500mpa grade heavy industrial atmosphere corrosion resistant bridge steel plate and production method thereof

Abstract

The application provides a 500MPa-grade heavy industrial atmosphere corrosion resistant bridge steel plate, which comprises the following components in percentage by weight: C: 0.03%-0.06%, Si: 0.07%-0.27%, Mn: 0.90%-1.40%, P: ≤0.010%, S: ≤0.003%, Nb: 0.04%-0.06%, Ni: 0.25%-0.45%, Cu: 0.30%-0.60%, Mo: 0.20%-0.40%, Cr: 2.0%-3.3%, Ti: 0.010%-0.03%, Sb: 0.03-0.12%, Al: 0.015%-0.040%, and Cr / Mo: 6-12. The balance is iron and inevitable impurities. The production method of the steel plate comprises smelting, continuous casting, slab heating, rolling, cooling, straightening and tempering. The yield strength of the steel plate is greater than or equal to 500MPa, the tensile strength is greater than or equal to 670MPa, the elongation after fracture is greater than or equal to 23%, the yield strength ratio is less than or equal to 0.80, the thickness direction section shrinkage is greater than or equal to 58%, and the low temperature impact energy at-40 DEG C is greater than or equal to 270J. The annual corrosion rate in the heavy industrial atmosphere environment is less than or equal to 0.03mm / a, and the corrosion performance is 5-10 times higher than that of common Q500qE.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials, and in particular relates to a 500MPa grade heavy industrial atmospheric corrosion resistant bridge steel plate and its production method. Background Technology

[0002] Material corrosion is widespread in all sectors of social and economic development. Accidents caused by corrosion are alarming and have a serious impact on social and economic progress. Metallic materials are often exposed to the atmosphere. Data shows that approximately 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 its atmospheric environment, the influencing factors are complex. 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.

[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 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] The relevant patents and documents retrieved are as follows:

[0007] Related Patent 1: Chinese Invention Patent Application No. 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.

[0008] Related Patent 2: Chinese Invention Patent Application No. 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, and 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, the drawbacks of this patent application are its lack of resistance to industrial atmospheric corrosion and its relatively low strength, which cannot meet the requirements of some long-span bridge projects.

[0009] Related Patent 3: Chinese Invention Patent Application No. 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 front-end cooling mode. This improves the steel plate's resistance to corrosion in high-temperature, high-humidity, and high-salinity marine climates. The invention in this patent document is limited to the production of thin-gauge steel plates using hot rolling. Furthermore, the steel plates produced by hot rolling have high internal stress, making them unsuitable for further manufacturing of complex-shaped bridge components. In addition, this type of steel does not have low-temperature toughness and is not suitable for use in railway-highway bridges.

[0010] Related Patent 4: Chinese Invention Patent Application No. CN 107177803 B, "A High-Strength Bolt Steel Resistant to Industrial Atmospheric Corrosion for Bridge Structures Without Painting and its Manufacturing Method," belongs to the technical field of high-strength bolt steel for bridge structures. Its components, by weight percentage, 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.

[0011] In summary, current research on steel plates for heavy industrial bridges is still insufficient, and the main problems with bridge steel plates at present are as follows:

[0012] 1. Steel plates are not resistant to corrosion in heavy industrial atmospheric environments and have poor safety performance.

[0013] 2. Weathering steel contains a large amount of rare elements, making smelting difficult and resulting in higher costs.

[0014] 3. The steel plate has low strength and poor toughness, which cannot meet the requirements of bridge engineering in cold regions.

[0015] 4. The high yield strength ratio of the steel plate has a certain impact on the seismic safety of the bridge.

[0016] 5. The addition of more alloying elements results in higher costs.

[0017] 6. There are relatively few medium and heavy plate products, mainly hot-rolled coils and bolts, which cannot meet the needs of long-span bridge projects. Summary of the Invention

[0018] To address the shortcomings of existing technologies, this invention provides a 500MPa grade heavy industrial atmospheric corrosion resistant bridge steel plate and its production method. The product manufactured according to the chemical composition and production process requirements of this invention exhibits high strength, high toughness, low yield strength ratio, high plasticity, and excellent resistance to heavy industrial atmospheric corrosion. Utilizing TMCP+tempering rolling, the steel plate exhibits more uniform properties, improving construction efficiency and overall safety in bridge structural engineering. The weathering steel requires little or no coating, thus saving resources and being environmentally friendly, making it a low-carbon product.

[0019] The objective of this invention is achieved as follows:

[0020] A 500MPa grade heavy industrial atmospheric corrosion resistant bridge steel plate, comprising the following components by weight percentage: C: 0.03%–0.06%, Si: 0.07%–0.27%, Mn: 0.90%–1.40%, P≤0.010%, S≤0.003%, Nb: 0.04%–0.06%, Ni: 0.25%–0.45%, Cu: 0.30%–0.60%, Mo: 0.20%–0.40%, Cr: 2.0%–3.3%, Ti: 0.010%–0.03%, Sb: 0.03%–0.12%, Al: 0.015%–0.040%, with the balance being iron and unavoidable impurities.

[0021] Furthermore, the steel plate has a Cr / Mo ratio of 6 to 12.

[0022] Furthermore, the steel plate has an I value ≥ 7.9, 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 ≥7.9.

[0023] Furthermore, the microstructure of the steel plate is a multiphase structure of ferrite + lath bainite + MA islands, wherein the volume percentage of ferrite is 15% to 35%.

[0024] Furthermore, the thickness of the steel plate is 6 to 100 mm.

[0025] Furthermore, the steel plate has a yield strength ≥500MPa, tensile strength ≥670MPa, elongation after fracture ≥23%, yield strength ratio ≤0.80, reduction of area in the thickness direction ≥58%, and impact energy at -40℃ ≥270J.

[0026] The rationale for the design of the components in this invention is as follows:

[0027] This invention discloses a 500MPa grade 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, refining the grain size and controlling the core microstructure to improve uniformity. The precipitation of Nb and Ti during rapid cooling after rolling strengthens the steel plate, enhancing its strength. Nb's inhibition of austenite recrystallization increases the rolling temperature, further refining the grains and improving corrosion resistance. Simultaneously, Cr, Ni, Cu, and Sb elements enhance the atmospheric corrosion resistance, and the combined addition of Cr and Mo increases the hardenability, improving the cooling rate and refining the grains during cooling, thus achieving increased strength and uniform microstructure in the thickness direction. Combined with appropriate smelting, heating, and rolling processes, this results in 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.

[0028] C: 0.03%~0.06%

[0029] 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, carbon content below 0.030% results in lower strength and greater difficulty in smelting and welding. Carbon content above 0.06% 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 0.03%–0.06%.

[0030] Si: 0.07%–0.27%

[0031] 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 this steel grade, the Si content is limited to 0.07% to 0.27%.

[0032] Mn: 0.90%~1.40%

[0033] 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 0.90% to 1.40%.

[0034] P≤0.010%

[0035] 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%.

[0036] S≤0.003%

[0037] 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. This invention controls the sulfur content in the steel grade to ≤0.003%.

[0038] Nb: 0.040%~0.060%

[0039] 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; during rapid water cooling, it combines with carbon and nitrogen to form stable, fine carbide and nitride precipitates. These dispersed precipitates contribute to uniform corrosion. Therefore, in this invention, the Nb content is limited to 0.040%–0.060%.

[0040] Ti: 0.010%~0.030%

[0041] 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 material and the weld heat-affected zone. Therefore, in this invention, the Ti content is limited to 0.010%–0.030%, depending on the N content in the steel.

[0042] Cr: 2.0%–3.3%

[0043] 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 2.0%, the resistance to industrial atmospheric corrosion is poor; when Cr is above 3.3%, steelmaking becomes difficult, the hot workability of the steel plate deteriorates, and the cost is too high. Therefore, the Cr content is limited to 2.0%–3.3%.

[0044] Cu: 0.30%–0.60%

[0045] 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 cracks 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 0.30%–0.60%.

[0046] Sb: 0.03%~0.12%

[0047] 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%–0.12%.

[0048] Mo: 0.20%–0.40%

[0049] 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 industrial atmospheric environments containing sulfides, it can significantly improve resistance to pitting and crevice corrosion. Furthermore, Mo helps refine austenite grains during rolling; however, additions exceeding 0.4% 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%–0.40%.

[0050] Ni: 0.25%–0.45%

[0051] 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 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 0.25% to 0.45%.

[0052] Al: 0.015%~0.040%

[0053] 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%.

[0054] The second technical solution of the present invention is to provide a method for manufacturing a low yield strength ratio, uncoated 420MPa grade marine atmospheric corrosion resistant steel, including smelting, continuous casting, slab heating, rolling, cooling, straightening, and tempering;

[0055] Continuous casting

[0056] Among them, the superheating temperature of the continuously cast billet is 12-24℃, and the ratio of the thickness of the continuously cast billet to the thickness of the finished steel plate is 3-30. 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.

[0057] Slab heating

[0058] The temperature of the continuous casting billet heating section is 1230~1260℃, the temperature of the soaking section is 1210~1240℃, and the soaking time is not less than 98min. 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.

[0059] Rolling

[0060] The initial rolling temperature of roughing is 1060–1110℃, and the final rolling temperature of roughing is 1010–1050℃. The rolling temperature and deformation process in the roughing stage cause austenite grains to recrystallize and inhibit grain growth. In the roughing stage, it is ensured that the deformation rate of each pass in at least the last two passes is greater than 13% 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 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 heavy industrial atmospheric corrosion resistant bridge steel plates.

[0061] The thickness of the intermediate preheating billet is 1.5t to 3.5t, where t is the thickness of the finished steel plate. The initial rolling temperature of the finishing rolling is 810 to 840℃, and the final rolling temperature of the finishing rolling is 770 to 800℃. The deformation rate per pass is not less than 10%. The appropriate thickness of the intermediate preheating billet can satisfy the 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.

[0062] cool down

[0063] After rolling, the steel plate undergoes accelerated water cooling. After rolling, the steel plate is allowed to warm up before initial water cooling at 640–690℃, followed by a reheating temperature of 300–450℃, with a cooling rate of 10–25℃ / s. Subsequently, hot straightening is performed. Controlling the initial water cooling temperature helps prevent excessive stress during cooling, ensuring proper plate shape. Simultaneously, controlling the initial cooling temperature allows for the formation of proeutectoid ferrite, resulting in more uniform grain size and further reducing the yield strength ratio. The final cooling temperature promotes core microstructure refinement, ensuring the formation of lath bainite, increasing tensile strength, and further reducing the yield strength ratio.

[0064] Tempering

[0065] The rolled steel plate undergoes tempering heat treatment at a heating temperature of 350–450℃, with a total holding time of 2.5 min / mm to 5 min / mm. After being removed from the furnace, it is air-cooled to room temperature. The purpose of tempering is twofold: firstly, to reduce the brittleness of the steel plate and effectively improve the ductility and toughness of high-strength steel; secondly, tempering can eliminate internal stress in the steel plate, meeting the requirements of subsequent workpiece processing. The thickness of the finished steel plate is 6–100 mm.

[0066] The final microstructure of the steel plate is mainly composed of fine ferrite, lath bainite, and MA islands, with the ferrite volume percentage ranging from 15% to 35%. The steel plate has a low yield strength ratio, high elongation, and good low-temperature toughness, which meets the requirements for use in bridge engineering under heavy industrial atmospheric conditions.

[0067] The beneficial effects of this invention are as follows:

[0068] 1. This invention is based on low C and low Si, focusing on using Nb and Ti elements to suppress austenite grain growth and the precipitation phases formed during rapid cooling to refine grains and increase strength. Through the proportions of alloying elements such as Cr, Mo, Cu, Ni, and Sb, which are resistant to heavy industrial atmospheric corrosion, and through a unique corresponding production process, a high-strength bridge steel with excellent comprehensive performance and resistance to heavy industrial atmospheric corrosion is produced. The product microstructure is a multiphase structure of ferrite + lath bainite + MA islands, wherein the ferrite volume percentage is 15%–35%, yield strength ≥500MPa, tensile strength ≥670MPa, elongation after fracture ≥23%, yield ratio ≤0.80, reduction of area in the thickness direction ≥58%, and impact energy at -40℃ ≥270J.

[0069] 2. The annual corrosion rate in heavy industrial atmospheric environments is ≤0.03mm / a, which is 5 to 10 times better than ordinary Q500qE. It can be widely used in engineering structures such as bridges and pipe corridors that are resistant to heavy industrial atmospheric environments. 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 a gap in this field. Attached Figure Description

[0070] Figure 1 The optical microstructure (ferrite + lath bainite + MA islands) is shown in the embodiment of the present invention. Detailed Implementation

[0071] The present invention will be further illustrated below through examples.

[0072] According to the component ratio of the technical solution, the embodiments of the present invention carry out smelting, continuous casting, slab heating, rolling, cooling, straightening and tempering.

[0073] Slab heating

[0074] The temperature of the heating section of the continuously cast billet is 1230~1260℃, the temperature of the soaking section is 1210~1240℃, and the soaking time is not less than 98min;

[0075] Rolling

[0076] The roughing rolling start temperature is 1060~1110℃, the roughing rolling finish temperature is 1010~1050℃, and the roughing rolling stage ensures that the deformation rate of each pass of at least the last two passes is greater than 13% and the pass interval is no more than 15s, with a cumulative reduction rate ≥50%.

[0077] The thickness of the intermediate billet is 1.5t to 3.5t, where t is the thickness of the finished steel plate. The initial rolling temperature of the finishing rolling is 810 to 840℃, the final rolling temperature of the finishing rolling is 770 to 800℃, and the deformation rate per pass is not less than 10%.

[0078] cool down

[0079] After rolling, the steel plate is subjected to accelerated water cooling. After rolling, the steel plate is allowed to heat up. The initial water cooling temperature is 640-690℃, the reheating temperature is 300-450℃, and the cooling rate is 10-25℃ / s.

[0080] Heat treatment

[0081] The rolled steel plate is subjected to tempering heat treatment at a heating temperature of 350-450℃ and a total holding time of 2.5-5 min / mm. After being taken out of the furnace, it is air-cooled to room temperature.

[0082] Furthermore, the continuous casting process involves casting billets with a superheat of 12–24°C.

[0083] 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 cooling process of the corresponding embodiments is shown in Table 5; the performance and microstructure ratio of the corresponding embodiments are shown in Table 6; the main components and contents of the heavy industrial atmospheric corrosion-resistant solution are shown in Table 7; the dry and wet alternating corrosion rate of the embodiments in the heavy industrial atmosphere is shown in Table 8.

[0084] Table 1 Chemical composition (wt%) of the embodiments of the present invention

[0085]

[0086] Table 2 Continuous casting and billet heating processes in embodiments of the present invention

[0087]

[0088] Table 3 Roughing process of embodiments of the present invention

[0089]

[0090] Table 4 Finishing process of embodiments of the present invention

[0091]

[0092] Table 5 Cooling and tempering processes of embodiments of the present invention

[0093]

[0094] Table 6 Performance and Microstructure Ratio of Embodiments of the Invention

[0095]

[0096] The heavy-duty industrial atmospheric corrosion-resistant steel of the above embodiments and the comparative example Q500qE steel were processed into corrosion samples. Accelerated corrosion tests under heavy-duty industrial atmospheric conditions were conducted using the immersion method, involving alternating wet and dry conditions. 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.

[0097] Table 7. Main components and content of heavy-duty industrial atmospheric corrosion resistant solutions

[0098] 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

[0099] Table 8. Corrosion rates of the examples under alternating wet and dry conditions in heavy industrial atmospheres (360 h).

[0100]

[0101] This invention is based on low C and low Si, focusing on using Nb and Ti elements to suppress austenite grain growth and the precipitation phases formed during rapid cooling to refine grains and increase strength. Through the proportions of alloying elements such as Cr, Mo, Cu, Ni, and Sb, which are resistant to heavy industrial atmospheric corrosion, and through a unique corresponding production process, a high-strength bridge steel with excellent comprehensive performance and resistance to heavy industrial atmospheric corrosion is produced. The steel exhibits a yield strength ≥500MPa, tensile strength ≥670MPa, elongation after fracture ≥23%, yield strength ratio ≤0.80, reduction of area in the thickness direction ≥58%, and impact energy at -40℃ ≥270J. The annual corrosion rate in heavy industrial atmospheric environments is ≤0.03mm / a, which is 5-10 times better than ordinary Q500qE, making it widely applicable to engineering structures such as bridges and pipe corridors in heavy industrial atmospheric environments.

[0102] 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 500MPa grade heavy industrial atmospheric corrosion resistant bridge steel plate, characterized in that, The steel plate comprises the following components by weight percentage: C: 0.03%–0.048%, Si: 0.07%–0.19%, Mn: 0.90%–1.18%, P≤0.010%, S≤0.003%, Nb: 0.04%–0.059%, Ni: 0.25%–0.45%, Cu: 0.30%–0.47%, Mo: 0.22%–0.40%, Cr: 2.0%–3.3%, Ti: 0.010%–0.024%, Sb: 0.06%–0.12%, Al: 0.015%–0.037%, with the balance being iron and unavoidable impurities; the Cr / Mo ratio in the bridge steel plate is 6–12; the microstructure of the steel plate is a multiphase structure of ferrite + lath bainite + MA islands, wherein the volume percentage of ferrite is 15%–35%. A method for manufacturing a 500MPa grade heavy industrial atmospheric corrosion resistant bridge steel plate includes smelting, continuous casting, slab heating, rolling, cooling, straightening, and tempering. Slab heating The temperature of the heating section of the continuously cast billet is 1230~1260℃, the temperature of the soaking section is 1210~1240℃, and the soaking time is not less than 98min; Rolling The initial rolling temperature of roughing is 1060–1110℃, and the final rolling temperature of roughing is 1010–1050℃. During the roughing stage, the deformation rate of each pass in at least the last two passes must be greater than 13% and the interval between passes must not exceed 15 seconds. The cumulative reduction rate must be ≥50%. The thickness of the intermediate preheated billet is 1.5t to 3.5t, where t is the thickness of the finished steel plate. The initial rolling temperature of the finishing rolling is 810 to 840℃, the final rolling temperature of the finishing rolling is 770 to 800℃, and the deformation rate per pass is not less than 10%. cool down After rolling, the steel plate is subjected to accelerated water cooling. After rolling, the steel plate is allowed to heat up. The initial water cooling temperature is 640-690℃, the reheating temperature is 300-450℃, and the cooling rate is 10-25℃ / s. Heat treatment The rolled steel plate is subjected to tempering heat treatment at a heating temperature of 350-450℃ and a total holding time of 2.5-5 min / mm. After being taken out of the furnace, it is air-cooled to room temperature.

2. The 500MPa grade heavy industrial atmospheric corrosion resistant bridge steel plate according to claim 1, characterized in that, The steel plate has an I value ≥ 7.9, and 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 ≥7.

9.

3. The 500MPa grade heavy industrial atmospheric corrosion resistant bridge steel plate according to claim 1, characterized in that, The thickness of the steel plate is 6~100mm.

4. The 500MPa grade heavy industrial atmospheric corrosion resistant bridge steel plate according to claim 1, characterized in that, The steel plate has a yield strength ≥500MPa, tensile strength ≥670MPa, elongation after fracture ≥23%, yield strength ratio ≤0.80, reduction of area in the thickness direction ≥58%, and impact energy at -40℃ ≥270J.

5. The 500MPa grade heavy industrial atmospheric corrosion resistant bridge steel plate according to claim 1, characterized in that, The continuous casting process involves casting billets with a superheat of 12–24°C.

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