits uniform overall performance and can be produced using hot rolling, further improving production efficiency and enhancing the construction efficiency and overall safety of bridge structures. The weathering steel requires little or no coating, thus saving resources and protecting the environment; it is a low-carbon product.

[0011] This invention discloses a low yield strength ratio bridge steel plate resistant to heavy industrial atmospheric corrosion and its production method. The composition design improves the weldability and toughness of the material through low C and low Mn content. Nb and Ti elements are used to inhibit austenite grain growth and promote nucleation during austenite transformation, thus refining the grain size, controlling the core microstructure of the steel plate, and improving microstructure uniformity. Nb's inhibitory effect on austenite recrystallization increases the rolling temperature, further refining the grain size and improving corrosion resistance. Simultaneously, Cr, Ni, and Cu elements enhance the weather resistance of the steel plate, and the combined addition of Cr and Mo increases the hardenability of the steel plate, improving the cooling rate during air cooling, refining the grain size, and achieving increased strength and thickness-direction microstructure uniformity. Combined with appropriate smelting, heating, and rolling processes, a steel plate with large thickness, low yield strength ratio, excellent atmospheric corrosion resistance, weldability, and other comprehensive properties, as well as an ideal microstructure, is obtained.

[0012] The objective of this invention is achieved as follows:

[0013] A low yield strength ratio bridge steel plate resistant to heavy industrial atmospheric corrosion, comprising the following components by weight percentage: C: 0.07%–0.10%, Si: 0.10%–0.30%, Mn: 0.60%–1.00%, P≤0.010%, S≤0.003%, Nb: 0.02%–0.04%, Ni: 0.15%–0.35%, Cu: 0.10%–0.40%, Mo: 0.20%–0.50%, Cr: 1.50%–2.40%, Ti: 0.01%–0.030%, Sb: 0.03%–0.10%, Al: 0.015%–0.040%, with the balance being iron and unavoidable impurities.

[0014] Furthermore, the steel plate has a Cr / Mo ratio of 3 to 7.

[0015] Furthermore, the atmospheric corrosion resistance index (I) of the steel plate is ≥6.20, where I = 26.01 (% Cu) + 3.88 (% Ni) + 1.20 (% Cr) + 1.49 (% Si) + 17.28 (% P) - 7.29 (% Cu)(% Ni) - 9.10 (% Ni)(% P) - 33.39 (% Cu) 2 .

[0016] Furthermore, the microstructure of the steel plate is mainly ferrite + pearlite, with the ferrite volume percentage accounting for 60% to 85%, the ferrite grain size ≥ 9, and the average ferrite grain size < 20 μm.

[0017] Furthermore, the thickness of the steel plate is 6 to 100 mm.

[0018] Furthermore, the steel plate has a yield strength ≥345MPa, tensile strength ≥510MPa, elongation after fracture ≥30%, yield strength ratio ≤0.75, reduction of area in the thickness direction ≥70%, and impact energy at -40℃ ≥300J.

[0019] The rationale for the design of the components in this invention is as follows:

[0020] C: 0.07%~0.10%

[0021] Carbon (C) has a significant impact on the strength, toughness, and weldability of steel, as well as its corrosion resistance. Lower carbon content improves toughness, weldability, and corrosion resistance. However, a carbon content below 0.070% results in lower strength and greater difficulty in smelting and welding. A carbon content above 0.10% leads to the formation of more pearlite, which is detrimental to the performance of bridge steel resistant to atmospheric corrosion and reduces strength, elongation, and toughness. Therefore, this invention limits the C content to 0.07%–0.10%.

[0022] Si: 0.10%~0.30%

[0023] Si is an essential element for deoxidation in steelmaking and can also play a role in solid solution strengthening, increasing the strength of steel. Si can also improve the corrosion resistance of steel. However, too high a Si content will reduce the toughness of the steel and is also detrimental to its weldability. Therefore, in the steel grade of this invention, the Si content is limited to 0.10% to 0.30%.

[0024] Mn: 0.60%~1.00%

[0025] Manganese (Mn) can form substitutional solid solutions in steel, resulting in strong solid solution strengthening and a linear increase in yield strength and tensile strength. Within a certain range, its content increases steel strength while almost not reducing its plasticity and toughness. However, excessively high manganese content can increase the carbon equivalent of the steel and reduce its resistance to heavy industrial atmospheric corrosion. Therefore, in the steel grades of this invention, the appropriate range for adding Mn, depending on the strength requirements, is 0.60% to 1.00%.

[0026] P≤0.010%

[0027] Petrochemical phosphorus (P) is one of the most effective alloying elements for improving the corrosion resistance of steel plates. When P is added to steel in combination with Cu, a barrier layer mainly composed of Cu and P can be formed between the matrix and the rust layer, exhibiting a better composite effect. However, P deteriorates the weldability, plasticity, and toughness of steel, especially drastically reducing low-temperature impact toughness; it also easily leads to local segregation, forming banded structures. Therefore, in this invention, the P content is controlled at P ≤ 0.010%.

[0028] S≤0.003%

[0029] Sulfur (S) is the most detrimental element to the corrosion resistance of steel. Reducing sulfur content has a positive effect on the steel's resistance to industrial atmospheric corrosion and H2S corrosion. However, high sulfur content also negatively impacts the steel's toughness and plasticity. The steel grade of this invention controls S content to ≤0.003%.

[0030] Nb: 0.02%–0.04%

[0031] Nitrogen (Nb) is an important additive element in this invention. In salt solutions, Nb forms Nb₂O₅, a very stable oxide that adheres to the steel matrix, isolating it from corrosive media and oxygen, thus inhibiting corrosion. It effectively delays the recrystallization of deformed austenite, prevents austenite grain growth, increases the austenite recrystallization temperature, refines the grain size, and improves the strength and toughness of the steel. Furthermore, Nb is a strong carbide and nitride forming element, capable of combining with carbon and nitrogen to form stable, fine carbide and nitride precipitates. The dispersed distribution of these precipitates promotes uniform corrosion. Therefore, in this invention, the Nb content is limited to 0.02%–0.04%.

[0032] Ti: 0.01%~0.03%

[0033] The addition of Ti can refine the austenite grains during reheating of the billet and in the weld heat-affected zone, thereby improving the plasticity and toughness of the steel plate. Furthermore, Ti can form fine carbides or nitrides with C and N, preventing grain growth during heating, rolling, and welding of the billet, thus improving the toughness of the base metal and the weld heat-affected zone. Therefore, in this invention, the Ti content is limited to 0.01%–0.03%, depending on the N content in the steel.

[0034] Cr: 1.5%–2.4%

[0035] Cr is the key element in this invention for improving resistance to heavy industrial atmospheric corrosion. Cr enrichment in the rust layer accelerates the conversion of unstable γ-FeOOH into the more stable α-FeOOH, resulting in finer rust grains. The enriched Cr fills cracks and pores in the rust layer, improving its density and stability. The addition of Cr alters the rust layer structure, forming a dense oxide layer with Cu, preventing oxygen from entering. Cu and Cr simultaneously dissolve in the matrix and, as corrosion progresses, combine with oxygen at defects (cracks, pores) in the rust layer, thus blocking corrosive media from entering the matrix and slowing down metal corrosion. Cu and Sb work synergistically to form a dense α-FeOOH and δ-FeOOH rust film on the steel plate surface, protecting the steel from further corrosion. When Cr is below 1.5%, the resistance to heavy industrial atmospheric corrosion is poor; when Cr is above 2.4%, steelmaking becomes difficult, the hot workability of the steel plate deteriorates, and the cost is too high. Therefore, the Cr content is limited to 1.5%–2.4%.

[0036] Cu: 0.10%–0.40%

[0037] Cu (Cu) can effectively improve the corrosion resistance of steel under heavy industrial atmospheres. Cu promotes anodic passivation of the steel matrix, inhibits rust crystallization, hinders rust crystal growth, refines the grains of the inner rust layer, and repairs cracks and voids in the rust layer, thus generating a more protective rust layer. Cu enrichment can hinder rust crystallization, inhibit oxygen ingress, reduce the conductivity of the rust layer, and surface deposition can inhibit corrosion. However, high Cu content deteriorates the surface properties of the steel plate. Furthermore, at a certain Cu content, it is beneficial to the strength and hot workability of the steel plate, effectively reducing the tendency for hot-rolled edge cracking and significantly improving the surface quality. Cu also reduces work hardening, improves the plasticity of the steel plate, and greatly enhances low-temperature toughness. Therefore, in the steel grade of this invention, the Cu content is limited to 0.10%–0.40%.

[0038] Sb: 0.03%~0.10%

[0039] The addition of Sb promotes the formation of a uniform and dense oxide film (rich in elements such as Sb, Cu, and Cr) on the surface of the steel plate substrate. The Cu in the oxide film... 2+ Increased δ-FeOOH content effectively prevents moisture, oxygen, sulfides, and other pollutants from heavy industrial atmospheres from entering the matrix and creating a corrosive internal environment. Sb can synergistically enhance the corrosion resistance of the matrix by promoting the increase of α-FeOOH and δ-FeOOH. If the Sb content is too low, the passivation film will be unevenly dispersed, failing to achieve overall corrosion resistance; if it exceeds the design limit, it will provide corrosion protection but significantly reduce hot working performance. Therefore, the Sb content is limited to 0.03%–0.10%.

[0040] Mo: 0.20%–0.50%

[0041] Mo plays a significant role in improving the resistance of weathering steel to heavy industrial atmospheres. Mo in the rust layer readily transforms into molybdate. As corrosion progresses, molybdate reacts with iron ions to form FeMoO4, which is deposited on the anodic active sites, thus inhibiting anodic dissolution and significantly slowing down corrosion. Particularly in environments containing sulfides, it can significantly improve resistance to pitting and crevice corrosion. Furthermore, Mo helps refine austenite grains during rolling; however, additions exceeding 0.5% reduce weldability. In addition, Mo is a valuable element, leading to a substantial increase in steel cost. Therefore, the Mo content in this steel grade is limited to 0.20%–0.50%.

[0042] Ni: 0.15%–0.35%

[0043] The addition of Ni can shift the self-corrosion potential of the metal positively and refine the grains of the internal rust layer, increasing its density and thus slowing down corrosion. Ni can effectively improve the low-temperature toughness of steel and also mitigate the hot brittleness caused by copper in steel. Ni has no adverse effect on the hardening properties and toughness of the weld heat-affected zone of steel; however, Ni is a valuable element, and its content should not be too high. Therefore, in the steel grade of this invention, the Ni content is limited to 0.15% to 0.35%.

[0044] Al: 0.015%~0.040%

[0045] Al is a commonly used deoxidizer in steel. Adding a small amount of Al to steel can refine the grains and improve impact toughness. Al also has antioxidant and corrosion resistance. When Al is used in combination with Cr and Si, it can significantly improve the high-temperature non-scaling performance of steel and improve the surface quality of steel plates. However, if Al is too high, oxide inclusions are easily formed. Therefore, in this invention, the Al content is limited to 0.015% to 0.040%.

[0046] The second technical solution of the present invention is to provide a method for manufacturing a bridge steel plate with low yield strength ratio and resistance to atmospheric corrosion in heavy industry, including molten iron pretreatment, smelting, continuous casting, slab heating, rolling and straightening.

[0047] Among them, the superheating temperature of the continuously cast billet is 10-25℃, and the ratio of the thickness of the continuously cast billet to the thickness of the finished steel plate is 3-50. Controlling the superheating temperature and the casting speed of the continuously cast billet can effectively reduce the quality defects of the billet. Increasing the compression ratio from the continuously cast billet to the finished steel plate can effectively control the grain size.

[0048] The temperature of the heating section of the continuously cast billet is 1200-1250℃, the temperature of the soaking section is 1190-1230℃, and the soaking time is not less than 90 minutes. The heating temperature can meet the solid solution requirements of the alloy, especially Nb, Cr, and Ni elements, while preventing excessive growth of austenite grains. The heating time can ensure the uniformity of billet temperature.

[0049] The initial rolling temperature of the roughing rolling is 1070–1095℃, and the final rolling temperature of the roughing rolling is 1010–1045℃. The rolling temperature and deformation process in the roughing rolling stage cause the austenite grains to recrystallize and inhibit grain growth. In the roughing rolling stage, it is ensured that the deformation rate of each pass in at least the last two passes is greater than 15% and the interval between passes does not exceed 15s, with a cumulative reduction rate ≥50%. The use of large reduction and short interval processes in the final stage of roughing rolling can reduce the equipment load of construction steel. By utilizing the superposition effect of deformation with large reduction rates in multiple passes, the recrystallization of austenite is promoted, achieving the grain refinement target. This invention is suitable for the production of bridge steel plates resistant to atmospheric corrosion in heavy industry.

[0050] The thickness of the intermediate preheating billet is 1.25t to 3.5t, where t is the thickness of the finished steel plate. The initial rolling temperature of the finishing rolling is 820 to 849℃, and the final rolling temperature of the finishing rolling is 750 to 779℃. The deformation rate per pass is not less than 10%. The appropriate thickness of the intermediate preheating billet can meet the requirements of austenite deformation and deformation energy accumulation in the non-recrystallization zone, and also ensure that sufficient deformation rate is obtained in the rough rolling stage under the condition that the original billet thickness is certain, so as to achieve the purpose of grain refinement. The low finishing rolling temperature promotes the accumulation of austenite deformation energy and the induction of fine precipitates of Nb and Ti, increasing the nucleation sites. Sufficient deformation near the phase transformation point temperature at the end of the finishing rolling is conducive to the formation of fine ferrite, which can reduce the effective grain size and significantly improve the low-temperature toughness. The thickness of the rolled steel plate is 6 to 100 mm.

[0051] After rolling, the steel plates undergo hot straightening and air cooling. To achieve optimal results, the steel plates are then stacked and heat-insulated at a temperature of 300–450°C. During this self-tempering process, the strength of the steel is adjusted, while its toughness and plasticity are improved, achieving uniform performance.

[0052] The final microstructure of the steel plate is mainly composed of fine ferrite and pearlite, with ferrite volume percentage ranging from 60% to 85%, ferrite grain size ≥ 9, and average size of polygonal ferrite grains < 20 μm. The steel plate has a low yield strength ratio, high elongation, good weldability, and low-temperature toughness, meeting the requirements for use in bridge engineering under heavy industrial atmospheric conditions.

[0053] The beneficial effects of this invention are as follows:

[0054] 1. This invention is based on low C and low Si, and focuses on using Nb and Ti elements to inhibit austenite grain growth and promote nucleation during austenite transformation to refine grains. By adjusting the proportions of alloying elements such as Cr, Mo, Cu, Ni, and Sb, which are resistant to heavy industrial atmospheric corrosion, and through a corresponding unique production process, a bridge steel with excellent comprehensive performance and resistance to heavy industrial atmospheric corrosion is produced. The microstructure of the steel plate is ferrite + pearlite, with a ferrite volume percentage of 60% to 85%, a ferrite grain size ≥ 9, and an average size of polygonal ferrite grains < 20 μm.

[0055] 2. The present invention discloses a low yield strength ratio bridge steel plate resistant to heavy industrial atmospheric corrosion, with a yield strength ≥345MPa, tensile strength ≥510MPa, elongation after fracture ≥30%, yield strength ratio ≤0.75, reduction of area in the thickness direction ≥70%, and impact energy at -40℃ ≥300J. The steel plate has a low yield strength ratio, high elongation, good weldability, and low-temperature toughness, meeting the requirements for use in bridge engineering under heavy industrial atmospheric conditions.

[0056] 3. The low yield strength ratio bridge steel plate resistant to heavy industrial atmospheric corrosion described in this invention has an annual corrosion rate of ≤0.05mm / a under simulated heavy industrial atmospheric environment, which is 4 to 8 times higher than that of ordinary Q345qE. It can be widely used in engineering structures such as bridges and pipe corridors that are resistant to heavy industrial atmospheric environment. At the same time, it can also replace repeated coating of galvanizing or paint, which is beneficial to environmental protection and belongs to green manufacturing, filling the gap in this field. Attached Figure Description

[0057] Figure 1 This is a metallographic image of the microstructure (ferrite + pearlite) of Example 1 of the present invention. Detailed Implementation

[0058] The present invention will be further illustrated below through examples.

[0059] According to the component ratio of the technical solution, the embodiments of the present invention perform molten iron pretreatment, smelting, continuous casting, slab heating, rolling and straightening.

[0060] Slab heating

[0061] The temperature of the heating section of the continuously cast billet is 1200-1250℃, the temperature of the soaking section is 1190-1230℃, and the soaking time is not less than 90 minutes.

[0062] Rolling

[0063] The roughing rolling start temperature is 1070–1095℃, and the roughing rolling finish temperature is 1010–1045℃. During the roughing stage, the deformation rate of each of the last two passes must be greater than 15% and the interval between passes must not exceed 15s. The cumulative reduction rate is ≥50%. The thickness of the intermediate billet is 1.25t–3.5t, where t is the thickness of the finished steel plate. The finishing rolling start temperature is 820–849℃, and the finishing rolling finish temperature is 750–779℃. The deformation rate per pass is not less than 10%. After rolling, the steel plate is hot straightened and air-cooled.

[0064] Furthermore, the continuous casting process involves a billet superheat of 10–25°C and a billet thickness / finished steel plate thickness of 3–50 mm.

[0065] Furthermore, after the rolling process, the steel plates are stacked and heat-insulated, with a stacking temperature of 300–450°C.

[0066] The chemical composition of the embodiments of the present invention is shown in Table 1; the smelting, continuous casting and slab heating processes of the corresponding embodiments are shown in Table 2; the roughing process of the corresponding embodiments is shown in Table 3; the finishing process of the corresponding embodiments is shown in Table 4; the performance and microstructure ratio of the corresponding embodiments are shown in Table 5; the main components and contents of the heavy industrial atmospheric corrosion-resistant solution are shown in Table 6; and the dry-wet alternating corrosion rate of the embodiments in the heavy industrial atmosphere is shown in Table 7.

[0067] Table 1 Chemical composition (wt%) of the embodiments of the present invention

[0068]

[0069] Table 2 Continuous casting and billet heating processes in embodiments of the present invention

[0070]

[0071] Table 3 Roughing process of embodiments of the present invention

[0072]

[0073] Table 4 Finishing process of embodiments of the present invention

[0074]

[0075] Table 5 Performance and microstructure ratio of embodiments of the present invention

[0076]

[0077] The heavy industrial atmospheric corrosion resistant steel of the above embodiments and the comparative example Q345qE steel were processed into corrosion samples. Accelerated corrosion tests under heavy industrial atmospheric conditions with alternating wet and dry conditions were conducted using the immersion method. The physicochemical properties of the corrosion solution are shown in Table 6. After 360 hours of corrosion in the medium, the test materials were removed and the data were processed. The corrosion test results are shown in Table 7.

[0078] Table 6. Main components and content of heavy-duty industrial atmospheric corrosion resistant solutions

[0079] Media Name Content (mol / L) <![CDATA[NaHSO3]]> 0.01 <![CDATA[NaHCO3]]> 0.01 <![CDATA[NaNO3]]> 0.01 <![CDATA[(NH4)2SO4]]> 0.002 NaCl 0.001 NaF 0.001

[0080] Table 7. Corrosion rates of the examples in alternating wet and dry conditions in heavy industrial atmospheres (360 h).

[0081]

[0082] As can be seen from the above, the steel plate of this invention has a yield strength ≥345MPa, tensile strength ≥510MPa, elongation after fracture ≥30%, yield strength ratio ≤0.75, reduction of area in the thickness direction ≥70%, and impact energy at -40℃ ≥300J. The steel plate possesses a low yield strength ratio, high elongation, good weldability, and low-temperature toughness, meeting the requirements for use in bridge engineering under heavy industrial atmospheric conditions. The annual corrosion rate under simulated heavy industrial atmospheric conditions is ≤0.05mm / a, which is 4 to 8 times better than ordinary Q345qE. It can be widely used in bridge, pipe gallery, and other engineering structures resistant to heavy industrial atmospheric conditions. Furthermore, it can replace repeated galvanizing or painting, which is beneficial to environmental protection and belongs to green manufacturing, filling a gap in this field.

[0083] To illustrate the present invention, the present invention has been appropriately and sufficiently described above through embodiments. The above embodiments are only for illustrating the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., should be included within the protection scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. A bridge steel plate with low yield strength ratio and resistance to heavy industrial atmospheric corrosion, characterized in that, By weight percentage, it includes the following components: C: 0.077%~0.10%, Si: 0.11%~0.30%, Mn: 0.60%~1.00%, P≤0.010%, S≤0.003%, Nb: 0.02%~0.04%, Ni: 0.22%~0. 35%, Cu: 0.27% ~ 0.40%, Mo: 0.20% ~ 0.49%, Cr: 1.50% ~ 2.40%, Ti: 0.01% ~ 0.029%, Sb: 0.038% ~ 0.096%, Al: 0.01 The content of the steel plate is 5% to 0.040%, with the remainder being Fe and unavoidable impurities; the Cr / Mo ratio of the bridge steel plate is 3 to 7; the microstructure of the steel plate is ferrite + pearlite, with the ferrite volume percentage being 60% to 85%, the ferrite grain size being ≥9, and the average ferrite grain size being <20μm; the yield strength of the steel plate is ≥345MPa, the tensile strength is ≥510MPa, the elongation after fracture is ≥30%, the yield ratio is ≤0.75, the reduction of area in the thickness direction is ≥70%, and the impact energy at -40℃ is ≥315J; The method for manufacturing a low yield strength ratio bridge steel plate resistant to heavy industrial atmospheric corrosion includes hot metal pretreatment, smelting, continuous casting, slab heating, rolling, and straightening. Slab heating The temperature of the heating section of the continuously cast billet is 1200-1250℃, the temperature of the soaking section is 1190-1230℃, and the soaking time is not less than 90 minutes. Rolling The roughing rolling start temperature is 1070–1095℃, and the roughing rolling finish temperature is 1010–1045℃. During the roughing rolling stage, the deformation rate of each of the last two passes must be greater than 15% and the interval between passes must not exceed 15s. The cumulative reduction rate is ≥50%. The thickness of the intermediate billet to be heated is 1.25t–3.5t, where t is the thickness of the finished steel plate. The finishing rolling start temperature is 820–849℃, and the finishing rolling finish temperature is 750–779℃. The deformation rate per pass is not less than 10%. After rolling, the steel plate is hot straightened and air-cooled.

2. The low yield strength ratio bridge steel plate resistant to heavy industrial atmospheric corrosion according to claim 1, characterized in that, The atmospheric corrosion resistance index (I) of the steel plate is ≥6.20, where I = 26.01(%Cu) + 3.88(%Ni) + 1.20(%Cr) + 1.49(%Si) + 17.28(%P) - 7.29(%Cu)(%Ni) - 9.10(%Ni)(%P) - 33.39(%Cu) 2 .

3. The low yield strength ratio bridge steel plate resistant to heavy industrial atmospheric corrosion according to claim 1, characterized in that, The thickness of the steel plate is 6 to 100 mm.

4. A method for manufacturing a low yield strength ratio bridge steel plate resistant to heavy industrial atmospheric corrosion according to any one of claims 1 to 3, comprising hot metal pretreatment, smelting, continuous casting, slab heating, rolling, and straightening, characterized in that, Slab heating The temperature of the heating section of the continuously cast billet is 1200-1250℃, the temperature of the soaking section is 1190-1230℃, and the soaking time is not less than 90 minutes. Rolling The roughing rolling start temperature is 1070–1095℃, and the roughing rolling finish temperature is 1010–1045℃. During the roughing rolling stage, the deformation rate of each of the last two passes must be greater than 15% and the interval between passes must not exceed 15s. The cumulative reduction rate is ≥50%. The thickness of the intermediate billet to be heated is 1.25t–3.5t, where t is the thickness of the finished steel plate. The finishing rolling start temperature is 820–849℃, and the finishing rolling finish temperature is 750–779℃. The deformation rate per pass is not less than 10%. After rolling, the steel plate is hot straightened and air-cooled.

5. The method for manufacturing a low yield strength ratio bridge steel plate resistant to heavy industrial atmospheric corrosion according to claim 4, characterized in that, The continuous casting process involves casting billets at a superheat of 10–25°C, and the ratio of billet thickness to finished steel plate thickness is 3–50 mm.

6. The method for manufacturing a low yield strength ratio bridge steel plate resistant to heavy industrial atmospheric corrosion according to claim 4, characterized in that, After the rolling process, the steel plates are stacked and insulated at a temperature of 300~450℃.

Images