390mpa grade hot-rolled steel sheet for building structure resistant to corrosion in splash zone of sea waves and method for manufacturing the same

Abstract

390MPa grade hot-rolled steel plate for building structure resisting sea-spray corrosion and its manufacturing method, the hot-rolled steel plate comprises a base layer, a corrosion-resistant layer and an interface transition layer between the base layer and the corrosion-resistant layer; the base layer has the following components by mass percentage: C 0.03-0.10%, Si 0.1-0.3%, Mn 1.00-1.50%, P 0.0005-0.003%, S 0.0005-0.01%, Cr 0.02-0.15%, Ni 0.01-0.1%, Cu 0.002-0.020%, Al 0.015-0.03%, Ti 0.008-0.012%, Nb 0.02-0.045%, N 0.0005-0.005%, and the balance contains Fe and inevitable impurities; the corrosion-resistant layer is made of industrial pure titanium.The yield strength of the hot-rolled steel plate for building structure is greater than or equal to 390MPa, the tensile strength is greater than or equal to 515MPa, the yield strength ratio is less than or equal to 0.75, the impact energy at-40℃ is greater than or equal to 190J, the sea-spray corrosion rate is less than or equal to 0.006mm / year, the interface transition layer thickness is less than or equal to 10μm, and the interface shear strength is greater than or equal to 270MPa.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building structure steel, and particularly relates to a building structure hot-rolled steel plate resistant to corrosion in a sea-spray zone and a manufacturing method thereof. BACKGROUND

[0002] The sea is a very harsh and complex corrosion environment. Seawater is a strong electrolyte solution containing a high concentration of chloride ions. Steel facilities as the main structure of marine facilities are prone to electrochemical reactions with the surrounding medium and are severely corroded, greatly reducing the service life of these facilities. Especially in the sea-spray zone, which is the most harsh marine environment corrosion area, various facilities are subjected to a series of external factors such as dry-wet alternating, sea spray, sunlight, corrosive components in the atmosphere and oxygen, and the corrosion of materials is particularly serious.

[0003] Investigations have shown that the steel piles of facilities such as marine wharfs and offshore oil platforms in China are severely corroded in this area, which is 3-10 times that of the seawater immersion area. Once severe localized corrosion damage occurs in this area, the carrying capacity of the entire facility will be greatly reduced, the service life will be shortened, production safety will be affected, and even the facility will be prematurely scrapped.

[0004] In the sea-spray zone, due to being in the dry-wet alternating zone, oxygen supply is sufficient, and the corrosion products produced have no protective effect; due to the splashing of seawater, the spray can directly hit the metal surface, causing severe corrosion. Corrosion tests and investigation results show that, under normal circumstances, the average corrosion rate of ordinary carbon steel, low alloy steel and the like in the marine atmosphere is about 0.03-0.08 mm / year, and in the sea-spray zone, it is 0.3-0.5 mm / year. Severe corrosion damage easily occurs in the sea-spray zone, greatly reducing the carrying capacity of the entire steel structure and affecting safe production, shortening the service life and prematurely scrapping the facility.

[0005] According to the above working conditions, industrial pure titanium is selected as the corrosion-resistant layer. Titanium has high chemical activity and is extremely easy to react with oxygen in the air to form an oxide. The oxide on the surface of titanium metal is dense, stable and has strong self-healing ability. The self-healing ability of titanium oxide mainly refers to the fact that after the titanium oxide film at a certain place on the surface of titanium material is damaged, a new titanium oxide film can be rapidly generated to prevent the corrosive medium from further contacting titanium.

[0006] For marine construction steel, in addition to the requirement of corrosion resistance, it also needs to have good mechanical properties, among which the yield ratio and low temperature impact toughness are becoming the focus of attention. The yield ratio is the ratio of yield strength to tensile strength of steel, which reflects the ability of steel to produce strain concentration during plastic deformation. The lower the yield ratio, the more uniform the plastic deformation of steel can be distributed to a wider range. The plastic deformation of steel structure system made of low yield ratio steel can be uniformly distributed to a wider range under the action of earthquake force; while the material with high yield ratio may have strain concentration, which reduces the overall plastic deformation of steel, thus leading to brittle failure of the structure and sudden collapse of the structure at room temperature. Steel will undergo brittle transition at low temperature, and the fracture mode of steel will change from ductile fracture to brittle fracture. The engineering significance is that the structure steel needs to meet the corresponding requirements of low temperature impact performance according to the service environment of the material. The temperature difference of different latitudes of the ocean is large. For example, the temperature near the sea in winter in the Bohai Bay of China can be below-20℃, which requires that the building materials meet the impact performance of-40℃ to ensure that brittle fracture does not occur. If the tensile strength of the material improves while the plasticity and toughness improve, the yield ratio will increase significantly, and it will be difficult to control the low yield ratio.

[0007] Chinese patent CN201210260231.7 discloses a method for preparing titanium-steel-titanium double-sided composite plate. Four titanium plates and three steel plates are stacked in a closed frame made by welding the outermost two steel plates, and a separator made by mixing 1 part by weight of active α-Al2O3 and 1.5 parts by weight of 4% polyvinyl alcohol aqueous solution is added between the titanium plates. Nickel-based alloy is used as the transition layer between the titanium plate and the steel plate. The assembly is heated to 500-630℃ and vacuumized, and the vacuum degree is maintained at 20-200 Pa for 1-2 h. The feature is that the assembly is first welded and then vacuumized. The welding only needs ordinary electric arc welding and submerged arc welding, which has low requirements and low cost compared with vacuum welding, and does not require an additional vacuum chamber. Then the combined blank is rolled in a conventional heating furnace at a rolling temperature of 700-900℃. The outermost steel plate is sealed and vacuumized to block the C in coal gas, and the nickel-based alloy isolation layer is added to prevent the generation of TiC at the interface, thus obtaining a titanium-steel composite plate with a shear strength of 230-260 MPa and an interface bonding rate of 99.6%-100%.

[0008] Chinese patent CN201710769999.X discloses a method for preparing a titanium-steel composite plate, selecting the surfaces of titanium-steel combination blanks in contact with each other, coating the titanium material surface in contact with a high-temperature-resistant anti-carburizing and nitriding isolation coating, and drying at room temperature; after drying treatment is completed, the titanium blanks are aligned and stacked two by two, with a steel blank in between, to complete the combination blank to obtain a composite blank, wherein the thickness of the titanium plate is greater than 2 mm, and the thickness of the steel plate is greater than 5 mm, then the composite blank is sealed and welded around and a certain size of un-welded area is left, the blank is vacuumized to 10 -2 ~10 -3 Pa, and then welded; the plate blank is heated to 500-700°C and rolled, with the first pass reduction rate exceeding 25%, the last pass reduction rate not exceeding 15%, the total reduction rate being 60-70%, and the rolling speed being 0.1-1.0 mm / s. The patent uses a coating with high-temperature anti-permeation protection effect, which prevents the diffusion and oxidation of other impurity elements at high temperatures and blocks the diffusion of elements such as C and N. The examples use Q235 combined with TA1, and the shear strength of the produced steel plate reaches 176 MPa, 181 MPa, and 182 MPa.

[0009] The above two patents mainly avoid the generation of brittle Ti compounds by adding an additional nickel-based alloy isolation layer between titanium and carbon steel.

[0010] Chinese patent CN201811327623.4 discloses a titanium-steel-titanium composite plate and a preparation method thereof, by fixing a carbon steel between two titanium plates of the same size, warm composite rolling is performed by an irreversible large rolling force warm rolling mill to make the three-layer strip composite into one body, after rolling is completed, the rolled composite plate is subjected to heat treatment operation, including initial annealing at 500-600°C for 20-60 min and recrystallization annealing at 680-700°C for 30-120 min, and finally the product is obtained through straightening, flattening, shearing, and shaping, etc. The patent mainly describes a preparation method of a non-heat-rolled composite titanium-steel plate. Since an irreversible rolling mill is used for rolling, only single-pass rolling production can be performed, and heat treatment is also required. The examples mainly relate to a steel strip production method, and the performance after compounding is not mentioned.

[0011] Chinese patent CN201510543767.3 discloses a method for preparing titanium-steel composite plate. The titanium-steel composite plate prepared by the method has high bonding strength. The patent fixes a titanium plate between two carbon steel plates or billets, welds the billets around in a vacuum environment, heats the combined billets to 850-900℃, heats for 120-360 min, controls the open rolling temperature to be above 800℃, the final rolling temperature to be below 700℃, and the single pass reduction rate to be 20-30%, the total reduction rate to be ≥90%, and performs large reduction rolling to break the brittle phase compounds generated at the interface and reduce their influence on the bonding surface. The titanium-steel composite plate prepared by the method has a bonding strength greater than 240 MPa. The pass reduction rate and the total reduction rate required by the patent are very high, which is easy to cause edge weld cracking and destroy the vacuum degree during rolling, and is not suitable for interface bonding.

[0012] Chinese patent CN201610994234.1 discloses a production method of titanium-steel composite plate, which relates to an annealing technology production method of titanium-steel plate. First, the titanium plate and the steel plate are combined to form a symmetric multi-layer combined billet of steel plate-titanium plate-separator-titanium plate-steel plate. The combined billet is combined by rolling or explosion, and then is annealed and pickled by a continuous annealing and pickling line. The billet is first heated to 500-750℃ to recrystallize the titanium plate, and then is heated to 950-1050℃ to recrystallize the steel plate. The patent aims to obtain the properties of the composite material and the base material by two-stage heat treatment. However, the two-stage heat treatment will cause excessive diffusion of titanium, iron and carbon elements, produce brittle intermetallic compounds and titanium carbide, and deteriorate the interface shear strength.

[0013] Chinese patent CN201710996925.X discloses a thin composite double-sided titanium-steel composite plate and a preparation method thereof. The patent realizes good compounding between titanium and steel by large-thickness combined billet and large reduction rolling technology. The double-sided titanium composite plate is composed of a titanium composite layer, a base layer and a titanium composite layer. The titanium composite layer is made of TA2, and the thickness of the titanium composite layer is 0.2-1 mm. The combined billet is sequentially placed from top to bottom as a cover plate, a titanium composite material, a carbon steel base material, a titanium composite material and a cover plate. After vacuumizing in a vacuum chamber, the four around gaps are vacuum electron beam sealed and welded. The vacuum degree is 1.0-4.5×10 -2Pa, the composite blank after the sealing welding treatment is heated to 900-920℃ and kept for a certain time, the holding time is calculated according to 1min / mm x total thickness of the composite blank, the rolling temperature is 880-900℃, the final rolling temperature is above 800℃, air cooling to room temperature, the single pass reduction is ≥15%, and the first three pass reductions are ≥20%, the total reduction is ≥80%, the composite plate obtained after rolling is cut, divided and surface ground to obtain a double-sided titanium steel composite plate, the patent controls the rolling temperature and adopts a large reduction in the way of composite blank surface cleaning treatment and cover isolation of air, so that titanium iron and titanium carbide generated at the composite interface are broken, refined and dispersedly distributed in the composite interface, the distribution state of the compound is improved, the composite quality and performance stability are further ensured, and the shear strength reaches 241MPa.

[0014] Chinese patent CN201710983322.6 discloses a thin composite titanium steel composite plate and a preparation method thereof, which adopts a double-layer structure of titanium and carbon steel composite, the assembly mode and heating process are similar to those of Chinese patent CN201710996925.X, the rolling temperature is 880-900℃, the single pass reduction is 25-30%, the total reduction is ≥85%, while controlling the single pass reduction and the total reduction, the thickness of the titanium steel composite plate is limited to 3-16mm, the final rolling temperature is above 800℃, air cooling to room temperature, the titanium steel composite plate is obtained through surface treatment, the thickness of the titanium composite layer is ≤1mm, the patent improves the composite quality through the symmetrical assembly mode and the sealing of titanium into the carbon steel plate, the shear strength of the steel plate after rolling reaches above 238MPa, and the composite interface bonding rate is 100%, and the carbon steel layer reaches the national standard requirement of Q390 grade carbon steel.

[0015] The above two patents do not mention the detailed design of the composite layer and the base layer, only the tensile properties and shear strength are described, the pass reduction and total reduction of the composite layer are both high, and the corrosion resistance of the material, the low-temperature impact performance of the base material, the yield ratio and other performance indicators are not controlled, which do not meet the requirements of the steel structure for building structures.

[0016] In summary, the above patents mainly describe the preparation method of the composite steel plate, and the specific embodiments mainly briefly explain the interface shear strength and tensile properties, etc. in terms of performance. The steel structure for the sea-spray area not only needs to resist corrosion in the sea-spray area, but also needs to ensure necessary performance requirements of the steel structure, such as the low yield ratio and the corresponding low-temperature impact performance to ensure the safety of the structure. However, the above patents do not design the relevant components and processes for the corrosion rate of the corrosion-resistant layer, the yield ratio and the low-temperature impact, which cannot guarantee that the steel structure for the steel plate in the sea-spray area can meet the use requirements of the high corrosion-resistant steel structure. SUMMARY

[0017] The application aims to provide a 390MPa-grade hot-rolled steel plate for building steel structure resistant to corrosion in splash zone of sea waves and a manufacturing method thereof, the yield strength of the hot-rolled steel plate for building structure is greater than or equal to 390MPa, the tensile strength is greater than or equal to 515MPa, the yield strength ratio is less than or equal to 0.75, the impact energy at-40℃ is greater than or equal to 190J, the corrosion rate in splash zone of sea waves is less than or equal to 0.006mm / year, the thickness of the interface transition layer is less than or equal to 10μm, and the interface shear strength is greater than or equal to 270MPa; the hot-rolled steel plate can meet the corrosion resistance requirements in the splash zone of sea waves, has good mechanical properties resistant to corrosion in the splash zone of sea waves, and has high economy, and can be applied to steel structural members such as steel piles of facilities such as seaports and offshore oil platforms.

[0018] To achieve the above-mentioned purpose, the technical scheme of the application is:

[0019] The application adopts low-carbon micro-alloying component design, realizes good combination of titanium and carbon steel under the condition of no addition of metal isolation layer, controls the thickness of the interface transition layer, and in the case that the corrosion resistance of the corrosion-resistant layer is not reduced, the mechanical properties of the base layer (carbon steel) can also meet the corresponding strength grade requirements, and the base layer has excellent yield strength ratio and low-temperature impact toughness.

[0020] Specifically, the 390MPa-grade hot-rolled steel plate for building structure resistant to corrosion in splash zone of sea waves comprises a base layer, a corrosion-resistant layer and an interface transition layer between the base layer and the corrosion-resistant layer.

[0021] The chemical component of the base layer is as follows: C 0.03-0.10%, Si 0.1-0.3%, Mn 1.00-1.50%, P 0.0005-0.003%, S 0.0005-0.01%, Cr 0.02-0.15%, Ni 0.01-0.1%, Cu 0.002-0.020%, Al 0.015-0.03%, Ti 0.008-0.012%, Nb 0.02-0.045%, N 0.0005-0.005%, and the balance contains Fe and other inevitable impurities.

[0022] The corrosion-resistant layer is made of industrial pure titanium.

[0023] The yield strength of the hot-rolled steel plate for building structure is greater than or equal to 390MPa, the tensile strength is greater than or equal to 515MPa, the yield strength ratio is less than or equal to 0.75, the impact energy at-40℃ is greater than or equal to 190J, the corrosion rate in splash zone of sea waves is less than or equal to 0.006mm / year, the thickness of the interface transition layer is less than or equal to 10μm, and the interface shear strength is greater than or equal to 270MPa.

[0024] Preferably, the chemical component of the base layer also satisfies the following relationship:

[0025] 0.02%≤Cu+Ni≤0.10%.

[0026] 2(C+N)≤Ti+Nb+Cr≤0.20%.

[0027] Further, the balance of the base layer component is Fe and other unavoidable impurities.

[0028] The microstructure of the base layer is ferrite + bainite + martensite, the content of bainite + martensite is 5-15%, and the average grain size of ferrite is ≥8.5 level.

[0029] The yield strength of the base layer is ≥390MPa, the tensile strength is ≥515MPa, the yield strength ratio is ≤0.75, and the impact energy at-40℃ is ≥190J.

[0030] Preferably, the corrosion-resistant layer uses TA1, TA2, TA3 or TA4.

[0031] The microstructure of the corrosion-resistant layer is single and equiaxed α-Ti.

[0032] The sea wave splashing corrosion rate of the corrosion-resistant layer is ≤0.006mm / year.

[0033] Preferably, the interface transition layer realizes 100% metallurgical bonding, atomic high coherence, the interface transition layer thickness is ≤10μm, and the interface shear strength is ≥270MPa.

[0034] Preferably, the interface transition layer has small grain size, the average grain size is 15-50μm, and contains less than 120nm (Ti, Nb) C precipitated particles.

[0035] Preferably, the thickness of the hot-rolled steel plate for building structure is 10-70mm.

[0036] In the base layer component design of the hot-rolled steel plate for building steel structure in the application:

[0037] C: C plays a role of solid solution strengthening in steel, which can significantly improve the strength of steel, but 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 TiC hard phase 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 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 strength ratio of the steel. Therefore, in the base layer component in the application, the content of C is controlled at 0.03-0.10%.

[0038] Si: Si element can effectively deoxidize in steel to improve the purity of steel. In addition, Si element can play a solid solution strengthening effect in steel, which can improve the strength and hardness of steel material, but Si element is not conducive to the welding performance of the material. Therefore, the Si content in the base layer component is controlled at 0.10-0.30% in the present application.

[0039] 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 steel. However, too high Mn content can easily cause segregation band and martensite structure, which is not conducive to the toughness of the steel. Therefore, the Mn content in the base layer component is controlled at 1.0%-1.5% in the present application.

[0040] Al: Al is mainly added to steel as a deoxidizing element to ensure that the O content in the steel is as low as possible. After deoxidization, the excess Al combines with N element in the steel to form AlN precipitates. AlN hinders the growth of austenite grains during heating, refines the austenite grains, and improves the strength and toughness of the matrix. At the same time, the formation of AlN fixes part of the N in the matrix, reduces the diffusion of interstitial atoms N in the carbon steel base layer to the interface transition layer to form hard TiN, and deteriorates the interface shear strength of the clad plate. At the same time, the addition amount of Ti and Nb can be reduced, and the total cost can be reduced. Therefore, the Al content in the base layer component is controlled at 0.015-0.03% in the present application.

[0041] 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 interstitial C and N atoms in the carbon steel base layer to the interface, and forms hard TiN or Ti(N,C) precipitates in the interface transition layer to obtain a clad plate with high interface shear strength. At the same time, TiN hinders the growth of austenite during heating, refines the austenite grains, and can improve the strength and toughness of the matrix. In subsequent welding, especially in the heat affected zone (HAZ) close to the weld fusion boundary, the growth of austenite grains is inhibited, thereby improving the toughness of the welding HAZ, which can meet the needs of large welding heat input process. In order to improve the strength of the low-carbon matrix, reduce the diffusion of C and N to the interface, and obtain a clad plate with high interface shear strength. Therefore, the Ti content in the base layer component is controlled at 0.008-0.012% in the present application.

[0042] Nb: Nb exists in the form of solid solution Nb and Nb(C,N) in the steel, and plays a role of solid solution drag and precipitate pinning in the process of recrystallization. A small amount of Nb is added in the base carbon steel mainly to increase the recrystallization temperature, so that the base carbon steel is rolled in the recrystallization and non-recrystallization zone, and the grain is refined, which is beneficial to improve the low temperature impact toughness of the base carbon steel. Due to the effect of Nb(C,N) precipitate phase, the original austenite grain 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, N atoms in the matrix, reduce the diffusion of C, N to the interface, and obtain high interface shear strength clad plate. Based on this, the content of Nb in the base layer described in the application is controlled at 0.02-0.045%.

[0043] Cu: Cu plays a role of solid solution strengthening, and with the increase of Cu content, the room temperature impact toughness of the steel is slightly improved, therefore, the content of Cu in the base layer composition described in the application is controlled at 0.002-0.02%.

[0044] N: N element can generate second phase particles with Ti and Al, refine austenite grains, and improve the strength and toughness of the matrix. However, when the content of N is too high, the amount of TiN generated is large and the particles are too coarse, which will affect the plasticity and toughness of the base carbon steel of the application. Based on this, the content of N in the base layer described in the application is controlled at 0.0005-0.005%.

[0045] Ni: Ni is an element for stabilizing austenite, and has a certain effect on improving toughness and strength. Adding Ni in the steel can greatly improve the low temperature impact toughness of the steel. However, nickel is expensive, and adding too much will increase the cost of the clad plate. Based on this, an appropriate amount of Ni is added in the base layer composition described in the application, and the content of Ni is controlled at 0.01-0.10%.

[0046] Cr: Cr is a strong carbide forming element, and has a small diffusion speed in austenite, and at the same time, hinders the diffusion of C element. Fine carbides are formed in the low temperature process, which plays a role of precipitate strengthening, and at the same time, can fix the gap C, N atoms in the matrix, reduce the diffusion of C, 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 described in the application is controlled at 0.02-0.15%.

[0047] S, P, both are inevitable impurity elements, and the lower the content is the better. Considering the actual steelmaking level of the steel plant, the content of S and P in the application is controlled as follows: S≤0.010%; P≤0.003%;

[0048] The corrosion-resistant layer adopts industrial pure titanium, preferably TA1, TA2, TA3 and TA4, and the composition meets the GB / T3620.1-2016 standard of 'Titanium and Titanium Alloy Grade and Chemical Composition'.

[0049] In addition, in the base layer chemical composition design of the hot-rolled steel plate for building steel structure according to the application:

[0050] Since Cu and Ni can both improve the toughness of the base layer, and the combined addition effect is particularly significant, at the same time, the addition of Ni element can reduce the diffusion rate of C in the steel and reduce the diffusion of C to the interface, therefore, the application controls 0.02%≤Cu+Ni≤0.10%, and the interface transition layer can be controlled within 10 μm.

[0051] Since Ti, Nb, Cr and V are all strong carbonitride forming elements, corresponding carbonitrides will be formed in the base layer carbon steel, which can fix the interstitial atoms in the base layer, hinder the diffusion of C, N interstitial atoms to the interface to form large particles, aggregated carbonitrides in the interface transition layer, and the interface transition layer can be controlled within 10 μm, thereby improving the interface shear strength. At the same time, Ti, Nb and Cr can play a role in refining the base layer carbon steel grains at different stages of hot rolling processing and improving the toughness. Therefore, the application controls: 2(C+N)≤Ti+Nb+Cr≤0.20%.

[0052] The manufacturing method of the 390MPa grade hot-rolled steel plate for building structure resistant to corrosion in sea wave splash area according to the application comprises the following steps:

[0053] 1) Smelting and casting

[0054] The base layer and the corrosion-resistant layer are smelted and cast into blanks according to the above compositions respectively;

[0055] 2) Grouping

[0056] The base layer and the corrosion-resistant layer blanks are surface polished, and the surrounding welding sealing is performed on the blank bonding surface to form a composite blank; the bonding surface after welding sealing is subjected to vacuum extraction treatment;

[0057] 3) Heating

[0058] The composite blank is heated to 900-1000℃;

[0059] 4) Rolling

[0060] The final rolling temperature is controlled at 750-850℃, and the pass reduction rate is controlled at 5-20%, and the cumulative reduction rate is ≥85%;

[0061] 5) Cooling

[0062] After rolling, the water cooling method is used to cool down, the cooling speed is controlled at 10-15℃ / s, and the final cooling temperature is 450-600℃.

[0063] Preferably, the thickness of the corrosion-resistant layer in step 1) is 0.5-20% of the total thickness of the composite blank.

[0064] Preferably, the pass reduction rate used in step 4) is 10-15%.

[0065] In the manufacturing method described in the present application:

[0066] 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 the smelting process to improve the quality of the billet. The clean steel production technology is used to reduce the gas and inclusion content in the steel and improve the comprehensive performance of the steel, especially the resistance to lamellar tearing performance.

[0067] 2) Grouping: The thickness of the corrosion-resistant layer is prepared according to 0.5-20% of the total thickness of the composite blank. The corrosion-resistant layer and the carbon steel base material are pretreated, and the four sides of the steel billet are welded and sealed, and the combined surface after welding and sealing is vacuumized. The vacuum treatment protects the surface of the corrosion-resistant layer from being oxidized, which is an important condition for ensuring the corrosion resistance of the corrosion-resistant layer in the splash area, and at the same time, it can ensure that the corrosion-resistant layer avoids edge cracking and corrosion-resistant layer cracking during the subsequent large cumulative reduction deformation process.

[0068] 3) Heating: For single carbon steel, the slab heating temperature is generally controlled at 1000-1250℃, which is beneficial to the dissolution and sufficient diffusion of the precipitates in the steel, promotes the homogenization of the slab elements, and plays a strengthening role of the micro-alloying elements in the steel; for single industrial pure titanium plate, the heating temperature is generally controlled at 850-1000℃, and a high heating temperature will cause β phase transformation, and the β phase will grow rapidly, which will deteriorate the performance of the industrial pure titanium. Because the heating temperature is too high, it will also make the elements fully diffuse, promote the subsequent realization of 100% metallurgical bonding of the interface; but a higher heating temperature will increase the tendency of austenite grain coarsening, increase the difficulty of subsequent controlled rolling, and most importantly, it will accelerate the diffusion of C, N, Ti, Fe to the interface, form a thick brittle precipitate and intermetallic compound at the interface, form a thick interface transition layer, and deteriorate the interface shear strength. Preferably, a relatively low heating temperature is used compared with traditional carbon steel production, and the heating temperature is set to 900-1000℃.

[0069] 4) Rolling: large reduction ratio reduction is carried out in the high-temperature rough rolling area, so that the structure is fully recrystallized, the grain is refined, and the strength and toughness of the material are improved; controlled rolling is carried out in the non-recrystallization area of the finishing rolling, no austenite recrystallization occurs in this stage, and through reasonable reduction ratio and finish rolling temperature, deformation energy and dislocation are accumulated, high-density deformation bands are formed inside the austenite grains, the number of ferrite phase nucleation points is increased, the grain size after phase transformation of the matrix phase is further refined, the strength and toughness of the material are improved, at the same time, deformation induces the precipitation of Nb, Ti, Cr and V carbonitride, improves the strength of the matrix, suppresses the diffusion of C to the interface, avoids the formation of too thick TiC at the interface to degrade the interface shear strength. The pass reduction ratio is ensured to be 5-20%, and the cumulative reduction ratio is greater than or equal to 85%; preferably, the finish rolling temperature of the finishing rolling is controlled to be 750-850 DEG C, while ensuring the corrosion performance of titanium, avoiding the rolling of the base layer in the two-phase region, and at the same time obtaining ferrite with an average grain size of greater than or equal to 8.5 and bainite+martensite with a content of 5-15%.

[0070] 5) Cooling: through the control of opening cooling, final cooling and cooling speed, the control of the rolling organization type, organization size and content is realized. If the cooling speed is too fast, a large amount of bainite and martensite organization will be formed, which is not conducive to the performance of the steel plate due to the low toughness and high yield ratio of the martensite phase, and if the cooling speed is too slow, a large amount of coarse ferrite organization will be formed, which is beneficial to the crack propagation and causes the impact performance to decrease, so the cooling speed should be reasonably controlled; the control of the finish rolling temperature of the finishing rolling can avoid the formation of abnormal coarse organization in the two-phase region; at the same time, the rolling can be quickly cooled to the phase transformation temperature after rolling, further inhibiting the growth of the organization, improving the strength and low-temperature impact toughness of the material through the way of refining the grain, and forming more than 5-15% of the hard phase organization to ensure the strength. Preferably, the water cooling mode is used for cooling, the cooling speed is controlled to be 10-15 DEG C / s, and the final cooling temperature is 450-600 DEG C, so as to ensure that the base layer has low yield ratio and high low-temperature impact toughness.

[0071] 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 ratio of the corrosion-resistant layer to the total thickness of the composite blank in the above blanking process is preferably 0.5-20%.

[0072] The present application forms a corrosion-resistant layer on the surface of the base layer, i.e. the carbon steel plate, through the rolling process, combines the composition design and the thickness ratio design of the two, forms a steel plate with good mechanical properties and high economic efficiency, and finally forms a steel plate with good mechanical properties and high economic efficiency, and the steel plate is machined into a structural member, which can be effectively applied to the steel structural member used in the sea-spray area.

[0073] Compared with the prior art, the present application has the following beneficial effects:

[0074] The present application adopts low-carbon micro-alloying component design, realizes excellent combination of titanium and carbon steel under the condition of no addition of metal isolation layer, controls the thickness of the interface transition layer, and in the case of not reducing the corrosion resistance of the corrosion resistant layer, the mechanical properties of the base layer (carbon steel) can also meet the corresponding strength level requirements, and the base layer has excellent yield ratio and low temperature impact toughness.

[0075] In addition, the present application reduces the formation of TiC compounds in the interface transition layer and the formation of carbonitride in the base layer by reducing C, hinders grain growth, improves the low temperature impact toughness of the base layer, and at the same time, the addition of micro-alloying elements and the reasonable rolling cooling process solve the problem of low material strength under the condition of low carbon, the yield strength is greater than or equal to 390 MPa, the tensile strength is greater than or equal to 515 MPa, and at the same time, the material yield ratio is less than or equal to 0.75, and the-40℃ impact energy is greater than or equal to 190J, which are all higher than the performance requirements in the national standard GB / T 19879-2015 "Steel plate for building structure".

[0076] In addition, the present application reduces the formation of TiC compounds in the interface transition layer and the formation of carbonitride in the base layer by reducing C, hinders grain growth, improves the low temperature impact toughness of the base layer, and at the same time, the addition of micro-alloying elements and the reasonable rolling cooling process solve the problem of low material strength under the condition of low carbon, the yield strength is greater than or equal to 390 MPa, the tensile strength is greater than or equal to 515 MPa, and at the same time, the material yield ratio is less than or equal to 0.75, and the-40℃ impact energy is greater than or equal to 190J, which are all higher than the performance requirements in the national standard GB / T 19879-2015 "Steel plate for building structure".

[0077] Chinese patent CN201210260231.7 does not specify the heating temperature, and by adding a layer of nickel plate as an isolation layer between the composite layer and the base layer, the generation of interface TiC is prevented, and the interface bonding rate of the titanium steel composite plate obtained is 99.6-100%. The present application specifies that the heating temperature of the composite blank is 900-1000℃, reduces the addition of Ni through low-carbon and micro-alloying design, reduces the production cost, and at the same time, through process optimization such as heating and rolling, a certain thickness of transition layer organization can be formed, the formation of brittle phase TiC in the interface transition layer is reduced, and the interface bonding rate of 100% is realized.

[0078] The slab heating temperature is 500-700 DEG C, the total reduction is 60-70%, and the interface shear strength of the produced steel plate is at most 182 MPa. The application fully considers the influence of the high-temperature phase change of the corrosion-resistant layer of industrial pure titanium on corrosion resistance and the strength and toughness control of the base layer of carbon steel. In combination with low-carbon micro-alloy design, the global design of the processing technology is used, the heating temperature of the composite blank is set to 900-1000 DEG C, the corrosion-resistant layer does not change at the temperature, and the precipitates in the base layer of carbon steel are fully dissolved, the base layer grains are refined, the strength and toughness of the base layer are improved, the cumulative reduction is greater than or equal to 85%, the brittle phase of the interface transition layer is broken, and the interface shear strength is improved.

[0079] The above two patents mainly avoid the generation of brittle Ti compounds by adding an additional nickel-based alloy isolation layer between titanium and carbon steel, while the application does not add an isolation layer through component and process design, and the composite blank method and the material of the base layer of carbon steel are obviously different from the above two patents.

[0080] Under the process conditions of the application, the original corrosion resistance of the corrosion-resistant layer of industrial pure titanium is ensured, and the mechanical properties of the base layer are ensured, solving the problem that the traditional processing technology windows of titanium and carbon steel are too different to be considered together. Meanwhile, the elements of the base layer and the corrosion-resistant layer are fully diffused to form an interface transition layer with a size of not greater than 10 microns, the grain size of the layer is small, the average grain size is 15-50 microns, and the layer contains less than 120 nm (Ti, Nb) C precipitated particles, which strengthens the interface bonding performance and ensures that the interface shear strength is greater than or equal to 260 MPa, which is higher than the interface shear strength of 182 MPa in the patent.

[0081] The patent CN201811327623.4 realizes the compounding by warm rolling, and then needs to be subjected to two-stage heat treatment operation, including primary annealing at 500-600 DEG C for 20-60 min and recrystallization annealing at 680-700 DEG C for 30-120 min, which is a preparation method of a non-hot-rolled composite titanium steel plate, and is completely different from the manufacturing method of the application.

[0082] The patent CN201510543767.3 requires that the heating temperature is 850-900 DEG C, the final rolling temperature is below 700 DEG C, the single-pass reduction is 20-30%, the total reduction is greater than or equal to 90%, and the shear strength of the titanium steel composite plate is greater than 240 MPa. The single-pass reduction and the total reduction required by the patent are very high, and the edge weld is prone to cracking during rolling, the vacuum degree is damaged, the compounding is not easy, and the rolling stability is poor. The single-pass reduction of the application is controlled to be 5-20%, the weld is not cracked during rolling, the vacuum degree inside the slab is ensured, and the interface shear strength, the rolling stability and the success rate are improved.

[0083] Chinese patent CN201610994234.1 is a kind of titanium steel plate annealing technology production method, first titanium plate and steel plate are formed into steel plate-titanium plate-isolating agent-titanium plate-steel plate symmetrical multi-layer combination blank, through the way of rolling composite or explosion composite composite, the blank after composite adopts continuous annealing pickling line to anneal and pickle, first heated to 500~750℃, so that the heart titanium plate recrystallizes, then heated to 950~1050℃, so that the base steel plate recrystallizes, the rolling process and the corrosion and structural performance of the obtained steel plate are not specific and clear. The manufacturing process of the present invention is obviously different from the present invention, the present invention does not need to carry out two-stage heat treatment, and the two-stage heat treatment will cause excessive diffusion of titanium, iron and carbon elements, produce brittle intermetallic compound of iron and titanium and titanium carbide, and deteriorate the interface shear strength.

[0084] Chinese patent CN201710996925.X is a corrosion-resistant layer material TA2, wherein the titanium complex layer thickness is 0.2~1mm, heated to 900~920℃, open rolling temperature is 880~900℃, final rolling temperature is above 800℃, air cooling to room temperature, shear strength reaches 241MPa. The heating temperature of the present invention is 900~1000℃, the finish rolling temperature is 750℃~850℃, and the two-stage cooling method is used for cooling. Under this process, TA1, TA2, TA3 and TA4 can be used as corrosion-resistant layer, the corrosion-resistant layer accounts for 0.5~20% of the total thickness of the hot-rolled plate, and the interface shear strength is ≥260MPa.

[0085] Chinese patent CN201710983322.6 is similar to Chinese patent CN201710996925.X in terms of blanking method and heating process, the single pass reduction rate is 25~30%, the total reduction rate is ≥85%, while controlling the single pass reduction rate and the total reduction rate, the thickness of the titanium steel composite plate is limited to 3~16mm, the final rolling temperature is above 800℃, air cooling to room temperature, the titanium steel composite plate is obtained by surface treatment, and the titanium complex layer thickness is ≤1mm. The single pass reduction rate of the present invention is 5~20%, the rolling stability is controlled, the two-stage cooling method is adopted, the material organization type is ensured, and the yield ratio and toughness are controlled. There is also a significant difference in the thickness of the corrosion-resistant layer and the total thickness of the composite steel plate.

[0086] In summary, the 390MPa grade building structure hot-rolled steel plate resistant to corrosion in sea-spray area according to the present application can solve the essential pain points of stainless steel or carbon steel used in sea-spray area environment; the 390MPa grade building structure hot-rolled steel plate resistant to corrosion in sea-spray area can be effectively applied to the manufacture of steel structural parts used in sea-spray area environment, for example, the steel structural parts of facilities such as seaport wharf, offshore oil platform, etc. in sea-spray area, which can meet the requirements of these components for corrosion resistance and mechanical properties in sea-spray area, greatly improve the applicability, safety and durability of these components, and have great economic and social benefits. BRIEF DESCRIPTION OF DRAWINGS

[0087] Figure 1 It is a schematic diagram of an interlayer structure of the 390MPa grade building structure hot-rolled steel plate resistant to corrosion in sea-spray area according to the present application.

[0088] Figure 2 It is another schematic diagram of an interlayer structure of the 390MPa grade building structure hot-rolled steel plate resistant to corrosion in sea-spray area according to the present application.

[0089] Figure 3 It is a microstructure photo of the corrosion resistant layer of Example 3 of the present application.

[0090] Figure 4 It is a scanning image of the interface transition layer of the combination of the base layer and the corrosion resistant layer of Example 3 of the present application.

[0091] Figure 5 It is a microstructure photo of the base layer of Example 3 of the present application. DETAILED DESCRIPTION

[0092] The technical solutions of the present 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 present application and do not constitute any limitation on the protection scope of the present application.

[0093] Reference Figure 1 , Figure 2 , Figure 4 , which shows two kinds of schematic diagrams of interlayer structures of the building structure hot-rolled steel plate according to the present application, wherein 1 is a base layer, 2 is a corrosion resistant layer, and 3 is an interface transition layer.

[0094] The composition of the base layer of the building structure hot-rolled steel plate (composite steel plate) embodiment according to the present application is shown in Table 1, and the remaining amount of the composition is Fe and unavoidable impurities. Table 2 shows the manufacturing process parameters of the composite steel plate embodiment according to the present application. Table 3 shows the metallographic structure and mechanical properties of the base layer and the corrosion resistant layer in the composite steel plate of the example and the comparative example, and the thickness of the interface transition layer.

[0095] The yield strength and tensile strength of the composite steel plate are measured according to GB / T 6396-2008 "Mechanical and Technological Properties of Clad Steel Plates" and GB / T 228-2010 "Metallic Materials - Tensile Testing at Ambient Temperature - Methods".

[0096] The impact energy KV2 / J at -40°C (longitudinal direction) of the base carbon steel is measured according to GB / T 6396-2008 "Mechanical and Technological Properties of Clad Steel Plates" and GB / T 229-2020 "Metallic Materials - Charpy Pendulum Impact Test Method".

[0097] 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 "Metallic Materials - Determination of Average Grain Size - Method of Section" using the intercept method.

[0098] The comparative examples are prepared using the above steps substantially the same as the examples of the present application, except that the composition of the base carbon steel and certain process parameters used in the rolling or cooling steps do not meet the requirements of the present application.

[0099] The metallographic structure of the corrosion-resistant layer of Example 3 is shown in Figure 3 , which shows a single, equiaxed α-Ti with an average grain size of 103.8 um.

[0100] The interface transition layer of Example 3 is shown in Figure 4 , the interface transition layer has a thickness of 6.6 um, and the discontinuous fine particles are TiC with a size of less than 120 nm.

[0101] The metallographic structure of the base layer of Example 3 is shown in Figure 5 , which shows that the metallographic structure of the base carbon steel is ferrite + bainite + martensite, with a bainite + martensite volume fraction of 7.8%, and a ferrite grain size rating of ≥8.5.

[0102] Table 4 shows the corrosion of the composite steel plate hanging samples of Examples 1-8 and Comparative Examples 1-4 after 6 months in the splash zone of the South China Sea. The observation results show that the corrosion rate of the other examples and comparative examples is ≤0.006 mm / year, except for Comparative Example 4.

[0103] Comparative Examples 1-5 do not meet the requirements of the composition design requirements and hot working process conditions, resulting in certain properties of the composite steel plate not meeting the use requirements (performance parameters not within the scope of the invention). Among them:

[0104] Comparative Example 1 has a pass reduction rate and cooling speed that is not within the scope of the present application, so its tensile strength, yield ratio, and impact energy cannot meet the requirements.

[0105] Comparative Example 2 cannot effectively hinder the diffusion of C, N interstitial atoms to the interface to form large particles in the interface transition layer due to insufficient addition amount of Ti, Nb and Cr and insufficient cumulative reduction, and insufficient recrystallization due to insufficient cumulative reduction, so that the yield strength, interface transition layer thickness and shear strength cannot meet the requirements.

[0106] Comparative Example 3 cannot meet the impact energy requirement due to the decrease in toughness caused by the Cu+Ni addition amount being less than 0.02%.

[0107] Comparative Example 4 cannot meet the requirement of yield ratio due to the large amount of bainite+martensite in the metallographic structure caused by the final cooling temperature not being within the range defined in the application.

[0108] Comparative Example 5 cannot meet the performance requirement of shear strength due to the interface transition layer thickness being too thick caused by the high heating temperature and finish rolling temperature, and the β-Ti cannot be completely eliminated during subsequent processing and cooling, resulting in high corrosion rate.

[0109] The base layer of the steel plate exhibits low yield ratio and good low-temperature impact toughness, and the cladding layer has excellent corrosion resistance and high bonding strength by the preparation method of the application, especially the control of heating, rolling and cooling process. The yield strength is 399-479 MPa, the tensile strength is 570-651 MPa, the yield ratio is ≤0.75, the impact energy at -40℃ is above 190 J, and the interface shear strength is greater than 270 MPa.

[0110] It should be noted that all the technical features described in the application can be freely combined or combined in any way, unless they contradict each other. Various modifications and changes can be made to the application without departing from the scope of the 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 application is intended to cover these modifications falling within the scope of the appended claims and their equivalents.

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Claims

1. 390MPa grade hot-rolled steel plate for building structures resistant to corrosion in the splash zone of sea waves, including a base layer, a corrosion-resistant layer and an interface transition layer between the base layer and the corrosion-resistant layer; The chemical composition of the base layer, by mass percentage, is as follows: C 0.03~0.10%, Si 0.1~0.3%, Mn 1.00~1.50%, P 0.0005~0.003%, S 0.0005~0.01%, Cr 0.02~0.15%, Ni 0.01~0.1%, Cu 0.002~0.020%, Al 0.015~0.03%, Ti 0.008~0.012%, Nb 0.02~0.045%, N 0.0005~0.005%, with the balance being Fe and other unavoidable impurities. The corrosion-resistant layer is made of industrial pure titanium; The hot-rolled steel plates used in the building structure have a yield strength ≥390MPa, tensile strength ≥515MPa, yield-to-tensile ratio ≤0.75, impact energy at -40℃ ≥190J, sea wave splash corrosion rate ≤0.006mm / year, interface transition layer thickness ≤10μm, and interface shear strength ≥270MPa.

2. The hot-rolled steel plate for building structures as described in claim 1, characterized in that, The chemical composition of the base layer also satisfies the following relationship: 0.02%≤Cu+Ni≤0.20%; 2(C+N)≤Ti+Nb+Cr≤0.20%.

3. The hot-rolled steel plate for building structures as described in claim 1 or 2, characterized in that, The industrial pure titanium is TA1, TA2, TA3 or TA4.

4. The hot-rolled steel plate for building structures as described in claim 1 or 2, characterized in that, The microstructure of the base layer is ferrite + bainite + martensite, with bainite + martensite content of 5%~15% and average ferrite grain size ≥8.

5.

5. The hot-rolled steel plate for building structures as described in claim 1 or 2, characterized in that, The base layer has a yield strength ≥390MPa, tensile strength ≥515MPa, yield-to-tensile ratio ≤0.75, and impact energy at -40℃ ≥190J.

6. The hot-rolled steel plate for building structures as described in claim 4, characterized in that, The base layer has a yield strength ≥390MPa, tensile strength ≥515MPa, yield-to-tensile ratio ≤0.75, and impact energy at -40℃ ≥190J.

7. The hot-rolled steel plate for building structures as described in claim 1, characterized in that, The microstructure of the corrosion-resistant layer is a single, equiaxed α-Ti.

8. The hot-rolled steel plate for building structures as described in claim 1 or 7, characterized in that, The corrosion resistance rate of the corrosion-resistant layer is ≤0.006 mm / year.

9. The hot-rolled steel plate for building structures as described in claim 1, characterized in that, The interface transition layer achieves 100% metallurgical bonding, with atomically coherent structure. The thickness of the interface transition layer is ≤8μm. The layer has fine grains with an average grain size of 15~50μm and contains (Ti, Nb) C precipitates smaller than 120nm. The interfacial shear strength is ≥270MPa.

10. The hot-rolled steel plate for building structures as described in claim 1, characterized in that, The thickness of the hot-rolled steel plate used in the building structure is 10~70mm.

11. The method for manufacturing 390MPa grade hot-rolled steel plate resistant to seawater splash corrosion as described in any one of claims 1 to 10, characterized in that, Includes the following steps: 1) Smelting and casting The base layer and corrosion-resistant layer as described in claim 1 or 2 are smelted and cast into billets respectively; 2) Billet assembly The base layer and corrosion-resistant layer blanks are ground and polished, and the bonding surfaces of the blanks are welded and sealed around the perimeter to form a composite blank; the bonding surfaces after welding and sealing are vacuumed. 3) Heating The composite preform is heated to 900~1000℃; 4) Rolling The final rolling temperature is controlled at 750~850℃, the reduction rate per pass is controlled at 5~20%, and the cumulative reduction rate is ≥85%; 5) Cooling After rolling, the material is cooled by water at a rate of 10-15℃ / s, with a final cooling temperature of 450-600℃.

12. The manufacturing method as described in claim 11, characterized in that, Step 1) The thickness of the corrosion-resistant layer is 0.5~20% of the thickness of the composite blank.

13. The manufacturing method as described in claim 11, characterized in that, Step 4) The reduction rate used during rolling is 10-15%.

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