Highly homogenized steel for nuclear island equipment with excellent high-temperature oxidation resistance and manufacturing method thereof

Abstract

The application belongs to the technical field of metal materials, and provides high-homogenization nuclear island equipment steel with excellent high-temperature oxidation resistance and a manufacturing method thereof; through the joint action of Si, Ni, Cr and Mo and the cooperation of Nb, Zr and Re in the component design, the steel plate has high oxidation resistance while having good strength and toughness; the manufacturing method comprises smelting, continuous casting, electroslag remelting, forging, heating, rolling, cooling and heat treatment; the nuclear island equipment steel prepared by the application has not only good strength and toughness and high-temperature oxidation resistance, but also excellent comprehensive performance, and can fully meet the requirement of high service safety of the nuclear island equipment.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials, and in particular relates to a highly homogeneous steel for nuclear island equipment with excellent high-temperature oxidation resistance and its manufacturing method. Background Technology

[0002] Key equipment within the pressurized water reactor nuclear island, such as steam generators, pressurizers, and safety injection tanks, serve as core components of the primary circuit pressure boundary and operate under harsh environments of high temperature, high pressure, and neutron irradiation for extended periods. These devices are typically manufactured using low-alloy high-strength steel. In addition to possessing conventional mechanical and processing properties, this low-alloy high-strength steel must also exhibit high microstructure homogeneity and excellent resistance to high-temperature oxidation.

[0003] However, existing technologies still face severe challenges in practical engineering applications, mainly due to the contradiction between material preparation processes and service reliability. On the one hand, the industrial production of steel plates inevitably requires multiple rounds of high-temperature heating and heat treatment. If existing heating processes lack precise oxidation control, they can easily lead to severe oxidation burn-off and decarburization on the steel plate surface. This surface damage not only destroys the geometric integrity of the material but also, due to stress concentration effects during service, induces the initiation and propagation of early fatigue cracks, directly threatening the operational safety of nuclear power units.

[0004] On the other hand, nuclear island equipment places extremely high demands on the homogeneity of materials. Traditional manufacturing processes struggle to completely eliminate microstructural differences along the thickness of steel plates. This heterogeneity, under the combined effects of high temperature and intense radiation, accelerates the degradation of material properties, such as irradiation swelling or embrittlement. Existing low-alloy steel materials often fail to simultaneously meet the dual requirements of "high-temperature oxidation resistance on the surface" and "high homogeneity of the bulk material."

[0005] Therefore, developing a type of steel for nuclear island equipment that can suppress surface oxidation and decarburization during high-temperature processing, while possessing high homogeneity and excellent toughness, and its manufacturing method, has become an urgent need to improve the intrinsic safety level of nuclear power equipment.

[0006] Currently, there are many patents for nuclear power steel both domestically and internationally, but there are almost none for highly homogeneous nuclear power steel with high-temperature oxidation resistance. According to keyword searches, the following are the main related items.

[0007] Patent document "A Heat Treatment Method for Nuclear Power Steel P460NH with High Temperature Resistance, High Strength, and High Toughness" (Publication No.: CN117512278A) provides a heat treatment method for nuclear power steel P460NH with high temperature resistance, high strength, and high toughness. This method includes staged controlled cooling during quenching and tempering. Staged high-pressure quenching ensures the steel plate has good hardenability, high temperature resistance, and toughness, improving production efficiency and avoiding the temperature unevenness problem associated with multiple quenching processes to increase strength, thus reducing production costs to some extent. The steel plate has a yield strength ≥520MPa, tensile strength ≥570MPa in tensile tests at 200℃ and room temperature, elongation ≥25-30%, and impact energy at 0℃ of 160J-200J. The method does not address the high-temperature oxidation resistance of the steel plate.

[0008] Patent document "Steel for Thick-Grade Nuclear Power Plant Safety Injection Boxes with Excellent High-Temperature Performance and Manufacturing Method Thereof" (Application No.: CN201810717819.8) provides a steel for thick-grade nuclear power plant safety injection boxes with excellent high-temperature performance and a manufacturing method thereof. The steel plate thickness is 80-150 mm, and the chemical composition is as follows: C: 0.14%-0.20%, Si: 0.10%-0.60%, Mn: 0.30%-0.40%, P≤0.008%, S≤0.002%, Mo: 0.30%-0.60%, Ni: 0.45%-0.90%, Cr: 0.50%-0.80%, Cu≤0.05%, Alt≤0.04%, H≤0.00015%, O≤0.0020%, with the remainder being Fe and unavoidable impurities. By rationally controlling the content of chemical elements in steel and reducing the content of gases and non-metallic inclusions, the steel plate can effectively ensure excellent comprehensive mechanical properties. In particular, after 16 hours of simulated post-weld heat treatment, the steel plate's tensile strength at 150℃ and impact resistance at -50℃ still fully meet the manufacturing requirements of nuclear power plant safety injection tank equipment. This does not involve the steel plate's high-temperature oxidation resistance.

[0009] Patent document "A Nuclear Power Steel Plate with Extremely Wide Specifications for High-Temperature Gas-Cooled Reactor Pressure Plate Components and its Preparation Method" (Application No.: 202310925730.1) provides a nuclear power steel plate with extreme wide specifications for high-temperature gas-cooled reactor pressure plate components and its preparation method. The chemical composition and mass percentage of the nuclear power steel plate are as follows: C: 0.10%~0.14%, Si: 0.10%~0.30%, Mn: 0.30%~0.60%, P≤0.006%, S≤0.002%, Cr: 2.05%~2.55%, Mo: 0.80%~1.10%, Nb: 0.01%~0.03%, Alt: 0.020%~0.045%, with the balance being Fe and unavoidable inclusions. This invention utilizes C, Si, and Mn strengthening elements, combined with the addition of Cr, Mo, and Nb alloying elements, and a three-stage rolling + high-temperature tempering heat treatment process to obtain an ultra-wide-specification nuclear power steel plate with a multiphase structure (ferrite + bainite tempered structure), excellent high-temperature resistance up to 570℃, and superior processing performance; it does not involve the high-temperature oxidation resistance of the steel plate. Summary of the Invention

[0010] The purpose of this invention is to overcome the above-mentioned problems and deficiencies and provide a steel plate with a thickness of 60-150 mm, R m >640MPa, R p0.2 >550MPa, A 50 >20%; 150℃ high temperature tensile strength R m >620MPa, R p0.2 A high-homogeneity nuclear island equipment steel with excellent high-temperature oxidation resistance and its manufacturing method, characterized by strength index fluctuations of no more than 1% at 1 / 4 and 1 / 2 of the steel plate thickness and grain size fluctuations of no more than 0.5 grade.

[0011] The objective of this invention is achieved as follows:

[0012] A high-homogeneity steel for nuclear island equipment with excellent high-temperature oxidation resistance, wherein the elemental composition of the steel by mass percentage is as follows: C: 0.15%~0.23%, Si: 0.46%~0.90%, Mn: 0.60%~1.35%, P≤0.008%, S≤0.002%, Ni: 0.20%~0.68%, Cr: 0.95%~2.0%, Mo: 0.50%~1.66%, Nb: 0.05%~0.12%, Zr: 0.20%~0.90%, Re: 0.01%~0.06%, Al: 0.02%~0.06%, with the remainder being Fe and unavoidable impurities.

[0013] Furthermore, in the steel used for the nuclear island equipment, 1.8 < Cr / Si < 2.3.

[0014] Furthermore, the Ni+Cr content in the steel used for the nuclear island equipment is greater than 1.5%.

[0015] Furthermore, the grain size fluctuation at 1 / 4 and 1 / 2 of the thickness of the steel plate used for the nuclear island equipment is no greater than level 0.5.

[0016] Furthermore; the steel plates used for nuclear island equipment are 60–150 mm thick; at room temperature, R m >640MPa, Rp 0.2 >550MPa, A 50 >20%; High-temperature tensile strength R at 150℃ m >620MPa, Rp 0.2 >520MPa; Impact energy KV2 at -20℃ >160J; Oxidation rate at 700℃ ≤0.6mg / cm³ 2 •h; R at 1 / 4 and 1 / 2 thickness of steel plate at room temperature and 150°C m With Rp 0.2 Fluctuations are no greater than 1%.

[0017] The rationale behind the ingredient design is as follows:

[0018] C: Increases the strength of the steel plate; improves the hardenability of the steel plate during quenching, and promotes the uniform formation of martensite in the thickness direction; forms stable carbides with alloying elements, improving the stability of the microstructure and high-temperature strength; excessive carbon content damages the low-temperature toughness, weldability, and high-temperature oxidation resistance of the steel plate. Therefore, the C content in the steel of this invention is designed to be 0.15% to 0.23%.

[0019] Si: Silicon reacts with oxygen at high temperatures to form SiO2, creating a dense oxide layer that effectively prevents further oxygen diffusion and improves the oxidation resistance of heat-resistant steel. When silicon and chromium work together, and the ratio 1.8 < Cr / Si < 2.3 is satisfied, silicon promotes the formation of a Cr2O3 oxide layer, further enhancing oxidation resistance. It also inhibits the formation of the σ phase (a brittle phase) under high Cr conditions, improving the toughness and high-temperature performance stability of the steel plate. In this invention, the Si content is controlled at 0.46%–0.90%.

[0020] Mn forms a substitutional solid solution in steel, improving the room temperature and high temperature strength of the steel plate; it expands the austenite phase region, improves the stability of austenite, and helps maintain the high temperature strength and oxidation resistance of the steel; it also improves the homogenization properties of the steel plate. Because the carbon content in the steel of this invention is relatively high, excessively high manganese content will not only fail to achieve the above-mentioned beneficial effects but will also aggravate core segregation in the steel plate. Therefore, the Mn content in the steel of this invention is controlled at 0.60%–1.35%.

[0021] P: A harmful element in steel, affecting the homogeneity and purity of steel. P can cause segregation of the structure and has a significant adverse effect on low-temperature toughness. The lower the content, the better. However, considering steelmaking conditions and costs, this invention controls the P content in steel to be ≤0.008%.

[0022] S: Harmful element in steel. It easily forms sulfide inclusions in steel, which reduces the impact toughness of steel, impairs welding performance, and aggravates defects such as center segregation and porosity. Therefore, this invention requires S≤0.002%.

[0023] Ni (Ni) can improve the low-temperature toughness of steel and lower the brittle transition temperature. Nickel and chromium work together; when Ni + Cr > 1.5%, they can promote the formation of the Cr2O3 oxide layer, enhancing the steel's oxidation resistance. At high temperatures, nickel can affect the precipitation and distribution of carbides, improving their stability at high temperatures, preventing carbide coarsening and growth, reducing stress concentration, and inhibiting crack initiation. In this invention, the Ni content in the steel is controlled at 0.20%–0.68%.

[0024] Cr: At high temperatures, it reacts with oxygen to form a dense Cr2O3 oxide layer, which effectively prevents further oxygen diffusion and significantly improves the oxidation resistance of heat-resistant steel; it can improve the hardenability of steel and has a secondary strengthening effect, promotes alloying, and increases the strength of steel; chromium combines with carbon to form stable carbides (such as Cr2O3). 23 C6, Cr7C3, etc., these carbides have high stability at high temperatures and can effectively hinder grain boundary slip and dislocation movement, thereby improving the high-temperature strength and performance stability of the steel. The Cr content in the steel of this invention is controlled at 0.95% to 2.0%.

[0025] Mo: Molybdenum dissolves in the iron matrix to form a substitutional solid solution, significantly improving the strength and hardness of steel. At high temperatures, the solid solution strengthening effect of molybdenum remains effective, contributing to increased high-temperature strength. It improves the hardenability of steel plates, promotes the formation and homogenization of martensite along the thickness section, inhibits the formation of the σ phase (a brittle phase) under high Cr conditions, and improves the toughness and high-temperature stability of steel. At high temperatures, it stabilizes carbides in steel, delaying their coarsening and decomposition, thereby improving high-temperature strength and microstructure stability. The Mo content in the steel of this invention is controlled at 0.50%–1.66%.

[0026] Niobium combines with carbon and nitrogen to form fine NbC, NbN, or Nb(C,N) particles. These particles can pin grain boundaries at high temperatures, inhibiting grain growth and thus refining the grain size. Niobium-formed carbonitrides (such as NbC and NbN) exhibit high stability at high temperatures, effectively hindering dislocation movement and grain boundary slip, thereby improving the high-temperature strength and performance stability of the steel. Niobium can also reduce embrittlement in the weld heat-affected zone, improving the weldability of the steel. The Nb content in the steel of this invention is controlled at 0.05%–0.12%.

[0027] Zr: In this invention, an appropriate amount of Zr is added. Part of it forms oxides in the molten steel, acting as non-spontaneous nucleation sites to refine austenite grains. It precipitates at the austenite grain boundaries, and the pinning effect of dispersed fine inclusions prevents the growth of austenite grains, thereby refining the microstructure formed by phase transformation and improving the strength and toughness of the material. At high temperatures, it reacts with oxygen to form a dense ZrO2 oxide layer, effectively preventing further oxygen diffusion and significantly improving the oxidation resistance of the steel. It also stabilizes carbides in the steel, delaying their coarsening and decomposition at high temperatures, thus improving high-temperature strength and microstructure stability. The Zr content in the steel of this invention is controlled at 0.20%–0.90%.

[0028] Re: It can inhibit grain growth and precipitation of harmful phases at high temperatures, thereby improving the high-temperature stability of steel; it can promote the formation of protective oxide layers of Al2O3 or Cr2O3, improving the oxidation resistance of steel. Re is relatively expensive, and this invention controls the Re content in steel to be 0.01% to 0.06% as needed.

[0029] Al: At high temperatures, it forms a protective Al2O3 oxide layer, effectively preventing further oxidation and enhancing the material's oxidation resistance. It is used to generate fine AlN, improving the hardenability of steel, refining grains, and enhancing the strength and toughness of steel plates. In this invention, the Al content is controlled at 0.02%~0.06%.

[0030] The second technical solution of the present invention is to provide a method for manufacturing high homogeneous nuclear island equipment steel with excellent high temperature oxidation resistance, including smelting, continuous casting, electroslag remelting, forging, heating, rolling, cooling and heat treatment;

[0031] Smelting and continuous casting:

[0032] The continuously cast billets are produced using the converter twin-casting method. By controlling the P, S and gas content in the steel, the non-metallic inclusions in the steel are reduced to ≤1.0 grade.

[0033] Electroslag remelting:

[0034] Before electroslag remelting of the continuously cast billet, argon gas is blown into the crystallizer for 15–25 minutes at a flow rate of 17–21 m³ / min. 3 / h; During remelting, the water temperature in the crystallizer is controlled at 15-28℃, and the melting rate is controlled at 0.8-1.2t / h. Preferably; After demolding, the electroslag ingot is slowly cooled, and then kept at 400-500℃ in a slow cooling pit for 15-21h before being slowly cooled to room temperature; The electroslag ingot has a thickness of 750-900mm, a width of 1700-1900mm, and a length of 3200-4000mm.

[0035] forging:

[0036] The electroslag ingot is heated to 1250–1330℃ at a heating rate of 75–100℃ / h, held at that temperature for 14–18 hours, and then forged. Forging is performed using an upsetting and drawing method, with each reduction controlled at 45–60 mm, and a final forging temperature >830℃. The final electroslag intermediate billet has dimensions of 480–580 mm in thickness, 1900–2200 mm in width, and 4300–5100 mm in length.

[0037] heating:

[0038] The electroslag billet is heated to 1260–1330℃ for 2.5–4 hours. The steel of this invention has a high alloy content, typically requiring a longer heating time to allow the alloying elements to fully dissolve in the matrix, improving the compositional inhomogeneity of the billet, reducing component segregation, and consequently mitigating subsequent microstructure segregation. However, the billet is sufficiently homogenized through electroslag remelting and forging in the early stages, thus eliminating the need for a longer heating time and significantly improving production efficiency while ensuring steel plate quality.

[0039] Rolling:

[0040] Large reduction rolling is adopted in the recrystallization zone. The initial rolling temperature is 1190-1270℃, the rolling speed is 0.9-1.4m / s, the reduction in the first pass is 35-45mm, the reduction in the second to fourth passes is 45-60mm, the reduction rate in the last two passes is controlled at 11%-17%, and the final rolling temperature is 930-960℃ to obtain finished steel plates with a thickness of 60-150mm.

[0041] Heat treatment: The steel plate adopts a heat treatment process of double quenching + single tempering.

[0042] The first quenching temperature is 950–980℃, the holding time is 60–120 min, and the quenching cooling rate is 12–17℃ / s. The higher quenching temperature effectively promotes the dissolution of alloying elements in austenite, laying the foundation for the formation of uniform martensite or the retention of alloyed austenite during subsequent cooling, thereby enhancing high-temperature strength and microstructure stability. The second quenching temperature is 900–930℃, the holding time is 120–180 min, and the quenching cooling rate is 18–25℃ / s. Through this second quenching, the microstructure and properties are further optimized, the grains are refined, and the high cooling rate promotes the formation of uniform martensite at the steel plate thickness interface.

[0043] The tempering temperature is 660–700℃, the holding time is 3–5 hours, and the steel is air-cooled after being removed from the furnace. Under a suitable tempering process, the martensite in the steel plate transforms into stable tempered sorbite. Simultaneously, it promotes the formation of fine strengthening phases (such as carbides and intermetallic compounds). During high-temperature tempering, these strengthening phases undergo aggregation, growth, and spheroidization, forming a more stable structure and reducing the risk of performance degradation due to the instability of the strengthening phases during long-term high-temperature service. Furthermore, during high-temperature tempering, some alloying elements oxidize to form a protective oxide layer, improving the oxidation resistance of the steel plate.

[0044] The technical advantages of this invention are as follows:

[0045] (1) This invention utilizes the combined action of Si, Ni, Cr, and Mo, along with appropriate amounts of Nb, Zr, and Re, to ensure that the steel plate possesses good strength and toughness while exhibiting high oxidation resistance, with an oxidation rate ≤0.6 mg / cm³ at 700℃. 2 ·h.

[0046] (2) By adopting the manufacturing process of electroslag remelting + forging + recrystallization zone rolling + secondary quenching + primary tempering, a 60-150mm thick high homogeneous nuclear power steel was obtained, with the strength index fluctuation range at 1 / 4 and 1 / 2 of the thickness not exceeding 1% and the grain size fluctuation not exceeding 0.5 grade.

[0047] (3) The steel plate prepared according to the present invention not only has good strength, toughness and high temperature oxidation resistance, but also has a thickness of 60-150 mm for nuclear island equipment steel plates; at room temperature, R m >640MPa, Rp 0.2 >550MPa, A 50 >20%; High-temperature tensile strength R at 150℃ m >620MPa, Rp 0.2 >520MPa; Impact energy KV2 at -20℃ >160J; Oxidation rate at 700℃ ≤0.6mg / cm³ 2 •h; R at 1 / 4 and 1 / 2 thickness of steel plate at room temperature and 150°C m With Rp 0.2 Fluctuations are no greater than 1%. Excellent overall performance fully meets the requirements for high service safety of nuclear island equipment. Attached Figure Description

[0048] Figure 1 This is a metallographic image of the microstructure of Embodiment 1 of the present invention. Detailed Implementation

[0049] The present invention will be further illustrated below through examples.

[0050] According to the component ratio of the technical solution in this embodiment of the invention, the elemental composition of the steel by mass percentage is as follows: C: 0.15%~0.23%, Si: 0.46%~0.90%, Mn: 0.60%~1.35%, P≤0.008%, S≤0.002%, Ni: 0.20%~0.68%, Cr: 0.95%~2.0%, Mo: 0.50%~1.66%, Nb: 0.05%~0.12%, Zr: 0.20%~0.90%, Re: 0.01%~0.06%, Al: 0.02%~0.06%, with the remainder being Fe and unavoidable impurities; the process involves smelting, continuous casting, electroslag remelting, forging, heating, rolling, cooling, and heat treatment.

[0051] Electroslag remelting:

[0052] Before electroslag remelting of the continuously cast billet, argon gas is blown into the crystallizer for 15–25 minutes at a flow rate of 17–21 m³ / min. 3 / h; During remelting, the inlet water temperature of the crystallizer is 15~28℃, and the melting rate is 0.8~1.2t / h;

[0053] forging:

[0054] The electroslag ingot is heated to 1250-1330℃ at a heating rate of 75-100℃ / h, held at that temperature for 14-18h, and then taken out of the furnace for forging. The forging is carried out by upsetting and drawing, with each reduction controlled at 45-60mm, and the final forging temperature is >830℃.

[0055] heating:

[0056] The electroslag billet is heated at a temperature of 1260–1330℃ for 2.5–4 hours.

[0057] Rolling:

[0058] Large reduction rolling is adopted in the recrystallization zone, with an initial rolling temperature of 1190-1270℃, a rolling speed of 0.9-1.4m / s, a reduction of 35-45mm in the first pass, a reduction of 45-60mm in the second to fourth passes, a reduction rate of 11%-17% in the last two passes, and a final rolling temperature of 930-960℃.

[0059] Heat treatment: The steel plate adopts a heat treatment process of two quenchings + one tempering;

[0060] The first quenching temperature is 950-980℃, the holding time is 60-120 min, and the quenching cooling rate is 12-17℃ / s; the second quenching temperature is 900-930℃, the holding time is 120-180 min, and the quenching cooling rate is 18-25℃ / s.

[0061] The tempering temperature is 660-700℃, the holding time is 3-5 hours, and the furnace is air-cooled after being taken out.

[0062] Furthermore, after the electroslag ingot is demolded, it is slowly cooled and kept at 400~500℃ in a slow cooling pit for 15~21 hours before being slowly cooled to room temperature.

[0063] The composition of the steel in this embodiment of the invention is shown in Table 1. The main process parameters for smelting and forging of the steel in this embodiment of the invention are shown in Table 2. The process parameters for heating, rolling, and heat treatment of the steel in this embodiment of the invention are shown in Table 3. The properties of the steel in this embodiment of the invention are shown in Table 4. The grain size and oxidation rate at 700℃ of the steel in this embodiment of the invention are shown in Table 5.

[0064] Table 1. Composition (wt%) of steel in embodiments of the present invention

[0065] 1 0.15 0.49 0.74 0.007 0.002 0.62 1.12 0.63 0.09 0.61 0.03 0.034 2.29 1.74 2 0.18 0.46 0.6 0.006 0.002 0.68 0.99 0.74 0.08 0.33 0.05 0.028 2.15 1.67 3 0.16 0.56 0.88 0.008 0.001 0.43 1.26 0.5 0.06 0.2 0.01 0.047 2.25 1.69 4 0.19 0.67 0.83 0.005 0.002 0.55 1.38 1.19 0.05 0.74 0.02 0.03 2.06 1.93 5 0.2 0.83 0.95 0.006 0.001 0.2 1.87 1.37 0.11 0.82 0.04 0.06 2.25 2.07 6 0.21 0.78 1.17 0.008 0.002 0.34 1.54 1.48 0.09 0.9 0.06 0.055 1.97 1.88 7 0.17 0.52 1.22 0.005 0.002 0.58 0.95 1.66 0.07 0.46 0.03 0.02 1.83 1.53 8 0.18 0.88 0.69 0.006 0.001 0.27 2 0.95 0.08 0.58 0.05 0.042 2.27 2.27 9 0.23 0.74 1.35 0.008 0.002 0.39 1.61 1.58 0.12 0.69 0.04 0.051 2.18 2 10 0.22 0.9 1.29 0.007 0.002 0.46 1.73 1.26 0.1 0.77 0.06 0.06 1.92 2.19

[0066] Table 2 Main process parameters for steel smelting and forging in the embodiments of the present invention

[0067] 1 0.5 17 18 22 1.1 400 17 783 1806 2 1 19 21 26 1 456 18 866 1843 3 1 15 20 28 1 445 18 764 1754 4 0.5 20 19 15 0.8 500 15 750 1700 5 1 25 17 19 1.2 496 19 777 1808 6 0.5 22 19 19 1.1 487 21 805 1882 7 0.5 24 18 18 0.9 432 20 821 1781 8 0.5 18 18 21 0.9 425 16 883 1822 9 1 16 21 22 0.8 408 18 852 1900 10 1 21 17 20 1.2 419 19 900 1893 Example Electroslag ingot length / mm Electroslag ingot heating rate / ℃ / h Insulation temperature / ℃ Insulation time / h pass reduction / mm Final forging temperature / °C Electroslag billet thickness / mm Electroslag billet width / mm Electroslag billet length / mm 1 3200 75 1283 17 45 880 490 1953 5014 2 3706 84 1309 18 53 895 510 2007 4300 3 3653 91 1250 14 60 840 500 1907 4512 4 3811 76 1276 16 48 865 560 2108 4608 5 4000 85 1330 15 55 832 580 2066 5100 6 3760 100 1322 17 57 847 550 2200 4946 7 3310 96 1314 16 46 900 480 2059 4821 8 3445 93 1262 14 48 925 530 1983 4760 9 3521 88 1286 18 49 930 520 2163 4483 10 3922 84 1330 17 50 870 540 2200 5036

[0068] Table 3. Process parameters for steel heating, rolling, and heat treatment in embodiments of the present invention.

[0069] 1 1283 2.5 1190 1.4 37 46 55 45 12 13 2 1260 2.9 1211 1.2 35 50 52 53 15 14 3 1307 3.0 1254 1.0 39 47 45 50 11 11 4 1271 3.3 1226 1.1 40 45 51 48 14 16 5 1294 2.7 1237 1.3 35 49 48 53 15 12 6 1330 2.8 1205 0.9 43 52 55 45 17 14 7 1316 3.2 1244 1.0 42 48 48 52 11 15 8 1302 4.0 1270 1.4 41 50 53 55 14 16 9 1287 3.9 1258 1.2 45 48 60 57 12 16 10 1330 3.5 1263 1.1 42 56 50 60 15 13 Example Final rolling temperature / ℃ Finished steel plate thickness / mm First quenching temperature / ℃ Insulation time / min Quenching cooling rate / ℃ / s Second quenching temperature / ℃ Insulation time / min Quenching cooling rate / ℃ / s Tempering temperature / °C Tempering holding time / h 1 952 60 960 70 15 900 120 20 670 3 2 946 65 950 100 12 910 150 18 680 3 3 930 70 980 60 16 920 170 22 660 4.5 4 960 77 955 120 16 920 160 25 700 5 5 952 83 970 80 14 900 130 25 690 4 6 935 86 950 110 17 930 150 24 660 4 7 948 105 975 75 13 910 180 22 680 3.5 8 958 120 965 90 12 920 120 23 690 5 9 941 126 980 85 15 930 140 21 700 4 10 959 130 970 100 17 910 170 19 680 5

[0070] The mechanical properties of the steel plate are shown in Table 4, and the grain size and oxidation rate at 700℃ are shown in Table 5.

[0071] Table 4 Properties of steel in embodiments of the present invention

[0072] 1-T / 4 586 674 25 553 641 178，177，175 8 1-T / 2 580 671 24 556 639 176，177，179 8 2-T / 4 593 682 26 560 650 182，179，180 8.5 2-T / 2 597 685 26 564 656 184，186，183 8.5 3-T / 4 555 643 27 526 622 190，187，188 8 3-T / 2 564 642 26 524 623 185，188，186 8 4-T / 4 576 668 25.5 538 631 198，200，196 7.5 4-T / 2 579 672 25 537 635 197，196，202 7.5 5-T / 4 603 688 26 569 654 161，164，162 8 5-T / 2 600 689 26 573 660 165，163，162 8 6-T / 4 593 673 27 561 648 174，177，175 9 6-T / 2 595 677 26 558 650 173，178，174 8.5 7-T / 4 567 655 24 538 629 192，189，190 8.5 7-T / 2 570 658 24.5 539 632 195，191，193 8.5 8-T / 4 611 694 22 584 667 188，184，190 9 8-T / 2 610 693 21 578 661 189，187，186 8.5 9-T / 4 602 684 23 566 646 203，207，200 8 9-T / 2 600 689 24 570 649 205，206，201 8 10-T / 4 583 667 25 553 640 177，179，174 8.5 10-T / 2 586 670 23.5 557 643 180，176，177 8

[0073] Table 5. Oxidation rate, microstructure, and property fluctuations of the steel in the embodiments of the present invention at 700℃.

[0074] 1 0.5 0 1.0 0.4 0.5 0.3 60 2 0.6 0 0.7 0.4 0.7 0.9 65 3 0.4 0 1.6 0.2 0.4 0.2 70 4 0.3 0 0.5 0.6 0.2 0.6 77 5 0.5 0 0.5 0.1 0.7 0.9 83 6 0.3 0.5 0.3 0.6 0.5 0.3 86 7 0.6 0 0.5 0.5 0.2 0.5 105 8 0.4 0.5 0.2 0.2 1.0 0.9 120 9 0.6 0 0.3 0.7 0.7 0.5 126 10 0.3 0.5 0.5 0.4 0.7 0.5 130

[0075] The steel plates for nuclear island equipment produced using this invention have a thickness of 60-150 mm; tensile strength R at room temperature m >640MPa, Rp 0.2 >550MPa, A 50 >20%; High-temperature tensile strength R at 150℃ m >620MPa, Rp 0.2 >520MPa; Impact energy KV2 at -20℃ >160J; Oxidation rate at 700℃ ≤0.6mg / cm³ 2 •h; The strength index fluctuation range at 1 / 4 and 1 / 2 of the thickness is no greater than 1%.

[0076] To illustrate the present invention, the present invention has been appropriately and sufficiently described above through embodiments. The above embodiments are only for illustrating the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., should be included within the protection scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. A high-homogeneity steel for nuclear island equipment with excellent high-temperature oxidation resistance, characterized in that, The element composition in the steel plate is as follows in terms of mass percentage: C: 0.15%~0.23%, Si: 0.46%~0.90%, Mn: 0.60%~1.35%, P≤0.008%, S≤0.002%, Ni: 0.20%~0.68%, Cr: 0.95%~2.0%, Mo: 0.50%~1.66%, Nb: 0.05%~0.12%, Zr: 0.20%~0.90%, Re: 0.01%~0.06%, Al: 0.02%~0.06%, the rest is Fe and inevitable impurities; at room temperature, R m > 640 MPa, Rp 0.2 > 550 MPa, A 50 > 20%; at 150°C, high-temperature tensile R m > 620 MPa, Rp 0.2 > 520 MPa; impact energy KV2 at -20°C > 160 J; at 700°C, oxidation rate ≤0.6 mg / cm 2 ·h; at room temperature and 150°C, R m and Rp 0.2 at the thickness 1 / 4 and the thickness 1 / 2 of the steel plate fluctuate by no more than 1%.

2. The high-homogeneity nuclear island equipment steel with excellent high-temperature oxidation resistance according to claim 1, characterized in that, The elemental composition of the steel used in the nuclear island equipment, by mass percentage, is 1.8 < Cr / Si < 2.

3.

3. The high-homogeneity nuclear island equipment steel with excellent high-temperature oxidation resistance according to claim 1, characterized in that, The elemental composition of the steel used in the nuclear island equipment, by mass percentage, is Ni+Cr>1.5%.

4. The high-homogeneity nuclear island equipment steel with excellent high-temperature oxidation resistance according to claim 1, characterized in that, The grain size fluctuation at 1 / 4 and 1 / 2 of the thickness of the steel plate used for the nuclear island equipment is no greater than level 0.

5.

5. The high-homogeneity nuclear island equipment steel with excellent high-temperature oxidation resistance according to claim 1, characterized in that, The thickness of the steel plates used for nuclear island equipment is 60-150mm.

6. A method for manufacturing a high-homogeneity nuclear island equipment steel with excellent high-temperature oxidation resistance as described in any one of claims 1-5, characterized in that, This includes smelting, continuous casting, electroslag remelting, forging, heating, rolling, cooling, and heat treatment; Electroslag remelting: Before electroslag remelting of continuous casting billet, argon is blown into the crystallizer for 15-25 minutes at a flow rate of 17-21 m 3 / h; the water inlet temperature of the crystallizer during remelting is 15-28℃, and the melting rate is 0.8-1.2 t / h; forging: The electroslag ingot is heated to 1250-1330℃ at a heating rate of 75-100℃ / h, held at that temperature for 14-18h, and then taken out of the furnace for forging. The forging is carried out by upsetting and drawing, with each reduction controlled at 45-60mm, and the final forging temperature is >830℃. heating: The electroslag billet is heated at a temperature of 1260–1330℃ for 2.5–4 hours. Rolling: Large reduction rolling is adopted in the recrystallization zone, with an initial rolling temperature of 1190-1270℃, a rolling speed of 0.9-1.4m / s, a reduction of 35-45mm in the first pass, a reduction of 45-60mm in the second to fourth passes, a reduction rate of 11%-17% in the last two passes, and a final rolling temperature of 930-960℃. Heat treatment: The steel plate adopts a heat treatment process of two quenchings + one tempering; The first quenching temperature is 950-980℃, the holding time is 60-120 min, and the quenching cooling rate is 12-17℃ / s; the second quenching temperature is 900-930℃, the holding time is 120-180 min, and the quenching cooling rate is 18-25℃ / s. The tempering temperature is 660-700℃, the holding time is 3-5 hours, and the furnace is air-cooled after being taken out.

7. The method for manufacturing a high-homogeneity nuclear island equipment steel with excellent high-temperature oxidation resistance according to claim 6, characterized in that, After the electroslag ingot is demolded, it is slowly cooled. It is kept at 400~500℃ in a slow cooling pit for 15~21 hours and then slowly cooled to room temperature.

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