345-mpa-grade hot-rolled steel plate resistant to corrosion by marine atmospheres and used for building structures, and manufacturing method therefor

Abstract

The present invention relates to a 345-MPa-grade hot-rolled steel plate that is resistant to corrosion by 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 percentage by mass: 0.030-0.060% of C, 0.150-0.200% of Si, 1.00-1.30% of Mn, 0.100-0.150% of Cr, 0.010-0.070% of Ni, 0.015-0.030% of Al, 0.0080-0.0110% of Ti, 0.020-0.035% of Nb, and 0.0020-0.0040% of V, wherein the inevitable impurities comprise P and S, the content of P being 0.0005-0.003%, and the content of S being 0.0005-0.010%. In addition to Fe and inevitable impurities, the corrosion-resistant layer further comprises the following chemical components in percentages by mass: 0.001-0.030% of C, 0.2-1.5% of Si, 1.00-2.00% of Mn, 16.0-18.0% of Cr, 10.0-14.0% of Ni, 0.02-0.10% of Cu, 0.02-0.15% of N, and 2.0-3.0% of Mo, wherein the inevitable impurities comprises P and S, the content of P being 0.005-0.030%, and the content of S being 0.005-0.030%. The hot-rolled steel plate of the present invention has a thickness of 10-100 mm, a yield strength of greater than or equal to 345 MPa, a tensile strength of greater than or equal to 490 MPa, a yield ratio of less than or equal to 0.75, an impact energy KV2 at -40°C of greater than or equal to 190 J, a marine atmospheric corrosion rate of less than or equal to 0.004 mm / a, and an interface shear strength of greater than or equal to 270 MPa, and the thickness of the interface transition layer thereof is less than or equal to 10 μm.

Description

345mpa grade hot-rolled steel plate for building structure resistant to marine atmospheric corrosion and manufacturing method thereof TECHNICAL FIELD

[0001] The present application belongs to the technical field of building structure steel, and particularly relates to a 345MPa grade hot-rolled steel plate 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 engineering facilities related to the marine industry (including coastal industry, offshore wind power, marine large channel engineering, artificial islands and wharfs, offshore oil platforms, submarine oil and gas pipelines, etc.) have increased exponentially. The ocean is a very harsh corrosive environment for various structural materials, which can cause corrosion damage and loss of function of various infrastructure, 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. Sea salt particles are brought by sea wind, and the influence factors include height, wind speed, rainfall, temperature, radiation, etc., and sea salt particles 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 microns. The operation steps of the coating construction method are steel surface bottom treatment, undercoating, intermediate coating and top coating. The bottom treatment generally requires mechanical sand blasting treatment to process the steel surface. The undercoating paint includes organic zinc-rich paint, inorganic zinc-rich paint and special undercoating material according to different coatings. The inorganic zinc-rich paint is a undercoating coating with excellent rust prevention performance made by using zinc powder as a substitute anode. The organic zinc-rich paint has poorer rust prevention effect than the inorganic zinc-rich paint, but has good adhesion, and can be coated on the steel surface even if the dynamic tool is not used for bottom treatment as the shot blasting treatment. The coatings used for intermediate coating and top coating should have better adhesion and be more suitable for the surrounding environment than the undercoating coatings. After the construction is completed, film thickness measurement and air hole test must be carried out to confirm whether the coating film is sound.

[0005] This coating protection method has long construction period, complex process, and difficult to guarantee quality; the coating is too thick, the adhesion is limited, and the coating is easy to fail in the processing area such as welding and riveting during on-site construction of the component, and the corrosion resistance cannot be guaranteed; in the service process, 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 precious metal elements such as Cr, Ni and Mo, 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, and to compare the results of the traditional carbon structural steel and the weather-resistant steel in the immersion corrosion experiment. The results 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. In the case of appropriately controlling the high cost of alloy elements Ni and Mo, the corrosion resistance is significantly better than that of plain carbon steel, and meets the requirements of the mechanical properties of the steel for bridge structure in high-humidity and high-temperature marine atmospheric environment.

[0009] Both of the above two patents are in the category of single material, and alloy elements are added to the material to meet the corrosion resistance requirements. However, the addition of a large amount of alloy elements further increases the overall cost of the material and the difficulty of impurity control in the smelting process, and the overall corrosion resistance is relatively limited.

[0010] 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 the like of the steel.

[0011] 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. The invention adds more Ni, Cr, Mo, Cu and other precious metal alloys with 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.

[0012] 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, A1s: 0.02-0.05, Cu: 0.30-0.70, Ni: 0.7-1.5, the rest is Fe and inevitable 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 500MPa weathering steel produced by the invention has complex process and needs tempering heat treatment, which increases the manufacturing cost, and the corrosion resistance of the steel plate is not described.

[0013] 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. The invention needs to brush anti-oxidation paint on the slab during heating, and also needs to be tempered, which increases the manufacturing cost and also increases the smelting difficulty.

[0014] 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 also need to add other elements for necessary inhibition due to the easy production 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

[0015] In view of the deficiencies and shortcomings of the prior art, the purpose of the present application is to provide a 345MPa 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 ≥345MPa, the tensile strength is ≥490MPa, the yield strength ratio is ≤0.75, the impact energy KV2 at-40℃ is ≥190J, the corrosion rate of the hot-rolled steel plate for building structure resisting marine atmospheric corrosion is ≤0.004mm / a, the interface transition layer thickness is ≤10μm, and the interface shear strength is ≥270MPa. The hot-rolled steel plate for building structure has the properties of resisting marine atmospheric corrosion, high bonding strength, excellent yield strength ratio, low temperature impact toughness and high economy, and can meet the use requirements in marine atmospheric environment, and is suitable for steel structural members such as profiled steel plate, purlin, wall beam, roof truss and steel frame. It has great economic and social benefits.

[0016] To achieve the above purpose, the technical scheme of the present application is as follows:

[0017] 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 mist 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, and achieves high shear strength at the interface, so as to obtain a building structure steel plate with excellent corrosion resistance, yield strength ratio and low temperature impact toughness.

[0018] Specifically, the first aspect of the present application provides a 345MPa 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.

[0019] The base layer contains the following chemical components in the mass percentage content of 0.030-0.060% of C, 0.150-0.200% of Si, 1.00-1.30% of Mn, 0.100-0.150% of Cr, 0.010-0.070% of Ni, 0.015-0.030% of Al, 0.0080-0.0110% of Ti, 0.020-0.035% of Nb, 0.0020-0.0040% of V, and inevitable impurities including 0.0005-0.003% of P and 0.0005-0.010% of S;

[0020] The corrosion-resistant layer contains the following chemical components in the mass percentage content of 0.001-0.030% of C, 0.2-1.5% of Si, 1.00-2.00% of Mn, 16.0-18.0% of Cr, 10.0-14.0% of Ni, 0.02-0.10% of Cu, 0.02-0.15% of N, 2.0-3.0% of Mo, and inevitable impurities including 0.005-0.030% of P and 0.005-0.030% of S;

[0021] The microstructure of the corrosion-resistant layer is equiaxed recrystallized austenite or elongated unrecrystallized austenite and high-temperature ferrite, the content of the high-temperature ferrite in the thickness direction of the corrosion-resistant layer is ≤2%, preferably 0.9-2%;

[0022] The interface transition layer realizes 100% metallurgical bonding, atomic high coherence, the thickness of the interface transition layer is ≤10 μm, preferably 4-10 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 ≥270 MPa;

[0023] The yield strength of the hot-rolled steel plate is ≥345 MPa, the tensile strength is ≥490 MPa, the yield strength ratio is ≤0.75, the impact energy KV2 at -40 ℃ is ≥190 J, and the corrosion resistance to marine atmosphere is ≤0.004 mm / a.

[0024] Preferably, the chemical components of the base layer also satisfy the following relationship:

[0025] 2.8% of C ≤ (Ti+Nb+V+Cr)% ≤ 0.2%, wherein the symbols of the elements are substituted into the values before the mass percentage content of each element.

[0026] Preferably, the chemical components of the corrosion-resistant layer also satisfy the following relationship:

[0027] Preferably, 1.20-1.5, wherein each element symbol is substituted into the value before the percentage of the mass percentage content of each element.

[0028] Preferably, the chemical composition of the corrosion-resistant layer also satisfies the following relationship:

[0029] PREN≥23.0%, PREN=Cr%+3.3*Mo%+16*N%, wherein each element symbol is substituted into the value before the percentage of the mass percentage content of each element.

[0030] Preferably, the base layer contains the following chemical components with mass percentage contents as follows: C: 0.030-0.060%, Si: 0.150-0.200%, Mn: 1.00-1.30%, Cr: 0.100-0.150%, Ni: 0.010-0.070%, Al: 0.015-0.030%, Ti: 0.0080-0.0110%, Nb: 0.020-0.035%, V: 0.0020-0.0040%, the balance being Fe and inevitable impurities, the inevitable impurities including P and S, wherein P is 0.0005-0.003% and S is 0.0005-0.010%;

[0031] The corrosion-resistant layer contains the following chemical components with mass percentage contents as follows: C: 0.001-0.030%, Si: 0.2-1.5%, Mn: 1.00-2.00%, Cr: 16.0-18.0%, Ni: 10.0-14.0%, Cu: 0.02-0.10%, N: 0.02-0.15%, Mo: 2.0-3.0%, the balance being Fe and inevitable impurities, the inevitable impurities including P and S, wherein P is 0.005-0.030% and S is 0.005-0.030%.

[0032] In the present application, preferably, the microstructure of the base layer in the hot-rolled steel plate is ferrite+pearlite, or ferrite+pearlite+bainite; the content of pearlite in the microstructure of the base layer is ≥5%, preferably 5-15%; the content of bainite in the microstructure of the base layer is ≤5%, preferably 1-5%.

[0033] In the present application, preferably, the corrosion-resistant layer of the hot-rolled steel plate has a marine atmospheric corrosion resistance rate ≤0.004 mm / a.

[0034] Preferably, the thickness of the hot-rolled steel plate is 10-100 mm.

[0035] Preferably, 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.

[0036] In the present application, preferably, the microstructure of the base layer is ferrite + pearlite and / or a small amount of bainite structure, which can ensure that the base layer itself has a certain strength while the yield strength ratio is low. Since the toughness of pearlite is poorer than that of ferrite, the content of pearlite needs to be further controlled to ensure the impact toughness of the base layer. The content of pearlite is ≥ 5%, preferably 5% to 15%, and the content of bainite in the microstructure of the base layer is ≤ 5%, preferably 1 to 5%. After the metallographic preparation is completed, different types of structures are determined by artificial judgment, and different metallographic structures are color-coded using image software. Finally, the area ratio is obtained by the ratio of the pixel number of different metallographic structures to the pixel number of the whole metallographic photo. The meaning of the content of pearlite is that the area ratio of pearlite in different microstructures of the base layer under the metallographic microscope. The meaning of the content of bainite is that the area ratio of bainite in different microstructures of the base layer under the metallographic microscope.

[0037] Preferably, the microstructure of the corrosion-resistant layer is equiaxed recrystallized austenite or elongated unrecrystallized austenite and a small amount of high-temperature ferrite. An 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. Therefore, the content of high-temperature ferrite in the thickness direction should be controlled to be ≤ 2%, preferably 0.9 to 2%. After the metallographic preparation is completed, different types of structures are determined by artificial judgment, and different metallographic structures are color-coded using image software. Finally, the area ratio is obtained by the ratio of the pixel number of different metallographic structures to the pixel number of the whole metallographic photo. The meaning of the content of high-temperature ferrite is that the area ratio of high-temperature ferrite in different microstructures of the corrosion-resistant layer under the metallographic microscope.

[0038] The interface transition layer realizes 100% metallurgical bonding and atomic high coherence. The thickness of the interface transition layer is ≤ 10 μm, preferably 4 to 10 μm. An excessively thick interface transition layer will significantly reduce the interface shear strength and easily cause delamination defects in the subsequent bending processing of the steel plate. The microstructure of the interface transition layer is fine, with an average grain size ≤ 0.5 μm, preferably 0.1 to 0.5 μm, which further improves the interface bonding degree. The interface shear strength is ≥ 270 MPa.

[0039] In the component design of the base layer of the hot-rolled steel plate for building steel structure in the present application:

[0040] C: C plays a role of solid solution strengthening in steel, which can obviously improve the strength of steel. However, too high C content is not conducive to the welding performance and toughness, and more importantly, too high C content will diffuse to the composite interface, forming a large amount of granular carbide in the interface transition layer, reducing the strength of the composite interface. In order to ensure the shear strength of the interface, low C content is used in the present application. The change of C content has less effect on the yield strength of steel than on the tensile strength. On the premise of ensuring the forming and welding performance of the product, appropriately increasing the content of C is beneficial to reduce the yield strength ratio of the steel. Based on this, the C content in the base layer composition described in the present application is controlled at 0.030-0.060%.

[0041] 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 of solid solution strengthening, which can improve the strength and hardness of steel, but Si element is not conducive to the welding performance of the material. Therefore, the Si content in the base layer composition described in the present application is controlled at 0.150-0.200%.

[0042] Mn: Mn is the cheapest strengthening matrix element, which can reduce the austenite transformation temperature, delay the pearlite transformation, refine the ferrite grain, and improve the strength of steel. At the same time, Mn can also eliminate the effect of S on steel. However, too high Mn content is easy to appear segregation band and martensite structure, which is not conducive to the toughness of steel. Therefore, the Mn content in the base layer composition described in the present application is controlled at 1.00-1.30%.

[0043] Al: Al is mainly added to steel as excess deO element to ensure that the O content in steel is as low as possible. After deO, the excess Al combines with N element in 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 N in the matrix, reduces the diffusion of interstitial atom N in the carbon steel base layer to the composite interface, forms hard TiN in the interface transition layer, and deteriorates the shear strength of the composite plate interface. At the same time, the addition amount of Ti and Nb can be reduced, and the alloy cost can be reduced. Based on this, the Al content in the base layer composition described in the present application is controlled at 0.015-0.030%.

[0044] Ti: Ti forms stable TiN or Ti(N,C) at high temperature, which plays a role of fixing C and N, prevents the diffusion of gap C and N atoms in the carbon steel base layer to the interface, forms hard TiN or Ti(N,C) precipitates in the interface transition layer, and obtains a high interface shear strength composite plate. At the same time, TiN hinders the growth of austenite during the heating process, refines the austenite grains, and can improve the strength and toughness of the matrix. In the 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 high interface shear strength composite plate, the Ti content in the base layer composition described in the present application is controlled at 0.0080-0.0110%.

[0045] Nb: Nb exists in the form of solid solution Nb and Nb(C,N) in the steel, which plays a role of solid solution drag and precipitated 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 zone, 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, and at the same time, Nb can fix the gap C and N atoms in the matrix, reduce the diffusion of C and N to the interface, and obtain a high interface shear strength composite plate. Based on this, the Nb content in the base layer described in the present application is controlled at 0.020-0.035%.

[0046] Ni: Ni is an element that can stabilize austenite, can improve the hardenability of the base layer carbon steel, so that the 60-100mm thick composite 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 effectively prevent the diffusion of Ti into the base layer carbon steel, which has an advantageous effect on the thickness control of the interface transition layer, and can improve the corrosion resistance of the base layer carbon steel in combination with Cr and Mo. However, nickel is expensive, and excessive addition will increase the cost of the composite plate. Based on this, an appropriate amount of Ni is added to the base layer composition described in the present application, and the Ni content is controlled at 0.010-0.070%.

[0047] Cr: Cr is a strong carbide forming element, which has a small diffusion speed in austenite and can hinder the diffusion of C element. In the low temperature process, fine carbides are formed, which play a role of precipitation strengthening, and at the same time, can fix the gap C and N atoms in the matrix, reduce the diffusion of C and N to the interface, and obtain a high interface shear strength composite plate. Cr can improve the strength of the matrix while reducing the toughness of the steel. In order to obtain the best match of strength and toughness, the Cr content in the base layer composition described in the present application is controlled at 0.100-0.150%.

[0048] V: V is a strong carbonitride forming element, and when Ti and Nb are added in the steel, fine compound carbonitrides can be formed, and the precipitation temperature range is widened, which can effectively inhibit the austenite grain growth and the recrystallization process, and improve the strength and toughness of the base carbon steel. Meanwhile, the carbonitride precipitation temperature of V is low, and the precipitation during the phase transition can effectively organize the growth of ferrite grains and strengthen the ferrite matrix strength. Therefore, in the base composition of the present application, an appropriate amount of V is added, and the V content is controlled to be 0.0020-0.0040%.

[0049] P and S are both inevitable impurity elements, and the lower the content is, the better. Considering the actual steelmaking level of the steel plant, the S and P contents are controlled as follows: S: 0.0005-0.010%; P: 0.0005-0.003%.

[0050] As preferred, the base chemical composition also comprehensively controls the total amount of Cr, Ti, Nb and V, which are carbide forming elements, and the total amount is controlled to be more than 2.8 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 is also dissolved in the matrix, 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 matrix. 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.

[0051] Preferably, the base chemical composition also satisfies the following relationship:

[0052] 2.8C%≤(Ti+Nb+V+Cr) %≤0.2%, in which the symbols of the elements are substituted into the values before the mass percentage content of each element.

[0053] The corrosion-resistant layer of the present application further improves the marine atmospheric corrosion resistance of the cladding layer based on the composition of 316L stainless steel by increasing the Si and N contents and adding Cu element.

[0054] Si: In the corrosion-resistant layer of the present application, Si can promote the formation of passivation film and stabilize the passivation film, and will not form easily soluble products in Cl-containing medium, maintain the continuity of the passivation film, and improve the pitting corrosion resistance of the corrosion-resistant layer. However, Si is a ferrite element, and the increase of Si content will increase the high-temperature ferrite content in the austenite matrix, which is easy 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 element should not be too high, and the mass percentage of Si element is controlled to be 0.2-1.5%.

[0055] N: In the corrosion resistant layer described in the present application, N is a very strong element for forming, stabilizing and expanding the austenite zone; 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 corrosive media, and help to improve the stability of the passivation film, making it more dense and stable, thereby improving the resistance to pitting corrosion and intergranular corrosion of the corrosion resistant layer. At the same time, it can offset the influence of high Si on the formation of high temperature ferrite, balance the content of austenite / ferrite stabilizing elements, and determine 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, making it difficult to produce. Therefore, in the corrosion resistant layer described in the present application, the mass percentage of N element is controlled between 0.02-0.15%.

[0056] Cu: In the corrosion resistant layer described 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 point of the surface of the stainless steel by improving the chemical properties of the alloy composition, making it more anodic, which 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 improving the pitting corrosion and intergranular corrosion resistance of the corrosion resistant layer. However, too high a content of Cu will reduce the impact performance and welding performance, so the mass percentage of Cu element is controlled between 0.02-0.10%.

[0057] Preferably, the chemical composition of the corrosion resistant layer described in the present application also satisfies the following relationship (i.e. the ratio of ferrite elements to austenite elements):

[0058] Preferably, it is 1.20-1.5, wherein the element symbols are replaced by the mass percentage of each element before the percentage sign.

[0059] 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 high temperature ferrite below 2% and improve the intergranular corrosion resistance of the corrosion resistant layer.

[0060] Preferably, the chemical composition of the corrosion resistant layer needs to satisfy:

[0061] PREN≥23.0%, PREN=Cr%+3.3×Mo%+16×N%, wherein the element symbols are replaced by the mass percentage of each element before the percentage sign.

[0062] The second aspect of the present application provides a method for manufacturing a 345MPa-grade hot-rolled steel plate for marine atmospheric corrosion-resistant building structure, which comprises the following steps in sequence:

[0063] 1) smelting and casting:

[0064] The base layer and the corrosion-resistant layer of the above-mentioned corrosion-resistant steel plate are smelted and cast respectively to form base layer blanks and corrosion-resistant layer blanks.

[0065] 2) blank assembly:

[0066] The base layer blanks and the corrosion-resistant layer blanks are subjected to surface grinding and polishing to remove surface oxide scales and oil stains, and then the blanks are assembled and subjected to four-side welding sealing to form a composite blank; the bonding surface of the four-side welded and sealed composite blank is subjected to vacuum treatment to obtain a vacuum-treated composite blank.

[0067] 3) heating:

[0068] 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 7.6-10°C / min.

[0069] 4) rolling:

[0070] The heated composite blank is rolled to obtain a rolled composite blank, wherein the reduction in the first pass and the second pass is controlled at 5-10%, the reduction in the other passes is controlled at 5-20%, the cumulative reduction is ≥70%, and the finish rolling temperature is controlled at 850-950°C.

[0071] 5) cooling:

[0072] The rolled composite blank is cooled by water cooling to obtain a hot-rolled steel plate, wherein the cooling rate is controlled at 10-20°C / s, and the final cooling temperature is 600-700°C.

[0073] In the method for manufacturing the hot-rolled steel plate described in the present application:

[0074] 1) smelting: P and S elements can deteriorate the fracture toughness of the steel, so low P and low S control should be performed during smelting to improve the quality of the steel blank. 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.

[0075] 2) blank assembly: the corrosion-resistant layer and the base layer carbon steel blank are pretreated to remove surface oxide scales and oil stains to prevent the introduction of impurities affecting the bonding, and the bonding surface of the steel blank is subjected to four-side welding sealing. The bonding surface after welding sealing is subjected to vacuum treatment. The vacuum treatment protects the surface of the corrosion-resistant layer from being oxidized and is also an important condition for ensuring the corrosion resistance of the corrosion-resistant layer in the splash zone.

[0076] 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 slab heating temperature is controlled at 1150-1250℃, taking into account the control of high-temperature ferrite content and interface bonding of the cladding layer, which is beneficial to the dissolution and sufficient diffusion of precipitates in the base layer and cladding layer steel, promotes the slab element homogenization, and plays a strengthening role of micro-alloy elements in the 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 the diffusion of elements, promotes the realization of 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, and most importantly, it will accelerate the diffusion of C and N to the interface, and 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 bond, so the heating rate should not be too fast. Preferably, the heating temperature is set to be between 1150-1250℃, and the heating rate is controlled to be within 10℃ / min.

[0077] 4) Rolling: in the high-temperature zone, large reduction ratio is carried out to make the structure fully recrystallize, refine the grains, and improve the strength and toughness of the base layer material; at the same time, the metal atoms of the interface are subjected to sufficient compression stress, forming interpenetration through diffusion to make the interface reach the atomic bonding. The pass reduction rate is ensured to be 5-20%, and the cumulative reduction rate is ≥70%, of which the reduction rate of the first and second passes is controlled at 5%-10%. Due to the difference in deformation difficulty of 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 bonding of the two layers, and small reduction is used to achieve the preliminary bonding of the two layers; controlled rolling is carried out in the unrecrystallized zone, and no austenite recrystallization occurs in this stage. By reasonable reduction rate and finish rolling temperature, the deformation energy and dislocation are accumulated to form high-density deformation bands inside the austenite grains, increase the phase nucleation points, further refine the equivalent size of the base layer after phase transformation, and improve the strength and toughness of the base layer material. At the same time, in this stage, deformation induces the precipitation of Nb, Ti, and Cr carbonitride, which improves the strength of the base layer, suppresses the diffusion of C to the interface, and avoids the formation of large-size carbides at the interface to deteriorate the interface shear strength. Because too high finish rolling temperature will cause the austenite grains of the corrosion-resistant layer to be coarse, and too low finish rolling temperature will cause a large amount of precipitates mainly in the form of carbides to precipitate in the stainless steel in a short time, which will deteriorate the intergranular corrosion resistance of the corrosion-resistant layer. At the same time, in order to obtain ferrite + pearlite and / or a small amount of bainite structure, the strength and toughness of the base layer are matched. Preferably, the finish rolling temperature is controlled at 850-950℃.

[0078] 5) cooling: through the control of cooling by open cooling, final cooling and cooling speed, the control of the microstructure type and size of the base layer after rolling and the control and inhibition of the decomposition of the corrosion-resistant layer high-temperature ferrite are realized, the sensitization zone is quickly passed through, and the corrosion resistance of the cladding layer is ensured. However, if the cooling speed is too fast, the base layer will form a martensite microstructure, which is a low-toughness and high-yield ratio microstructure, which is not conducive to the performance of the steel plate, and if the cooling speed is too slow, a large amount of coarse ferrite microstructure will be formed, which is conducive to the expansion of cracks and causes the impact performance to decrease, so the cooling speed should be reasonably controlled; the control of the final rolling temperature can realize rapid cooling to the phase transition temperature after rolling, further inhibit the growth of the microstructure, and improve the strength and low-temperature impact toughness of the material through the way of refining the grains, and further promote the combination of the composite interface through phase transition. Preferably, the water cooling mode is used for cooling, the cooling speed is controlled at 10-20℃ / s, and the final cooling temperature is controlled at 600-700℃, which can promote the precipitation of fine V(C / N), improve the strength of the base layer, and further ensure that the base layer has a low yield ratio and good low-temperature impact toughness.

[0079] Preferably, when the corrosion-resistant layer is too thick, the mechanical properties of the material and the production cost will be affected; and when the corrosion-resistant layer is too thin, the corrosion resistance and service life of the material will be reduced. 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.

[0080] The present application forms a corrosion-resistant layer on the surface of the base layer, i.e. a carbon steel plate, through the combination of the corrosion-resistant layer and the base layer, the composition design and the thickness ratio design of the two, and finally forms a steel plate with good mechanical properties and high economic efficiency, which can be equivalent to a steel structure used in a splash zone environment.

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

[0082] The base layer of the present application adopts a low-carbon micro-alloyed composition design, the corrosion-resistant layer adopts an increase in the content of Si and N elements and the addition of Cu elements, and under a reasonable rolling process, the excellent combination of stainless steel and carbon steel is realized, the thickness of the interface transition layer is controlled, and a high-strength structural steel plate that meets the requirements of marine environment is obtained, which has excellent marine atmospheric corrosion resistance and mechanical properties.

[0083] In addition, the base layer of the present application avoids the formation of large-size carbides at the interface by reducing C, and equivalently controls the thickness of the interface transition layer and the grain size, thereby improving the interface shear strength and toughness. Meanwhile, the addition of micro-alloying elements and the reasonable rolling and cooling process solve the problem of low strength of the material under low carbon conditions; the yield strength is ≥345 MPa, the tensile strength is ≥490 MPa, the yield strength ratio is ≤0.75, and the impact energy KV2 at -40℃ is ≥190 J, all of which are higher than the performance requirements in the national standard GB / T 19879-2015 "Steel Plate for Building Structure".

[0084] 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 mainly replaces the addition amount of Cr by adding trace elements such as Sn, Sb, Nb, Re, etc. to slow down the corrosion of the steel plate in the humid and hot marine atmospheric environment. The results of the 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.

[0085] 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 alloying elements Cu, Ni and Mo on the basis of the Cu-Ni-Mo low-alloy steel alloy system, combined with the economy of low-alloy steel, to obtain a ferrite-pearlite microstructure corrosion-resistant low-alloy steel. Its advantage is that in the case of appropriately controlling the high cost of alloying elements Ni and Mo, the corrosion-resistant steel in the present application has certain economy and good corrosion resistance, which is significantly better than plain carbon steel, and meets the mechanical property requirements of bridge structure steel in high-humidity and high-temperature marine atmospheric environment.

[0086] The above two patents mainly improve the corrosion resistance of steel by adding corrosion-resistant micro-alloying elements or increasing the content of corrosion-resistant elements Cr, Ni and Mo. The corrosion resistance of the steel can be improved by about 30% compared with plain carbon steel or weather-resistant steel. The structural steel of the present application is 10-20 times more corrosion-resistant than plain carbon steel or weather-resistant steel based on ensuring the mechanical properties of the base.

[0087] Chinese Patent 3 (Publication No. CN112647014A) selectively contains any one or both of Sn: 0.01%-0.02% and V: 0.05-0.1% in its chemical composition, and simultaneously adds more low-melting-point elements such as P-Sb-Ce, which affects the low-temperature toughness, weldability, cold formability, etc. of the steel, and the impact energy at -20℃ 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 the impact energy at -40℃ is ≥190J.

[0088] Chinese patent 4 (publication number CN108004488A) adds a large amount of Ni, Cr, Mo, Cu, and other precious metal alloys in its chemical composition, which is high in cost. Sb is prone to segregation, increasing the difficulty of smelting process. The addition of a large amount of Si is not conducive to surface quality and will affect the welding performance of the steel plate. The steel plate needs to be tempered after rolling to regulate performance. The present invention only adds necessary elements to the corrosion-resistant layer and can control the thickness of the corrosion-resistant layer to meet the corrosion life requirement. At the same time, the steel plate does not need to be tempered after rolling to regulate performance.

[0089] Chinese patent 5 (application number CN202210570630.7) is suitable for producing steel with a thickness specification of ≤60mm and a yield strength of ≥500MPa and a tensile strength of ≥540MPa. The 500MPa weather-resistant steel produced by this invention has a complex production process that requires tempering heat treatment, increasing the manufacturing cost. Moreover, the corrosion resistance of the steel plate is not described. The present invention can produce a thickness specification of up to 100mm due to the necessary component design in the base layer. Moreover, due to the low alloy content, the cost is reduced, and there is no need for tempering process to improve performance. The corrosion resistance is more explicit compared to the comparative patent.

[0090] 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 10-40mm, 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 of alloy elements such as Cu and Ni. The present 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 adds less alloy, eliminating the need for anti-oxidation paint and tempering treatment, reducing production costs, and producing a specification of up to 100mm with a yield strength ratio of ≤0.75. Compared to the comparative patent, the use scenario is more extensive.

[0091] The corrosion-resistant layer and the base layer are combined into a blank, and suitable heating, rolling and cooling processes are applied, so that a steel plate for steel structure with resistance to marine atmospheric corrosion, good mechanical properties and high economic efficiency is obtained, the yield strength is greater than or equal to 345 MPa, the tensile strength is greater than or equal to 490 MPa, the yield strength ratio is less than or equal to 0.75, the impact energy KV2 at-40 DEG C is greater than or equal to 190 J; under the environment of marine atmosphere with an annual average salt mist concentration of 0.0189-0.1581 mg / m3, an annual average relative humidity of 30-80% and an annual average total solar radiation of 3298.02-7350.13 MJ / m2, the average corrosion rate is less than or equal to 0.004 mm / a; and an interface transition layer with a thickness of less than or equal to 10 microns is formed by controlling the full diffusion of elements in the base layer and the corrosion-resistant layer, the interface transition layer has fine grain structure with an average grain size of less than or equal to 0.5 microns, has good deformation coordination ability, and ensures that the interface shear strength is greater than or equal to 270 MPa.

[0092] In summary, the 345 MPa grade hot-rolled steel plate for building structure with resistance to marine atmospheric corrosion can solve the essential problems of stainless steel or carbon steel used in the marine atmospheric environment; the 345 MPa grade hot-rolled steel plate for building structure with resistance to marine atmospheric corrosion can be equivalently applied to the manufacture of steel structural parts used in the marine atmospheric environment, such as steel structural parts of facilities such as seaport terminals and offshore oil platforms in the marine atmospheric environment, which can meet the requirements of these components for resistance to marine atmospheric corrosion and mechanical properties, greatly improve the applicability, safety and durability of these components, and have great economic and social benefits. BRIEF DESCRIPTION OF DRAWINGS

[0093] Fig. 1 is a schematic diagram of an interlayer structure of the 345 MPa grade hot-rolled steel plate for building structure with resistance to marine atmospheric corrosion.

[0094] Fig. 2 is a schematic diagram of another interlayer structure of the 345 MPa grade hot-rolled steel plate for building structure with resistance to marine atmospheric corrosion.

[0095] Fig. 3 is a microstructure photograph of the corrosion-resistant layer in the hot-rolled steel plate manufactured in Example 3 of the present application.

[0096] Fig. 4 is a scanning image of the interface transition layer between the base layer and the corrosion-resistant layer in the hot-rolled steel plate manufactured in Example 3 of the present application.

[0097] Fig. 5 is a microstructure photograph of the base layer in the hot-rolled steel plate manufactured in Example 3 of the present application. DETAILED DESCRIPTION

[0098] The technical solutions of the present application will be further described in detail below in combination with the embodiments and the drawings. It should be clear that the following embodiments are only used to describe the specific embodiments of the present application and do not constitute any limitation on the protection scope of the present application.

[0099] Examples 1-8 and Comparative Examples 1-8

[0100] 1) Smelting and casting:

[0101] The base layer and the corrosion-resistant layer of the hot-rolled steel plate in Table 1-2 were smelted and cast based on the chemical composition, respectively, to form a base layer blank and a corrosion-resistant layer blank;

[0102] 2) Blanking:

[0103] The base layer blank and the corrosion-resistant layer blank were subjected to surface grinding and polishing to remove surface oxide scale and oil stains, and then blanking was performed and the blanks were sealed by four-side welding to form a composite blank. The bonding surface of the four-side welded and sealed composite blank was subjected to vacuum treatment to obtain a vacuum-treated composite blank;

[0104] 3) Heating:

[0105] The vacuum-treated composite blank was heated to obtain a heated composite blank;

[0106] 4) Rolling:

[0107] The heated composite blank was rolled to obtain a rolled composite blank;

[0108] 5) Cooling:

[0109] The rolled composite blank was cooled by water cooling to obtain a hot-rolled steel plate.

[0110] Referring to FIGS. 1 and 2, which are schematic diagrams of two interlayer structures of the hot-rolled steel plate for building structures according to the present application, 1 is the base layer, 2 is the corrosion-resistant layer, and 3 is the interface transition layer. Examples 1-3 and Comparative Examples 3-6 adopt the interlayer structure of FIG. 1 for blanking. Examples 4-8 and Comparative Examples 1-2, 7-8 adopt the interlayer structure of FIG. 2 for blanking. The meaning of "each layer" is that, if the blanking method of FIG. 1 is adopted, the thickness of the single corrosion-resistant layer is "2", and if the blanking method of FIG. 2 is adopted, the thickness of the corrosion-resistant layer is "2" on the top or the bottom.

[0111] The chemical composition of the base layer of the hot-rolled steel plate (composite steel plate) examples and comparative examples of the building structure according to the present application is shown in Table 1, and the balance of the composition is Fe and inevitable 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 0.010%, respectively. The composition of the corrosion-resistant layer of the hot-rolled steel plate (composite steel plate) examples and comparative examples of the building structure according to the present application is shown in Table 2, and the balance of the composition is Fe and inevitable 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 0.030% and 0.030%, respectively. Table 3 shows the manufacturing process parameters of the composite steel plate in the examples and comparative examples. The reduction 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 of the examples and comparative examples, and the thickness of the interface transition layer.

[0112] The yield strength and tensile strength of the composite steel plate are measured in accordance with GB / T 6396-2008 "Method of Mechanical and Technological Properties of Clad Steel Plate" and GB / T 228-2010 "Metallic Materials-Tensile Testing at Ambient Temperature".

[0113] The impact energy KV2 / J (-40℃) (longitudinal) is measured in accordance with GB / T 6396-2008 "Method of Mechanical and Technological Properties of Clad Steel Plate" and GB / T 229-2020 "Metallic Materials Charpy Pendulum Impact Test Method".

[0114] The marine atmospheric corrosion rate is calculated from the corrosion weight loss of the composite steel plate in different chloride ion concentrations and temperature atmospheric environments simulated by salt spray test, and from the time and corrosion area to the annual corrosion rate (mm / a).

[0115] The microstructure of each layer in the hot-rolled steel plate is prepared according to GB / T 13298-2015 "Metallic Material Microstructure Test Method", and different organizations are distinguished and measured by using image analysis software.

[0116] The thickness of the interface transition layer is measured according to GB / T 13298-2015 "Metallic Material Microstructure Test Method" by taking advantage of the difference in microstructure between the transition layer and the corrosion-resistant layer and the base layer of carbon steel.

[0117] The thickness of the corrosion-resistant layer is measured after preparing the sample according to GB / T 13298-2015 "Metallic Material Microstructure Test Method" and observing and measuring the thickness of the corrosion-resistant layer under a microscope.

[0118] The interface shear strength of the interface transition layer is tested according to the shear test in GB / T 6396-2008 "Method of Mechanical and Technological Properties Test of Clad Steel Plate".

[0119] Grain size rating is carried out as follows: ferrite structure in stainless steel and carbon steel is respectively rated by intercept method according to GB / T 6394-2017 "Metal Average Grain Size Determination Method".

[0120] The thickness of the corrosion-resistant layer blank and the base layer blank of the heated composite blank changes by substantially equal proportion before and after rolling. Therefore, the thickness proportion of the corrosion-resistant layer and the base layer in the finished hot-rolled steel plate obtained by the present application remains consistent with the thickness proportion of the corrosion-resistant layer blank and the base layer blank in the composite blank.

[0121] The comparative examples are prepared by the above steps substantially the same as the embodiments of the present application, except that the composition of the base layer carbon steel and certain process parameters adopted during the rolling or cooling steps do not meet the requirements of the present application.

[0122] The metallographic structure of the corrosion-resistant layer in the hot-rolled steel plate manufactured in Example 3 is shown in FIG. 3, which is equiaxed or slightly elongated recrystallized austenite.

[0123] The interface transition layer in the hot-rolled steel plate manufactured in Example 3 is shown in FIG. 4, with a thickness of 4.3 μm and fine grains.

[0124] The metallographic structure of the base layer in the hot-rolled steel plate manufactured in Example 3 is shown in FIG. 5, which shows that the metallographic structure of the base layer carbon steel is ferrite + pearlite and / or a small amount of bainite structure, with a pearlite content of ≥5% and an average grain size of ≥8.5 grade.

[0125] Table 5 shows the corrosion of the hanging piece samples of the composite steel plates 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 4, Comparative Example 6, Comparative Example 7 and Comparative Example 8, due to the composition or rolling process not being within the range defined by the present application, the corrosion rate is ≥0.004 mm / a under high chloride ion concentration.

[0126] Comparative Examples 1-8 do not meet the use requirements due to the use of composition design requirements and hot working process conditions that do not meet the requirements, resulting in certain properties of the composite steel plate not meeting the use requirements (performance parameters not within the range defined by the present application). Among them:

[0127] Comparative Example 1 has a base layer (Ti+Nb+V+Cr) % less than 2.8C %, insufficient carbon fixation capacity, and a high final cooling temperature, resulting in a low pearlite content in the steel plate structure and poor toughness of the steel plate with a low impact energy.

[0128] Comparative Example 2 has a base layer Mn exceeding the composition design range, and a high cooling speed, resulting in the presence of martensite in the structure, a high yield strength ratio, and a bainite content exceeding the limited range.

[0129] Comparative Example 3 has a base layer Nb exceeding the composition design range, so its yield strength does not meet the requirements.

[0130] The corrosion rate of Comparative Example 4 is greater than or equal to 0.004 mm / a under high chloride ion concentration because the Cu content of the corrosion-resistant layer exceeds the composition design range, and the grain refinement degree is insufficient because the pass reduction rate and the finish rolling temperature are not within the range defined in the present application, and the interface diffusion rate is relatively fast because the finish rolling temperature is too high, so that the yield strength does not meet the requirements.

[0131] The tensile strength and the yield ratio of Comparative Example 5 do not meet the requirements because the Si content of the base layer exceeds the composition design range, and the interface shear strength does not meet the requirements because the heating rate is too fast.

[0132] The interface shear strength is insufficient because the ratio of the ferrite stabilizing element to the austenite stabilizing element in the corrosion-resistant layer is greater than 1.5, the high-temperature ferrite of the corrosion-resistant layer exceeds the range, and the interface transition layer is too thick because the cumulative reduction of the steel plate is insufficient.

[0133] The high-temperature ferrite content in the steel plate exceeds the range because the PREN of the corrosion-resistant layer is less than 23 and the heating temperature is not within the limited range, so that the corrosion rate is greater than or equal to 0.004 mm / a under high chloride ion concentration.

[0134] The intergranular corrosion resistance of the steel plate is affected because carbide precipitates appear at the grain boundaries of the steel plate due to the low finish rolling temperature, so that the corrosion rate is greater than or equal to 0.004 mm / a under high chloride ion concentration.

[0135] By the manufacturing method of the present application, especially the control of the heating, rolling and cooling processes, the base layer in the steel plate exhibits excellent yield ratio and low-temperature impact toughness, and the cladding layer has excellent corrosion resistance and high bonding strength, the yield strength is greater than or equal to 345 MPa, the tensile strength is greater than or equal to 490 MPa, the yield ratio is less than or equal to 0.75, the impact energy KV2 at -40°C is greater than or equal to 190 J, the corrosion rate under marine atmosphere is less than or equal to 0.004 mm / a, and the interface shear strength is greater than 270 MPa. Thus, the present application obtains a new 345 MPa grade hot-rolled steel plate for marine atmospheric corrosion resistant structure, which can meet the use under marine atmospheric environment, and finally forms a steel structural member such as a profiled steel sheet, a purlin, a wall beam, a roof truss, a steel frame, etc. which has marine atmospheric corrosion resistance, good mechanical properties and high economic efficiency, and has great economic and social benefits.

[0136] It should be noted that all the technical features described in the present application can be freely combined or integrated in any manner, unless they contradict 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, 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 encompass these modifications within the scope of the appended claims and their equivalents.

[0137] Table 1 is the chemical composition of the base layer (unit: mass percentage):

[0138] Table 2 is the chemical composition of the corrosion-resistant layer (unit: mass percentage):

[0139] Note: The ferrite elements in Table 2 include Cr, Mo, Si and Cu, and the austenite elements include Ni, C, N and Mn.

[0140] Table 3 is the manufacturing process parameters of the hot-rolled steel plate:

[0141] Note: The "composite blank thickness" in Table 3 is the thickness of the composite blank after vacuum treatment.

[0142] 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: 0.030-0.060%, Si: 0.150-0.200%, Mn: 1.00-1.30%, Cr: 0.100-0.150%, Ni: 0.010-0.070%, Al: 0.015-0.030%, Ti: 0.0080-0.0110%, Nb: 0.020-0.035%, V: 0.0020-0.0040%, inevitable impurities including P and S, wherein P is 0.0005-0.003% and S is 0.0005-0.010%. The corrosion-resistant layer comprises the following chemical components in the mass percentage: C: 0.001-0.030%, Si: 0.2-1.5%, Mn: 1.00-2.00%, Cr: 16.0-18.0%, Ni: 10.0-14.0%, Cu: 0.02-0.10%, N: 0.02-0.15%, Mo: 2.0-3.0%, inevitable impurities including P and S, wherein P is 0.005-0.030% and S is 0.005-0.030%. The microstructure of the corrosion-resistant layer is equiaxed recrystallized austenite or elongated unrecrystallized austenite and high-temperature ferrite, the content of the high-temperature ferrite in the thickness direction of the corrosion-resistant layer is ≤2%, preferably 0.9-2%. The interface transition layer is 100% metallurgical bonding, the thickness of the interface transition layer is ≤10 μm, preferably 4-10 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 ≥270 MPa. The hot-rolled steel plate has a yield strength of ≥345 MPa, a tensile strength of ≥490 MPa, a yield strength ratio of ≤0.75, preferably 0.69-0.75, 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: 2.8C%≤(Ti+Nb+V+Cr) %≤0.2%, 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, 1.20-1.5, 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≥23.0%, wherein PREN=Cr%+3.3×Mo%+16×N%, and 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: 0.030-0.060%, Si: 0.150-0.20%, Mn: 1.00-1.30%, Cr: 0.100-0.150%, Ni: 0.010-0.070%, Al: 0.015-0.030%, Ti: 0.0080-0.0110%, Nb: 0.020-0.035%, V: 0.0020-0.0040%, the balance of Fe and inevitable impurities, the inevitable impurities including P and S, wherein P is 0.0005-0.003% and S is 0.0005-0.010%; The corrosion-resistant layer comprises the following chemical components with mass percentage content as follows: C: 0.001-0.030%, Si: 0.2-1.5%, Mn: 1.00-2.00%, Cr: 16.0-18.0%, Ni: 10.0-14.0%, Cu: 0.02-0.10%, N: 0.02-0.15%, Mo: 2.0-3.0%, the balance of Fe and inevitable impurities, the inevitable impurities including P and S, wherein P is 0.005-0.030% and S is 0.005-0.030%.

6. Hot-rolled steel sheet according to anyone of claims 1 to 5 characterized in that, The microstructure of the base layer is ferrite + pearlite, or ferrite + pearlite + bainite; the content of pearlite in the microstructure of the base layer is ≥5%, preferably 5%-15%, and the content of bainite in the microstructure of the base layer is ≤5%, preferably 1%-5%.

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 1-8, characterized by, 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 7.6-10°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 5-20%, the cumulative reduction rate is ≥70%, and the finish rolling temperature is controlled at 850-950°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 10-20°C / s, and the final cooling temperature is 600-700°C.

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