Steel plate for the core casing of an advanced nuclear power unit and its manufacturing method

Abstract

The present invention provides a steel plate for a cylindrical body of a core casing of an advanced nuclear power unit and a manufacturing method thereof. The composition of the present invention is, in mass%, C: 0.10%-0.14%, Si: 0.20%-0.30%, Mn: 0.30%-0.60%, P≦0.006%, S≦0.002%, Cr: 1.65%-1.95%, Mo: 0.80%-1.20%, Ni: 0.80%-1.20%, Nb: 0.04%-0.08%, V: 0.1 0%~0.20%, Ti: 0%~0.03%, Alt: 0%~0.02%, Ca: 0.001%~0.004%, N: 0.01%~0.03%, Sn≦0.001%, H≦0.0001%, O≦0.0020%, balance: Fe and unavoidable impurities. High temperature temper embrittlement resistance coefficient J=(Si+Mn)×(P+Sn)×10 4 ≦50. The steel plate and its manufacturing method according to the present invention can ensure the comprehensive performance requirements of the steel plate for the core casing cylinder of advanced nuclear power unit.

Description

[Technical Field]

[0001] The present invention relates to the field of metallic materials, and in particular to a steel plate for the cylindrical body of the core casing of an advanced nuclear power unit and a method for manufacturing the same. [Background technology]

[0002] Nuclear power has been used by humanity for over 70 years as a clean and efficient source of energy. Since the 2000s, the conflict between increased human activity and global economic growth, energy shortages, and extreme climates has become increasingly apparent. In this climate of global integration, the advantages of nuclear power appear even more pronounced. Therefore, the peaceful development of more advanced nuclear power remains a pressing need. Currently, nuclear technology has evolved from the first-generation prototype reactor, the second-generation pressurized water reactor, and the third-generation advanced light water reactor. Nuclear experts around the world have proposed fourth-generation advanced nuclear technologies, including sodium-cooled fast reactors, air-cooled fast reactors, lead-cooled fast reactors, very-high-temperature gas-cooled reactors, molten salt reactors, and supercritical-pressure light water reactors, setting the direction for future nuclear technology development.

[0003] The key features of Generation IV nuclear technology are improved safety, improved economy, reduced nuclear waste, and effective prevention of nuclear proliferation. This places extremely high demands on nuclear technology and equipment. For example, the structural steel used to support the core of nuclear safety level I components is exposed to high temperatures and hydrogen atmospheres, as well as intense irradiation by fast neutrons. The risks of base embrittlement and hydrogen erosion due to water decomposition are several times higher than in previous generations of nuclear power plants, placing extremely high technical requirements on component materials. Therefore, developing the key nuclear equipment and materials required to meet the needs of advanced Generation IV nuclear power plants has become a core challenge that the world's major nuclear powers must urgently address.

[0004] In Patent Document 1 (Heat Treatment Method for Forgings of Core Cylinder of Nuclear Reactor Pressure Vessel, China Patent Application No. 200910057359.1), it can be seen from the disclosed ingredients, manufacturing method and beneficial effects that the patent specifies the standard of 16MND5, which is widely used in the manufacture of third generation nuclear power generation equipment, with an operating temperature of 350°C, and does not apply to fourth generation nuclear power generation equipment, which has higher operating temperatures and technical requirements.

[0005] The above-mentioned Patent Document 1 mainly relates to metallic materials required for third-generation nuclear power generation equipment, which, compared to the component materials required for fourth-generation nuclear power generation technology, have the characteristics of relatively low high-temperature use temperature, no hydrogen in the contact atmosphere, short post-weld heat treatment time, and relatively uniform material mechanical property index. Therefore, there is an urgent need to develop component materials required to meet the requirements of important equipment for fourth-generation nuclear power plants.

[0006] Therefore, the present invention invents new materials and processes required for the important equipment of advanced nuclear power units, in order to meet the high purity requirements for the steel material of the core casing cylindrical body of fourth-generation nuclear power generation equipment, as well as technical features such as thermal strength and fracture toughness at 500°C, low NDT temperature, excellent hydrogen-induced cracking prevention performance, stable structural performance after long-term post-weld heat treatment at high temperatures, and good processing and forming properties. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Chinese Patent Application Publication No. 101906523 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in view of the above technical challenges, and provides a steel plate for the core casing cylinder of an advanced nuclear power unit, and its manufacturing method. The invention employs a completely new chemical composition design and appropriate manufacturing process, based on medium to low C, Si, and Mn components, with Cr, Mo, Ni, Nb, V, Ti, and N added as alloying elements, while strictly controlling the contents of harmful elements P, S, and Sn, and gases O and H. By further employing unique smelting, rolling, and heat treatment manufacturing processes, the steel plate has high strength at temperatures up to 500°C, good high-temperature fracture toughness, and excellent resistance to low-temperature ball drop and hydrogen-induced cracking, which meets the manufacturing and use requirements of the core casing cylinder of a fourth-generation advanced nuclear power unit. [Means for solving the problem]

[0009] The technical means of the present invention are as follows: One embodiment of the present invention is a steel plate for a cylindrical body of a core casing of an advanced nuclear power unit, the steel plate having a composition, in mass %, of C: 0.10% to 0.14%, Si: 0.20% to 0.30%, Mn: 0.30% to 0.60%, P≦0.006%, S≦0.002%, Cr: 1.65% to 1.95%, Mo: 0.80% to 1.20%, Ni: 0.80% to 1.20%, Nb : 0.04% to 0.08%, V: 0.10% to 0.20%, Ti: 0% to 0.03%, Alt: 0% to 0.02%, Ca: 0.001% to 0.004%, N: 0.01% to 0.03%, Sn≦0.001%, H≦0.0001%, O≦0.0020%, balance: Fe and unavoidable impurities, and high-temperature temper embrittlement resistance coefficient J=(Si+Mn)×(P+Sn)×10 4 ≦50.

[0010] Furthermore, in the delivered state, 500MPa≦R at room temperature el ≦520MPa, 610MPa≦R m ≦640MPa, and 470MPa≦R at 500℃ m ≦485MPa, and in the post-weld heat treatment state of 700℃×26h, 450MPa≦R m (500℃)≦470MPa, KV2 (80℃)≧420J, T NDT≦-40℃, the CSR of HIC (solution A) is 0%, and the 1 / 2 ≦K IC ≦285MPa m 1 / 2 Steel plates for cylindrical bodies with thickness specifications of 40 to 65 mm were obtained.

[0011] The principles for selecting each chemical component and the reasons for designing the content of each component in the present invention are as follows:

[0012] C: In the present invention, the main solute and compound C ensure the high-temperature tensile strength of the steel during heat treatment and post-weld heat treatment. However, a relatively high carbon content affects the steel toughness and weldability, so the present invention sets the C content range to 0.10% to 0.14%.

[0013] Si: Si is an excellent reducing agent and deoxidizer in the steelmaking process. Its combined use with Alt significantly enhances the deoxidizing ability of Alt. Si forms a dense, oxidation-resistant SiO2 protective film on the surface at high temperatures. Furthermore, the cooperative action of Si and Mo results in the formation of MoSi2, an intermetallic compound with excellent high-temperature oxidation resistance, due to the coexistence of metallic and covalent bonds in the atomic bonds in the crystal structure. Therefore, in a preferred embodiment, the Mo / Si ratio in this invention is limited to a range of 2.80 to 5.50 to ensure the formation of a certain amount of MoSi2 structure. However, in the tempering embrittlement temperature range of 350 to 550°C, a high silicon content increases the tempering embrittlement susceptibility of the steel. Therefore, the present invention does not recommend the addition of excessive silicon. Therefore, the present invention sets the Si content range to 0.20% to 0.30%.

[0014] Mn: In the present invention, the amount of deoxidizers such as Si and Al added is small, so the addition of Mn compensates for the insufficient deoxidation effect. Furthermore, Mn is an alloying element with strong solid solution strengthening ability, and can increase the strength of the matrix. However, Mn is a sensitive element that increases temper embrittlement, and therefore must be strictly controlled in the present invention. Therefore, the present invention sets the Mn content range to 0.30% to 0.60%.

[0015] S, P: As harmful elements in steel, they must be strictly controlled to ensure comprehensive indexes such as steel purity, J coefficient, and fracture toughness. Therefore, the contents are limited to S≦0.002% and P≦0.006%.

[0016] Cr: A strong carbide-forming element that combines with Fe, Mn, and Mo in steel to form stable M 23 It forms alloy carbides with a C6 structure, ensuring high-temperature performance during long-term post-weld heat treatment, and also fulfills Cr's high-temperature antioxidant and oxidation corrosion resistance functions. However, if the Cr content is too high, the brittle transition temperature of the steel will increase, so the present invention sets the Cr content range to 1.65% to 1.95%.

[0017] Mo: Improves the hardenability of steel and ensures the strength of the steel matrix. Mo is also a strong carbide former, forming a stable Mo2C thermal strengthening phase with carbon, which strengthens the steel at high temperatures. In this application, a large amount of Cr and a certain amount of Mn are added, which can easily cause co-polymerization with impurities such as P and Sn at grain boundaries, resulting in high-temperature temper embrittlement and affecting the high-temperature performance of the steel. Mo, on the other hand, has the opposite effect, precipitating P within the crystals to prevent grain boundary segregation. In a preferred embodiment, the present invention limits the (Cr + Mn) / Mo ratio to 1.65-2.90 to ensure the structural and performance stability of the core casing cylindrical steel during operation at 500°C. However, because a high Mo content can actually embrittle the steel, the present invention sets the Mo content range to 0.80%-1.20%.

[0018] Ni: In the present invention, the Ni element mainly improves the hydrogen corrosion resistance, plasticity, and toughness of the steel, lowers the brittle transition temperature of ferrite, and prevents the rise in the non-ductile transition temperature due to the effect of radiation irradiation. However, if the Ni content is too high, the radiation resistance of the material will be reduced, so the present invention sets the Ni content range to 0.80% to 1.20%.

[0019] Nb: In the present invention, Nb acts to refine the crystal grains, which improves the toughness and resistance to hydrogen-induced cracking of the steel. Nb also forms carbides and consumes carbon, which gives the steel good hydrogen resistance. Therefore, the Nb content is limited to 0.04% to 0.08%.

[0020] V: Added in large quantities in the present invention. One of its main functions is to stabilize the carbon and nitrogen complex compounds formed with C and N during the long-term, high-temperature post-weld tempering process, thereby ensuring high-temperature strength in the high-temperature post-weld heat treatment state. Secondly, V bonds C to vanadium carbide, significantly improving the stability of hydrogen resistance of the steel under high temperature and pressure. Furthermore, the addition of V alloy effectively suppresses the grain boundary segregation of Cr and Mn due to irradiation, so the V content is limited to 0.10% to 0.20%.

[0021] Ti: One of the elements that strongly forms ferrite. In the present invention, Ti is present as a contributing element or a small amount of added element. When added, the A1 and A3 temperatures of the steel are significantly increased. Titanium can increase the plasticity and toughness of steel. Titanium bonds carbon and nitrogen to form titanium carbide and titanium nitride, thereby improving the strength of the steel. After normalizing and heat treatment, the grains are refined and carbides are precipitated, significantly improving the plasticity and impact toughness of the steel. Therefore, the Ti content is limited to 0% to 0.03%.

[0022] Alt: In the present invention, the Alt element is present as a contributing element or a small amount of added element and acts as a deoxidizer. The main purpose of not adding or adding a small amount of Alt is to ensure the purity of the steel and prevent the formation of aluminum oxides from affecting fatigue performance. Therefore, the Alt content is limited to 0% to 0.02%.

[0023] Ca: In the present invention, the inclusions are spheroidized with Ca, converting MnS inclusions into CaS or composite inclusions containing CaS, thereby converting Al2O3-based inclusions into calcium aluminate-based oxide inclusions. These inclusions are spherical and dispersed, undergo minimal deformation at the rolling temperature of the steel, and remain spherical after rolling. Therefore, Ca treatment can reduce the steel's susceptibility to hydrogen-induced cracking. However, if too much Ca is added, the size of the formed Ca(O,S) becomes too large, increasing brittleness and allowing it to become the initiation point for fracture cracks, reducing the low-temperature toughness, elongation, and weldability of the steel, as well as reducing the purity of the steel. Therefore, the present invention sets the Ca content range to 0.001% to 0.004%.

[0024] N: Forms nitrides with elements such as Nb and V, which precipitate at grain boundaries, pinning the grain boundaries and refining the crystal grains, thereby enhancing the high-temperature strength of the grain boundaries. Therefore, the N content is limited to 0.01% to 0.03%.

[0025] Sn: A residual element in steel that not only affects the purity of the steel but also has an important effect on the temper embrittlement coefficient J, and therefore must be strictly controlled. Therefore, the Sn content is limited to 0.001% or less.

[0026] H, O: Exist as harmful gases. For example, H can cause defects such as "white spots" or "hydrogen embrittlement" in steel, which can have a serious impact on the service life of the material and the safety of the equipment. O can also form non-metallic oxides with Al and Si, which can cause many other defects and affect the purity of the steel and the mechanical properties of the material. Therefore, they must be strictly controlled, with the O content limited to 0.0020% or less and the H content limited to 0.0001% or less.

[0027] To achieve the objectives of the present invention, the present invention further provides a method for manufacturing steel plate for the cylindrical body of the core casing of an advanced nuclear power unit, which includes the steps of hot metal pretreatment - converter dephosphorization - converter decarburization - extra-furnace refining (LF+RH) - slab continuous casting - slow cooling of the stack - billet cleaning - electroslag remelting - slow cooling of the electroslag steel ingot - billet heating - finished product rolling - hot straightening - slow cooling - heat treatment - flaw detection - inspection and verification, and the main specific steps of the present invention are as follows:

[0028] 1) Smelting process: Molten steel is smelted in a converter, using high-quality scrap steel and molten pig iron as raw materials. The content of the molten pig iron is controlled to 70-80%. In order to effectively reduce the content of the harmful element P, dephosphorization and decarburization are carried out separately using a converter, where the oxygen injection for dephosphorization is controlled to 7-10 minutes, and that for decarburization is controlled to 8-12 minutes, ultimately reducing the phosphorus mass fraction to within 0.006%. Deep desulfurization is performed in an LF furnace to reduce sulfur content to below 0.002%. Simultaneous calcium treatment is performed by feeding a CaSi wire into the steel. The wire feed speed is 200-350 m / min, and the wire feed depth is 1.0-2.0 m below the slag layer. This treatment changes the morphology of nonmetallic inclusions, forming fine CaS or calcium aluminate spherical inclusions. This increases the axial ratio of the billet and refines the steel, improving its purity and hydrogen resistance. The resulting slag layer is 60-90 mm thick, ensuring sufficient inclusion floating. Degassing is completed in an RH furnace. The net circulation time is 10-15 min, with a settling time of 3-5 min before casting begins.

[0029] 2) Casting process: After the vacuum is broken, casting is carried out using a continuous casting machine, the superheat temperature is 20~30℃, and the casting process is stable at a constant speed. The billets taken off the production line are piled up into stacks and slowly cooled. The stacks are slowly cooled for 36~54 hours, and the stacks are dismantled at temperatures below 300℃ to prevent cracks from occurring inside the billets due to rapid cooling.

[0030] 3) Electroslag remelting process: In order to further increase the purity of the steel, remove internal defects such as segregation and porosity, reduce non-metallic inclusions, and homogenize the cast structure, the electroslag remelting process is extremely important for high-temperature performance and preventing hydrogen-induced cracking. This method uses cylindrical steel plates made by rolling electroslag steel ingots with a thickness of 300 to 400 mm to a thickness of 65 mm or less. After demolding, the electroslag steel ingots are stacked and slowly cooled for 48 to 72 hours, and then disassembled at 300°C or below and air-cooled.

[0031] 4) Heating process: By controlling the heating process of the steel billet, sufficient solid solution of alloying elements is ensured and the growth of prior austenite grains is effectively suppressed. The heating temperature of the electroslag steel ingot is controlled to 1180-1250°C, the heating time is controlled to 8-10 hours, and the soaking time is controlled to 0.5-1.0 hours.

[0032] 5) Rolling process: The rolling start temperature of the recrystallized region is 1050-1150°C, the single-pass deformation rate of the recrystallized region is 10-14%, and the reduction rates of each of the first three passes are 12% or more, resulting in a total deformation rate of 50% or more. The thickness of the intermediate blank is 2.0-4.0 times the thickness of the finished steel plate. The rolling start temperature of the unrecrystallized region is 850-900°C, the rolling end temperature of the unrecrystallized region is 820-850°C, resulting in a cumulative deformation rate of 50% or more. The above parameters are designed based on the composition and performance requirements of the steel. The organic bonding of the micro-alloying elements Nb, V, and Ti with the elements C and N maximizes the dispersed precipitation strengthening and grain refinement effects, resulting in a relatively fine rolled structure and providing a relatively homogeneous rolled structure for subsequent heat treatment. The finished product thickness is 40-65mm.

[0033] 6) Heat treatment process: In order to obtain a structure that satisfies the strict performance requirements of the present invention, a final heat treatment process is required. The present invention employs multiple heat treatment processes of high-temperature normalizing + two-phase region quenching + high-temperature tempering, and the steel type A of the present invention is C3 The temperature is approximately 870°C, and the high-temperature normalizing temperature is A C3The temperature is designed to be +(80-130)°C, i.e., 950-1000°C, with a soaking time of 0.5-1.0 min / mm, followed by air cooling to room temperature. This process eliminates grain variations and structural segregation caused by temperature variations in the rolled material. The relatively large grain variations and segregation bands can significantly reduce the product's resistance to hydrogen-induced cracking. The two-phase quenching temperature is 800-850°C, with a soaking time of 1.0-1.5 min / mm and a cooling rate of 5-10°C / s. After reaching a self-tempering temperature of 350-450°C, the material is air-cooled to room temperature. This two-phase heating process refines the grain size of undissolved ferrite, resulting in a dual-phase structure of ferrite and bainite.

[0034] Furthermore, to obtain the excellent processing and usability of the product of the present invention, it is necessary to estimate that the upper limit of the tensile strength of the material after heat treatment based on the design allowable stress does not exceed 640 MPa, and to ensure that the tensile strength after post-weld heat treatment at 500°C is 450 MPa or more. Therefore, it is necessary to further adjust and control the structure and performance of the process through accurate tempering heat treatment. The present invention is designed to have a tempering temperature of 710-730°C and a heat-holding time of 60 min + 2.0-4.0 min / mm. During this tempering process, the bainite structure recovers its softening and the addition of (Fe, Mn, Cr, Mo) 23 The C6 structure alloy carbides grow without agglomeration and are highly spherically dispersed in the bainite ferrite matrix or grain boundaries. This type of structure is characterized by its extremely high temperature stability, and the structure remains unchanged even after post-weld heat treatment at 700°C for 26 hours. This ensures the overall performance of long-term post-weld heat treatment, especially high-temperature toughness, fracture toughness, and low-temperature ball drop performance. [Effects of the Invention]

[0035] The present invention has the following advantages: 1. Based on medium to low C, Si, and Mn components, the contents of harmful elements P, S, Sn and gases O and H are strictly controlled, the tempering embrittlement coefficient is controlled to 50 or less, and alloying elements Cr, Mo, Ni, Nb, V, Ti, and N are added in combination. Through a unique manufacturing process, a composite structure containing 10% to 15% undissolved ferrite and tempered bainite is obtained, where the bainite structure contains a large amount of dispersed precipitates (Fe, Mn, Cr, Mo). 23 The C6 structure alloy carbides are included to ensure the irradiation resistance and comprehensive mechanical properties of the core casing cylindrical steel plate. 2. The mechanical properties of the steel plate for the core casing of advanced nuclear power units, obtained through a unique manufacturing process, are 500MPa or less R at room temperature in the delivered state. el ≦520MPa, 610MPa≦R m ≦640MPa, and 470MPa≦R at 500℃ m ≦485MPa, and in the post-weld heat treatment state of 700 × 26h, 450MPa ≦ R m (500℃)≦470MPa, KV2 (80℃)≧420J, T NDT ≦-40℃, the CSR of HIC (solution A) is 0%, and the 1 / 2 ≦K IC ≦285MPa m 1 / 2 This has resulted in the production of steel plates for cylindrical bodies with thickness specifications of 40 to 65 mm, filling the gap in this type of product despite its excellent overall performance and dimensional specifications. DETAILED DESCRIPTION OF THE INVENTION

[0036] In order to clarify the objectives, technical solutions and advantages of the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be described more clearly and completely below, but it goes without saying that the described embodiments are only some of the embodiments of the present invention, not all of the embodiments. Any other embodiments that a person skilled in the art can derive based on the embodiments of the present invention without any creative effort shall fall within the scope of protection of the present invention.

[0037] The chemical compositions of the examples of the present invention are shown in Table 1. The process parameters for each example are shown in Table 2. The final effect of the structural performance of the examples is shown in Table 3. The hydrogen induced cracking prevention HIC test results are shown in Table 4. The high temperature fracture toughness test results are shown in Table 5.

[0038] [Table 1]

[0039] [Table 2-1]

[0040] [Table 2-2]

[0041] [Table 3]

[0042] [Table 4]

[0043] [Table 5]

[0044] As can be seen from the above results, the steel plate for the core casing cylinder of the advanced nuclear power unit according to the present invention has high internal purity, the content of harmful elements P and S is controlled to an extremely low level, the temper embrittlement prevention coefficient J≦50, and the strength at room temperature in the delivered state is 500MPa≦R el ≦520MPa, 610MPa≦R m ≦640MPa, and 470MPa≦R at 500℃ m ≦485MPa, and in the post-weld heat treatment state of 700℃×26h, 450MPa≦R at 500℃ m ≦470MPa, KV2≧420J at 80℃, T NDT≦-40℃, the CSR of HIC (solution A) is 0%, and the 1 / 2 ≦K IC ≦285MPa m 1 / 2 is.

[0045] Finally, it should be noted that the above embodiments are merely for illustrating the technical means of the present invention, and are not intended to limit the same. Although the present invention has been described in detail with reference to the above embodiments, it is understood by those skilled in the art that the technical means described in the above embodiments may be modified or equivalent replacements may be made for part or all of the technical features, and such modifications or replacements will not depart from the scope of the technical means of the embodiments of the present invention.

[0046] (Addendum) (Appendix 1) The composition, in mass%, is C: 0.10% to 0.14%, Si: 0.20% to 0.30%, Mn: 0.30% to 0.60%, P≦0.006%, S≦0.002%, Cr: 1.65% to 1.95%, Mo: 0.80% to 1.20%, Ni: 0.80% to 1.20%, Nb: 0.04% to 0.08%, V: 0.10%. ~0.20%, Ti: 0%~0.03%, Alt: 0%~0.02%, Ca: 0.001%~0.004%, N: 0.01%~0.03%, Sn≦0.001%, H≦0.0001%, O≦0.0020%, balance: Fe and unavoidable impurities. High temperature temper embrittlement resistance coefficient J=(Si+Mn)×(P+Sn)×10 4 ≦50, A steel plate for a cylindrical body of a core casing of an advanced nuclear power unit, characterized by:

[0047] (Appendix 2) The steel plate, as delivered, has a yield strength of 500 MPa or less at room temperature. el ≦520MPa, and the tensile strength is 610MPa≦R m ≦640Mpa, and the tensile strength at 500℃ is 470MPa≦R m ≦485Mpa, 2. A steel plate for a cylindrical body of a core casing of an advanced nuclear power unit according to claim 1.

[0048] (Appendix 3) After heat treatment at 700°C for 26 hours after welding, the tensile strength at 500°C is 450MPa or less. m ≦470MPa, impact energy KV2 at 80℃ ≧420J, and inductile transition temperature T NDT ≤ -40°C, the CSR of the HIC A solution is 0%, and the fracture toughness is 280 MPa m 1 / 2 ≦K IC ≦285MPa m 1 / 2 That is, 2. A steel plate for a cylindrical body of a core casing of an advanced nuclear power unit according to claim 1.

[0049] (Appendix 4) A structure containing 10% to 15% undissolved ferrite and tempered bainite was obtained, and the bainite structure contained dispersed precipitates of M. 23 It contains alloy carbides with a C6 structure, where M is a combination of Fe, Mn, Cr and Mo. 2. A steel plate for a cylindrical body of a core casing of an advanced nuclear power unit according to claim 1.

[0050] (Appendix 5) Mo / Si is 2.80 to 5.50, and (Cr+Mn) / Mo is 1.65 to 2.90. 2. A steel plate for a cylindrical body of a core casing of an advanced nuclear power unit according to claim 1.

[0051] (Appendix 6) A smelting process in which deep desulfurization is performed in an LF refining furnace to control the sulfur content to 0.002% or less, and at the same time, calcium treatment is performed by feeding a CaSi wire into the steel, the thickness of the generated slag layer is 60-90 mm, degassing is completed in an RH furnace, the net circulation time is 10-15 min, and the settling time before starting casting is 3-5 min. After breaking the vacuum, a continuous casting machine is used to cast the billets at a constant speed with a superheat of 20 to 30°C, and the billets are stacked to form a stack, which is then slowly cooled and disassembled at a predetermined temperature. an electroslag remelting process in which 300-400 mm electroslag steel ingots are rolled to a standard cylindrical steel plate of 65 mm or less, and the electroslag steel ingots are released from the mold, stacked, and slowly cooled, and the stack is dismantled at a predetermined temperature; a heating process in which the heating temperature of the electroslag steel ingot is controlled to 1180 to 1250°C, the heating time is controlled to 8 to 10 hours, and the soaking time is controlled to 0.5 to 1.0 hours; a rolling process in which the rolling start temperature of the recrystallized region is 1050-1150°C, the single-pass deformation rate of the recrystallized region is 10-14%, and the rolling reduction rates of the first three passes are all 12% or more, the total deformation rate is 50% or more, the thickness of the intermediate blank is 2.0-4.0 times that of the finished steel plate, the rolling start temperature of the unrecrystallized region is 850-900°C, the rolling end temperature of the unrecrystallized region is 820-850°C, the cumulative deformation rate of the unrecrystallized region is 50% or more, and the thickness of the finished product after rolling is 40-65 mm; A C3 a heat treatment process in which high-temperature normalizing is performed at +(80-130)°C, the temperature is maintained for 0.5-1.0 min / mm, and air-cooling is performed to room temperature; a two-phase region quenching temperature is 800-850°C, the temperature is maintained for 1.0-1.5 min / mm, the cooling rate is 5-10°C / s, and the self-tempering temperature is 350-450°C, and air-cooling is performed to room temperature; and 6. A method for manufacturing a steel plate for a cylindrical body of a core casing of an advanced nuclear power unit according to any one of appendices 1 to 5.

[0052] (Appendix 7) In the smelting process, molten steel is smelted in a converter, using molten pig iron and scrap steel as raw materials, controlling the molten pig iron content to 70-80%, and dephosphorization and decarburization are performed separately using a converter. The oxygen injection time for dephosphorization is controlled to 7-10 minutes, and the oxygen injection time for decarburization is controlled to 8-12 minutes, ultimately reducing the phosphorus mass fraction to within 0.006%. 7. The method of claim 6,

[0053] (Appendix 8) In the smelting process, during calcium treatment, the wire feed speed is 200 to 350 m / min, and the wire feed depth is 1.0 to 2.0 m below the slag layer; 7. The method of claim 6,

[0054] (Appendix 9) In the casting process, the billets are stacked to form a stack, which is slowly cooled for 36 to 54 hours, and the stack is disassembled at 300°C or less. In the electroslag remelting process, the electroslag steel ingot is released from the mold, stacked to form a stack, which is slowly cooled for 48 to 72 hours, and the stack is disassembled at 300°C or less. 7. The method of claim 6,

[0055] (Appendix 10) The specific process parameters of the high-temperature tempering heat treatment are: tempering temperature 710-730°C, and heat retention time 60min + 2.0-4.0min / mm; 7. The method of claim 6,

Claims

1. The composition, in mass%, is C: 0.10% to 0.14%, Si: 0.20% to 0.30%, Mn: 0.30% to 0.60%, P≦0.006%, S≦0.002%, Cr: 1.65% to 1.95%, Mo: 0.80% to 1.20%, Ni: 0.80% to 1.20%, Nb: 0.04% to 0.08%, V: 0.10% 0.20%, Ti: 0% to 0.03%, Alt: 0% to 0.02%, Ca: 0.001% to 0.004%, N: 0.01% to 0.03%, Sn≦0.001%, H≦0.0001%, O≦0.0020%, balance: Fe and inevitable impurities, and high-temperature temper embrittlement resistance coefficient J=(Si+Mn)×(P+Sn)×10 ４ ≦50, The steel plate, in a delivered state, has a yield strength at room temperature of 500 MPa≦R e1 ≦520 MPa, a tensile strength of 610 MPa≦R m ≦640 MPa, and a tensile strength at 500°C of 470 MPa≦R m ≦485 MPa; In a post-weld heat treatment state of 700°C x 26h, the tensile strength at 500°C is 450 MPa ≦ R m ≦ 470 MPa, the impact energy at 80°C is KV 2 ≧ 420 J, the non-ductile transition temperature T NDT ≦ −40°C, the CSR of HIC A solution is 0%, and the fracture toughness is 280 MPa·m 1 / 2 ≦ K IC ≦ 285 MPa·m 1 / 2 ; Mo / Si is 2.80 to 5.50, and (Cr+Mn) / Mo is 1.65 to 2.

90. A steel plate for a cylindrical body of a core casing of an advanced nuclear power unit, characterized by:

2. A structure containing 10 mass % to 15 mass % undissolved ferrite and tempered bainite was obtained, and the bainite structure contained dispersed precipitated M ２３ C ６ alloy carbides of the structure, wherein M is any combination of Fe, Mn, Cr, and Mo; The steel plate for the cylindrical body of the core casing of an advanced nuclear power unit according to claim 1.

3. A smelting process in which deep desulfurization is performed in an LF refining furnace to control the sulfur content to 0.002% or less, and simultaneously calcium treatment is performed by feeding a CaSi wire into the steel, the thickness of the generated slag layer is 60-90 mm, degassing is completed in an RH furnace, the net circulation time is 10-15 min, and the settling time before starting casting is 3-5 min; a casting process in which, after breaking the vacuum, casting is performed using a continuous casting machine, the superheat is 20 to 30°C, the billets are stacked, the stack is slowly cooled, and the stack is disassembled at a predetermined temperature; an electroslag remelting process in which 300 to 400 mm electroslag steel ingots are released from the mold, stacked, and slowly cooled, and then dismantled at a predetermined temperature; a heating step in which the heating temperature of the electroslag steel ingot is controlled to 1180 to 1250°C, the heating time is controlled to 8 to 10 hours, and the soaking time is controlled to 0.5 to 1.0 hours; a rolling process in which the rolling start temperature of the recrystallized region is 1050-1150°C, the single pass deformation rate of the recrystallized region is 10-14%, and the rolling reduction rates of each of the first three passes are 12% or more, the total deformation rate is 50% or more, the thickness of the intermediate blank is 2.0-4.0 times that of the finished steel plate, the rolling start temperature of the unrecrystallized region is 850-900°C, the rolling end temperature of the unrecrystallized region is 820-850°C, the cumulative deformation rate of the unrecrystallized region is 50% or more, and the thickness of the finished product after rolling is 40-65 mm; A Ｃ３ a heat treatment process of performing normalizing based on +(80 to 130) ° C, a warming time per thickness of the finished product being 0.5 to 1.0 min, air-cooling to room temperature, a two-phase region quenching temperature being 800 to 850 ° C, a warming time per thickness of the finished product being 1.0 to 1.5 min, a cooling rate being 5 to 10 ° C / s, a self-tempering temperature being 350 to 450 ° C, air-cooling to room temperature, and then performing tempering heat treatment; In the smelting process, molten steel is smelted in a converter, using molten pig iron and scrap steel as raw materials, controlling the molten pig iron content to 70-80%, and smelting dephosphorization and decarburization separately using a converter. The oxygen blowing time for dephosphorization is controlled to 7 to 10 minutes, and the oxygen blowing time for decarburization is controlled to 8 to 12 minutes, and the phosphorus mass fraction is finally reduced to within 0.006%. In the smelting step, during calcium treatment, the wire feed speed is 200 to 350 m / min, and the wire feed depth is 1.0 to 2.0 m below the slag layer; In the casting step, the billets are stacked to form a stack, which is slowly cooled for 36 to 54 hours, and the stack is disassembled at 300°C or less; in the electroslag remelting step, the electroslag steel ingot is released from the mold, stacked to form a stack, which is slowly cooled for 48 to 72 hours, and the stack is disassembled at 300°C or less; The specific process parameters of the tempering heat treatment are: tempering temperature is 710-730°C; and the temperature retention time per thickness of the finished product is 60 min + 2.0-4.0 min; 3. A method for manufacturing steel plates for the cylindrical body of the core casing of an advanced nuclear power unit according to claim 1 or 2.

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