420 mpa-grade marine atmospheric corrosion-resistant hot-rolled steel plate for building structure, and manufacturing method therefor

Abstract

The present invention relates to a 420 MPa-grade marine atmospheric corrosion-resistant hot-rolled steel plate for a building structure, and a manufacturing method therefor. The hot-rolled steel plate comprises: a base layer, a corrosion-resistant layer on at least one side of the base layer, and an interfacial transition layer between the base layer and the corrosion-resistant layer. In addition to Fe and inevitable impurities, the base layer further contains the following chemical components in percentage by mass: C: 0.040-0.100%, Si: 0.15-0.25%, Mn: 1.00-1.50%, Cr: 0.10-0.35%, Ni: 0.050-0.100%, Al: 0.020-0.050%, Ti: 0.009-0.016%, Nb: 0.030-0.050%, and B: 0.00020-0.00040%; and the inevitable impurities comprise P and S, wherein the content of P is 0.0005-0.003%, and the content of S is 0.0005-0.01%. In addition to Fe and inevitable impurities, the corrosion-resistant layer further contains the following chemical components in percentage by mass: C: 0.010-0.040%, Si: 0.2-1.5%, 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%, and Mo: 2.0-3.0%; the inevitable impurities comprise P and S, wherein the content of P is 0.005-0.03%, and the content of S is 0.005-0.03%. The hot-rolled steel plate of the present invention has a thickness of 10-100 mm, a yield strength greater than or equal to 420 MPa, a tensile strength greater than or equal to 570 MPa, a yield ratio less than or equal to 0.78, an impact energy KV2 at -40°C greater than or equal to 190 J, a marine atmospheric corrosion resistance rate less than or equal to 0.004 mm / a, an interfacial transition layer thickness less than or equal to 10 μm, and an interfacial shear strength greater than or equal to 300 MPa.

Description

420mpa 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 420MPa grade 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 large channel engineering, artificial islands and wharfs, offshore oil platforms, submarine oil and gas pipelines, etc.) involves the exponential increase 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 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, small sea salt particles brought by sea wind, height, wind speed, rainfall, temperature, radiation, etc. Sea salt particles accelerate corrosion.

[0004] Currently, the main way to protect the steel structure 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. Inorganic zinc-rich paint is a zinc powder substitute anode that has 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 dynamic tool is not used for bottom treatment. The coating used for intermediate coating and top coating should have better adhesion and be more suitable for the surrounding environment than the undercoating coating. After the 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 in the processing area such as welding, riveting and the like during the on-site construction of the component, and the corrosion resistance cannot be guaranteed; 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, but 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; at the same time, the welding and machining of 300 series austenitic stainless steel are 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, which mainly solves the problem by adding trace elements such as Sn, Sb, Nb and Re to replace the addition amount of Cr to slow down the corrosion of the steel plate in the humid and hot marine atmospheric environment, and the results of the comparison with 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.

[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, which solves the problem by reasonably adjusting the contents of alloy elements Cu, Ni and Mo on the basis of the Cu-Ni-Mo low-alloy steel alloy system and combining the economy of low-alloy steel to obtain a ferrite-pearlite structure corrosion-resistant low-alloy steel. Its advantage lies in 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] Both of the above two patents are in the category of single material, and alloy elements are added in the material to meet the corrosion resistance requirement, but 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 other properties 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. 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.

[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 test → 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, the tensile strength is ≥540MPa. The 500MPa weathering steel produced by patent 5 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 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, the thickness of the steel is 10-40mm. The patent 6 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 of alloy elements such as Cu and Ni.

[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 420MPa 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 ≥420MPa, the tensile strength is ≥570MPa, the yield ratio is ≤0.78, 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 ≥300MPa. The steel plate has the advantages of resisting marine atmospheric corrosion, high bonding strength, excellent yield ratio, low temperature impact toughness and high economy, and can meet the use requirements in marine atmospheric environment. It is suitable for steel structural parts such as profiled steel plate, purlin, wall beam, roof truss and steel frame, and 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 ratio and low temperature impact toughness.

[0018] Specifically, the first aspect of the present application provides a 420MPa 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 with mass percentage content as follows: C: 0.040-0.100%, Si: 0.15-0.25%, Mn: 1.00-1.50%, Cr: 0.10-0.35%, Ni: 0.050-0.10%, Al: 0.020-0.050%, Ti: 0.009-0.016%, Nb: 0.030-0.050%, B: 0.00020-0.00040%, 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.

[0020] The corrosion-resistant layer contains the following chemical components with mass percentage content as follows: C: 0.010-0.040%, Si: 0.2-1.5%, 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%, 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.

[0021] 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 1.1-2%;

[0022] The interface transition layer achieves 100% metallurgical bonding, the thickness of the interface transition layer is ≤10 μm, preferably 5-10 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 ≥300 MPa;

[0023] The yield strength of the hot-rolled steel plate is ≥420 MPa, the tensile strength is ≥570 MPa, the yield strength ratio is ≤0.78, preferably 0.73-0.78, 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 composition of the base layer also satisfies the following relationship:

[0025] 3C% ≤ (Ti+Nb+Cr)% ≤ 0.4%, wherein the symbols of the elements are substituted into the values before the mass percentage content of each element.

[0026] Preferably, the chemical composition of the corrosion-resistant layer also satisfies the following relationship (i.e. the ratio of ferrite elements to austenite elements): Preferably, 092~1.35, wherein each element symbol is substituted into the value before the percentage of the mass percentage content of each element.

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

[0028] PREN≥25.0%, 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.

[0029] Preferably, the base layer contains the following chemical components with mass percentage contents as follows: C: 0.040~0.100%, Si: 0.15~0.25%, Mn: 1.00~1.50%, Cr: 0.10~0.35%, Ni: 0.050~0.10%, Al: 0.020~0.050%, Ti: 0.009~0.016%, Nb: 0.030~0.050%, B: 0.00020~0.00040%, the balance being Fe and inevitable impurities other than Fe, and the inevitable impurities include 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: 0.2~1.5%, 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%, the balance being Fe and inevitable impurities other than Fe, and the inevitable impurities include 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 in the present application is polygonal ferrite+granular bainite+degenerate pearlite; wherein the content of martensite-austenite islands in the granular bainite is ≤3%.

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

[0033] 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.

[0034] Preferably, the thickness of the hot-rolled steel plate is 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 should be controlled to be ≤2%, preferably 1.1-2%. 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 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.

[0036] The interface transition layer realizes 100% metallurgical bonding and atomic high coherence, the thickness of the interface transition layer is ≤10 μm, preferably 5-10 μm, and the interface transition layer is too thick, which will significantly reduce the interface shear strength, and the delamination defect is prone to occur in the subsequent bending processing of the steel plate. The layer has small grain size, and the average grain size is ≤0.5 μm, preferably 0.1-0.5 μm, which further improves the interface bonding degree, and the interface shear strength is ≥300 MPa.

[0037] In the base layer component design of the hot-rolled steel plate of 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, reducing 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. 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 of the present application, the C content is controlled to be 0.040-0.100%.

[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 of the present application, the Si content is controlled to be 0.15-0.25%.

[0040] 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 the steel. At the same time, Mn can also eliminate the effect of S on the steel. However, too high Mn content is prone to cause segregation band and martensite structure, which is not conducive to the toughness of the steel. Therefore, in the base layer component of the present application, the Mn content is controlled to be 1.00-1.50%.

[0041] Al: Al is mainly added to the steel as a deoxidizing element in excess to ensure that the O content in the steel is as low as possible. After deoxidization, the excess Al combines with the N element in the steel to form AlN precipitates. The 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 the interstitial atoms N in the carbon steel base layer to the interface transition layer to form hard TiN in the interface transition layer, 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. Based on this, the Al content in the base layer composition described in the present application is controlled to be 0.020-0.050%.

[0042] Ti: Ti forms stable TiN or Ti(N,C) at high temperature, plays a role of fixing C and N, prevents the interstitial C and N atoms in the carbon steel base layer from diffusing 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, and the toughness of the welding HAZ is improved, 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 described in the present application is controlled to be 0.009-0.016%.

[0043] Nb: Nb exists in the steel in the form of solid solution Nb and Nb(C,N), and plays a role of solid solution drag and precipitate pinning during recrystallization. A small amount of Nb is added to the base layer carbon steel 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 to obtain an 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. Based on this, the Nb content in the base layer described in the present application is controlled to be 0.030-0.050.

[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 0.050-0.100%.

[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 element. Fine carbides are formed during low temperature process, which plays a role of 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 0.10-0.35%.

[0046] B: B can promote the refinement of grains in the 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, that is, the weight percentage of B element is controlled to be 0.00020-0.00040%.

[0047] P and S 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 in the application is controlled as follows: S: 0.0005-0.010%; P: 0.0005-0.003%.

[0048] As preferred, the base layer chemical composition also needs to comprehensively control the total amount of the three carbide forming elements of Cr, Ti and Nb, and the total amount of the three elements is controlled to be more than 3 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. Therefore, the chemical composition of the base layer in the present application satisfies the following relationship:

[0049] 3C%≤(Ti+Nb+Cr)%≤0.4%, wherein the symbols of the elements are substituted into the values before the percentage sign of the mass percentage content of each element.

[0050] The corrosion-resistant layer in the present application further improves the marine atmospheric corrosion resistance of the corrosion-resistant layer by increasing the Si and N contents and adding Cu element on the basis of the composition of 316L stainless steel.

[0051] Si: In the corrosion-resistant layer 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, thereby 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 the increase of Si content will increase the high-temperature ferrite content in the austenitic matrix, and the high-temperature ferrite is easy to decompose into brittle phases such as sigma and chi, which will reduce the intergranular corrosion resistance and toughness of the steel plate. Therefore, the content of Si element should not be too high, and the mass percentage of Si element is controlled to be 0.2-1.5%.

[0052] N: In the corrosion-resistant layer 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 prevent 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. At the same time, it can also offset the influence of high Si on the generation 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, the risk of forming N-containing intermetallic phases will be increased, and the smelting and hot working difficulty will be increased, which will lead to difficulty in production. Therefore, in the corrosion-resistant layer in the present application, the mass percentage of N element is controlled to be 0.02-0.15%.

[0053] Cu: In the corrosion-resistant layer shown in the present application, Cu is a ferrite element, which 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, so that it is more biased towards the anode, 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 stability and promoting the pitting corrosion and intergranular corrosion resistance of the corrosion-resistant layer. However, too high Cu content will reduce the impact performance and welding performance of the corrosion-resistant layer. Therefore, in the corrosion-resistant layer described in the present application, the mass percentage of Cu element is controlled at 0.02-0.10%.

[0054] At the same time, C and Ni are austenite stabilizing elements, which can further expand the austenite phase range, and still maintain the austenite state at a lower final rolling temperature. The content of C and Ni is increased, but too much C will increase the 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 the cost and to offset the corrosion tendency caused by the increase of ferrite stabilizing elements Cr, Mo, Si and Cu.

[0055] Preferably, Si element, Cu element and N element are further controlled to control the high-temperature ferrite content. The chemical composition of the corrosion-resistant layer of the hot-rolled steel plate described in the present application also satisfies the following relationship:

[0056] Preferably, 092-1.35, wherein the element symbols are replaced by the mass percentage of each element before the percentage number.

[0057] 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.

[0058] Preferably, the chemical composition of the corrosion-resistant layer also satisfies the following relationship:

[0059] PREN≥25.0%, PREN=Cr%+3.3×Mo%+16×N%, wherein the element symbols are replaced by the mass percentage of each element before the percentage number.

[0060] The second aspect of the present application provides a manufacturing method of a 420MPa-grade hot-rolled steel plate for building structure resistant to marine atmospheric corrosion, which comprises the following steps performed in sequence:

[0061] 1) smelting, casting:

[0062] Based on the chemical composition of the base layer and the corrosion- resistant layer in the hot-rolled steel plate, the base layer and the corrosion- resistant layer are smelted and cast respectively to form base billets and corrosion- resistant layer billets;

[0063] 2) grouping:

[0064] The base billets and the corrosion- resistant layer billets are subjected to surface grinding and polishing to remove surface oxide scale and oil stains, and then the billets are grouped and sealed by four- side welding to form composite billets. The joint surface of the four- side welded composite billets is subjected to vacuum treatment to obtain vacuum treated composite billets.

[0065] 3) heating:

[0066] The vacuum treated composite billets are heated to 1150-1250°C, and the heating rate is ≤10°C / min, preferably 7.9-10°C / min, to obtain heated composite billets.

[0067] 4) rolling:

[0068] The heated composite billets are rolled to obtain rolled composite billets, 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 5-25%, the cumulative reduction rate is ≥70%, and the finish rolling temperature is controlled at 820-900°C.

[0069] 5) cooling:

[0070] The rolled composite billets are cooled by water cooling to obtain hot-rolled steel plates, wherein the cooling speed is controlled at 13-25°C / s, and the final cooling temperature is 500-650°C.

[0071] Preferably, in the grouping process of step 2), the thickness ratio of each corrosion- resistant layer billet to the total thickness of the composite billet is controlled at 0.5-15%.

[0072] In the manufacturing method of the hot-rolled steel plate described in the present application:

[0073] 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 billets. 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.

[0074] 2) grouping: the corrosion- resistant layer billets and the base billets (or base carbon steel billets) are pretreated to remove surface oxide scale and oil stains to prevent the introduction of impurities affecting the bonding. Then the steel billets (i.e. corrosion- resistant layer billets and base billets) are sealed by four- side welding, and the joint surface after welding is subjected to vacuum treatment. Vacuum treatment protects the surface of the corrosion- resistant layer from oxidation, which is also an important condition to ensure the corrosion resistance of the corrosion- resistant layer in the splash area.

[0075] 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 the slab element homogenization, and plays a strengthening role of micro-alloy elements in the steel. Especially, the corrosion-resistant layer is at the complete austenitizing temperature in this temperature range, 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 and 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, therefore the heating rate should not be too fast, preferably, the heating temperature is set to 1150-1250℃, and the heating rate is controlled at 10℃ / min or less.

[0076] 4) Rolling: in the high temperature zone, large reduction ratio is applied to make the structure fully recrystallize, refine the grain, and improve the strength and toughness of the material; at the same time, the metal atoms at the interface are subjected to sufficient compression stress to form interpenetration through diffusion, so that the interface can reach the interatomic bonding. The pass reduction ratio is ensured to be 5-25%, and the cumulative reduction ratio is ≥70%, wherein the reduction ratio 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 ratio will cause too large difference in elongation between the two layers, causing interface dislocation, which is not conducive to the combination of the two layers. Small reduction is used to achieve the preliminary combination of the two layers; in the high temperature recrystallization temperature range, the base layer is fully recrystallized, the grain is refined, and the impact toughness of the base layer is improved; in the non-recrystallization zone, austenite recrystallization does not occur, and the deformation energy and dislocation are accumulated through reasonable reduction ratio and finish rolling temperature to form high-density deformation bands inside the austenite grains, increase the phase nucleation points, further refine the equivalent size of the base phase after phase transformation, and improve the strength and toughness of the material. 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 deteriorate the interface shear strength. Due to the fact that 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 the stainless steel to precipitate a large amount of carbide-based precipitates in a short time, which will deteriorate the intergranular corrosion resistance of the corrosion-resistant layer, and in order to obtain ferrite + pearlite and / or a small amount of bainite structure to match the strength and toughness of the base layer, the finish rolling temperature is preferably controlled to be 820-900°C, which ensures the corrosion resistance of the corrosion-resistant layer while obtaining polygonal ferrite + granular bainite + degenerated pearlite, and the martensite island content in the granular bainite is ≤3%.

[0077] 5) Cooling: through the control of opening cooling, final cooling, and cooling speed, the control of the base layer rolling organization type and organization size, the precipitation control in the corrosion-resistant layer, and the suppression of the decomposition of high-temperature ferrite in the corrosion-resistant layer are realized to ensure the corrosion resistance of the corrosion-resistant layer. However, if the cooling speed is too fast, the base layer will form martensite structure, which is a low-toughness and high-yield-ratio structure, and is not conducive to the performance of the steel plate. If the cooling speed is too slow, a large amount of coarse ferrite structure will be generated, which is conducive to crack propagation and will cause the impact performance to decrease, so the cooling speed should be reasonably controlled; the control of the finish rolling temperature can realize rapid cooling to the phase transition temperature after rolling, further suppress the growth of the structure, and improve the strength and low-temperature impact toughness of the material through grain refinement, and further promote the combination of the composite interface through phase transition. Preferably, water cooling is used to cool, the cooling speed is controlled to be 13-25°C / s, and the final cooling temperature is controlled to be 500-650°C to ensure that the base layer has a low yield ratio and high low-temperature impact toughness.

[0078] Preferably, when the corrosion-resistant layer is too thick, the mechanical properties of the material and the production cost are affected; and when the corrosion-resistant layer is too thin, the corrosion resistance and service life of the material are reduced. Therefore, the thickness of each corrosion-resistant layer in the hot-rolled steel plate after rolling accounts for 0.5% to 15% of the total thickness of the hot-rolled steel plate.

[0079] The present application forms a corrosion-resistant layer on the surface of the base layer, i.e. the carbon steel plate, through rolling process, and finally forms a steel plate with marine atmospheric corrosion resistance, good mechanical properties and high economic efficiency. The steel plate can be reprocessed into a structural member and applied to a steel structural member used in a splash zone environment.

[0080] Compared with the prior art, the present application has the following beneficial effects:

[0081] The base layer of the present application adopts low-carbon micro-alloying composition design, the corrosion-resistant layer adopts increasing Si element, N element content, adding Cu element, and at the same time increasing C and Ni content, to expand the austenite zone and meet the requirement of low finish rolling temperature. Under the reasonable rolling process, the excellent combination of stainless steel and carbon steel is realized, the interface transition layer thickness is controlled, and the high-strength structural steel plate meeting the marine environment is obtained, which has excellent marine atmospheric corrosion resistance and mechanical properties.

[0082] 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 interface transition layer thickness and grain size, and improves the interface shear strength and toughness. At the same time, the addition of micro-alloying elements and the reasonable rolling and cooling process solve the problem of low material strength under low carbon condition; the yield strength is greater than or equal to 420 MPa, the tensile strength is greater than or equal to 570 MPa, the yield strength ratio is less than or equal to 0.78, and the impact energy KV2 at-40℃ is greater than or equal to 190 J, all of which are higher than the performance requirements in the national standard GB / T 19879-2015 "Steel Plate for Building Structure".

[0083] 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. The solution mainly replaces 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 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.

[0084] 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.

[0085] 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 structural steel of the present application is 10-20 times that of plain carbon steel or weathering steel based on ensuring the mechanical properties of the base body.

[0086] 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.

[0087] Chinese patent 4 (publication number CN108004488A) adds more Ni, Cr, Mo, Cu, etc.expensive metal alloys in its chemical composition, Sb is easy to segregate, which 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 be tempered to control the performance.

[0088] Chinese patent 5 (application number CN202210570630.7) is suitable for producing steel with a thickness specification of ≤60mm, with a yield strength of ≥500MPa and a tensile strength of ≥540MPa for use in marine atmospheric corrosion-resistant environments. The production process of this patent is complex and requires a tempering heat treatment, which increases the manufacturing cost, and 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, and due to the lower alloy content, the cost is reduced and the performance does not need to be improved through tempering process, and the corrosion resistance is more explicit compared to the comparative patent.

[0089] 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 and controlled cooling and heat treatment. The steel thickness is 10-40mm, and the yield strength ratio is ≤0.86. The invention requires brushing anti-oxidation paint on the slab during heating, and also requires tempering treatment, which increases the manufacturing cost and also increases the smelting difficulty of alloy elements such as Cu, Ni, etc. The present invention can better balance the corrosion resistance and mechanical properties by realizing them in the corrosion-resistant layer and the base layer, respectively, and the base layer adds less alloy without the need for anti-oxidation paint and tempering treatment, reducing production costs, and the production specification can reach 100mm with a yield strength ratio of ≤0.78, making the use scenario more extensive compared to the comparative patent.

[0090] The combination of the corrosion-resistant layer and the base layer into a billet, and the application of appropriate heating, rolling, and cooling processes, can produce a hot-rolled steel plate for steel structures that has good marine atmospheric corrosion resistance, good mechanical properties, and high economic efficiency. The hot-rolled steel plate has a yield strength of ≥420MPa, a tensile strength of ≥570MPa, a yield strength ratio of ≤0.78, and a -40℃ impact energy KV2 of ≥190J; in a marine atmospheric environment with an average annual salt fog concentration of 0.0189-0.1581mg / m3, an average annual relative humidity of 30-80%, and an average annual total solar radiation of 3298.02-7350.13MJ / m 2 Under these conditions, the average corrosion rate is ≤0.004mm / a; at the same time, the base layer and the corrosion-resistant layer are controlled to fully diffuse to form an interface transition layer with a thickness of ≤10μm, the layer has fine grain structure with an average grain size of ≤0.5μm, has good deformation coordination ability, and ensures that the interface shear strength is ≥300MPa.

[0091] In summary, the 420MPa-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 420MPa-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

[0092] Fig. 1 is a schematic diagram of an interlayer structure of the 420MPa-grade hot-rolled steel plate for building structure with marine atmospheric corrosion resistance provided by the application.

[0093] Fig. 2 is a schematic diagram of another interlayer structure of the 420MPa-grade hot-rolled steel plate for building structure with marine atmospheric corrosion resistance provided by the application.

[0094] Fig. 3 is a microstructure photograph of the corrosion-resistant layer of the hot-rolled steel plate manufactured in Example 3 of the application.

[0095] Fig. 4 is a scanning image of the interface transition layer of the combination of the base layer and the corrosion-resistant layer of the hot-rolled steel plate manufactured in Example 3 of the application.

[0096] Fig. 5 is a microstructure photograph of the base layer of the hot-rolled steel plate manufactured in Example 3 of the application. DETAILED DESCRIPTION

[0097] 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.

[0098] Examples 1-8 and Comparative Examples 1-8

[0099] 1) Smelting and casting:

[0100] 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;

[0101] 2) Grouping blanks:

[0102] 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 joint surface of the four-side sealed composite blanks was subjected to vacuum treatment to obtain vacuum-treated composite blanks;

[0103] 3) Heating:

[0104] heating the vacuum treated composite blank to obtain a heated composite blank;

[0105] 4) Rolling:

[0106] rolling the heated composite blank to obtain a rolled composite blank;

[0107] 5) Cooling:

[0108] cooling the rolled composite blank by water cooling to obtain a hot-rolled steel plate.

[0109] 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 the base layer, 2 is the corrosion-resistant layer, and 3 is the interface transition layer. Among them, examples 1-2, 7 and comparative examples 6-8 adopt the blanking mode of FIG. 1. Examples 3-6, 8 and comparative examples 1-5 adopt the blanking mode of FIG. 2. 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.

[0110] 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 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. 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 of the composite steel plate of the examples and the comparative examples, and the thickness of the interface transition layer. Table 5 shows the performance parameters of the composite steel plate of the examples and the comparative examples according to the present application.

[0111] Among them, the yield strength and tensile strength of the composite steel plate are measured in accordance with GB / T 6396-2008 "Mechanical and Technological Properties of Composite Steel Plate - Methods" and GB / T 228-2010 "Metallic Materials - Room Temperature Tensile Test Method".

[0112] The impact energy KV2 / J at -40℃ (longitudinal direction) is measured in accordance with GB / T 6396-2008 "Mechanical and Technological Properties of Composite Steel Plate - Methods" and GB / T 229-2020 "Metallic Materials Charpy Pendulum Impact Test Method".

[0113] 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 way of simulating the atmospheric environment with different chloride ion concentrations and temperatures by the salt spray test.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] 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 Clad Steel Plates.

[0118] 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 Method for Determining the Average Grain Size of Metals by using the intercept method.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] The interface transition layer in the hot-rolled steel plate manufactured in Example 3 is shown in FIG. 4, the thickness of the interface transition layer is 4.3 μm, and the grain size is small.

[0123] 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 polygonal ferrite + granular bainite + degenerated pearlite, wherein the content of martensite-austenite islands in the granular bainite is ≤ 3%.

[0124] Table 6 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 2, Comparative Example 5, Comparative Example 6, and Comparative Example 8, 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.

[0125] Comparative Examples 1-8 do not meet the use requirements (performance parameters are not within the range defined in the application) due to the use of composition design requirements that do not meet the requirements, and the hot working process conditions, which result in certain properties of the composite steel plate not meeting the use requirements (performance parameters are not within the range defined in the application). Among them:

[0126] Comparative Example 1 has a base layer B that is outside the composition design range, and martensite appears in the structure, and the yield ratio and impact performance do not meet the requirements.

[0127] Comparative Example 2 has a low heating temperature, which results in high-temperature ferrite in the structure after rolling being outside the range defined in the application, and the corrosion rate is ≥0.004 mm / a under high chloride ion concentration.

[0128] Comparative Example 3 has a cooling rate that is not within the range defined in the application, so its yield ratio does not meet the requirements, and because the ratio of ferrite stabilizing elements to austenite stabilizing elements in the corrosion-resistant layer is greater than 1.3, the corrosion rate is ≥0.004 mm / a under high chloride ion concentration.

[0129] Comparative Example 4 has insufficient pass reduction and insufficient grain refinement, resulting in yield strength and tensile strength that do not meet the requirements.

[0130] Comparative Example 5 has a base layer (Ti+Nb+Cr) % less than 3C %, insufficient carbon fixation capacity, and a too fast heating rate, resulting in insufficient interfacial bonding strength, and a too low finish rolling temperature resulting in carbide precipitates at the grain boundaries of the steel plate, and the corrosion rate is ≥0.004 mm / a under high chloride ion concentration.

[0131] Comparative Example 6 has a base layer Mn that is outside the composition design range, and the yield strength does not meet the requirements, and because the PREN of the corrosion-resistant layer is not within the range defined in the application, the corrosion rate is ≥0.004 mm / a under high chloride ion concentration.

[0132] Comparative Example 7 has a cumulative reduction rate that is not within the range defined in the application, the average grain size of the grains in the interfacial transition layer does not meet the requirements, and the bonding strength of the base layer and the corrosion-resistant layer is too low.

[0133] Comparative Example 8 has a finish cooling temperature and cooling speed that are not within the range defined in the application, and the martensite-austenite island structure in the base layer exceeds the range defined in the application, affecting the toughness of the structure, and the impact energy of the steel plate does not meet the requirements, and because the Ni content in the corrosion-resistant layer is insufficient, the ratio of ferrite stabilizing elements to austenite stabilizing elements in the corrosion-resistant layer is greater than 1.3, and the corrosion rate is ≥0.004 mm / a under high chloride ion concentration.

[0134] By the manufacturing method of the present application, especially the control of the heating, rolling and cooling process, the base layer in the steel plate exhibits excellent yield ratio and low temperature impact toughness, while the corrosion resistant layer has excellent corrosion resistance and high bonding strength, the yield strength is 430-475 MPa, the tensile strength is 578-623 MPa, the yield ratio is 0.73-0.77, the impact energy at-40℃ is above 190J, and the interface shear strength is above 300MPa. Therefore, the 420MPa grade hot-rolled steel plate for marine atmospheric corrosion resistant structure manufactured by the present application 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.

[0135] It should be noted that all the technical features described in the present application can be freely combined or integrated in any way, unless they contradict each other. Various modifications and changes can be made to the present application without departing from the scope thereof, 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.

[0136] Table 1 is the chemical composition of the base layer (unit: weight percentage):

[0137] Table 2 is the chemical composition of the corrosion resistant layer (unit: weight percentage):

[0138] Note: The ferrite elements in Table 2 include Cr, Mo, Si and Cu, and the austenite elements include Ni, C, N and Mn.

[0139] Table 3 is the manufacturing process parameters of the hot-rolled steel plate:

[0140] Note: The "composite blank thickness" in Table 3 is the thickness of the composite blank after vacuum treatment.

[0141] Table 5 is the performance parameters of the hot-rolled steel plate:

[0142] Table 6:

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: 0.040-0.100%, Si: 0.15-0.25%, Mn: 1.00-1.50%, Cr: 0.10-0.35%, Ni: 0.050-0.100%, Al: 0.020-0.050%, Ti: 0.009-0.016%, Nb: 0.030-0.050%, B: 0.00020-0.00040%, 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: 0.2-1.5%, 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 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 1.1-2%. The interface transition layer is 100% metallurgical bonding, the thickness of the interface transition layer is ≤10 μm, preferably 5-10 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 ≥300 MPa. The yield strength of the hot-rolled steel plate is ≥420 MPa, the tensile strength is ≥570 MPa, the yield strength ratio is ≤0.78, preferably 0.73-0.78, the impact energy KV2 at -40 ℃ is ≥190 J, and the corrosion resistance to marine atmosphere is ≤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: 3C%≤(Ti+Nb+Cr)%≤0.4%, 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, 0.92-1.35, 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≥25.0%, 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. The hot-rolled steel plate according to any one of claims 1-4, characterized in that, The base layer comprises the following chemical components with mass percentage content as follows: C: 0.040-0.100%, Si: 0.15-0.25%, Mn: 1.00-1.50%, Cr: 0.10-0.35%, Ni: 0.050-0.10%, Al: 0.020-0.050%, Ti: 0.009-0.016%, Nb: 0.030-0.050%, B: 0.00020-0.00040%, the balance being Fe and inevitable impurities, and the inevitable impurities include 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: 0.2-1.5%, 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%, the balance being Fe and inevitable impurities, and the inevitable impurities include 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 polygonal ferrite + granular bainite + degenerated pearlite; and the content of martensite-austenite islands in the granular bainite is ≤3%.

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 the blanks are assembled and sealed by welding around the periphery to form a composite blank; the joint surface of the peripherally welded and sealed 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 7.9-10°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 to be 5-10%, the reduction rate of other passes is controlled to be 5-25%, the cumulative reduction rate is ≥70%, and the finish rolling temperature is controlled to be 820-900°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 to be 13-25°C / s, and the final cooling temperature is 500-650°C.

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