345mpa grade hot-rolled steel sheet for building structure resistant to corrosion in splash zone of sea waves and method for manufacturing the same

Abstract

345MPa grade building structure hot-rolled steel plate resistant to sea wave splash zone corrosion 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 0.03~0.10%, Si 0.1~0.3%, Mn 1.00~1.50%, P 0.0005~0.003%, S 0.0005~0.01%, Cr 0.02~0.2%, Ni 0.01~0.1%, Cu 0.002~0.020%, Al 0.015~0.03%, Ti 0.008~0.018%, Nb 0.02~0.065%, N 0.0005~0.005%, the balance includes Fe and inevitable impurities; the corrosion resistant layer uses industrial pure titanium.The building structure hot-rolled steel plate of the application has yield strength ≥350MPa, tensile strength ≥490MPa, yield ratio is 0.71~0.80, impact energy at-40 DEG C is ≥190J, sea wave splash corrosion rate is ≤0.006mm / year, interface transition layer thickness is ≤10 μm, interface shear strength is ≥252MPa.

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 the 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 alternation, sea spray, sunlight, corrosive components in the atmosphere and oxygen, and the corrosion of the materials is particularly serious.

[0003] Investigations show that the steel piles of facilities such as harbor wharfs 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 is greatly reduced, the service life is shortened, production safety is affected, and even the facility is prematurely scrapped.

[0004] In the sea-spray zone, due to being in the dry-wet alternation area, 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.

[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 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 is rapidly generated to prevent the corrosive medium from further contacting titanium.

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

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

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

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

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

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

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

[0013] 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.

[0014] 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 symmetrical 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.

[0015] 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, low temperature impact performance, yield ratio and other performance indicators of the base material are not controlled, which does not meet the requirements of building structure steel.

[0016] 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 sea-spray zone needs to not only resist the corrosion of the sea-spray zone, but also 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 structural safety. However, the above patents do not perform the related component and process design on the corrosion rate of the corrosion-resistant layer, the yield ratio, the low-temperature impact, etc., and cannot guarantee that the steel structure steel plate in the sea-spray zone environment can meet the high corrosion resistance requirements. SUMMARY

[0017] The present application aims to provide a 345MPa grade hot-rolled steel plate for building steel structure resistant to corrosion in sea-spray zone and a manufacturing method thereof. The yield strength of the hot-rolled steel plate for building structure is ≥350MPa, the tensile strength is ≥490MPa, the yield ratio is 0.71-0.80, the impact energy at-40℃ is ≥190J, the corrosion resistance in sea-spray zone is ≤0.006mm / year, the interface transition layer thickness is ≤10μm, and the interfacial shear strength is ≥252MPa. The steel plate can meet the corrosion resistance requirements in the sea-spray zone environment, has good mechanical properties resistant to corrosion in the sea-spray zone, and has high economic efficiency, and can be applied to steel structural members such as steel piles of facilities such as seaports and offshore oil platforms.

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

[0019] The present application adopts low-carbon micro-alloying component design, realizes the excellent combination of titanium and carbon steel under the condition of no addition of metal isolation layer, controls the interface transition layer thickness, and ensures that 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.

[0020] Specifically, the 345MPa grade hot-rolled steel plate for building structure resistant to corrosion in sea-spray zone comprises a base layer, a corrosion-resistant layer, and an interface transition layer between the base layer and the corrosion-resistant layer.

[0021] The chemical composition of the base layer is as follows: C 0.03-0.10%, Si 0.1-0.3%, Mn 1.00-1.50%, P 0.0005-0.003%, S 0.0005-0.01%, Cr 0.02-0.2%, Ni 0.01-0.1%, Cu 0.002-0.020%, Al 0.015-0.03%, Ti 0.008-0.018%, Nb 0.02-0.065%, N 0.0005-0.005%, and the balance contains Fe and other unavoidable impurities.

[0022] The corrosion-resistant layer adopts industrial pure titanium;

[0023] The yield strength of the hot-rolled steel plate for building structure is greater than or equal to 350 MPa, the tensile strength is greater than or equal to 490 MPa, the yield strength ratio is 0.71-0.80, the impact energy at-40 ℃ is greater than or equal to 190 J, the corrosion rate of sea wave splashing is less than or equal to 0.006 mm / year, the thickness of the interface transition layer is less than or equal to 10 microns, and the interface shear strength is greater than or equal to 252 MPa.

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

[0025] 0.02%≤Cu+Ni≤0.2%;

[0026] 2(C+N)≤Ti+Nb+Cr≤0.22%.

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

[0028] Preferably, the microstructure of the base layer is ferrite+pearlite and / or a small amount of bainite structure, the pearlite content is greater than or equal to 5%, and the average grain size is greater than or equal to 8.5 levels.

[0029] The yield strength of the base layer is greater than or equal to 350 MPa, the tensile strength is greater than or equal to 497 MPa, the yield strength ratio is 0.71-0.80, and the impact energy at-40 ℃ is greater than or equal to 190 J.

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

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

[0032] The corrosion-resistant layer has a sea wave splashing corrosion rate of less than or equal to 0.006 mm / year.

[0033] Preferably, the interface transition layer realizes 100% metallurgical bonding, atomic high coherence, the thickness of the interface transition layer is less than or equal to 10 microns, and the interface shear strength is greater than or equal to 252 MPa.

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

[0035] Preferably, the thickness of the hot-rolled steel plate for building structure is 3-80 millimeters.

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

[0037] C: C plays a role of solid solution strengthening in steel, and can obviously 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, and 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 in the application. The change of C content has less effect on the yield strength of the steel than on the tensile strength, under the premise of ensuring the forming and welding performance of the product, appropriately increasing the C content is beneficial to reducing the yield strength ratio of the steel, based on this, the C content in the base layer composition described in the application is controlled to be 0.03-0.10%.

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

[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 the steel, at the same time, Mn can also eliminate the effect of S on the steel. But too high Mn content is easy to appear segregation band and martensite organization, which is not conducive to the toughness of the steel. Therefore, the Mn content in the base layer composition described in the application is controlled to be 1.0%-1.5%.

[0040] Al: Al is mainly added to the steel as a deoxidizing element to ensure that the O content in the steel is as low as possible, after deoxidization, the excess Al combines with N element in the steel to form AlN precipitates, which hinder the growth of austenite grains during heating, refine the austenite grains, and improve 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. Based on this, the Al content in the base layer composition described in the application is controlled to be 0.015-0.03%.

[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 of the present application is controlled at 0.008-0.018%.

[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 composition of the present application is controlled at 0.02-0.065%.

[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 of the present application is controlled at 0.002-0.02%.

[0044] N: N element can generate second phase particles with Ti and Al, refine austenite grains, and improve the strength and toughness of the matrix. However, when the 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 present application. Based on this, the N content in the base layer composition of the present application is controlled at 0.0005-0.005%.

[0045] Ni: Ni is an element for stabilizing austenite, which 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, nickel is expensive, and excessive addition will increase the cost of the composite plate. Based on this, an appropriate amount of Ni is added in the base layer composition of the present application, and the Ni content is controlled at 0.01-0.1%.

[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, which play a role in precipitation strengthening, and at the same time, can fix 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 can increase the strength of the matrix in the steel while reducing the toughness, and in order to obtain the best match of strength and toughness, the content of Cr in the base layer composition described in the application is controlled at 0.02-0.20%.

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

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

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

[0050] Because Cu and Ni can both 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 application controls 0.02%≤Cu+Ni≤0.2%, and the interface transition layer can be controlled within 10 μm.

[0051] Because Ti, Nb and Cr are all 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 the interface transition layer can be controlled within 10 μm, thereby improving the interface shear strength. At the same time, Ti, Nb and Cr can 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≤0.22%.

[0052] The manufacturing method of the 345MPa grade hot-rolled steel plate for building structure resistant to corrosion in sea wave splash zone described in the application comprises the following steps:

[0053] 1) Smelting and casting

[0054] According to the composition of the above-mentioned base layer and corrosion-resistant layer, the billets are smelted and cast respectively;

[0055] 2) Grouping

[0056] The base layer and the corrosion-resistant layer blank are polished and the bonding surface of the blank is welded to form a composite blank; the bonding surface of the welded blank is vacuumized;

[0057] 3) heating

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

[0059] 4) rolling

[0060] The pass reduction rate is controlled to be 5-20% and the cumulative reduction rate is ≥70% and the final rolling temperature is controlled to be 750-850℃;

[0061] 5) cooling

[0062] The rolled blank is cooled by water cooling and the cooling speed is controlled to be 5-20℃ / s and the final cooling temperature is 300-650℃.

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

[0064] Preferably, the pass reduction rate in step 4) is 10-20%.

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

[0066] 1) smelting: P and S elements deteriorate the fracture toughness of the steel, so low P and low S control is performed in the smelting process to improve the quality of the 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.

[0067] 2) blanking; the thickness of the corrosion-resistant layer is prepared according to 0.5-20% of the total thickness of the composite blank. The corrosion-resistant layer and the carbon steel blank of the base layer are pretreated and the bonding surface of the blank is welded to form a composite blank; the bonding surface of the welded blank is vacuumized. The vacuum treatment protects the surface of the corrosion-resistant layer from being oxidized and is also an important condition for ensuring the corrosion resistance of the corrosion-resistant layer in the splash area.

[0068] 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℃.

[0069] 4) Rolling: large deformation reduction 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 austenite recrystallization does not occur in this stage, the deformation energy and dislocation are accumulated through 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 grain size after phase transformation of the matrix, and improve the strength and toughness of the material; at the same time, the deformation induces the precipitation of Nb, Ti, 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 ensures the corrosion performance of titanium while avoiding rolling in the two-phase zone to obtain ferrite pearlite and / or a small amount of bainite structure with an average grain size greater than 8.5.

[0070] 5) Cooling: the cooling after rolling is controlled by controlling the opening cooling, final cooling and cooling speed to control the type and size of the rolling structure. Too fast cooling speed will form bainite and 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 speed 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 speed should be reasonably controlled; the control of the finish rolling temperature can avoid the formation of abnormal coarse structure in the two-phase zone; 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 refining the grains. Preferably, the water cooling method is used for cooling, the cooling speed is controlled at 5-20℃ / s, and the final cooling temperature is controlled at 300-650℃ to ensure that the base layer has a low yield ratio and high low temperature impact toughness.

[0071] 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%.

[0072] 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 component design and the thickness ratio design of the corrosion-resistant layer and the base layer, and finally forms 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 and can be effectively applied to a steel structural member used in a sea wave splash area environment.

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

[0074] The present application adopts low-carbon micro-alloying component design, realizes excellent combination of titanium and carbon steel under the condition of no addition of metal isolation layer, controls the thickness of the interface transition layer, and 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.

[0075] In addition, the present application reduces the formation of TiC compounds in the interface transition layer and the formation of carbonitride in the base layer by reducing C, hinders 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 ≥350 MPa, the tensile strength is ≥490 MPa, the material yield ratio is 0.71-0.80, and the-40℃ impact energy is ≥190 J, all of which are higher than the performance requirements in the national standard GB / T19879-2015 "Building structure steel plate".

[0076] Chinese patent CN201210260231.7 does not specify the heating temperature, adds a layer of nickel plate as an isolation layer between the composite layer and the base layer to prevent the formation of TiC at the interface, and the interface bonding rate of the titanium steel composite plate obtained is 99.6-100%. The present application specifies that the heating temperature of the composite blank is 900-1000℃, reduces the addition of Ni through low-carbon and micro-alloying design, reduces the production cost, and forms a certain thickness of the transition layer organization through heating, rolling and other process optimization, reduces the formation of brittle phase TiC in the interface transition layer, and realizes the complete metallurgical bonding with the interface bonding rate of 100%.

[0077] The slab heating temperature is 500-700 DEG C, the total reduction is 60-70%, and the interface shear strength of the produced steel plate is at most 182 MPa. The application fully considers the influence of the high-temperature phase change of the corrosion-resistant layer of industrial pure titanium on corrosion resistance and the strength and toughness control of the base layer of carbon steel. In combination with low-carbon micro-alloy design, the global design of the processing technology is used, the heating temperature of the composite blank is set to 900-1000 DEG C, the corrosion-resistant layer does not change at the temperature, and the precipitates in the base layer of carbon steel are fully dissolved, the base layer grains are refined, the strength and toughness of the base layer are improved, in combination with the total reduction of greater than or equal to 70%, the brittle phase of the interface is broken, and the interface shear strength is improved.

[0078] The above two patents mainly avoid the generation of brittle Ti compounds by adding an additional nickel-based alloy isolation layer between titanium and carbon steel, while the application does not add an isolation layer through component and process design, and the composite blank method and the material of the base layer of carbon steel are obviously different from the above two patents.

[0079] Under the process conditions of the application, the original corrosion resistance of the corrosion-resistant layer of industrial pure titanium is ensured, and the mechanical properties of the base layer are ensured, solving the problem that the traditional processing technology windows of titanium and carbon steel are too different to be considered together; meanwhile, the base layer and the corrosion-resistant layer elements are fully diffused to form an interface transition layer of not greater than 10 microns, the layer has small grains, the average grain size is 15-50 microns, 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 greater than or equal to 252 MPa, which is higher than the interface shear strength of 182 MPa in the patent.

[0080] The patent CN201811327623.4 realizes compounding by warm rolling, and then needs to be subjected to two-stage heat treatment operation, including primary annealing at 500-600 DEG C for 20-60 minutes and recrystallization annealing at 680-700 DEG C 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 application.

[0081] The patent CN201510543767.3 requires that the heating temperature is 850-900 DEG C, the final rolling temperature is below 700 DEG C, the single-pass deformation amount is controlled to be 20-30%, and the total deformation amount is greater than or equal to 90%, and the shear strength of the titanium steel composite plate is greater than 240 MPa. The pass reduction and the total deformation amount required by the patent are very high, and the edge weld is prone to cracking during rolling, the vacuum degree is damaged, the compounding is not easy, and the rolling stability is poor. The single-pass reduction of the application is controlled to be 5-20%, which can effectively control the weld from cracking during rolling, ensure the vacuum degree inside the slab, and improve the interface shear strength, the stability of rolling, and the success rate.

[0082] Chinese patent CN201610994234.1 is a kind of titanium steel plate annealing technology production method, first titanium plate and steel plate are formed into billet, form steel plate-titanium plate-separator-titanium plate-steel plate symmetry type multilayer combination billet, through the way of rolling composite or explosion composite is compounded, the billet after compounding is annealed and pickled by continuous annealing and pickling line, first heated to 500~750 DEG C, so that the heart titanium plate recrystallizes, then heated to 950~1050 DEG C, 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 application is obviously different from the present application, the present application 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.

[0083] The corrosion-resistant layer material of Chinese patent CN201710996925.X is TA2, the titanium composite layer thickness is 0.2~1mm, heated to 900~920 DEG C, the opening rolling temperature is 880~900 DEG C, the final rolling temperature is above 800 DEG C, air cooling to room temperature, the shear strength reaches 241 MPa. The heating temperature of the present application is 900~1000 DEG C, the final rolling temperature is 750 DEG C~850 DEG C, water cooling is used, the control cooling speed is 5~20 DEG C / 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 3-80mm hot-rolled plate, and the interface shear strength is ≥252 MPa.

[0084] The billet forming 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 DEG C, air cooling to room temperature, the titanium steel composite plate is obtained through surface treatment, the titanium composite layer thickness is ≤1mm. The single pass reduction rate of the present application is 5~20%, the rolling stability is controlled. There are also obvious differences in the thickness of the corrosion-resistant layer and the total thickness of the composite steel plate.

[0085] In summary, the 345MPa grade hot-rolled steel plate for building structure resistant to corrosion in sea-spray area can solve the essential problems of stainless steel or carbon steel used in sea-spray area environment; the 345MPa grade hot-rolled steel plate for building structure resistant to corrosion in sea-spray area can be effectively applied to the manufacture of steel structural parts used in sea-spray area environment, such as steel structural parts of facilities in sea-spray area, such as seaport wharf, offshore oil platform, etc., which can meet the requirements of these components for corrosion resistance and mechanical properties in sea-spray area, greatly improving the applicability, safety and durability of these components, and having great economic and social benefits. BRIEF DESCRIPTION OF DRAWINGS

[0086] Figure 1 A schematic diagram of an interlayer structure of the 345MPa grade hot-rolled steel plate for building structure with resistance to corrosion in sea wave splash zone according to the present application.

[0087] Figure 2 A schematic diagram of another interlayer structure of the 345MPa grade hot-rolled steel plate for building structure with resistance to corrosion in sea wave splash zone according to the present application.

[0088] Figure 3 A microstructure photo of the corrosion resistant layer of Example 3 of the present application.

[0089] Figure 4 A scanning image of the interface transition layer of the combination of the base layer and the corrosion resistant layer of Example 3 of the present application.

[0090] Figure 5 A microstructure photo of the base layer of Example 3 of the present application. DETAILED DESCRIPTION

[0091] The technical solutions of the present application will be further described in detail below in combination with the examples and the 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.

[0092] Reference is made to Figure 1 , Figure 2 , Figure 4 which shows a schematic diagram of two interlayer structures of the hot-rolled steel plate for building structure according to the present application, wherein 1 is the base layer, 2 is the corrosion resistant layer, and 3 is the interface transition layer.

[0093] The composition of the base layer of the hot-rolled steel plate (composite steel plate) embodiment according to the present application is shown in Table 1, and the remaining amount of the composition is Fe and unavoidable impurities. Table 2 shows the manufacturing process parameters of the composite steel plate embodiment according to the present application. Table 3 shows the metallographic structure and mechanical properties of the base layer and the corrosion resistant layer in the composite steel plate of the example and the comparative example, and the thickness of the interface transition layer.

[0094] The yield strength and tensile strength of the composite steel plate are measured in accordance with GB / T 6396-2008 “Method of Mechanical and Technological Properties of Composite Steel Plate” and GB / T 228-2010 “Metallic Materials Tensile Testing at Ambient Temperature”.

[0095] The impact energy KV2 / J (longitudinal) of the carbon steel base layer at -40℃ is measured in accordance with GB / T 6396-2008 “Method of Mechanical and Technological Properties of Composite Steel Plate” and GB / T 229-2020 “Metallic Materials Charpy Pendulum Impact Test Method”.

[0096] Grain size rating was carried out according to GB / T 6394-2017 "Metallic Materials - Determination of Average Grain Size" by intercept method for ferrite structure in stainless steel and carbon steel, respectively.

[0097] Comparative examples were prepared by the same steps as the inventive examples, except that the base layer carbon steel composition and some process parameters during rolling or cooling steps did not meet the requirements of the present application.

[0098] The metallographic structure of the corrosion resistant layer of Example 3 is shown in Figure 3 , which shows single and equiaxed a-Ti with an average grain size of 102.8 um.

[0099] The interface transition layer of Example 3 is shown in Figure 4 , the thickness of the interface transition layer 3 is 7.5 um, and the discontinuous fine particles are TiC with a size of less than 120 nm.

[0100] The metallographic structure of the base layer of Example 3 is shown in Figure 5 , which shows the metallographic structure of the base layer carbon steel as ferrite + pearlite, with a pearlite volume fraction of 6.8% and a grain size rating of ≥8.5.

[0101] Table 4 shows the corrosion of the hanging sample of the composite steel plate of Examples 1-8 and Comparative Examples 1-4 after 6 months in the sea spray zone. 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.

[0102] Comparative Examples 1-4 do not meet the use requirements (performance parameters are not within the scope of the invention) due to the use of composition design requirements, hot working process conditions that do not meet the requirements. Among them:

[0103] Comparative Example 1 does not meet the requirements for yield strength, yield ratio, impact performance and interface shear strength due to the use of no Ti, Nb and Cr addition, and the use of rolling reduction rate not within the scope of the invention.

[0104] Comparative Example 2 does not meet the requirements for yield ratio and impact performance due to the absence of Ni addition in the chemical composition, the final rolling temperature, the cooling rate, and the final cooling temperature not within the scope of the invention.

[0105] Comparative Example 3 does not meet the requirements for metallographic structure, mechanical properties, yield ratio and impact performance due to the Cu + Ni addition amount less than 0.02% and the cooling rate and final cooling temperature not within the scope of the invention.

[0106] Comparative Example 4 has an interface transition layer thickness that is too thick because the heating temperature and finish rolling temperature are not within the range defined by the present application, and the shear strength does not meet the performance requirements. Because the heating temperature is too high, the beta-Ti cannot be completely eliminated during subsequent processing and cooling, resulting in a high corrosion rate.

[0107] By the preparation method of the present application, especially the control of the heating, rolling and cooling processes, the base layer in the steel plate exhibits excellent yield ratio and low temperature impact toughness, and the cladding layer has excellent corrosion resistance and high bonding strength. The yield strength is 352-445 MPa, the tensile strength is 497-602 MPa, the yield ratio is 0.71-0.80, the impact energy at -40℃ is above 190 J, and the interface shear strength is greater than 252 MPa.

[0108] It should be noted that all the technical features described in the present application can be freely combined or integrated in any way, unless they contradict each other. Various modifications and changes can be made to the present application without departing from the scope of the present application, which will be apparent to those skilled in the art. For example, features shown or described as part of one embodiment can be used with another embodiment to produce yet another embodiment. Therefore, the present application is intended to 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 345 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 0.03-0.10%, Si 0.1-0.3%, Mn 1.00-1.50%, P 0.0005-0.003%, S 0.0005-0.01%, Cr 0.02-0.2%, Ni 0.01-0.1%, Cu 0.002-0.020%, Al 0.015-0.03%, Ti 0.008-0.018%, Nb 0.02-0.065%, N 0.0005-0.005%, 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 ≥350 MPa, a tensile strength of ≥490 MPa, a yield strength ratio of 0.71-0.80, an impact energy at -40 ℃ 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 ≥252 MPa.

2. The hot-rolled steel sheet for a building structure according to claim 1, characterized by, the base layer chemical composition also satisfies the following relationship: 0.02%≤Cu+Ni≤0.2%; 2(C+N)≤Ti+Nb+Cr≤0.22%.

3. The hot-rolled steel sheet for a building structure according to claim 1, 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 base layer has a microstructure of ferrite + pearlite, or ferrite + pearlite + bainite, a pearlite content of ≥5%, and an average grain size of ≥8.5 grade.

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 ≥350 MPa, a tensile strength of ≥497 MPa, a yield strength ratio of 0.71-0.80, and an impact energy at -40 ℃ 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 ≥350 MPa, a tensile strength of ≥497 MPa, a yield strength ratio of 0.71-0.80, and an impact energy at -40 ℃ of ≥190 J.

7. The hot-rolled steel sheet for a building structure according to claim 1, wherein the corrosion-resistant layer has a microstructure of single, 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, a small grain size, an average grain size of 15-50 μm, and contains less than 120 nm (Ti, Nb)C precipitated particles.

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 3-80 mm.

11. The method of producing a hot-rolled steel sheet for a building structure of 345 MPa grade resistant to corrosion in a splash zone of sea waves 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 surrounding surface of the blanks 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 cumulative reduction rate at ≥70% and the finish rolling temperature at 750-850 ℃; 5) cooling cooling after rolling by using water cooling, and controlling the cooling speed at 5-20 ℃ / s and the final cooling temperature at 300-650 ℃.

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

13. The production method according to claim 11, wherein In step 4), the pass reduction is 10 to 20%.

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