A corrosion-resistant steel for a photovoltaic pile foundation and a method of manufacturing the same

Abstract

The application discloses a kind of corrosion-resistant steel for photovoltaic pile foundation and a manufacturing method thereof.The corrosion-resistant steel has the following components by weight percentage: C 0.03-0.12%, Si 0.20-0.50%, Mn 0.4-0.9%, P≤0.018%, S≤0.006%, Al 0.2-0.8%, Cu 0.10-0.50%, Cr 0.3-1.2%, Ni≤0.20%, N≤0.006%, the balance comprising Fe and inevitable impurities, and 1.0≤Cr / Al≤4.0, Cu+1.22Cr+35.3Al≥9.2.The corrosion-resistant steel has the following advantages: the corrosion resistance of steel plate in a soil corrosion environment with a high sulfate ion concentration of 300-30000 mg / kg and a chloride ion concentration of 1500-8000 mg / kg is more than 6 times that of ordinary steel, the relative corrosion rate is less than 16.5%;the relative corrosion rate of the corrosion-resistant steel in an industrial atmospheric environment is less than or equal to 55% compared with that of plain carbon steel, thereby meeting the corrosion resistance requirements in various environments;in addition, the corrosion-resistant steel is delivered in a rolled state without heat treatment, and does not contain Sb, which is more environmentally friendly.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of low alloy steel manufacturing, in particular to a kind of corrosion-resistant steel for photovoltaic pile foundation and manufacturing method thereof. BACKGROUND

[0002] Corrosion of steel is a common and serious problem. In soil, due to the presence of microorganisms, water, oxygen and various minerals, there is also a certain corrosion to steel structure. Especially in the central and western regions of China such as Xinjiang, Ningxia and Inner Mongolia, due to the marine environment in the Paleozoic era, the soil contains a large amount of sulfate and chloride ions, which threatens the safe use of steel structure.

[0003] In order to effectively prolong the service life of equipment and reduce the use cost, corrosion-resistant steel emerges as the times require. On the basis of Corten steel in the United States, countries have developed a series of corrosion-resistant steel products according to resources and use requirements, and the strength and performance have also developed from the early 235MPa level to 450MPa level high-strength weathering steel and high-corrosion-resistant high-corrosion-resistant steel with better corrosion resistance, and many related steel grade patents have also been produced.

[0004] Chinese patent publication No. CN101660099B discloses "high-strength low-alloy hot-rolled ferritic bainite weathering steel and its production method", the yield strength of which reaches 450MPa level, and the corrosion resistance is at the level of conventional weathering steel by using higher Mn content design, which does not involve soil corrosion.

[0005] Several patents such as Chinese patent publication No. CN1986864 discloses "a high-strength low-alloy atmospheric corrosion-resistant steel and its production method", Chinese patent publication No. CN102168229B discloses "weathering steel plate and its manufacturing method", and Chinese patent publication No. CN107779740A discloses "yield strength 700MPa level atmospheric corrosion-resistant hot-rolled steel strip and manufacturing method" involve steel plates with higher strength of 450MPa or more, but in composition, higher Mn is used, and the cost is higher by adding Mo, Nb, V, Ti and other strengthening elements. The weathering level is also equivalent to that of traditional weathering steel, i.e. relative corrosion rate ≤55%. But it does not meet the requirements of soil corrosion resistance.

[0006] In order to meet the application requirements under more working conditions, in addition to high strength, weathering steel also develops towards high corrosion resistance and high toughness, and requires good machinability and lower cost.

[0007] "Corrosion Resistant Steel" disclosed in Japanese Patent No. JP10025550A, "Corrosion Resistent Steel Having Excellent Toughness in Base Material and Heat Affected Zone" disclosed in Japanese Patent No. JP2002363704 and "High Corrosion Resistant Cr-Containing Weathering Steel with Excellent Toughness" disclosed in Chinese Patent Publication No. CN102127717A, these patents involve steel grades with better corrosion resistance, lower relative corrosion rate, but do not involve sulfate and chloride corrosion resistance; and the steel contains high Cr, Al, Ni and other elements, which is difficult to smelt and has high manufacturing cost.

[0008] In Xinjiang region, the concentration of sulfate ions in the soil ranges from 300 to 30000 mg / kg, and the concentration of chloride ions reaches 1500 to 8000 mg / kg. The corrosion is caused by a large amount of chloride ions and sulfate ions in the soil, which is significantly different from the conventional weathering steel environment.

[0009] "Railway Vehicle Atmospheric Corrosion Resistant Hot Rolled Steel Plate and Manufacturing Method Thereof" disclosed in Chinese Patent Publication No. CN102268613A involves sulfate and chloride corrosion, and the steel contains 0.01 to 0.04% P, and also needs to add appropriate amounts of Ca, Mg, Ce and Sb. The higher P is not conducive to low temperature toughness and forming performance, and the addition of Mg and Ce increases the production difficulty, and the addition of Sb is harmful to human body and environment.

[0010] "Steel for Neutral Soil Corrosion Resistant Buried Structure and Manufacturing Method Thereof" disclosed in Chinese Patent Publication No. CN109023071A contains 2.0 to 3.5% Cr, 0.2 to 0.4% Ni and 0.3 to 0.5% Mo, and also contains 0.08 to 0.18% Sb. Sb combined with Cu can form a Cu2Sb protective film on the surface, thereby improving the sulfate dew point corrosion resistance. However, the addition of Sb is obviously harmful to the environment and human body. Sb is a typical toxic and harmful heavy metal element, which has chronic toxicity and potential carcinogenicity to human and animal bodies. With the improvement of environmental awareness and the tightening of environmental protection policies, the production and application of Sb-containing steel will inevitably be more restricted.

[0011] From the comparison with the existing patents, it can be found that the current weathering steel, whether it is a conventional level weathering steel or a high corrosion-resistant weathering steel, has a corrosion-resistant performance mainly aiming at atmospheric corrosion environment, and is not suitable for the high-sulfate and high-chloride ion corrosion environment in Xinjiang region; and the existing weathering steel capable of improving the soil medium corrosion environment adds Sb element, and Sb is harmful to the environment and human health. SUMMARY

[0012] The purpose of the present application is to provide a kind of photovoltaic pile with corrosion-resistant steel and its manufacturing method, the corrosion-resistant steel in the soil corrosion environment of 300-30000 mg / kg high sulfate ion concentration, 1500-8000 mg / kg concentration chloride ion concentration, the corrosion-resistant performance of steel plate reaches more than 6 times of ordinary steel, and the relative corrosion rate is less than 16.5%;It also has good atmospheric corrosion resistance, and the corrosion rate of industrial atmosphere relative to plain carbon steel is ≤55%, thereby meeting the corrosion-resistant performance requirements in various environments;The steel plate is produced by controlled rolling and controlled cooling, has a wider process window, and the production method is simple;It is delivered in rolling state without heat treatment, has a short production cycle and low steel cost;The yield strength of the steel meets the high strength requirement of 345 MPa or more, the tensile strength is ≥485 MPa, the elongation A is ≥20%, the low temperature impact energy at-40℃ is more than 160 J, and the steel also has good welding, cold bending and other processing properties, excellent elongation, and is particularly suitable for various cold forming processes in the production process of pile foundation;It can also be applied to other high-concentration sulfate ion and chloride ion corrosion environments such as seawater and gas pipelines;In addition, the photovoltaic pile with corrosion-resistant steel according to the present application does not contain Sb, and is more friendly to the environment.

[0013] To achieve the above purpose, the technical scheme of the present application is:

[0014] The present application obtains high strength and good low temperature toughness by selecting and adding appropriate amounts of V, Ti and Nb precipitation strengthening on the basis of lower C-Si-Mn, and realizes good corrosion resistance in soil corrosion environment under the concentration of 300-30000 mg / kg sulfate ion and 1500-8000 mg / kg chloride ion by adopting Cu-Cr-Al component design, thereby realizing the combination of corrosion resistance, high strength and high toughness on the basis of low cost.

[0015] Specifically, the hot-rolled corrosion-resistant steel for photovoltaic pile according to the present application has the following composition by weight percentage: C: 0.03-0.12%, Si: 0.20-0.50%, Mn: 0.4-0.9%, P≤0.018%, S≤0.006%, Al: 0.2-0.8%, Cu: 0.10-0.50%, Cr: 0.3-1.2%, Ni≤0.20%, N≤0.006%, the balance comprising Fe and other unavoidable impurity elements, and the following conditions must be met simultaneously:

[0016] 1.0≤Cr / Al≤4.0,

[0017] Cu+1.22Cr+35.3Al≥9.2.

[0018] Further, the balance is Fe and other inevitable impurity elements.

[0019] Still further, it also contains one or more of Ti: 0.01-0.06%, Nb: 0.01-0.03% and V: 0.01-0.04%.

[0020] Still further, it also contains one or both of Sn: 0.01-0.12% and RE: 0.01-0.12%.

[0021] Preferably, the Mn content is 0.5-0.8%.

[0022] Preferably, the Cu content is 0.15-0.35%.

[0023] Preferably, the Cr content is 0.6-1.0%.

[0024] The microstructure of the corrosion-resistant steel described in the present application is ferrite + pearlite and a small amount of bainite.

[0025] The yield strength of the corrosion-resistant steel described in the present application is ≥345 MPa, the tensile strength is ≥485 MPa, the elongation A is ≥20%, and the impact energy value at -40℃ is ≥160 J.

[0026] In the chemical composition design of the corrosion-resistant steel plate for photovoltaic pile foundation described in the present application:

[0027] C is an effective strengthening element in steel, which has a solid solution strengthening effect when dissolved in the matrix, and exists in the form of carbide in the steel, and plays a role in precipitate strengthening and grain refinement in combination with alloy elements, so the addition amount should not be less than 0.03%; while too much C forms more carbides in the steel, which plays the role of a primary cell, promotes the corrosion process and thus reduces the corrosion resistance of the steel, and is not conducive to welding, so the C content is limited to not more than 0.12%.

[0028] Si is generally added to the steel for deoxidization, and is also a corrosion-resistant element with a solid solution strengthening effect, so the lower limit of the content is controlled to be 0.20%, and a higher Si content will lead to deterioration of weldability and toughness of the heat-affected zone, so the upper limit is specified to be 0.50%.

[0029] Mn is an important toughening element, which plays a role of solid solution strengthening, improves the strength and toughness of the steel, and is also an austenite-expanding element, which can reduce the transformation temperature of supercooled austenite, promote the transformation of the low-temperature strengthening structure in the steel, and is beneficial to the improvement of the strength of the steel. However, too much Mn increases the hardenability, thereby leading to the deterioration of the weldability and the toughness of the heat-affected zone, and a high Mn also increases the cost. Therefore, the content of Mn is limited to 0.4-0.9% in the present application, preferably 0.5-0.8%.

[0030] P is a main corrosion-resistant element in traditional atmospheric corrosion-resistant steel, which can promote the formation of a protective rust layer on the surface, effectively improve the atmospheric corrosion resistance of the steel, but P is prone to segregation at the grain boundary, which reduces the grain boundary binding energy and the toughness and plasticity of the steel; moreover, the coexistence of P and Mn will exacerbate the temper brittleness of the steel, the segregation of P makes the steel plate prone to intergranular fracture, and reduces the impact toughness of the steel plate. Moreover, P is not conducive to the welding performance. The steel of the present application requires high toughness, so P is controlled as an impurity element to reduce the content of P in the steel as much as possible. However, too low P content also increases the difficulty of steelmaking and manufacturing cost, so the content of P is limited to not more than 0.018%.

[0031] S in the steel is controlled as a harmful impurity element. S not only reduces the low-temperature toughness of the steel, but also promotes the anisotropy of the steel plate, which is not conducive to the cold forming performance, and the sulfide inclusions also significantly reduce the weather resistance of the steel. Therefore, the steel of the present application is designed to have a very low S content, which is controlled to be less than or equal to 0.006%.

[0032] Al is usually added in the steel as a deoxidizer in the steelmaking process, and a small amount of Al is beneficial to the refinement of the grain, and the improvement of the strength and toughness of the steel. The addition of appropriate Al improves the corrosion potential of the steel, which is beneficial to the inhibition of corrosion; meanwhile, the formation and aggregation of the nanoscale complex oxides containing Al and Si in the internal rust layer can increase the charge mass transfer resistance, thereby inhibiting the corrosion process. However, Al reduces the stability of austenite, reduces the supercooling degree of austenite, makes the new phase nuclei grow rapidly, thereby reducing the hardenability and increasing the critical quenching speed; meanwhile, Al as a ferrite-forming element, too much Al reduces the strength of the steel plate, increases the brittleness of ferrite in the steel, and leads to the reduction of the toughness of the steel. Therefore, the content of Al is limited to 0.2-0.8% in the present application.

[0033] Cr is a valuable alloying element, which is also an effective element for improving the corrosion resistance of the steel plate. Cr forms a continuous solid solution with Fe in the steel, has a solid solution strengthening effect, and forms various types of carbides such as M3C, M7C3 and M23C6 with C, which can effectively improve the corrosion resistance of the steel plate. 23C6, etc. to produce a secondary strengthening effect. Cr has a significant effect on improving the passivation ability of the steel, which can promote the formation of a dense passivation film or protective rust layer on the surface of the steel, and the enrichment of the rust layer can effectively improve the selective permeability of the rust layer to corrosive media; at the same time, the addition of Cr can effectively improve the self-corrosion potential of the steel and improve the atmospheric corrosion resistance of the steel. However, the addition of more Cr will increase the manufacturing cost. Therefore, considering the cost reduction, the present application limits the Cr content to 0.30-1.2%, preferably Cr: 0.6-1.0%.

[0034] Cu in steel mainly plays a role in solid solution and precipitation strengthening, and at the same time, the electrochemical potential of Cu is higher than that of Fe, which can promote the formation of a dense rust layer on the surface of the steel, and is beneficial to the improvement of corrosion resistance, and at the same time, a proper amount of Cu combines with residual S in the steel to form a Cu2S protective film, which can alleviate the corrosion in high-sulfate corrosion environment. However, too high Cu will not only damage the toughness of the weld heat affected zone, but also easily cause net cracking during hot rolling, which will worsen the surface performance of the steel plate and increase the cost. Therefore, the Cu content in the present application is limited to 0.10-0.50%, preferably Cu: 0.15-0.35%.

[0035] Ni is an element for expanding austenite. Ni can improve low-temperature impact toughness by refining grains and reducing stacking fault energy; at the same time, grain refinement also has a fine-grain strengthening effect. In addition, Ni is also an important element for improving the corrosion resistance of steel, which can promote the stability of the rust layer and improve the hot working brittleness problem caused by Cu. However, Ni is a precious element, and it is recommended to be selected and controlled to be below 0.2%.

[0036] N in steel can form nitrides with Al and Ti, and the fine precipitates have the effect of pinning grain boundaries, thereby refining the austenite grains. Higher N in steel is easy to form AlN, thereby significantly increasing the number of nitrides in the steel. When AlN exists independently in the steel as a non-metallic inclusion, it destroys the continuity of the steel matrix, especially when the Al content is high, the number of AlN formed is large and the distribution is aggregated, the degree of harm is more serious, and at the same time, poor plasticity oxides are formed; and higher N is easy to enrich at defects, which will worsen the low-temperature impact toughness. The N content must be controlled to be below 0.0060%.

[0037] In addition to the above elements, in order to further improve the performance, the steel grade can further select to add one or more of Nb, V, Ti and Sn, RE. Among them:

[0038] Ti is a strong ferrite forming element and carbonitride forming element, and is easy to form compounds with C, N, O, S and the like. Ti mainly exists in the form of TiC or Ti(C,N) in the steel. In the present application, the addition of Ti mainly utilizes TiN to inhibit the growth of austenite grains, and plays a role in refining the structure; meanwhile, it produces precipitation strengthening effect during the cooling process. In addition, Ti has the effects of preventing recrystallization of deformed austenite and promoting formation of granular bainite, and the precipitated Ti carbonitride particles can prevent the grain coarsening in the welding heat affected zone and improve the welding performance. When the content of Ti is too high, the titanium nitride particles are easy to grow and agglomerate at high temperature, which damages the plasticity and toughness of the steel. Therefore, the content of Ti is limited to 0.01-0.06% and is selectively added.

[0039] Nb is a strong carbonitride forming element, and can form intermediate phases such as NbC, Nb(CN) and NbN by combining with carbon and nitrogen in the steel during the cooling process after rolling. The fine carbonitride particles formed can refine the structure, produce fine-grain strengthening and precipitation strengthening effect, and significantly improve the strength of the steel plate. At the same time, the refinement of the structure is beneficial to the improvement of the toughness of the steel plate. In addition, Nb can inhibit the expansion of the austenite interface, and increase the recrystallization temperature of the steel, so that non-recrystallization zone rolling can be realized at a higher temperature. Therefore, the addition of an appropriate amount of Nb in the steel is beneficial to the improvement of the strength, and when the content of Nb is too high, coarse carbonitride particles are formed at the grain boundaries, which deteriorates the impact toughness. Nb is also a valuable alloying element, and the content is limited to 0.01-0.03% and is selectively added.

[0040] V is a strong carbonitride forming element, and can be precipitated during phase transformation, has solid solution strengthening and carbonitride precipitation strengthening effect in the steel, and increases the tempering stability, thereby improving the strength, and the content is limited to 0.01-0.04%.

[0041] Sn has good corrosion inhibition effect in the steel, and Sn ions can be dissolved in the anode to inhibit the anode reaction and reduce the formation of β-FeOOH which is detrimental to the corrosion resistance, and the content of Sn is limited to ≤0.12%.

[0042] RE (rare earth) forms RE compounds, RE / Fe intermetallic compounds and solid-solution rare earth in the steel, and hydrolyzes in the corrosion thin liquid film and precipitates at the cathode at a higher pH value, thereby playing a corrosion inhibition effect, and the content of RE is limited to ≤0.12%.

[0043] The present application relates to a hot-rolled corrosion-resistant steel for photovoltaic pile foundation, which has good corrosion resistance in a soil environment containing 300-30000 mg / kg concentration of sulfate ions and 1500-8000 mg / kg concentration of chloride ions, and at the same time has atmospheric corrosion resistance comparable to conventional weathering steels. The steel plate also has good formability and low-temperature impact toughness, meeting the processing requirements of photovoltaic pile foundation steel, and is also suitable for seawater environments with high chloride ion content and coal gas pipelines with high sulfate ions.

[0044] The main innovation of the present application is the use of a Cu-Cr-Al composition system design, which achieves significant improvement in corrosion resistance in high-sulfate, high-chloride soil corrosion environments through the synergistic effect of multiple corrosion-resistant elements.

[0045] Cu is an effective element for improving sulfate ion corrosion, while Cr is a commonly used corrosion-resistant element. In addition to solid solution strengthening and improving quenching depth, the addition of Cr also increases the corrosion potential. However, the addition of Cu and Cr alone cannot improve the corrosion resistance in high-sulfate, high-chloride soil corrosion environments. Research shows that the addition of about 1% Cr in the steel increases the self-corrosion potential by about 40 milliamperes, and corrosion evaluation shows that a potential difference of less than 70 milliamperes will not cause significant galvanic corrosion. Therefore, a corrosion potential difference of 40 milliamperes will not significantly change the corrosion current, change the corrosion tendency, and have little effect on improving corrosion resistance. Cu is a necessary element in acid-resistant steel, but about 0.1% Sb must also be added to achieve the expected corrosion resistance. The present application discards the addition of Sb for environmental and human health considerations, so relying solely on Cr and Cu cannot achieve excellent corrosion resistance in high-concentration sulfate ion and chloride ion soil environments.

[0046] Al itself is relatively active and easy to react with oxygen in the air. In the natural environment, it has a passivation effect and can form a thin film of Al2O3 on the surface layer, thereby having corrosion resistance. Therefore, Al is usually added as a deoxidizing element in steel. Although a certain amount of Al is added in the 10CrMoAl steel, the improvement mechanism of its corrosion resistance in seawater environment is not mentioned. According to the research of the present application, it is found that Cr and Al have a synergistic effect in steel, which can significantly improve the corrosion resistance of steel in high-concentration sulfate and chloride environments. The mechanism is that: on the one hand, the combined addition of Cr and Al significantly improves the corrosion potential of the steel, and the improvement amplitude is about 200 milliamperes, while 1% Cr only makes the corrosion potential of the steel increase by 40 milliamperes; on the other hand, Cr and Al form intermetallic compounds Fe2CrAl and Cr8Al5 in the steel. In high sulfate and chloride environments, these two compounds gather on the surface of the steel, improving the corrosion resistance of the steel. The increase of corrosion potential reduces the corrosion current and reduces the occurrence of corrosion; while the intermetallic compounds of Cr and Al protect the surface layer and hinder the deepening of corrosion, playing an isolation role. It is in this synergistic effect of Cr and Al that the corrosion resistance in high sulfate and chloride environments is obtained. Therefore, Cu and Cr must be combined with an appropriate amount of Al to obtain excellent corrosion resistance in soil corrosion environments with a high sulfate ion concentration of 300-30000 mg / kg and a chloride ion concentration of 1500-8000 mg / kg.

[0047] Therefore, the present application limits the addition amount of Cu, Cr and Al and requires that the content satisfies the relationship: 1.0≤Cr / Al≤4.0, Cu+1.22Cr+35.3Al≥9.2, so that the corrosion resistance in the above-mentioned environment is more than 6 times that of plain carbon steel, and the relative corrosion rate is less than 16.5%; and the atmospheric corrosion resistance is equivalent to that of conventional weathering steel, and the relative corrosion rate of plain carbon steel is ≤55%, thereby meeting the corrosion resistance requirements in various environments. The new corrosion-resistant component system avoids the toxic pollution of Sb to the environment and human body in conventional sulfate ion corrosion-resistant steel, and at the same time, the corrosion resistance is greatly improved, which belongs to an environmentally friendly product.

[0048] The present application utilizes the solid solution strengthening of C and Mn, and the precipitation strengthening and fine-grain strengthening effects of V, Nb and Ti to obtain a yield strength of 345 MPa or more, while having good low-temperature impact toughness, a low-temperature impact energy value of more than 160 J at-40 ℃, and an elongation of more than 20%, realizing the matching of high corrosion resistance and high toughness, and having good forming performance, meeting the application requirements of pile foundation steel.

[0049] The manufacturing method of the photovoltaic pile foundation high-strength corrosion-resistant steel according to the present application comprises the following steps:

[0050] 1) Smelting, casting

[0051] Smelting and casting into billets according to the above components; wherein the steelmaking adopts LF refining;

[0052] 2) Billet heating

[0053] The heating furnace is a reducing atmosphere, the billet discharge temperature is above 1230℃, and the holding time is 2-4h, wherein the soaking holding time is not less than 40min;

[0054] 3) Rolling

[0055] Hot continuous rolling is adopted, the end temperature of the billet rough rolling is above 1000℃, the cumulative reduction rate in the rough rolling stage is ≥80%, ferrite rolling process is adopted in the finishing rolling, the finishing rolling starting temperature is ≤950℃, the finish rolling temperature is 820-880℃, then cooling is carried out, the cooling rate is controlled to be ≥10℃ / s, and the coiling temperature is 520-580℃.

[0056] In the manufacturing method of the high-strength corrosion-resistant steel for photovoltaic pile foundation provided in the application:

[0057] The steelmaking adopts LF refining, the RH link is reduced, and the cost is further reduced.

[0058] Billet heating: the heating furnace is required to be a reducing atmosphere, and the billet discharge temperature is controlled to be above 1230℃. Considering that trace Ti is added in the steel, in order to ensure that the Ti carbonitride is fully solid-solved, the heating temperature is selected to be above 1230℃, and the holding time is 2-4h, wherein the soaking holding time is not less than 40min. In addition, the billet can be hot-charged into the furnace after casting is completed, that is, after confirming that the surface of the billet has no quality problems, the billet is directly transported from the casting area to the heating furnace for heating and holding, so that the energy consumption can be reduced.

[0059] Rolling adopts hot continuous rolling, the end temperature of the billet rough rolling is not less than 1000℃, the cumulative reduction rate in the rough rolling stage is ≥80%, ferrite rolling process is adopted in the finishing rolling stage, the finishing rolling starting temperature is controlled to be ≤950℃, and the finishing rolling end temperature is 820-880℃. In the application, more Cr and Al elements are added, both of which are ferrite forming elements, which reduces the low austenite stability and reduces the austenite supercooling degree, and improves the ferrite forming stability. Figure 1Look, ferrite starts to form at about 945℃ under continuous cooling conditions; to avoid sudden changes in rolling force caused by rolling in the two-phase region, the application requires ferrite rolling process in the finishing rolling stage. According to the requirement of ferrite formation temperature, the starting temperature of finishing rolling is controlled to be no higher than 950℃, which is too high to enter the ferrite and austenite two-phase region, resulting in rolling force fluctuation and poor plate shape, and increasing the equipment load and affecting the thickness control accuracy; it is too low to enter the pearlite phase transition region, and the strip deformation resistance increases, increasing the equipment load and energy consumption, which is not conducive to the plate shape and corrosion resistance, and damages the equipment. Therefore, the finishing rolling end temperature is controlled to be 820-880℃.

[0060] The application requires that the coiling temperature is controlled to be 520-580℃. From the phase diagram, the steel described in the application forms ferrite structure in a wide range; after the temperature decreases to 740℃, pearlite starts to form. With the decrease of temperature, whether the cooling speed is high or low, bainite phase transition will occur, forming a small amount of bainite structure. Therefore, the matrix structure of the steel in the application is mainly ferrite + pearlite, supplemented by a small amount of bainite structure. In order to obtain better strength and toughness, water cooling is required immediately after rolling to refine the structure as much as possible and form fine ferrite + pearlite structure. The pearlite in the matrix is high in C component, which is easy to form a primary cell in the matrix and promote the occurrence of corrosion. In order to improve the corrosion resistance of the steel, the formation of pearlite in the matrix should be minimized. From the CCT curve of the application, it is required to control the cooling speed after rolling to be higher than 10℃ / s to reduce the formation of pearlite during the cooling process; but at the same time, the coiling temperature should be controlled to be no higher than 600℃ to avoid the generation of pearlite in the subsequent slow cooling process of the coil, which is not conducive to the corrosion resistance. Figure 1

[0061] From the TTT temperature curve of the application, about 538℃ is the fastest temperature for bainite formation, so the coiling temperature is selected at this temperature to form more bainite in the matrix to obtain higher strength. If the coiling temperature is too high, it will enter the pearlite phase transition region, and if it is too low, it is not conducive to the formation of more bainite structure. The steel in the application does not need heat treatment after rolling, which shortens the production cycle and reduces the production cost. Figure 2

[0062] The application has the following advantages:

[0063] 1. The steel in the application has excellent corrosion resistance in a soil corrosion environment with high sulfate ion concentration of 300-30000mg / kg and chloride ion concentration of 1500-8000mg / kg, which ensures the corrosion resistance of the photovoltaic pile made of the steel in the soil, and its corrosion resistance in the same corrosion environment is more than 6 times that of plain carbon steel, and the relative corrosion rate is less than 16.5%; the atmospheric corrosion resistance also reaches the level of conventional weathering steel, and the relative corrosion rate of Q345B is less than 55%, thereby meeting the corrosion resistance requirements in various environments.

[0064] ​​2. The steel has excellent mechanical properties, the yield strength is greater than or equal to 345 MPa, the tensile strength is greater than or equal to 485 MPa, the elongation A is greater than or equal to 20%, and the low-temperature impact energy value at -40℃ is greater than or equal to 160J; meanwhile, the cold bending performance is excellent, and the cold bending requirement of D=2a, 180° is met.

[0065] 3. The steel does not contain Sb, and the harm to the environment and human health is avoided, and the steel belongs to an environmentally friendly product.

[0066] 4. The steel is produced by adopting a ferrite rolling process, and the rolling force fluctuation and the plate shape difference problems caused by rolling in a two-phase region are avoided. The bainite structure can be obtained at a cold speed of more than 10℃, and the ferrite+pearlite and a small amount of bainite matrix structure can be obtained by cooperating with a coiling temperature. The steel is delivered in a rolled state, the production process is simple, the production cycle is short, and the existing rolling equipment can be used to implement the steel. BRIEF DESCRIPTION OF DRAWINGS

[0067] Figure 1 CCT phase change temperature curve of the steel in the embodiment of the present application;

[0068] Figure 2 TTT phase change temperature curve of the steel in the embodiment of the present application. DETAILED DESCRIPTION

[0069] The present application will be further described below in combination with the embodiments and the drawings.

[0070] The composition of the steel in the embodiment of the present application is shown in Table 1, Table 2 shows the production process parameters of the steel in the embodiment of the present application, and Table 3 shows the performance parameters of the steel in the embodiment of the present application.

[0071] Among them, Comparative Example 1 is a "high corrosion resistance Cr-containing weathering steel with excellent toughness" disclosed in Chinese Patent Publication No. CN102127717A, Comparative Example 2 is a "railway vehicle atmospheric corrosion resistant hot-rolled steel plate and manufacturing method thereof" disclosed in Chinese Patent Publication No. CN102268613A, and Comparative Patent 3 is a "steel for neutral soil corrosion resistant buried structure and manufacturing method thereof" disclosed in Chinese Patent Publication No. CN109023071A.

[0072] From table 1 to table 3 can see, the steel grade of the application and the chemical composition of comparative patent 1 are obviously different, the steel grade of the application is obtained by using Cu-Cr-Al component system to have excellent corrosion resistance in the soil environment of 300-30000 mg / kg sulfate ion concentration, 1500-8000 mg / kg concentration chloride ion concentration. Comparative patent 1 is high Cr-Ni component design, wherein Cr content is 2.5-7.0%, Ni is 0.2-1.2%, which is much higher than the steel grade; and comparative patent 2 not only contains Sb, but also contains high P, and also needs to add Mg and Ce. The high P design is not conducive to low temperature toughness and forming performance, and the addition of Mg and Ce increases the production difficulty. Especially Sb is a typical toxic and harmful heavy metal element, which has chronic toxicity and potential carcinogenicity to human and animal bodies. Comparative patent 3 has high content of Cr and Mo in addition to Sb.

[0073] The application is produced by adopting hot continuous rolling process, and ferrite rolling process is adopted in the finishing rolling stage, only the cooling rate after rolling is required to be controlled above 10 ℃ / s in the layer cooling process, the process window is wider, the production difficulty is reduced, and the on-site production is facilitated. Comparative document 1 requires that the cooling rate after rolling is controlled to be 5-20 ℃ / s, and the range of cooling rate is definitely limited, which obviously increases the control difficulty of water cooling; comparative document 2 requires that after 880-950 ℃ finish rolling, 1-35 seconds air cooling is carried out, and then cooling is carried out to 550-690 ℃ at a cooling rate above 10 ℃ / s and coiling, the cooling process of air cooling after rolling and then water cooling obviously increases the production difficulty, especially the air cooling leads to the extension of production time, and affects the production rhythm.

[0074] The performance requirements of the steel of the application are different from those of the comparative examples, the yield strength of the steel grade of the application is above 345 MPa, the elongation is more than 20%, the impact energy value at-40 ℃ is above 160 J, and the steel has good corrosion resistance in the soil corrosion environment of 300-30000 mg / kg high sulfate ion concentration, 1500-8000 mg / kg concentration chloride ion concentration and industrial atmospheric environment.

[0075] The steel of the present application is compared with two common atmospheric corrosion resistant steels, wherein the comparative examples 1 and 2 are a high corrosion resistant weathering steel, and the comparative examples 3 and 4 are a 450 MPa grade conventional weathering steel. The prepared steel plate is mainly ferrite + pearlite structure. According to TB / T2375 "Railway Weathering Steel Periodic Immersion Corrosion Test Method", the relative corrosion rate of Q345B is less than 55%; in the simulated high sulfate + chloride ion corrosion environment, the immersion test is carried out according to GB 10124-1988 "Metal Material Laboratory Uniform Corrosion Immersion Test Method", the test solution is 10.0% H2SO4+3.5% NaCl, the test time is 24h, the test temperature is 23±2℃, the corrosion resistance reaches more than 6 times of plain carbon steel, and the relative corrosion rate is less than 16.5%; the atmospheric corrosion resistance also reaches the level of conventional weathering steel, and the relative corrosion rate of Q345B is less than 55%, thereby meeting the corrosion resistance requirements in various environments. Among the two comparative weathering steels, although the comparative examples 1 and 2 have far superior corrosion resistance to ordinary weathering steel in the atmospheric environment, but in the simulated high sulfate, chloride ion concentration soil environment, the relative corrosion rate is much higher than that of the present application, which shows that the corrosion resistance does not meet the requirements of the present application, and the low temperature impact toughness of the comparative examples 1 and 2 is poor; the comparative examples 3 and 4 have little improvement, and the corrosion resistance of the comparative example 3 is for nitrate and chloride, which is different from the present application.

[0076] In summary, the steel of the present application has high strength and high toughness, and also has good corrosion resistance in atmospheric and high sulfate ion, chloride ion concentration soil corrosion environments, and the corrosion resistance reaches more than 6 times of plain carbon steel in the soil environment with a high sulfate ion concentration of 300-30000 mg / kg and a chloride ion concentration of 1500-8000 mg / kg, and the relative corrosion rate is less than 16.5%; the atmospheric corrosion resistance also reaches the level of conventional weathering steel, and the relative corrosion rate of Q345B is less than 55%, thereby meeting the corrosion resistance requirements in various environments, especially meeting the corrosion requirements of photovoltaic pile foundation in western regions; it can also be applied to equipment with chloride ion and sulfate ion corrosion such as seawater and gas pipeline, and conventional steel structure manufacturing with industrial atmospheric corrosion resistance requirements.

[0077]

[0078]

[0079]

Claims

1. A hot-rolled corrosion-resistant steel for photovoltaic pile foundations, comprising the following composition by weight percentage: C: 0.03~0.12%, Si: 0.20~0.50%, Mn: 0.4~0.9%, P≤0.018%, S≤0.006%, Al: 0.2~0.8%, Cu: 0.10~0.50%, Cr: 0.3~1.2%, Ni≤0.20%, N≤0.006%, with the balance including Fe and other unavoidable impurity elements, and simultaneously satisfying the following: 1.0≤Cr / Al≤4.0 Cu + 1.22Cr + 35.3Al ≥ 9.2; The corrosion resistance of the steel plate in soil corrosion environments with high sulfate ion concentrations of 300~30000 mg / kg and chloride ion concentrations of 1500~8000 mg / kg is 16.5% lower than that of ordinary carbon steel Q345B; in industrial atmospheric environments, the corrosion rate of the steel plate is ≤55% relative to that of ordinary carbon steel Q345B; and the corrosion resistance of the steel plate is ≥345MPa, tensile strength ≥485MPa, elongation A ≥20%, and impact energy value at -40℃ ≥160J. The microstructure of the corrosion-resistant steel is ferrite + pearlite and a small amount of bainite.

2. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 1, characterized in that, The balance consists of Fe and other unavoidable impurity elements.

3. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 1 or 2, characterized in that, It also contains one or more of Ti: 0.01~0.06%, Nb: 0.01~0.03% and V: 0.01~0.04%.

4. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 1 or 2, characterized in that, It also contains one or both of Sn: 0.01~0.12% and RE: 0.01~0.12%.

5. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 3, characterized in that, It also contains one or both of Sn: 0.01~0.12% and RE: 0.01~0.12%.

6. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 1 or 2, characterized in that, The Mn content is 0.5~0.8%.

7. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 3, characterized in that, The Mn content is 0.5~0.8%.

8. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 4, characterized in that, The Mn content is 0.5~0.8%.

9. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 1 or 2, characterized in that, The Cu content is 0.15~0.35%.

10. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 3, characterized in that, The Cu content is 0.15~0.35%.

11. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 4, characterized in that, The Cu content is 0.15~0.35%.

12. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 5, characterized in that, The Cu content is 0.15~0.35%.

13. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 6, characterized in that, The Cu content is 0.15~0.35%.

14. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 7, characterized in that, The Cu content is 0.15~0.35%.

15. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 8, characterized in that, The Cu content is 0.15~0.35%.

16. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 1 or 2, characterized in that, The Cr content is 0.6~1.0%.

17. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 3, characterized in that, The Cr content is 0.6~1.0%.

18. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 4, characterized in that, The Cr content is 0.6~1.0%.

19. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 5, characterized in that, The Cr content is 0.6~1.0%.

20. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 6, characterized in that, The Cr content is 0.6~1.0%.

21. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 7, characterized in that, The Cr content is 0.6~1.0%.

22. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 8, characterized in that, The Cr content is 0.6~1.0%.

23. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 9, characterized in that, The Cr content is 0.6~1.0%.

24. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 10, characterized in that, The Cr content is 0.6~1.0%.

25. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 11, characterized in that, The Cr content is 0.6~1.0%.

26. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 12, characterized in that, The Cr content is 0.6~1.0%.

27. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 13, characterized in that, The Cr content is 0.6~1.0%.

28. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 14, characterized in that, The Cr content is 0.6~1.0%.

29. The hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in claim 15, characterized in that, The Cr content is 0.6~1.0%.

30. The method for manufacturing hot-rolled corrosion-resistant steel for photovoltaic pile foundations as described in any one of claims 1 to 29, characterized in that, Includes the following steps: 1) Smelting and casting The steel is smelted and cast into billets according to the stated composition; wherein the steelmaking process employs LF refining. 2) Heating of the billet The heating furnace is in a reducing atmosphere. The billet exit temperature is above 1230℃ and the holding time is 2~4 hours, of which the soaking holding time is not less than 40 minutes. 3) Rolling Hot continuous rolling is adopted. The roughing temperature of the billet is above 1000℃ and the cumulative reduction rate during the roughing stage is ≥80%. The finishing rolling adopts the ferritic rolling process. The starting temperature of the finishing rolling is ≤950℃, the finishing rolling temperature is 820~880℃, and then it is cooled, with the cooling rate controlled at ≥10℃ / s, and then coiled at the coiling temperature of 520~580℃.

Images