CN117947333A

CN117947333A - Corrosion-resistant steel for photovoltaic pile foundation and manufacturing method thereof

Info

Publication number: CN117947333A
Application number: CN202211334257.1A
Authority: CN
Inventors: 宋凤明; 温东辉; 周庆军; 陆敏; 李育霖; 华骏山; 徐嘉春
Original assignee: Baoshan Iron and Steel Co Ltd
Current assignee: Baoshan Iron and Steel Co Ltd
Priority date: 2022-10-28
Filing date: 2022-10-28
Publication date: 2024-04-30
Also published as: WO2024088378A1

Abstract

A corrosion-resistant steel for a photovoltaic pile foundation and a manufacturing method thereof are provided, wherein the corrosion-resistant steel comprises the following components in percentage by weight ：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％,, and the balance of Fe and unavoidable impurities, and Cr/Al is not less than 1.0 and not more than 4.0, and Cu+1.22Cr+35.3Al is not less than 9.2. The corrosion resistance of the corrosion-resistant steel plate in the soil corrosion environment with the high sulfate ion concentration of 300-30000 mg/kg and the chloride ion concentration of 1500-8000 mg/kg reaches more than 6 times of that of common steel, and the relative corrosion rate is lower than 16.5%; meanwhile, the corrosion rate of the relatively common carbon steel in the industrial atmospheric environment is less than or equal to 55 percent, so that the corrosion resistance requirement in various environments is met; in addition, the corrosion-resistant steel is delivered in a rolled state without heat treatment, does not contain Sb, and is more environment-friendly.

Description

Corrosion-resistant steel for photovoltaic pile foundation and manufacturing method thereof

Technical Field

The invention relates to the field of low alloy steel manufacturing, in particular to corrosion-resistant steel for a photovoltaic pile foundation and a manufacturing method thereof.

Background

Corrosion of steel is a common and serious problem. In the soil, there is also some corrosion to the steel structure due to the presence of microorganisms, water, oxygen and various minerals. Especially in the areas of China such as Xinjiang, ningxia, inner Mongolia and the like, the soil contains a large amount of sulfate and chloride ions because of the marine environment in ancient times, and the use safety of the steel structure is threatened.

To effectively prolong the service life of equipment and reduce the use cost, corrosion resistant steel is produced. On the basis of Corten steel in the United states, series of corrosion resistant steel products are developed according to the resource and use requirements in various countries, the strength and the performance of the corrosion resistant steel products are also developed from the early 235MPa level to the 450MPa level of high-strength weathering steel and the high corrosion resistant steel with better corrosion resistance, and a plurality of related steel patents are also generated.

The high-strength low-alloy hot-rolled ferrite bainite weathering steel and the production method thereof disclosed in China patent publication No. CN101660099B have the yield strength reaching 450MPa, adopt a design with higher Mn content, have the corrosion resistance of the conventional weathering steel level and do not relate to soil corrosion.

The steel plates disclosed in Chinese patent publication No. CN1986864, namely the high-strength low-alloy atmospheric corrosion resistant steel and the production method thereof, the weather resistant steel plate disclosed in Chinese patent publication No. CN102168229B, the manufacturing method thereof and the yield strength 700MPa grade atmospheric corrosion resistant hot rolled steel strip disclosed in Chinese patent publication No. CN107779740A, the manufacturing method and the like have higher strength of more than 450MPa, but the components adopt higher Mn, and the cost is higher through the composite addition of Mo, nb, V, ti and other reinforcing elements; the weather-proof level is equal to that of the traditional weather-proof steel, namely, the relative corrosion rate is less than or equal to 55 percent. But do not meet the soil erosion resistance requirements.

In order to meet the application requirements under more conditions, weathering steel is also being developed towards high corrosion resistance and high toughness in addition to high strength, and is required to have good workability and lower cost.

The steel types disclosed in Japanese patent No. JP10025550A "CORROSION RESISTANT STEEL", japanese patent No. JP2002363704 "CORROSION RESISTENT STEEL HAVING EXCELLENT TOUGHNESS IN BASE MATERIAL AND HEAT AFFECTED ZONE" and Chinese patent No. CN102127717A "high corrosion resistance Cr-containing weathering steel with excellent toughness", which are all of better corrosion resistance and lower relative corrosion rate, but do not relate to sulfate and chloride corrosion performance; the steel contains high Cr, al, ni and other elements, and has high steelmaking difficulty and high manufacturing cost.

In Xinjiang, the concentration of sulfate ions in soil is varied from 300 to 30000mg/kg, and the concentration of chloride ions also reaches 1500 to 8000 mg/kg. The corrosion is caused by a large amount of chloride ions and sulfate ions in the soil, and is obviously different from the use environment of the conventional weathering steel.

The "hot rolled steel sheet resistant to atmospheric corrosion for railway vehicles and a method for manufacturing the same" disclosed in chinese patent publication No. CN102268613a involves sulfate and chloride corrosion, and the steel contains 0.01 to 0.04% of P and requires addition of appropriate amounts of Ca, mg, ce and Sb. Wherein, the higher P is unfavorable for low-temperature toughness and forming performance, while the addition of Mg and Ce increases the production difficulty, and the addition of Sb is unfavorable for human body and environment.

"A neutral soil corrosion resistant steel for buried structure and method for manufacturing the same", disclosed in chinese patent publication No. CN109023071a, contains 0.08 to 0.18% Sb in addition to higher 2.0 to 3.5% cr, 0.2 to 0.4% ni and 0.3 to 0.5% mo. The combination of Sb and Cu can form a Cu2Sb protective film on the surface, so that the dew point corrosion performance of sulfuric acid is improved. But the addition of Sb is clearly detrimental to the environment and the human body. Sb is a typical toxic and harmful heavy metal element, and has chronic toxicity and potential carcinogenicity to human and animal bodies. With the improvement of environmental protection consciousness and the tightening of environmental protection policies in the whole society, the production and application of Sb-containing steel are necessarily more limited.

As can be found from comparison with the prior patent, the corrosion resistance of the current weathering steel, whether the weathering steel is of a conventional level or a high corrosion resistance, is mainly aimed at the atmospheric corrosion environment, and is not suitable for the high sulfate radical and high chloride ion corrosion environment in Xinjiang; the existing weathering steel capable of improving the corrosive environment of the soil medium is added with Sb, and Sb is unfavorable to the environment and human health.

Disclosure of Invention

The invention aims to provide corrosion-resistant steel for a photovoltaic pile foundation and a manufacturing method thereof, wherein the corrosion resistance of a steel plate in a soil corrosion environment with high sulfate ion concentration of 300-30000 mg/kg and chloride ion concentration of 1500-8000 mg/kg is more than 6 times that of common steel, and the relative corrosion rate is lower than 16.5%; meanwhile, the corrosion rate of the carbon steel is less than or equal to 55% relative to common carbon steel in an industrial atmospheric environment, so that the corrosion resistance requirement in various environments is met; the steel plate is produced in a controlled rolling and cooling mode, so that the steel plate has a wider process window and a simple production method; the rolled goods delivery does not need heat treatment, the production period is short, and the steel cost is low; the yield strength of the steel meets the high-strength requirement of 345MPa or more, the tensile strength is not less than 485MPa, the elongation A is not less than 20%, the low-temperature impact power value at minus 40 ℃ is not less than 160J, and the steel also has good processability such as welding, cold bending and the like, has excellent elongation, and is particularly suitable for various cold forming processes in the pile foundation production process; meanwhile, the method can be applied to other high-concentration sulfate ions and chloride ion corrosion environments such as seawater, gas pipelines and the like; in addition, the corrosion-resistant steel for the photovoltaic pile foundation does not contain Sb and is more environment-friendly.

In order to achieve the above purpose, the technical scheme of the invention is as follows:

The invention obtains high strength and good low temperature toughness by selecting and adding proper amount of V, ti and Nb precipitation strengthening on the basis of lower C-Si-Mn, and adopts Cu-Cr-Al component design to realize good corrosion resistance under the soil corrosion environment with concentration of sulfate ions of 300-30000 mg/kg and chloride ions of 1500-8000 mg/kg, thereby realizing the combination of corrosion resistance, high strength and high toughness on the basis of low cost.

Specifically, the hot-rolled corrosion-resistant steel for the light Fu Zhuangji comprises the following components in percentage by weight ： 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％,, and the balance of Fe and other unavoidable impurity elements, and simultaneously satisfies the following requirements:

1.0≤Cr/Al≤4.0，

Cu+1.22Cr+35.3Al≥9.2。

Further, the balance is Fe and other unavoidable impurity elements.

Still further, it further comprises Ti:0.01 to 0.06 percent of Nb:0.01 to 0.03 percent and V:0.01 to 0.04% of one or more of the following components.

Further, sn:0.01 to 0.12 percent of RE:0.01 to 0.12 percent of one or two of the following components.

Preferably, the Mn content is 0.5 to 0.8%.

Preferably, the Cu content is 0.15-0.35%.

Preferably, the Cr content is 0.6 to 1.0%.

The microstructure of the corrosion-resistant steel is ferrite, pearlite and a small amount of bainite.

The yield strength of the corrosion-resistant steel is more than or equal to 345MPa, the tensile strength is more than or equal to 485MPa, the elongation A is more than or equal to 20 percent, and the impact energy value at minus 40 ℃ is more than or equal to 160J.

The invention relates to a corrosion-resistant steel plate for a photovoltaic pile foundation, which comprises the following chemical components in design:

C is an effective strengthening element in the steel, is dissolved into a matrix to have solid solution strengthening effect, exists in the form of carbide in the steel, and combines with alloy elements to play roles of precipitation strengthening and grain refinement, so that the addition amount is not less than 0.03%; and excessive C forms more carbide in the steel to play a role of a primary cell, promotes corrosion to reduce corrosion resistance of the steel, and is unfavorable for welding, so that the content of C is limited to be not higher than 0.12%.

Since Si is an element added for deoxidizing steel and is also a corrosion resistant element and has a solid solution strengthening effect, the lower limit of the content is controlled to 0.20%, and a higher Si content results in deterioration of weldability and toughness of a weld heat affected zone, and the upper limit thereof is set to 0.50%.

Mn is an important strengthening element, plays a role of solid solution strengthening, improves the strength and toughness of steel, enlarges austenite element, can reduce supercooled austenite transformation temperature, promotes transformation of medium-low temperature strengthening structure in steel, and is beneficial to improving the strength of steel. However, too much Mn increases hardenability, resulting in deterioration of weldability and toughness of a weld heat affected zone, while higher Mn also increases costs. The Mn content range specified in the present invention is therefore limited to 0.4 to 0.9%, preferably 0.5 to 0.8%.

P is a main corrosion resistant element in the traditional atmospheric corrosion resistant steel, can promote the formation of a surface protective rust layer, and effectively improves the atmospheric corrosion resistant performance of the steel, but meanwhile, P is easy to generate segregation at a grain boundary, so that the grain boundary bonding energy and the toughness and the plasticity of the steel are reduced; and the coexistence of P and Mn can aggravate the tempering brittleness of the steel, and the segregation of P can easily cause the steel plate to break along crystals, so that the impact toughness of the steel plate is reduced. And P is detrimental to welding performance. The steel of the invention requires high toughness, so P is controlled as an impurity element, and the content of P in the steel is reduced as much as possible. But the limited P content is too low and increases the steelmaking difficulty and the manufacturing cost, so the limited P content is not more than 0.018 percent.

S in steel is controlled as a detrimental impurity element. S not only reduces the low-temperature toughness of the steel, but also promotes the anisotropy of the steel plate, is unfavorable for cold forming performance, and sulfide inclusion can obviously reduce the weather resistance of the steel. Therefore, the steel grade design of the invention adopts extremely low S content, and is controlled below 0.006 percent.

Al is usually added into steel as deoxidizer in the steelmaking process, and trace Al is beneficial to grain refinement and improves the toughness of the steel. The corrosion potential of the steel is improved by adding proper Al, which is beneficial to inhibiting corrosion; meanwhile, the formation and aggregation of the nano-scale complex oxide containing Al and Si in the inner rust layer can increase the charge transfer resistance, so that the corrosion process is inhibited. However, al reduces the stability of austenite and the supercooling degree of austenite, so that new-phase crystal nuclei grow up rapidly, the hardenability is reduced, and the critical quenching speed is improved; meanwhile, al is used as a ferrite forming element, and more Al reduces the strength of the steel plate on one hand and increases the brittleness of ferrite in the steel to reduce the toughness of the steel. The present invention is therefore limited to Al contents of 0.2 to 0.8%.

Cr is a noble alloy element and is also an effective element for improving the corrosion resistance of the steel plate. Cr forms a continuous solid solution with Fe in steel, has a solid solution strengthening effect, and forms various types of carbides such as M ₃C、M₇C₃ and M ₂₃C₆ with C, etc., resulting in a secondary strengthening effect. Cr has remarkable effect of improving the passivation capability of steel, can promote the formation of a compact passivation film or protective rust layer on the surface of the steel, and can effectively improve the selective permeability characteristic of the rust layer to corrosive media due to the enrichment of the Cr in the rust layer; meanwhile, the addition of Cr can effectively improve the self-corrosion potential of the steel and improve the atmospheric corrosion resistance of the steel. But the addition of more Cr will increase the manufacturing cost. Therefore, the present invention is limited to Cr content of 0.30 to 1.2% in view of cost reduction, preferably Cr:0.6 to 1.0 percent.

Cu mainly plays a solid solution and precipitation strengthening role in steel, and meanwhile, the electrochemical potential of Cu is higher than that of Fe, so that the formation of a compact rust layer on the surface of the steel can be promoted, the improvement of corrosion resistance is facilitated, meanwhile, a proper amount of Cu is combined with residual S in the steel to form a Cu ₂ S protective film, and the corrosion under the high sulfate radical corrosion environment is relieved. However, too high Cu not only deteriorates toughness of a weld heat affected zone, but also is susceptible to occurrence of net cracking during hot rolling, deteriorating surface properties of the steel sheet, and increasing costs. The Cu content of the present invention is limited to 0.10 to 0.50%, preferably Cu:0.15 to 0.35 percent.

Ni is an enlarged austenite forming element. Ni improves low-temperature impact toughness by refining grains and reducing stacking fault energy; meanwhile, the grain refinement also has the fine grain strengthening effect. In addition, ni is also an important element for improving the corrosion resistance of steel, and can promote the stability of rust layers and improve the problem of hot working brittleness caused by Cu. However, ni is a noble element, and it is recommended to selectively add Ni and control the content to be less than 0.2%.

N can form nitrides with Al and Ti in steel, and fine precipitates have a role of pinning grain boundaries to refine austenite grains. Higher N combines with Al in the steel to easily form AlN, thereby significantly increasing the amount of nitride in the steel. When AlN is independently present in steel as a nonmetallic inclusion, the continuity of a steel matrix is damaged, especially when the AlN is formed in a large quantity and in aggregation distribution when the Al content is high, the AlN is more harmful, and meanwhile, oxide with poor plasticity is formed; and the higher N is easy to concentrate at the defect, and the low-temperature impact toughness is deteriorated. The N content must be controlled below 0.0060%.

In addition to the above elements, one or more of Nb, V, ti, sn, and RE may be further optionally added to the steel grade in order to further improve the properties. Wherein:

Ti is a strong ferrite forming element and a carbonitride forming element, and is easily combined with C, N, O, S or the like. Ti exists mainly in the form of TiC or Ti (C, N) in steel. In the invention, ti is added mainly by utilizing TiN to inhibit the growth of austenite grains, thereby playing a role in refining the structure; and simultaneously, precipitation strengthening effect is generated in the cooling process. In addition, ti has the functions of preventing the deformed austenite from recrystallization and promoting the formation of granular bainite, and the precipitated carbonitride particles of Ti can prevent coarsening of grains in a weld heat affected zone and improve welding performance. When the Ti content is too high, titanium nitride particles are easy to grow up and agglomerate at high temperature, and the plasticity and toughness of the steel are damaged. Therefore, the Ti content is limited to 0.01 to 0.06%, and the addition is selected.

Nb is a strong nitrogen carbide forming element, and can combine with carbon and nitrogen in steel to form intermediate phases such as NbC, nb (CN), nbN and the like in the cooling process after rolling, and the formed fine carbide particles can refine the structure, generate fine grain strengthening and precipitation strengthening effects, and remarkably improve the strength of the steel plate. Meanwhile, 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 an austenite interface, raise the recrystallization temperature of steel, and realize rolling in a non-recrystallization zone at a higher temperature. Therefore, adding an appropriate amount of Nb to the steel is advantageous in improving the strength, and when the Nb content is high, coarse carbonitride particles are formed at grain boundaries, deteriorating the impact toughness. Nb is a noble alloy element, the limiting content is 0.01-0.03%, and the Nb is selectively added.

V is a strong carbon-nitrogen compound forming element, can be precipitated in the phase transformation process, has solid solution strengthening and carbon nitride precipitation strengthening effects in steel, and increases tempering stability, thereby improving strength, and limiting the content thereof to 0.01-0.04%.

Sn has a good corrosion inhibition effect in steel, and Sn ions can be dissolved in an anode to inhibit anode reaction, so that the formation of beta-FeOOH with unfavorable corrosion resistance is reduced, and the Sn content is limited to be less than or equal to 0.12 percent.

RE forms RE compound, RE/Fe intermetallic compound, solid solution RE, etc. in steel, and is hydrolyzed in the corrosive thin liquid film and deposited in cathode with relatively high pH value to inhibit corrosion and limit RE content less than or equal to 0.12%.

The invention relates to hot-rolled corrosion-resistant steel for a photovoltaic pile foundation, which has good corrosion resistance under the soil environment containing sulfate ions with the concentration of 300-30000 mg/kg and chloride ions with the concentration of 1500-8000 mg/kg, and has the atmospheric corrosion resistance equivalent to that of conventional weathering steel. The steel plate has good forming performance and low-temperature impact toughness, meets the use and processing requirements of steel for photovoltaic pile foundations, and is also suitable for seawater environments with high chloride ion content, gas pipelines with high sulfate ion content and the like.

The main innovation point of the invention is that the Cu-Cr-Al component system design is adopted, and the remarkable improvement of the corrosion resistance under the high sulfate radical and high chloride ion soil corrosion environment is realized through the synergistic effect of various corrosion resistant elements.

Cu is an effective element for improving sulfate ion corrosion; cr is a common corrosion resistant element, and the addition of Cr not only enhances solid solution strengthening and improves hardenability, but also improves corrosion potential. However, the pure addition of Cu and Cr does not realize the improvement of corrosion resistance in the soil corrosion environment with high sulfate ion and chloride ion concentration. Researches show that the corrosion potential is improved by about 40 milliamperes by adding about 1% of Cr into the steel, and corrosion evaluation shows that obvious galvanic corrosion cannot be caused when the potential difference is lower than 70 milliamperes, so that the corrosion potential difference of 40 milliamperes cannot obviously change the corrosion current, the corrosion tendency is changed, and the corrosion resistance is not greatly improved; cu is an essential element in the current acid-resistant steel, but about 0.1% of Sb is also added at the same time, so that expected corrosion resistance is expected to be obtained. The invention abandons the addition of Sb from the environmental and human health consideration, so that the pure dependence on Cr and Cu cannot obtain excellent corrosion resistance under the high-concentration sulfate ion and chloride ion soil environment.

Al itself is relatively reactive and reacts readily with oxygen in the air. Has passivation effect in natural environment, and can form a layer of Al ₂O₃ film on the surface layer, thereby having corrosion resistance. Al is usually added as a deoxidizing element in the steel. Although a certain amount of Al is added to the steel 10CrMoAl, the mechanism for improving the corrosion performance in the seawater environment is not mentioned. According to the research of the invention, cr and Al have a synergistic effect in steel, and the corrosion resistance of the steel in the environment of high-concentration sulfate radical and chloride ions can be obviously improved. The mechanism is as follows: on one hand, the corrosion potential of the steel is obviously improved by the matched addition of Cr and Al, the improvement range is about 200 milliamperes, and the corrosion potential of the steel is only improved by 40 milliamperes by 1% of Cr; on the other hand, cr and Al form intermetallic compounds Fe ₂ CrAl and Cr ₈Al₅ in the steel. Under the environment of high sulfate radical and chloride ion, the two compounds gather on the surface of the steel, so that the corrosion resistance of the steel is improved. The corrosion current is reduced by the improvement of the corrosion potential, and the occurrence of corrosion is reduced; the Cr and Al intermetallic compounds protect the surface layer and prevent corrosion from going deep, thereby playing an isolated role. It is under this synergistic effect of Cr and Al that the corrosion resistance under the environment of high sulfate radical and chloride ion is obtained. Therefore, cu and Cr must be matched with proper amount of Al so as to obtain excellent corrosion resistance under the soil corrosion environment with high sulfate ion concentration of 300-30000 mg/kg and chloride ion concentration of 1500-8000 mg/kg.

The present invention therefore limits the amounts of Cu, cr and Al added and requires that the contents satisfy the relationship: cr/Al is more than or equal to 1.0 and less than or equal to 4.0, cu+1.22Cr+35.3Al is more than or equal to 9.2, so that the corrosion resistance in the environment is more than 6 times that of ordinary carbon steel, and the relative corrosion rate is lower than 16.5%; and the corrosion resistance of the steel is equal to that of the conventional weathering steel, and the corrosion rate of the steel is less than or equal to 55 percent relative to that of common carbon steel, so that the corrosion resistance requirement in various environments is met. The novel corrosion-resistant component system avoids toxic pollution of Sb in the conventional sulfate ion corrosion-resistant steel to the environment and human bodies, and simultaneously greatly improves the corrosion resistance, thereby belonging to an environment-friendly product.

The invention obtains the yield strength of more than 345MPa by utilizing the solid solution strengthening of C, mn and the precipitation strengthening and fine grain strengthening effects of V, nb, ti and the like, has good low-temperature impact toughness, has a low-temperature impact work value of more than 160J at-40 ℃, has an elongation rate of more than 20%, realizes the matching of high corrosion resistance and high toughness, has good forming performance, and meets the applicable requirements of pile foundation steel.

The invention relates to a manufacturing method of high-strength corrosion-resistant steel for a photovoltaic pile foundation, which comprises the following steps:

1) Smelting and casting

Smelting and casting into blanks according to the components; wherein LF refining is adopted for steelmaking;

2) Heating of cast blanks

The heating furnace is in a reducing atmosphere, the casting blank discharging temperature is above 1230 ℃, and the heat preservation time is 2-4 hours, wherein the soaking heat preservation time is not less than 40min;

3) Rolling

Hot continuous rolling is adopted, the rough rolling finishing temperature of the billet is more than 1000 ℃, and the accumulated rolling reduction rate in the rough rolling stage is more than or equal to 80 percent; the finish rolling adopts a ferrite rolling process, the initial rolling temperature of the finish rolling is less than or equal to 950 ℃, the final rolling temperature is 820-880 ℃, then the finish rolling is cooled, the cooling speed is controlled to be more than or equal to 10 ℃/s, and the finish rolling is carried out until the coiling temperature is 520-580 ℃.

The method for manufacturing the high-strength corrosion-resistant steel for the photovoltaic pile foundation comprises the following steps:

LF refining is adopted in steelmaking, RH links are reduced, and cost is further reduced.

Heating a casting blank: the heating furnace is required to be in a reducing atmosphere, and the tapping temperature of the casting blank is controlled to be more than 1230 ℃. Considering that a trace amount of Ti is added into the steel, the heating temperature is selected to be more than 1230 ℃ for 2-4 hours in order to ensure that the carbonitride of Ti is fully dissolved, wherein the soaking and heat preserving time is not less than 40 minutes. In addition, the casting blank can be hot charged into the furnace after casting, namely, the casting blank is directly conveyed to the heating furnace from the casting area through the roller way for heating and heat preservation after no quality problem on the surface of the casting blank is confirmed, so that the energy consumption can be reduced.

The rolling adopts hot continuous rolling, the steel grade of the invention is required that the finishing temperature of rough rolling is not lower than 1000 ℃, the accumulated rolling reduction rate in the rough rolling stage is not less than 80%, the ferrite rolling process is adopted in the finish rolling stage, the starting temperature of finish rolling is not more than 950 ℃, and the finishing temperature of finish rolling is 820-880 ℃. In the invention, more Cr and Al elements are added, and the two elements are ferrite forming elements, so that the low austenite stability is reduced, the supercooling degree of austenite is reduced, and the ferrite forming stability is improved. As seen in fig. 1, the ferrite formation start temperature under continuous cooling conditions is about 945 ℃; in order to avoid abrupt changes in rolling force caused by two-phase zone rolling, the present invention requires the use of a ferrite rolling process in the finish rolling stage. Controlling the finish rolling starting temperature to be not higher than 950 ℃ according to the ferrite forming temperature requirement, and entering a ferrite and austenite two-phase region if the finishing rolling starting temperature is too high, so that rolling force fluctuation and plate shape variation are caused, equipment load is increased, and thickness control precision is affected; if the temperature is too low, the steel enters a pearlite phase transformation area, meanwhile, the deformation resistance of the steel strip is improved, the load and the energy consumption of the equipment are increased, the plate shape and the corrosion resistance are unfavorable, and the equipment is damaged. Therefore, the finishing temperature is controlled to be 820 to 880 ℃.

The invention requires controlling the coiling temperature to be 520-580 ℃. From the phase diagram, the steel grade forms ferrite structure in a large range; pearlite begins to form after the temperature is reduced to 740 ℃. As the temperature decreases, no matter how fast the cooling speed is, the bainite phase change can occur, and a small amount of bainite structure is formed. Therefore, the matrix structure of the steel of the invention is mainly ferrite and pearlite, and a small amount of bainite structure is added. To obtain better toughness, water cooling is required immediately after rolling to refine the structure as much as possible, forming a fine ferrite + pearlite structure. Pearlite in the matrix is a high C component, so that a primary cell is easily formed in the matrix, and corrosion is promoted. To improve the corrosion resistance of the steel, the formation of pearlite in the matrix should be minimized. From the CCT curve of fig. 1, it is required to control the cooling rate after rolling by 10 ℃/s or more to reduce the formation of pearlite during cooling; but at the same time, the coiling temperature is required to be controlled not to exceed 600 ℃ so as to avoid pearlite generation in the subsequent slow cooling process of the steel coil, and the corrosion resistance is not good.

From the TTT temperature profile of fig. 2, 538 ℃ is the temperature at which bainite is formed most rapidly, and coiling is selected at this temperature in order to allow as much bainite as possible to be formed in the matrix for higher strength. Too high a coiling temperature will enter the pearlite transformation zone and too low a coiling temperature will be detrimental to the formation of more bainite structure. The steel grade of the invention does not need post-rolling heat treatment, shortens the production period and reduces the production cost.

The invention has the following advantages:

1. The steel has excellent corrosion resistance under the soil corrosion environment with high sulfate ion concentration of 300-30000 mg/kg and chloride ion concentration of 1500-8000 mg/kg, so that the corrosion resistance of the photovoltaic pile foundation manufactured by the steel in the soil is guaranteed to be more than 6 times of that of common carbon steel under the same corrosion environment, and the relative corrosion rate is lower than 16.5%; the atmospheric corrosion resistance also reaches the level of the conventional weathering steel, and the corrosion rate relative to Q345B is lower than 55 percent, thereby meeting the corrosion resistance requirements in various environments.

2. The steel has excellent mechanical properties, the yield strength is more than or equal to 345MPa, the tensile strength is more than or equal to 485MPa, the elongation A is more than or equal to 20 percent, and the low-temperature impact power value at minus 40 ℃ is more than or equal to 160J; meanwhile, the cold bending performance is excellent, and the cold bending requirements of D=2a and 180 degrees are met.

3. The steel does not contain Sb, avoids the harm to the environment and human health, and belongs to an environment-friendly product.

4. The steel is produced by adopting a ferrite rolling process, and the problems of fluctuation of rolling force and poor plate shape of two-phase zone rolling are avoided. The steel strip can obtain bainite structure at cooling rate above 10deg.C, and can obtain ferrite, pearlite and matrix structure of small amount of bainite by matching with coiling temperature. The steel rolling state delivery method has the advantages of simple production process and short production period, and can be implemented by using the existing steel rolling equipment.

Drawings

FIG. 1 is a graph showing the CCT transformation temperature of the steel according to the example of the present invention;

FIG. 2 is a TTT transformation temperature curve of the steel according to the embodiment of the present invention.

Detailed Description

The invention is further described below with reference to examples and figures.

The components of the steel according to the embodiment of the present invention are shown in table 1, table 2 is the production process parameters of the steel according to the embodiment of the present invention, and table 3 is the performance parameters of the steel according to the embodiment of the present invention.

Among them, comparative example 1 is "excellent-toughness high-corrosion-resistance Cr-containing weathering steel" disclosed in chinese patent publication No. CN102127717a, comparative example 2 is "an atmospheric corrosion-resistant hot-rolled steel sheet for railway vehicles and a method for producing the same" disclosed in chinese patent publication No. CN102268613a, and comparative patent 3 is "a neutral soil corrosion-resistant buried structure steel and a method for producing the same" disclosed in chinese patent publication No. CN109023071 a.

As can be seen from tables 1 to 3, the steel grade of the present invention is significantly different from the chemical composition of comparative patent 1, and the steel grade of the present invention is excellent in corrosion resistance under the soil environment of 300 to 30000mg/kg sulfate ion concentration and 1500 to 8000mg/kg chloride ion concentration by adopting a Cu-Cr-Al composition system. The comparative patent 1 is designed for high Cr-Ni component, wherein the Cr content is 2.5-7.0% and the Ni content is 0.2-1.2% which are far higher than the steel grade; and the comparative patent 2 contains not only Sb but also higher P, and also needs to add Mg and Ce at the same time. Wherein, the higher P design is unfavorable for low-temperature toughness and forming performance, and the addition of Mg and Ce increases the production difficulty. Especially, sb belongs to a typical poisonous and harmful heavy metal element, and has chronic toxicity and potential carcinogenicity to human bodies and animal bodies. The contents of Cr and Mo are also high in addition to Sb in comparative patent 3.

The hot continuous rolling process is adopted for production, the ferrite rolling process is adopted in the finish rolling stage, and the cooling speed is only required to be controlled to be more than 10 ℃/s in the post-rolling layer cooling process, so that the process window is wider, the production difficulty is reduced, and the on-site production is convenient. The comparison document 1 requires to control the cooling speed after rolling to be 5-20 ℃/s, and the cooling speed range is definitely limited, which obviously increases the difficulty of controlling water cooling; the comparison document 2 requires air cooling at 880-950 ℃ for 1-35 seconds after finishing rolling, cooling to 550-690 ℃ at a cooling speed of more than 10 ℃/s and coiling, and the cooling process of air cooling and water cooling after rolling obviously increases the production difficulty, particularly the production time is prolonged due to air cooling, and the production rhythm is influenced.

The steel has the characteristics that the performance requirement is different from that of a comparative example, the steel has the yield strength of more than 345MPa, the elongation rate of more than 20 percent, the impact power value of more than 160J at minus 40 ℃, and good corrosion resistance under the soil corrosion environment and the industrial atmospheric environment under the high sulfate ion concentration of 300-30000 mg/kg and the chloride ion concentration of 1500-8000 mg/kg.

The steel of the invention is compared with two common atmospheric corrosion resistant steels at present, wherein, comparative examples 1 and 2 are high corrosion resistant weathering resistant steels, and comparative examples 3 and 4 are 450MPa grade conventional weathering resistant steels. The prepared steel plate is mainly composed of ferrite and pearlite. According to the detection of the TB/T2375 'periodic infiltration corrosion test method of weather-resistant steel for railways', the relative Q345B corrosion rate is lower than 55%; under the simulated high sulfate radical and chloride ion corrosion environment, the full immersion test is carried out according to GB 10124-1988 'a metal material laboratory uniform corrosion full immersion test method', the test solution is 10.0% H ₂SO₄ +3.5% NaCl, the test time is 24 hours, the test temperature is 23+/-2 ℃, the corrosion resistance is more than 6 times of that of plain carbon steel, and the relative corrosion rate is lower than 16.5%; the atmospheric corrosion resistance also reaches the level of the conventional weathering steel, and the corrosion rate relative to Q345B is lower than 55 percent, thereby meeting the corrosion resistance requirements in various environments. In the two types of weathering steel compared, although the comparative examples 1 and 2 have corrosion resistance far exceeding that of the common weathering steel in the atmospheric environment, the relative corrosion rate is far higher than that of the present invention in the soil environment simulating high sulfate radical and chloride ion concentration, which indicates that the corrosion resistance can not meet the requirement of the present invention, and the low temperature impact toughness of the comparative examples 1 and 2 is poor; the corrosion resistance of comparative example 3 was different from that of the present invention with respect to nitrate and chloride ions, with little improvement in comparative examples 3 and 4.

In conclusion, the steel has high strength and toughness, good corrosion resistance performance in the environment of atmospheric corrosion and soil with high sulfate ion concentration and chloride ion concentration, the corrosion resistance performance in the environment of 300-30000 mg/kg high sulfate ion concentration and 1500-8000 mg/kg chloride ion soil reaches more than 6 times that of common carbon steel, and the relative corrosion rate is lower than 16.5%; the atmospheric corrosion resistance also reaches the level of the conventional weathering steel, and the corrosion rate relative to Q345B is lower than 55%, so that the corrosion resistance requirement under various environments is met, and particularly the corrosion requirement of the photovoltaic pile foundation in the western region is met; the method can also be applied to equipment with corrosion of chloride ions and sulfate ions such as seawater and gas pipelines and the like and conventional steel structure manufacturing requiring industrial atmospheric corrosion performance.

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Claims

1. The hot-rolled corrosion-resistant steel for the photovoltaic pile foundation comprises the following components in percentage by weight ：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％, and the balance of Fe and other unavoidable impurity elements, and simultaneously meets the following requirements:

1.0≤Cr/Al≤4.0，

Cu+1.22Cr+35.3Al≥9.2。

2. the high-strength corrosion-resistant steel for a photovoltaic pile foundation according to claim 1, wherein the balance is Fe and other unavoidable impurity elements.

3. The high strength corrosion resistant steel for photovoltaic pile foundation according to claim 1 or 2, further comprising Ti:0.01 to 0.06 percent of Nb:0.01 to 0.03 percent and V:0.01 to 0.04% of one or more of the following components.

4. A high strength corrosion resistant steel for a photovoltaic pile foundation according to claim 1, 2 or 3, further comprising Sn:0.01 to 0.12 percent of RE:0.01 to 0.12 percent of one or two of the following components.

5. The high strength corrosion resistant steel for a photovoltaic pile foundation according to any one of claims 1 to 4, wherein the Mn content is 0.5 to 0.8%.

6. The high-strength corrosion-resistant steel for a photovoltaic pile foundation according to any one of claims 1 to 5, wherein the Cu content is 0.15 to 0.35%.

7. The high-strength corrosion-resistant steel for a photovoltaic pile foundation according to any one of claims 1 to 6, wherein the Cr content is 0.6 to 1.0%.

8. The high strength corrosion resistant steel for a photovoltaic pile foundation according to any one of claims 1 to 7, wherein the microstructure of the corrosion resistant steel is ferrite + pearlite and a small amount of bainite.

9. The high-strength corrosion-resistant steel for a photovoltaic pile foundation according to any one of claims 1 to 8, wherein the corrosion resistance of the steel sheet in a soil corrosion environment with a high sulfate ion concentration of 300to 30000mg/kg and a chloride ion concentration of 1500 to 8000mg/kg is 6 times that of ordinary steel, and the relative corrosion rate is lower than 16.5%; the corrosion rate of the carbon steel is less than or equal to 55 percent relative to common carbon steel in the industrial atmospheric environment; moreover, the yield strength of the corrosion-resistant steel is more than or equal to 345MPa, the tensile strength is more than or equal to 485MPa, the elongation A is more than or equal to 20 percent, and the impact energy value at minus 40 ℃ is more than or equal to 160J.

10. A method of producing a high strength corrosion resistant steel for a photovoltaic pile foundation according to any one of claims 1 to 9, comprising the steps of:

1) Smelting and casting

Smelting and casting into billets from the composition according to any one of claims 1 to 7; wherein LF refining is adopted for steelmaking;

2) Heating of cast blanks

3) Rolling