390 MPa class hot-rolled steel strip for building structures resistant to corrosion in ocean spray areas, and method for manufacturing the same.

Abstract

The present invention provides a hot-rolled steel strip for building structures, comprising a base layer, a corrosion-resistant layer, and an interfacial transition layer between the base layer and the corrosion-resistant layer. The hot-rolled steel strip for building structures of the present invention has a yield strength of ≥390 MPa, a tensile strength of ≥515 MPa, a yield-to-tensile ratio of ≤0.75, an impact energy of ≥190 J at -40°C, a corrosion rate against sea spray of ≤0.006 mm / year, an interfacial transition layer thickness of ≤8 μm, and an interfacial shear strength of ≥260 MPa, which exhibits excellent overall performance. The present invention also provides a method for manufacturing the above hot-rolled steel strip.

Description

Technical Field

[0001] The present invention relates to the technical field of steel for building structures, and particularly to hot-rolled strip steel for building structures that is resistant to corrosion in the splash zone of sea waves and a method for manufacturing the same.

Background Art

[0002] Background The marine environment is an extremely harsh and complex corrosion environment. Seawater, which is a strong electrolyte solution, contains a high concentration of chloride ions. As the main structures of marine engineering facilities, steel facilities tend to undergo electrochemical reactions with the surrounding media and corrode severely, greatly reducing the service life of these facilities. In particular, in the splash zone of sea waves, which represents the most severe corrosive area of the marine environment, various facilities are subjected to a series of external factors such as alternating wet and dry conditions, seawater spray, sunlight, corrosive atmospheric components, and oxygen, resulting in particularly severe material corrosion.

[0003] Investigations show that steel piles in facilities such as port docks and offshore oil platforms are corroded 3 to 10 times more severely in the splash zone of sea waves than in the fully immersed seawater zone. Once severe local corrosion damage occurs in such areas, it will greatly reduce the load-bearing capacity of the entire facility, shorten its service life, compromise operational safety, and even lead to premature abandonment measures for the facility.

[0004] Due to the fact that ocean spray zones are located in alternating wet and dry areas with sufficient oxygen supply, the resulting corrosion products offer no protective effect to the steel substrate. Furthermore, due to seawater spray, the seawater spray directly impacts the metal surface, causing serious corrosion. Corrosion tests and investigations show that under normal conditions, the average corrosion rate of ordinary carbon steel, low-alloy steel, etc., in the marine atmosphere is approximately 0.03 to 0.08 mm / year, whereas in ocean spray zones, it reaches 0.3 to 0.5 mm / year. In ocean spray zones, steel piles are prone to serious corrosion damage, greatly reducing the load-bearing capacity of the overall steel structure, compromising operational safety, shortening the service life, and leading to premature decommissioning.

[0005] Based on the aforementioned service conditions, commercial pure titanium is selected as the corrosion-resistant layer. Titanium exhibits high chemical reactivity and readily reacts with oxygen in the air to form oxides. The oxides on the surface of titanium metal are dense, stable, and possess strong "self-healing" capabilities. The "self-healing" capability of titanium oxide mainly refers to the rapid formation of a new layer of titanium oxide film on the damaged surface of the titanium material, which prevents corrosive media from further contact with the titanium.

[0006] For steel used in marine building structures, in addition to meeting corrosion resistance requirements, it is also necessary to exhibit good mechanical properties. Among these, the yield-to-tensile ratio and low-temperature impact toughness are increasingly important indicators of interest for building steel. The yield-to-tensile ratio is the ratio of the yield strength of steel to its tensile strength, reflecting the steel's ability to undergo plastic deformation without strain concentration. The lower the yield-to-tensile ratio, the more evenly and widely the plastic deformation of the steel can be distributed. Plastic deformation of a steel structural system made of steel with a low yield-to-tensile ratio can be evenly distributed over a wide area under seismic forces; on the other hand, materials with a high yield-to-tensile ratio may experience strain concentration, reducing the steel's overall plastic deformation capacity and potentially leading to brittle fracture of the structure, thereby resulting in structural instability and sudden collapse. Steel undergoes a brittle transition at low temperatures, and its fracture mode changes from ductile fracture to brittle fracture. The engineering significance lies in the fact that when steel is used at temperatures higher than this, the component will not undergo brittle fracture. Therefore, structural steel usually needs to have corresponding requirements for its low-temperature impact performance based on the material's service environment. Ocean temperatures vary greatly at various latitudes. Taking the vicinity of the Bohai Bay in China as an example, winter coastal temperatures can be below -20°C. This requires building materials to have good impact performance at -40°C to ensure that brittle fracture does not occur. However, when improving the ductility and toughness of steel, if the increase in tensile strength is small, the yield-to-tensile ratio will increase significantly, making it difficult to maintain a low yield-to-tensile ratio.

[0007] Chinese Patent Application CN201210260231.7 discloses a method for manufacturing titanium-steel-titanium double-sided clad plates. The method comprises: stacking four titanium plates and three steel plates in a specific order within a sealed frame formed by welding two outermost steel plates; applying a separator between the titanium plates, prepared by mixing 1 part by weight of activated α-Al2O3 and 1.5 parts by weight of a 4% polyvinyl alcohol aqueous solution; and using a nickel-based alloy as a transition layer between the titanium and steel plates. The assembly is heated to 500-630°C and vacuum-pumped at a vacuum of 20-200 Pa for 1-2 hours. It is characterized in that welding is performed after the slab is assembled, before vacuum pumping, and conventional arc welding and submerged arc welding are sufficient for the welding process. Compared to welding under vacuum conditions, the welding requirements are lower, the cost is lower, and there is no need to construct a separate vacuum chamber. Subsequently, the clad slab is subjected to a conventional heating furnace and rolled at a rolling temperature of 700-900°C to achieve the coating. By sealing the outermost steel plate with welding and vacuuming, carbon in the gas can be separated, while a nickel-based alloy isolation layer is applied to prevent the formation of TiC at the interface, resulting in a titanium-steel clad plate 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 comprises: selecting surfaces of the titanium-steel clad slabs that are in contact with each other; applying a high-temperature resistant, carburizing-resistant, and nitriding-resistant isolation coating to the contacting titanium surfaces; and drying at room temperature. After drying is complete, the titanium slabs are aligned and stacked in pairs with the steel slabs placed in between to complete the assembly and obtain the clad slab. The thickness of the single titanium sheet used is greater than 2 mm, and the thickness of the steel sheet is greater than 5 mm. The outer edge of the clad slab is then sealed welded, leaving a certain size of unwelded portion. The slab is 10 before welding. -2 ~10-3 The slab is vacuum-assisted to Pa. The slab is heated and rolled to 500-700°C, where the reduction ratio in the first pass is greater than 25%, the reduction ratio in the last pass is not greater than 15%, the total reduction ratio is 60-70%, and the rolling speed is 0.1-1.0 mm / s. The patent application achieves protection against the diffusion and oxidation of impurity elements at high temperatures by using a coating with high-temperature penetration resistance that blocks the diffusion of elements such as carbon and nitrogen. In the example, Q235 steel and TA1 were bonded together, and the resulting clad plate exhibited shear strengths of 176 MPa, 181 MPa, and 182 MPa.

[0009] The two patent applications mentioned above primarily aim to avoid the formation of brittle Ti compounds by applying 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 sandwiching a carbon steel sheet between two titanium sheets of the same size, and then performing hot clad rolling using a hot rolling mill with irreversible high rolling force to integrally bond the three layers. After rolling, the rolled clad sheet is subjected to heat treatment, including initial annealing at 500-600°C for 20-60 minutes, and recrystallization annealing at 680-700°C for 30-120 minutes. Finally, the product is obtained by destraining, leveling, shearing, and forming. The patent application mainly describes a method for producing clad titanium steel sheets without using hot rolling cladding. Due to the use of an irreversible rolling mill, only single-pass rolling production is possible, and heat treatment is also required. The examples mainly include a method for producing steel strips and do not mention the performance of the product after cladding.

[0011] Chinese patent application CN201510543767.3 discloses a method for manufacturing titanium-steel clad sheets. The bond strength of the titanium-steel clad sheets obtained by this method is high. The patent 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; heating the clad slab to 850-900°C for 120-360 minutes; controlling the rolling process with a starting rolling temperature of 800°C or higher and a finishing rolling temperature of 700°C or lower; and controlling the deformation of each pass to 20-30% and the total deformation during rolling to ≥90%. This high-pressure rolling process helps to break the brittle intermetallic compounds formed at the interface, thereby mitigating their adverse effects on the bonding interface. After rolling, the resulting titanium-steel clad sheet achieves a bond strength greater than 240 MPa. However, the patent application requires a high pass reduction ratio and total deformation, which can easily lead to end weld cracks during the rolling process and impair the vacuum, making it unsuitable for interfacial bonding.

[0012] Chinese Patent Application CN201610994234.1 discloses a method for producing titanium-steel clad sheets, including an annealing technique for manufacturing titanium steel sheets. First, titanium sheets and steel sheets are assembled to form a symmetrical multilayer clad slab having a steel sheet-titanium sheet-separating agent-titanium sheet-steel sheet structure. The cladding is carried out by rolling cladding or explosion cladding. The clad slab is then annealed and pickled. It is first heated to 500-750°C to recrystallize the core titanium sheets, and then heated to 950-1050°C to recrystallize the base steel sheets. The objective of the patent application is to achieve the properties of the cladding material and the base material simultaneously through a two-stage heat treatment. However, the two-stage heat treatment may lead to excessive diffusion of the elements titanium, iron, and carbon, resulting in intermetallic compounds of brittle materials such as iron and titanium and titanium carbide, which degrades the interfacial shear strength.

[0013] Chinese patent application CN201710996925.X discloses a thin clad double-sided titanium-steel clad sheet and a method for manufacturing the same. The method achieves good coating between titanium and steel by using a thick slab assembly and high-pressure rolling technology. The patent application is directed to a double-sided titanium clad sheet comprising a titanium clad layer, a base layer and a titanium clad layer. The titanium clad layer is made of TA2, where the titanium clad layer has a thickness of 0.2 to 1 mm. The slab assembly is stacked in the following top-to-bottom order: cover plate, titanium clad material, carbon steel base, titanium clad material, and cover plate in the center. After the vacuum is drawn out in a vacuum chamber, the seams around the assembly are 1.0 × 10 -2 ~4.5×10 -2 The clad slab is sealed and welded by vacuum electron beam welding with a vacuum of Pa. The sealed and welded 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 starting rolling temperature is 880-900°C, and the finishing rolling temperature is ≥800°C, followed by air cooling to room temperature. The single-pass reduction ratio is ≥15%, the reduction ratio for the first three passes is ≥20%, and the total reduction ratio is ≥80%. The clad sheet obtained after rolling is subjected to trimming, sheet splitting, and surface grinding to obtain a double-sided titanium-steel clad sheet. In this patent application, the titanium-iron and titanium-carbon compounds formed at the clad interface are crushed, granulated, and dispersed within the clad interface through surface cleaning of the clad slab, covering and air isolation effect of the cover plate, controlled rolling temperature, and high reduction ratio. This improves the distribution of the compound, further ensuring bond quality and performance stability, resulting in a shear strength of 241 MPa.

[0014] Chinese Patent Application CN201710983322.6 discloses a thin clad titanium-steel sheet and a method for manufacturing the same, employing a two-layer structure of coated titanium and carbon steel. The slab assembly approach and heating process are similar to those in Chinese Patent Application CN201710996925.X, having a starting rolling temperature of 880-900°C, a single-pass reduction ratio of 25-30%, and a total reduction ratio of ≥85%. The thickness of the titanium-steel sheet is limited to 3 to 16 mm while controlling the single-pass reduction ratio and total reduction ratio. The finishing rolling temperature is 800°C or higher, followed by air cooling to room temperature. The titanium-steel sheet is obtained through surface treatment, and the titanium coating layer has a thickness of ≤1 mm. The patent application describes a symmetrical slab assembly method and enhances bonding quality by encapsulating titanium within the carbon steel sheet through sealing welding. After rolling, the steel sheet achieves a shear strength of 238 MPa or higher, and the cladding interface bonding rate is 100%. The carbon steel layer meets the requirements of the Chinese national standard for Q345 grade carbon steel.

[0015] However, the two aforementioned patent applications do not specify detailed designs for the coating and base layers, and only describe tensile properties and shear strength. The required pass reduction ratio and total reduction ratio for the coating layer are high, and no control is exercised over performance indicators such as the corrosion resistance of the material, the low-temperature impact performance of the base layer material, and the yield-to-tensile ratio, which does not meet the requirements for steel used in building structures.

[0016] In summary, the above patent application primarily describes a method for manufacturing clad steel sheets, and the specific embodiments only provide a brief description of performance aspects such as interfacial shear strength and tensile properties. Steel used in steel structures in marine splash zones should not only be resistant to corrosion in marine splash zones, but should also meet the necessary structural steel performance requirements, such as the low yield-to-tensile ratio and corresponding low-temperature impact performance mentioned above, in order to ensure structural safety. However, the above patent does not include any relevant composition or process design regarding the corrosion rate of the corrosion-resistant layer, yield-to-tensile ratio, and low-temperature impact performance, and therefore cannot be assured that it can meet the requirements for using highly corrosion-resistant steel sheets for steel structures in marine splash zone environments. [Overview of the project]

[0017] overview One object of the present invention is to provide a 390 MPa class hot-rolled steel strip for building steel structures and a method for manufacturing the same, which is resistant to corrosion in sea spray zones. Without impairing the corrosion resistance of the corrosion-resistant layer itself, the mechanical properties of the base layer (carbon steel) also meet the requirements of the corresponding strength level, and the base layer has an excellent yield-to-tensile ratio and low-temperature impact toughness. The hot-rolled steel strip for building structures has a yield strength of ≥390 MPa, a tensile strength of ≥515 MPa, a yield-to-tensile ratio of ≤0.75, an impact energy of ≥190 J at -40°C, a corrosion rate against sea spray of ≤0.006 mm / year, an interface transition layer thickness of ≤8 μm, and an interface shear strength of ≥260 MPa. The steel strip can meet the corrosion resistance requirements in sea spray zone environments and has good mechanical properties and high economic efficiency for corrosion resistance in sea spray zones. It can be used for steel structural components such as steel piles in facilities such as seaport terminals and offshore oil platforms.

[0018] In this invention, by adopting a low-carbon microalloy composition design and reducing the carbon content in the carbon steel of the base layer, the formation of TiC compounds in the interfacial transition layer and the formation of carbonitrides in the base layer are reduced, thereby inhibiting particle growth and improving the low-temperature impact toughness of the base layer. On the other hand, the addition of microalloying elements to the steel, along with the rolling and cooling processes, solves the problem of low material strength under low-carbon conditions. Furthermore, excellent bonding of titanium and carbon steel is achieved without adding a metal isolation layer. Meanwhile, by controlling the thickness of the interfacial transition layer, the mechanical properties of the base layer (carbon steel) can meet the requirements of the corresponding strength level without impairing the corrosion resistance of the corrosion-resistant layer itself. Furthermore, the base layer exhibits excellent yield-to-tensile ratio and low-temperature impact toughness.

[0019] Specifically, the hot-rolled steel strip for building structures of the present invention comprises a base layer, a corrosion-resistant layer, and an interfacial transition layer 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: 0.02-0.15%, Ni: 0.01-0.10%, Cu: 0.002-0.020%, Al: 0.015-0.03%, Ti: 0.008-0.012%, Nb: 0.02-0.045%, N: 0.0005-0.005%, and V: 0.05-0.20%; and Here, the corrosion-resistant layer is made of commercial pure titanium, and its composition conforms to the standard GB / T 3620.1-2016 "Specifications and Compositions of Titanium and Titanium Alloys".

[0020] Preferably, the hot-rolled steel strip for building structures of the present invention has a yield strength of ≥390 MPa, a tensile strength of ≥515 MPa, a yield-to-tensile ratio of ≤0.75, an impact energy of ≥190 J at -40°C, a corrosion rate against sea spray of ≤0.006 mm / year, an interface transition layer thickness of ≤8 μm, and an interface shear strength of ≥260 MPa.

[0021] During the heating and rolling processes, atoms diffuse at the interface between titanium and carbon steel in the base layer to form an interfacial transition layer between the two. In the present invention, the position where the Fe content in the carbon steel decreases by 5% compared to the matrix is defined as the first boundary of the interfacial transition layer, and the position where the Ti content in the pure titanium layer decreases by 5% compared to 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 further satisfies the following relationships: 0.02% ≦ Cu + Ni ≦ 0.10%; 2(C + N) ≦ Ti + Nb + Cr + V ≦ 0.35% (wherein, in calculating the relationships, the symbols for each element are to be substituted with the mass percentages of the corresponding elements in the base layer).

[0023] Preferably, the base layer contains the following chemical elements in mass percentages: 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 - 0.15%, Ni: 0.01 - 0.10%, Cu: 0.002 - 0.020%, Al: 0.015 - 0.03%, Ti: 0.008 - 0.012%, Nb: 0.02 - 0.045%, N: 0.0005 - 0.005%, V: 0.05 - 0.20%, and the balance is Fe and other inevitable impurities. and.

[0024] Preferably, the base layer in the present invention has a microstructure of ferrite + bainite + martensite, the content of bainite + martensite is 5 - 15%, and the ferrite has an average particle size of ≧ 8.5 grades. Unless otherwise specified, the content of each microstructure in the steel is expressed as a volume fraction.

[0025] Preferably, the base layer in the present invention has a yield strength of ≧ 390 MPa, a tensile strength of ≧ 515 MPa, a yield-to-tensile ratio of ≦ 0.75, and an impact energy at -40 °C of ≧ 190 J.

[0026] Preferably, the corrosion-resistant layer is made of TA1, TA2, TA3 or TA4.

[0027] Preferably, the corrosion-resistant layer has a fine structure of single equiaxed α-Ti.

[0028] Preferably, the corrosion-resistant layer has a corrosion rate against sea spray of ≦ 0.006 mm / year.

[0029] Preferably, the interface transition layer achieves 100% metallurgical bonding and has a high degree of atomic coherence; and / or the interface transition layer has a thickness of ≦ 8 μm and an interface shear strength of ≧ 260 MPa. Preferably, the interface transition layer has fine particles with an average particle size of 15 - 40 μm and contains precipitation particles of (Ti,Nb)C with a size of less than 120 nm.

[0030] Preferably, the thickness of the hot-rolled strip steel for building structures is 1.0 to 20 mm.

[0031] In the base layer of the hot-rolled strip steel for building steel structures of the present invention, the design concept of each element is as follows:

[0032] C: It plays a role in solid solution strengthening in steel and can significantly improve the strength of the steel. However, excessively high C content is detrimental to weldability and toughness. More importantly, when the C content is too high, it will diffuse into the coating interface, forming a hard phase of large granular TiC in the interface transition layer, thereby reducing the strength of the coating interface. To ensure shear strength at the interface, 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 product formation performance and weldability, appropriately increasing the C content is beneficial in reducing the yield-to-tensile ratio of the steel. Based on this, in the composition of the base layer of the hot-rolled strip steel according to the present invention, the C content is controlled to 0.03-0.10%.

[0033] Si: Adding Si to steel can effectively deoxidize it and improve its purity. Furthermore, Si has a solid solution strengthening effect in steel and can increase its strength and hardness. However, Si is detrimental to the weldability of the material. Therefore, the Si content in the base layer composition of the hot-rolled steel strip according to the present invention is controlled to 0.10-0.30%.

[0034] 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 increase the strength of the steel. Mn can also counteract the unfavorable effects of sulfur on steel. However, excessively high Mn content can easily lead to segregation bands and martensite microstructure, which adversely affect the toughness of the steel. Therefore, the Mn content in the base layer composition of the hot-rolled strip steel according to the present invention is controlled to 1.00% to 1.50%.

[0035] Al: Al is primarily added to steel in excess as a deoxidizing element to ensure that the oxygen content in the steel is as low as possible. The excess Al after deoxidation combines with the nitrogen element in the steel to form AlN precipitates. During the heating process, AlN inhibits the growth of austenite particles, refines the austenite particles, and improves the strength and toughness of the matrix. On the other hand, the formation of AlN creates hard TiN in the interfacial transition layer, which fixes some of the nitrogen in the matrix and reduces the diffusion of interstitial atoms of nitrogen in the carbon steel base layer toward the cladding interface, thereby degrading the interfacial shear strength of the cladding plate. Furthermore, the addition of Al appropriately reduces the amount of Ti and Nb to be added, thereby lowering production costs. Based on this, the Al content in the base layer composition of the hot-rolled steel strip according to the present invention is controlled to 0.015~0.03%.

[0036] Ti: Ti plays a role in fixing C and N, forming stable TiN or Ti(N,C) at high temperatures, preventing interstitial C and N atoms in the carbon steel base layer from diffusing to the interface, and forming hard TiN or Ti(N,C) precipitates in the interface transition layer, thereby obtaining a clad plate with high interfacial shear strength. On the other hand, TiN inhibits austenite growth during heating, refines austenite particles, and improves the strength and toughness of the matrix. During subsequent welding, it inhibits the growth of austenite particles, especially in the heat-affected zone (HAZ) directly adjacent to the weld molten boundary, thereby improving the toughness of the weld HAZ and adapting to welding processes with high heat input. Ti enhances the strength of the low-carbon matrix and reduces the diffusion of C and N to the interface, resulting in a clad plate with high interfacial shear strength. For this reason, the Ti content in the composition of the base layer of the hot-rolled strip steel according to the present invention is controlled to 0.008~0.012%.

[0037] Nb: Nb exists in steel as solid-solution Nb and Nb(C,N), playing a role in solution resistance and pinning by precipitates during the recrystallization process. Small amounts of Nb are added to the base carbon steel, mainly to raise the recrystallization temperature, so that the particles in the base carbon steel are refined in the recrystallized and non-recrystallized regions after rolling, which improves the low-temperature impact toughness of the base carbon steel. Due to the formation of Nb(C,N) precipitates, the previous austenite particles become finer, promoting the formation of finer recrystallized particles and achieving an ideal combination of high strength and high toughness. Furthermore, Nb can fix interstitial C and N atoms in the matrix, reducing diffusion toward their interfaces and contributing to obtaining clad plates with high interfacial shear strength. For this reason, the Nb content in the base layer composition of the hot-rolled strip steel according to the present invention is controlled to 0.02~0.045%.

[0038] Cu: Cu plays a role in solid solution strengthening. Furthermore, increasing the Cu content slightly improves the impact toughness of the steel at room temperature. Therefore, the Cu content in the base layer composition of the hot-rolled strip steel according to the present invention is controlled to 0.002-0.020%.

[0039] N: The element N can produce second-phase particles with Ti and Al, refine austenite particles, and improve the strength and toughness of the matrix. However, excessively high N content results in excess TiN and coarse particles, which can affect the plasticity and toughness of the carbon steel in the base layer. Based on this, the N content in the base layer of the hot-rolled strip steel according to the present invention is controlled to 0.0005-0.005%.

[0040] Ni: Ni is an element that stabilizes austenite and has a certain effect on improving toughness and strength. Adding Ni to steel can greatly improve the low-temperature impact toughness of the steel. However, nickel is expensive, and excessive addition can increase the cost of clad sheets. Therefore, an appropriate amount of Ni is added to the composition of the base layer of the hot-rolled strip steel according to the present invention, and the Ni content is controlled to 0.01-0.10%.

[0041] Cr: Cr is a strong carbide-forming element, has a low diffusion rate in austenite, and inhibits the diffusion of element C. During low-temperature processing, it forms fine carbides, which act as precipitation strengthening. At the same time, it can fix interstitial C and N atoms in the matrix, reducing the diffusion of C and N to the interface, resulting in a clad plate with high interfacial shear strength. While Cr improves the strength of the matrix in steel, it also reduces toughness. To achieve an optimal balance of strength and toughness, the Cr content in the base layer composition of the hot-rolled strip steel according to the present invention is controlled to 0.02-0.15%.

[0042] V: V is a strong carbonitride-forming element. When V is added to steel in combination with Ti and Nb, it can form fine and complex carbonitrides. Furthermore, it broadens the precipitation temperature range, effectively preventing the growth of austenite particles, inhibiting the recrystallization process, and improving the strength and toughness of the base layer carbon steel. In addition, the precipitation temperature of V carbonitrides is relatively low, effectively preventing the growth of ferrite particles during the phase transformation process and strengthening the ferrite matrix. Based on this, an appropriate amount of V is added to the base layer composition of the hot-rolled strip steel according to the present invention, and the V content is controlled to 0.05-0.20%.

[0043] Both S and P are unavoidable impurity elements, and their content should be as low as possible. Considering the actual steelmaking process, in the base layer of the hot-rolled steel strip according to the present invention, the content of S and P is controlled to be: 0.0005% ≤ S ≤ 0.010%; 0.0005% ≤ P ≤ 0.003%.

[0044] The corrosion-resistant layer of the hot-rolled steel strip according to the present invention is made of commercial pure titanium, preferably TA1, TA2, TA3, and TA4, and its composition satisfies the standard GB / T 3620.1-2016 "Specifications and Compositions of Titanium and Titanium Alloys".

[0045] Furthermore, in the chemical composition design of the base layer of the hot-rolled steel strip for building structures according to the present invention:

[0046] Both Cu and Ni can improve the toughness of the base layer, and the effect of combined addition is particularly significant. Furthermore, the addition of Ni can reduce the diffusion rate of C in the steel and reduce the diffusion of C into the interface. Therefore, in a preferred embodiment of the present invention, their content can be controlled to 0.02% ≤ Cu + Ni ≤ 0.10%, and the interface transition layer can be controlled to be within 8 μm.

[0047] Furthermore, Ti, Nb, Cr, and V are all strong carbonitride-forming elements. They form corresponding carbonitrides in the base carbon steel, which can fix interstitial atoms in the base layer and prevent the diffusion of C and N interstitial atoms into the interface to form large particles and aggregated carbonitrides in the interface transition layer, which helps to control the interface transition layer to be within 8 μm, thereby improving the interface shear strength. On the other hand, Ti, Nb, and Cr can play a role in refining the particles in the base carbon steel particles and improving toughness at various stages of hot rolling. Therefore, in a preferred embodiment of the present invention, their content is limited to 2(C+N)≦Ti+Nb+Cr+V≦0.35%.

[0048] In calculating the above relationship, the symbols for each chemical element are to be replaced by the mass percentage of the corresponding element in the base layer.

[0049] In another embodiment, the present invention provides a method for producing hot-rolled steel strips for building structures, comprising the following steps, performed in sequence: 1) Smelting and casting Smelting and casting of the base layer and the corrosion-resistant layer into slabs, respectively, based on the composition of the base layer and the corrosion-resistant layer; 2) Assembling the slab Surface grinding and polishing are performed on the slab for the base layer and the corrosion-resistant layer; the slab for the base layer and the slab for the corrosion-resistant layer are joined together; and perimeter welding and sealing are performed along the bonding interface of the slab to form a clad slab containing the base layer and the corrosion-resistant layer; vacuum treatment is performed on the bonding interface 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 method involves rolling the clad slab to obtain a steel strip, wherein the rough rolling is controlled to be carried out at a temperature of 860°C or higher; the finish rolling is controlled to be carried out at a temperature of 780-850°C; the pass reduction ratio is 5-20%, preferably 10-15%; and the cumulative reduction ratio is ≥85%. 5) Cooling In the first stage, the steel strip is cooled to 700-750°C at a cooling rate of ≤10°C / s after leaving the rolling mill stand; in the second stage, it is cooled to 400-500°C at a cooling rate of 30-50°C / s; and then wound up at this temperature to produce hot-rolled steel strip.

[0050] Preferably, in step 2), the thickness of the corrosion-resistant layer is 0.5 to 20% of the total thickness of the clad slab.

[0051] Preferably, in step 3), the thickness of the interface transition layer formed between the base layer and the corrosion-resistant layer is ≤8 μm. More preferably, the thickness of the interface transition layer is 0.5 μm or more.

[0052] Preferably, in step 4), the pass reduction ratio used during rolling is 10 to 15%.

[0053] In the manufacturing method of the present invention, the design principles of each process are as follows: 1) Smelting: P and S elements degrade the toughness of steel during fracture; therefore, the P and S content must be kept at a low level during the smelting process to improve the quality of the steel slab. By adopting clean steel production technology, the content of gases and inclusions in the steel can be reduced, improving the overall performance of the steel, and in particular its resistance to delamination. 2) Assembling the slab: The thickness of the corrosion-resistant layer is set to 0.5-20% of the total thickness of the clad slab. The slab is pre-treated for the corrosion-resistant layer and the base carbon steel, and periphery welding seals are performed along the joint interfaces of the slab. The joint surfaces after welding seals are then vacuumed. Vacuum treatment can protect the surface of the corrosion-resistant layer from oxidation and is also an important condition to ensure that the corrosion-resistant layer is resistant to corrosion in the ocean spray zone. On the other hand, it can also ensure that the corrosion-resistant layer avoids phenomena such as end cracking and crushing of the corrosion-resistant layer during deformation at large cumulative reduction rates. 3) Heating: For base carbon steel, the slab heating temperature is generally controlled to 1000-1250°C. This facilitates the dissolution and sufficient diffusion of precipitates in the steel, promotes the homogenization of elements in the slab, and maximizes the strengthening effect of microalloying elements in the steel. For coating commercial pure titanium sheets, the heating temperature is generally controlled to 850-1000°C. Excessively high heating temperatures can cause β-phase transformation, and the β-phase will grow rapidly, degrading the performance of commercial pure titanium. Furthermore, excessively high heating temperatures also promote sufficient diffusion of elements, facilitating 100% metallurgical bonding at the interface. However, higher heating temperatures increase the tendency of austenite grains to coarseen, making subsequent controlled rolling more difficult. Most importantly, it accelerates the diffusion toward the C, N, Ti, and Fe interfaces, leading to the formation of thick brittle precipitates and intermetallic compounds at the interfaces, resulting in a thick interfacial transition layer and degrading the interfacial shear strength. Preferably, a lower heating temperature is used compared to conventional carbon steel production, and the heating temperature is set to 900-1000°C. 4) Rolling: Rough rolling is controlled to be carried out at a temperature of 860°C or higher. High reduction ratio rolling in the high-temperature rough-rolled zone allows for sufficient recrystallization of the microstructure, resulting in grain refinement and improving the strength and toughness of the material. Controlled rolling is carried out in the non-recrystallized zone, and austenite recrystallization no longer occurs at this stage. Using a reasonable reduction ratio and finish rolling temperature, deformation energy and deformation dislocations are accumulated, resulting in the formation of high-density deformation zones within the austenite particles. This increases the number of deformation nucleations in the ferrite phase, further refining the particle size of the matrix after phase transformation and improving the strength and toughness of the material. Furthermore, deformation induces the precipitation of Nb, Ti, Cr, and V carbonitrides at this stage, enhancing the strength of the matrix, inhibiting the diffusion of C into the interface, and preventing the formation of excessively thick TiC at the interface, which would worsen the interfacial shear strength. The reduction ratio per pass is maintained at 5-20%, with a cumulative reduction ratio of ≥85%. For finish rolling, the finish rolling temperature is preferably controlled to 750-850°C to ensure the corrosion resistance of titanium while avoiding rolling the base layer in a two-phase region. Meanwhile, ferrite with an average particle size of ≥8.5 grade and bainite + martensite with a content of 5-15% were obtained. 5) Cooling: In this invention, initial cooling, finish cooling, and cooling rate are controlled to achieve control over the type, size, and various content of the rolled microstructure. An excessively fast cooling rate will result in the formation of large amounts of bainite and martensite. The cooling rate should be reasonably controlled due to the fact that the martensite phase is a microstructure with low toughness and a high yield-to-tensile ratio, and does not help the performance of the steel sheet; an excessively slow cooling rate will lead to the formation of large amounts of coarse ferrite; and a coarse microstructure has a tendency to amplify cracks, resulting in a decrease in impact performance.

[0054] By controlling the finish rolling temperature during the finish rolling process, the formation of abnormally coarse microstructures in the two-phase region caused by rolling can be avoided. Furthermore, rapid cooling to the phase transformation temperature can be achieved after rolling, inhibiting further microstructure growth. By refining the particles, material strength and low-temperature impact toughness are improved, and a hard phase microstructure is formed at temperatures above 5-15°C, ensuring sufficient strength.

[0055] Preferably, a two-stage cooling method is used. After leaving the rolling mill stand, it is first cooled to the ferrite phase transformation temperature at a cooling rate of ≤10°C / s, and then rapidly cooled to 400-500°C at a cooling rate of 30-50°C / s for winding, thereby obtaining a small amount of bainite and martensite, achieving microstructure recovery during winding, promoting the precipitation of carbonitrides of V, and ensuring that the base layer has a low yield-to-tensile ratio and high low-temperature impact toughness.

[0056] Preferably, if the corrosion-resistant layer is too thick, the mechanical properties and production costs of the material will be affected. If the corrosion-resistant layer is too thin, the corrosion resistance and service life of the material will be impaired. Therefore, in the process of assembling the slab described above, the corrosion-resistant layer preferably accounts for 0.5 to 20% of the total thickness of the clad slab.

[0057] In this invention, along with compositional design and thickness ratio design, a corrosion-resistant layer (resistant to corrosion in sea spray zones) is formed on the surface of the base layer (i.e., carbon strip steel) by a rolling process through coating the base layer with a corrosion-resistant layer, ultimately obtaining a strip steel that exhibits resistance to corrosion in sea spray zones, good mechanical properties, and high economic efficiency. This strip steel is further processed into a structure that can be used as a steel structure for use in sea spray zone environments.

[0058] Compared to prior art, the present invention offers the following beneficial effects:

[0059] In this invention, by employing a low-carbon microalloy composition design, excellent bonding between titanium and carbon steel is achieved without the addition of a metal isolation layer. Simultaneously, by controlling the thickness of the interfacial transition layer, the mechanical properties of the base layer (carbon steel) meet the required strength level without compromising the corrosion resistance of the corrosion-resistant layer itself. Furthermore, the base layer exhibits excellent yield-to-tensile ratio and low-temperature impact toughness.

[0060] In this invention, reducing the carbon content in the base layer carbon steel reduces the formation of TiC compounds in the interfacial transition layer and carbonitrides in the base layer, hindering particle growth and improving the low-temperature impact toughness of the base layer. On the other hand, the addition of microalloying elements to the steel solves the problem of low material strength under low-carbon conditions. The resulting hot-rolled strip has a yield strength of ≥390 MPa, a tensile strength of ≥515 MPa, a yield-to-tensile ratio of ≤0.75, and an impact energy of ≥190 J at -40°C. All of these properties are higher than the property requirements of the national standard GB / T 19879-2015 "Steel Sheets for Building Structures".

[0061] Chinese patent application CN201210260231.7 does not specify a heating temperature. By adding a nickel plate as an isolation layer between the cladding layer and the base layer, the formation of TiC at the interface is prevented, resulting in a titanium-steel cladding sheet having an interfacial bonding rate of 99.6-100%. However, this invention specifies heating the cladding slab at a temperature of 900-1000°C. Low carbon and microalloying design reduces the amount of Ni added and lowers production costs. Meanwhile, optimization of processes such as heating and rolling allows for the formation of a transition layer of a certain thickness, reduces the formation of brittle TiC phases in the interfacial transition layer, and achieves 100% metallurgical bonding (perfect metallurgical bonding) at the interface.

[0062] In Chinese patent application CN201710769999.X, the slab is heated to a temperature of 500-700°C, the total reduction rate is 60-70%, and the resulting strip steel has a maximum interfacial shear strength of 182 MPa. However, in this invention, the effect of high-temperature phase transformation of commercial pure titanium on the corrosion resistance of the corrosion-resistant layer is fully considered, as well as the strength and toughness of the base carbon steel. Through a comprehensive processing technology design combined with a low-carbon microalloying design, the heating temperature of the clad slab is set to 900-1000°C. At this temperature, the corrosion-resistant layer undergoes no phase transformation, and this ensures that precipitates in the base carbon steel are sufficiently dissolved. During the controlled rolling process, the particles of the base layer are refined to improve the strength and toughness of the base layer. Combined with a cumulative reduction rate of ≥85%, the brittle phase of the interfacial transition layer is broken, thereby improving the interfacial shear strength.

[0063] In the two aforementioned patent applications, the formation of brittle Ti compounds is avoided primarily by adding an additional nickel-based alloy isolation layer between the titanium and carbon steel. However, in the present invention, no isolation layer is added through composition and process design. In the present invention, the method of assembling the slab differs from the two aforementioned patent applications, and the material of the base carbon steel is also significantly different.

[0064] The process conditions of the present invention ensure both the corrosion resistance of commercial pure titanium in the corrosion-resistant layer and the mechanical properties of the base layer, solving the problem of the imbalance caused by the excessively different processing windows of conventional titanium and carbon steel. At the same time, the elements in the base layer and the corrosion-resistant layer are sufficiently diffused to form an interfacial transition layer having a thickness of 10 μm or less. This layer has fine particles with an average particle size of 15 to 40 μm and contains (Ti,Nb)C precipitates with a size of less than 120 nm, thereby enhancing the interfacial bonding properties and ensuring an interfacial shear strength of ≥260 MPa, exceeding the interfacial shear strength of 182 MPa specified in Chinese patent application CN201710769999.X.

[0065] In Chinese patent application CN201811327623.4, the coating process is achieved by a two-step heat treatment process, which includes warm rolling, followed by initial annealing at a temperature of 500-600°C for 20-60 minutes, and recrystallization annealing at a temperature of 680-700°C for 30-120 minutes. This method is a non-hot-rolling coating method for producing clad titanium-steel strips and is completely different from the manufacturing method of the present invention.

[0066] In Chinese patent application CN201510543767.3, the heating temperature is 850-900°C, the finish rolling temperature is 700°C or less, the deformation per pass is controlled to 20-30%, the total rolling deformation is controlled to be ≥90%, and the shear strength of the titanium-steel clad sheet is greater than 240 MPa. Both the pass reduction ratio and total deformation required by the invention are very high, which can easily cause weld end cracking during the rolling process, collapse the vacuum, make bonding difficult, and result in poor rolling stability. However, in the present invention, by controlling the reduction ratio per pass to 5-20%, it is possible to effectively prevent weld cracking during rolling, ensure a vacuum within the slab, and significantly improve interfacial shear strength and rolling stability and success rate.

[0067] Chinese patent application CN201610994234.1 discloses an annealing production method for titanium steel sheets. First, titanium and steel sheets are assembled to form a symmetrical multilayer clad slab consisting of steel sheets, titanium sheets, separators, titanium sheets, and steel sheets. The cladding is carried out by rolling cladding or explosive cladding. The clad slab is annealed and pickled, first heated to 500-750°C to recrystallize the core titanium sheets, and then heated to 950-1050°C to recrystallize the base steel sheets. The rolling process, as well as the resulting corrosion and structural properties of the steel sheets, are not specified. This method differs significantly from the present invention in its manufacturing process. This application does not require a two-stage heat treatment. Furthermore, a two-stage heat treatment can lead to excessive diffusion of elemental titanium, iron, and carbon, resulting in brittle iron-titanium intermetallic compounds and titanium carbide, which degrade the interfacial shear strength.

[0068] In Chinese patent application CN201710996925.X, the corrosion-resistant layer is made of TA2, where the titanium clad layer has a thickness of 0.2 to 1 mm. The material is heated to 900 to 920°C and maintained for a certain period of time. The initial rolling temperature is 880 to 900°C, and the finish rolling temperature is 800°C or higher, after which it is 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 is carried out at a temperature of 750 to 850°C, and a two-stage cooling method is used. Under such a process, it is possible to obtain a hot-rolled sheet, where TA1, TA2, TA3, or TA4 is used as a corrosion-resistant layer, the corrosion-resistant layer accounts for 0.5% to 20% of the total thickness of the clad slab, and the interfacial shear strength is ≥ 260 MPa.

[0069] In Chinese patent application CN201710983322.6, the method and heating process for assembling the slab are similar to those in Chinese patent application CN201710996925.X. In this application, 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 it is air-cooled to room temperature. The titanium-steel clad sheet is obtained by surface treatment, where the thickness of the titanium clad layer is ≤1 mm. In this invention, the single-pass reduction ratio is 5-20%, controlling the rolling stability, and a two-stage air-cooling method is used to ensure the microstructure of the material, thereby controlling the yield-to-tensile ratio and toughness. There are also significant differences in the thickness of the corrosion-resistant layer and the total thickness of the composite band.

[0070] The 390 MPa class hot-rolled steel strip for building structures, which is corrosion-resistant in marine splash zones according to the present invention, can solve the essential problems of stainless steel or carbon steel used in marine splash zone environments. This 390 MPa class hot-rolled steel strip for building structures, which is corrosion-resistant in marine splash zones, can be effectively applied to the manufacture of steel structures used in marine splash zone environments (e.g., port terminals, offshore oil platforms, and other facilities). It can meet the requirements of these components regarding corrosion resistance and mechanical properties in marine splash zones, significantly improving their applicability, safety, and durability, as well as providing significant economic and social advantages. [Brief explanation of the drawing]

[0071] [Figure 1] Figure 1 is a schematic diagram of the interlayer structure of the hot-rolled steel strip for building structures according to the present invention. [Figure 2] Figure 2 is a schematic diagram of another interlayer structure of the hot-rolled steel strip 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 strip for building structures in Example 3 of the present invention. [Figure 4] Figure 4 is a scanned image of the interface transition layer of the hot-rolled steel strip 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 the hot-rolled steel strip 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]

[0072] Detailed description of the embodiment The technical solutions of the invention will be further described in detail below with reference to examples and drawings. It should be understood that the following examples are used solely to illustrate specific embodiments of the invention and do not constitute any limitation on the scope of protection of the invention.

[0073] Referring to Figures 1 and 2, schematic diagrams of two types of interlayer structures of the hot-rolled steel strip for building structures of the present invention are shown, where 1 is the base layer, 2 is the corrosion-resistant layer, and 3 is the interface transition layer.

[0074] Table 1 shows the composition of the base layer of the hot-rolled steel strip (clad steel sheet) for building structures according to the present invention, where the remainder of the composition is Fe and unavoidable impurities. Table 2 shows the manufacturing process parameters for the clad steel sheets in the examples and comparative examples according to the present invention. Table 3 shows the metallographic structure of the base layer (carbon steel) in the hot-rolled steel strips of the examples and comparative examples, as well as the mechanical properties, the thickness of the interface transition layer, and the shear strength of the hot-rolled steel strips. The metallographic structure of the carbon steel consisted of bainite and martensite, with the remainder being ferrite. Taking the hot-rolled steel strip of Example 1 as an example, the volume fraction of ferrite was 91.9%.

[0075] Specifically, 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 - Test Methods at Room Temperature". The impact energy KV2 / J (longitudinal direction) of the clad steel sheets 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". The interfacial shear strength of the clad steel sheets was measured according to GB / T 6396-2008 "Clad Steel Sheets - Mechanical and Technical Tests".

[0076] The yield strength and tensile strength of the base layer carbon steel were measured according to GB / T 6396-2008 "Clad Steel Sheets - Mechanical and Technical Tests" and GB / T 228-2010 "Metallic Materials - Tensile Tests - Test Methods at Room Temperature". The impact energy KV2 / J (longitudinal) of the base layer carbon steel 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 Methods".

[0077] The particle size of ferrite in the base carbon steel was evaluated as follows: The particle size of ferrite 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".

[0078] Comparative examples were prepared by the above process, which is essentially the same as the examples of the present invention, except that the composition of the base carbon steel and the specific process parameters used in the rolling or cooling process do not meet the requirements of the present invention.

[0079] Figure 3 shows the microstructure of the corrosion-resistant layer in Example 3, which exhibits a single equiaxed α-Ti with an average particle size of 103.4 μm.

[0080] Figure 4 shows the microstructure of the interface transition layer in Example 3, where the thickness of the interface transition layer is 7.4 μm, and the discontinuous fine particles are TiC having a size of less than 120 nm.

[0081] Figure 5 shows the microstructure of the base layer in Example 3, indicating that the microstructure of the base layer carbon steel was ferrite + bainite + martensite, where the volume fraction of bainite + martensite was 7.8%, and the particle size grade of ferrite was ≥ 8.5 grade.

[0082] Table 4 shows the corrosion performance of clad steel plate test specimens from Examples 1-8 and Comparative Examples 1-4 after 6 months in the South China Sea sea spray zone. The corrosion tests were conducted in accordance with GB / T 5776-2005, "Corrosion of metals and alloys - Guidelines for exposure and evaluation of metals and alloys in surface seawater." Chloride ion concentration (%) represents the ratio of the mass of chloride ions to the total mass of the solution. For example, a chloride ion concentration of 5% means that 5 grams of chloride ions are present in 100 grams of solution.

[0083] The observation results show that, with the exception of Comparative Example 4, the corrosion rates of all other examples and comparative examples were ≤0.006 mm / year.

[0084] In Comparative Examples 1-4, some properties of the clad steel sheets failed to meet the usage requirements due to the use of compositional design requirements or thermal working process conditions that did not meet the requirements (performance parameters were not within the range limited by the present invention). Specifically:

[0085] In Comparative Example 1, a chemical composition without the addition of Ti, Nb, and Cr was used, and the rolling reduction ratio used was outside the range limited by the present invention. Consequently, the yield strength, yield-to-tensile ratio, impact performance, and interfacial shear strength did not meet the requirements.

[0086] In Comparative Example 2, a chemical composition without Ni addition was used, and the finish rolling temperature and the cooling rate in the second stage were not within the range limited by the present invention. Therefore, its yield-to-tensile ratio and impact performance did not meet the requirements.

[0087] In Comparative Example 3, the amount of Cu+Ni added was less than 0.02%, and the cooling rates in the first and second stages were not within the range limited by the present invention. As a result, the metal structure contained a large amount of bainite+martensite, and the mechanical properties, yield-to-tensile ratio, and impact performance did not meet the requirements.

[0088] In Comparative Example 4, the heating temperature, finish rolling temperature, and cooling rate in the first stage were not within the limits set by the present invention. As a result, the thickness of the interface transition layer was too thick, causing the shear strength to fail to meet the performance requirements. Additionally, the heating temperature was too high, preventing the complete removal of β-Ti during the subsequent processing and cooling processes, leading to a high corrosion rate.

[0089] According to the technical solution of the present invention, the base layer of the steel strip exhibited a low yield-to-tensile ratio and good low-temperature impact toughness, while the coating layer exhibited excellent corrosion resistance and high bond strength. The hot-rolled steel strip exhibited a yield strength of 391-481 MPa, a tensile strength of 551-668 MPa, a yield-to-tensile ratio of ≤0.75, an impact energy at -40°C of 190 J or more, and an interfacial shear strength greater than 260 MPa. According to the preparation method of the present invention, the control of the heating, rolling, and cooling processes in particular also contributed to achieving the corresponding steel properties.

[0090] It should be noted that all technical features recorded in this invention can be freely combined or related in any way, provided that no contradiction arises. It will be apparent to those skilled in the art that various modifications and changes can be made to the invention without departing from the scope of the invention. For example, features exemplified or described as part of one embodiment can be used with another embodiment to produce further embodiments. That is, the invention is intended to cover such modifications and changes that fall within the scope of the appended claims and their equivalents.

[0091] [Table 1]

[0092] [Table 2]

[0093] [Table 3]

[0094] [Table 4]

Claims

1. A hot-rolled steel strip for building structures, wherein the hot-rolled steel strip comprises a base layer, a corrosion-resistant layer, and an interfacial transition layer between the base layer and the corrosion-resistant layer; The base layer contains, in addition to Fe and other unavoidable impurities, the following chemical elements in mass percent: It contains 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: 0.02-0.15%, Ni: 0.01-0.10%, Cu: 0.002-0.020%, Al: 0.015-0.03%, Ti: 0.008-0.012%, Nb: 0.02-0.045%, N: 0.0005-0.005%, and V: 0.05-0.20%; and The corrosion-resistant layer is made of commercial pure titanium, preferably TA1, TA2, TA3, or TA4, in a hot-rolled steel strip for building structures.

2. The chemical composition of the base layer is further related to the following: 0.02% ≤ Cu + Ni ≤ 0.10%; 2(C+N)≦Ti+Nb+Cr+V≦0.35% The hot-rolled steel strip for building structures according to claim 1, satisfying the following: (In the formula, the symbols for each element are to be replaced by the mass percentage of the corresponding element in the base layer when calculating the relationship.)

3. The base layer contains the following chemical elements in mass percentage: 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: 0.02–0.15%, Ni: 0.01–0.10%, Cu: 0.002–0.020%, Al: 0.015–0.03%, Ti: 0.008–0.012%, Nb: 0.02–0.045%, N: 0.0005–0.005%, V: 0.05–0.20%, and the remainder being Fe and other unavoidable impurities. A hot-rolled steel strip for building structures according to claim 1 or 2, comprising:

4. The hot-rolled steel strip for building structures according to any one of claims 1 to 3, wherein the base layer has a microstructure of ferrite + bainite + martensite, the bainite + martensite content is 5% to 15%, and the ferrite has an average particle size of ≥ 8.5 grade.

5. The hot-rolled steel strip for building structures according to any one of claims 1 to 4, wherein the base layer has a yield strength of ≥390 MPa, a tensile strength of ≥515 MPa, a yield-to-tensile ratio of ≤0.75, and an impact energy of ≥190 J at -40°C.

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

7. The hot-rolled steel strip for building structures according to claim 1 or 6, wherein the corrosion-resistant layer has a corrosion rate against sea spray of ≤0.006 mm / year.

8. The hot-rolled steel strip for building structures according to claim 1, wherein the interface transition layer contains precipitated (Ti,Nb)C particles having a thickness of ≤8 μm and an average particle size of 15 to 40 μm, and a size of less than 120 nm, and has an interface shear strength of ≥260 MPa.

9. The hot-rolled steel strip for building structures according to claim 1, wherein the hot-rolled steel strip has a thickness of 1.0 to 20 mm.

10. The hot-rolled steel strip for building structures according to any one of claims 1 to 9, wherein the hot-rolled steel strip has a yield strength of ≥390 MPa, a tensile strength of ≥515 MPa, a yield-to-tensile ratio of ≤0.75, an impact energy of ≥190 J at -40°C, a corrosion rate against sea spray of ≤0.006 mm / year, an interface transition layer thickness of ≤8 μm, and an interface shear strength of ≥260 MPa.

11. A method for producing a hot-rolled steel strip for building structures according to any one of claims 1 to 10, wherein the method comprises the following steps, performed in order: 1) Smelting and casting Smelting and casting of the base layer and the corrosion-resistant layer into a slab, respectively, based on the base layer and corrosion-resistant layer compositions described in claim 1, 2, or 3; 2) Assembling the slab Surface grinding and polishing of the base layer and the corrosion-resistant layer on the slab; joining the slab with respect to the base layer and the slab with respect to the corrosion-resistant layer together; and performing peripheral welding and sealing along the joining surface of the slab to form a clad slab containing the base layer and the corrosion-resistant layer; performing vacuum treatment on the joining interface 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 method involves rolling the clad slab to obtain a steel strip, wherein rough rolling is performed at a temperature of 860°C or higher; finish rolling is performed at a temperature of 780 to 850°C; the pass reduction ratio is 5 to 20%, preferably 10 to 15%; and the cumulative reduction ratio is ≥ 85%. 5) Cooling In the first stage, the steel strip is cooled to 700-750°C at a cooling rate of ≤10°C / s after leaving the rolling mill stand; and in the second stage, it is cooled to 400-500°C at a cooling rate of 30-50°C / s; and then wound up at this temperature to produce hot-rolled steel strip.

12. The method according to claim 11, wherein 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 ≤ 8 μm.

Images