High-performance brittle-crack-resistant steel for nuclear power pressure-bearing equipment and manufacturing method thereof

Abstract

The invention discloses high-performance brittle-crack-resistant steel for nuclear power pressure-bearing equipment and a manufacturing method of the high-performance brittle-crack-resistant steel. The high-performance brittle-crack-resistant steel comprises the following chemical components: 0.16%-0.24% of C, 0.20%-0.40% of Si, 1.25%-1.60% of Mn, less than or equal to 0.010% of P, less than or equal to 0.005% of S, 0.25%-0.45% of Cr, 0.25%-0.40% of Cu, 0.30%-0.50% of Ni, 0.005%-0.008% of Ca, 0.65%-1.25% of Mo and 0.04%-0.08% of V. The manufacturing method comprises the steps of smelting, continuous casting, heating rolling and heat treatment. The thickness of the steel plate is 30-120 mm, and through hardening and tempering and simulated postweld heat treatment, the normal-temperature tensile yield strength is larger than or equal to 620 MPa, the tensile strength is larger than or equal to 770 MPa, the 360-DEG C high-temperature tensile yield strength is larger than or equal to 518 MPa, the tensile strength is larger than or equal to 618 MPa, the impact absorption energy at the temperature of-40 DEG C is 195 J or above, the non-ductility transition temperature is smaller than or equal to-52 DEG C, and the grain size is larger than or equal to 8.5 grades. The steel provided by the invention has good mechanical properties and brittle crack resistance, and fully meets the requirements of steel for pressure-bearing equipment of a nuclear power unit.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal material production, and in particular relates to high-performance brittle crack-resistant steel for nuclear power pressure equipment and a manufacturing method thereof. Background Art

[0002] In the context of global carbon reduction, nuclear energy, as a low-carbon, clean energy source, offers advantages over other renewable energy sources, such as high density, cleanliness, low carbon emissions, and long-term stable operation. It can serve as a baseload energy source that provides continuous and reliable electricity supply. Currently, my country has 26 nuclear power units under construction, with a total installed capacity of 30.3 million kilowatts, maintaining its position as the world's largest. The proportion of nuclear power generation in my country's total electricity generation is on an upward trend, rising from 2.11% in 2013 to 4.86% in 2023, but remains well below the global average of 9.6%. Therefore, China's nuclear power development still holds enormous potential.

[0003] Nuclear power pressure equipment steel is used in nuclear reactors for pressure vessels, pressurizers, various pipelines, boxes, tanks, and other important nuclear-grade equipment. It plays a vital role in the safe operation of nuclear power plants. It requires not only high strength and toughness, but also high-temperature resistance and ease of welding. Due to its critical application location, the overall quality and performance stability of the steel plate are very stringent. Its operational safety and performance stability directly affect the safe operation of the equipment and the entire unit. With the national sustainable development strategy, nuclear power pressure equipment is gradually moving towards high quality and integration, which requires materials with higher strength and better overall performance.

[0004] At present, many patents have been developed for nuclear power steel at home and abroad, and the main ones related to this invention include the following:

[0005] Wuhan Iron and Steel Group Corporation filed an application titled "Steel for -50°C Nuclear Power Pressure Equipment and Production Method" (Application No. CN201110117612.5). The chemical composition and weight percentages of the steel are: C: 0.05-0.15%, Si: 0.25-0.50%, Mn: 1.00-1.28%, Alt: 0.02-0.04%, Ni: 0.40-0.80%, Cu: 0.10-0.24%, Mo: 0.10-0.20%, V: 0.02-0.05%, with the remainder being Fe and unavoidable impurities. The production steps are: using a clean steel smelting process; continuous casting or electroslag remelting of the ingot; cooling the ingot to room temperature; heating and holding the ingot; rough rolling; finish rolling; conventional quenching and tempering; and natural cooling to room temperature. This invention can improve the safety and reliability of nuclear power plant operations. It exhibits high toughness, high strength, low radiation embrittlement, excellent tensile properties, and weldability at -50°C, with a tensile strength exceeding 585 MPa. However, the steel plates produced by this invention have relatively low strength properties, and some are produced using electroslag remelting, which increases production costs. This makes it unsuitable for large-scale production of steel for nuclear power pressure equipment.

[0006] Wuhan Iron and Steel Group Corporation applied for "High-toughness, high-ductility, low-irradiation embrittlement steel for nuclear power pressure equipment and its manufacturing method" (application number: CN201010211184.8). The chemical composition of this steel, calculated by weight percentage, is as follows: C: 0.08~0.15%, Si: 0.20~0.35%, Mn: 0.80~1.60%, P≤0.012%, S≤0.005%, Alt: 0.01~0.05%, Ti: 0.008~0.015%, N≤0.010%, and the rest is Fe and unavoidable impurities; the chemical composition of this steel also meets the following requirements: Ni+Cr+Mo+Cu≤0.70; Alt / N≥2.0; Cu+6Sn≤0.30; Sn+Sb+As+Pb≤0.020. This invention designs a controlled-rolling and normalizing manufacturing method based on the varying delivery conditions and thicknesses of steel products. This method simplifies the rolling process, produces a high yield of steel plates, and is well-suited for large-scale production. It can be widely used in the manufacture of second-generation, second-improved, and third-generation nuclear power pressure equipment. However, the maximum thickness of the steel produced by this invention is 60 mm, and the performance of the steel after normalizing heat treatment is relatively low, making it difficult to meet the technical requirements of nuclear power pressure equipment.

[0007] Ansteel Co., Ltd. filed an application for "Steel for Nuclear Power Pressure Equipment and Its Manufacturing Method" (Application Number: CN201110417360.8). The steel's chemical composition by weight is as follows: C: 0.12-0.18%, Si: 0.15-0.35%, Mn: 1.20-1.65%, P ≤ 0.015%, S ≤ 0.010%, Ni: 0.50-0.85%, Cr ≤ 0.15%, Al: 0.020-0.050%, V ≤ 0.02%, Ti ≤ 0.02%. The remainder is Fe and unavoidable impurities. Non-metallic inclusions in the steel are also controlled to ensure that Class A, B, C, and D inclusions are ≤ 1.5. The manufacturing method primarily involves steel smelting, rolling, and tempering. By further optimizing the chemical composition, heat treatment process, and reducing gas and non-metallic inclusions in the steel, the mechanical properties of the steel plate remain high in the heat-treated state, simulated post-weld heat treatment state, and at 200°C. Simultaneously, the 0°C impact absorption energy is also maintained at a high level, demonstrating a good match between the steel plate's strength and toughness. However, the steel plate produced by this invention has low strength properties, and some of the production is done through spot-casting, which increases production costs. This makes it unsuitable for the production of steel for large-scale nuclear power pressure equipment.

[0008] Ansteel Co., Ltd. filed an application for "A Thick, Z-Direction, Easily Weldable Steel for Nuclear Power Pressure Equipment and Its Preparation Method" (Application Number: CN202310586098.2). The chemical composition of the steel by weight is as follows: C: 0.06-0.12%, Si: 0.25-0.40%, Mn: 1.15-1.55%, P ≤ 0.015%, S ≤ 0.005%, Ni: 0.40-0.65%, Mo: 0.25-0.45%, V: 0.04-0.06%, Als: 0.020-0.050%, Nb: 0.015-0.035%, Ti: 0.015-0.025%, RE: 0.004-0.018%, with the balance being Fe and unavoidable impurities. The steel plate provided by this invention is a high-strength steel plate with a dense structure, clean quality, and uniform properties, and is suitable for use in thick, easily weldable nuclear power pressure equipment. However, the component design concept and manufacturing process of this invention are different from those of the present invention, and it does not pay attention to the low-temperature toughness and brittle crack resistance at lower operating temperatures. Summary of the Invention

[0009] The purpose of the present invention is to provide a high-performance steel for nuclear power pressure equipment that is resistant to brittle cracks and a method for manufacturing the same. By strictly controlling the chemical composition of the steel and using appropriate smelting, heating, rolling and heat treatment processes, the produced steel plates not only have good mechanical properties in the tempered state and simulated post-weld heat treatment, but also have excellent resistance to brittle cracks, which can fully meet the needs of steel for pressure equipment of nuclear power units.

[0010] The present invention provides a high-performance steel for nuclear power pressure equipment that is resistant to brittle cracks. The specific technical solution is as follows: the steel comprises the following components by weight: C: 0.16-0.24%, Si: 0.20-0.40%, Mn: 1.25-1.60%, P≤0.010%, S≤0.005%, Cr: 0.25-0.45%, Cu: 0.25-0.40%, Ni: 0.30-0.50%, Ca: 0.005-0.008%, Mo: 0.65-1.25%, V: 0.04-0.08%, and the remainder is Fe and unavoidable impurities.

[0011] The present invention adopts the above-mentioned component design reasons as follows:

[0012] C: In the present invention, C not only dissolves in the matrix to provide solid solution strengthening, but also interacts with alloying elements to form fine alloy carbides, refining the grain size. This strongly hinders dislocation slip during deformation, significantly increasing the strength of the steel. To improve the low-temperature toughness and weldability of the steel plate, it is desirable to keep the C content in the steel at a low level. However, from the perspective of the steel plate's hardenability and strength-toughness balance, the C content should not be too low. Therefore, the C content in the steel of the present invention is designed to be 0.16-0.24%.

[0013] Si: In steel, Si primarily acts as a reducing agent and deoxidizer. It also improves the steel's strength and hardenability, enhances the stability of retained austenite, thereby increasing its toughness and effectively inhibiting crack initiation and propagation. However, excessive Si can cause severe segregation, resulting in anisotropy in the steel and adversely affecting its structural uniformity. Therefore, the present invention requires a Si content of 0.20-0.40%.

[0014] Mn: Mn is a good deoxidizer and desulfurizer, effectively eliminating or reducing the hot brittleness of steel caused by sulfur, thereby improving the steel's hot workability. Furthermore, Mn and Fe form a solid solution in steel, effectively increasing the strength of the steel plate through solid solution strengthening. Furthermore, Mn lowers the critical transition temperature in steel, refining the grain size and indirectly improving the steel's strength. However, excessive Mn content can easily lead to elemental enrichment and segregation, resulting in uneven composition and structure of the matrix material and the development of brittle cracks. Therefore, the present invention requires that the Mn content in steel be controlled between 1.25% and 1.60%.

[0015] P and S: harmful elements in steel. Too much P and S will affect the homogeneity and purity of the steel. P will cause structural segregation and have a significant adverse effect on low-temperature toughness. It is easy to segregate at the austenite grain boundaries, which weakens the interatomic bonding force at the grain boundaries of the matrix material and causes the material to have high temper brittleness. S is distributed in the steel in the form of MnS. MnS elongates along the rolling direction during hot rolling, which significantly reduces the transverse mechanical properties of the steel, aggravates the anisotropy of the steel, reduces the ductility and toughness of the steel, and causes cracks during rolling. Therefore, the lower the content of P and S, the better. However, considering the process conditions and cost factors of steelmaking, the present invention requires controlling P≤0.010% and S≤0.005% in the steel.

[0016] Cr: Cr improves the hardenability of steel and has a secondary strengthening effect, promoting alloying and increasing the strength of the steel without making it brittle. Furthermore, Cr easily combines with carbon to form various carbides. These carbides are distributed within the steel matrix and pin dislocations, delaying the recovery of the martensitic matrix, thereby improving the material's high-temperature performance. This plays a significant role in enhancing the strength and thermal stability of the nuclear power steel of the present invention. However, if the Cr content is too high, other alloying elements in the carbides will be replaced by Cr during high-temperature tempering or simulated post-weld heat treatment, forming coarse, softer high-Cr carbides, which reduce the steel's thermal strength. Therefore, the present invention requires a Cr content of 0.25-0.45% in the steel.

[0017] Cu: The present invention adds an appropriate amount of Cu, causing the copper phase particles to grow into rod-shaped copper particles, which acts as precipitation strengthening, increasing the strength of the steel and improving the fluidity of the molten steel, thereby contributing to the uniformity of the billet. However, if the Cu content is too high, exceeding the solubility of the matrix, some Cu will precipitate as ε-Cu, causing stress concentration during impact, resulting in a certain loss of impact toughness and causing hot brittleness in the steel, making hot rolling difficult. Therefore, the present invention requires that the Cu content in the steel be controlled between 0.25% and 0.40%.

[0018] Ni: On the one hand, Ni can significantly improve the strength of steel, and on the other hand, it always keeps the toughness at an extremely high level and reduces the tough-to-brittle transition temperature of the material. Ni can prevent grain growth at high temperatures and maintain a fine grain structure. At the same time, the lattice constant of Ni is similar to that of γ-Fe, and it can form a continuous solid solution, which can lower the critical point and increase the stability of austenite, and especially improve the hardenability of steel. During the tempering process, the Ni element will be enriched around the carbide, hindering the continued diffusion of C atoms in the ferrite around the carbide, thereby hindering the growth of carbide, reducing stress concentration, and making the surface of the steel less prone to cracks. However, too high a Ni content will increase production costs, and will also cause lattice distortion, reduce the diffusion rate of C in the matrix, hinder the phase transformation kinetics, and delay the dissolution process of undissolved carbides into austenite. Therefore, the present invention requires that the Ni content in the steel be controlled to be 0.30~0.50%.

[0019] Ca: Ca in steel can refine the alloy's dendritic structure, eliminating structural anisotropy and refining the grain size. It can also improve the composition, quantity, and morphology of non-metallic inclusions, thereby enhancing the steel's high-temperature resistance, impact toughness, and resistance to brittle cracking. Furthermore, adding a certain amount of Ca to steel can reduce smelting difficulty, significantly increase molten steel fluidity, and improve the surface quality of the ingot. Therefore, the present invention selects a Ca content of 0.005-0.008%.

[0020] Mo: Mo enhances the strength and hardness of steel by solid solution strengthening. Mo dissolved in the matrix will segregate around dislocations to reduce the degree of collective lattice distortion, hinder dislocation movement, play a pinning role, increase the tempering stability of the material, and enable parts to be tempered at higher temperatures, thereby more effectively eliminating residual stress and improving plasticity. In addition, the M6C carbides precipitated during tempering are small in size and dispersed in distribution, which can improve the thermal stability of steel. At the same time, for materials with large thickness and large cross-section, it can improve the hardenability of steel and make the material deeply quenched and hardened. However, if the Mo content is too high, the M6C carbide particles will increase, making the material brittle and reducing toughness. Therefore, the present invention chooses to add a Mo content of 0.65~1.25%.

[0021] V: V and C have a strong binding force, easily forming fine carbides in steel. During the austenitization process, they can pin grain boundaries and prevent austenite grain growth, effectively reducing the matrix grain size and achieving a fine grain strengthening effect. These carbides are evenly dispersed throughout the material and have high melting points, high hardness, strong stability, and are not prone to growth. During high-temperature tempering, they can precipitate from the matrix, promoting secondary hardening of the material and improving its high-temperature stability. Furthermore, V has high thermal stability and is not prone to aggregation and growth, tending to a fine and dispersed distribution state, giving the material excellent high-temperature strength. However, if the V content is too high, more V-based carbides are formed, resulting in a decrease in the amount of C dissolved into the matrix during austenitization, reducing the stability of the supercooled austenite and, in turn, reducing the hardenability of the steel. Furthermore, the addition of excessive V can reduce the plastic toughness of the material. Therefore, the V content added in the present invention is 0.04-0.08%.

[0022] The present invention controls the Mo+V content to 0.70-1.30%. This, on the one hand, increases the content of MC and M2C carbides precipitated during tempering. These two carbides are finely sized and dispersed, significantly contributing to secondary hardening, helping the material's surface layer achieve high hardness and a certain degree of plasticity, effectively improving the steel's resistance to brittle cracking. It also helps improve the material's high-temperature stability. Uncontrolled Mo and V additions restrict the precipitation of uniformly dispersed, fine, and stable carbides, adversely affecting the material's thermal stability and high-temperature performance.

[0023] On this basis, a certain amount of Cr and Ni are added for a composite effect. On the one hand, Cr can improve the hardenability of steel and ensure the uniformity of the structural properties in the thickness direction. On the other hand, it can reduce the degree of decarburization and oxidation. In addition, without reducing the plastic toughness of the steel, its strengthening effect can be guaranteed. If Cr is not controlled, Cr and C will form too many high-Cr carbides, reducing the formation of VC, reducing the thermal strength of the material, and also preventing the formation of V4C3, delaying the coherent precipitation of Mo2C. The interaction between V4C3 and Mo2C will enhance the high temperature strength and tempering resistance of the steel. Ni promotes the precipitation of V-containing MC carbides in the steel. The fine MC carbides are stable in size and have a better pinning effect on dislocations. A large number of nano-scale carbides can be precipitated during the tempering process, which has a significant pinning effect on dislocations. Through the joint action of Ni and V, M can also be delayed. 23 The precipitation and transformation of C6 effectively hinder the coarsening and transformation process of fine carbides, improve the thermal stability of the material, and compensate for the adverse effects of the V element on the plastic toughness of the mold steel of the present invention.

[0024] The present invention also provides a method for manufacturing high-performance brittle crack-resistant steel for nuclear power pressure equipment. To implement the present invention, the following technical measures need to be taken in the production process, including smelting, continuous casting, hot rolling and heat treatment, among which:

[0025] Hot rolling: The heating temperature of the ingot is controlled at 1150-1200°C. After the ingot is discharged from the furnace, high-pressure water is used to remove phosphorus. The steel is then rolled in two stages: the recrystallization zone and the non-recrystallization zone. The first stage, rolling in the recrystallization zone, consists of 4-5 passes with a reduction of 18% or more for each pass. This breaks up the coarse columnar crystals and forms fine, uniform grains. The starting rolling temperature is 1050-1100°C, and the finishing rolling temperature is 1020-1070°C. The second stage, rolling in the non-recrystallization zone, consists of 3-4 passes with a reduction of 10% or more for each pass. The starting rolling temperature is 970-1020°C, and the finishing rolling temperature is 920-970°C. The steel plate thickness produced is 30-120 mm.

[0026] Heat Treatment: After rolling, the steel is quenched at 900-950°C for 2-4 hours, followed by water cooling to room temperature. This quenching process allows carbides at the grain boundaries to diffuse completely into the austenite grains at high temperatures, which contributes to the refinement of the steel plate structure while retaining a large number of dislocations in the structure, ensuring high strength in the quenched steel plate.

[0027] After the steel plate is quenched, it is subjected to secondary low-temperature quenching at a temperature of 750-780 °C and a holding time of 1-4 h. The purpose is to obtain an appropriate amount of evenly distributed fine ferrite structure to inhibit crack propagation. A lower tempering temperature can be used subsequently, which has higher toughness, inhibits stress concentration, and hinders crack initiation and propagation. At the same time, it can reduce the segregation of harmful impurity elements at the austenite grain boundaries, play a role in purifying the grain boundaries, and is beneficial to increase strength and toughness and reduce high-temperature temper brittleness.

[0028] After the above heat treatments are completed, the steel plate undergoes tempering at a holding temperature of 580-620°C for 1.5-3 hours. After exiting the furnace, the plate is air-cooled to room temperature. The tempering process eliminates residual stress and homogenizes the microstructure, which helps improve material strength while also maintaining good toughness.

[0029] Furthermore, the smelting process utilizes deep desulfurization of molten iron and converter smelting. Due to the high Mo content designed into the present invention, the converter tapping temperature is controlled between 1640°C and 1660°C to increase the Mo content of the final converter molten steel, improve the alloy yield, and prevent corrosion of the furnace lining at high temperatures. Bottom argon is blown at the beginning of refining to fully float and remove inclusions in the molten steel, accelerate alloy diffusion, and ensure uniform composition of the molten steel. Prior to entering the RH process, the ladle is maintained at a static argon purge time of 8-15 minutes at a flow rate of 205-220 L / min. RH vacuum treatment is then performed, with a vacuum degree of <0.2 kPa and a vacuum hold time of ≥15 minutes. Steel is then tapped at a temperature of 1560-1570°C.

[0030] Furthermore, the continuous casting pouring temperature is 1530-1540°C, and the tundish superheat is 15-35°C. To promote densification and homogenization of the internal structure of the ingot, thereby eliminating defects such as segregation and porosity, a heavy reduction method is used at the end of the continuous casting process, with the reduction controlled at 15-22 mm. The secondary cooling water temperature and casting speed are strictly controlled, with the secondary cooling water temperature maintained at 20-25°C and the casting speed at 0.9-1.2 m / min, fully ensuring the internal and external quality of the ingot. After the continuous casting is completed, the ingots are stacked and slowly cooled for at least 48 hours. The thickness of the ingots is 300-400 mm.

[0031] The steel grade of this invention exhibits high mechanical properties in both quenching and tempering heat treatment and simulated post-weld heat treatment. Under different conditions, the steel plate exhibits a room-temperature tensile yield strength of ≥620 MPa and a tensile strength of ≥770 MPa, a high-temperature tensile yield strength of ≥518 MPa and a tensile strength of ≥618 MPa at 360°C, an impact energy absorption of ≥195 J at -40°C, a non-ductile transition temperature of ≤-52°C, and a grain size of ≥8.5. The results demonstrate uniform and stable microstructure and properties, and the plate maintains good strength even after simulated post-weld heat treatment, fully meeting the technical requirements for steel used in nuclear power pressure equipment.

[0032] The present invention provides a high-performance brittle crack-resistant steel for nuclear power pressure equipment and a manufacturing method thereof. The produced steel plate has a thickness of 30 to 120 mm, and the width and length can be produced according to actual needs.

[0033] Compared with the prior art, the beneficial effects are as follows:

[0034] (1) The steel plate of the present invention adopts the design concept of low C and high Mn, and at the same time adds appropriate amounts of alloying elements such as Cr, Ni, Mo, and V to work together, so that the continuous casting billet has a good and uniform cast structure, ensuring that the steel plate has good hardenability and resistance to brittle cracks. Various carbides formed during the subsequent heat treatment process are dispersed in the steel matrix, playing an important role in improving the strength and toughness of the nuclear power steel of the present invention.

[0035] (2) Through the optimization design of chemical composition, combined with appropriate rolling and heat treatment processes, not only the process flow is shortened, but also the carbides can be completely diffused into the austenite grains at high temperatures, the organizational composition is more uniform, the grains are fine, and the carbides are finely and evenly dispersed. The strength index of the steel plate is guaranteed by the refinement of the organization, so that the steel plate still has good strength and toughness after simulated post-weld heat treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 : is a typical metallographic structure diagram (tempered troostite) of the embodiment. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The description of the following embodiments is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0038] The following examples are intended only to provide some preferred embodiments of the present invention and are not intended to limit the scope of the invention or its technical approach. Table 1 lists the chemical composition of the steel produced in each example, Table 2 lists the smelting and continuous casting process parameters for each example, Table 3 lists the rolling heat treatment process parameters for each example, and Table 4 lists the mechanical properties of the steel plates produced in each example.

[0039]

[0040]

[0041]

[0042] The mechanical properties of the steel plates are shown in Table 4.

[0043] The room temperature tensile yield strength is ≥620 MPa, the tensile strength is ≥770 MPa, the high temperature tensile yield strength at 360 ℃ is ≥518 MPa, the tensile strength is ≥618 MPa, the impact absorption energy at -40 ℃ is above 195 J, the non-ductile transition temperature of the steel plate is ≤-52 ℃, and the grain size of the steel plate is ≥8.5.

[0044]

[0045] Through the mechanical property test of 30~120 mm specification steel plates in different states, the results all meet the index requirements and fully meet the requirements for nuclear power pressure equipment manufacturing.

Claims

1. A high-performance steel for nuclear power pressure equipment with brittle crack resistance, characterized in that: The chemical composition of the steel plate is: C: 0.16%~0.24%, Si: 0.20%~0.40%, Mn: 1.25%~1.60%, P≤0.010%, S≤0.005%, Cr: 0.25%~0.45%, Cu: 0.25%~0.40%, Ni: 0.30%~0.50%, Ca: 0.005%~0.008%, Mo: 0.65%~1.25%, V: 0.04%~0.08%, and the rest is Fe and inevitable inclusions.

2. The high-performance brittle crack-resistant steel for nuclear power pressure equipment according to claim 1, characterized in that: The thickness of the steel plates produced is 30~120 mm.

3. The high-performance brittle crack-resistant steel for nuclear power pressure equipment according to claim 1, characterized in that: The steel plate shall have a room temperature tensile yield strength ≥620 MPa and a tensile strength ≥770 MPa after quenching and tempering heat treatment and simulated post-weld heat treatment, a high temperature tensile yield strength ≥518 MPa and a tensile strength ≥618 MPa at 360°C, an impact absorption energy at -40°C above 195 J, a non-ductile transition temperature ≤-52°C, and a grain size ≥8.

5.

4. A method for manufacturing the high-performance brittle crack-resistant steel for nuclear power pressure equipment according to any one of claims 1 to 3, comprising smelting, continuous casting, hot rolling and heat treatment, characterized in that: Hot rolling: The heating temperature of the ingot is controlled at 1150~1200℃, and a two-stage rolling process is adopted. The first stage is rolling in the recrystallization zone, with 4~5 rolling passes, and the reduction rate of each pass is controlled at ≥18%, the starting rolling temperature is 1050~1100℃, and the final rolling temperature is 1020~1070℃. The second stage is rolling in the non-recrystallization zone, with 3~4 rolling passes, and the reduction rate of each pass is controlled at ≥10%, the starting rolling temperature is 970~1020℃, and the final rolling temperature is controlled at 920~970℃. Heat treatment: After rolling, quenching heat treatment is adopted, the quenching temperature is 900~950℃, the heat preservation time is 2~4 hours, and the steel plate is water-cooled to room temperature; after the steel plate quenching is completed, a secondary low-temperature quenching is carried out, the quenching temperature is 750~780℃, and the heat preservation time is 1~4 hours; after the steel plate heat treatment is completed, tempering heat treatment is required, the tempering heat preservation temperature is 580~620℃, the heat preservation time is 1.5~3 hours, and the steel plate is air-cooled to room temperature after being taken out of the furnace.

5. The method for manufacturing high-performance brittle crack-resistant steel for nuclear power pressure equipment according to claim 4, characterized in that: The smelting process adopts deep desulfurization treatment of molten iron, converter smelting, and steel tapping temperature of 1640~1660℃. Before entering RH, the static argon blowing time of the ladle is guaranteed to be 8~15 minutes, and the argon blowing flow rate is 205~220 L / min. After that, RH vacuum treatment is carried out, the vacuum degree is less than 0.2 kPa, the vacuum holding time is ≥15 minutes, and the temperature reaches 1560-1570℃ for steel tapping.

6. The method for manufacturing high-performance brittle crack resistant steel for nuclear power pressure equipment according to claim 4, characterized in that: The continuous casting pouring temperature is 1530~1540 ℃, the tundish superheat is 15~35 ℃, the end adopts the heavy reduction method, the reduction amount is controlled at 15~22 mm, the secondary cooling water temperature is controlled at 20~25 ℃, and the casting speed is controlled at 0.9~1.2 m / min.

7. The method for manufacturing high-performance brittle crack resistant steel for nuclear power pressure equipment according to claim 6, characterized in that: The continuous casting slabs are stacked and slowly cooled for more than 48 hours after coming off the production line. The thickness of the continuous casting slabs is 300~400 mm.

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