Corrosion-resistant 460MPa-class steel plate and its manufacturing method

Abstract

This invention provides a corrosion-resistant 460 MPa-class steel plate and its manufacturing method. This steel plate employs a corrosion-resistant alloying composition system with the combined addition of Cr, Ni, Mo, Cu, and P, ensuring corrosion resistance and weldability while reducing the amount of valuable alloying elements used. While strictly controlling impurity elements, one or more rare earth elements selected from La, Ce, Pr, and Nd are used to purify the molten steel, further improving corrosion resistance. Based on a comprehensive chemical composition design, precise control of process parameters in the rolling and cooling processes allows for precise control of the steel plate's structure, inclusion content, and size, resulting in a 460 MPa-class steel plate for wind power towers with excellent overall performance and marine atmospheric corrosion resistance.

Description

[Technical Field]

[0001] The present invention relates to the field of alloy technology, specifically to a corrosion-resistant 460 MPa grade steel plate and a manufacturing method thereof. [Background technology]

[0002] Compared to onshore wind power plants, offshore wind power generation offers advantages such as higher power generation efficiency, less environmental pollution, and no land occupation. However, offshore wind power plants face extremely harsh corrosive environments, particularly in steel towers installed in the highly humid and saline marine atmosphere. Water vapor in the marine atmosphere forms a highly conductive electrolyte solution layer invisible to the naked eye on steel surfaces through capillary action, adsorption, and chemical coagulation. This solution contains dissolved oxygen, chloride ions, sulfate ions, and other salts. Chloride ions have a strong penetrating effect, causing localized corrosion, such as pitting corrosion, stress corrosion, intergranular corrosion, and crevice corrosion. This hinders the formation of a stable, dense rust layer on steel surfaces, resulting in increased corrosion rates. While long-life corrosion-resistant coating systems are commonly used as corrosion prevention measures, coating degradation issues arise during service life. Therefore, improving the corrosion resistance of the steel itself represents a new technological approach to corrosion protection design.

[0003] Existing marine and atmospheric corrosion-resistant steel manufacturing technologies mainly address this issue by adding large amounts of P and Ni. However, if the P content is too high, the steel's weldability decreases, making it unsuitable for the production of steel plates for wind power towers, which require large-scale welding. Furthermore, adding large amounts of Ni to improve corrosion resistance increases alloy costs, which is detrimental to cost management for offshore wind power generation equipment and makes widespread application difficult. Meanwhile, other steel plates have low strength and are unsuitable for the construction of large-scale offshore wind power generation facilities. Summary of the Invention

[0004] An object of the present invention is to provide a corrosion-resistant 460 MPa class steel sheet and a method for producing the same.

[0005] The present invention provides a method for producing a corrosion-resistant 460 MPa-class steel sheet, whose chemical composition, by mass percentage, includes 0.06-0.09% C, 0.2-0.3% Si, 0.9-1.0% Mn, 0.5-0.6% Cr, 0.30-0.40% Ni, 0.40-0.45% Cu, 0.05-0.10% Mo, 0.02-0.04% Nb, 0.02-0.04% Al, 0.015-0.025% P, and 0.015-0.025% rare earth elements, with the remainder being Fe and unavoidable impurities, and the impurity elements, by mass percentage, satisfy the following: S≦0.002%, O≦0.002%, and N≦0.004%.

[0006] The atmospheric corrosion resistance index I of the steel plate is 6.5 or more, and the atmospheric corrosion resistance index I is I=26.01(%Cu)+3.88(%Ni)+1.20(%Cr)+1.49(%Si)+17.28(%P)-7.29(%Cu)(%Ni)-9.10(%Ni)(%P)-33.39(%Cu) 2 In the formula, the element symbol in parentheses indicates the mass percentage of the corresponding element, and the % element symbol indicates the mass percentage of the corresponding element multiplied by 100.

[0007] The manufacturing method includes: a step of performing steelmaking and casting according to the blending ratio of the chemical components to obtain a cast slab; a step of subjecting the slab to two-stage controlled rolling, the step including a first stage of austenite recrystallization region rolling and a second stage of austenite non-recrystallization region rolling, controlling the reduction rate in the first stage of austenite recrystallization region rolling to 50% or more, and controlling the finish rolling temperature in the second stage of austenite non-recrystallization region rolling to 800±20°C; The method includes a step of subjecting the steel plate to a cooling treatment, controlling the cooling rate to form a microstructure containing acicular ferrite and granular bainite in the steel plate, and the content of the acicular ferrite is 85% or more.

[0008] As a further improvement of the present invention, the carbon equivalent CE of the steel plate satisfies 0.39≦CE≦0.42, and the carbon equivalent CE is CE=(%C)+(%Mn) / 6+(%Cr+%Mo+%V) / 5+(%Ni+%Cu) / 15 In the formula, the element symbol in parentheses indicates the mass percentage of the corresponding element, and the % element symbol indicates the mass percentage of the corresponding element multiplied by 100.

[0009] As a further improvement of the present invention, in the chemical composition of the steel sheet, the rare earth elements are one or more of La, Ce, Pr, and Nd.

[0010] As a further improvement of the present invention, The method further includes a step of rolling the cast slab into a steel plate having a thickness of 100 mm or less.

[0011] In a further improvement of the present invention, the cooling treatment of the steel sheet comprises: The method includes subjecting the steel sheet after rolling to a water cooling treatment, controlling the cooling rate to 10 to 28°C / s, and controlling the finish cooling temperature of the steel sheet to 350±30°C.

[0012] In another aspect, the present invention provides a corrosion-resistant 460 MPa-class steel sheet having a chemical composition, in mass percentages, of C: 0.06-0.09%, Si: 0.2-0.3%, Mn: 0.9-1.0%, Cr: 0.5-0.6%, Ni: 0.30-0.40%, Cu: 0.40-0.45%, Mo: 0.05-0.10%, Nb: 0.02-0.04%, Al: 0.02-0.04%, P: 0.015-0.025%, rare earth elements: 0.015-0.025%, and the balance being Fe and unavoidable impurities, with the partial impurity elements satisfying the following mass percentages: S≦0.002%, O≦0.002%, and N≦0.004%.

[0013] The microstructure of the steel sheet includes acicular ferrite and granular bainite, and the content of the acicular ferrite is 85% or more; Under the GB / T10125-2012 test conditions, the average corrosion weight loss rate of the steel plate was 1.315g / (m 2 h) is less than or equal to When sampled in accordance with GB / T2975 and subjected to tensile and impact tests in accordance with GB / T228 and GB / T229, the steel plate has a yield strength of 460 MPa or more, a tensile strength of 540 to 720 MPa, a breaking elongation of 20% or more, and a -50°C impact absorption energy KV2 of 100 J or more.

[0014] As a further improvement of the present invention, the length x width of the largest inclusion in the steel sheet is 150 μm 2 Under the conditions of GB / T10561, the grades of A, B, C, and D inclusions are all 1.5 or less, and the total grade of A, B, C, and D inclusions is 3.0 or less.

[0015] As a further improvement of the present invention, the steel plate has a -50°C impact absorption energy KV2 of 80J or more in the heat affected zone after welding when the welding heat input is 80kJ / cm or less.

[0016] In a further refinement of the invention, the thickness of said steel plate is less than or equal to 100 mm. [Effects of the Invention]

[0017] This invention uses a corrosion-resistant alloying composition system with the combined addition of Cr, Ni, Mo, Cu, and P, which ensures corrosion resistance and weldability while reducing the amount of valuable alloying elements used. While strictly controlling impurity elements, one or more rare earth elements selected from La, Ce, Pr, and Nd can be added to purify the molten steel, further improving corrosion resistance. Based on comprehensive chemical composition design and precise control of rolling and cooling process parameters, the steel plate's structure, inclusion content, and size can be precisely controlled, resulting in a 460 MPa-class steel plate for wind power towers with excellent overall performance and marine atmospheric corrosion resistance. [Brief explanation of the drawings]

[0018] [Figure 1]1 is a process flow diagram of a method for producing a corrosion-resistant 460 MPa class steel plate according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] In order to make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described clearly and completely below with reference to specific embodiments of the present invention and corresponding drawings. Of course, the described embodiments are only some embodiments of the present invention, and are not all embodiments. All other embodiments that can be obtained by those skilled in the art based on the embodiments of the present invention without creative work shall also fall within the protection scope of the present invention.

[0020] Hereinafter, embodiments of the present invention will be described in detail. Examples of embodiments are shown in the drawings, and the same or similar reference numerals indicate the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the drawings are illustrative and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0021] This embodiment provides a corrosion-resistant 460 MPa-class steel plate and a manufacturing method thereof. The manufactured steel plate is particularly suitable for use as a marine atmospheric corrosion-resistant steel plate. The steel plate provided in this embodiment employs a corrosion-resistant alloying composition system with the combined addition of Cr, Ni, Mo, Cu, and P. Compared with existing marine atmospheric corrosion-resistant steel plates, this embodiment employs a low-P and low-Ni alloying composition system, improving the weldability of the steel plate while reducing alloy costs. Under conditions of low P and Ni content, the present invention adds small amounts of rare earth elements during the manufacturing process to improve the cleanliness of the molten steel. Furthermore, by controlling the rolling and cooling process parameters, a microstructure mainly composed of acicular ferrite is formed in the steel plate, thereby improving the corrosion resistance and strength of the steel plate.

[0022] The chemical composition of the steel sheet provided in this embodiment includes, in mass percentage, C: 0.06-0.09%, Si: 0.2-0.3%, Mn: 0.9-1.0%, Cr: 0.5-0.6%, Ni: 0.30-0.40%, Cu: 0.40-0.45%, Mo: 0.05-0.10%, Nb: 0.02-0.04%, Al: 0.02-0.04%, P: 0.015-0.025%, rare earth elements: 0.015-0.025%, and the remainder is Fe and unavoidable impurities, and the mass percentages of some impurity elements are as follows: S≦0.002%, O≦0.002%, and N≦0.004%.

[0023] Specifically, the design principles of the chemical composition of steel sheets will be explained below.

[0024] C: C is a strengthening element, and the C content significantly affects the microstructure of steel, thereby directly affecting the strength of the steel sheet. However, if the C content is too high, the low-temperature toughness and weldability of the steel sheet will decrease. Therefore, in the present invention, by controlling the C content to 0.06 to 0.09% and combining it with a comprehensive design of other elements, it is possible to improve the low-temperature toughness and weldability of the steel sheet while ensuring the strengthening effect.

[0025] Si: Si is a solid-solution strengthening and deoxidizing element. While there are currently differing views in academia and industry regarding the mechanism by which Si affects corrosion resistance in steel, it is generally believed that the addition of Si results in a three-dimensional network structure of SiO2, which promotes the formation of α-FeOOH and grain refinement. Furthermore, Si replaces Fe in Fe3O4 in the rust layer, forming more stable SiO2. Furthermore, when Si and Cu are used together, the SiO2 in the rust layer increases the concentration of Cu, improving industrial atmospheric corrosion resistance. However, excessive Si content promotes the segregation of P at grain boundaries, reducing the low-temperature toughness and weldability of the steel sheet and weakening the corrosion resistance of P. Therefore, in this invention, the Si content is controlled to 0.2-0.3% to prevent P segregation while maintaining the deoxidizing effect.

[0026] Mn: Mn is a solid-solution strengthening element that improves the hardenability of steel sheets, thereby increasing their strength. At the same time, Mn can bind with the harmful element S to reduce the hot shortness of steel sheets. However, excessive Mn promotes the segregation of elements such as C and P, forming MnS inclusions in the center of the steel sheet, reducing the corrosion resistance of the steel sheet and degrading the low-temperature toughness and weldability of the center of the steel sheet. Therefore, in the present invention, the Mn content is controlled to 0.9 to 1.0%, which compensates for the strength reduction caused by low carbon, while also reducing segregation and suppressing the formation of inclusions, thereby improving the low-temperature toughness and weldability of the center of the steel sheet.

[0027] Cr: Cr is a common corrosion-resistant element. It promotes the conversion of sparse and unstable γ-FeOOH in the rust layer on the steel surface to stable α-FeOOH, suppressing the formation of pores and cracks in the rust layer and improving the corrosion resistance of the steel. Cr concentrates on the substrate side of the rust layer, forming a passivation film that reduces the anion selectivity of the rust layer, blocking the penetration of external anions, and protecting the steel substrate. Cr also acts synergistically with Cu to refine the rust layer grains, improving the rust layer's density and stability. Furthermore, Cr substitutes for some of the Fe sites in FeOOH to form CrxFe(1-x)OOH, imparting cation selectivity to the rust layer and effectively blocking the penetration of chloride ions and sulfate ions. However, excessive Cr content easily forms carbides, causing pitting corrosion and reducing the corrosion resistance of the steel. Therefore, in this invention, the Cr content is controlled to 0.5-0.6% to prevent the corrosion resistance of the steel sheet from deteriorating over time.

[0028] Ni: The addition of Ni shifts the self-corrosion potential of steel toward the nobler side, increases the resistance to anodic dissolution reactions, promotes the formation of the α-FeOOH phase in the rust layer, refines the grain size of the internal rust layer, and improves the stability of the rust layer. Ni also concentrates within the rust layer, reducing the anion selectivity of the rust layer and inhibiting corrosion of the steel substrate. Furthermore, while the addition of Ni improves the low-temperature toughness and weldability of steel sheets, excessive Ni addition increases alloy costs. Therefore, in this invention, the Ni content is controlled to 0.3-0.4% to ensure the corrosion resistance, low-temperature toughness, and weldability of steel sheets while rationally controlling alloy costs.

[0029] Cu: The addition of Cu to steel significantly improves corrosion resistance and is inexpensive, making it widely used in corrosion-resistant steels. Its main mechanisms of action are as follows: Cu inhibits the crystallization of the rust layer and promotes the formation of α-FeOOH and amorphous Fe3O4. Cu also concentrates in the weak areas of the rust layer, forming oxides during the corrosion process that tightly bond the rust layer to the steel substrate, reducing cracks and voids in the rust layer and improving pitting corrosion resistance. Furthermore, Cu activates the cathode, passivating the steel substrate and slowing the corrosion rate. However, excessive Cu content adversely affects the weldability of steel sheets. Therefore, in this invention, the Cu content is controlled to 0.40-0.45% to improve the corrosion resistance of steel sheets without affecting weldability.

[0030] Mo: Mo refines grains and improves the hardenability of steel. Mo also forms MoO4 2- This gives the inner rust layer cation selectivity, and Cl - The combined use of Mo and Cu promotes the concentration of Cu in the weak areas of the rust layer, inhibits the occurrence of pitting corrosion, and improves corrosion resistance. Furthermore, the addition of Mo reduces the cooling rate required for the formation of acicular ferrite. However, the addition of excessive Mo increases alloy costs. Therefore, in the present invention, the Mo content is controlled to 0.05 to 0.10%, thereby ensuring the strength and corrosion resistance of the steel sheet while rationally controlling alloy costs.

[0031] Nb: Nb is a grain refiner and strong carbide former. It prevents the bonding of C and Cr, thereby avoiding an adverse effect on the corrosion resistance of steel sheets, and promotes the rapid formation of α-FeOOH and an increase in its content. Nb also increases the amount of rare earth elements dissolved in steel, improving the corrosion resistance of steel sheets. Too high a Nb content can degrade the low-temperature toughness of the heat-affected zone of welded joints and adversely affect corrosion resistance. Therefore, in the present invention, the Nb content is controlled to 0.02-0.04% to ensure the grain refinement effect and corrosion resistance without adversely affecting the low-temperature toughness of the heat-affected zone of welded joints.

[0032] Al: Al is an important deoxidizing element, but if the content is too high, nozzles tend to clog during casting. In the present invention, the Al content is controlled to 0.02 to 0.04%, ensuring the beneficial effects of Al while reducing the difficulty of smelting.

[0033] P: P is a typical element that improves the corrosion resistance of steel and acts as an anodic depolarizer. 2+ It accelerates the oxidation rate of PO4 and the uniform dissolution of steel, and effectively promotes the formation of a uniform α-FeOOH rust layer on the steel surface. 3- On the other hand, PO4 3- H + It forms a complex with PO4 to improve the interfacial pH, inhibiting the cathodic hydrogen evolution reduction reaction and the dissolution of the rust layer. 3- During the anodic dissolution process, Fe 2+ and Mn 2+ P combines with Cu to form a sparingly soluble phosphate film, which inhibits the anodic dissolution reaction and acts as a corrosion inhibitor. Furthermore, P and Cu have a good synergistic corrosion-resistant effect, which has the effect of comprehensively improving the corrosion resistance of steel. However, P is an element that is prone to segregation, and if its content is too high, it significantly reduces the low-temperature toughness and weldability of the steel sheet center. Therefore, in the present invention, the P content is controlled to 0.015 to 0.025% to prevent serious segregation and prevent deterioration of the low-temperature toughness and weldability of the steel sheet while maintaining corrosion resistance.

[0034] Rare earth elements: Rare earth elements purify molten steel, refine inclusions in steel, convert elongated manganese sulfides into spherical rare earth sulfides or sulfates, and transform high-hardness alumina inclusions into spherical sulfates and rare earth aluminates. The combined use of rare earth elements and P promotes the formation of a uniform α-FeOOH rust layer on the steel sheet surface, strengthens the bonding strength between the rust layer and the substrate, and improves corrosion resistance. Considering cost factors, the present invention limits the rare earth element content to 0.015-0.025%, achieving both the effects of purifying molten steel and improving the corrosion resistance of steel sheet.

[0035] In this embodiment, one or more rare earth elements are selected from La, Ce, Pr, and Nd. La, Ce, Pr, and Nd are all light rare earth elements with similar ionic radii, similar mechanisms of action in steel, and coexist closely in nature, making the cost of refining a single rare earth metal high. In this embodiment, by using one or more elements from La, Ce, Pr, and Nd, corrosion resistance is maintained while the cost of the rare earth metal is reduced.

[0036] S, O, and N are impurity elements, and rare earth elements added to steel will first react with these impurity elements. If the impurity element content is too high, the added rare earth elements will be consumed in large quantities, weakening the corrosion resistance effect of the rare earth elements. On the other hand, further limiting the impurity elements will make production difficult. In this invention, by controlling S≦0.002%, O≦0.002%, and N≦0.004% and combining this with the overall chemical composition design, we can ensure the effective function of the rare earth elements while avoiding the production difficulties and increased production costs that result from overly strict impurity element content control requirements.

[0037] Furthermore, the atmospheric corrosion resistance index I of the steel plate is 6.5 or more, and the atmospheric corrosion resistance index I is: I=26.01(%Cu)+3.88(%Ni)+1.20(%Cr)+1.49(%Si)+17.28(%P)-7.29(%Cu)(%Ni)-9.10(%Ni)(%P)-33.39(%Cu) 2 In the formula, the element symbol in parentheses indicates the mass percentage of the corresponding element, and the % element symbol indicates the mass percentage of the corresponding element multiplied by 100.

[0038] The carbon equivalent CE of the steel plate satisfies 0.39≦CE≦0.42, which ensures good weldability of the steel plate. CE=(%C)+(%Mn) / 6+(%Cr+%Mo+%V) / 5+(%Ni+%Cu) / 15 In the formula, the element symbol in parentheses indicates the mass percentage of the corresponding element, and the % element symbol indicates the mass percentage of the corresponding element multiplied by 100.

[0039] As described above, this embodiment employs a corrosion-resistant alloying composition system with the combined addition of Cr, Ni, Mo, Cu, and P. Compared to existing marine and atmospheric corrosion-resistant steel plates, the use of a low-P and Ni alloy composition system improves the strength and weldability of the steel plate while simultaneously reducing alloy costs. Adding small amounts of rare earth elements under conditions where the added amounts of P and Ni are low improves the cleanliness of the molten steel and further improves corrosion resistance.

[0040] As shown in FIG. 1, the manufacturing method includes the following steps: S1: Smelting and casting are carried out according to the above chemical composition ratio to obtain a slab. S2: The slab is subjected to two-stage controlled rolling, including the first stage of austenite recrystallization region rolling and the second stage of austenite non-recrystallization region rolling. In the first stage of austenite recrystallization region rolling, the reduction ratio is controlled to 50% or more, and in the second stage of austenite non-recrystallization region rolling, the finish rolling temperature is controlled to 800±20°C. S3: The steel sheet is subjected to a cooling treatment, and the cooling rate is controlled to form a microstructure containing acicular ferrite and granular bainite, where the acicular ferrite content is 85% or more.

[0041] Step S1 involves sequentially carrying out a converter smelting process, an LF refining process, an RH refining process, and a continuous casting process according to the chemical composition ratio to obtain a slab.

[0042] In the hot metal pre-desulfurization process, the hot metal is subjected to KR desulfurization to control the sulfur content in the hot metal, and the desulfurization slag is removed. After that, the hot metal is charged into a converter for converter smelting.

[0043] In converter smelting, molten steel is obtained by converter smelting using pre-desulfurized molten iron and scrap as raw materials. During the smelting process, ferrosilicon alloy, manganese metal, carbon powder, etc. are added to the molten steel to deoxidize it.

[0044] After the molten steel has been refined to meet the specified requirements, a vacuum is applied and the steel undergoes a cyclic degassing process.

[0045] After refining, the molten steel is evacuated and subjected to a circulating degassing process to remove inclusions, after which further refining takes place.

[0046] After the refined molten steel is alloyed by wire feeding, the molten steel is cast into a slab, which is heated and held at a soaking temperature in preparation for the rolling process.

[0047] Step S2 specifically includes the following steps.

[0048] A two-stage controlled rolling process is used, including the first stage of austenite recrystallization region rolling and the second stage of austenite non-recrystallization region rolling. In the first stage of austenite recrystallization region rolling, the reduction is controlled to 50% or more. By repeatedly alternating between deformation and recrystallization under a large reduction, the original austenite grains are fully recrystallized. The large reduction gradually refines the austenite grains, ultimately resulting in fine equiaxed austenite grains. This increases the total area of ​​effective austenite grain boundaries and provides more nucleation sites for the austenite-to-ferrite phase transformation.

[0049] The second stage rolling involves rolling with a large reduction below the recrystallization temperature, increasing the number of nucleation sites and the driving force for recrystallization, thereby refining the original austenite grains. It also promotes the strain-induced precipitation of trace alloying elements, resulting in austenite grain refinement and work hardening. As the austenite grains elongate, deformation bands and a large number of dislocations are generated, storing sufficient deformation energy within the austenite grains, providing more nucleation sites for phase transformation and promoting grain refinement.

[0050] Specifically, in the second stage of rolling, the finish rolling temperature is controlled to 800±20°C, and the slab is rolled into a steel plate with a thickness of 100 mm or less. By combining this with the components and amounts of the aforementioned trace alloy elements, it is possible to effectively refine the crystal grains and improve the low-temperature toughness of the steel plate.

[0051] Step S3 specifically includes the following steps.

[0052] The steel sheet after rolling is water-cooled, controlling the cooling rate to 10 to 28°C / s, and the final cooling temperature of the steel sheet to 350±30°C. By controlling the cooling rate, a microstructure containing acicular ferrite and granular bainite is formed, with the acicular ferrite content being 85% or more.

[0053] The rapid cooling rate allows the steel plate to form a fine structure primarily composed of acicular ferrite. Acicular ferrite is a plate-shaped, mixed structure with multiphase characteristics. Its grain boundaries are carbon-rich layers with high potential and corrosion resistance, protecting the ferrite inside. Therefore, steel plate primarily composed of acicular ferrite has excellent corrosion resistance. Furthermore, during the formation process, acicular ferrite forms a supersaturated solid solution, a fine substructure, and multidirectional precipitation, significantly improving the strength and toughness of the steel plate. Acicular ferrite not only ensures the high strength of the steel plate, but also has the lowest ductile-to-brittle transition temperature. Controlled rolling and controlled cooling processes fully utilize strengthening methods such as solid solution strengthening, grain refinement, and precipitation strengthening, effectively improving the overall performance of the steel plate.

[0054] This embodiment provides a corrosion-resistant 460 MPa-class steel plate. This steel plate is manufactured by the above-mentioned manufacturing method. When sampled in accordance with GB / T2975 and subjected to tensile tests and impact tests in accordance with GB / T228 and GB / T229, the steel plate has a yield strength of 460 MPa or more, a tensile strength of 540 to 720 MPa, a fracture elongation of 20% or more, and a -50°C impact absorption energy KV2 of 100 J or more.

[0055] After purifying the molten steel by adding rare earth elements, the maximum length x width of the inclusion in the steel plate is 150 μm 2 Under the conditions of GB / T10561, the grades of A, B, C, and D inclusions are all 1.5 or less, and the total grade of A, B, C, and D inclusions is 3.0 or less.

[0056] Average corrosion weight loss rate under GB / T10125-2012 test conditions≦1.315g / (m 2 ·h).

[0057] The -50°C impact absorption energy KV2 of the heat-affected zone after welding when the welding heat input is ≦80 kJ / cm is ≧80 J.

[0058] As described above, this embodiment employs a corrosion-resistant alloying composition system with the combined addition of Cr, Ni, Mo, Cu, and P, ensuring corrosion resistance and weldability while conserving the amount of valuable alloying elements. While strictly controlling impurity elements, one or more rare earth elements selected from La, Ce, Pr, and Nd are used to purify the molten steel, further improving corrosion resistance. Based on the comprehensive chemical composition design, precise control of the rolling and cooling process parameters allows for precise control of the steel plate's structure, inclusion content, and size, resulting in a 460 MPa-class marine atmospheric corrosion-resistant steel plate for wind power towers with excellent overall performance.

[0059] Specific embodiments of the present invention will be further described below with reference to four examples and three comparative examples.

[0060] Table 1 shows the chemical compositions of the steel sheets of Examples 1 to 4 and Comparative Examples 1 to 3.

[0061] In Comparative Example 1, the rare earth element content is below the 0.02 to 0.03% required by the present invention.

[0062] In Comparative Example 2, the P content is below the 0.015 to 0.025% required by the present invention, the Cr content is below the 0.50 to 0.60% required by the present invention, the Ni content is below the 0.30 to 0.40% required by the present invention, the Cu content is below the 0.40 to 0.45% required by the present invention, and the atmospheric corrosion resistance index I is below the 6.5 required by the present invention.

[0063] Comparative Example 3 is a general Q460 high strength steel, which does not contain corrosion-resistant elements such as Ni, Cu, Mo, or rare earth elements, and the P and Cr contents are below the requirements of the present invention.

[0064] [Table 1]

[0065] The steel sheets of Examples 1 to 4 and Comparative Examples 1 to 3 were all produced by the above-mentioned production method, and steel sheets having the thicknesses shown in Table 2 were produced using two-stage controlled rolling in the rolling process.

[0066] In the controlled rolling and cooling process, the reduction ratio, finish rolling temperature, final cooling temperature, and cooling rate in the austenite recrystallization region rolling stage of Examples 1 to 4 and Comparative Examples 1 to 3 are as shown in Table 2.

[0067] [Table 2]

[0068] After cooling each of the steel plates of Examples 1 to 4 and Comparative Examples 1 to 3, sampling inspection was carried out.

[0069] The results of the inclusion inspection for Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Table 3. The length x width of the largest inclusion in the steel for Examples 1 to 4 and Comparative Example 2 was 150 μm. 2 Under the conditions of the GB / T10561 standard, the evaluation of A, B, C, and D types of inclusions was all 1.5 or less, and the total evaluation of the four types of inclusions (A+B+C+D) was 3.0 or less. Since Comparative Examples 1 and 3 do not contain rare earth elements, the total evaluation of the four types of inclusions in the steel sheet exceeded 3.0, and the length x width of the largest inclusion in the steel sheet was 150 μm. 2 It exceeded that.

[0070] [Table 3]

[0071] Sampling was performed in accordance with GB / T2975, and tensile tests and impact tests were performed in accordance with GB / T228 and GB / T229. Table 4 shows the yield strength, tensile strength, fracture elongation, and impact absorption energy KV2 at a low temperature of -50°C of the steel plates of Examples 1 to 4 and Comparative Examples 1 to 3. The steel plates of Examples 1 to 4 and Comparative Examples 1 and 3 had a yield strength of 460 MPa or more, a tensile strength of 540 to 720 MPa, a fracture elongation of 20% or more, and an impact absorption energy KV2 of 100 J or more at -50°C. In Comparative Example 2, the carbon equivalent was less than 0.39, and therefore the yield strength of the steel plate was less than 460 MPa and the tensile strength was less than 540 MPa. Comparative Example 3 is a typical Q460 high-strength steel, and its microstructure is acicular ferrite + granular bainite. However, since the acicular ferrite content does not meet the 85% or more required by the present invention, the impact absorption energy KV2 of the steel plate at -50°C was less than 100J.

[0072] The marine atmospheric corrosion resistance of the steel plates of Examples 1 to 4 and Comparative Examples 1 to 3 was measured under conditions of an environmental temperature of 35±2°C and 50±5 g / L of neutral NaCl salt spray corrosion, with reference to GB / T10125-2012 "Artificial Atmospheric Corrosion Test (Salt Spray Test)". The average corrosion weight loss rates of the steel plates after 72 hours of testing are shown in Table 4. The average corrosion weight loss rates of the steel plates of Examples 1 to 4 were 1.079 to 1.315 g / (m 2 The steel plate of Comparative Example 1 suffered from severe pitting corrosion, with an average corrosion weight loss rate of 1.946 g / (m 2 ·h), which was higher than that of the Examples. The average corrosion weight loss rate of Comparative Example 2 was 2.975 g / (m 2 ·h), which was higher than that of the Examples. Comparative Example 3 was made of general Q460 high-strength steel, and had the highest average corrosion weight loss rate of 3.428 g / (m 2 ·h). In Examples 1 to 4, the corrosion rate was reduced by 50% or more compared to that of the general Q460 high strength steel in Comparative Example 3.

[0073] [Table 4]

[0074] For Example 4, two-wire submerged arc welding was performed with a welding heat input of 77±3 kJ / cm. Table 5 shows the results of measuring the −50°C low-temperature impact value at the fusion line (FL), FL+2, FL+5, and FL+20 positions in the heat-affected zone of the welded joint.

[0075] [Table 5]

[0076] It should be noted that although this specification is described according to embodiments, each embodiment does not necessarily include only a single technical solution. This description style is merely for the sake of clarity, and those skilled in the art should understand the specification as a whole. The technical solutions in each embodiment may be appropriately combined to form other embodiments that are understandable to those skilled in the art.

[0077] The detailed description given above is merely a concrete description of possible embodiments of the present invention, and does not limit the scope of protection of the present invention. Any equivalent embodiments or modifications made within the scope of the technical idea of ​​the present invention are also included in the scope of protection of the present invention.

Claims

1. A method for manufacturing a corrosion-resistant 460 MPa class steel plate, The chemical composition of the steel plate includes, in mass percentage, C: 0.06 to 0.09%, Si: 0.2 to 0.3%, Mn: 0.9 to 1.0%, Cr: 0.5 to 0.6%, Ni: 0.30 to 0.40%, Cu: 0.40 to 0.45%, Mo: 0.05 to 0.10%, Nb: 0.02 to 0.04%, Al: 0.02 to 0.04%, P: 0.015 to 0.025%, and rare earth elements: 0.015 to 0.025%, with the remainder being Fe and unavoidable impurities, and the impurity elements are, in mass percentage, S≦0.002%, O≦0.002%, and N≦0.004%, The atmospheric corrosion resistance index I of the steel plate is 6.5 or more, and the atmospheric corrosion resistance index I is I = 26.01 (% Cu) + 3.88 (% Ni) + 1.20 (% Cr) + 1.49 (% Si) + 17.28 (% P) - 7.29 (% Cu) (% Ni) - 9.10 (% Ni) (% P) - 33.39 (% Cu) 2 In the formula, the element symbol in parentheses indicates the mass percentage of the corresponding element, and the % element symbol indicates the mass percentage of the corresponding element multiplied by 100. The manufacturing method includes: a step of obtaining a cast slab by performing steelmaking and casting according to the blending ratio of the chemical components; a step of subjecting the slab to two-stage controlled rolling including a first stage of austenite recrystallization region rolling and a second stage of austenite non-recrystallization region rolling, wherein the rolling reduction in the first stage of austenite recrystallization region rolling is controlled to 50% or more, and the finish rolling temperature in the second stage of austenite non-recrystallization region rolling is controlled to 800±20°C; a step of subjecting the steel plate to a cooling treatment, controlling the cooling rate to form a microstructure containing acicular ferrite and granular bainite in the steel plate, and the content of the acicular ferrite is 85% or more; A method for manufacturing a corrosion-resistant 460 MPa class steel plate comprising:

2. The carbon equivalent CE of the steel plate satisfies 0.39≦CE≦0.42, and the carbon equivalent CE is CE=(%C)+(%Mn) / 6+(%Cr+%Mo+%V) / 5+(%Ni+%Cu) / 15 In the formula, the element symbol in parentheses indicates the mass percentage of the corresponding element, and the % element symbol indicates the mass percentage of the corresponding element multiplied by 100. A method for producing the corrosion-resistant 460 MPa class steel plate according to claim 1.

3. In the chemical composition of the steel sheet, the rare earth element is one or more of La, Ce, Pr, and Nd. A method for producing the corrosion-resistant 460 MPa class steel plate according to claim 1.

4. Further comprising a step of rolling the cast piece into a steel plate having a thickness of 100 mm or less. A method for producing the corrosion-resistant 460 MPa class steel plate according to claim 1.

5. The cooling treatment of the steel plate is The steel plate after rolling is subjected to a water cooling treatment, the cooling rate is controlled to 10 to 28 ° C. / s, and the finish cooling temperature of the steel plate is controlled to 350 ± 30 ° C. A method for producing the corrosion-resistant 460 MPa class steel plate according to claim 1.

6. A corrosion-resistant 460 MPa class steel plate, The chemical composition of the steel plate includes, in mass percentage, C: 0.06 to 0.09%, Si: 0.2 to 0.3%, Mn: 0.9 to 1.0%, Cr: 0.5 to 0.6%, Ni: 0.30 to 0.40%, Cu: 0.40 to 0.45%, Mo: 0.05 to 0.10%, Nb: 0.02 to 0.04%, Al: 0.02 to 0.04%, P: 0.015 to 0.025%, and rare earth elements: 0.015 to 0.025%, with the remainder being Fe and unavoidable impurities, and the impurity elements are, in mass percentage, S≦0.002%, O≦0.002%, and N≦0.004%, The microstructure of the steel sheet includes acicular ferrite and granular bainite, and the content of the acicular ferrite is 85% or more. Under the GB / T10125-2012 test conditions, the average corrosion weight loss rate of the steel sheet is 1.315 g / (m 2 h) or less, and when sampled in accordance with GB / T2975 and subjected to a tensile test and an impact test in accordance with GB / T228 and GB / T229, the steel plate has a yield strength of 460 MPa or more, a tensile strength of 540 to 720 MPa, a breaking elongation of 20% or more, and a -50°C impact absorption energy KV2 of 100 J or more; Corrosion-resistant 460MPa-class steel plate.

7. The length x width of the largest inclusion in the steel plate is 150 μm 2 or less, and the grades of A, B, C, and D inclusions under GB / T10561 conditions are all 1.5 or less, and the total grade of A, B, C, and D inclusions is 3.0 or less. The corrosion-resistant 460 MPa class steel plate according to claim 6.

8. The steel plate has a -50°C impact absorption energy KV2 of 80J or more in the heat-affected zone after welding when the welding heat input is 80kJ / cm or less. The corrosion-resistant 460 MPa class steel plate according to claim 6.

9. The thickness of the steel plate is 100 mm or less. The corrosion-resistant 460 MPa class steel plate according to claim 6.

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