Acid-resistant and weather-resistant steel plate with tensile strength of 550MPa and preparation method and application thereof

Abstract

The invention provides an acid-resistant and weather-resistant steel plate with tensile strength of 550MPa as well as a preparation method and application of the acid-resistant and weather-resistant steel plate. The steel plate comprises the following chemical elements in percentage by weight: 0.03 to 0.12 percent of carbon, 0.15 to 0.30 percent of silicon, 0.3 to 0.45 percent of manganese, 0.02 to 0.035 percent of sulfur, 0.01 to 0.02 percent of phosphorus, 0.01 to 0.035 percent of titanium, 0.70 to 1.20 percent of chromium, 0.6 to 1.0 percent of nickel, 0.6 to 1.0 percent of copper, 0.5 to 0.8 percent of molybdenum, 0.02 to 0.05 percent of acid-soluble aluminum, 0.3 to 0.5 percent of antimony and the balance of Fe. According to the prepared steel plate, Rel is 420-450 MPa, Rm is 550-620 MPa, Rel / Rm is small, A (%) is larger than 25%, and KV2 type impact energy at the temperature of-40 DEG C is larger than 100 J. The corrosion inhibitor is soaked in a mixed solution of 50% concentrated sulfuric acid and 3.5% NaCl at a constant dew point temperature of 70 DEG C for 24 hours, and the average corrosion rate is 0.012 mg / (m < 2 >. H).

Description

Technical Field

[0001] The invention belongs to the technical field of steel production, and particularly relates to an acid-resistant and weather-resistant steel plate with a tensile strength of 550MPa, and a preparation method and application thereof. Background Art

[0002] Flue gas discharged from the production of chemical raw materials, such as boiler flue gas using high-sulfur oil or coal as fuel, flue gas from nonferrous metal smelting, etc., contains high levels of S, HCl, and HF. The steam in the flue gas will condense during the cooling process, which will cause severe dew point corrosion of sulfuric acid, hydrochloric acid, and hydrofluoric acid to equipment made of super stainless steel materials such as 316L, 2250, and 2507, such as economizers. Therefore, it is imperative to develop an acid-resistant and weather-resistant steel.

[0003] In the prior art, in order to cope with special application environments and improve the acid and weather resistance of steel, the commonly used methods are: ① coating anti-corrosion coatings, such as a corrosion-resistant large-diameter steel pipe with publication number CN117867360A, which not only has excellent adhesion, but also has excellent corrosion resistance and hydrophobic properties; ② electroplating to form an anti-corrosion layer, such as an acid-resistant and high-temperature-resistant high-nickel alloy steel rod for valves with publication number CN117512728A, in which a nickel metal coating is prepared by pulse electroplating during the preparation process. The presence of the nickel-based metal layer ensures that the alloy has good coating quality and corrosion resistance; ③ improving the corrosion resistance of steel by adding corrosion-resistant elements, such as an acid-resistant martensitic wear-resistant steel plate with publication number CN111575581A, which adds relatively high corrosion-resistant elements Cr, Ni, Sb, and Cu, which can ensure the corrosion resistance of the steel plate on the one hand, and its The acid corrosion resistance index I can reach above 7.0; on the other hand, a higher Cr content can ensure a higher hardness at a relatively low C content. Through the composite addition of Sb and Cr, they are synergistically enriched in the rust layer to form a dense oxide film rich in Sb, Cr and other elements that is several times higher than the matrix, which significantly hinders the transmission of corrosive ions and is more resistant to the corrosion environment where sulfate and chloride ions coexist; for example, a niobium-titanium microalloyed acidic medium corrosion-resistant steel plate with a yield strength of 600MPa and publication number CN112176257A ensures good acidic medium corrosion resistance through reasonable matching of Cu, Cr, Ni and Sb elements, while also having good atmospheric corrosion resistance, because Cu, Cr, Ni and other elements are enriched in the rust layer close to the matrix, forming a dense, nearly amorphous stable rust layer, thereby improving the atmospheric corrosion resistance of the steel.

[0004] The acid resistance obtained by coating and adding electroplating is not stable. After the outer protective layer is accidentally removed, it is difficult for the steel to maintain its acid and weather resistance. Therefore, the preferred method to improve the acid and weather resistance of steel is to improve the acid and weather resistance of the steel itself. In the prior art, the ability to improve the corrosion resistance by corrosion-resistant elements is not enough to meet the requirements. Summary of the invention

[0005] The purpose of the present invention is to provide an acid-resistant and weather-resistant steel plate with a tensile strength of 550MPa, which solves the problem of corrosion and weight loss of existing acid-resistant steel materials under long-term service under low-temperature dew point conditions in hydrochloric acid and sulfuric acid media. It is used to replace super stainless steels such as 316L, 2250, and 2507 in an environment of "resistance to low-temperature dew point corrosion of sulfuric acid and hydrochloric acid", and is used to manufacture economizers, air preheaters, heat exchangers, evaporators, sewage treatment devices and other equipment serving in high-sulfur flue gas to resist sulfur-containing and chlorine dew point corrosion.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions to achieve the above problems:

[0007] A 550MPa tensile strength acid-resistant and weather-resistant steel plate comprises the following chemical elements in percentage by weight:

[0008] Carbon (C) 0.03-0.12%, silicon (Si) 0.15-0.30%, manganese (Mn) 0.3-0.45%, sulfur (S) 0.02-0.035%, phosphorus (P) 0.01-0.02%, titanium (Ti) 0.01-0.035%, chromium (Cr) 0.70-1.20%, nickel (Ni) 0.6-1.0%, copper (Cu) 0.6-1.0%, molybdenum (Mo) 0.5-0.8%, acid-soluble aluminum (Als) 0.02-0.05%, antimony (Sb) 0.3-0.5%, nitrogen (N) ≤0.00060%, O (oxygen) ≤0.0015%, hydrogen (H) ≤0.00015%, and the rest are Fe and impurity elements remaining in the smelting process.

[0009] Furthermore, the acid-resistant and weather-resistant steel plate with a tensile strength of 550 MPa includes the following chemical elements in percentage by weight:

[0010] Carbon 0.045-0.065%, silicon 0.20-0.25%, manganese 0.3-0.4%, sulfur 0.02-0.03%, phosphorus 0.010-0.015%, titanium 0.02-0.030%, chromium 0.8-1.1%, nickel 0.75-0.95%, copper 0.65-0.85%, molybdenum 0.65-0.75%, acid-soluble aluminum 0.025-0.035%, antimony 0.35-0.40%, nitrogen ≤0.00060%, oxygen ≤0.0015%, hydrogen ≤0.00015%, and the rest are Fe and impurity elements remaining in the smelting process.

[0011] The structure of the steel plate of the present invention is a ferrite+pearlite composite structure.

[0012] Carbon: Low carbon content design can significantly increase the phase transformation temperature and is conducive to the formation of proeutectoid ferrite. Low carbon design can reduce component segregation, ensure the uniformity of the organization, and improve corrosion resistance and welding performance. A certain content of carbon can ensure the precipitation of the second phase of carbide and ensure the strength and welding performance of the steel plate. The carbon content is controlled at 0.03-0.12%, preferably 0.045-0.065%.

[0013] Silicon: Silicon can be deoxidized during the smelting process, but too high a content of silicon will affect weldability and toughness. The content of silicon is controlled at 0.15-0.3%, preferably 0.20-0.25%.

[0014] Manganese: Manganese is beneficial to improving high-temperature brittleness and is easy to form MnS inclusions. MnS inclusions are harmful to impact toughness, corrosion resistance, and welding performance. Its content is controlled at 0.30-0.45%, preferably 0.3-0.4%.

[0015] Sulfur: Sulfur can form a CuS passivation film during the contact between steel and acid medium, which can effectively isolate the contact between the acid and the steel matrix medium. Therefore, its content is in the range of 0.02-0.035%, preferably controlled at 0.02-0.03%.

[0016] Phosphorus: Too high phosphorus will cause grain boundary segregation and increase the brittleness of steel. A small amount of phosphorus can improve the weather resistance of steel. The phosphorus content is controlled at 0-0.02%, preferably 0.010-0.015%.

[0017] Titanium: During the continuous casting solidification process, titanium combines with nitrogen to form TiN, reducing the effect of nitrogen on boron. The presence of TiN can inhibit the coarsening of grains in the welding heat affected zone. The titanium content is controlled at 0.01-0.035%, preferably 0.020-0.030%.

[0018] Acid-soluble aluminum: Aluminum and a small amount of boron are beneficial to promoting the formation of ferrite, but too much aluminum will damage the toughness of the steel. The content of aluminum is controlled at 0.02-0.05%, preferably 0.025-0.035%.

[0019] Chromium: Chromium content greater than 0.2% can improve corrosion resistance, while enhancing the liquid permeability of steel and promoting the formation of ferrite. Chromium content controlled at 0.70-1.20% can promote a denser rust layer structure and ensure good isolation between the substrate and the medium. It is more preferably controlled at 0.8-1.1%.

[0020] Copper: Adding a certain amount of copper can increase the electrode potential of the substrate, form a CuS passivation film in the corrosion-resistant steel, and form a Cu2Sb precipitation phase. Sb will form a denser Sb2O5 after contacting the medium in the later stage, forming a dense passivation film, inhibiting the segregation of Sb elements at the grain boundaries and improving the brittleness of the grain boundaries. The copper content is controlled at 0.6-1.0%, preferably 0.65-0.85%.

[0021] Nickel: Ni and Cr work synergistically to enhance the corrosion resistance of the steel matrix, reduce the copper brittleness of copper-containing steel, and avoid cracks on the edge and surface of the steel plate. The nickel content is controlled at 0.6-1.0%, preferably 0.75-0.95%.

[0022] Molybdenum: Mo is beneficial to the refinement of ferrite and the improvement of the yield strength of steel, but it also improves the yield strength ratio of steel, can increase the ability of the rust layer or passivation film to resist the corrosion of chloride ions, and enhance the corrosion resistance in the hydrochloric acid dew point environment. Therefore, the molybdenum content is controlled to 0.5-0.8%, preferably 0.65-0.75%.

[0023] Antimony: Antimony is the chemical element that has the most significant effect in improving the corrosion resistance of steel in a sulfuric acid environment. Sb significantly improves the corrosion resistance of steel. However, Sb is an element that has an adverse effect on the strength, toughness, plasticity and weldability of steel. Sb added to the metal surface can form Sb2O5 in the corrosive medium, which has higher stability than the steel matrix and helps to prevent the metal matrix from being further corroded by the corrosive medium. In the present invention, the antimony content is controlled at 0.3-0.5%, preferably at 0.35-0.40%. Sb is coupled with Cu and Mo to have good corrosion resistance without damaging strength and toughness.

[0024] Gaseous elements such as nitrogen, oxygen, and hydrogen are extremely detrimental to the performance stability of steel and should be strictly controlled: nitrogen ≤ 0.00060%, oxygen ≤ 0.00015%, and hydrogen ≤ 0.0015%.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] In view of the complex and changeable medium conditions containing sulfur, chlorine and other components in coal-fired mineral flue gas, a certain amount of antimony, sulfur and other elements are added on the basis of adding traditional chromium, nickel, molybdenum and copper to improve corrosion resistance. The ratio of each element is optimized according to the composition of the passivation film and the preparation process is matched with the composition to prepare acid-resistant steel that can corrode at low temperatures at the dew point of hydrochloric acid and sulfuric acid.

[0027] The present invention also proposes a method for preparing the acid-resistant and weather-resistant steel plate with a tensile strength of 550 MPa, which includes molten iron pretreatment, converter smelting, LF refining, RH refining, continuous casting, slab stack cooling, slab heating, hot rolling, laminar cooling, and cross-cutting to obtain the steel plate, wherein the key control points are:

[0028] Converter smelting: After converter smelting, argon is blown through the ladle, and the terminal temperature of the argon station is controlled to be greater than 1535℃.

[0029] LF refining: the inlet temperature is greater than 1522℃, the outlet temperature of LF is 1585-1620℃, the refining time is 40-45 minutes, the furnace is refined and the composition is fine-tuned to the target composition, the molten steel temperature is greater than 1538℃ and transferred to RH for vacuum treatment.

[0030] RH refining: vacuum degree requirement ≤67MPa, RH cycle time 30-35min.

[0031] Continuous casting: The continuous casting speed is controlled at 1.4-1.6m / min, and the casting adopts the light pressure mode.

[0032] The ingot is cooled to room temperature, and then the slab is heated in the furnace. After rough rolling by the rough rolling unit, it is finished rolled. After rolling, it enters the laminar cooling system for tissue control to complete the hot rolling.

[0033] The slab heating temperature is 1180-1220℃, the required heating time is 150-250min, and the solution time is 30min.

[0034] The hot rolling mechanical controlled rolling and controlled cooling process is as follows: the starting temperature of rough rolling is 1150-1180℃, the final rolling temperature of rough rolling is 1000-1080℃, the starting temperature of finishing rolling is 950-1050℃, the final rolling temperature of finishing rolling is 800-850℃, laminar cooling after final finishing rolling, the cooling rate is 20-30℃ / s, and the final cooling is to 650-680℃ for coiling.

[0035] Hot rolling is based on metal deformation, phase change and other processes, and completes solid solution strengthening, precipitation strengthening, dislocation strengthening and other hardening measures under specified deformation and temperature conditions to obtain mechanical properties and good corrosion resistance. To reduce manufacturing costs and make full use of the rolling and cooling capacity of the continuous rolling mill, the present invention adopts controlled rolling and accelerated cooling to produce, and obtains the best mechanical effect through the coupling effect of deformation recrystallization in the high-temperature austenite zone, deformation in the low-temperature austenite non-recrystallization zone, and accelerated cooling after rolling. In the high-temperature austenite zone, corrosion-resistant elements such as Cr, Ni, Cu, Mo, and Sb are dissolved into the matrix, and controlled rolling and controlled cooling technology are used to ensure that the alloy elements are in a solid solution state, and to ensure that the passivation film has sufficient alloy elements to participate in the film formation.

[0036] In the present invention, at a cooling rate of 20-30°C / s, the ferrite starting transformation temperature is 660°C, the ferrite transformation termination temperature is 560°C, and pearlite transformation occurs below 560°C.

[0037] The steel plate prepared by the present invention has the following properties: yield strength Rel: 420-450MPa, tensile strength Rm: 550-620MPa, yield strength ratio Rel / Rm is small, elongation A (%) is greater than 25%, -40℃ KV2 type impact energy is greater than 100J. The average corrosion rate is 0.025mg / (m 2 .h). Immersed in 50% concentrated sulfuric acid + 3.5% NaCl mixed solution at 70°C hydrochloric acid dew point for 24 hours, the average corrosion rate is 0.012mg / (m 2 .h). BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a metallographic structure diagram of a steel plate with a thickness of 4 mm according to Example 1 of the present invention;

[0039] Figure 2 This is a metallographic structure diagram of a steel plate with a thickness of 16 mm according to Example 1 of the present invention;

[0040] Figure 3 The figure is a flow chart of the preparation of the steel plate of the present invention. DETAILED DESCRIPTION

[0041] In order to make the technical problems to be solved, technical solutions and advantages of the present invention more clear, they are described in detail below in conjunction with specific embodiments.

[0042] like Figure 3As shown, the implementation process of the acid-resistant and weather-resistant steel plate with a tensile strength of 550 MPa of the present invention includes converter smelting, LF furnace refining, RH furnace refining, continuous casting, slab stack cooling, slab heating, hot rolling (rough rolling and finishing rolling), laminar cooling, steel plate coiling, steel coil stack cooling, cross-cutting and flattening to obtain steel plates, and then inspection and storage.

[0043] The molten iron is desulfurized by KR and then smelted in a 210-ton converter;

[0044] Then argon is blown through the ladle: the terminal temperature of the argon station is controlled to be greater than 1535℃;

[0045] LF furnace refining: the inlet temperature is greater than 1522℃, the outlet temperature of LF is 1585-1620℃, the refining time is 40-45 minutes, the furnace is refined and the composition is fine-tuned to the target composition, the molten steel temperature is greater than 1538℃ and transferred to the RH furnace for vacuum treatment;

[0046] RH furnace refining: vacuum degree 67MPa, RH cycle time 30-35min;

[0047] Continuously cast into 230mm thick slabs;

[0048] The ingot is cooled to room temperature for 48 hours;

[0049] The ingot is then charged into the furnace and heated to 1180-1220℃;

[0050] After 5 rough rolling passes and 2 finish rolling passes, the steel is subjected to thermomechanical controlled rolling and controlled cooling by a 7-stand 2250 continuous rolling unit. The starting temperature of the rough rolling is 1150-1180°C, the final rolling temperature of the rough rolling is 1000-1080°C, the starting temperature of the finish rolling is 950-1050°C, the final rolling temperature of the finish rolling is 800-850°C, and the steel is subjected to laminar cooling after the final rolling at a cooling rate of 20-30°C / s. The steel is finally cooled to 650-680°C for coiling.

[0051] The thickness specifications of the hot-rolled steel coil of the present invention are 4 mm and 16 mm.

[0052] The alloy element compositions of different numbers of the present invention are shown in Table 1. The data mentioned in each number in Table 1 are expressed as the mass percentage of the corresponding element, and nitrogen ≤0.00060%, oxygen ≤0.00015%, and hydrogen ≤0.0015% in each numbered alloy. They are not reflected in Table 1, and the balance in each numbered alloy is iron.

[0053] The controlled rolling and controlled cooling process parameters of each embodiment and comparative example are shown in Table 2, the corresponding mechanical properties are shown in Table 3, and the cyclic infiltration test results are shown in Table 4.

[0054] Table 1

[0055]

[0056] Numbers (7)-(12) add smaller amounts of S, Cu, Cr, Ni, Mo, and Sb elements compared to numbers (1)-(6), respectively, proving that the amounts of the above elements have the minimum requirements for the corrosion resistance of the steel plates.

[0057] Table 2 Specific rolling process parameters of each embodiment and comparative example

[0058]

[0059]

[0060] Table 3 Specific mechanical properties of the steel plates obtained by rolling under the corresponding rolling process parameters of each embodiment and comparative example

[0061] Steel thickness Rel(MPa) <![CDATA[R m (MPa)]]> A(％) Longitudinal, -40℃ impact energy (J) Example 1 4mm 450 610 27 245 Example 2 16mm 442 600 26 235 Example 3 4mm 430 585 25 265 Example 4 16mm 420 550 28 258 Example 5 4mm 450 560 25 250 Example 6 16mm 432 620 30 253 Comparative Example 1 4mm 408 540 26 180 Comparative Example 2 16mm 384 545 25 190 Comparative Example 3 4mm 398 530 28 175 Comparative Example 4 16mm 397 525 29 168 Comparative Example 5 4mm 389 540 26 188 Comparative Example 6 16mm 402 510 27 193 Comparative Example 7 4mm 435 552 20 176 Comparative Example 8 16mm 410 536 22 182 Comparative Example 9 4mm 416 505 28 161 Comparative Example 10 16mm 408 534 26 159 Comparative Example 11 4mm 428 548 27 173 Comparative Example 12 16mm 438 548 25 155 Comparative Example 13 10mm 481 595 26.5 188

[0062] From Table 3, it can be seen that, compared with Examples 1-6, when the relevant alloy elements are reduced, the performance of Comparative Examples 1-6 tends to decrease, while it can be seen from Comparative Examples 7-12 that the performance of the steel plate also tends to decrease when the rolling temperature is changed. Figure 1 and Figure 2 .

[0063] Table 4 Cyclic infiltration test results corresponding to different steel plates:

[0064]

[0065]

[0066] From the corrosion resistance of comparative examples 1-6 in Table 4 above, it can be seen that by changing the key rolling process parameters, the results show that the corrosion performance is greatly affected. It can be seen that the rolling parameters in the hot rolling process play a vital role in forming a sufficient amount of passivation film in the alloy. In order to achieve a sufficient amount of passivation film, in addition to the influence of the process parameters, the dosage of related metal elements is also necessary. As a verification, under the condition of not changing the rolling process parameters, a smaller amount of S, Cu, Cr, Ni, Mo, and Sb elements are used to verify the corrosion resistance of the steel. From comparative examples 7-12 in Table 4, it can be seen that the corresponding steel anti-corrosion performance is significantly reduced. The reasons are analyzed. First, the alloy element itself is the basis for the steel plate to obtain good mechanical properties and good corrosion resistance. Cr, Ni, Cu, Mo, Sb, etc. are all corrosion resistant. Secondly, the alloy elements have different performances at different temperatures. The rolling and cooling technology are controlled to ensure that the alloy elements are in a solid solution state and that the passivation film has sufficient alloy elements to participate in the film formation.

[0067] The above embodiments are only used to illustrate the ideas and features of the present invention, and their purpose is to enable people who understand this technology to understand the content of the present invention and implement it accordingly, and are not limited to the protection scope of the present invention. Any equivalent changes or modifications made based on the technical elements of the present invention should be within the protection scope of the present invention.

Claims

1. A 550MPa-grade acid-resistant and weather-resistant steel plate, characterized in that: The chemical elements included are as follows in weight percentage: Carbon 0.03-0.12%, silicon 0.15-0.30%, manganese 0.3-0.45%, sulfur 0.02-0.035%, phosphorus 0.01-0.02%, titanium 0.01-0.035%, chromium 0.70-1.20%, nickel 0.6-1.0%, copper 0.6-1.0%, molybdenum 0.5-0.8%, acid-soluble aluminum 0.02-0.05%, antimony 0.3-0.5%, nitrogen ≤0.00060%, O ≤0.0015%, hydrogen ≤0.00015%, and the rest are Fe and impurity elements remaining in the smelting process.

2. The acid-resistant and weather-resistant steel plate with a tensile strength of 550 MPa as claimed in claim 1, characterized in that: The chemical elements included are as follows in weight percentage: Carbon 0.045-0.065%, silicon 0.20-0.25%, manganese 0.3-0.4%, sulfur 0.02-0.03%, phosphorus 0.010-0.015%, titanium 0.02-0.030%, chromium 0.8-1.1%, nickel 0.75-0.95%, copper 0.65-0.85%, molybdenum 0.65-0.75%, acid-soluble aluminum 0.025-0.035%, antimony 0.35-0.40%, nitrogen ≤0.00060%, oxygen ≤0.0015%, hydrogen ≤0.00015%, and the rest are Fe and impurity elements remaining in the smelting process.

3. The method for preparing a 550MPa-tensile strength acid-resistant and weather-resistant steel plate according to claim 1 or 2, characterized in that: The steps include: The steel plate is obtained by converter smelting, LF refining, RH refining, continuous casting, slab stack cooling, slab heating, hot rolling, laminar cooling, and cross-cutting. The hot rolling includes rough rolling and finish rolling. The starting temperature of rough rolling is 1150-1180℃, and the finishing temperature of rough rolling is 1000-1080℃.

4. The method for preparing a 550MPa-tensile strength acid-resistant and weather-resistant steel plate according to claim 3, characterized in that: The starting temperature of finishing rolling is 950-1050℃, and the final rolling temperature of finishing rolling is 800-850℃.

5. The method for preparing an acid-resistant and weather-resistant steel plate with a tensile strength of 550 MPa as claimed in claim 3, characterized in that: The cooling rate of laminar cooling is 20-30℃ / s, and the final cooling temperature is 650-680℃ for coiling.

6. The method for preparing a 550MPa-tensile strength acid-resistant and weather-resistant steel plate according to claim 3, characterized in that: Converter smelting: After converter smelting, argon is blown through the ladle, and the terminal temperature of the argon station is controlled to be greater than 1535℃.

7. The method for preparing a 550MPa-tensile strength acid-resistant and weather-resistant steel plate according to claim 3, characterized in that: LF refining: the inlet temperature is greater than 1522℃, the outlet temperature of LF is 1585-1620℃, the refining time is 40-45 minutes, the furnace is refined and the composition is fine-tuned to the target composition, the molten steel temperature is greater than 1538℃ and transferred to RH for vacuum treatment; RH refining: vacuum degree requirement ≤67MPa, RH cycle time 30-35min.

8. The method for preparing an acid-resistant and weather-resistant steel plate with a tensile strength of 550 MPa as claimed in claim 3, characterized in that: The continuous casting speed is controlled at 1.4-1.6m / min, and the casting adopts the light pressure mode; The ingot is cooled to room temperature, and then the slab is heated in the furnace. After rough rolling by the rough rolling unit, it is finished rolled. After rolling, it enters the laminar cooling system for tissue control to complete the hot rolling.

9. The method for preparing an acid-resistant and weather-resistant steel plate with a tensile strength of 550 MPa as claimed in claim 3, characterized in that: The slab heating temperature is 1180-1220℃, the required heating time is 150-250min, and the solution time is 30min.

10. Use of the steel plate obtained by the method for preparing an acid-resistant and weather-resistant steel plate with a tensile strength of 550 MPa as described in any one of claims 4 to 9 in the preparation of economizers, boiler preheaters, coal burner equipment, flue gas conveying pipes, flues, and chimneys.

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