500-mpa-grade hot-rolled steel plate that is resistant to corrosion from marine atmospheres and used for building structures, and manufacturing method therefor

Abstract

A 500-MPa-grade hot-rolled steel plate that is resistant to corrosion from marine atmospheres and used for building structures, and a manufacturing method therefor. The hot-rolled steel plate comprises: a substrate, a corrosion-resistant layer on at least one side of the substrate, and an interface transition layer between the substrate and the corrosion-resistant layer. In addition to Fe and inevitable impurities, the substrate further comprises the following chemical components in percentages by mass: C: 0.050-0.150%, Si: 0.15-0.30%, Mn: 1.20-1.80%, Cr: 0.300-0.500%, Ni: 0.100-0.150%, Al: 0.020-0.050%, Ti: 0.010-0.018%, Nb: 0.040-0.060%, Mo: 0.10-0.40%, and B: 0.0003-0.0005%, wherein the inevitable impurities comprise P and S, the content of P being 0.0005-0.003%, and the content of S being 0.0005-0.01%. In addition to Fe and inevitable impurities, the corrosion-resistant layer further comprises the following chemical components in percentages by mass: C: 0.010-0.040%, Si: 0.20-1.50%, Mn: 1.00-2.00%, Cr: 16.0-18.0%, Ni: 14.0-17.0%, Cu: 0.02-0.10%, N: 0.02-0.15%, Mo: 2.0-3.0%, and Nb: 0.05-0.20%, wherein the inevitable impurities comprise P and S, the content of P being 0.005-0.03%, and the content of S being 0.005-0.03%.

Description

500mpa grade hot-rolled steel sheet for building structure resistant to marine atmospheric corrosion and method for manufacturing the same TECHNICAL FIELD

[0001] The present application belongs to the technical field of building structure steel, and particularly relates to a hot-rolled steel sheet for building structure resistant to marine atmospheric corrosion and a manufacturing method thereof. BACKGROUND

[0002] With the continuous development and utilization of marine resources, the marine industry (including coastal industry, offshore wind power, marine superhighway engineering, artificial islands and wharfs, offshore oil platforms, and submarine oil and gas pipelines) involves a large number of marine engineering facilities. The ocean is a very harsh corrosive environment for various structural materials, which can cause corrosion damage and loss of function of various infrastructures, equipment and structures, shorten the service life of materials and structures, cause huge waste of resources, materials and energy, and even lead to sudden disaster accidents.

[0003] Marine atmospheric corrosion is the result of the interaction between materials and their surrounding atmospheric environment, and is the most widely existing form of metal corrosion. Various environmental factors affecting the atmospheric corrosion of materials include temperature, humidity, irradiance, chloride ion concentration, salinity, and pollutants. For building components in the marine atmospheric zone, the influence factors are different with the distance from the coast, the sea salt particles brought by the sea wind, height, wind speed, rainfall, temperature, radiation, etc. Sea salt particles can accelerate corrosion.

[0004] At present, the main protection method for steel structural members of buildings in marine atmospheric environment is coating protection. Compared with conventional anticorrosive coatings, this type of anticorrosive coating can be applied in relatively harsh corrosive environments and has a longer protection period than conventional anticorrosive coatings. The total thickness of the coating is generally more than 200 μm. The operation steps of the coating construction method are steel surface bottom treatment, undercoating, intermediate coating, and top coating. The steel surface must be treated by mechanical sand blasting. The undercoating paint includes organic zinc-rich paint, inorganic zinc-rich paint, and special undercoating material according to different coatings. Inorganic zinc-rich paint is a zinc powder substitute anode coating with excellent rust prevention performance. Organic zinc-rich paint has poorer rust prevention performance than inorganic zinc-rich paint, but has good adhesion, and can be applied to the steel surface even if the bottom treatment is not as good as the shot blasting method. The intermediate coating and top coating should have better adhesion and be more suitable for the surrounding environment than the undercoating paint. After construction is completed, film thickness measurement and air hole test must be performed to confirm whether the coating film is sound.

[0005] This coating protection method has long construction period, complex process, and difficult to guarantee the quality; the coating is too thick, the adhesion is limited, and the coating is easy to fail during the on-site construction of the components, such as welding, riveting and other processing areas, and the corrosion resistance cannot be guaranteed; during the service, the coating is easy to fall off and damage due to common problems such as contact and collision. In addition, in the high-temperature, high-radiation and high-humidity marine atmospheric environment, the service life of the coating will be reduced, and various common failure and degradation problems will occur, and the actual application effect is not ideal.

[0006] In addition, some building designers and researchers also try to use 300 series austenitic stainless steel to make building components. However, compared with carbon steel, the structural strength of 300 series austenitic stainless steel is lower, and the required thickness is larger, thereby increasing the amount of material used; at the same time, the welding and machining of 300 series austenitic stainless steel are more difficult; in addition, 300 series stainless steel itself contains a large amount of Cr, Ni, Mo and other valuable metal elements, and the cost of using pure stainless steel is relatively high during production, manufacturing and installation.

[0007] Chinese Patent 1 (Publication No. CN106756476A) discloses a high-strength weather-resistant steel for high-humidity and high-temperature marine atmospheric environment and a preparation method. The solution is mainly to replace the addition amount of Cr by adding trace elements such as Sn, Sb, Nb and Re to slow down the corrosion of the steel plate in the humid and hot marine atmospheric environment. The results of the comparison with traditional carbon structural steel and weather-resistant steel in the immersion corrosion experiment show that the corrosion rate is reduced by about 30% in 96 hours.

[0008] Chinese Patent 2 (Publication No. CN111621699A) discloses a corrosion-resistant low-alloy steel for bridge structure in high-humidity and high-temperature marine atmospheric environment and a preparation method. The solution is to reasonably adjust the content of alloy elements Cu, Ni and Mo on the basis of Cu-Ni-Mo low-alloy steel alloy system, combine the economy of low-alloy steel, and obtain a ferrite-pearlite structure corrosion-resistant low-alloy steel. The advantage is that in the case of appropriately controlling the high cost of alloy elements Ni and Mo, the obtained corrosion-resistant steel has certain economy and good corrosion resistance, the corrosion resistance is significantly better than that of plain carbon steel, and the mechanical properties of the corrosion-resistant steel meet the requirements of bridge structure steel in high-humidity and high-temperature marine atmospheric environment.

[0009] Chinese patent 3 (publication number CN112647014A) discloses a building structure steel suitable for marine atmospheric environment, the chemical composition and its mass fraction are as follows: C: 0.07%~0.17%, Si: 0.6%~0.8%, Mn: 0.3%~1.0%, P: 0.08%~0.15%, S: 0.005~0.035%, Cu: 0.15%~0.2%, Sb: 0.1%~0.2%, Ce: 0.0025%~0.0045%; and optionally containing: Sn: 0.01%~0.02%, V: 0.05-0.1% of any one or both, the rest is iron and inevitable impurities. The steel complexly adds more low-melting-point elements such as P-Sb-Ce, which affects the low-temperature toughness, weldability, cold formability and other properties of the steel.

[0010] Chinese patent 4 (publication number CN108004488A) proposes a marine climate resistant high toughness bridge steel plate and its production method. The mass percentage of the chemical composition of the raw material of the steel plate is C: 0.041~0.087%, Mn: 1.03~2.00%, Si: 0.67~1.43%, P≤0.007%, S≤0.003%, Nb: 0.047~0.083%, Ti: 0.010~0.027%, Mo: 0.32~0.73%, Cr: 0.50~1.17%, Cu: 0.50~1.05%, Ni: 2.51~6.70%, Ca: 0.0021~0.0073%, Sb: 0.08~0.31%, the rest is Fe and inevitable impurities. Patent 4 adds more Ni, Cr, Mo, Cu and other precious metal alloys, which has high cost, Sb is easy to segregate, which increases the difficulty of smelting process, and the addition of more Si is not good for surface quality and will affect the welding performance of the steel plate.

[0011] Chinese patent 5 (application number CN202210570630.7) discloses "a production method of Q500-grade high-corrosion-resistance high-strength offshore structural steel", the process steps are hot metal pretreatment → converter steelmaking → LF secondary refining → RH vacuum treatment → continuous casting → heating → rolling → controlled rolling and cooling → tempering → finishing → performance testing → ultrasonic flaw detection. Its characteristics are: the mass percentage composition of the steel is: C: 0.03-0.07, Si: 0.15-0.40, Mn: 0.95-1.05, P≤0.020, S≤0.003, Nb: 0.04-0.06, Ti: 0.01-0.02, Al: 0.02-0.05, Cu: 0.30-0.70, Ni: 0.7-1.5, the rest is Fe and unavoidable impurity elements. It is suitable for producing steel with thickness specification ≤60mm, with resistance to marine atmospheric corrosion environment, the yield strength of the steel is ≥500MPa, and the tensile strength is ≥540MPa. The production of 500MPa weathering steel by patent 5 has complex process and requires tempering heat treatment, which increases the manufacturing cost, and the corrosion resistance of the steel plate is not described.

[0012] Chinese patent 6 (application number CN201810908224.0) discloses "a 500MPa-grade low-yield-strength ratio marine atmospheric corrosion-resistant bridge steel and its production method", the steel contains the following mass percentage of chemical components: C: 0.04-0.20%, Si: 0.15-0.45%, Mn: 0.85-1.80%, Alt: 0.015-0.050%, Ni: 2.50-4.75%, Cu: 0.20-0.60%, Nb: 0.020-0.080%, Ti: 0.015-0.036%, Ca: 0.0020-0.0050%, P: ≤0.020%, S: ≤0.002%, N: ≤0.004%, the balance is Fe and other unavoidable impurities; through component design, inclusion control, controlled rolling and controlled cooling and heat treatment, it can be used to manufacture various bridges in marine atmospheric environment, and the thickness of the steel is 10-40mm. In the production process of patent 6, the slab needs to be brushed with anti-oxidation paint during heating, and tempering treatment is also required, which increases the manufacturing cost and also increases the smelting difficulty.

[0013] In summary, the current production method of the steel plate for resisting marine atmospheric corrosion mainly reflects that the corrosion resistance of the steel plate is achieved by adding a large amount of corrosion-resistant alloy elements, and the addition of alloy elements inevitably increases the smelting cost and process difficulty, and some elements need to be additionally added with other elements for necessary inhibition due to the easy generation of metallurgical defects. Secondly, since a single material is used, the corrosion resistance and necessary mechanical properties of the steel plate need to be considered, and the composition design and process design need to be compromised, and some materials still need to be heat treated to improve the performance of the steel plate. These all increase the production cost, and due to the narrow window of process parameter design, in order to ensure the necessary compression ratio, the thickness of the product can only be 60 mm and below, which greatly limits the application scene of the steel plate, and cannot guarantee to meet the use requirements of the hot-rolled steel plate for resisting marine atmospheric corrosion structure. SUMMARY

[0014] In view of the deficiencies and shortcomings of the prior art, the purpose of the present application is to provide a 500MPa grade hot-rolled steel plate for building structure resisting marine atmospheric corrosion and a manufacturing method thereof. The yield strength of the hot-rolled steel plate for building structure is ≥500MPa, the tensile strength is ≥640MPa, the yield ratio is ≤0.80, the impact energy KV2 at-40℃ is ≥190J, the corrosion rate of the steel plate is ≤0.004mm / a, the interface transition layer thickness is ≤10μm, and the interface shear strength is ≥320MPa. The hot-rolled steel plate for building structure has the advantages of resisting marine atmospheric corrosion, high bonding strength, excellent yield ratio and low temperature impact toughness, and high economy, and can meet the use requirements in marine atmospheric environment. It is suitable for steel structural members such as profiled steel plate, purlin, wall beam, roof truss, steel frame, etc., and has great economic and social benefits.

[0015] To achieve the above purpose, the technical scheme of the present application is as follows:

[0016] The base layer of the present application adopts low-carbon micro-alloying composition design, the corrosion-resistant layer increases the content of Si and N and adds Cu element to improve the resistance to marine atmospheric corrosion, realizes the resistance to high temperature, high humidity, high salt spray and high radiation of the marine atmospheric corrosion, realizes the excellent combination of stainless steel and carbon steel, controls the thickness of the interface transition layer, achieves high shear strength of the interface, and the base layer has excellent yield ratio and low temperature impact toughness.

[0017] Specifically, the first aspect of the present application provides a 500MPa grade hot-rolled steel plate for building structure resisting marine atmospheric corrosion, which comprises: a base layer, a corrosion-resistant layer on at least one side of the base layer, and an interface transition layer between the base layer and the corrosion-resistant layer.

[0018] The base layer contains the following chemical components with mass percentage content as follows: C: 0.050-0.150%, Si: 0.15-0.30%, Mn: 1.20-1.80%, Cr: 0.300-0.500%, Ni: 0.100-0.150%, Al: 0.020-0.050%, Ti: 0.010-0.018%, Nb: 0.040-0.060%, Mo: 0.10-0.40%, B: 0.0003-0.0005%, inevitable impurities including P and S, wherein P is 0.0005-0.003% and S is 0.0005-0.01%, in addition to Fe and inevitable impurities;

[0019] The corrosion-resistant layer contains the following chemical components with mass percentage content as follows: C: 0.010-0.040%, Si: 0.20-1.50%, Mn: 1.00-2.00%, Cr: 16.0-18.0%, Ni: 14.0-17.0%, Cu: 0.02-0.10%, N: 0.02-0.15%, Mo: 2.0-3.0%, Nb: 0.05-0.20%, inevitable impurities including P and S, wherein P is 0.005-0.03% and S is 0.005-0.03%, in addition to Fe and inevitable impurities;

[0020] The microstructure of the corrosion-resistant layer is equiaxed recrystallized austenite or elongated unrecrystallized austenite and high-temperature ferrite, and the content of high-temperature ferrite in the thickness direction of the corrosion-resistant layer is ≤2%, preferably 1.2-2%;

[0021] The interface transition layer realizes 100% metallurgical bonding, the thickness of the interface transition layer is ≤10 μm, preferably 7.3-10 μm, the average grain size of the grains in the interface transition layer is ≤0.5 μm, preferably 0.1-0.5 μm, and the interface shear strength is ≥320 MPa;

[0022] The hot-rolled steel plate has a yield strength ≥500 MPa, a tensile strength ≥640 MPa, a yield strength / tensile strength ratio ≤0.80, preferably 0.76-0.80, a -40 ℃ impact energy KV2 ≥190 J, and a marine atmospheric corrosion resistance ≤0.004 mm / a.

[0023] Preferably, the chemical components of the corrosion-resistant layer also satisfy the following relationship (ratio of ferrite elements to austenite elements):

[0024] Preferably, the ratio is 0.94-1.3, wherein the element symbols are substituted into the values before the mass percentage content of each element.

[0025] Preferably, the chemical components of the base layer also satisfy the following relationship:

[0026] 3. 5%≤(Ti+Nb+Mo+Cr)%≤0.6%, wherein each element symbol is substituted into the value before the percentage sign of the mass percentage content of each element.

[0027] To take into account the mechanical properties of the base layer of carbon steel and not affect the corrosion resistance of the corrosion-resistant layer, preferably, the chemical composition of the corrosion-resistant layer also satisfies the following relationship:

[0028] PREN≥26, PREN=Cr%+3.3×Mo%+16×N%, wherein each element symbol is substituted into the value before the percentage sign of the mass percentage content of each element.

[0029] Preferably, the base layer contains the following chemical components with mass percentage contents as follows: C: 0.050-0.150%, Si: 0.15-0.30%, Mn: 1.20-1.80%, Cr: 0.300-0.500%, Ni: 0.100-0.150%, Al: 0.020-0.050%, Ti: 0.010-0.018%, Nb: 0.040-0.060%, Mo: 0.10-0.40%, B: 0.0003-0.0005%, the balance being Fe and unavoidable impurities, the unavoidable impurities including P and S, wherein P is 0.0005-0.003% and S is 0.0005-0.01%.

[0030] The corrosion-resistant layer contains the following chemical components with mass percentage contents as follows: C: 0.010-0.040%, Si: 0.20-1.50%, Mn: 1.00-2.00%, Cr: 16.0-18.0%, Ni: 14.0-17.0%, Cu: 0.02-0.10%, N: 0.02-0.15%, Mo: 2.0-3.0%, Nb: 0.05-0.20%, the balance being Fe and unavoidable impurities, the unavoidable impurities including P and S, wherein P is 0.005-0.03% and S is 0.005-0.03%.

[0031] Preferably, the microstructure of the base layer of the present application is granular bainite + lath bainite, and the equivalent grain size is ≤15 μm, preferably 8-15 μm.

[0032] Preferably, the corrosion-resistant layer of the present application has a marine atmospheric corrosion rate of ≤0.004 mm / a.

[0033] Preferably, in the hot-rolled steel plate for building structures of the present application, the thickness of each corrosion-resistant layer accounts for 0.5%-15% of the total thickness of the hot-rolled steel plate.

[0034] Preferably, the hot-rolled steel plate for building structure according to the present application has a thickness of 10-100 mm.

[0035] Preferably, the microstructure of the corrosion-resistant layer is equiaxed recrystallized austenite or elongated unrecrystallized austenite and a small amount of high-temperature ferrite, and the appropriate amount of high-temperature ferrite can improve the subsequent weldability, but too much high-temperature ferrite will reduce the corrosion resistance of the corrosion-resistant layer, so the content of high-temperature ferrite in the thickness direction of the corrosion-resistant layer should be controlled to be ≤2%, preferably 1.2-2%. After the metallographic preparation is completed, different types of microstructure are determined by artificial judgment, and different metallographic structures are color-coded by using image software, and finally the area ratio is obtained by the ratio of the number of pixels of different metallographic structures to the number of pixels of the whole metallographic photo. The content of high-temperature ferrite means: the area ratio of high-temperature ferrite in different microstructures of the corrosion-resistant layer under the metallographic microscope.

[0036] Preferably, the interface transition layer realizes 100% metallurgical bonding, atomic high coherence, and the thickness of the interface transition layer is ≤10 μm, preferably 7.3-10 μm, and the interface transition layer is too thick, which will significantly reduce the interface shear strength, and the delamination defect is easy to occur in the subsequent bending processing of the steel plate. The interface transition layer has fine grain size, and the average grain size of the grain is ≤0.5 μm, preferably 0.1-0.5 μm, which further improves the interface bonding degree, and the interface shear strength is ≥320 MPa.

[0037] In the base layer component design of the hot-rolled steel plate according to the present application:

[0038] C: C in steel plays a role in solid solution strengthening, which can significantly improve the strength of the steel. However, too high C content is not conducive to the weldability and toughness, and more importantly, too high C content will diffuse to the composite interface and form a large amount of granular carbide in the interface transition layer, which reduces the strength of the composite interface. In order to ensure the shear strength of the interface, low C content is used. The change of C content has less effect on the yield strength of the steel than on the tensile strength, and under the premise of ensuring the forming and welding performance of the product, appropriately increasing the content of C is beneficial to reducing the yield ratio of the steel. Therefore, in the base layer component according to the present application, the C content is controlled to be 0.050-0.150%.

[0039] Si: the addition of Si element in steel can equivalent deoxidize and improve the purity of steel. In addition, Si element in steel can play a role in solid solution strengthening, which can improve the strength and hardness of the steel, but Si element is not conducive to the welding performance of the material. Therefore, in the base layer component according to the present application, the Si content is controlled to be 0.15-0.30%.

[0040] Mn: Mn is the cheapest reinforcing matrix element, which can reduce the austenite transformation temperature, delay the pearlite transformation, refine the ferrite grain, and increase the strength of the steel. Meanwhile, Mn can also eliminate the effect of S on the steel. However, too high Mn content can easily cause segregation band and martensite structure, which is not conducive to the toughness of the steel. Therefore, the Mn content in the base layer composition of the present application is controlled at 1.20-1.80%.

[0041] Al: Al is mainly added to the steel as a deoxidizing element to ensure that the O content in the steel is as low as possible. After deoxidization, the excess Al combines with N in the steel to form AlN precipitates. AlN hinders the growth of austenite grains during heating, refines the austenite grains, and improves the strength and toughness of the matrix. At the same time, the formation of AlN fixes part of the N in the matrix, reduces the diffusion of interstitial atoms N in the carbon steel base layer to the interface transition layer to form hard TiN, and deteriorates the interfacial shear strength of the clad plate. At the same time, the addition amount of Ti and Nb can be reduced, and the total cost can be reduced. Therefore, the Al content in the base layer composition of the present application is controlled at 0.020-0.050%.

[0042] Ti: Ti forms stable TiN or Ti(N,C) at high temperature, which plays a role in fixing C and N, prevents the diffusion of interstitial C and N atoms in the carbon steel base layer to the interface, and forms hard TiN or Ti(N,C) precipitates in the interface transition layer to obtain a clad plate with high interfacial shear strength. At the same time, TiN hinders the growth of austenite during heating, refines the austenite grains, and can improve the strength and toughness of the matrix. In subsequent welding, especially in the heat-affected zone (HAZ) close to the weld fusion boundary, the growth of austenite grains is inhibited, thereby improving the toughness of the welding HAZ, which can meet the needs of large welding heat input process. In order to improve the strength of the low-carbon matrix, reduce the diffusion of C and N to the interface, and obtain a clad plate with high interfacial shear strength, the Ti content in the base layer composition of the present application is controlled at 0.010-0.018%.

[0043] Nb: Nb exists in the form of solid solution Nb and Nb(C,N) in the steel, which plays a role in solid solution dragging and precipitate pinning during recrystallization. The addition of a small amount of Nb in the base layer carbon steel is mainly to increase the recrystallization temperature, so that the base layer carbon steel is refined after rolling in the recrystallization and unrecrystallization zones, which is beneficial to improve the low-temperature impact toughness of the base layer carbon steel. Due to the effect of Nb(C,N) precipitates, the original austenite grains will be finer, thereby promoting the formation of finer recrystallized grains, obtaining the ideal combination of high strength and high toughness. At the same time, Nb can fix the interstitial C and N atoms in the matrix, reduce the diffusion of C and N to the interface, and obtain a clad plate with high interfacial shear strength. Therefore, the Nb content in the base layer of the present application is controlled at 0.040-0.060%.

[0044] Ni: Ni is an element that stabilizes austenite, can improve the hardenability of the base carbon steel, so that the 60-100mm thick clad plate can also obtain full bainite structure, and can greatly improve the low temperature impact toughness and plasticity of the steel. At the same time, Ni can equivalent to prevent the diffusion speed of Ti into the base carbon steel, and has an advantageous effect on the thickness control of the interface transition layer, and can improve the corrosion resistance of the base carbon steel in combination with Cr and Mo. However, nickel is expensive, and excessive addition will increase the cost of the clad plate. Based on this, an appropriate amount of Ni is added in the base layer composition, and the content of Ni is controlled to be 0.100-0.150%.

[0045] Cr: Cr is a strong carbide forming element, and the diffusion speed in austenite is small, and at the same time, it hinders the diffusion of C elements. Fine carbides are formed during low temperature process, which plays a role in precipitation strengthening. At the same time, it can fix the interstitial C and N atoms in the matrix, reduce the diffusion of C and N to the interface, and obtain high interface shear strength clad plate. Cr can improve the strength of the matrix in the steel while reducing the toughness, in order to obtain the best match of strength and toughness, the content of Cr in the base layer composition is controlled to be 0.300-0.500%.

[0046] Mo: In the base layer described in the application, Mo can significantly refine the grain, improve the strength and toughness of the matrix, and form stable carbides with C to improve the strength of the base layer. At the same time, it can improve the hardenability of the base carbon steel, which is beneficial to the formation of bainite structure in the base layer. Based on this, an appropriate amount of Mo can be added in the base layer described in the application, and the mass percentage of Mo element is controlled to be 0.10-0.40%.

[0047] B: B can promote the refinement of grains in steel, which helps to improve the toughness and impact toughness of the steel, and can form high-hardness compounds such as borides with C, N and other elements in the steel, thereby enhancing the hardness and wear resistance of the steel. B can also improve the plasticity and welding performance of the steel, and reduce the risk of cracks during welding. B can significantly improve the wear resistance and corrosion resistance of the steel. B can significantly improve the hardenability of the steel, and even a small amount of boron can achieve obvious effect, so it is not suitable to add too much. Based on this, an appropriate amount of B can be added in the base layer described in the application, and the mass percentage of B element is controlled to be 0.0003-0.0005%.

[0048] P, S, both are inevitable impurity elements, and the lower the content is the better. Considering the actual steelmaking level of the steel plant, the content of S and P is controlled as follows: S: 0-0.010%, preferably 0.0005-0.010%; P: 0-0.003%, preferably 0.0005-0.003%.

[0049] As preferred, the base layer chemical composition also needs to comprehensively control the total amount of Cr, Ti, Nb and Mo carbide forming elements, and the total amount of the added elements is controlled to be more than 3.5 times the C content, so that the C in the base layer is fully fixed, the diffusion opportunity to the bonding interface is reduced, the formation of large-size carbides near the interface is avoided, and the interface bonding strength is improved. At the same time, in order to ensure the strength of the base layer, a certain amount of the above-mentioned alloy needs to be dissolved in the base body, which plays a solid solution drag role in the heating and rolling process, hinders the grain growth, refines the austenite grains, and improves the strength and toughness of the base body. However, too high content of the above-mentioned alloy will significantly increase the carbon equivalent of the base layer, which is not conducive to the welding performance of the material, so the upper limit of the total amount should be limited.

[0050] Preferably, the base layer chemical composition satisfies the following relationship:

[0051] 3.5C%≤(Ti+Nb+Mo+Cr)%≤0.6%, wherein the symbols of the elements are substituted into the values before the percentage sign of the mass percentage content of each element.

[0052] The corrosion-resistant layer described in the present application is based on the composition of 316L stainless steel, with increased Si and N content, and added Cu and Nb elements, to further improve the marine atmospheric corrosion resistance of the corrosion-resistant layer.

[0053] Si: In the corrosion-resistant layer described in the present application, Si can promote the formation of a passivation film and stabilize the passivation film, and will not form easily soluble products in a Cl- containing medium, maintaining the continuity of the passivation film and improving the pitting corrosion resistance of the corrosion-resistant layer. However, Si is a ferrite element, and an increase in Si content will increase the high-temperature ferrite content in the austenitic matrix, which is prone to decompose into brittle phases such as sigma and chi, thereby reducing the intergranular corrosion resistance and toughness of the steel plate. Therefore, the mass percentage of Si should not be too high, and is controlled to be 0.20-1.50%.

[0054] N: In the corrosion-resistant layer described in the present application, N is a very strong element for forming, stabilizing and expanding the austenite region; N can combine with alloying elements such as Cr and Mo to form stable nitrides. These nitrides can form a dense protective film on the surface of the stainless steel, effectively preventing the corrosion of the corrosion medium, and help to improve the stability of the passivation film, making it more dense and stable, thereby improving the pitting corrosion and intergranular corrosion resistance of the corrosion-resistant layer, and offsetting the influence of high-temperature ferrite generated by high Si, balancing the austenite / ferrite stable element content and determining the phase composition in the balanced state. However, when the N content in the steel is too high, it will increase the risk of forming N-containing intermetallic phases, and increase the difficulty of melting and hot working, leading to difficulty in production. Therefore, in the corrosion-resistant layer described in the present application, the mass percentage of N is controlled to be 0.02-0.15%.

[0055] Cu: In the corrosion-resistant layer shown in the present application, Cu is a ferrite element that can improve the strength and hardness of the corrosion-resistant layer and improve its tensile strength and ductility. At the same time, Cu can improve the local points on the surface of the stainless steel by improving the chemical properties of the alloy composition, making it more anodic, and can improve the corrosion resistance of the corrosion-resistant layer, especially for the corrosion of chloride ions. The presence of Cu can promote the oxidation reaction and form a dense oxide film, thereby promoting the pitting corrosion and intergranular corrosion resistance of the corrosion-resistant layer. However, too high a content of Cu can reduce the impact performance and welding performance of the corrosion-resistant layer, so the mass percentage of Cu element is controlled at 0.02-0.10%.

[0056] Nb: Niobium is mainly added as a stabilizing element to prevent the occurrence of intergranular corrosion in the sensitized state. The affinity of niobium for carbon is much greater than that of chromium, and when added to austenitic stainless steel, it preferentially combines with carbon to form NbC, thereby preventing the occurrence of intergranular corrosion in the sensitized state. At the same time, due to the increase in the C content of the base layer, the effect of interfacial diffusion is more obvious, and the Nb in the corrosion-resistant layer can fix a part of C at the interface, further improving the interfacial bonding strength, and the addition amount of Nb is usually about 4-10 times the addition amount of C to ensure that the C element is fixed. Based on the economic considerations of the corrosion-resistant layer, the addition amount of Nb is set to 5 times the C content, and is controlled between 0.05-0.20%.

[0057] Due to the fact that C and Ni are austenite stabilizing elements that can further expand the austenite phase region, austenite can still be maintained at a lower final rolling temperature. The content of C and Ni is increased, but too much C can cause an increase in intergranular corrosion sensitivity, so the content should be limited. The mass percentage of C element is controlled between 0.010-0.040%, and the mass percentage of Ni element is controlled between 14.0-17.0% based on cost and to offset the corrosion tendency caused by the increase in ferrite stabilizing elements Cr, Mo, Si, and Cu.

[0058] Preferably, Si element, Cu element and N element are further controlled to control the high-temperature ferrite content. The composition content in the corrosion-resistant layer satisfies:

[0059] Preferably, it is 0.94-1.3, and in the formula, each element symbol is replaced by the mass percentage content of each element before the number in the percentage sign.

[0060] Since Cr, Mo, Si, and Cu are ferrite stabilizing elements, and Ni, C, N, and Mn are austenite stabilizing elements, the ratio of the two elements is controlled by the above formula to control the content of high-temperature ferrite to below 2% and improve the intergranular corrosion resistance of the corrosion-resistant layer.

[0061] Preferably, the chemical composition of the corrosion-resistant layer also satisfies the following relationship:

[0062] PREN≥26, PREN=Cr%+3.3×Mo%+16×N%, wherein each element symbol is substituted into the value before the percentage symbol of the mass percentage content of each element.

[0063] The second aspect of the present application provides a method for manufacturing a 500MPa-grade hot-rolled steel plate for building structures resistant to marine atmospheric corrosion, which comprises the following steps performed in sequence:

[0064] 1) Smelting and casting:

[0065] Based on the chemical composition of the base layer and the corrosion-resistant layer in the hot-rolled steel plate described above, the base layer billet and the corrosion-resistant layer billet are smelted and cast respectively;

[0066] 2) Grouping:

[0067] The base layer billet and the corrosion-resistant layer billet are subjected to surface grinding and polishing to remove surface oxide scale and oil stains, and then are grouped and sealed by four-side welding to form a composite billet; the bonding surface of the four-side welded and sealed composite billet is subjected to vacuum treatment to obtain a vacuum-treated composite billet;

[0068] 3) Heating:

[0069] The vacuum-treated composite billet is heated to 1150-1250℃ to obtain a heated composite billet, wherein the heating rate is ≤10℃ / min, preferably 8.3-10℃ / min;

[0070] 4) Rolling:

[0071] The heated composite billet is rolled to obtain a rolled composite billet, wherein the reduction rate of the first pass and the second pass is controlled to be 5-10%, the reduction rate of other passes is controlled to be 10-30%, the cumulative reduction rate is ≥70%, and the finish rolling temperature is controlled to be 800-860℃;

[0072] 5) Cooling:

[0073] The rolled composite billet is cooled by water cooling to obtain a hot-rolled steel plate, wherein the cooling rate is controlled to be 15-30℃ / s, and the final cooling temperature is 450-600℃.

[0074] In the method for manufacturing the hot-rolled steel plate of the present application:

[0075] 1) Smelting: P and S elements can deteriorate the fracture toughness of steel, so low P and low S control should be performed during smelting to improve the quality of the billet. Clean steel production technology is adopted to reduce the gas and inclusion content in the steel and improve the comprehensive performance of the steel, especially the resistance to lamellar tearing.

[0076] 2) Group billet; the corrosion-resistant layer, the base layer carbon steel billet is pretreated to remove the surface oxide scale and oil stains, so as to prevent the introduction of impurities affecting the combination, and the steel billet is sealed by welding around the bonding surface, and the bonding surface after welding sealing is vacuumized. Vacuum treatment protects the surface of the corrosion-resistant layer from being oxidized, which is also an important condition to ensure the corrosion resistance of the corrosion-resistant layer in the splash area.

[0077] 3) Heating: for single carbon steel, the slab heating temperature is generally controlled at 1120-1200℃, but for the corrosion-resistant steel plate of the present application, the high-temperature ferrite content control and interface bonding degree control of the corrosion-resistant layer need to be considered, the slab heating temperature is controlled at 1150-1250℃, which is beneficial to the dissolution and sufficient diffusion of precipitates in the base layer and corrosion-resistant layer steel, promotes slab element homogenization, plays a strengthening role of micro-alloy elements in steel, especially the corrosion-resistant layer at this temperature interval is the complete austenitizing temperature, which promotes the full diffusion of elements and can effectively control the generation of high-temperature ferrite; At the same time, high-temperature heating accelerates element diffusion and promotes 100% metallurgical bonding of the interface; But higher heating temperature will increase the tendency of coarse austenite grains in the base layer, increase the difficulty of subsequent controlled rolling, most importantly, it will accelerate the diffusion of C and N to the interface, if large-size carbides are formed at the interface, it will deteriorate the interface shear strength, and the long-distance diffusion of C will also affect the corrosion resistance of the corrosion-resistant layer. While too fast heating rate will increase the risk of weld cracking, leading to vacuum failure and thus unable to form a combination, so the heating rate should not be too fast, preferably, the heating temperature is set to 1150-1250℃, and the heating rate is controlled within 10℃ / min.

[0078] 4) Rolling: large reduction is performed above the recrystallization temperature, so that the structure is fully recrystallized, the grains are refined, and the strength and toughness of the material are improved; at the same time, the metal atoms at the interface are subjected to sufficient compression stress, and the atoms form interpenetration by diffusion, so that the interface can reach the interatomic bonding. The reduction rate of other passes is ensured to be 10-30%, and the cumulative reduction rate is ≥70%, wherein the reduction rate of the first pass and the second pass is controlled to be 5%-10%. Due to the difference in deformation difficulty between the base layer and the corrosion-resistant layer, excessive reduction rate will cause too large difference in elongation between the two layers, causing the interface to move, which is not conducive to the combination of the two layers. Small reduction is used to achieve the preliminary combination of the two layers; the base layer is fully recrystallized, the grains are refined, and the impact toughness of the base layer is improved at the high-temperature recrystallization temperature interval; controlled rolling is performed in the non-recrystallization zone, and austenite recrystallization does not occur at this stage. By using reasonable reduction rate and finish rolling temperature, the deformation energy and dislocation are accumulated, high-density deformation bands are formed inside the austenite grains, the phase nucleation points are increased, the equivalent grain size of the base phase after phase transformation is further refined, and the strength and toughness of the material are improved. At the same time, the deformation induces the precipitation of Nb, Ti, and Cr carbonitride, improves the strength of the base, suppresses the diffusion of C to the interface, and avoids the formation of large-size carbides at the interface to degrade the interface shear strength. Preferably, the finish rolling temperature is controlled to be 800-860°C, which ensures the corrosion resistance of the corrosion-resistant layer and obtains a granular bainite + lath bainite structure with an equivalent grain size of ≤15μm.

[0079] 5) Cooling: by controlling the cooling rate, the type and size of the rolled structure are controlled. Too fast cooling rate will form martensite structure, which is low toughness and high yield ratio structure, and is not conducive to the performance of the steel plate. Too slow cooling rate will lead to the formation of a large amount of coarse ferrite structure, which is conducive to crack propagation and causes the impact performance to decrease, so the cooling rate should be reasonably controlled; the control of the finish rolling temperature can avoid the formation of ferrite and reduce the strength of the base layer; at the same time, the rolled steel can be quickly cooled to the phase transformation temperature after rolling, which further suppresses the growth of the structure and improves the strength and low-temperature impact toughness of the material by refining the grains. Preferably, water cooling is used to cool the steel plate, the cooling rate is controlled to be 15-30°C / s, and the final cooling temperature is controlled to be 450-600°C, so as to ensure that the base layer has low yield ratio and high low-temperature impact toughness.

[0080] Preferably, when the corrosion-resistant layer is too thick, it will affect the mechanical properties of the material and the production cost; and when the corrosion-resistant layer is too thin, it will reduce the corrosion resistance and service life of the material. Therefore, the thickness of each corrosion-resistant layer in the hot-rolled steel plate accounts for 0.5%-15% of the total thickness of the hot-rolled steel plate.

[0081] The application forms the corrosion-resistant layer on the surface of the base layer, i.e. the carbon steel plate, through rolling process by combining the component design and the thickness ratio design of the corrosion-resistant layer and the base layer, and finally forms the steel plate with the corrosion resistance to the marine atmospheric zone, good mechanical properties and high economic efficiency, and the steel plate is reprocessed into a structural member and can be equivalent to the steel structural member used in the sea-spray zone environment.

[0082] Compared with the prior art, the application has the following beneficial effects:

[0083] The base layer adopts the low-carbon micro-alloying component design, the corrosion-resistant layer adopts the increase of the Si element and N element content, the addition of the Cu element, the increase of the C and Ni content to expand the austenite zone, the reduction of the C content to reduce the intergranular corrosion tendency and the interface diffusion effect, and the increase of the trace Nb element to fix C, so that the excellent combination of the stainless steel and the carbon steel is realized under the reasonable rolling process, the interface transition layer thickness is regulated, the high-strength structural steel plate meeting the marine environment is obtained, and the excellent marine atmospheric corrosion resistance and mechanical properties are obtained.

[0084] In addition, the base layer reduces the C content to avoid the formation of large-size carbides at the interface, and equivalently controls the interface transition layer thickness and the grain size, and improves the interface shear strength and toughness. At the same time, the addition of the micro-alloying element and the reasonable rolling and cooling process solve the problem of low material strength under the low-carbon condition; the yield strength is greater than or equal to 500 MPa, the tensile strength is greater than or equal to 640 MPa, the yield strength ratio is less than or equal to 0.8, and the impact energy KV2 at-40 DEG C is greater than or equal to 190 J, which are all higher than the performance requirements in the national standard GB / T 19879-2015 "Building structure steel plate".

[0085] Chinese patent 1 (publication number CN106756476A) discloses a high-strength weather-resistant steel for high-humidity and high-temperature marine atmospheric environment and a preparation method, which mainly solves the problem of the corrosion of the steel plate in the humid and hot marine atmospheric environment by adding trace elements such as Sn, Sb, Nb and Re to replace the addition amount of Cr, and performs a comparison with the traditional carbon structural steel and weather-resistant steel through a week immersion corrosion experiment. The results show that the corrosion rate is reduced by about 30% in 96 hours.

[0086] Chinese patent 2 (publication number CN111621699A) discloses a kind of high humidity and heat marine atmospheric environment bridge structure corrosion-resistant low alloy steel and preparation method, its solution is in the basis of Cu-Ni-Mo low alloy steel alloy system, in combination with the economy of low alloy steel, the content of alloying element Cu, Ni and Mo is reasonably adjusted, and the corrosion-resistant low alloy steel of ferrite-perlitic structure is obtained.The advantage lies in that, in the case of high cost brought by proper control of alloying elements Ni and Mo, the corrosion-resistant steel in the present application has certain economy and good corrosion resistance, its corrosion resistance is significantly better than that of plain carbon steel, and meets the requirements of bridge structure steel in high humidity and heat marine atmospheric environment on its mechanical properties.

[0087] The above two patents mainly improve the corrosion resistance of steel by adding corrosion-resistant micro-alloy elements or increasing the content of corrosion-resistant elements Cr, Ni and Mo. The corrosion resistance of the present application structural steel is 10-20 times that of plain carbon steel or weathering steel based on ensuring the mechanical properties of the base body.

[0088] Chinese patent 3 (publication number CN112647014A) selectively contains any one or both of Sn: 0.01%-0.02% and V: 0.05-0.1% in its chemical composition, while adding more low-melting-point elements such as P-Sb-Ce, which affects the low-temperature toughness, weldability, cold formability, etc. of the steel, and its-20℃ impact energy is only 47J. The present application does not add related low-melting-point elements, the smelting difficulty is relatively smaller, and the formability is better, and at the same time, the-40℃ impact energy is ≥190J.

[0089] Chinese patent 4 (publication number CN108004488A) adds more Ni, Cr, Mo, Cu and other precious metal alloys in its chemical composition, which has high cost, Sb is easy to segregate, increases the smelting process difficulty, and the addition of more Si is not good for surface quality and will affect the welding performance of steel plate, and the steel plate needs to be tempered after rolling for performance control. The present application only adds necessary elements in the corrosion-resistant layer, and the thickness of the corrosion-resistant layer can be controlled to meet the corrosion life requirement, and the steel plate after rolling does not need to go through the tempering process to control the performance.

[0090] The Chinese patent 5 (application number CN202210570630.7) is suitable for producing a steel with a thickness specification of ≤60 mm, with a yield strength of ≥500 MPa, and a tensile strength of ≥540 MPa. The 500 MPa weather-resistant steel produced by this invention has a complex production process that requires a tempering heat treatment, which increases the manufacturing cost. Moreover, the corrosion resistance of the steel plate is not described. This invention can produce a thickness specification of up to 100 mm due to the necessary component design in the base layer. Additionally, the lower alloy content reduces costs and eliminates the need for a tempering process to improve performance. The corrosion resistance is more explicit compared to the comparative patent.

[0091] The Chinese patent 6 (application number CN201810908224.0) can be used to manufacture various bridges in marine atmospheric environments through component design, inclusion control, controlled rolling, controlled cooling, and heat treatment. The steel thickness is 10-40 mm, and the yield strength ratio is ≤0.86. This invention requires brushing anti-oxidation paint on the slab during heating and tempering treatment, which increases the manufacturing cost and smelting difficulty due to the addition of alloy elements such as Cu and Ni. This invention can better balance the corrosion resistance and mechanical properties by implementing them in the corrosion-resistant layer and the base layer, respectively. The base layer has fewer alloy additions, eliminating the need for anti-oxidation paint and tempering treatment, reducing production costs, and producing a specification of up to 100 mm with a yield strength ratio of ≤0.8. The use scenario is more extensive compared to the comparative patent.

[0092] The combination of the corrosion-resistant layer and the base layer, along with appropriate heating, rolling, and cooling processes, results in a steel plate for steel structures that is resistant to marine atmospheric corrosion, has good mechanical properties, and is economically efficient. The yield strength is ≥500 MPa, the tensile strength is ≥640 MPa, the yield strength ratio is ≤0.8, and the impact energy at -40°C is KV2≥190 J. In an environment with an average annual salt mist concentration of 0.0189-0.1581 mg / m3, an average annual relative humidity of 30-80%, and an average annual total solar radiation of 3298.02-7350.13 MJ / m2, the average corrosion rate is ≤0.004 mm / a. The base layer and the corrosion-resistant layer are controlled to form an interface transition layer with a thickness of ≤10 μm, which has fine grain structure with an average grain size of ≤0.5 μm and good deformation coordination ability, ensuring an interface shear strength of ≥320 MPa.

[0093] In summary, the 500MPa-grade hot-rolled steel plate for building structure with marine atmospheric corrosion resistance provided by the application can solve the essential problems of stainless steel or carbon steel used in a sea wave atmospheric environment; the 500MPa-grade hot-rolled steel plate for building structure with marine atmospheric corrosion resistance can be equivalently applied to the manufacture of steel structural parts used in a marine atmospheric environment, for example, steel structural parts of facilities such as seaports and offshore oil platforms in a marine atmospheric environment, which can meet the requirements of these components for marine atmospheric corrosion resistance and mechanical properties, greatly improve the applicability, safety and durability of these components, and have great economic and social benefits. BRIEF DESCRIPTION OF DRAWINGS

[0094] Fig. 1 is a schematic diagram of an interlayer structure of the 500MPa-grade hot-rolled steel plate for building structure with marine atmospheric corrosion resistance provided by the application.

[0095] Fig. 2 is a schematic diagram of another interlayer structure of the 500MPa-grade hot-rolled steel plate for building structure with marine atmospheric corrosion resistance provided by the application.

[0096] Fig. 3 is a microstructure photograph of the corrosion-resistant layer in the hot-rolled steel plate manufactured in Example 3 of the application.

[0097] Fig. 4 is a scanning image of the interface transition layer of the base layer and the corrosion-resistant layer in the hot-rolled steel plate manufactured in Example 3 of the application.

[0098] Fig. 5 is a microstructure photograph of the base layer in the hot-rolled steel plate manufactured in Example 3 of the application. DETAILED DESCRIPTION

[0099] The technical solutions of the application will be further described in detail below in combination with examples and drawings. It should be clear that the following examples are only used to describe the specific embodiments of the application and do not constitute any limitation on the protection scope of the application.

[0100] Examples 1-8 and Comparative Examples 1-8

[0101] 1) Smelting and casting:

[0102] The base layer and the corrosion-resistant layer in Table 1-2 were smelted and cast respectively to form base layer blanks and corrosion-resistant layer blanks;

[0103] 2) Grouping blanks:

[0104] The base layer blanks and the corrosion-resistant layer blanks were subjected to surface grinding and polishing to remove surface oxide scales and oil stains, and then were grouped and sealed by four-side welding to form composite blanks; the bonding surface of the composite blanks sealed by four-side welding was subjected to vacuum treatment to obtain vacuum-treated composite blanks;

[0105] 3) Heating:

[0106] The vacuum-treated composite blank is heated to obtain a heated composite blank;

[0107] 4) Rolling:

[0108] The heated composite blank is rolled to obtain a rolled composite blank.

[0109] 5) Cooling:

[0110] The rolled composite blank is cooled by water cooling to obtain a hot-rolled steel plate.

[0111] Referring to FIG. 1 and FIG. 2, which are schematic diagrams of two interlayer structures of the hot-rolled steel plate for building structure according to the present application, wherein 1 is a base layer, 2 is a corrosion-resistant layer, and 3 is an interface transition layer. Examples 1-3 and Comparative Examples 2-4 adopt the interlayer structure of FIG. 1 for blanking. Examples 4-8 and Comparative Examples 1, 5-8 adopt the interlayer structure of FIG. 2 for blanking. The thickness of each corrosion-resistant layer in the hot-rolled steel plate according to the present application accounts for 0.5-15% of the total thickness of the hot-rolled steel plate. The meaning of “each” is that, if the blanking mode of FIG. 1 is adopted, the thickness of the single corrosion-resistant layer “2” is used, and if the blanking mode of FIG. 2 is adopted, the thickness of any one of the upper and lower corrosion-resistant layers “2” is used.

[0112] The composition of the base layer of the hot-rolled steel plate (composite steel plate) according to the present application is shown in Table 1, and the balance of the composition is Fe and unavoidable impurities. The mass percentage content of P and S in the base layer steel of Examples 1-8 and Comparative Examples 1-8 is 0.003% and 0.01%, respectively. The composition of the corrosion-resistant layer of the hot-rolled steel plate (composite steel plate) according to the present application and the comparative examples is shown in Table 2, and the balance of the composition is Fe and unavoidable impurities. The mass percentage content of P and S in the corrosion-resistant layer steel of Examples 1-8 and Comparative Examples 1-8 is 0.03% and 0.03%, respectively. Table 3 shows the manufacturing process parameters of the composite steel plate according to the present application and the comparative examples. The reduction rate of the first pass and the second pass in Examples 1-8 and Comparative Examples 1-8 is controlled to be 10%. Table 4 shows the metallographic structure and mechanical properties of the base layer and the corrosion-resistant layer in the composite steel plate according to the examples and the comparative examples, and the thickness of the interface transition layer.

[0113] The yield strength and the tensile strength of the composite steel plate are measured in accordance with GB / T 6396-2008 “Mechanical and Technological Properties of Clad Steel Plates-Method” and GB / T 228-2010 “Metallic Materials-Tensile Testing at Ambient Temperature”.

[0114] The impact energy KV2 / J at -40℃ (longitudinal direction) is measured in accordance with GB / T 6396-2008 “Mechanical and Technological Properties of Clad Steel Plates-Method” and GB / T 229-2020 “Metallic Materials Charpy Pendulum Impact Test Method”.

[0115] The marine atmospheric corrosion resistance rate is converted into the annual corrosion rate (mm / a) according to the time and the corrosion area, according to the weight loss of the composite steel plate caused by corrosion in the atmospheric environment with different chloride ion concentrations and temperatures simulated by the salt spray test.

[0116] The microstructure of each layer in the hot-rolled steel plate is prepared according to GB / T 13298-2015 Metallographic Examination Method of Metals, and different organizations are distinguished and measured by using image analysis software.

[0117] The thickness of the interface transition layer is measured according to GB / T 13298-2015 Metallographic Examination Method of Metals by means of the difference in the microstructure of the transition layer and the corrosion-resistant layer and the base layer carbon steel.

[0118] The thickness of the corrosion-resistant layer is observed and measured under a microscope after preparing the sample according to GB / T 13298-2015 Metallographic Examination Method of Metals.

[0119] The interface shear strength of the interface transition layer is tested according to the shear test in GB / T 6396-2008 Test Methods for Mechanical and Technological Properties of Composite Steel Plates.

[0120] The grain size rating is as follows: the ferrite structure in the stainless steel and carbon steel is rated according to GB / T 6394-2017 Metallographic Examination Method of Metals by using the intercept method.

[0121] The thickness of the corrosion-resistant layer and the base layer in the hot-rolled steel plate product obtained by the present application changes substantially in proportion before and after rolling. Therefore, the thickness ratio of the corrosion-resistant layer and the base layer in the hot-rolled steel plate product obtained by the present application is consistent with the thickness ratio of the corrosion-resistant layer and the base layer in the composite blank.

[0122] The comparative example is prepared by using the above steps substantially the same as the embodiment of the present application, except that the composition of the base layer carbon steel and certain process parameters used during the rolling or cooling step do not meet the requirements of the present application.

[0123] The metallographic structure of the corrosion-resistant layer in the hot-rolled steel plate manufactured in Example 3 is shown in Figure 3, which is equiaxed or slightly elongated recrystallized austenite.

[0124] The interface transition layer in the hot-rolled steel plate manufactured in Example 3 is shown in Figure 4, the thickness of the interface transition layer is 4.3 μm, and the grain size is small.

[0125] The metallographic structure of the base layer in the hot-rolled steel plate manufactured in Example 3 is shown in Figure 5, which shows that the metallographic structure of the base layer carbon steel is granular bainite.

[0126] Table 5 shows the corrosion of the composite steel plate hanging piece samples of Examples 1-8 and Comparative Examples 1-8 after 6 months in simulated different atmospheric environment scenarios. The observation results show that, in Comparative Example 1, Comparative Example 4, Comparative Example 6, and Comparative Example 7, because the composition or rolling process is not within the range defined in the application, the corrosion rate is ≥0.004 mm / a under high chloride ion concentration.

[0127] Comparative Examples 1-8 do not meet the use requirements due to the use of unqualified composition design requirements and hot working process conditions, resulting in certain properties of the composite steel plate not meeting the use requirements (performance parameters not within the range defined in the application). Among them:

[0128] Comparative Example 1 has a heating temperature exceeding the composition design range, resulting in high-temperature ferrite in the rolled structure not within the range defined in the application, and a corrosion rate ≥0.004 mm / a under high chloride ion concentration.

[0129] Comparative Example 2 has a base layer (Ti+Nb+V+Cr) % less than 3.5C %, insufficient carbon precipitation capacity, and interface bonding strength that cannot meet the use requirements. In addition, the final rolling temperature is too low, resulting in carbide precipitates at the grain boundaries of the steel plate, and a corrosion rate ≥0.004 mm / a under high chloride ion concentration. The yield strength ratio does not meet the requirements due to the final cooling temperature not being within the defined range.

[0130] Comparative Example 3 has a cumulative reduction rate not within the defined range, resulting in an average grain size of the grains in the interface transition layer not meeting the requirements, and a low bonding strength between the base layer and the corrosion-resistant layer.

[0131] Comparative Example 4 has insufficient pass reduction and insufficient grain refinement, resulting in yield strength and tensile strength not meeting the requirements.

[0132] Comparative Example 5 has Mo element in the base layer exceeding the composition design range, so the tensile strength does not meet the requirements.

[0133] Comparative Example 6 has a cooling speed that is too fast, resulting in a yield strength ratio that does not meet the requirements.

[0134] Comparative Example 7 has a final cooling temperature and cooling speed not within the defined range, resulting in an impact energy that does not meet the requirements. In addition, the corrosion-resistant layer does not contain Nb element, resulting in precipitates during low-temperature rolling, and a corrosion rate ≥0.004 mm / a under high chloride ion concentration.

[0135] Comparative Example 8 has B in the base layer exceeding the composition design range, resulting in martensite in the structure, and a yield strength ratio and impact performance that do not meet the requirements. In addition, the final rolling temperature is too low, resulting in carbide precipitates at the grain boundaries of the steel plate, and a corrosion rate ≥0.004 mm / a under high chloride ion concentration.

[0136] By the preparation method of the present application, especially the control of heating, rolling and cooling process, the base layer in the steel plate shows excellent yield ratio and low temperature impact toughness, meanwhile the corrosion resistant layer has excellent corrosion resistance and high bonding strength, the yield strength is 510-578 MPa, the tensile strength is 642-726 MPa, the yield ratio is 0.76-0.80, the impact energy at-40℃ is above 190J, and the interface shear strength is above 320MPa. Thus, the present application obtains a new 500MPa grade hot-rolled steel plate for marine atmospheric corrosion resistant structure, which can meet the use in marine atmospheric environment, and finally forms the profiled steel plate, purlin, wall beam, roof truss, steel frame and other steel structural members with marine atmospheric corrosion resistance, good mechanical properties and high economic efficiency, which has great economic and social benefits.

[0137] It should be noted that all the technical features described in the present application can be freely combined or integrated in any way, unless contradictory to each other. Various modifications and changes can be made to the present application without departing from the scope of the present application, which will be apparent to those skilled in the art. For example, the features shown or described as part of one embodiment can be used with another embodiment to produce yet another embodiment. Therefore, the present application is intended to cover these modifications falling within the scope of the appended claims and their equivalents.

[0138] Table 5:

Claims

1. A hot-rolled steel sheet characterized by, The hot-rolled steel plate comprises a base layer, a corrosion-resistant layer on at least one side of the base layer, and an interface transition layer between the base layer and the corrosion-resistant layer; The base layer comprises the following chemical components in the mass percentage: C: 0.050-0.150%, Si: 0.15-0.30%, Mn: 1.20-1.80%, Cr: 0.300-0.500%, Ni: 0.100-0.150%, Al: 0.020-0.050%, Ti: 0.010-0.018%, Nb: 0.040-0.060%, Mo: 0.10-0.40%, B: 0.0003-0.0005%, and inevitable impurities including P and S, wherein P is 0.0005-0.003% and S is 0.0005-0.01%. The corrosion-resistant layer comprises the following chemical components in the mass percentage: C: 0.010-0.040%, Si: 0.20-1.50%, Mn: 1.00-2.00%, Cr: 16.0-18.0%, Ni: 14.0-17.0%, Cu: 0.02-0.10%, N: 0.02-0.15%, Mo: 2.0-3.0%, Nb: 0.05-0.20%, and inevitable impurities including P and S, wherein P is 0.005-0.03% and S is 0.005-0.03%. The microstructure of the corrosion-resistant layer is equiaxed recrystallized austenite or elongated unrecrystallized austenite and high-temperature ferrite, and the content of the high-temperature ferrite is ≤2% in the thickness direction of the corrosion-resistant layer, preferably 1.2-2%. The interface transition layer is 100% metallurgical bonding, the thickness of the interface transition layer is ≤10 μm, preferably 7.3-10 μm, the average grain size of the grains in the interface transition layer is ≤0.5 μm, preferably 0.1-0.5 μm, and the interface shear strength is ≥320 MPa. The hot-rolled steel plate has a yield strength of ≥500 MPa, a tensile strength of ≥640 MPa, a yield strength ratio of ≤0.80, preferably 0.76-0.80, a -40 ℃ impact energy KV2 of ≥190 J, and a marine atmospheric corrosion resistance of ≤0.004 mm / a.

2. Hot-rolled steel sheet according to claim 1, characterized in that, The chemical components of the base layer also satisfy the following relationship: 3.5C%≤(Ti+Nb+Mo+Cr)%≤0.6%, wherein the symbols of the elements are substituted into the values before the mass percentage of each element.

3. Hot-rolled steel sheet according to claim 1 or 2, characterized in that, The chemical components of the corrosion-resistant layer also satisfy the following relationship: Preferably, 0.94-1.3, wherein the symbols of the elements are substituted into the values before the mass percentage of each element.

4. Hot-rolled steel sheet according to any one of claims 1 to 3, characterized in that, The chemical components of the corrosion-resistant layer also satisfy the following relationship: PreN≥26, PreN=Cr%+3.3×Mo%+16×N%, wherein the symbols of the elements are substituted into the values before the mass percentage of each element.

5. Hot-rolled steel sheet according to anyone of claims 1 to 4 characterized in that, The base layer comprises the following chemical components with mass percentage content as follows: C: 0.050-0.150%, Si: 0.15-0.30%, Mn: 1.20-1.80%, Cr: 0.300-0.500%, Ni: 0.100-0.150%, Al: 0.020-0.050%, Ti: 0.010-0.018%, Nb: 0.040-0.060%, Mo: 0.10-0.40%, B: 0.0003-0.0005%, the balance being Fe and inevitable impurities, the inevitable impurities including P and S, wherein P is 0.0005-0.003% and S is 0.0005-0.01%; The corrosion-resistant layer comprises the following chemical components with mass percentage content as follows: C: 0.010-0.040%, Si: 0.20-1.50%, Mn: 1.00-2.00%, Cr: 16.0-18.0%, Ni: 14.0-17.0%, Cu: 0.02-0.10%, N: 0.02-0.15%, Mo: 2.0-3.0%, Nb: 0.05-0.20%, the balance being Fe and inevitable impurities, the inevitable impurities including P and S, wherein P is 0.005-0.03% and S is 0.005-0.03%.

6. Hot-rolled steel sheet according to anyone of claims 1 to 5 characterized in that, The microstructure of the base layer is granular bainite + lath bainite, and the equivalent grain size is ≤15 μm, preferably 8-15 μm.

7. Hot-rolled steel sheet according to anyone of claims 1 to 6 characterized in that, The thickness of the hot-rolled steel plate is 10-100 mm.

8. Hot-rolled steel sheet according to anyone of claims 1 to 7 characterized in that, The thickness of each corrosion-resistant layer in the hot-rolled steel plate accounts for 0.5%-15% of the total thickness of the hot-rolled steel plate.

9. The method of producing a hot-rolled steel sheet according to any one of claims 1 to 8, characterized in that, The manufacturing method comprises the following steps performed in sequence: 1) smelting and casting: The base layer and the corrosion-resistant layer in the hot-rolled steel plate according to any one of claims 1-5 are smelted and cast respectively to form a base layer blank and a corrosion-resistant layer blank; 2) blank assembly: The base layer blank and the corrosion-resistant layer blank are subjected to surface grinding and polishing to remove surface oxide scale and oil stains, and then are assembled and sealed by four-side welding to form a composite blank; the bonding surface of the four-side welded composite blank is subjected to vacuum treatment to obtain a vacuum-treated composite blank; 3) heating: The vacuum-treated composite blank is heated to 1150-1250 °C to obtain a heated composite blank, wherein the heating rate is ≤10 °C / min, preferably 8.3-10 °C / min; 4) rolling: The heated composite blank is rolled to obtain a rolled composite blank, wherein the reduction rate of the first pass and the second pass is controlled at 5-10%, the reduction rate of other passes is controlled at 10-30%, the cumulative reduction rate is ≥70%, and the finish rolling temperature is controlled at 800-860 °C; 5) cooling: The rolled composite blank is cooled by water cooling to obtain a hot-rolled steel plate, wherein the cooling speed is controlled at 15-30 °C / s, and the final cooling temperature is 450-600 °C.

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