345MPa-grade marine atmosphere corrosion-resistant hot-rolled steel plate for building structure and manufacturing method thereof

Abstract

The invention discloses a 345MPa-grade marine atmosphere corrosion-resistant hot-rolled steel plate for a building structure and a manufacturing method of the 345MPa-grade marine atmosphere corrosion-resistant hot-rolled steel plate. The hot-rolled steel plate comprises a base layer, a corrosion-resistant layer and an interface transition layer between the base layer and the corrosion-resistant layer, the base layer comprises the following components in percentage by mass: 0.03 to 0.06 percent of C, 0.15 to 0.2 percent of Si, 1 to 1.3 percent of Mn, 0.0005 to 0.003 percent of P, 0.0005 to 0.01 percent of S, 0.1 to 0.15 percent of Cr, 0.01 to 0.07 percent of Ni, 0.015 to 0.03 percent of Al, 0.008 to 0.011 percent of Ti, 0.02 to 0.035 percent of Nb, 0.002 to 0.004 percent of V and the balance of Fe and impurities; and the corrosion-resistant layer comprises the following components in percentage by mass: 0.001 to 0.03 percent of C, 0.2 to 1.5 percent of Si, 1 to 2 percent of Mn, 0.005 to 0.03 percent of P, 0.005 to 0.03 percent of S, 16 to 18 percent of Cr, 10 to 14 percent of Ni, 0.02 to 0.1 percent of Cu, 0.02 to 0.15 percent of N, 2 to 3 percent of Mo and the balance of Fe and impurities. The yield strength of the hot-rolled steel plate is larger than or equal to 345 MPa, the yield ratio is smaller than or equal to 0.75, and the marine atmosphere corrosion resisting rate is smaller than or equal to 0.004 mm / a.

Description

Technical Field

[0001] This invention relates to the field of steel technology for building structures, and in particular to a 345MPa grade hot-rolled steel plate for building structures resistant to marine atmospheric corrosion and its manufacturing method. Background Technology

[0002] With the continuous development and utilization of marine resources, the marine industry, including coastal industries, offshore wind power, marine waterway projects, artificial islands and wharves, as well as offshore oil platforms, subsea oil and gas pipelines, has increased exponentially. The ocean is an extremely harsh corrosive environment for all kinds of structural materials, causing corrosion damage and functional loss to various infrastructures, equipment, and structures, shortening their service life, resulting in huge waste of resources, materials, and energy, and even leading to sudden disasters.

[0003] Marine atmospheric corrosion is the result of the interaction between materials and their surrounding atmospheric environment. It is one of the most widespread forms of metal corrosion. Various environmental factors affecting atmospheric corrosion of materials include temperature, humidity, irradiance, chloride ion concentration, salinity, and pollutants. For building components located in marine atmospheric zones, the corrosion rate varies depending on the distance from the coast. Sea breezes bring small sea salt particles, and influencing factors include altitude, wind speed, rainfall, temperature, and radiation. Sea salt particles accelerate corrosion.

[0004] Currently, the primary method of protecting steel structural components in marine atmospheric environments is through coating protection. Compared to conventional anti-corrosion coatings, coatings can be applied in relatively harsh corrosive environments and offer a longer protection period. The total thickness of the coating typically exceeds 200μm. The coating application process involves the following steps: surface preparation, undercoat, intermediate coat, and top coat. Surface preparation generally requires mechanical sandblasting. Undercoat coatings include organic zinc-rich paints and inorganic zinc-rich paints, with specific materials selected based on the type of coating. Inorganic zinc-rich paints utilize the substitution of anodizing by zinc powder to create an undercoat with excellent rust-preventive properties. Organic zinc-rich paints have weaker rust prevention than inorganic zinc-rich paints, but better adhesion; they can be applied to steel surfaces even with power tools less effective than shot blasting for surface preparation. The intermediate and top coats should have better adhesion and be more suitable for the surrounding environment than the undercoat coating. After the construction is completed, film thickness measurement and pore test must be carried out to confirm whether the coating is intact.

[0005] This type of coating protection has a long construction cycle, complex procedures, and difficulty in guaranteeing quality. If the coating is too thick, its adhesion is limited, and the coating is prone to failure during on-site construction, such as in welding and riveting areas, compromising corrosion resistance. During service, it is easily detached and damaged due to common issues like contact and collisions. Furthermore, in high-temperature, high-radiation, and high-humidity marine atmospheric environments, the coating's lifespan will decrease, leading to various common failures and deterioration problems, resulting in less than ideal practical application results.

[0006] In addition, some architectural designers and researchers have tried to use 300 series austenitic stainless steel to make building components. However, compared with carbon steel, 300 series austenitic stainless steel has lower structural strength and requires a larger thickness, which increases the amount of material used. At the same time, 300 series austenitic stainless steel is more difficult to weld and machine. Furthermore, 300 series stainless steel itself contains more precious metallic elements such as Cr, Ni, and Mo. In the production, manufacturing, and installation process, the cost of using pure stainless steel is relatively high.

[0007] Therefore, in view of the shortcomings and defects in the above-mentioned prior art, the present invention aims to obtain a new 345MPa grade hot-rolled steel plate for marine atmospheric corrosion-resistant structures, which can meet the requirements for use in marine atmospheric environments, and ultimately form steel structural components such as profiled steel plates, purlins, wall beams, roof trusses, and steel frames that have both marine atmospheric corrosion resistance, good mechanical properties, and high economic efficiency, which have great economic and social benefits.

[0008] Chinese patent CN106756476A discloses a high-strength weathering steel for use in high-humidity and hot marine atmospheric environments and its preparation method. The solution is mainly to reduce the corrosion of steel plates in humid and hot marine atmospheric environments by adding trace elements such as Sn, Sb, Nb, and Re to replace the amount of Cr added. The corrosion rate was reduced by about 30% after 96 hours when compared with traditional carbon structural steel and weathering steel in a immersion corrosion test.

[0009] Chinese patent CN111621699A discloses a corrosion-resistant low-alloy steel for bridge structures in high-humidity and hot marine atmospheric environments and its preparation method. The solution involves rationally adjusting the contents of the alloying elements Cu, Ni, and Mo based on the Cu-Ni-Mo low-alloy steel system, taking into account the economic advantages of low-alloy steel, to obtain a corrosion-resistant low-alloy steel with a ferrite-pearlite microstructure. While appropriately controlling the high costs associated with the alloying elements Ni and Mo, its corrosion resistance is significantly superior to that of ordinary carbon steel, and it meets the mechanical property requirements for bridge structural steel in high-humidity and hot marine atmospheric environments.

[0010] Both of the above patents fall under the category of single material, adding alloying elements to the material to meet corrosion resistance requirements. However, the addition of a large number of alloying elements further increases the overall cost of the material and the difficulty of controlling impurities in the smelting process, and the overall improvement in corrosion resistance is relatively limited.

[0011] Chinese patent CN112647014A discloses a structural steel suitable for marine atmospheric environments, with the following chemical composition and mass fractions: C: 0.07%–0.17%, Si: 0.6%–0.8%, Mn: 0.3%–1.0%, P: 0.08%–0.15%, S: 0.005%–0.035%, Cu: 0.15%–0.2%, Sb: 0.1%–0.2%, Ce: 0.0025%–0.0045%; and selectively including: Sn: 0.01%–0.02%, V: 0.05%–0.1% of any one or two of these, with the remainder being iron and unavoidable impurities. This steel contains a significant amount of low-melting-point elements such as P, Sb, and Ce, which affects its low-temperature toughness, weldability, and cold formability.

[0012] Chinese patent CN108004488A discloses a high-toughness bridge steel plate resistant to marine climates and its production method. The raw material chemical composition of the steel plate is as follows (mass percentage): C: 0.041–0.087%, Mn: 1.03–2.00%, Si: 0.67–1.43%, P≤0.007%, S≤0.003%, Nb: 0.047–0.083%, Ti: 0.010–0.027%, Mo: 0.32–0.73%, Cr: 0.50–1.17%, Cu: 0.50–1.05%, Ni: 2.51–6.70%, Ca: 0.0021–0.0073%, Sb: 0.08–0.31%, with the remainder being Fe and unavoidable impurities. The invention adds a lot of precious metal alloys such as Ni, Cr, Mo and Cu, which increases the cost. Sb is prone to segregation, which increases the difficulty of the smelting process. The addition of more Si is detrimental to the surface quality and will affect the weldability of the steel plate.

[0013] Chinese patent application CN202210570630.7 discloses a "production method of Q500 grade high corrosion-resistant and high-strength near-shore structural steel". The process steps are: hot metal pretreatment → converter steelmaking → ladle refining (LF) → vacuum treatment (RH) → continuous casting → heating → rolling → controlled rolling cooling → tempering → finishing → performance testing → ultrasonic flaw detection. The key feature is that the steel's mass percentage composition is: C: 0.03~0.07, Si: 0.15~0.40, Mn: 0.95~1.05, P≤0.020, S≤0.003, Nb: 0.04~0.06, Ti: 0.01~0.02, Als: 0.02~0.05, Cu: 0.30~0.70, Ni: 0.7~1.5, with the remainder being Fe and unavoidable impurity elements. This invention is suitable for producing steel with a thickness ≤60mm, designed for use in marine atmospheric corrosion environments, with a yield strength ≥500MPa and a tensile strength ≥540MPa. However, the 500MPa weathering steel produced by this invention involves a complex process requiring tempering heat treatment, increasing manufacturing costs, and it does not provide a description of the steel plate's corrosion resistance.

[0014] Chinese patent application CN201810908224.0 discloses "a 500MPa grade low yield strength ratio resistant marine atmospheric corrosion bridge steel and its production method," wherein the steel contains the following chemical composition in the following mass percentages: C: 0.04-0.20%, Si: 0.15-0.45%, Mn: 0.85-1.80%, Alt: 0.015-0.050%, Ni: 2.50-4.75%, Cu: 0.20%. The composition is as follows: 0.60% Nb: 0.020-0.080%, Ti: 0.015-0.036%, Ca: 0.0020-0.0050%, P: ≤0.020%, S: ≤0.002%, N: ≤0.004%, with the balance being Fe and other unavoidable impurities. Through composition design, inclusion control, controlled rolling, and controlled cooling and heat treatment, this material can be used to manufacture various bridges for marine and atmospheric environments, with steel thicknesses ranging from 10 to 40 mm. The production process requires applying an anti-oxidation coating to the slab during heating and also necessitates tempering. The addition of alloying elements such as Cu and Ni increases manufacturing costs and smelting difficulty.

[0015] In summary, current production methods for marine atmospheric corrosion-resistant steel primarily involve adding a large number of corrosion-resistant alloying elements to achieve the steel plate's corrosion resistance. This addition inevitably increases smelting costs and process complexity. Furthermore, some elements are prone to causing metallurgical defects, requiring additional additions for suppression. Secondly, because a single material is used, both corrosion resistance and necessary mechanical properties must be considered, necessitating trade-offs in both composition and process design. Some materials still require heat treatment to improve steel plate performance, further increasing production costs. The narrowed window for process parameter design limits product thickness to 60mm or less to ensure a necessary compression ratio, significantly restricting the steel plate's application scenarios and failing to meet the requirements for hot-rolled steel plates used in marine atmospheric corrosion-resistant structures. Summary of the Invention

[0016] The purpose of this invention is to provide a 345MPa grade hot-rolled steel plate for building structures resistant to marine atmospheric corrosion and its manufacturing method. The hot-rolled steel plate for building structures has a yield strength ≥345MPa, tensile strength ≥490MPa, yield-to-tensile ratio ≤0.75, impact energy KV2 ≥190J at -40℃, marine atmospheric corrosion rate ≤0.004mm / a, interface transition layer thickness ≤10μm, and interface shear strength ≥270MPa. It combines marine atmospheric corrosion resistance, high bonding strength, excellent yield-to-tensile ratio and low-temperature impact toughness, as well as high economic efficiency. It can meet the requirements for use in marine atmospheric environments and is suitable for steel structural components such as profiled steel sheets, purlins, wall beams, roof trusses, and steel frames. It has great economic and social benefits.

[0017] To achieve the above objectives, the technical solution of the present invention is as follows:

[0018] The base layer of this invention adopts a low-carbon micro-alloying composition design. The corrosion-resistant layer improves its resistance to marine atmospheric corrosion by increasing the content of Si and N and adding Cu elements. This enables the corrosion-resistant layer to withstand high temperature, high humidity, high salt spray and high radiation marine atmospheric corrosion, and achieves an excellent combination of stainless steel and carbon steel. At the same time, the thickness of the interface transition layer is controlled to achieve high shear strength at the interface, thereby obtaining a building structural steel plate with excellent corrosion resistance, yield strength ratio and low temperature impact toughness.

[0019] Specifically, the 345MPa grade hot-rolled steel plate for building structures resistant to marine atmospheric corrosion described in this invention includes a base layer, a corrosion-resistant layer, and an interface transition layer between the base layer and the corrosion-resistant layer.

[0020] The chemical composition of the base layer, by mass percentage, is as follows: C 0.03–0.06%, Si 0.15–0.2%, Mn 1–1.3%, P 0.0005–0.003%, S 0.0005–0.01%, Cr 0.1–0.15%, Ni 0.01–0.07%, Al 0.015–0.03%, Ti 0.008–0.011%, Nb 0.02–0.035%, V 0.002–0.004%, with the balance including Fe and other unavoidable impurities.

[0021] The chemical composition of the corrosion-resistant layer is as follows (by mass percentage): C 0.001–0.03%, Si 0.2–1.5%, Mn 1.0–2.0%, P 0.005–0.03%, S 0.005–0.03%, Cr 16–18%, Ni 10–14%, Cu 0.02–0.1%, N 0.02–0.15%, Mo 2–3%, with the balance including Fe and other unavoidable impurities.

[0022] The microstructure of the corrosion-resistant layer is equiaxed recrystallized austenite or elongated non-recrystallized austenite and trace amounts of high-temperature ferrite, with the high-temperature ferrite content in the thickness direction ≤2%.

[0023] The interface transition layer achieves 100% metallurgical bonding, with atomically coherent structure, a thickness of ≤10μm, fine grains with an average grain size of ≤0.5μm, and an interfacial shear strength of ≥270MPa.

[0024] The hot-rolled steel plates used in the building structure have a yield strength ≥345MPa, tensile strength ≥490MPa, yield-to-tensile ratio ≤0.75, impact energy KV2 ≥190J at -40℃, and resistance to marine atmospheric corrosion rate ≤0.004mm / a.

[0025] Preferably, the chemical composition of the base layer also satisfies the following relationship:

[0026] 2.8C%≤(Ti+Nb+V+Cr)%≤0.2%.

[0027] Preferably, the chemical composition of the corrosion-resistant layer also satisfies the following relationship:

[0028]

[0029] Preferably, the chemical composition of the corrosion-resistant layer also satisfies the following relationship:

[0030] PREN≥23.0%, PREN=Cr%+3.3×Mo%+16×N%.

[0031] Furthermore, the remaining components of the base layer and corrosion-resistant layer are Fe and other unavoidable impurities.

[0032] The microstructure of the base layer described in this invention is ferrite + pearlite, or ferrite + pearlite + a small amount of bainite; the pearlite content is ≥5%.

[0033] The corrosion-resistant layer of this invention has a marine atmospheric corrosion resistance rate of ≤0.004 mm / a.

[0034] Preferably, the thickness of the hot-rolled steel plate used in the building structure is 10 to 100 mm.

[0035] Preferably, the thickness of the corrosion-resistant layer of the hot-rolled steel plate used in the building structure accounts for 0.5% to 15% of the total thickness of the steel plate.

[0036] The microstructure of the base layer described in this invention is ferrite + pearlite and / or a small amount of bainite. This type of structure can ensure that the base layer itself has a certain strength while having a low yield strength ratio. Since the toughness of pearlite is worse than that of ferrite, the content of pearlite needs to be further controlled in order to ensure the impact toughness of the matrix. The pearlite content is ≥5%.

[0037] The microstructure of the corrosion-resistant layer consists of equiaxed recrystallized austenite or elongated non-recrystallized austenite and trace amounts of high-temperature ferrite. An appropriate amount of high-temperature ferrite can improve subsequent weldability, but excessive high-temperature ferrite will reduce the corrosion resistance of the corrosion-resistant layer. Therefore, the content of high-temperature ferrite in the thickness direction should be controlled to ≤2%.

[0038] The interface transition layer achieves 100% metallurgical bonding. The thickness of the interface transition layer is ≤10μm. If the interface transition layer is too thick, it will significantly reduce the interfacial shear strength and make it easy to cause delamination defects during subsequent bending of the steel plate. The microstructure of this layer has fine and highly coherent grains with an average grain size of ≤0.5μm, which further improves the degree of interfacial bonding and the interfacial shear strength is ≥270MPa.

[0039] In the base composition design of the hot-rolled steel plate for building steel structures described in this invention:

[0040] Carbon (C) plays a role in solid solution strengthening in steel, significantly improving its strength. However, excessively high C content is detrimental to weldability and toughness. More importantly, high C content can diffuse to the composite interface, forming a large number of large-particle carbides in the interface transition layer, reducing the composite interface strength. To ensure the shear strength of the interface, this invention uses a low C content. The effect of C content variation on the yield strength of steel is less than its effect on tensile strength. While ensuring product formability and weldability, appropriately increasing the C content is beneficial for reducing the yield strength ratio of the steel. Based on this, the C content in the base layer composition described in this invention is controlled at 0.03–0.06%.

[0041] Si: Adding Si to steel can effectively deoxidize it, improving the purity of the steel. Furthermore, Si can act as a solid solution strengthening element in steel, increasing its strength and hardness; however, Si is detrimental to the weldability of the material. Therefore, in the base layer composition described in this invention, the Si content is controlled at 0.15–0.20%.

[0042] Mn: Mn is the cheapest matrix strengthening element. It can lower the austenite transformation temperature, delay the pearlite transformation, refine ferrite grains, and improve the strength of steel. Simultaneously, Mn can also eliminate the influence of sulfur on steel. However, excessively high Mn content can easily lead to segregation bands and martensitic structures, which are detrimental to the toughness of the steel. Therefore, in the matrix composition described in this invention, the Mn content is controlled at 1.0–1.3%.

[0043] Al: Al is mainly added in excess to steel as a de-oxidizing element to ensure that the O content in the steel is as low as possible. After de-oxidation, the excess Al combines with the N element in the steel to form AlN precipitates. During heating, AlN hinders the growth of austenite grains, refines the austenite grains, and improves the strength and toughness of the matrix. At the same time, the formation of AlN fixes some of the N in the matrix, reducing the diffusion of interstitial N atoms from the carbon steel base layer to the composite interface, forming hard TiN in the interface transition layer, which deteriorates the interfacial shear strength of the composite plate. It can also reduce the amount of Ti and Nb added, reducing the alloy cost. Based on this, the Al content in the base layer composition described in this invention is controlled at 0.015-0.03%.

[0044] Ti: At high temperatures, Ti forms stable TiN or Ti(N,C), which acts to solidify C and N, preventing interstitial C and N atoms in the carbon steel base layer from diffusing to the interface. Hard TiN or Ti(N,C) precipitates at the interface transition layer, resulting in a composite plate with high interfacial shear strength. Simultaneously, during heating, TiN hinders austenite growth, refining austenite grains and improving the matrix strength and toughness. In subsequent welding, especially in the heat-affected zone (HAZ) close to the weld melt boundary, austenite grain growth is suppressed, thereby improving the toughness of the weld HAZ and meeting the needs of high welding heat input processes. To improve the strength of the low-carbon matrix and reduce the diffusion of C and N to the interface, a composite plate with high interfacial shear strength is obtained. Based on this, the Ti content in the base layer composition of this invention is controlled at 0.008–0.011%.

[0045] Nb exists in steel in the form of solid-solution Nb and Nb(C,N), playing a role in solid-solution dragging and precipitation pinning during recrystallization. Adding a small amount of Nb to the base carbon steel is mainly to increase the recrystallization temperature, resulting in grain refinement after rolling in both the recrystallized and non-recrystallized regions, which is beneficial for improving the low-temperature impact toughness of the base carbon steel. Due to the effect of the Nb(C,N) precipitates, the original austenite grains become finer, thereby promoting the formation of even finer recrystallized grains and achieving an ideal combination of high strength and high toughness. Simultaneously, Nb can fix interstitial C and N atoms in the matrix, reducing the diffusion of C and N to the interface, resulting in a composite plate with high interfacial shear strength. Based on this, the Nb content in the base layer described in this invention is controlled at 0.02–0.035%.

[0046] Ni: Ni is an austenite-stabilizing element that can improve the hardenability of the base carbon steel, enabling composite plates with a thickness of 60-100mm to achieve a full bainitic structure, and significantly improving the low-temperature impact toughness and plasticity of the steel. Simultaneously, Ni can effectively inhibit the diffusion rate of Ti into the base carbon steel, which is beneficial for controlling the thickness of the interfacial transition layer. When used in combination with Cr and Mo, it improves the corrosion resistance of the base carbon steel. However, nickel is expensive, and excessive addition will increase the cost of the composite plate. Therefore, an appropriate amount of Ni is added to the base composition described in this invention, with the Ni content controlled at 0.01-0.07%.

[0047] Cr: Cr is a strong carbide-forming element with a low diffusion rate in austenite, while also hindering the diffusion of C. During low-temperature processes, it forms fine carbides, playing a role in precipitation strengthening. Simultaneously, it can fix interstitial C and N atoms in the matrix, reducing the diffusion of C and N to the interface, resulting in a composite plate with high interfacial shear strength. While Cr increases the matrix strength in steel, it reduces toughness. To achieve the optimal balance between strength and toughness, the Cr content in the base layer composition described in this invention is controlled at 0.1–0.15%.

[0048] V: V is a strong carbonitride forming element. When added to steel in combination with Ti and Nb, it can form fine, complex carbonitrides with a wider precipitation temperature range. This effectively inhibits austenite grain growth and recrystallization, improving the strength and toughness of the base carbon steel. Simultaneously, V carbonitrides have a relatively low precipitation temperature, effectively inhibiting ferrite grain growth during phase transformation and strengthening the ferrite matrix. Therefore, an appropriate amount of V is added to the base steel composition described in this invention, with the V content controlled at 0.002–0.004%.

[0049] S and P are both unavoidable impurity elements, and their content should be as low as possible. Considering the actual steelmaking level of steel plants, the content of S and P in this invention is controlled as follows: S: 0.0005~0.010%; P: 0.0005~0.003%.

[0050] As a preferred option, the chemical composition of the base layer should comprehensively control carbide-forming elements such as Cr, Ti, Nb, and V, with the total addition exceeding 2.8 times the C content. This ensures that the C in the base layer is fully fixed, reducing the chance of diffusion to the bonding interface, preventing the formation of large-sized carbides near the interface, and improving the interfacial bonding strength. Simultaneously, to guarantee the base layer strength, a certain amount of the aforementioned alloys should be dissolved in the matrix. During heating and rolling, this alloys act as a solid solution dragging agent, hindering grain growth, refining austenite grains, and improving the strength and toughness of the matrix. However, excessively high alloy content will significantly increase the carbon equivalent of the base layer, which is detrimental to the weldability of the material. Therefore, its total upper limit should be restricted.

[0051] The chemical composition of the base layer also satisfies the following relationship:

[0052] 2.8C%≤(Ti+Nb+V+Cr)%≤0.2%.

[0053] The corrosion-resistant layer of the present invention is based on 316L, with increased Si and N content and added Cu element, to further improve the coating's resistance to marine atmospheric corrosion.

[0054] Si: In the corrosion-resistant layer described in this invention, Si can promote the formation of the passivation film and stabilize its function. In the presence of Cl... - The medium does not form easily soluble products, maintaining the continuity of the passivation film and improving the pitting corrosion resistance of the corrosion-resistant layer. However, Si is a ferritic element, and increasing the Si content will increase the high-temperature ferrite content in the austenitic matrix. High-temperature ferrite is prone to decompose into brittle phases such as σ and χ, which will reduce the steel plate's resistance to intergranular corrosion and toughness. Therefore, the Si content should not be too high, and the mass percentage of Si should be controlled between 0.2% and 1.5%.

[0055] Nitrogen (N): In the corrosion-resistant layer described in this invention, nitrogen (N) is a very strong element for forming, stabilizing, and expanding the austenite region. N can combine with alloying elements such as Cr and Mo to form stable nitrides. These nitrides can form a dense protective film on the stainless steel surface, effectively preventing corrosion and contributing to improved passivation film stability, making it denser and more stable, thus enhancing the corrosion-resistant layer's resistance to pitting and intergranular corrosion. Simultaneously, it can counteract the effect of high Si promoting high-temperature ferrite formation, balancing the austenite / ferrite stabilizing element content and determining the phase composition in equilibrium. However, when the N content in the steel is too high, it increases the risk of N-containing intermetallic phase formation, while also increasing the difficulty of smelting and hot working, leading to production difficulties. Therefore, in the corrosion-resistant layer described in this invention, the mass percentage of N is controlled between 0.02% and 0.15%.

[0056] Cu: In the corrosion-resistant layer shown in this invention, Cu is a ferritic element that can improve the strength and hardness of the corrosion-resistant layer, as well as its tensile strength and ductility. Simultaneously, Cu improves the chemical properties of the alloy composition, increasing the local pitting on the stainless steel surface, making it more anodic, thus enhancing the corrosion resistance of the layer, particularly its inhibitory effect on chloride ion corrosion. The presence of Cu promotes the oxidation reaction, forming a dense oxide film and improving its stability, thereby enhancing the corrosion-resistant layer's resistance to pitting and intergranular corrosion. However, excessive Cu content will reduce impact resistance and weldability; therefore, the mass percentage of Cu is controlled between 0.02% and 0.1%.

[0057] Preferably, the chemical composition of the corrosion-resistant layer of the present invention also satisfies the following relationship:

[0058]

[0059] Since Cr, Mo, Si, and Cu are all ferrite stabilizing elements, while Ni, C, N, and Mn are all austenite stabilizing elements, the ratio of these two elements can be controlled using the above formula to achieve the goal of keeping high-temperature ferrite at 2%, thereby improving the corrosion-resistant layer's resistance to intergranular corrosion.

[0060] Preferably, the chemical composition of the corrosion-resistant layer needs to meet the following requirements:

[0061] PREN≥23.0%, PREN=Cr%+3.3×Mo%+16×N%.

[0062] The method for manufacturing the 345MPa grade marine atmospheric corrosion resistant hot-rolled steel plate for building structures according to the present invention includes the following steps:

[0063] 1) Smelting and casting

[0064] The above-mentioned base layer and corrosion-resistant layer components are smelted and cast into billets respectively;

[0065] 2) Billet assembly

[0066] The base layer and corrosion-resistant layer blanks are ground and polished to remove surface oxide scale and oil stains, and the blanks are welded and sealed around the perimeter to form a composite blank; the joint surfaces after welding and sealing are vacuumed.

[0067] 3) Heating

[0068] The composite blank is heated to 1150-1250℃, and the heating rate is controlled within 10℃ / min.

[0069] 4) Rolling

[0070] The reduction rate per pass is controlled at 5% to 20%, the reduction rate of the first two passes is controlled at 5% to 10%, the cumulative reduction rate is ≥70%, and the final rolling temperature is controlled at 850 to 950℃.

[0071] 5) Cooling

[0072] After rolling, the material is cooled by water at a rate of 10–20℃ / s, with a final cooling temperature of 600–700℃.

[0073] In the manufacturing method described in this invention:

[0074] 1) Smelting: P and S elements can worsen the fracture toughness of steel, so low P and low S control is necessary during the smelting process to improve billet quality. Adopting clean steel production technology reduces the content of gases and inclusions in steel, improving the overall performance of the steel, especially its resistance to lamellar tearing.

[0075] 2) Billet assembly: The carbon steel billets for the corrosion-resistant layer and base layer are pretreated to remove surface oxide scale and oil stains to prevent the introduction of impurities that may affect bonding. The bonding surfaces of the steel billets are then sealed by welding around the perimeter, and the welded and sealed surfaces are subjected to vacuum treatment. Vacuum treatment protects the surface of the corrosion-resistant layer from oxidation and is also an important condition for ensuring the corrosion-resistant layer's resistance to corrosion from splash zones.

[0076] 3) Heating: For single carbon steel, the slab heating temperature is generally controlled between 1120 and 1200℃. However, for the corrosion-resistant steel plate of this invention, it is necessary to consider both the control of the high-temperature ferrite content in the cladding and the interfacial bonding. The slab heating temperature is controlled between 1150 and 1250℃, which is conducive to the dissolution and full diffusion of precipitates in the base layer and cladding steel, promotes the homogenization of elements in the slab, and gives full play to the strengthening effect of microalloying elements in the steel. In particular, the corrosion-resistant layer is at the complete austenitization temperature in this temperature range, which promotes the full diffusion of elements and can effectively control the formation of high-temperature ferrite. At the same time, high-temperature heating accelerates element diffusion and promotes the realization of 100% metallurgical bonding at the interface. However, the higher heating temperature will increase the tendency of the austenite grains in the base layer to be coarse, which increases the difficulty of subsequent controlled rolling. Most importantly, it will accelerate the diffusion of C and N to the interface. If large-sized carbides are formed at the interface, it will deteriorate the interfacial shear strength. The long-distance diffusion of C will also affect the corrosion resistance of the corrosion-resistant layer. However, excessively rapid heating rates can increase the risk of weld cracking, leading to vacuum failure and preventing bonding. Therefore, the heating rate should not be too fast. Preferably, the heating temperature is set between 1150 and 1250°C, and the heating rate is controlled within 10°C / min.

[0077] 4) Rolling: High reduction rate is applied in the high temperature zone to allow the microstructure to recrystallize fully, resulting in finer grains and improved strength and toughness of the base material; at the same time, the metal atoms at the interface are subjected to sufficient compressive stress, forming interpenetration through diffusion, enabling the interface to achieve interatomic bonding. The reduction rate per pass is maintained at 5%–20%, with a cumulative reduction rate ≥70%. The reduction rate of the first two passes is controlled at 5%–10%. Due to the difference in the deformation difficulty between the base layer and the corrosion-resistant layer, an excessive reduction rate before complete bonding is achieved will cause a large difference in the elongation of the two layers, resulting in misalignment at the interface, which is not conducive to the bonding of the two layers. A small reduction rate is used to achieve the initial bonding of the two layers. Controlled rolling is carried out in the non-recrystallization zone. At this stage, austenite recrystallization no longer occurs. By using a reasonable reduction rate and final rolling temperature, deformation energy and deformation dislocations are accumulated, forming a high-density deformation band inside the austenite grains, increasing the phase deformation nuclei, further refining the equivalent size of the matrix grains after phase transformation, and improving the strength and toughness of the base material. At the same time, deformation induces the precipitation of carbonitrides of Nb, Ti, and Cr at this stage, improving the strength of the base layer, inhibiting the diffusion of C to the interface, and avoiding the formation of large-sized carbides at the interface, which would degrade the interfacial shear strength. Excessively high final rolling temperature will cause coarse austenite grains in the corrosion-resistant layer, while excessively low final rolling temperature will cause a large amount of carbide-based precipitates to be formed in the stainless steel in a short period of time, which will worsen the intergranular corrosion resistance of the corrosion-resistant layer. At the same time, in order to obtain a ferrite + pearlite and / or a small amount of bainite structure and achieve a balance between the strength and toughness of the base layer, the final rolling temperature is preferably controlled at 850-950℃.

[0078] 5) Cooling: By controlling the initial cooling, final cooling, and cooling rate, the type and size of the microstructure after rolling of the base layer can be controlled, as well as the precipitation within the corrosion-resistant layer and the high-temperature ferrite decomposition of the corrosion-resistant layer can be suppressed. This allows for rapid passage through the sensitization zone, ensuring the corrosion resistance of the coating. However, excessively rapid cooling will lead to the formation of martensite in the base layer. Since martensite has low toughness and a high yield strength ratio, it is detrimental to the performance of the steel plate. Excessively slow cooling will result in the formation of a large amount of coarse ferrite, which promotes crack propagation and reduces impact performance. Therefore, the cooling rate should be reasonably controlled. Controlling the final rolling temperature can achieve rapid cooling to the phase transformation temperature after rolling, further suppressing microstructure growth, improving material strength and low-temperature impact toughness by refining the grains, and further promoting the bonding of the composite interface through phase transformation. Preferably, water cooling is used, with the cooling rate controlled at 10-20℃ / s and the final cooling temperature controlled at 600-700℃. This promotes the precipitation of fine V(C / N) particles, improves the matrix strength, and further ensures that the base layer has a low yield strength ratio and good low-temperature impact toughness.

[0079] Preferably, if the corrosion-resistant layer is too thick, it will affect the mechanical properties of the material and the production cost; while if the corrosion-resistant layer is too thin, it will reduce the corrosion resistance and service life of the material. Therefore, the thickness of the corrosion-resistant layer of the rolled steel plate accounts for 0.5% to 15% of the total thickness of the steel plate.

[0080] This invention combines a corrosion-resistant layer with a base layer, and through composition design and thickness ratio design, forms a corrosion-resistant layer on the surface of the base layer, i.e., carbon steel plate, which is resistant to corrosion in the marine atmosphere through a rolling process. The final product is a steel plate that combines resistance to marine atmospheric corrosion, good mechanical properties, and high economic efficiency. The steel plate can then be processed into structural components that can be used in steel structural components for use in environments with splashing waves.

[0081] Compared with the prior art, the present invention has the following beneficial effects:

[0082] The base layer of this invention adopts a low-carbon micro-alloying composition design, and the corrosion-resistant layer adopts an increased content of Si and N elements and the addition of Cu elements. Under a reasonable rolling process, an excellent combination of stainless steel and carbon steel is achieved. The thickness of the interface transition layer is controlled to obtain a high-strength structural steel plate that meets the requirements of marine environments, and has excellent resistance to marine atmospheric corrosion and mechanical properties.

[0083] Furthermore, the base layer of this invention avoids the formation of large-sized carbides at the interface by reducing carbon content, and effectively controls the thickness and grain size of the interface transition layer, thereby improving the interfacial shear strength and toughness. Simultaneously, the addition of microalloying elements, combined with a reasonable rolling and cooling process, solves the problem of low material strength under low-carbon conditions; its yield strength ≥345MPa, tensile strength ≥490MPa, yield-to-tensile ratio ≤0.75, and impact energy KV2 ≥190J at -40℃ are all higher than the performance requirements in the national standard GB / T 19879-2015 "Steel Plates for Building Structures".

[0084] Chinese patent CN106756476A discloses a high-strength weathering steel for use in high-humidity and hot marine atmospheric environments and its preparation method. The solution is mainly to reduce the corrosion of steel plates in humid and hot marine atmospheric environments by adding trace elements such as Sn, Sb, Nb, and Re to replace the amount of Cr added. The corrosion rate was reduced by about 30% after 96 hours when compared with traditional carbon structural steel and weathering steel in a immersion corrosion test.

[0085] Chinese patent CN111621699A discloses a corrosion-resistant low-alloy steel for bridge structures in high-humidity and hot marine atmospheric environments and its preparation method. The solution involves rationally adjusting the content of alloying elements Cu, Ni, and Mo based on the Cu-Ni-Mo low-alloy steel system, taking into account the economic advantages of low-alloy steel, to obtain a corrosion-resistant low-alloy steel with a ferrite-pearlite microstructure. Its advantages lie in that, while appropriately controlling the high costs associated with alloying elements Ni and Mo, the corrosion-resistant steel of this invention combines a certain degree of economy with good corrosion resistance. Its corrosion resistance is significantly superior to that of ordinary carbon steel, and it meets the mechanical performance requirements for bridge structural steel in high-humidity and hot marine atmospheric environments.

[0086] The two patents above mainly improve the overall corrosion resistance of steel by adding corrosion-resistant microalloying elements or increasing the content of corrosion-resistant elements Cr, Ni and Mo. Compared with ordinary carbon steel or weathering steel, the corrosion resistance can be improved by about 30%. The structural steel of this invention, while ensuring the mechanical properties of the matrix, has 10-20 times the corrosion resistance of ordinary carbon steel or weathering steel.

[0087] Chinese patent CN112647014A selectively includes one or both of the following in its chemical composition: Sn: 0.01%–0.02%, V: 0.05%–0.1%. It also incorporates significant amounts of low-melting-point elements such as P, Sb, and Ce, affecting the steel's low-temperature toughness, weldability, and cold formability; its impact energy at -20℃ is only 47J. This invention does not contain these low-melting-point elements, making it easier to smelt and resulting in better formability. Furthermore, its impact energy at -40℃ is ≥190J.

[0088] Chinese patent CN108004488A contains a high amount of precious metal alloys such as Ni, Cr, Mo, and Cu in its chemical composition, resulting in high costs. Sb segregation is prone to occur, increasing the difficulty of the smelting process. Furthermore, the addition of a large amount of Si is detrimental to surface quality and affects the weldability of the steel plate. The rolled steel plate requires tempering for performance adjustment. This invention only adds necessary elements to the corrosion-resistant layer and allows for control of the corrosion-resistant layer thickness to meet corrosion life requirements. Moreover, the rolled steel plate does not require a tempering process to adjust its performance.

[0089] Chinese patent application CN202210570630.7 applies to the production of steel with a thickness ≤60mm, resistant to marine atmospheric corrosion, with a yield strength ≥500MPa and a tensile strength ≥540MPa. The 500MPa weathering steel produced by this invention has a complex process requiring tempering heat treatment, increasing manufacturing costs, and does not describe the corrosion resistance of the steel plate. This invention, due to necessary compositional design at the base layer, can produce steel with a thickness up to 100mm. Furthermore, due to the lower alloy content, costs are reduced, and performance improvement is not achieved through tempering. Moreover, the corrosion resistance is more clearly defined compared to the prior art.

[0090] Chinese patent application CN201810908224.0, through composition design, inclusion control, controlled rolling, and controlled cooling and heat treatment, can be used to manufacture various bridges for marine and atmospheric environments, with steel thicknesses ranging from 10 to 40 mm and a yield strength ratio ≤0.86. This invention requires applying an anti-oxidation coating to the slab during heating and undergoing tempering, and the addition of alloying elements such as Cu and Ni increases manufacturing costs and smelting difficulty. This invention achieves corrosion resistance and mechanical properties in the corrosion-resistant layer and base layer respectively, better balancing these two properties. Furthermore, the base layer contains less alloying material, eliminating the need for anti-oxidation coating and tempering, thus reducing production costs. It can also produce steel up to 100 mm thick with a yield strength ratio ≤0.75, making it applicable to a wider range of scenarios compared to the contrasting patent.

[0091] By combining the corrosion-resistant layer and the base layer into a single billet and applying appropriate heating, rolling, and cooling processes, steel plates for steel structures can be obtained that possess resistance to marine atmospheric corrosion, good mechanical properties, and high economic efficiency. These plates exhibit a yield strength ≥345MPa, tensile strength ≥490MPa, yield-to-tensile ratio ≤0.75, and impact energy (KV2) ≥190J at -40℃. The annual average marine atmospheric salt spray concentration is 0.0189~0.1581mg / m³. 3 The average annual relative humidity is 30-80%, and the average annual total solar radiation is 3298.02-7350.13 MJ / m². 2 Under the given environment, the average corrosion rate is ≤0.004mm / a; at the same time, the formation of an interface transition layer with a thickness of ≤10μm is achieved by controlling the full diffusion of elements in the base layer and the corrosion-resistant layer. This layer has fine grains with an average grain size of ≤0.5μm, good deformation coordination ability, and ensures an interface shear strength of ≥270MPa.

[0092] In summary, the 345MPa-grade hot-rolled steel plate for building structures with marine atmospheric corrosion resistance described in this invention can solve the inherent pain points of stainless steel or carbon steel used in marine atmospheric environments. This 345MPa-grade hot-rolled steel plate can be equivalently applied to the manufacture of steel structural components used in marine atmospheric environments, such as those for facilities like harbor terminals and offshore oil platforms. It can meet the requirements of these components for corrosion resistance and mechanical properties in marine atmospheric environments, significantly improving their applicability, safety, and durability, and thus providing substantial economic and social benefits. Attached Figure Description

[0093] Figure 1 This is a schematic diagram of an interlayer structure of the 345MPa grade hot-rolled steel plate for building structures resistant to marine atmospheric corrosion described in this invention.

[0094] Figure 2This is a schematic diagram of another interlayer structure of the hot-rolled steel plate for building structures with a 345MPa grade resistant to marine atmospheric corrosion described in this invention.

[0095] Figure 3 This is a microstructure photograph of the corrosion-resistant layer in Embodiment 3 of the present invention.

[0096] Figure 4 This is a scanned image of the interface transition layer where the base layer and the corrosion-resistant layer are combined, as shown in Embodiment 3 of the present invention.

[0097] Figure 5 This is a photograph of the basic microstructure of Embodiment 3 of the present invention. Detailed Implementation

[0098] The technical solution of the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. It should be understood that the following embodiments are only used to describe specific implementations of the present invention and do not constitute any limitation on the scope of protection of the present invention.

[0099] See Figure 1 , Figure 2 The diagram shows two interlayer structures of the hot-rolled steel plate for building structures according to the present invention, wherein 1 is the base layer, 2 is the corrosion-resistant layer, and 3 is the interface transition layer.

[0100] The composition of the base layer of the hot-rolled steel plate (composite steel plate) for building structures described in this invention is shown in Tables 1 and 2, with the balance being Fe and unavoidable impurities. Table 3 shows the manufacturing process parameters of the composite steel plate embodiments of this invention. Table 4 shows the metallographic structure and mechanical properties of the base layer and corrosion-resistant layer, and the thickness of the interface transition layer in the composite steel plates of the embodiments and comparative examples.

[0101] The yield strength and tensile strength of the composite steel plate were measured in accordance with GB / T 6396-2008 "Mechanical and Technological Properties of Composite Steel Plates" and GB / T 228-2010 "Metallic Materials - Tensile Testing at Room Temperature".

[0102] The impact energy KV2 / J (longitudinal) of the base carbon steel at -40℃ was measured in accordance with GB / T 6396-2008 "Mechanical and Technological Properties of Composite Steel Plates" and GB / T 229-2020 "Charpy Pendulum Impact Test Method for Metallic Materials".

[0103] Grain size rating is performed as follows: according to GB / T 6394-2017 "Method for determination of average grain size of metals", the intercept point method is used to rate the grain size of ferrite structure in stainless steel and carbon steel respectively.

[0104] The comparative examples were prepared using essentially the same steps as those in the embodiments of the present invention, except that the composition of the base carbon steel and certain process parameters used during the rolling or cooling steps did not meet the requirements of the present invention.

[0105] The metallographic structure of the corrosion-resistant layer in Example 3 is shown below. Figure 3 The image shows equiaxed or slightly elongated recrystallized austenite.

[0106] See the interface transition layer in Example 3. Figure 4 The interface transition layer has a thickness of 4.3 μm and fine grains.

[0107] See the base metallographic structure of Example 3. Figure 5 The microstructure of the base carbon steel is ferrite + pearlite and / or a small amount of bainite, with a pearlite content ≥5% and an average grain size ≥8.5.

[0108] Table 5 shows the corrosion of the composite steel plate samples from Examples 1-8 and Comparative Examples 1-8 after 6 months in the atmospheric environment of the South China Sea. The observations show that, in Comparative Examples 4, 6, 7, and 8, due to their composition or rolling processes not being within the scope of the invention, the corrosion rate was ≥0.004 mm / a under high chloride ion concentrations.

[0109] Comparative Examples 1-8, due to the use of unsuitable composition design requirements and heat treatment process conditions, resulted in certain properties of the composite steel plates failing to meet usage requirements (performance parameters are not within the scope defined by the invention). Among them:

[0110] Comparative Example 1 shows that due to the base layer (Ti+Nb+V+Cr)% being less than 2.8C, the carbon fixation capacity is insufficient. At the same time, the final cooling temperature is too high, resulting in a lower pearlite content in the steel plate structure, poorer toughness, and lower impact energy.

[0111] Comparative Example 2 showed that because the Mn content in the base layer exceeded the design range and the cooling rate was too fast, martensite appeared in the microstructure, resulting in a high yield strength ratio.

[0112] In Comparative Example 3, the yield strength of the base layer does not meet the requirements because the Nb content exceeds the design range.

[0113] Comparative Example 4, due to the Cu content in the corrosion-resistant layer exceeding the design range, exhibited a corrosion rate ≥0.004 mm / a under high chloride ion concentration. Furthermore, because the pass reduction rate and final rolling temperature were outside the ranges specified in this invention, the grain refinement was insufficient, and the excessively high final rolling temperature resulted in a rapid interfacial diffusion rate. Consequently, its yield strength did not meet the requirements.

[0114] In Comparative Example 5, the tensile strength and yield strength ratio of the substrate Si exceeded the design range, which did not meet the requirements. At the same time, the interfacial shear strength did not meet the requirements due to the excessively rapid heating rate.

[0115] In Comparative Example 6, the ratio of ferrite stabilizing elements to austenite stabilizing elements in the corrosion-resistant layer was greater than 1.5, the high-temperature ferrite in the corrosion-resistant layer exceeded the range, and the cumulative reduction rate of the steel plate was insufficient, resulting in an excessively thick interfacial transition layer and insufficient interfacial shear strength.

[0116] Comparative Example 7, due to the corrosion-resistant layer PREN being less than 23 and the heating temperature being outside the specified range, resulted in the high-temperature ferrite content inside the steel plate exceeding the range, and the corrosion rate was ≥0.004 mm / a under high chloride ion concentration.

[0117] In Comparative Example 8, due to the low final rolling temperature, carbide precipitates appeared at the grain boundaries of the steel plate, which affected the steel plate's resistance to intergranular corrosion. Under high chloride ion concentration, the corrosion rate was ≥0.004 mm / a.

[0118] Through the manufacturing method of this invention, especially the control of heating, rolling and cooling processes, the base layer in the steel plate exhibits excellent yield strength ratio and low-temperature impact toughness, while the coating has excellent corrosion resistance and high bonding strength. Its yield strength is ≥345MPa, tensile strength is ≥490MPa, yield strength ratio is ≤0.75, impact energy at -40℃ KV2 is ≥190J, marine atmospheric corrosion rate is ≤0.004mm / a, and interfacial shear strength is greater than 270MPa.

[0119] It should be noted that all technical features described in this invention can be freely combined or integrated in any manner, unless they contradict each other. Various modifications and variations can be made to this invention without departing from its scope, as will be apparent to those skilled in the art. For example, features shown or described as part of one embodiment can be used with another embodiment to produce yet another embodiment. Therefore, this invention is intended to cover these modifications that fall within the scope of the appended claims and their equivalents.

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Claims

1. 345MPa grade hot-rolled steel plate for building structures resistant to marine atmospheric corrosion, including base layer, corrosion-resistant layer and interface transition layer between base layer and corrosion-resistant layer; The chemical composition of the base layer, by mass percentage, is as follows: C 0.03–0.06%, Si 0.15–0.2%, Mn 1–1.3%, P 0.0005–0.003%, S 0.0005–0.01%, Cr 0.1–0.15%, Ni 0.01–0.07%, Al 0.015–0.03%, Ti 0.008–0.011%, Nb 0.02–0.035%, V 0.002–0.004%, with the balance including Fe and other unavoidable impurities. The chemical composition of the corrosion-resistant layer by mass percentage is as follows: C 0.001–0.03%, Si 0.2–1.5%, Mn 1.0–2.0%, P 0.005–0.03%, S 0.005–0.03%, Cr 16–18%, Ni 10–14%, Cu 0.02–0.1%, N 0.02–0.15%, Mo 2–3%, with the balance including Fe and other unavoidable impurities; The microstructure of the corrosion-resistant layer is equiaxed recrystallized austenite or elongated non-recrystallized austenite and trace amounts of high-temperature ferrite, with the high-temperature ferrite content in the thickness direction ≤2%. The interface transition layer achieves 100% metallurgical bonding, with atomically coherent structure, a thickness of ≤10μm, fine grains with an average grain size of ≤0.5μm, and an interfacial shear strength of ≥270MPa. The hot-rolled steel plates used in the building structure have a yield strength ≥345MPa, tensile strength ≥490MPa, yield-to-tensile ratio ≤0.75, impact energy KV2 ≥190J at -40℃, and resistance to marine atmospheric corrosion rate ≤0.004mm / a.

2. The hot-rolled steel plate for building structures as described in claim 1, characterized in that, The chemical composition of the base layer also satisfies the following relationship: 2.8C%≤(Ti+Nb+V+Cr)%≤0.2%.

3. The hot-rolled steel plate for building structures as described in claim 1 or 2, characterized in that, The chemical composition of the corrosion-resistant layer also satisfies the following relationship:

4. The hot-rolled steel plate for building structures as described in claim 1, 2, or 3, characterized in that, The chemical composition of the corrosion-resistant layer also satisfies the following relationship: PREN≥23.0%, PREN=Cr%+3.3×Mo%+16×N%.

5. The hot-rolled steel plate for building structures as described in claim 1, 2, 3, or 4, characterized in that, The base layer and corrosion-resistant layer contain Fe and other unavoidable impurities in their composition.

6. The hot-rolled steel plate for building structures as described in claim 1, 2, 3, 4, or 5, characterized in that, The microstructure of the base layer is ferrite + pearlite, or ferrite + pearlite + a small amount of bainite; the pearlite content is ≥5%.

7. The hot-rolled steel plate for building structures as described in any one of claims 1 to 6, characterized in that, The thickness of the hot-rolled steel plate used in the building structure is 10-100mm.

8. The hot-rolled steel plate for building structures as described in any one of claims 1 to 7, characterized in that, The thickness of the corrosion-resistant layer of the hot-rolled steel plate used in the building structure accounts for 0.5% to 15% of the total thickness of the steel plate.

9. The method for manufacturing 345MPa grade marine atmospheric corrosion resistant hot-rolled steel plate for building structures as described in any one of claims 1 to 8, characterized in that, Includes the following steps: 1) Smelting and casting The components of the base layer and the corrosion-resistant layer as described in claim 1, 2, 3, 4 or 5 are respectively smelted and cast into billets; 2) Billet assembly The base layer and corrosion-resistant layer blanks are ground and polished to remove surface oxide scale and oil stains, and the blanks are welded and sealed around the perimeter to form a composite blank; the joint surfaces after welding and sealing are vacuumed. 3) Heating The composite blank is heated to 1150-1250℃, and the heating rate is controlled within 10℃ / min. 4) Rolling The reduction rate per pass is controlled at 5% to 20%, the reduction rate of the first two passes is controlled at 5% to 10%, the cumulative reduction rate is ≥70%, and the final rolling temperature is controlled at 850 to 950℃. 5) Cooling After rolling, the material is cooled by water at a rate of 10–20℃ / s, with a final cooling temperature of 600–700℃.

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