420mpa grade hot-rolled steel sheet for building structure resistant to corrosion in splash zone of sea waves and method for manufacturing the same

Abstract

420MPa grade hot-rolled steel plate for building structure resisting splash zone corrosion of sea wave and its manufacturing method, the hot-rolled steel plate includes base layer, corrosion resistant layer and interface transition layer between base layer and corrosion resistant layer; base layer component mass percentage is: C 0.03~0.15%, Si 0.15~0.35%, Mn 1.0~1.5%, P 0.0005~0.003%, S 0.0005~0.01%, Cr 0.1~0.65%, Ni 0.1~0.8%, Cu 0.05~0.3%, Al 0.02~0.05%, Ti 0.009~0.016%, Nb 0.03~0.06%, N 0.0005~0.005%, B 0.0002~0.0004%, the balance includes Fe and inevitable impurities; the corrosion resistant layer uses industrial pure titanium.The yield strength of the building structure hot-rolled steel plate is greater than or equal to 420MPa, the tensile strength is greater than or equal to 570MPa, the yield ratio is 0.73~0.81, the impact energy at-40 DEG C 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 10 μm, and the interface shear strength is greater than or equal to 265MPa.

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 quickly 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 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 above 800 °C, the final rolling temperature is below 700 °C, and the single-pass reduction rate is controlled to be 20-30%. The total reduction rate is ≥90%. Large reduction rate 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 rate and total reduction rate 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 iron-titanium 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 -2 Pa, the composite blank after sealing welding is heated to 900-920℃, 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, single pass reduction rate is ≥15%, and the first three pass reduction rate is ≥20%, the total reduction rate 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 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. The patent adopts a double-layer structure of titanium and carbon steel composite, 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℃, air cooling to room temperature, and 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 titanium into carbon steel plate. The shear strength of the steel plate after rolling reaches above 238MPa, and the composite interface bonding rate is 100%, which 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, the pass reduction rate and total reduction rate of the composite layer are high, and the corrosion resistance, low temperature impact performance and yield ratio of the base material 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 in the performance aspect. The steel structure in the splash zone of sea waves requires not only corrosion resistance in the splash zone of sea waves, but also necessary structural steel performance requirements, such as the aforementioned low yield ratio and corresponding low-temperature impact performance to ensure structural safety. At the same time, 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 perform related component and process design on the corrosion rate of the corrosion-resistant layer, the yield ratio, the low-temperature impact, and the like, and cannot guarantee that the use requirements of the high-corrosion-resistant high-strength steel structure steel plate in the splash zone of sea waves can be met. SUMMARY

[0018] The present application aims to provide a 420 MPa grade hot-rolled steel plate for building steel structure resistant to corrosion in the splash zone of sea waves and a manufacturing method thereof. The yield strength of the hot-rolled steel plate for building structure is ≥420 MPa, the tensile strength is ≥570 MPa, the yield ratio is 0.73-0.81, the-40℃ impact energy is ≥190 J, the corrosion resistance in the splash zone of sea waves is ≤0.006 mm / year, the interface transition layer thickness is ≤10 μm, and the interfacial shear strength is ≥265 MPa. The steel plate can meet the corrosion resistance requirements in the splash zone of sea waves, has good mechanical properties and high economic efficiency, and can be applied to steel structural members such as steel piles of facilities such as seaports and offshore oil platforms.

[0019] To achieve the above-mentioned purpose, the technical scheme 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 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.

[0021] Specifically, the 420 MPa grade hot-rolled steel plate for building structure resistant to corrosion in the 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.

[0022] The base layer has the following chemical composition: C 0.03-0.15%, Si 0.15-0.35%, Mn 1.0-1.5%, P 0.0005-0.003%, S 0.0005-0.01%, Cr 0.1-0.65%, Ni 0.1-0.8%, Cu 0.05-0.3%, Al 0.02-0.05%, Ti 0.009-0.016%, Nb 0.03-0.06%, N 0.0005-0.005%, B 0.0002-0.0004%, and the balance of Fe and other inevitable impurities;

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

[0024] The hot-rolled steel plate for building structure has a yield strength of ≥420 MPa, a tensile strength of ≥570 MPa, a yield strength ratio of 0.73-0.81, an impact energy at -40 ℃ of ≥190 J, a corrosion rate of sea wave splashing of ≤0.006 mm / year, an interface transition layer thickness of ≤10 μm, and an interface shear strength of ≥265 MPa.

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

[0026] 0.2%≤Cu+Ni≤0.8%;

[0027] 2(C+N)≤Ti+Nb+Cr≤0.65%.

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

[0029] Preferably, the microstructure of the base layer is polygonal ferrite+granular bainite+degenerate pearlite, wherein the size of the martensite-austenite island in the granular bainite is ≤5 um, the content of the granular bainite is ≤3%, and the content of the degenerate pearlite is ≤5%.

[0030] The base layer has a yield strength of ≥420 MPa, a tensile strength of ≥570 MPa, a yield strength ratio of 0.73-0.81, 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 microstructure of the corrosion-resistant layer is single and equiaxed α-Ti.

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

[0034] Preferably, the interface transition layer realizes 100% metallurgical bonding, atomic high coherence, interface transition layer thickness ≤ 10 μm, average grain size 15-50 μm, and contains less than 120 nm (Ti, Nb)C precipitated particles, interface shear strength ≥ 265 MPa.

[0035] Preferably, the hot-rolled steel plate for building structure has a thickness of 5-90 mm.

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

[0037] C: C in steel plays a role of solid solution strengthening, and can significantly improve the strength of the 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 to form a large number of TiC hard phases in the interface transition layer, reducing the strength of the composite interface. In order to ensure the shear strength of the interface, low C content is used. The change of C content has less effect on the yield strength of the steel than on the tensile strength. On the premise of ensuring the forming and welding performance of the product, appropriately increasing the C content is beneficial to reducing the yield strength ratio of the steel. Therefore, in the base layer component according to the present application, the C content is controlled to be 0.03-0.15%.

[0038] Si: adding Si element in steel can effectively deoxidize and improve the purity of the steel. In addition, Si element in steel can play a role of solid solution strengthening, and can improve the strength and hardness of the steel, but Si element is not conducive to the welding performance of the material. Therefore, in the base layer component according to the present application, the Si content is controlled to be 0.15-0.35%.

[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. Meanwhile, Mn can also eliminate the effect of S on the steel. However, too high Mn content is prone to segregation and martensite organization, which is not conducive to the toughness of the steel. Therefore, in the base layer component according to the present application, the Mn content is controlled to be 1.0-1.5%.

[0040] Al: Al is mainly added in excess 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 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 the 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 present application, the Al content is controlled to be 0.02-0.05%.

[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 gap C and N atoms in the carbon steel base layer to the interface, forms hard TiN or Ti(N,C) precipitates in the interface transition layer, and obtains a high interface shear strength composite plate. At the same time, TiN hinders the growth of austenite during the heating process, refines the austenite grains, and can improve the strength and toughness of the matrix. In the subsequent welding, especially in the heat affected zone (HAZ) close to the weld fusion boundary, the growth of austenite grains is inhibited, thereby improving the toughness of the welding HAZ, which can meet the needs of large welding heat input process. In order to improve the strength of the low-carbon matrix, reduce the diffusion of C and N to the interface, and obtain a high interface shear strength composite plate, the Ti content in the base layer composition described in the application is controlled at 0.009-0.016%.

[0042] Nb: Nb exists in the form of solid solution Nb and Nb(C,N) in the steel, which plays a role of solid solution drag and precipitated pinning during recrystallization. The addition of a small amount of Nb in the base layer carbon steel is mainly to increase the recrystallization temperature, so that the base layer carbon steel is rolled in the recrystallization and unrecrystallization zone, which is beneficial to improve the low temperature impact toughness of the base layer carbon steel. Due to the effect of Nb(C,N) precipitates, the original austenite grains will be finer, thereby promoting the formation of finer recrystallized grains, obtaining the ideal combination of high strength and high toughness, and at the same time, Nb can fix the gap C and N atoms in the matrix, reduce the diffusion of C and N to the interface, and obtain a high interface shear strength composite plate. Based on this, the Nb content in the base layer described in the application is controlled at 0.030-0.060%.

[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 Cu content in the base layer composition described in the application is controlled at 0.050-0.030%.

[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. Based on this, the N content in the base layer described in the application is controlled at 0.0005-0.005%.

[0045] Ni: Ni is an element that stabilizes austenite and has a certain effect on improving strength. The addition of Ni in the steel can greatly improve the low temperature impact toughness of the steel. However, the price of nickel is expensive, and the addition of too much will increase the cost of the composite plate. Based on this, an appropriate amount of Ni is added in the base layer composition described in the application, and the Ni content is controlled at 0.10-0.80%.

[0046] Cr: Cr is a strong carbide forming element, with a small diffusion rate in austenite, and hinders the diffusion of C elements. Fine carbides are formed during low-temperature processes, playing a role in precipitation strengthening. At the same time, it can fix the interstitial C, N atoms in the matrix, reduce the diffusion of C, N to the interface, and obtain high interface shear strength composite plate. Cr increases the strength of the matrix in the steel while reducing the toughness. In order to obtain the best match of strength and toughness, the Cr content in the base layer composition described in the application is controlled at 0.10-0.65%.

[0047] B: In the base layer described in the application, B element is added, which can greatly improve the hardenability of the steel, further improve the problem of low strength caused by poor hardenability of thick specifications, and the addition of B can also improve the material strength through phase change control without significantly adding other strengthening alloy elements. In order to ensure the strength of the steel and the requirement of yield ratio, it is necessary to select the appropriate amount of B element to ensure the hardenability and form bainite structure. Therefore, in the application, the mass percentage of B element is controlled at 0.0002-0.0004%.

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

[0049] The corrosion-resistant layer described in the application uses industrial pure titanium, preferably TA1, TA2, TA3 and TA4, and its composition meets the GB / T3620.1-2016 "Titanium and Titanium Alloy Grade and Chemical Composition" standard.

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

[0051] Because Cu and Ni can 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, reduce the diffusion of C to the interface, therefore, the application controls 0.2%≤Cu+Ni≤0.8%, and the interface transition layer can be controlled within 10 μm.

[0052] Because Ti, Nb, Cr, Mo are strong carbonitride forming elements, corresponding carbonitrides are 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, form large particles and aggregated carbonitrides in the interface transition layer, and control the interface transition layer within 10 μm, thereby improving the interface shear strength. At the same time, Ti, Nb and Cr can refine the grains of the base layer carbon steel at different stages of hot rolling and improve the toughness. Therefore, the application controls: 2(C+N)≤Ti+Nb+Cr≤0.65%.

[0053] The method for manufacturing the 420MPa-grade hot-rolled steel plate for building structure with resistance to splash zone corrosion 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 respectively according to the above-mentioned compositions;

[0056] 2) blank assembly

[0057] The base layer and the corrosion-resistant layer blanks are surface polished and the surrounding welding sealing is performed on the bonding surface to form a composite blank, and the bonding surface after the welding sealing is subjected to vacuum treatment;

[0058] 3) heating

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

[0060] 4) rolling

[0061] The pass reduction rate is controlled at 5-20% and the cumulative reduction rate is ≥70%, and the finish rolling temperature is controlled at 750-850℃;

[0062] 5) cooling

[0063] After rolling, the water cooling method is adopted for cooling, and the cooling speed is controlled at 5-15℃ / s, and the final cooling temperature is 400-650℃.

[0064] Preferably, the thickness of the corrosion-resistant layer in step 1) is 0.5-20% of the total thickness of the composite blank.

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

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

[0067] 1) smelting: P and S elements will 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 steel blank. The clean steel production technology is adopted to reduce the gas and inclusion content in the steel and improve the comprehensive performance of the steel, especially the resistance to lamellar tearing.

[0068] 2) blank assembly; 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 base layer carbon steel blank are pretreated, and the surrounding welding sealing is performed on the bonding surface of the steel blank, and the bonding surface after the welding sealing is subjected to vacuum treatment. The vacuum treatment protects the surface of the corrosion-resistant layer from being oxidized, which is also an important condition for ensuring the resistance of the corrosion-resistant layer to splash zone corrosion.

[0069] 3) Heating: for single carbon steel, the slab heating temperature is generally controlled at 1000-1250℃, which is beneficial to the dissolution and diffusion of precipitates in the steel, promotes the slab element homogenization, and plays a strengthening role of 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 rapid growth of the β phase, which will deteriorate the performance of the industrial pure titanium, because a high heating temperature will also make the elements fully diffuse, promote the subsequent realization of 100% metallurgical bonding of the interface; but a high heating temperature will increase the tendency of austenite grain coarsening, increase the difficulty of subsequent controlled rolling, and most importantly, 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, the heating temperature is set to 900-1000℃.

[0070] 4) Rolling: high reduction ratio is carried out in the high temperature zone to make the structure fully recrystallize, refine the grains, and improve the strength and toughness of the material; the pass reduction rate is ensured to be 5-20%, and the cumulative reduction rate is ≥70%; controlled rolling is carried out in the unrecrystallized zone, and no austenite recrystallization occurs in this stage, the deformation energy and dislocation are accumulated by reasonable reduction rate and finish rolling temperature to form high-density deformation bands in the austenite grain, increase the phase nucleation points, further refine the effective size of the matrix phase after phase transformation, and improve the strength and toughness of the material; at the same time, the deformation induces the precipitation of Nb, Ti, and Cr carbonitride, improves the strength of the matrix, suppresses the diffusion of C to the interface, and avoids the formation of too thick TiC at the interface to deteriorate the interface shear strength. Preferably, the finish rolling temperature is controlled at 750-850℃, which can ensure the corrosion performance of titanium and obtain a grainy bainite with 3% or less and a size of 5um or less, and a degenerated pearlite with a content of less than 5%.

[0071] 5) Cooling: the cooling after rolling is controlled by open cooling, final cooling and cooling rate to control the type and size of the rolling structure. Too fast cooling rate will form martensite structure, which is low toughness and high yield ratio structure, and is not conducive to the performance of the steel plate, and too slow cooling rate will lead to the formation of a large amount of coarse ferrite structure, which is conducive to the crack propagation and causes the impact performance to decrease, so the cooling rate should be reasonably controlled; the control of finish rolling temperature can avoid the formation of ferrite and reduce the strength of the base layer; at the same time, the rolling can be quickly cooled to the phase transformation temperature to further suppress the growth of the structure and improve the strength and low temperature impact toughness of the material by means of grain refinement. Preferably, water cooling is adopted, the cooling rate is controlled at 5-15℃ / s, and the final cooling temperature is controlled at 400-650℃ to ensure that the base layer has low yield ratio and high low temperature impact toughness.

[0072] Preferably, the corrosion-resistant layer is too thick, which affects the mechanical properties of the material and the production cost; and the corrosion-resistant layer is too thin, which reduces the corrosion resistance and service life of the material. Therefore, the ratio of the corrosion-resistant layer to the total thickness of the composite blank in the above blank assembling process is preferably 0.5-20%.

[0073] The present application forms a corrosion-resistant layer on the surface of the base layer, i.e. the carbon steel plate, by rolling process, through the combination of the corrosion-resistant layer and the base layer, the composition design and the thickness ratio design of the two, to finally form a steel plate with good corrosion resistance in the sea wave splash area, good mechanical properties and high economic efficiency. The steel plate is reprocessed into a structural member, which can be effectively applied to a steel structural member used in the sea wave splash area.

[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 addition of metal isolation layer, controls the thickness of the interface transition layer, and 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. The base layer has excellent yield strength ratio and low-temperature impact toughness.

[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 the grain growth, improves the low-temperature impact toughness of the base layer, and solves the problem of low material strength under low-carbon condition by adding micro-alloying elements and cooperating with reasonable rolling and cooling process. The yield strength is ≥420MPa, the tensile strength is ≥570MPa, the yield strength ratio is 0.73-0.81, 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 form a coated 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 form an uncoated 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-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, Cu: as a marine structure, preferably offshore structure, especially offshore wind power tower. Thus, the coating 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 coating, and achieves a one-time solution.

[0078] Chinese patent CN201210260231.7 does not specify the heating temperature, by adding a layer of nickel plate as an isolation layer between the composite layer and the base layer, to prevent the formation of interface TiC, the interface bonding rate of the titanium steel composite plate is 99.6-100%. The present invention specifies the composite blank heating temperature of 900-1000℃, through low-carbon and micro-alloy design, reduces the addition of Ni, reduces the production cost, and through heating, rolling and other process optimization, a certain thickness of transition layer organization is 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 slab heating temperature is 500-700℃, total reduction is 60-70%, the interface shear strength of the produced steel plate is highest 182MPa. The present invention fully considers the influence of 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 carbon steel. Combined with low-carbon micro-alloy design, by overall design of processing technology, the heating temperature of the composite blank is set to 900-1000℃, at this temperature, the corrosion-resistant layer does not change phase, and the precipitates in the base layer 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 in the controlled rolling process, combined with total reduction≥70%, the brittle phase of the interface multi-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 and cannot be considered together; at the same time, the interface transition layer with a thickness of not greater than 10 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 15-50 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 ≥265 MPa, which is higher than the interface shear strength of 182 MPa of the patent.

[0082] Chinese patent CN201811327623.4 realizes compounding by warm rolling, and then needs to perform two-stage heat treatment operation, including initial 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 below 700℃, and control of single pass reduction ratio at 20-30%, and total reduction ratio ≥90%, and the shear strength of the titanium steel composite plate is greater than 240 MPa, the pass reduction ratio and total reduction ratio required by the patent are very 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 ratio of the present application is controlled at 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 800℃ or above, 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 750~850℃, water cooling is used, the control cooling speed is 5~15℃ / s, 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 5-90mm hot-rolled plate, and the interface shear strength is ≥265MPa.

[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 800℃ or above, 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 cannot realize 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 more than 420MPa through composition and process design, and there is also obvious difference in corrosion-resistant layer thickness and composite steel plate total thickness compared with the patent.

[0087] In summary, the 420MPa grade hot-rolled steel plate for building structure with resistance to corrosion in splash zone of sea wave can solve the essential pain point of stainless steel or carbon steel used in splash zone of sea wave. The 420MPa grade hot-rolled steel plate for building structure with resistance to corrosion in splash zone of sea wave can be effectively applied to the manufacture of steel structural parts used in splash zone of sea wave, for example, the steel structural parts of facilities such as seaport wharf, offshore oil platform and the like in splash zone of sea wave, which can meet the requirements of these components for corrosion resistance and mechanical properties in splash zone of sea wave, greatly improve the applicability, safety and durability of these components, and have great economic and social benefits. BRIEF DESCRIPTION OF DRAWINGS

[0088] Figure 1 It is a schematic diagram of an interlayer structure of the 420MPa grade hot-rolled steel plate for building structure with resistance to corrosion in splash zone of sea wave.

[0089] Figure 2 It is another schematic diagram of an interlayer structure of the 420MPa grade hot-rolled steel plate for building structure with resistance to corrosion in splash zone of sea wave.

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

[0091] Figure 4 It is a scanning image of the interface transition layer combined with the base layer of Example 3 of the present application.

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

[0093] 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.

[0094] Reference Figure 1 , Figure 2 , Figure 4 , which shows two kinds of schematic diagrams of interlayer structures of the hot-rolled steel plate for building structure of the present 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 hot-rolled steel plate (composite steel plate) embodiment of 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 of 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.

[0096] The yield strength and tensile strength of the composite steel plate are measured according to GB / T 6396-2008 “Method of mechanical and technological properties of clad steel” and GB / T 228-2010 “Metallic materials-tensile testing at ambient temperature-method of test”.

[0097] The impact energy KV2 / J (longitudinal) of the base carbon steel at -40℃ is measured according to GB / T 6396-2008 “Method of mechanical and technological properties of clad steel” 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 test” 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 single, equiaxed α-Ti with an average grain size of 104.8 um.

[0101] The interface transition layer of Example 3 is shown in Figure 4 , the interface transition layer has a thickness of 7.6 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 polygonal ferrite + granular bainite + degenerated pearlite.

[0103] Table 4 shows the corrosion of the composite steel plate 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, 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 present application). Among them:

[0105] Comparative Example 1 does not add B in the chemical composition, and the tensile strength and yield strength do not meet the requirements.

[0106] Comparative Example 2 has too high tensile strength, which exceeds the tensile strength requirement of the strength grade, and has adverse effects on subsequent processing, etc., because the cooling rate and the content of B are not within the range defined in the application.

[0107] Comparative Example 3 has martensite in the microstructure, and the yield strength ratio cannot meet the requirement, because the finish rolling temperature and the finish cooling temperature are not within the range defined in the application.

[0108] Comparative Example 4 has too thick interface transition layer, resulting in that the shear strength cannot meet the performance requirement, and cannot completely eliminate β-Ti in the subsequent processing and cooling process due to the too high heating temperature, so that the corrosion rate is high, and the yield strength cannot meet the requirement due to the finish cooling temperature not being within the defined range.

[0109] Comparative Example 5 has insufficient grain recrystallization due to too small pass reduction, and cannot effectively refine the structure, so that the impact performance cannot meet the requirement.

[0110] Through the preparation method of the application, especially the control of the heating, rolling and cooling processes, the base layer in the steel plate exhibits excellent yield strength ratio and low-temperature impact toughness, and the cladding layer has excellent corrosion resistance and high bonding strength, the yield strength is ≥ 420 MPa, the tensile strength is ≥ 570 MPa, the yield strength ratio is 0.73-0.81, the impact energy at-40℃ is ≥ 190 J, and the interface shear strength is all ≥ 265 MPa.

[0111] It should be noted that all the technical features described in the application can be freely combined or integrated in any way, unless contradictory to 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, the 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. A hot-rolled steel plate for building structure with 420 MPa grade resistance to sea-spray corrosion, comprising 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 chemical composition by mass percentage: C 0.03-0.15%, Si 0.15-0.35%, Mn 1.0-1.5%, P 0.0005-0.003%, S 0.0005-0.01%, Cr 0.1-0.65%, Ni 0.1-0.8%, Cu 0.05-0.3%, Al 0.02-0.05%, Ti 0.009-0.016%, Nb 0.03-0.06%, N 0.0005-0.005%, B 0.0002-0.0004%, and the balance of Fe and other inevitable impurities; the corrosion-resistant layer is made of industrial pure titanium; the hot-rolled steel plate for building structure has a yield strength of ≥420 MPa, a tensile strength of ≥570 MPa, a yield strength ratio of 0.73-0.81, a -40℃ impact energy of ≥190 J, a sea-spray corrosion resistance rate of ≤0.006 mm / year, an interface transition layer thickness of ≤10 μm, and an interface shear strength of ≥265 MPa.

2. The hot-rolled steel sheet for a building structure according to claim 1, characterized by, the chemical composition of the base layer further satisfies the following relational expressions: 0.2%≤Cu+Ni≤0.8%; 2(C+N)≤Ti+Nb+Cr≤0.65%.

3. The hot-rolled steel sheet for a building structure according to claim 1 or 2, characterized by, the industrial pure titanium is TA1, TA2, TA3 or TA4.

4. The hot-rolled steel sheet for a building structure according to claim 1 or 2, characterized by, the microstructure of the base layer is polygonal ferrite + granular bainite + degenerated pearlite, wherein the size of the martensite-austenite islands in the granular bainite is ≤5 μm, the content of the martensite-austenite islands is ≤3%, and the content of the degenerated pearlite is ≤5%.

5. The hot-rolled steel sheet for a building structure according to claim 1 or 2, characterized by, the base layer has a yield strength of ≥420 MPa, a tensile strength of ≥570 MPa, a yield strength ratio of 0.73-0.81, and a -40℃ impact energy of ≥190 J.

6. The hot-rolled steel sheet for a building structure according to claim 4, characterized by, the base layer has a yield strength of ≥420 MPa, a tensile strength of ≥570 MPa, a yield strength ratio of 0.73-0.81, and a -40℃ impact energy of ≥190 J.

7. The hot-rolled steel sheet for a building structure according to claim 1, wherein the microstructure of the corrosion-resistant layer is single and equiaxed α-Ti.

8. The hot-rolled steel sheet for a building structure according to claim 1 or 7, characterized by, the corrosion-resistant layer has a sea-spray corrosion resistance rate of ≤0.006 mm / year.

9. The hot-rolled steel sheet for a building structure according to claim 1, wherein the interface transition layer realizes 100% metallurgical bonding, atomic high coherence, an interface transition layer thickness of ≤10 μm, an average grain size of 15-50 μm, contains less than 120 nm (Ti, Nb)C precipitated particles, and has an interface shear strength of ≥265 MPa.

10. The hot-rolled steel sheet for a building structure according to claim 1, wherein the hot-rolled steel plate for building structure has a thickness of 5-90 mm.

11. The method of producing a hot-rolled steel sheet for a building structure of 420 MPa grade for resistance to corrosion in a splash zone according to any one of claims 1 to 10, characterized in that, comprising the following steps: 1) smelting and casting smelting and casting the base layer and the corrosion-resistant layer according to claim 1 or 2 into blanks respectively; 2) blank assembly surface grinding and polishing the base layer and the corrosion-resistant layer blanks, and welding and sealing the blank assembly surface to form a composite blank; and performing vacuum treatment on the welded and sealed joint surface; 3) heating heating the composite blank to 900-1000℃; 4) rolling controlling the pass reduction rate at 5-20%, and controlling the final rolling temperature at 750-850℃; 5) cooling After rolling, the water cooling method is used to cool down, the cooling speed is controlled at 5~15℃ / s, and the final cooling temperature is 400~650℃.

12. The production method according to claim 11, wherein Step 1) The thickness of the corrosion-resistant layer is 0.5~20% of the thickness of the composite blank.

13. The production method according to claim 11, wherein Step 4) The pass reduction rate used during rolling is 10~20%.

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