500mpa grade hot-rolled strip for building structures resistant to corrosion in splash zone and method of manufacturing the same

Abstract

500MPa grade hot-rolled strip for building structure resisting splash zone corrosion of sea wave and its manufacturing method, the hot-rolled strip includes base layer, corrosion resistant layer and interface transition layer between base layer and corrosion resistant layer; the base layer component mass percentage is: C 0.05~0.10%, Si 0.15~0.3%, Mn 1.0~1.8%, P 0.0005~0.003%, S 0.0005~0.01%, Cr 0.8~1.6%, Ni 0.50~1.20%, Cu 0.20~0.40%, Al 0.02~0.05%, Ti 0.010~0.018%, Nb 0.02~0.10%, N 0.0005~0.005%, Mo 0.2~0.5%, the balance includes Fe and inevitable impurities; the corrosion resistant layer uses industrial pure titanium.The yield strength of the hot-rolled strip for building structure of the application is greater than or equal to 500MPa, the tensile strength is greater than or equal to 640MPa, the yield strength ratio is 0.75~0.85, the impact energy at-40℃ is greater than or equal to 190J, the corrosion rate of sea wave splash is less than or equal to 0.006mm / year, the interface transition layer thickness is less than or equal to 8μm, 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 strip steel resistant to corrosion in a sea-spray zone and a manufacturing method thereof. BACKGROUND

[0002] Traditional marine structure and equipment materials are mainly low-strength steel, but with the development of marine resources gradually moving from shallow water to deep water, the requirements for the strength, toughness and corrosion resistance of the structure and equipment are higher and higher, and new materials are urgently needed. The ocean is a very harsh and complex corrosion environment. Seawater is a strong electrolyte solution containing high concentrations 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 severe 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 China's seaport terminals and offshore oil platforms 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 this part of 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 very high chemical activity and is easily reacted 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, it can quickly generate a new titanium oxide film 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 deform plastically without strain concentration. The lower the yield ratio, the more uniform the plastic deformation of steel can be distributed to a wider range. The steel structure system made of low yield ratio steel can uniformly distribute plastic deformation to a wide range under the action of earthquake force; while high yield ratio material may have strain concentration, reducing 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] Japanese patent JP2011167002 discloses a steel marine structure with excellent corrosion resistance, which can reduce the cost of painting. The solution is to use coated steel with a specified coating thickness in the height direction area where the amount of sea salt particles exceeds the specified boundary value, and to use uncoated steel in the height direction area where the amount of sea salt particles is below the specified boundary value. In addition, the boundary value is 0.1 mdd or less. As a steel material for non-coating use, the mass % contains C: 0.08% or less, Si: 0.75% or less, Mn: 2.0% or less, P: 0.030% or less, S: 0.030% or less, Al: 0.01-0.05%, N: 0.010% or less, and contains W: 0.50-1.0%, Nb: 0.010-0.200%, Cr: 0.01-0.10% or less, in addition to Cu: 0.01-0.10% or less. As a marine structure, it is preferred to be an offshore structure, especially an offshore wind power tower. In this way, the painting area is greatly reduced, the painting operation is reduced, the repainting time is shortened, and the painting cost is reduced. Although this patent provides a marine steel structure, the corrosion resistance is achieved by painting.

[0008] Chinese patent CN201210260231.7 discloses a method for preparing a titanium-steel-titanium double-sided composite plate. Four titanium plates and three steel plates are stacked in a certain order in a closed frame formed by welding the outermost two steel plates. An isolation agent made by mixing 1 part by weight of active a-Al2O3 and 1.5 parts by weight of 4% polyvinyl alcohol solution is added between the titanium plates, and a nickel-based alloy is used as a transition layer between the titanium plates and the steel plates. The assembly is heated to 500-630°C 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 condition is low and the cost is low, and a vacuum chamber does not need to be additionally built. The outermost steel plate is then sealed and vacuumized to block C in the gas, and a nickel-based alloy isolation layer is added to prevent the formation of TiC at the interface, thereby obtaining a titanium-steel composite plate with a shear strength of 230-260 MPa and an interface bonding rate of 99.6-100%.

[0009] Chinese patent CN201710769999.X discloses a method for preparing a titanium-steel composite plate. The surfaces of the titanium-steel assembly in contact with each other are selected, and a high-temperature-resistant anti-carburizing and nitriding isolation coating is applied to the contact surface of the titanium material and dried at room temperature. After the drying treatment is completed, the titanium blanks are aligned and stacked, and a steel blank is placed in the middle to obtain a composite blank. The thickness of the titanium plate is greater than 2 mm, and the thickness of the steel plate is greater than 5 mm. The composite blank is then sealed 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. The first pass reduction is more than 25%, the final pass reduction is not more than 15%, the total reduction is 60-70%, and the rolling speed is 0.1-1.0 mm / s. The coating used in this patent has a high-temperature anti-infiltration protection effect, preventing the diffusion and oxidation of other impurity elements and blocking the diffusion of C, N and other elements. The examples use Q235 combined with TA1, and the shear strength of the produced steel plate reaches 176 MPa, 181 MPa and 182 MPa.

[0010] The above two patents mainly avoid the formation of brittle Ti compounds by adding an additional nickel-based alloy isolation layer between titanium and carbon steel.

[0011] Chinese patent CN201811327623.4 discloses a titanium-steel-titanium composite plate and a preparation method thereof. A carbon steel plate is fixed between two titanium plates of the same size, and warm composite rolling is performed by using an irreversible large rolling force warm rolling mill to make the three-layer strip composite into one body. After rolling, the rolled composite plate is subjected to heat treatment, including primary annealing at 500-600 °C for 20-60 min and recrystallization annealing at 680-700 °C for 30-120 min. Finally, the product is obtained by straightening, leveling, shearing and shaping. 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 embodiments mainly relate to a steel strip production method, and the performance of the composite is not mentioned.

[0012] Chinese patent CN201510543767.3 discloses a preparation method of a titanium steel composite plate. The titanium steel composite plate obtained by the method has high bonding strength. Two carbon steel plates or steel blanks are fixed with a titanium plate in the middle, and the blanks are welded around in a vacuum environment. The combined blanks are heated to 850-900 °C for 120-360 min. The open rolling temperature is controlled to be higher than 800 °C, the final rolling temperature is controlled to be lower than 700 °C, the single-pass deformation amount is controlled to be 20-30 %, and the total deformation amount is ≥ 90 %. Large reduction rolling is performed to break the brittle phase compounds generated at the interface and reduce their influence on the bonding surface. The titanium steel composite plate obtained by rolling has a bonding strength greater than 240 MPa. The pass reduction and total deformation amount required by the patent are very high. In the rolling process, edge weld cracking is easy to occur, the vacuum degree is destroyed, and the interface bonding is not suitable.

[0013] Chinese patent CN201610994234.1 discloses a production method of a titanium steel composite plate, which relates to an annealing technology production method of a titanium steel plate. First, titanium plates and steel plates are combined to form a symmetrical multi-layer combined blank of steel plate-titanium plate-separator-titanium plate-steel plate. The combined blank is subjected to annealing and pickling in a continuous annealing and pickling line. The blank is first heated to 500-750 °C to recrystallize the titanium plate, and then heated to 950-1050 °C to recrystallize the steel plate. The purpose of the patent is to obtain the properties of the composite and the base material by two-stage heat treatment. 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.

[0014] Chinese patent CN201710996925.X discloses a thin composite layer double-sided titanium steel composite plate and its preparation method. Through large thickness assembly and large reduction rolling technology, good composite between titanium and steel is realized. The patent is a double-sided titanium composite plate composed of a titanium composite layer, a base layer and a titanium composite layer. The material of the titanium composite layer is TA2, the thickness of the titanium composite layer is 0.2-1 mm, the assembly is placed in the middle according to the order of cover plate, titanium composite material, carbon steel base material, titanium composite material and cover plate from top to bottom, and the vacuum chamber is extracted after vacuumizing. The vacuum degree is 1.0x10-2-4.5x10-2Pa. The composite blank after sealing and welding treatment is heated to 900-920℃ and kept for 1 min / mm x total thickness of the composite blank. The rolling temperature is 880-900℃, the final rolling temperature is above 800℃, and the air cooling is cooled to room temperature. The single pass reduction rate is ≥15%, and the first three pass reduction rates are ≥20%. The total reduction rate is ≥80%. The composite plate obtained after rolling is edge cut, divided and surface ground to obtain a double-sided titanium steel composite plate. The patent controls the rolling temperature and adopts large reduction to make titanium iron and titanium carbide generated at the composite interface broken, refined and dispersedly distributed in the composite interface, improve the distribution state of the compound, further ensure the composite quality and performance stability, and the shear strength reaches 241MPa.

[0015] Chinese patent CN201710983322.6 discloses a thin composite layer titanium steel composite plate and its preparation method. A double-layer structure of titanium and carbon steel is adopted. The assembly method and heating process are similar to those of Chinese patent CN201710996925.X. The rolling temperature is 880-900℃, the single pass reduction rate is 25-30%, the total reduction rate is ≥85%, the thickness of the titanium steel composite plate is limited to 3-16mm, the final rolling temperature is above 800℃, and the air cooling is cooled 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 by symmetric assembly and 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%. The carbon steel layer meets the national standard requirements of Q345 grade carbon steel.

[0016] The above two patents do not mention the detailed design of the composite layer and the base layer, only describe the tensile properties and shear strength, and the pass reduction rate and total reduction rate required by the composite layer are 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 does not meet the requirements of building structure steel.

[0017] In summary, the above patents mainly describe the preparation method of the composite steel plate, and the specific embodiments mainly briefly describe the interfacial shear strength and tensile properties, etc. in terms of performance. In addition to the corrosion resistance in the sea-spray zone, the steel structure steel also needs to ensure the necessary performance requirements of the structural steel, such as the low yield ratio and the corresponding low-temperature impact performance to ensure the safety of the structure, as described above. The products involved in the above patents are of 345 MPa strength level, which cannot meet the use requirements of high-strength structural components. The above patents do not make relevant component and process design for the corrosion rate of the corrosion-resistant layer, the yield ratio, the low-temperature impact, etc., which cannot guarantee that the high-corrosion-resistant high-strength steel structure steel plate in the sea-spray zone environment can meet the use requirements. SUMMARY

[0018] The present application aims to provide a 500 MPa grade hot-rolled steel strip for building steel structure resistant to corrosion in the sea-spray zone and a manufacturing method thereof. The mechanical properties of the base layer (carbon steel) can meet the corresponding strength level requirements without reducing the corrosion resistance of the corrosion-resistant layer itself, and the base layer has excellent yield ratio and low-temperature impact toughness. The yield strength of the hot-rolled steel strip for building structure is ≥500 MPa, the tensile strength is ≥640 MPa, the yield ratio is 0.75-0.85, the-40℃ impact energy is ≥190 J, the sea-spray corrosion resistance rate is ≤0.006 mm / year, the interface transition layer thickness is ≤8 μm, and the interfacial shear strength is ≥270 MPa. It can meet the corrosion resistance requirements in the sea-spray zone environment, has good mechanical properties and high economic efficiency, and can be applied to steel structural members such as steel piles of harbor terminals, offshore oil platforms, etc.

[0019] To achieve the above-mentioned purpose, the technical solution of the present application is:

[0020] The present application adopts low-carbon micro-alloying component design, realizes excellent combination of titanium and carbon steel without adding a metal isolation layer, controls the interface transition layer thickness, and meets the corresponding strength level requirements of the base layer (carbon steel) without reducing the corrosion resistance of the corrosion-resistant layer itself. The base layer has excellent yield ratio and low-temperature impact toughness.

[0021] Specifically, the 500 MPa grade hot-rolled steel strip for building structure resistant to corrosion in the sea-spray zone described in the present application comprises a base layer, a corrosion-resistant layer, and an interface transition layer between the base layer and the corrosion-resistant layer.

[0022] The base layer has the following chemical composition: C 0.05-0.10%, Si 0.15-0.3%, Mn 1.0-1.8%, P 0.0005-0.003%, S 0.0005-0.01%, Cr 0.8-1.6%, Ni 0.50-1.20%, Cu 0.20-0.40%, Al 0.02-0.05%, Ti 0.010-0.018%, Nb 0.02-0.10%, N 0.0005-0.005%, Mo 0.2-0.5%, and the balance of Fe and other inevitable impurities;

[0023] The corrosion-resistant layer is made of industrial pure titanium.

[0024] The hot-rolled strip steel for building structure has a yield strength of ≥500 MPa, a tensile strength of ≥640 MPa, a yield strength ratio of 0.75-0.85, an impact energy at -40 ℃ of ≥190 J, a sea-spray corrosion rate of ≤0.006 mm / year, an interface transition layer thickness of ≤8 μm, and an interface shear strength of ≥270 MPa.

[0025] Preferably, the base layer has the following chemical composition:

[0026] 0.9%≤Cu+Ni≤1.45%;

[0027] 2(C+N)≤Ti+Nb+Cr+Mo≤1.90%.

[0028] Further, the balance of the base layer composition is Fe and other inevitable impurities.

[0029] The base layer has a microstructure of granular bainite + lath bainite, and an effective grain size of ≤10 um.

[0030] The base layer has a yield strength of ≥500 MPa, a tensile strength of ≥640 MPa, a yield strength ratio of 0.75-0.85, and an impact energy at -40 ℃ of ≥190 J.

[0031] Preferably, the corrosion-resistant layer is made of TA1, TA2, TA3 or TA4.

[0032] The corrosion-resistant layer has a microstructure of single, equiaxed α-Ti.

[0033] The corrosion-resistant layer has a sea-spray corrosion rate of ≤0.006 mm / year.

[0034] Preferably, the interface transition layer realizes 100% metallurgical bonding, atomic high coherence, interface transition layer thickness ≤8 μm, the layer organization grain size is small, average grain size 15-40 μm, and contains less than 120 nm (Ti, Nb) C precipitated particles, interface shear strength ≥270 MPa.

[0035] Preferably, the thickness of the hot-rolled strip steel for building structure is 3-16 mm.

[0036] In the base layer component design of the hot-rolled strip steel for building steel structure according to the application:

[0037] C: C in steel plays a role of solid solution strengthening, can obviously 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 number of TiC hard phase in the interface transition layer, reducing the strength of the composite interface, the application adopts low C content to ensure the shear strength of the interface. The change of C content has less effect on the yield strength of steel than on the tensile strength, and under the premise of ensuring the forming and welding performance of the product, appropriately increasing the content of C is beneficial to reducing the yield ratio of the steel. Therefore, in the base layer component according to the application, the content of C is controlled to be 0.05-0.10%.

[0038] Si: adding Si element in steel can effectively deoxidize and improve the purity of steel. In addition, Si element in steel can play a role of solid solution strengthening, and can improve the strength and hardness of steel, but Si element is not conducive to the welding performance of the material. Therefore, in the base layer component according to the application, the content of Si is controlled to be 0.15-0.30%.

[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 steel. Meanwhile, Mn can also eliminate the effect of S on steel. However, too high Mn content is prone to segregation and martensite organization, which is not conducive to the toughness of steel. Therefore, in the base layer component according to the application, the content of Mn is controlled to be 1.0-1.8%.

[0040] Al: Al is mainly added in excess as a deoxidizing element to ensure that the O content in steel is as low as possible. After deoxidization, the excess Al combines with N element in steel to form AlN precipitates. AlN hinders the growth of austenite grains during the heating process, refines the austenite grains, and improves the strength and toughness of the matrix. At the same time, the formation of AlN fixes part of N in the matrix, reduces the diffusion of interstitial atoms N in the carbon steel base layer to the composite interface to form hard TiN in the interface transition layer, and deteriorates the shear strength of the composite plate interface. At the same time, the addition amount of Ti and Nb can be reduced, and the total cost can be reduced. Therefore, in the base layer component according to the application, the content of Al is controlled to be 0.02-0.05%.

[0041] Ti: Ti forms stable TiN or Ti(N,C) at high temperature, plays the role of solid C, N, prevents the diffusion of gap C, N atoms in the carbon steel base layer to the interface, forms hard TiN or Ti(N,C) precipitates in the interface transition layer, obtains a high interface shear strength composite plate. 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 the subsequent welding, especially in the heat affected zone (HAZ) close to the weld fusion boundary, the growth of austenite grains is inhibited, thereby improving the toughness of the welding HAZ, which can meet the needs of large welding heat input process. In order to improve the strength of the low-carbon matrix, reduce the diffusion of C, N to the interface, and obtain a high interface shear strength composite plate. Based on this, the Ti content in the base layer composition described in the application is controlled at 0.010-0.018%.

[0042] Nb: Nb exists in the form of solid solution Nb and Nb(C,N) in the steel, and plays the role of solid solution drag and precipitated pinning during recrystallization. The addition of a small amount of Nb in the base layer carbon steel is mainly to increase the recrystallization temperature, so that the base layer carbon steel is rolled in the recrystallization and unrecrystallization zone after recrystallization. The grain is refined, which is beneficial to improve the low temperature impact toughness of the base layer carbon steel. Due to the effect of Nb(C,N) precipitated phase, the original austenite grains will be finer, thereby promoting the formation of finer recrystallized grains, obtaining the ideal combination of high strength and high toughness, and at the same time, Nb can fix the gap C, N atoms in the matrix, reduce the diffusion of C, N to the interface, and obtain a high interface shear strength composite plate. Based on this, the Nb content in the base layer described in the application is controlled at 0.02-0.10%.

[0043] Cu: Cu plays the 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 Cu content in the base layer composition described in the application is controlled at 0.20-0.40%.

[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 N content is too high, the amount of TiN generated is too large and the particles are too coarse, which will affect the plasticity and toughness of the base layer carbon steel of the application. Based on this, the N content in the base layer described in the application is controlled at 0.0005-0.005%.

[0045] Ni: Ni can improve the hardenability of the base layer carbon steel, and obtain full bainite structure, and is an element of stable austenite, which can promote the formation of stable martensite islands in the granular bainite during the coiling process, and can greatly improve the low temperature impact toughness and plasticity of the steel. At the same time, Ni can effectively prevent the diffusion speed of Ti into the base layer 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 layer carbon steel with Cr and Mo. However, the price of nickel is expensive, and the addition amount is too much, which will increase the cost of the clad plate. Based on this, an appropriate amount of Ni is added in the base layer composition of the present application, and the content of Ni is controlled to be 0.50-1.20%.

[0046] Cr: Cr is a strong carbonization element, and the diffusion speed in austenite is small, and at the same time, it hinders the diffusion of C element. Fine carbide is formed during low temperature process, which plays a role of precipitation strengthening, and at the same time, it 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 of the present application is controlled to be 0.80-1.60%.

[0047] Mo: In the base layer of the present application, Mo can significantly refine the grain, improve the strength and toughness of the matrix, and form stable carbide with C, thereby improving the strength of the base layer. At the same time, it can improve the hardenability of the base layer carbon steel, which is beneficial to the formation of bainite structure in the base layer. Based on this, an appropriate amount of Mo can be added in the base layer of the present application, and the mass percentage of Mo element is controlled to be 0.20-0.50%.

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

[0049] The corrosion resistant layer of the present application uses industrial pure titanium, preferably TA1, TA2, TA3 and TA4, and the composition meets the standard of GB / T3620.1-2016 "Titanium and titanium alloy grade and chemical composition".

[0050] In addition, in the base layer chemical composition design of the hot-rolled strip steel for building steel structure of the present application:

[0051] Because Cu and Ni can improve the toughness of the base layer, and the combined addition effect is particularly significant, and 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 present application controls 0.9%≤Cu+Ni≤1.45%, and the interface transition layer can be controlled within 8 microns.

[0052] Ti, Nb, Cr, Mo are all strong carbonitride forming elements, carbonitrides corresponding to the elements will be formed in the base layer carbon steel, which can fix the gap atoms in the base layer, hinder the diffusion of C, N gap atoms to the interface transition layer to form large particles, aggregated carbonitrides, and can control the interface transition layer within 8 μm, thereby improving the interface shear strength. At the same time, Ti, Nb and Cr can refine the grain size of the base layer carbon steel at different stages of hot rolling and improve the toughness. Therefore, the present application controls: 2(C+N)≤Ti+Nb+Cr+Mo≤1.90%.

[0053] The manufacturing method of the 500MPa grade hot-rolled strip steel for building structure resistant to corrosion in sea-spray zone according to the present application comprises the following steps:

[0054] 1) Smelting and casting

[0055] The base layer and the corrosion-resistant layer are smelted and cast into blanks according to the above-mentioned compositions respectively.

[0056] 2) Assembling blanks

[0057] The surface of the base layer and the corrosion-resistant layer blanks is polished, and the surrounding of the bonding surface of the blanks is welded and sealed to form a composite blank. The bonding surface after welding and sealing is subjected to vacuum treatment.

[0058] 3) Heating

[0059] The composite blank is heated to 900-1000℃.

[0060] 4) Rolling

[0061] The rough rolling temperature is controlled above 880℃, the finish rolling temperature is controlled at 760-850℃, the pass reduction rate is controlled at 5-20%, the cumulative reduction rate is ≥88%, and no descaling water is used, and a cover is used to cover the heat preservation cover.

[0062] 5) Cooling

[0063] The steel strip is cooled at a cooling rate of 10-25℃ / s to 300-450℃ after leaving the rolling stand, and is coiled.

[0064] Preferably, the thickness of the corrosion-resistant layer in step 1) is 1-10% of the total thickness of the composite blank.

[0065] Preferably, the pass reduction rate used in step 4) rolling is 10-20%.

[0066] In the manufacturing method according to the present application:

[0067] 1) Smelting: P, S elements will deteriorate the fracture toughness of steel, so in the smelting process to carry out low P, low S control, improve the quality of billet. Adopt clean steel production technology, reduce the content of gas and inclusion in steel, improve the comprehensive performance of steel, especially improve the resistance to lamellar tearing performance.

[0068] 2) Group billet; corrosion resistance layer thickness according to the total thickness of 1-10% preparation. Corrosion resistance layer, base layer carbon steel billet pretreatment, and the billet bonding surface four welding sealing, after welding sealing of the bonding surface vacuum treatment. Vacuum treatment to protect the surface of the corrosion resistance layer is not oxidized, is also an important condition to ensure the corrosion resistance of the layer of splash area.

[0069] 3) Heating: for single carbon steel, slab heating temperature is generally controlled at 1000-1250℃, beneficial to the dissolution of precipitates in steel and sufficient diffusion, promote slab element homogenization, play the role of micro alloying elements in steel strengthening; for single industrial pure titanium plate heating temperature is generally controlled at 850-1000℃, high heating temperature will produce β phase change, and β phase will grow rapidly, deteriorate the performance of industrial pure titanium, because the heating temperature is too high, will also make the element diffusion, promote the subsequent realization of interface 100% metallurgical bonding; but higher heating temperature will increase the tendency of austenite grain coarsening, increase the difficulty of subsequent controlled rolling, the most important is to accelerate the diffusion of C, N, Ti, Fe to the interface, form a thick interface transition layer, make the interface shear strength deterioration, preferably, the heating temperature is set to 900-1000℃.

[0070] 4) Rolling: the rough rolling temperature is controlled above 880℃. In high temperature zone, large reduction rate is pressed to make the organization recrystallize fully, so that the grain is refined, the strength and toughness of the material are improved; the pass reduction rate is ensured to be 5-20%, and the cumulative reduction rate is greater than or equal to 88%; in the unrecrystallized zone, the controlled rolling is carried out, and the austenite recrystallization does not occur again. Through reasonable reduction rate and finish rolling temperature, the deformation energy and dislocation are accumulated, the high density deformation band is formed in the austenite grain, the phase nucleation point is increased, the effective size of the matrix phase after phase transformation is further refined, the strength and toughness of the material are improved. At the same time, in this stage, the deformation induces the precipitation of Nb, Ti and Cr carbonitride, which improves the strength of the matrix, inhibits the diffusion of C to the interface, and avoids the formation of thick TiC at the interface to deteriorate the interface shear strength. Preferably, the finish rolling temperature is controlled at 760-850℃, which can ensure the corrosion performance of titanium and obtain the granular bainite or lath bainite structure with effective grain size less than or equal to 10um.

[0071] 5) Cooling: by controlling cooling through open cooling, final cooling and cooling speed, the control of the type and size of the microstructure after rolling is realized. Too fast cooling speed will form martensite microstructure, which is low toughness and high yield ratio, and is not conducive to the performance of the steel plate. Too slow cooling speed will lead to the formation of a large amount of coarse ferrite microstructure, which is conducive to the crack propagation and causes the impact performance to decrease, so the cooling speed should be reasonably controlled. The control of the final rolling temperature can avoid the formation of ferrite and reduce the base layer strength. At the same time, after rolling, it can be quickly cooled to the phase transition temperature, further inhibiting the growth of the microstructure, and improving the material strength and low temperature impact toughness by means of grain refinement. Preferably, the water cooling mode is used for cooling, the cooling speed is controlled at 10-25℃ / s, and the final cooling temperature is controlled at 300-450℃, so as to ensure that the base layer has low yield ratio and high low temperature impact toughness.

[0072] 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 1-10%.

[0073] The present application forms a corrosion-resistant layer on the surface of the base layer, i.e. the carbon steel plate, through rolling process by combining the composition design and the thickness ratio design of the corrosion-resistant layer and the base layer, and finally forms a steel strip with good mechanical properties and high economic efficiency, which can be effectively applied to steel structural members used in the splash zone environment.

[0074] Compared with the prior art, the present application has the following beneficial effects:

[0075] The present application adopts low-carbon micro-alloying composition design, realizes the excellent combination of titanium and carbon steel under the condition of no metal isolation layer, controls the thickness of the interface transition layer, and meets the corresponding strength level requirements of the mechanical properties of the base layer (carbon steel) without reducing the corrosion resistance of the corrosion-resistant layer itself. The base layer has excellent yield ratio and low temperature impact toughness.

[0076] In addition, the present application reduces the formation of TiC compounds in the interface transition layer and forms carbonitride in the base layer by reducing C, hinders the grain growth, improves the low temperature impact toughness of the base layer, and solves the problem of low material strength under the condition of low carbon by adding micro-alloying elements. The yield strength is ≥500MPa, the tensile strength is ≥640MPa, the yield ratio is 0.75-0.85, and the impact energy at-40℃ is ≥190J, all of which are higher than the performance requirements in the national standard GB / T 19879-2015 "Steel Plate for Building Structure".

[0077] Japanese patent JP2011167002 discloses a steel material marine structure with excellent corrosion resistance, which can reduce the cost of painting. The solution is to use painted steel material with a specified coating film thickness in the height direction area where the amount of sea salt particles exceeds the specified boundary value, and to use unpainted steel material in the height direction area where the amount of sea salt particles is below the specified boundary value. In addition, the boundary value is 0.1 mdd or less. As a steel material for non-painting use, the mass % contains C: 0.08% or less, Si: 0.75% or less, Mn: 2.0% or less, P: 0.030% or less, S: 0.030% or less, Al: 0.01-0.05%, N: 0.010% or less, and contains W: 0.50-1.0%, Nb: 0.010-0.200%, Cr: 0.01-0.10% or less, in addition, Cu: as a marine structure, preferably offshore structure, especially offshore wind power tower. Thus, the painting area is sharply reduced, the painting operation is reduced, the recoating time is shortened, and the painting cost is reduced. Although this patent provides a marine steel structure, corrosion resistance is achieved by painting. The present invention realizes 100% metallurgical bonding of the corrosion-resistant layer and the base layer by hot rolling, without painting, and achieves a one-time solution.

[0078] 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 formation of interface TiC is prevented, and the interface bonding rate of the titanium steel composite plate is 99.6-100%. The present invention specifies that the composite blank heating temperature is 900-1000℃, and by low-carbon and micro-alloy design, the addition of Ni is reduced, the production cost is reduced, and through heating, rolling and other process optimization, a certain thickness of the transition layer organization can be formed, and the formation of brittle phase TiC in the interface transition layer is reduced, realizing the complete metallurgical bonding of the interface bonding rate of 100%.

[0079] Chinese patent CN201710769999.X specifies that the slab heating temperature is 500-700℃, and the total reduction is 60-70%, and the interface shear strength of the produced steel plate is at most 182MPa. The present invention fully considers the influence of the high-temperature phase transition 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. Combined with low-carbon micro-alloy design, by overall design of the processing technology, the heating temperature of the composite blank is set to 900-1000℃, at which temperature the corrosion-resistant layer does not undergo phase transition, and the precipitates in the base layer of carbon steel are fully dissolved, which plays a role in refining the base layer grains and improving the strength and toughness of the base layer during controlled rolling, combined with cumulative reduction rate ≥88%, so that the brittle phase of the interface transition layer is broken, and the interface shear strength is improved.

[0080] 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 present application does not add an isolation layer through component and process design, and the assembly method is different from the above two patents, and the material of the base layer carbon steel is also significantly different.

[0081] Under the process conditions of the present application, the corrosion resistance of the industrial pure titanium corrosion resistant layer is ensured, and the mechanical properties of the base layer are also ensured, solving the problem that the traditional titanium and carbon steel processing process windows differ too much to be considered together; at the same time, the interface transition layer with a thickness of not greater than 8 μm is formed by controlling the full diffusion of the elements of the base layer and the corrosion resistant layer, the layer has fine grain structure with an average grain size of 15-40 μm and contains less than 120 nm (Ti, Nb) C precipitated particles, which strengthens the interface bonding performance and ensures that the interface shear strength is ≥270 MPa, which is higher than the interface shear strength of 182 MPa of Chinese patent CN201710769999.X.

[0082] Chinese patent CN201811327623.4 realizes compounding by warm rolling, and then needs to perform two-stage heat treatment operation, including primary annealing at 500-600℃ for 20-60 minutes and recrystallization annealing at 680-700℃ for 30-120 minutes, which is a preparation method of a non-hot-rolled composite titanium steel plate, and is completely different from the manufacturing method of the present application.

[0083] Chinese patent CN201510543767.3 requires heating temperature of 850-900℃, final rolling temperature of 700℃ or lower, and control of single pass deformation amount in 20-30%, and total deformation amount ≥90%, and the shear strength of the titanium steel composite plate is greater than 240 MPa, the pass reduction amount and total deformation amount required by the patent are both high, and edge weld cracking is easy to occur during rolling, which destroys the vacuum degree, and it is not easy to compound, and the rolling stability is poor. The single pass reduction rate of the present application is controlled in 5-20%, which can effectively control the weld from cracking during rolling, ensure the vacuum degree inside the slab, and improve the interface shear strength, rolling stability and success rate.

[0084] 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, 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.

[0085] The corrosion-resistant layer material of Chinese patent CN201710996925.X is TA2, the titanium complex layer thickness is 0.2~1mm, heated to 900~920℃, the opening rolling temperature is 880~900℃, the final rolling temperature is above 800℃, air-cooled to room temperature, the shear strength reaches 241MPa. The heating temperature of the present invention is 900~1000℃, the final rolling temperature is 750℃~880℃, water cooling is used, the control cooling speed is 10~25℃ / s, under this process, TA1, TA2, TA3 and TA4 can be used as corrosion-resistant layer, the corrosion-resistant layer accounts for 1~10% of the total thickness of the composite blank hot-rolled plate, and the interface shear strength is ≥270MPa.

[0086] The blanking method and heating process of Chinese patent CN201710983322.6 are similar to those of Chinese patent CN201710996925.X, 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-cooled to room temperature, the titanium steel composite plate is obtained through surface treatment, the titanium complex layer thickness is ≤1mm, the steel plate strength meets the 345MPa level, and it cannot meet the application requirements of higher strength level building structure parts. The single pass reduction rate of the present invention is 5~20%, the rolling stability is controlled, the material yield strength can reach above 500MPa through composition and process design, and there is also obvious difference in corrosion-resistant layer thickness and total thickness of composite strip steel compared with the patent.

[0087] The 500MPa-grade building structure hot-rolled strip steel capable of resisting corrosion in a sea-spray area according to the application can solve the essential problems of stainless steel or carbon steel used in a sea-spray area environment; the 500MPa-grade building structure hot-rolled strip steel capable of resisting corrosion in a sea-spray area can be effectively applied to the manufacture of steel structural parts used in a sea-spray area environment, such as steel structural parts of facilities such as seaports and offshore oil platforms in a sea-spray area, and can meet the requirements of these components for corrosion resistance and mechanical properties in a sea-spray area, greatly improving the applicability, safety and durability of these components, and having great economic and social benefits. BRIEF DESCRIPTION OF DRAWINGS

[0088] Figure 1 It is a schematic diagram of an interlayer structure of the 500MPa-grade building structure hot-rolled strip steel capable of resisting corrosion in a sea-spray area according to the application.

[0089] Figure 2 It is another schematic diagram of an interlayer structure of the 500MPa-grade building structure hot-rolled strip steel capable of resisting corrosion in a sea-spray area according to the application.

[0090] Figure 3 It is a microstructure photo of the corrosion-resistant layer of Example 3 of the application.

[0091] 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 application.

[0092] Figure 5 It is a microstructure photo of the base layer of Example 3 of the application. DETAILED DESCRIPTION

[0093] The technical solutions of the application will be further described in detail below in combination with the embodiments and the drawings. It should be clear that the following embodiments are only used to describe the specific embodiments of the application and do not constitute any limitation on the protection scope of the application.

[0094] Reference Figure 1 , Figure 2 , Figure 4 It is a schematic diagram of two interlayer structures of the building structure hot-rolled strip steel according to the application, wherein 1 is a base layer, 2 is a corrosion-resistant layer, and 3 is an interface transition layer.

[0095] The composition of the base layer of the building structure hot-rolled strip steel (composite steel plate) embodiment according to the 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 strip steel embodiment according to the application. Table 3 shows the metallographic structure and mechanical properties of the base layer and the corrosion-resistant layer in the composite strip steel of the embodiment and the comparative example, and the thickness of the interface transition layer.

[0096] The yield strength and tensile strength of the composite strip are measured according to GB / T 6396-2008 "Mechanical and Technological Properties of Clad Steel Plates - Methods" and GB / T 228-2010 "Metallic Materials - Tensile Testing at Ambient Temperature - Methods".

[0097] The impact energy KV2 / J at -40℃ (longitudinal direction) of the base carbon steel is measured according to GB / T 6396-2008 "Mechanical and Technological Properties of Clad Steel Plates - Methods" and GB / T 229-2020 "Metallic Materials - Charpy Pendulum Impact Test Method".

[0098] The grain size rating is performed 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 Sectioning" using the intercept method.

[0099] 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.

[0100] 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 105.6 um.

[0101] The interface transition layer of Example 3 is shown in Figure 4 , the thickness of the interface transition layer 3 is 6.9 um, and the discontinuous fine particles are TiC with a size of less than 120 nm.

[0102] The metallographic structure of the base layer of Example 3 is shown in Figure 5 , which shows the metallographic structure of the base carbon steel as granular bainite and lath martensite.

[0103] Table 4 shows the corrosion of the composite strip hanging sample 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.

[0104] Comparative Examples 1-5 do not meet the requirements of the composition design, and the hot working process conditions, resulting in some properties of the composite strip cannot meet the use requirements (performance parameters are not within the scope of the invention). Among them:

[0105] Comparative Example 1 does not meet the composition formula, and cannot effectively hinder the formation of carbides, so the thickness of the interface transition layer is too thick, and the bonding strength is insufficient.

[0106] Comparative Example 2 does not meet the requirements of the final rolling temperature and cooling speed, so its impact performance cannot meet the requirements.

[0107] The comparative example 3 cannot meet the requirements of yield strength, tensile strength and impact performance because the curling temperature is not in the range defined by the present application and the matrix ferrite content is high.

[0108] The comparative example 4 cannot meet the requirements of tensile strength and yield strength ratio because the cumulative reduction and pass reduction are not in the range defined by the present application and the grain is coarse.

[0109] The comparative example 5 cannot meet the requirement of corrosion rate because the heating temperature and finish rolling temperature are not in the range defined by the present application and the β-Ti cannot be completely eliminated in the subsequent processing and cooling process because the heating temperature is too high.

[0110] By the preparation method of the present application, especially the control of heating, rolling and cooling process, the base layer in the strip steel exhibits excellent yield strength ratio and low temperature impact toughness, and the coating has excellent corrosion resistance and high bonding strength, the yield strength is 510-576 MPa, the tensile strength is 640-751 MPa, the yield strength ratio is 0.75-0.85, the impact energy at-40℃ is more than 190 J, and the interface shear strength is more than 270 MPa.

[0111] It should be noted that all the technical features described in the present application can be freely combined or integrated in any way, unless contradictory to each other. Various modifications and changes can be made to the present application without departing from the scope of the present application, which will be apparent to those skilled in the art. For example, the features shown or described as part of one embodiment can be used with another embodiment to produce yet another embodiment. Therefore, the present application is intended to cover these modifications falling within the scope of the appended claims and their equivalents.

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Claims

1. 500MPa grade hot-rolled steel strip for building structures resistant to sea wave splash zone corrosion, including base layer, corrosion resistant layer and interface transition layer between the base layer and the corrosion resistant layer; The chemical composition of the base layer is as follows by mass percentage: C 0.05-0.10%, Si 0.15-0.3%, Mn 1.0-1.8%, P 0.0005-0.003%, S 0.0005-0.01%, Cr 0.8-1.6%, Ni 0.50-1.20%, Cu 0.20-0.40%, Al 0.02-0.05%, Ti 0.010-0.018%, Nb 0.02-0.10%, N 0.0005-0.005%, Mo 0.2-0.5%, and the balance is Fe and other inevitable impurities; The corrosion-resistant layer is made of industrial pure titanium; The hot-rolled steel strip for building structures has a yield strength of ≥500 MPa, a tensile strength of ≥640 MPa, a yield strength ratio of 0.75 to 0.85, an impact energy of ≥190 J at -40°C, a wave splash corrosion rate of ≤0.006 mm / year, an interface transition layer thickness of ≤8 μm, and an interface shear strength of ≥270 MPa; The chemical composition of the base layer also satisfies the following relationship: 0.9%≤Cu+Ni≤1.45%; 2(C+N)≤Ti+Nb+Cr+Mo≤1.90%.

2. The hot-rolled steel strip for building structures according to claim 1, wherein: The industrial pure titanium includes TA1, TA2, TA3 or TA4.

3. The hot-rolled steel strip for building structures according to claim 1 or 2, characterized in that: The microstructure of the base layer is granular bainite + lath bainite, and the effective grain size is ≤10um.

4. The hot-rolled steel strip for building structures according to claim 1 or 2, characterized in that: The yield strength of the base layer is ≥500MPa, the tensile strength is ≥640MPa, the yield strength ratio is 0.75-0.85, and the impact energy at -40°C is ≥190J.

5. The hot-rolled steel strip for building structures according to claim 3, wherein: The yield strength of the base layer is ≥500MPa, the tensile strength is ≥640MPa, the yield strength ratio is 0.75-0.85, and the impact energy at -40°C is ≥190J.

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

7. The hot-rolled steel strip for building structures according to claim 1 or 6, characterized in that: The sea wave splash corrosion resistance rate of the corrosion resistant layer is ≤0.006 mm / year.

8. The hot-rolled steel strip for building structures according to claim 1, wherein: The interface transition layer achieves 100% metallurgical bonding, with high atomic coherence. The thickness of the interface transition layer is ≤8 μm. The grains of the layer are fine, with an average grain size of 15 to 40 μm, and contain less than 120 nm (Ti, Nb)C precipitated particles, interface shear strength ≥270MPa.

9. The hot-rolled steel strip for building structures according to claim 1, wherein: The thickness of the hot-rolled steel strip for building structures is 3 to 16 mm.

10. The method for producing the 500 MPa grade hot rolled steel strip for building structures resistant to sea wave splash zone corrosion according to any one of claims 1 to 9, wherein: The steps include: 1) Smelting and casting The components of the base layer and the corrosion-resistant layer according to claim 1, 2 or 3 are smelted and cast into billets respectively; 2) Assembly The base layer and corrosion-resistant layer blanks are ground and polished, and the bonding surfaces of the blanks are welded and sealed on all sides to form a composite blank; the bonding surfaces after welding and sealing are vacuumed; 3) Heating heating the composite blank to 900-1000° C.; 4) Rolling The rough rolling temperature is controlled above 880℃; the finishing rolling temperature is controlled at 760~850℃, the pass reduction rate is controlled at 5~20%; the cumulative reduction rate is ≥88%; 5) Cooling After the steel strip leaves the rolling mill stand, it is cooled to 300-450°C at a cooling rate of 10-25°C / s and then coiled.

11. The manufacturing method according to claim 10, wherein: Step 1) The thickness of the corrosion-resistant layer is 1 to 10% of the thickness of the composite blank.

12. The manufacturing method according to claim 10, wherein: Step 4), the pass reduction rate is 10-20%.

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