Hot-rolled steel sheet for building structures with a 345 MPa rating resistant to corrosion in areas affected by ocean waves and its manufacturing method.

Abstract

The present invention provides a hot-rolled steel sheet for building structures, comprising a base layer, a corrosion-resistant layer, and an interfacial transition layer located between the base layer and the corrosion-resistant layer. The hot-rolled steel sheet of the present invention has a yield strength of ≥350 MPa, a tensile strength of ≥490 MPa, a yield-to-tensile ratio of 0.71 to 0.80, an impact energy of ≥190 J at -40°C, a corrosion resistance rate of ≤0.006 mm / year from sea spray, an interfacial transition layer thickness of ≤10 μm, and an interfacial shear strength of ≥252 MPa, and can be used to manufacture structural components suitable for sea spray environments. The present invention also provides a method for manufacturing the hot-rolled steel sheet.

Description

Technical Field

[0001] The present invention relates to steel for building structures, particularly to hot-rolled steel sheets for building structures resistant to corrosion in splash zones of sea waves, and to a method for manufacturing the same.

Background Art

[0002] Background The ocean is an extremely harsh and complex corrosion environment. Seawater is a strong electrolyte solution containing a high concentration of chloride ions. Steel facilities, which serve as the main structures of ocean engineering equipment, are highly susceptible to the influence of electrochemical reactions with the surrounding medium, leading to severe corrosion that significantly reduces the service life of these facilities. In particular, in the splash zone, which is the most corrosive area of the ocean environment, various facilities are subjected to a series of external factors such as alternating dry and wet conditions, seawater spray, sunlight, corrosive components in the atmosphere, and oxygen, resulting in particularly severe material corrosion.

[0003] Investigations show that the corrosion of steel piles in facilities such as seaport terminals and offshore oil platforms is severe in the splash zone and is generally 3 to 10 times more severe than in the fully immersed zone. Once severe local corrosion damage occurs in this area, the supporting force of the entire facility is greatly reduced, its service life is shortened, the safety of production is affected, and it may even lead to premature abandonment measures for the facility.

[0004] Because wave spray zones are located in areas with abundant oxygen supply and alternating wet-dry conditions, the resulting corrosion products offer no protective effect to the steel substrate. Since seawater spray can directly impact the metal surface, corrosion is severe. Corrosion tests and investigations show that under typical conditions, the average corrosion rate of ordinary carbon steel and low-alloy steel in the marine atmosphere is approximately 0.03–0.08 mm / year, while the average corrosion rate of these steels in wave spray zones is approximately 0.3–0.5 mm / year. In wave spray zones, steel is highly prone to severe corrosion damage, which significantly reduces the load-bearing capacity of the overall steel structure, impacts safety in production, shortens service life, and leads to premature decommissioning.

[0005] Based on the aforementioned working conditions, industrial-grade pure titanium is selected as the corrosion-resistant layer. Titanium exhibits high chemical activity and readily reacts with oxygen in the air to form oxides. The oxides on the titanium metal surface are dense, stable, and possess strong "self-healing" capabilities. The "self-healing" capability of titanium oxide primarily refers to the rapid formation of a new titanium oxide layer in any damaged area on the titanium surface, preventing further contact between the corrosive medium and the titanium.

[0006] Steel used in marine building structures must, in addition to meeting corrosion resistance requirements, also possess good mechanical properties. Among these, the yield-to-tensile ratio and low-temperature impact toughness have gradually become important indicators for building steel. The yield-to-tensile ratio is the ratio of the yield strength of steel to its tensile strength, and its value reflects the steel's ability to avoid strain concentration during plastic deformation. A lower yield-to-tensile ratio indicates that the plastic deformation of the steel can be distributed more uniformly over a wider area. In steel structures made of steel with a low yield-to-tensile ratio, plastic deformation under seismic forces can be distributed more evenly over a wider area. In contrast, materials with a high yield-to-tensile ratio may experience strain concentration, reducing the steel's overall plastic deformation capacity, which can lead to brittle fracture of the structure, resulting in structural failure and sudden collapse. In low-temperature environments, steel undergoes a brittle transition, where its fracture mode shifts from ductile fracture to brittle fracture. The engineering significance lies in ensuring that components do not experience brittle fracture when steel is used at temperatures above this transition point. Therefore, structural steels often need to be tuned in terms of low-temperature impact properties depending on their service environment. Ocean temperatures vary significantly across different latitudes. For example, in the Bohai Bay region of China, coastal temperatures can drop below -20°C in winter. In such cases, building materials are required to meet impact performance requirements at -40°C to prevent brittle fracture. If the increase in tensile strength is limited while increasing plasticity and toughness, the yield-to-tensile ratio will increase significantly, making it difficult to achieve a low yield-to-tensile ratio.

[0007] Chinese patent application CN201210260231.7 discloses a method for manufacturing a titanium-steel-titanium double-sided clad plate. The method involves stacking four titanium plates and three steel plates in a specific order within a sealed frame formed by welding two outermost steel plates. A separator, prepared by mixing 1 part by weight of activated α-Al2O3 and 1.5 parts by weight of a 4% polyvinyl alcohol aqueous solution, is added between the titanium plates. A nickel-based alloy is used as a transition layer between the titanium and steel plates. The assembly is heated to 500-630°C under vacuum and held at a vacuum of 20-200 Pa for 1-2 hours. A feature of this method is that welding is performed first after slab assembly, followed by vacuum pumping. Conventional arc welding and submerged arc welding are sufficient for the welding process. Compared to vacuum welding, these methods reduce welding requirements, lower costs, and eliminate the need for additional vacuum chamber construction. The clad slab is then rolled and coated in a conventional heating furnace at a rolling temperature of 700-900°C. The outermost steel sheet is sealed and welded, and a vacuum is applied to block carbon (C) from the gas. Simultaneously, a nickel-based alloy isolation layer prevents the formation of interfacial TiC, resulting in a titanium-steel clad sheet with a shear strength of 230-260 MPa and an interfacial bonding rate of 99.6-100%.

[0008] Chinese Patent Application CN201710769999.X discloses a method for manufacturing titanium-steel clad sheets. The method includes selecting surfaces of titanium-steel clad slabs that will come into contact with each other, applying a high-temperature carburizing-resistant and nitriding-resistant isolation coating to the contacting titanium surfaces, and drying them at room temperature. After drying, the titanium slabs are aligned and stacked in pairs with steel slabs placed in between to complete the slab assembly and obtain the clad slab. The individual titanium slabs used have a thickness greater than 2 mm, and the steel slabs have a thickness greater than 5 mm. The outer edges of the clad slabs are then seam-welded, leaving an unwelded strip of a certain size. Vacuum is applied 10°C before welding. -2 ~10 -3To achieve a pressure of Pa, the coating is applied to a slab. The slab is heated to 500-700°C and rolled with a first-pass reduction ratio of over 25%, a final-pass reduction ratio not exceeding 15%, a total reduction ratio of 60-70%, and a rolling speed of 0.1-1.0 mm / s. The coating used in this application provides high-temperature penetration protection to prevent the diffusion and oxidation of other impurity elements at high temperatures, as well as blocking the diffusion of elements such as C and N. In the examples, Q235 and TA1 are combined, and the resulting steel sheets achieve shear strengths of 176 MPa, 181 MPa, and 182 MPa.

[0009] The two applications above avoid the formation of brittle Ti compounds, primarily by introducing an additional nickel-based alloy isolation layer between titanium and carbon steel.

[0010] Chinese Patent Application CN201811327623.4 discloses a titanium-steel-titanium clad sheet and a method for producing the same. The method involves fixing a carbon steel sheet between two titanium sheets of the same size, and then performing hot coating rolling using a non-reversible rolling mill with high rolling force to integrally bond the three layers. After rolling, the clad sheet undergoes heat treatment, including an initial annealing at 500-600°C for 20-60 minutes, and a recrystallization annealing at 680-700°C for 30-120 minutes. The final product is obtained through leveling, planarization, shearing, and forming. This application mainly describes a method for producing clad titanium-steel sheets without hot rolling coating. Due to the use of a non-reversible rolling mill, only single-pass rolling production is feasible, and further heat treatment is required. The examples mainly describe the method for producing the strip, while the performance after coating is not mentioned.

[0011] Chinese Patent Application CN201510543767.3 discloses a method for manufacturing titanium-steel clad sheets that produce titanium-steel clad sheets with high bond strength. The application includes fixing a titanium sheet between two ordinary carbon steel sheets or slabs, welding the outer edges of the slabs in a vacuum environment, and heating the clad slab to 850-900°C for 120-360 minutes with an initial rolling temperature controlled above 800°C and a finish rolling temperature below 700°C, with each pass deformation controlled by 20-30% and a total rolling deformation of ≥90%. This high-reduction rolling process aims to pulverize brittle phase compounds formed at the interface and reduce their impact on the bond surface. The resulting titanium-steel clad sheet achieves a bond strength greater than 240 MPa. However, the application requires a high reduction ratio per pass and large total deformation, which tends to cause edge weld cracks during rolling. This compromises the integrity of the vacuum and is detrimental to interfacial bonding.

[0012] Chinese Patent Application CN201610994234.1 discloses a manufacturing method for titanium-steel clad sheets, relating to an annealing technology for titanium-steel sheets. First, titanium sheets and steel sheets are assembled to form a symmetrical multilayer clad slab having a steel sheet-titanium sheet-separator-titanium sheet-steel sheet structure, which is then coated by rolling or explosive coating. The clad slab is then annealed and pickled, first by heating to 500-750°C to recrystallize the core titanium sheets, and then by heating to 950-1050°C to recrystallize the base steel sheets. The object of this application is to simultaneously enhance the properties of both the clad material and the base material through a two-stage heat treatment. However, the two-stage heat treatment may cause excessive diffusion of titanium, iron, and carbon elements, leading to the formation of brittle intermetallic compounds such as iron-titanium and titanium carbide, which degrades the interfacial shear strength.

[0013] Chinese patent application CN201710996925.X discloses a thin-coated double-sided titanium-steel clad sheet and a method for manufacturing the same. A good bond between titanium and steel is achieved through thick slab assemblies and high reduction rolling technology. The application relates to a double-sided titanium clad sheet comprising a titanium clad layer, a base layer, and another titanium clad layer. The titanium clad material is TA2 having a thickness of 0.2 to 1 mm. The slab is assembled by stacking from top to bottom in the order of cover plate, titanium clad material, carbon steel base, titanium clad material, and cover plate. After vacuum drawing in a vacuum chamber, the surrounding gap is reduced to 1.0 × 10 -2 From 4.5 x 10 -2 The clad slab is sealed by vacuum electron beam welding under a vacuum of Pa. The sealed clad slab is heated to 900-920°C and held for a period calculated as 1 min / mm × the total thickness of the clad slab. The initial rolling temperature is 880-900°C, the finish rolling temperature is 800°C or higher, and the slab is air-cooled to room temperature. The single-pass reduction ratio is ≥15%, the first three passes have a reduction ratio of ≥20%, and the total reduction ratio is ≥80%. The rolled clad plate is trimmed, separated, and surface-finished to obtain a double-sided titanium-steel clad plate. By using surface cleaning of the clad slab, air isolation sealing with cover plates, control of the rolling temperature, and application of high reduction ratios, the titanium-iron and titanium-carbon compounds formed at the clad interface are crushed, refined, and dispersed to improve the distribution of the compounds and further ensure bonding quality and performance stability. The shear strength reaches 241 MPa.

[0014] Chinese Patent Application CN201710983322.6 discloses a thin clad titanium-steel clad sheet and a method for manufacturing the same. It employs a two-layer structure composed of titanium and carbon steel, having a slab assembly and heating process similar to that in Chinese Patent Application CN201710996925.X. The initial rolling temperature is 880-900°C, the single-pass reduction ratio is 25-30%, and the total reduction ratio is ≥85%. While controlling the single-pass reduction ratio and total reduction ratio, the thickness of the titanium-steel clad sheet is limited to 3-16 mm, the finish rolling temperature is 800°C or higher, and the sheet is air-cooled to room temperature. The titanium-steel clad sheet is obtained through surface treatment, and the thickness of the titanium clad is ≤1 mm. This application improves the bonding quality by assembling the slabs symmetrically and sealing the titanium within the carbon steel sheet through welding. The rolled steel sheet has a shear strength of 238 MPa or higher, an interfacial bonding rate of 100%, and the carbon steel layer meets the national standard for Q345 grade carbon steel.

[0015] However, the above application does not mention the detailed elemental composition or microstructure design of the cladding or base layer, but merely describes the tensile properties and shear strength. The cladding layer requires excessively high reduction ratios per pass and total reduction ratio, while not controlling performance indicators such as the corrosion resistance of the material, low-temperature impact performance, and yield-to-tensile ratio of the base material. Therefore, these steels do not meet the requirements for structural steel used in construction.

[0016] In summary, the above application primarily describes a method for manufacturing clad steel sheets, and the specific examples provided only offer a brief explanation of performance aspects such as interfacial shear strength and tensile properties. For structural steel used in ocean spray zones, it is essential to ensure the necessary structural steel performance requirements, such as the aforementioned low yield-to-tensile ratio and corresponding low-temperature impact performance, in addition to corrosion resistance to ocean spray zones, in order to guarantee structural safety. However, the above application does not provide relevant compositional and process designs regarding the corrosion rate of the corrosion-resistant layer, yield-to-tensile ratio, or low-temperature impact performance, and therefore does not ensure that the steel sheets meet the requirements for use as highly corrosion-resistant structural steel in ocean spray zone environments. [Overview of the Initiative]

[0017] overview One of the objectives of the present invention is to provide a 345 MPa class hot-rolled steel sheet for building structures, preferably having a yield strength of ≥350 MPa, a tensile strength of ≥490 MPa, a yield-to-tensile ratio of 0.71 to 0.80, an impact energy of ≥190 J at -40°C, a corrosion resistance rate of ≤0.006 mm / year from sea spray, an interfacial transition layer thickness of ≤10 μm, and an interfacial shear strength of ≥252 MPa. It can meet the corrosion resistance requirements for use in sea spray environments, while also providing good mechanical properties and high economic efficiency against corrosion in sea spray areas, making it suitable for use in steel structural components such as steel piles in facilities such as seaport terminals and offshore oil platforms.

[0018] This invention employs a low-carbon microalloy composition design to achieve excellent bonding between titanium and carbon steel without the need for a metal isolation layer. Meanwhile, by controlling the thickness of the interfacial transition layer, it ensures that the mechanical properties of the base layer (carbon steel) meet the corresponding strength grade requirements without reducing the corrosion resistance of the corrosion-resistant layer itself, while also exhibiting excellent yield-to-tensile ratio and low-temperature impact toughness.

[0019] Specifically, the hot-rolled steel sheet for building structures of the present invention comprises a base layer, a corrosion-resistant layer, and an interfacial transition layer located between the base layer and the corrosion-resistant layer; Here, the base layer contains, in addition to Fe and other unavoidable impurities, the following chemical elements in mass percent: C 0.03-0.10%, Si 0.10-0.30%, Mn 1.00-1.50%, P 0.0005-0.003%, S 0.0005-0.01%, Cr 0.02-0.20%, Ni 0.01-0.10%, Cu 0.002-0.020%, Al 0.015-0.03%, Ti 0.008-0.018%, Nb 0.02-0.065%, and N 0.0005-0.005%; Here, the corrosion-resistant layer is industrial-grade pure titanium, and its composition conforms to the standard GB / T 3620.1-2016 "Specifications and Composition of Titanium and Titanium Alloys".

[0020] Preferably, the hot-rolled steel sheet for building structures has a yield strength of ≥350 MPa, a tensile strength of ≥490 MPa, a yield-to-tensile ratio of 0.71 to 0.80, an impact energy of ≥190 J at -40°C, a corrosion resistance rate of ≤0.006 mm / year from ocean wave spray, a thickness of ≤10 μm of the interfacial transition layer, and an interfacial shear strength of ≥252 MPa.

[0021] During the heating and rolling process, atomic diffusion occurs at the interface between the titanium and the carbon steel substrate, forming an interfacial transition layer between the two. In this invention, a location in the carbon steel where the Fe content is 5% lower than that of the matrix is ​​defined as the first boundary of the interfacial transition layer, and a location in the pure titanium layer where the Ti content is 5% lower than that of the matrix is ​​defined as the second boundary of the interfacial transition layer. The distance from the first boundary to the second boundary is defined as the thickness of the interfacial transition layer.

[0022] Preferably, the chemical composition of the base layer is further given by the following formula: 0.02% ≤ Cu + Ni ≤ 0.20%; 2(C+N)≦Ti+Nb+Cr≦0.22% (Here, each chemical element in the formula represents the mass percentage of the corresponding chemical element in the base layer.)

[0023] Preferably, the base layer contains the following chemical elements in mass percentages: C 0.03 to 0.10%, Si 0.10 to 0.30%, Mn 1.00 to 1.50%, P 0.0005 to 0.003%, S 0.0005 to 0.01%, Cr 0.02 to 0.20%, Ni 0.01 to 0.10%, Cu 0.002 to 0.020%, Al 0.015 to 0.03%, Ti 0.008 to 0.018%, Nb 0.02 to 0.065%, N 0.0005 to 0.005% (the balance being Fe and other inevitable impurities).

[0024] Preferably, the base layer has a microstructure of ferrite + pearlite and / or a small amount of bainite structure, where the content of the pearlite is ≥ 5% and the ferrite has an average particle size of ≥ 8.5 grades; preferably, the content of the bainite structure is ≤ 10%. Unless otherwise specified, the content of each structure in the steel is expressed as a volume fraction.

[0025] Preferably, in the base layer of the hot-rolled steel sheet of the present invention, the volume fraction of ferrite is 80% to 90%, the volume fraction of pearlite is 5% to 10%, and the volume fraction of bainite is 8% or less.

[0026] Preferably, the base layer of the present invention has a yield strength of ≥ 350 MPa, a tensile strength of ≥ 497 MPa, a yield-to-tensile ratio of 0.71 to 0.80, and an impact energy at -40°C of ≥ 190 J.

[0027] In the hot-rolled strip steel of the present invention, the thickness of the base layer accounts for 80% or more of the total thickness of the hot-rolled strip steel, and the mechanical properties of the final hot-rolled strip steel are mainly controlled by the carbon steel base layer.

[0028] [[ID=​​​​​​ Preferably, the corrosion-resistant layer has a corrosion resistance rate of ≤0.006 mm / year from sea spray.

[0031] Preferably, the interface transition layer achieves 100% metallurgical bonding with atomic-level consistency; and / or the interface transition layer has a thickness of ≤10 μm and an interface shear strength of ≥252 MPa.

[0032] Preferably, the interface transition layer has fine particles having an average particle size of 15 to 50 μm and includes (Ti,Nb)C precipitated particles having a size of less than 120 nm.

[0033] Preferably, the hot-rolled steel sheet for building structures has a thickness of 3 to 80 mm.

[0034] In the base layer of the hot-rolled steel sheet for building structures of the present invention, the design principles for each chemical element are as follows:

[0035] C: C acts as a solid solution strengthening element in steel, significantly increasing its strength. However, excessively high C content unfavorably affects weldability and toughness. More importantly, when the C content is too high, it diffuses toward the cladding interface, forming a large amount of coarse, hard TiC phase in the interfacial transition layer, which reduces the strength of the cladding interface. To ensure interfacial shear strength, the present invention employs a low C content. Changes in C content have a smaller effect on the yield strength of the steel than on the tensile strength. Given the premise of ensuring the formability and weldability of the product, appropriately increasing the C content is beneficial for reducing the yield-to-tensile ratio of the steel. Based on this, the C content in the base layer composition of the hot-rolled steel sheet of the present invention is controlled to be 0.03-0.10%.

[0036] Si: The addition of Si to steel can effectively deoxidize it and improve its purity. Furthermore, Si provides solid solution strengthening in steel, enhancing its strength and hardness. However, Si unfavorably affects the weldability of the material. Therefore, the Si content in the base layer composition of the hot-rolled steel sheet of the present invention is controlled to be between 0.10 and 0.30%.

[0037] Mn: Mn is the most cost-effective matrix strengthening element. It can lower the austenite transformation temperature, delay the pearlite transformation, refine ferrite particles, and improve the strength of the steel. On the other hand, Mn can also mitigate the unfavorable effects of S on the steel. However, excessively high Mn content can lead to segregation bands and martensite structures, which are detrimental to the toughness of the steel. Therefore, the Mn content in the base layer composition of the hot-rolled steel sheet of the present invention is controlled to be between 1.00% and 1.50%.

[0038] Al: Al is primarily added to steel in excess as a deoxidizing element to minimize the O content in the steel. After deoxidation, the excess Al combines with N in the steel to form AlN precipitates. During heating, AlN inhibits the growth of austenite particles, refines the austenite particle structure, and enhances the strength and toughness of the matrix. At the same time, the formation of AlN fixes some of the N in the matrix where it would otherwise form hard TiN in the interfacial transition layer and degrade the interfacial shear strength of the clad sheet, thus reducing the diffusion of interstitial N atoms from the carbon steel base layer to the clad interface. Furthermore, the addition of Al allows for a proper reduction in the required amounts of Ti and Nb, thereby lowering production costs. Based on this, the Al content in the base layer composition of the hot-rolled steel sheet of the present invention is controlled to be 0.015~0.03%.

[0039] Ti: At high temperatures, Ti forms stable TiN or Ti(N,C) that fixes C and N, preventing interstitial C and N atoms in the carbon steel base layer from diffusing toward the interface. Hard TiN or Ti(N,C) precipitates form in the interface transition layer, leading to a clad sheet with high interfacial shear strength. Meanwhile, during heating, TiN inhibits the growth of austenite particles, refines them, and enhances the strength and toughness of the matrix. In the subsequent welding process, particularly in the heat-affected zone (HAZ) adjacent to the weld fusion boundary, TiN suppresses the growth of austenite particles, thereby improving the toughness of the weld HAZ and meeting the requirements of welding processes with high heat input. Ti increases the strength of the low-carbon matrix, reduces the diffusion of C and N toward the interface, and results in a clad sheet with high interfacial shear strength. Based on this, the Ti content in the composition of the base layer of the hot-rolled steel sheet of the present invention is controlled to be 0.008~0.018%.

[0040] Nb: Nb exists in steel in the form of solid solution Nb and Nb(C,N), playing a role in solid solution resistance and pinning by precipitates during the recrystallization process. Adding a small amount of Nb to the carbon steel base layer, mainly to increase the recrystallization temperature, enables finer particle size after rolling in the recrystallized and non-recrystallized regions, which helps improve the low-temperature impact toughness of the carbon steel base layer. Due to the formation of Nb(C,N) precipitates, the original austenite particles become finer, promoting the formation of even finer recrystallized particles, and achieving an ideal combination of high strength and high toughness. Furthermore, Nb fixes interstitial C and N atoms in the matrix, reducing diffusion toward the C and N interface, thereby contributing to the production of clad sheets with high interfacial shear strength. Based on this, the Nb content in the composition of the base layer of the hot-rolled steel sheet of the present invention is controlled to be 0.02~0.065%.

[0041] Cu: Cu serves as a solid solution strengthening element. Furthermore, as the Cu content increases, the impact toughness of the steel at room temperature improves slightly. Therefore, the Cu content in the base layer composition of the hot-rolled steel sheet of the present invention is controlled to be between 0.002% and 0.020%.

[0042] N: The element N can form second-phase particles with Ti and Al, refine austenite particles, and enhance the strength and toughness of the matrix. However, when the N content is too high, the amount of TiN formed increases, and the particles become excessively coarse, which unfavorably affects the plasticity and toughness of the carbon steel base layer. Based on this, the N content in the composition of the base layer of the hot-rolled steel sheet of the present invention is controlled to be between 0.0005% and 0.005%.

[0043] Ni: Ni is an element that stabilizes austenite and contributes to some extent to improved strength. Adding Ni to steel significantly enhances the low-temperature impact toughness of the steel. However, nickel is expensive, and excessive addition increases the cost of clad sheets. Based on this, an appropriate amount of Ni is added to the composition of the base layer of the hot-rolled steel sheet of the present invention, and the Ni content is controlled to be between 0.01 and 0.10%.

[0044] Cr: Cr is a strong carbide-forming element that has a relatively low diffusion rate in austenite and simultaneously inhibits the diffusion of C element. It provides precipitation strengthening by forming fine carbides during low-temperature processes. At the same time, it fixes interstitial C and N atoms in the matrix, reducing diffusion toward the C and N interface, thereby resulting in clad sheets with high interfacial shear strength. While Cr in steel enhances the strength of the matrix, it reduces toughness. To achieve an optimal balance of strength and toughness, the Cr content in the base layer composition of the hot-rolled steel sheet of this invention is controlled to be between 0.02 and 0.20%.

[0045] Both S and P are unavoidable impurity elements, and their content should be as low as possible. Considering the actual steelmaking process, the content of S and P in the base layer of the hot-rolled steel sheet of the present invention is controlled as follows: 0.0005% ≤ S ≤ 0.010%; 0.0005% ≤ P ≤ 0.003%.

[0046] The corrosion-resistant layer of the hot-rolled steel sheet of the present invention employs industrial pure titanium, preferably TA1, TA2, TA3, and TA4, having a composition that satisfies the standard GB / T 3620.1-2016 "Specifications and Composition of Titanium and Titanium Alloys".

[0047] Furthermore, in the chemical composition design of the base layer of the hot-rolled steel sheet for building structures according to the present invention:

[0048] Both Cu and Ni can improve the toughness of the base layer, and the combined effect of their addition is particularly significant. Furthermore, the addition of Ni can reduce the diffusion rate of C in the steel, thereby decreasing the diffusion of C toward the interface. Therefore, in a preferred embodiment of the present invention, controlling 0.02% ≤ Cu + Ni ≤ 0.20% helps to maintain the interface transition layer within 10 μm. A thickness of the interface transition layer exceeding 10 μm will have a detrimental effect on the tolerance of the coating.

[0049] Furthermore, Ti, Nb, and Cr are all strong carbonitride-forming elements. They form corresponding carbonitrides in the carbon steel substrate, which can fix interstitial atoms in the substrate and prevent diffusion of interstitial C and N atoms toward the interface. This helps to prevent the formation of large aggregated carbonitrides in the interface transition layer, thereby controlling the interface transition layer to within 10 μm and increasing the interface shear strength. On the other hand, Ti, Nb, and Cr can refine the particles in the carbon steel substrate and improve toughness at various stages of hot rolling. Therefore, in a preferred embodiment of the present invention, the following control is applied: 2(C+N)≦Ti+Nb+Cr≦0.22% (Here, each chemical element in the formula represents the mass percentage of the corresponding chemical element in the base layer.)

[0050] On the other hand, the present invention provides a method for manufacturing the above-mentioned hot-rolled steel sheet for building structures, comprising the following steps, which are carried out in order: 1) Smelting and casting Based on the composition of the base layer and corrosion-resistant layer described above, the base layer and the corrosion-resistant layer are smelted and cast separately to produce the slab; 2) Slab assembly Surface grinding and polishing on the base layer and corrosion-resistant layer slabs; joining the base layer slab and the corrosion-resistant layer slab together; welding and sealing the periphery of the joining surface of the slabs to form a clad slab containing the base layer and the corrosion-resistant layer; vacuum pumping treatment on the joining surface after welding and sealing; 3) Heating The clad slab is heated to 900-1000°C to form an interfacial transition layer between the base layer and the corrosion-resistant layer; 4) Rolling The clad slab is rolled at a reduction rate of 5-20% per pass, a cumulative reduction rate of ≥70%, and a finish rolling temperature of 750-850°C to achieve complete bonding between the base layer and the clad layer; 5) Cooling After rolling, hot-rolled steel sheets are produced by applying water cooling at a cooling rate of 5-20°C / s and a final cooling temperature of 300-650°C.

[0051] Preferably, in step 2), the thickness of the corrosion-resistant layer is 0.5 to 20% of the total thickness of the clad slab.

[0052] Preferably, in step 3), the interface transition layer formed between the base layer and the corrosion-resistant layer has a thickness of ≤10 μm. More preferably, the interface transition layer has a thickness of 0.5 μm or more.

[0053] Preferably, in step 4), the reduction ratio per pass used during rolling is 10-20%.

[0054] In the manufacturing method of the present invention, the design principles for each process are as follows: 1) Smelting: P and S elements degrade the fracture toughness of steel. Therefore, during the smelting process, the P and S content is controlled to a low level to improve the quality of the slab. Clean steel production technology is adopted to reduce the content of gases and inclusions in the steel, improving the overall properties of the steel and especially enhancing its resistance to delamination. 2) Assembly: The thickness of the corrosion-resistant layer is prepared to be 0.5-20% of the total thickness of the clad slab. Pretreatment is carried out on the corrosion-resistant layer and the carbon steel base slab, followed by welding and sealing around the joint surfaces of the slab. Vacuum pumping is applied to the welded and sealed joint interfaces. Vacuum treatment is an important condition for protecting the surface of the corrosion-resistant layer from oxidation and also for ensuring the corrosion resistance of the clad steel sheet in the sea spray zone corrosion during service. 3) Heating: For carbon steel substrates, the slab heating temperature is generally controlled to 1000-1250°C, which facilitates the dissolution and sufficient diffusion of precipitates in the steel, promotes the homogenization of elements in the slab, and enables the strengthening effect of microalloying elements in the steel. For clad industrial pure titanium sheets, the heating temperature is generally controlled to 850-1000°C. Excessively high heating temperatures can induce β-phase transformation, and the β-phase can grow rapidly, degrading the properties of industrial pure titanium. Furthermore, excessively high heating temperatures also promote sufficient elemental diffusion, facilitating the achievement of 100% metallurgical bonding at the subsequent interface. However, higher heating temperatures increase the tendency for coarsening austenite particles, adding difficulty to subsequent controlled rolling, and, most importantly, accelerate diffusion toward the C, N, Ti, and Fe interfaces, forming thick brittle precipitates and intermetallic compounds at the interfaces, resulting in thick interfacial transition layers and degrading interfacial shear strength. Preferably, the heating temperature is set between 900 and 1000°C. 4) Rolling: A large deformation reduction is performed in the high-temperature range to ensure sufficient recrystallization of the microstructure, refine the particles, and enhance the strength and toughness of the material. The reduction rate per pass is 5-20%, and the cumulative reduction rate is ≥70%. Controlled rolling is carried out in the non-recrystallization zone. At this stage, austenite recrystallization no longer occurs. By applying appropriate reduction rates and finish rolling temperatures, deformation energy and dislocations accumulate, forming high-density deformation zones within the austenite particles. This increases the phase transformation nucleation sites, further refines the particle size after matrix phase transformation, and improves the strength and toughness of the material. Furthermore, during this stage, strain-induced precipitation of Nb, Ti, and Cr carbonitrides occurs, enhancing the strength of the matrix, inhibiting the diffusion of C toward the interface, and preventing the formation of excessively thick TiC at the interface, which would worsen the interfacial shear strength. Preferably, the finish rolling temperature is controlled to 750-850°C. This ensures the corrosion resistance of titanium while avoiding rolling the base layer in a two-phase region, resulting in a ferrite + pearlite microstructure with an average particle size greater than 8.5 grade and / or a bainite structure content of ≤10%. 5) Cooling: The present invention achieves control over the type and size of the microstructure after rolling by performing controlled cooling with specific settings for the initial cooling temperature, final cooling temperature, and cooling rate. Excessively high cooling rates can lead to the formation of bainite and martensite structures. Since the martensite phase is a structure with low toughness and a high yield-to-tensile ratio, it is detrimental to the properties of the steel sheet. Excessively slow cooling rates can result in the formation of a large amount of coarse ferrite structure. Coarse structures facilitate crack propagation and lead to a decline in impact performance. Therefore, the cooling rate should be appropriately controlled.

[0055] Controlling the finish rolling temperature can prevent the formation of abnormally coarse microstructures in the two-phase region caused by rolling. Simultaneously, rapid cooling to the phase transformation temperature after rolling further inhibits microstructure growth, enhancing material strength and low-temperature impact toughness through particle refinement. Preferably, water cooling is applied with a controlled cooling rate of 5-20°C / s and a controlled final cooling temperature of 300-650°C to ensure that the base layer exhibits a low yield-to-tensile ratio and high low-temperature impact toughness.

[0056] Preferably, an excessively thick corrosion-resistant layer may adversely affect the mechanical properties and production costs of the material, while an excessively thin layer may reduce the corrosion resistance and service life of the material. Therefore, in the assembly process described above, the corrosion-resistant layer is preferably 0.5 to 20% of the total thickness of the clad slab.

[0057] This invention forms a corrosion-resistant layer on the surface of a base layer, i.e., a carbon steel sheet, through a combination of a corrosion-resistant layer and a base layer, combining compositional design and optimization of the thickness ratio by using a rolling process, thereby providing corrosion resistance in areas with ocean spray. The resulting steel sheet exhibits corrosion resistance in areas with ocean spray, good mechanical properties, and high cost-effectiveness. This steel sheet can further be processed into structural components for use as steel structural components in areas with ocean spray.

[0058] Compared to prior art, the present invention offers the following beneficial effects: By employing a low-carbon microalloy composition design, the invention achieves excellent bonding between titanium and carbon steel without the need for an additional metal isolation layer. Meanwhile, the thickness of the interface transition layer is controlled to ensure that the mechanical properties of the base layer (carbon steel) meet the requirements of the corresponding strength grade without reducing the corrosion resistance of the corrosion-resistant layer itself. Furthermore, the base layer exhibits excellent yield-to-tensile ratio and low-temperature impact toughness.

[0059] Furthermore, by reducing the carbon content in the carbon steel base layer, the present invention reduces the formation of TiC compounds in the interfacial transition layer and the precipitation of carbonitrides in the base layer, thereby inhibiting particle growth and improving the low-temperature impact toughness of the base layer. Meanwhile, the addition of microalloying elements to the steel, combined with an optimized rolling and cooling process, addresses the problem of low material strength under low-carbon conditions. The resulting clad steel sheets (hot-rolled steel sheets) all exceed the performance requirements specified in the national standard GB / T 19879-2015 "Steel Sheets for Building Structures," achieving a yield strength of ≥350 MPa, a tensile strength of ≥490 MPa, a yield-to-tensile ratio of 0.71-0.80, and an impact energy of ≥190 J at -40°C.

[0060] Chinese patent application CN201210260231.7 does not specify a heating temperature. It adds a nickel plate as an isolation layer between the cladding layer and the base layer to prevent the formation of interfacial TiC, achieving an interfacial bonding rate of 99.6-100% for titanium-steel cladding. In contrast, this invention explicitly defines the heating temperature of the cladding slab as 900-1000°C. Through a low-carbon and microalloying design, it reduces the addition of Ni, lowers production costs, and optimizes processes such as heating and rolling to form a transition layer structure of constant thickness. This approach also minimizes the formation of brittle TiC phases in the interfacial transition layer and achieves 100% metallurgical bonding (perfect metallurgical bonding) at the interface.

[0061] Chinese patent application CN201710769999.X uses a slab heating temperature of 500-700°C and a total reduction ratio of 60-70%. The resulting steel sheet has a maximum interfacial shear strength of 182 MPa. In contrast, the present invention fully considers the effect of high-temperature phase transformation of industrial pure titanium on the corrosion resistance of the corrosion-resistant layer, while also controlling the strength and toughness of the carbon steel base layer. By combining low-carbon microalloying design and overall processing optimization, the heating temperature of the clad slab is set to 900-1000°C. At this temperature, no phase transformation occurs in the corrosion-resistant layer, and precipitates in the carbon steel base layer are sufficiently dissolved. During controlled rolling, this refines the particles of the base layer, increasing its strength and toughness. Combined with a total reduction ratio of ≥70%, the brittle phase at the interface is broken, thereby improving the interfacial shear strength.

[0062] The two applications mentioned above primarily avoid the formation of brittle Ti compounds by adding an additional nickel-based alloy isolation layer between the titanium and carbon steel. In contrast, the present invention achieves this without adding an isolation layer through composition and process design, and differs from the two applications mentioned above in both the assembly method and the material of the carbon steel substrate.

[0063] The process conditions of the present invention ensure both the inherent corrosion resistance of industrial pure titanium in the corrosion-resistant layer and the mechanical properties of the base layer, addressing the problem of the conventional processing window for titanium and carbon steel being too divergent and unbalanced. Furthermore, the present invention controls sufficient diffusion of elements between the base layer and the corrosion-resistant layer to form an interfacial transition layer of 10 μm or less. This layer is characterized by a fine-grained microstructure with an average particle size of 15-50 μm and contains (Ti,Nb)C precipitate particles smaller than 120 nm, which enhance interfacial bonding performance and ensure an interfacial shear strength of ≥252 MPa, exceeding the interfacial shear strength of 182 MPa achieved by prior art.

[0064] Chinese patent application CN201811327623.4 describes a method for achieving cladding through a two-step heat treatment process including warm rolling, followed by initial annealing at 500-600°C for 20-60 minutes and recrystallization annealing at 680-700°C for 30-120 minutes. This represents a method for producing clad titanium-steel sheets via non-hot-rolled cladding, which is entirely different from the manufacturing method of the present invention.

[0065] Chinese patent application CN201510543767.3 describes a method for producing titanium-steel clad plates with shear strength greater than 240 MPa by using a heating temperature of 850-900°C, a finish rolling temperature of 700°C or less, and controlling the single-pass deformation rate to 20-30% with a total rolling deformation of ≥90%. This solution requires a high reduction rate per pass and large total deformation, which easily leads to end weld cracking during rolling, disruption of vacuum integrity, interference with coating, and poor rolling stability. In contrast, the present invention controls the single-pass reduction rate to 5-20%, effectively preventing weld cracking during rolling, maintaining the internal vacuum of the slab, and significantly increasing interfacial shear strength, as well as rolling stability and success.

[0066] Chinese patent application CN201610994234.1 discloses a method for manufacturing titanium-steel sheets using annealing technology. First, titanium sheets and steel sheets are assembled to form a symmetrical multilayer clad slab having a steel sheet-titanium sheet-isolated material-titanium sheet-steel sheet structure. The clading is achieved through rolling clading or explosive clading. The clad slab undergoes annealing and pickling, first heating to 500-750°C to recrystallize the core titanium sheets, and then heating to 950-1050°C to recrystallize the base steel sheets. The specific rolling process, as well as the resulting corrosion and structural properties of the steel sheets, are not explicitly described. This method differs significantly from the manufacturing process of the present invention, as it eliminates the need for a two-stage heat treatment. Furthermore, a two-stage heat treatment can cause excessive diffusion of titanium, iron, and carbon elements, leading to the formation of brittle intermetallic compounds such as iron-titanium and titanium carbide, which degrade the interfacial shear strength.

[0067] Chinese patent application CN201710996925.X uses TA2 as a corrosion-resistant layer material having a titanium cladding thickness of 0.2 to 1 mm. The slab is heated to 900 to 920°C, and held at an initial rolling temperature of 880 to 900°C, and a finish rolling temperature of 800°C or higher, and then air-cooled to room temperature to achieve a shear strength of 241 MPa. In this invention, the heating temperature is 900 to 1000°C, the finish rolling temperature is 750 to 850°C, and water cooling is applied at a controlled cooling rate of 5 to 20°C / s. This process enables the use of TA1, TA2, TA3, or TA4 as a corrosion-resistant layer, accounting for 0.5 to 20% of the total thickness (3 to 80 mm) of the hot-rolled sheet, and having an interfacial shear strength of ≥252 MPa.

[0068] Chinese patent application CN201710983322.6 uses a slab assembly method and heating process similar to those in Chinese patent application CN201710996925.X, having a single-pass reduction ratio of 25-30% and a total reduction ratio of ≥85%. While controlling the single-pass reduction ratio and total reduction ratio, it limits the thickness of the titanium-steel clad sheet to 3-16 mm at a finish rolling temperature of 800°C or higher and air cooling to room temperature. The titanium-steel clad sheet is obtained with a titanium cladding thickness of ≤1 mm through surface treatment. In this invention, the single-pass reduction ratio is 5-20%, ensuring rolling stability. There are also significant differences in the thickness of the corrosion-resistant layer and the total thickness of the clad steel sheet.

[0069] In summary, the 345 MPa class hot-rolled steel sheet for building structures with corrosion resistance in wave-splash zones described in this invention addresses the inherent weaknesses of using stainless steel or carbon steel in wave-splash zone environments. This 345 MPa class hot-rolled steel sheet for building structures with corrosion resistance in wave-splash zones can be effectively applied in the manufacture of steel structural components for use in wave-splash zone environments (e.g., facilities such as seaport terminals and offshore oil platforms). It significantly enhances the applicability, safety, and durability of these components by meeting the requirements for corrosion resistance and mechanical properties in wave-splash zones, while also delivering substantial economic and social benefits. [Brief explanation of the drawing]

[0070] [Figure 1] Figure 1 is a schematic diagram of the interlayer structure of the hot-rolled steel sheet for building structures according to the present invention. [Figure 2] Figure 2 is another schematic diagram of the interlayer structure of the hot-rolled steel sheet for building structures according to the present invention. [Figure 3] Figure 3 is a photograph of the microstructure of the corrosion-resistant layer of the hot-rolled steel sheet for building structures in Example 3 of the present invention. [Figure 4] Figure 4 is a scanned image of the interface transition layer of a hot-rolled steel sheet for building structures in Example 3 of the present invention. [Figure 5] Figure 5 is a photograph of the microstructure of the base layer of a hot-rolled steel sheet for building structures in Example 3 of the present invention. Reference numerals: 1 - base layer, 2 - corrosion-resistant layer, 3 - interface transition layer. [Modes for carrying out the invention]

[0071] Detailed explanation The technical solutions of the present invention will be described in further detail below with reference to the examples and drawings. It should be made clear that the following examples are intended only to illustrate specific embodiments of the present invention and do not limit the scope of protection of the present invention in any way.

[0072] Referring to Figures 1 and 2, schematic diagrams of two types of interlayer structures of the hot-rolled steel sheet for building structures of the present invention are shown, where 1 represents the base layer, 2 represents the corrosion-resistant layer, and 3 represents the interface transition layer.

[0073] Table 1 shows the composition of the base layer in the examples of the hot-rolled steel sheet (clad steel sheet) for building structures of the present invention, with the remainder being Fe and other unavoidable impurities. Table 2 provides manufacturing process parameters for the examples and comparative examples of the clad steel sheet of the present invention. Table 3 shows the metallographic structure of the base layer, the mechanical properties of the hot-rolled steel sheet, the thickness of the interfacial transition layer, and the shear strength in the examples and comparative examples of the clad steel sheet. The metallographic structure of carbon steel consists of pearlite and possibly a small amount of bainite, with ferrite as the remainder. Taking the hot-rolled steel sheet of Example 1 as an example, the volume fraction of ferrite is 95.0%.

[0074] Of these, the yield strength and tensile strength of the clad steel sheets were measured according to GB / T 6396-2008 "Clad Steel Sheets - Mechanical and Technical Tests" and GB / T 228-2010 "Metallic Materials - Tensile Tests at Room Temperature"; the impact energy KV2 / J (longitudinal) at -40°C was measured according to GB / T 6396-2008 "Clad Steel Sheets - Mechanical and Technical Tests" and GB / T 229-2020 "Metallic Materials - Charpy Pendulum Impact Test Method"; and the interfacial shear strength was measured according to GB / T 6396-2008 "Clad Steel Sheets - Mechanical and Technical Tests".

[0075] The yield strength and tensile strength of the carbon steel base layer were measured according to GB / T 6396-2008 "Clad Steel Sheets - Mechanical and Technical Tests" and GB / T 228-2010 "Metallic Materials - Tensile Tests at Room Temperature"; the impact energy KV2 / J (longitudinal) at -40°C was measured according to GB / T 6396-2008 "Clad Steel Sheets - Mechanical and Technical Tests" and GB / T 229-2020 "Metallic Materials - Charpy Pendulum Impact Test Method".

[0076] The particle size of ferrite in the carbon steel substrate was evaluated as follows: The particle size of the ferrite microstructure in carbon steel was evaluated using the intercept method in accordance with GB / T 6394-2017 "Decision on estimating the average particle size of metals".

[0077] Comparative examples were manufactured using the above-described process, which is essentially identical to that of the embodiments of the present invention, but differs in the composition of the carbon steel base layer and in specific process parameters used during the rolling or cooling process, thus failing to meet the requirements of the present invention.

[0078] Figure 3 shows the metallographic structure of the corrosion-resistant layer in Example 3, which exhibits a single equiaxed α-Ti structure with an average particle size of 102.8 μm. Figure 4 shows the structure of the interface transition layer in Example 3. The interface transition layer 3 has a thickness of 7.5 μm, and the discontinuous fine particles are TiC having a size of less than 120 nm. Figure 5 shows the microstructure of the base layer in Example 3, indicating that the microstructure of the carbon steel base layer contains ferrite + pearlite, with a pearlite volume fraction of 6.8% and a ferrite particle size grade of ≥8.5.

[0079] Table 4 shows the corrosion status of clad steel plate specimens from Examples 1-8 and Comparative Examples 1-4 after 6 months of exposure in the South China Sea spray zone. The corrosion tests were conducted according to GB / T 5776-2005, "Corrosion of Metals and Alloys - Guidelines for Exposure and Evaluation of Metals and Alloys in Surface Seawater." In Table 4, chloride ion concentration (%) represents the mass fraction of chloride ions relative to the total mass of the solution. For example, a chloride ion concentration of 5% indicates that there are 5 grams of chloride ions in 100 grams of solution. The observations show that, with the exception of Comparative Example 4, the corrosion rates of the Examples and the other Comparative Examples are ≤0.006 mm / year.

[0080] Comparative Examples 1-4 failed to meet certain performance requirements for clad steel sheets (i.e., performance parameters outside the scope defined by the present invention) due to the use of compositional designs or thermal processing conditions that did not meet the requirements. Specifically:

[0081] Comparative Example 1: Since no Ti, Nb, or Cr was added to the chemical composition, and the rolling reduction ratio was outside the range defined by the present invention, the yield strength, yield-to-tensile ratio, impact performance, and interfacial shear strength did not meet the requirements.

[0082] Comparative Example 2: Since no Ni was added to the chemical composition, and the finish rolling temperature, cooling rate, and final cooling temperature were outside the range defined by the present invention, the yield-to-tensile ratio and impact performance did not meet the requirements.

[0083] Comparative Example 3: Because the amount of Cu+Ni added to its chemical composition was less than 0.02%, and the cooling rate and final cooling temperature were outside the range defined by the present invention, its microstructure was bainite, and its mechanical properties, yield-to-tensile ratio, and impact performance did not meet the requirements.

[0084] Comparative Example 4: Because the heating temperature and finish rolling temperature were outside the range defined by the present invention, the interfacial transition layer was too thick, resulting in insufficient shear strength. Due to the excessively high heating temperature, β-Ti could not be completely removed during subsequent processing and cooling, leading to a high corrosion rate.

[0085] Through the technical solutions of the present invention, the base layer of the steel sheet exhibits excellent yield-to-tensile ratio and low-temperature impact toughness, while the cladding layer possesses outstanding corrosion resistance and high bond strength. The hot-rolled steel sheet achieves a yield strength of 352-445 MPa, a tensile strength of 497-602 MPa, a yield-to-tensile ratio of 0.71-0.80, an impact energy of over 190 J at -40°C, and an interfacial shear strength greater than 252 MPa. The manufacturing method of the present invention, particularly the control of the heating, rolling, and cooling processes, also contributes to achieving the corresponding steel properties.

[0086] It should be noted that all technical features described in this invention can be freely combined or incorporated in any way, provided they do not conflict with each other. Various modifications and variations of this invention can be made without departing from the scope of the invention, and this 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 further embodiments. Accordingly, this invention is intended to cover such modifications within the scope of the appended claims and their equivalents.

[0087] [Table 1]

[0088] [Table 2]

[0089] [Table 3-1]

[0090] [Table 3-2]

[0091] [Table 4]

Claims

1. A hot-rolled steel sheet for building structures, characterized in that the hot-rolled steel sheet includes a base layer, a corrosion-resistant layer, and an interfacial transition layer located between the base layer and the corrosion-resistant layer. Here, the base layer contains, in addition to Fe and other unavoidable impurities, the following chemical elements in mass percent: C 0.03–0.10%, Si 0.10–0.30%, Mn 1.00–1.50%, P 0.0005–0.003%, S 0.0005–0.01%, Cr 0.02–0.20%, Ni 0.01–0.10%, Cu 0.002–0.020%, Al 0.015–0.03%, Ti 0.008–0.018%, Nb 0.02–0.065%, N 0.0005–0.005%; Here, the corrosion-resistant layer is industrial-grade pure titanium, preferably TA1, TA2, TA3, or TA4, in a hot-rolled steel sheet for building structures.

2. The chemical composition of the base layer is further expressed by the following formula: 0.02% ≤ Cu + Ni ≤ 0.20%; 2(C+N)≦Ti+Nb+Cr≦0.22% The hot-rolled steel sheet for building structures according to claim 1, characterized in that it satisfies the following condition: (wherein each chemical element in the formula represents the mass percentage of the corresponding chemical element in the base layer).

3. The hot-rolled steel sheet for building structures according to claim 1 or 2, characterized in that the base layer contains the following chemical elements in mass percent: C 0.03-0.10%, Si 0.10-0.30%, Mn 1.00-1.50%, P 0.0005-0.003%, S 0.0005-0.01%, Cr 0.02-0.20%, Ni 0.01-0.10%, Cu 0.002-0.020%, Al 0.015-0.03%, Ti 0.008-0.018%, Nb 0.02-0.065%, N 0.0005-0.005% (the remainder being Fe and other unavoidable impurities).

4. A hot-rolled steel sheet for building structures according to any one of claims 1 to 3, characterized in that the base layer has a microstructure of ferrite + pearlite and / or bainite, wherein the pearlite content is ≥ 5%, and the ferrite has an average particle size of ≥ 8.5 grade; preferably, the bainite content is ≤ 10%.

5. A hot-rolled steel sheet for building structures according to any one of claims 1 to 4, characterized in that the base layer has a yield strength of ≥350 MPa, a tensile strength of ≥497 MPa, a yield-to-tensile ratio of 0.71 to 0.80, and an impact energy of ≥190 J at -40°C.

6. The hot-rolled steel sheet for building structures according to claim 1, characterized in that the corrosion-resistant layer has a single equiaxed α-Ti microstructure.

7. A hot-rolled steel sheet for building structures according to claim 1 or 6, characterized in that the corrosion-resistant layer has a corrosion resistance rate of ≤0.006 mm / year due to sea wave spray.

8. The hot-rolled steel sheet for building structures according to claim 1, characterized in that the interface transition layer contains (Ti,Nb)C precipitated particles having a thickness of 0.5 to 10 μm, an average particle size of 15 to 50 μm, and a size of less than 120 nm.

9. The hot-rolled steel sheet for building structures according to claim 1, characterized in that the hot-rolled steel sheet has a thickness of 3 to 80 mm.

10. A hot-rolled steel sheet for building structures according to any one of claims 1 to 9, characterized in that the hot-rolled steel sheet has a yield strength of ≥350 MPa, a tensile strength of ≥490 MPa, a yield-to-tensile ratio of 0.71 to 0.80, an impact energy of ≥190 J at -40°C, a corrosion resistance rate of ≤0.006 mm / year from ocean wave spray, an interface transition layer thickness of 0.5 to 10 μm, and an interface shear strength of ≥252 MPa.

11. A method for manufacturing a hot-rolled steel sheet for building structures according to any one of claims 1 to 10, the method comprising the following steps, performed in order: 1) Smelting and casting Producing a slab by separately smelting and casting the base layer and the corrosion-resistant layer based on the composition of the base layer and the corrosion-resistant layer described in claim 1, 2, or 3; 2) Slab assembly Surface grinding and polishing on the base layer and corrosion-resistant layer slabs; joining the base layer slab and the corrosion-resistant layer slab together; welding and sealing the periphery of the joining surface of the slabs to form a clad slab containing the base layer and the corrosion-resistant layer; vacuum pumping on the joining surface after welding and sealing; 3) Heating The clad slab is heated to 900 to 1000°C to form an interfacial transition layer between the base layer and the corrosion-resistant layer; 4) Rolling The clad slab is rolled at a reduction ratio of 5 to 20% per pass, preferably 10 to 20% per pass; a cumulative reduction ratio of ≥ 70%; and a finish rolling temperature of 750 to 850°C; 5) Cooling Hot-rolled steel sheets are produced by applying water cooling after rolling, with a controlled cooling rate of 5 to 20°C / s and a controlled final cooling temperature of 300 to 650°C.

12. The method according to claim 11, characterized in that, in step 2), the thickness of the corrosion-resistant layer is 0.5 to 20% of the thickness of the clad slab; and / or, in step 3), the interface transition layer formed between the base layer and the corrosion-resistant layer has a thickness of 0.5 to 10 μm.

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