Steel plate for nuclear power CB20 module and manufacturing method thereof

Abstract

The invention relates to a steel plate for a nuclear power CB20 module and a manufacturing method of the steel plate. The steel plate comprises the following chemical components in percentage by weight: 0.08%-0.22% of C, 0.55%-1.10% of Mn, less than or equal to 0.010% of P, 0.005%-0.015% of S, 0.67%-1.50% of Ni, less than or equal to 0.75% of Cr, 0.3%-1.0% of Mo, 0.02%-0.12% of Nb, 0.0005%-0.006% of B, 0.002%-0.050% of V, less than or equal to 0.10% of Ti, 0.12%-0.53% of Cu and the balance of Fe and inevitable impurities. Through cooperation of the chemical components and the production process, the produced steel plate has high strength and toughness, high die weldability and high temperature resistance, and can meet the requirement for high-strength nuclear power mechanical module steel at the present stage.

Description

Technical Field

[0001] The present invention relates to the technical field of steel production for nuclear power, and particularly relates to a steel plate for nuclear power CB20 module and a manufacturing method thereof. Background Art

[0002] The CB20 module is a steel structure water tank module of the passive containment cooling system (PCS) of the third-generation AP1000 nuclear power plant. It is located on top of the shield building and provides passive cooling water source for the steel containment in accident conditions. The CB20 module is a multi-component assembly, generally composed of many sub-modules assembled and welded. A module refers to an assembly composed of materials and components. After prefabrication in the workshop, the module as a whole unit facilitates and accelerates on-site construction. Prefabrication and assembly of the module before its installation avoid excessive work in the narrow space at its final position, thus allowing installation and civil engineering to be carried out in parallel. For the AP1000 nuclear power plant, divided by materials and components, the modules can be divided into structural modules and mechanical modules. The structural module is generally composed of steel plates, steel sections and internal concrete, and is used to form a complete plant structure. The mechanical module is composed of equipment, pipelines, pipe supports, pumps, etc. It is prefabricated and installed as a unit in the workshop, and finally transported to the site and installed in each area.

[0003] With the increasing maturity of modular technology and the accumulation of application experience, the scope of modular design and construction in nuclear power plants is becoming wider and wider, the designed mechanical modules are becoming larger and larger, and at the same time, the strength requirements for steel plates adapting to mechanical modules are also becoming higher and higher. Under this premise, the demand for high-strength steel for nuclear power mechanical modules is very urgent.

[0004] At present, there are some researches on high-strength steel for nuclear power mechanical modules at home and abroad, but the technical solutions involved in the published literature have obvious differences from the present invention in terms of composition, production method, performance, product category, etc.

[0005] The Chinese patent application with the application number 201310083274.7 discloses "a high-strength and tough steel plate for mechanical module supports in nuclear power plants and its manufacturing method". The mass percentage of its chemical elements is as follows: C: 0.08 - 0.22%; Si: 0.15 - 0.45%; Mn: 0.60 - 1.10%; P ≤ 0.020%; S ≤ 0.015%; Ni: 0.60 - 1.00%; Cr: 0.40 - 0.70%; Cu: 0.15 - 0.55%; Mo: 0.40 - 0.60%; V: 0.020 - 0.080%; Ti: 0.008 - 0.030%; B: 0.0005 - 0.005%; Al: 0.020 - 0.050%, and the balance is iron and impurities. On the basis of a low-carbon content design, alloying elements are appropriately added to make the tensile strength of the steel reach more than 800 MPa. Compared with the present invention, the chemical compositions of the two are different, the properties of the steel plates are also different, and the thickness of the finished steel plates produced is smaller.

[0006] The Chinese patent application with the application number 201110117614.4 discloses a "steel for nuclear containers with a tensile strength greater than 690 MPa and its production method". The mass percentage of its chemical elements is as follows: C ≤ 0.08%, Si: 0.15 - 0.50%, Mn: 1.30 - 1.60%, Alt: 0.01 - 0.05%, Ni: 0.42 - 0.70%, Mo: 0.32 - 0.60%, Cr: 0.10 - 0.30%, Ti: 0.01 - 0.04%, control elements: P ≤ 0.008%, S ≤ 0.005%, N ≤ 0.005%, Cu ≤ 0.03%, V ≤ 0.007%, Sn ≤ 0.005%, Sb ≤ 0.005%, As ≤ 0.010%, Pb ≤ 0.005%, and the rest is Fe and unavoidable impurities. The yield strength of the steel plate is ≥ 570 MPa, the tensile strength is 690 - 860 MPa, and the impact at -20°C is ≥ 100 J. The chemical composition of its steel plate is different from that of the present invention, and its requirements for elements such as P, S, N, and Cu in the chemical composition of the steel plate are very strict, resulting in greater smelting difficulty and stricter requirements for raw materials. At the same time, it does not involve the mechanical properties of the steel plate after long-term simulated post-weld heat treatment.

[0007] The Chinese patent application with the application number 200810119504.X discloses "a heat treatment method for high-strength building steel plates with a yield strength of 420 MPa grade". The chemical composition of the steel plate by weight percentage is C: 0.12 - 0.18%, Si: 0.30 - 0.40%, Mn: 1.40 - 1.50%, Nb: 0.03 - 0.05%, V: 0.05 - 0.1%, Ti: 0.01 - 0.02%, P < 0.015%, S < 0.005%, and the rest is Fe and inevitable inclusions. It requires the Nb content to reach more than 0.03% to meet the corresponding mechanical properties. The purpose is to expand the non-recrystallization zone temperature and increase the finish rolling temperature through a high Nb content. Its heat treatment process is normalizing and controlled cooling for the steel plate with controlled cooling. This method is conducive to controlling the shape of the steel plate, but after the finish rolling temperature is increased, the effect of ultra-fast cooling will be weakened, which is not conducive to the rapid passage of the steel plate core through the austenite zone to reach the phase transformation zone. Therefore, it is not conducive to the precipitation of Nb in the steel plate core during the phase transformation process, resulting in a lower strength of the steel plate core. Summary of the Invention

[0008] The present invention provides a steel plate for nuclear power CB20 module and its manufacturing method. Through the cooperation of chemical composition and production process, the produced steel plate has high strength and toughness, high modulus weldability and high temperature resistance, and can meet the current requirements for high-strength steel for nuclear power mechanical modules.

[0009] In order to achieve the above object, the present invention is realized by adopting the following technical solutions:

[0010] A steel plate for nuclear power CB20 module, the chemical composition by weight percentage is C: 0.08% - 0.22%, Mn: 0.55% - 1.10%, P ≤ 0.010%, S: 0.005% - 0.015%, Ni: 0.67% - 1.50%, Cr ≤ 0.75%, Mo: 0.3% - 1.0%, Nb: 0.02% - 0.12%, B: 0.0005% - 0.006%, V: 0.002% - 0.050%, Ti ≤ 0.10%, Cu: 0.12% - 0.53%, and the balance is Fe and inevitable impurities.

[0011] The mechanical properties of the finished steel plate are: at room temperature, the yield strength ≥ 620 MPa, the tensile strength is 730 - 1000 MPa; the elongation ≥ 16%, the reduction of area ≥ 35%; at 360 °C high temperature, the yield strength ≥ 530 MPa, the tensile strength ≥ 730 MPa, the elongation ≥ 10%, the reduction of area ≥ 50%; the impact energy at -20 °C ≥ 34 J.

[0012] A manufacturing method of a steel plate for nuclear power CB20 module, comprising the following steps:

[0013] (1) Smelting: Using a converter or an electric furnace for smelting;

[0014] (2) Continuous casting: Pour the molten steel after smelting into slab through continuous casting;

[0015] (3) Rolling: The heating temperature of the slab is 1150 - 1300 °C, the starting rolling temperature is 1150 - 1280 °C, and the finishing rolling temperature is 900 - 1150 °C;

[0016] (4) Quenching and tempering treatment: The quenching temperature is 850 °C - 960 °C, and the holding time is 1 - 10 min / mm; the tempering temperature is 580 °C - 680 °C, and the holding time is 1 - 10 min / mm.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] (1) Through the optimization of chemical composition and the reasonable design of process parameters, the steel plate produced by the present invention has excellent low-temperature toughness indexes; after the steel plate is quenched and tempered and simulated post-weld heat treatment (holding temperature 600 °C, holding time 15 hours), the impact energy absorbed at -20 °C remains above 34 J.

[0019] (2) The steel grades conforming to the chemical composition of the present invention have good strength and toughness in different states after quenching and tempering and simulated post-weld heat treatment (holding temperature 600 °C, holding time 15 hours); for the steel plate after quenching and tempering heat treatment and simulated post-weld heat treatment, the yield strength of normal-temperature tension ≥ 620 MPa, and the tensile strength is 730 - 1000 MPa; the yield strength of 360 °C high-temperature tension ≥ 530 MPa, and the tensile strength ≥ 730 MPa. Description of the Drawings

[0020] Figure 1 is the metallographic structure photo of a steel plate for nuclear power CB20 module described in the present invention. Detailed Embodiments

[0021] For the steel plate for nuclear power CB20 module described in the present invention, the chemical composition is by weight percentage: C: 0.08% - 0.22%, Mn: 0.55% - 1.10%, P ≤ 0.010%, S: 0.005% - 0.015%, Ni: 0.67% - 1.50%, Cr ≤ 0.75%, Mo: 0.3% - 1.0%, Nb: 0.02% - 0.12%, B: 0.0005% - 0.006%, V: 0.002% - 0.050%, Ti ≤ 0.10%, Cu: 0.12% - 0.53%, and the balance is Fe and unavoidable impurities.

[0022] The reasons for the composition design of the steel plate for nuclear power CB20 module described in the present invention are as follows:

[0023] (1) Carbon: To ensure that the steel plate has polygonal ferrite and acicular ferrite, a certain carbon content is required. At the same time, carbon can form carbides with alloying elements such as Nb and Cr and precipitate, increasing strength and toughness. If the carbon content is too high, the low-temperature toughness will decrease. To ensure that the steel plate has high strength and toughness and good crack arrest performance, the C content in the present invention is controlled at 0.08% - 0.22%.

[0024] (2) Manganese: It is the main alloying element in steel, which can improve the hardenability and strength of steel through solid solution strengthening, and at the same time can also improve the toughness of steel; however, if the Mn content is too high, it will have a detrimental effect on toughness. Therefore, the Mn content in the present invention is controlled at 0.55% - 1.10%.

[0025] (3) P, S: They are both harmful elements in the steel of the present invention, which will have an adverse effect on the low-temperature impact toughness and lamellar tearing resistance of the steel plate and increase the brittleness of the steel. Phosphorus also reduces the weldability, decreases plasticity, and deteriorates the cold bending performance; sulfur reduces the ductility and toughness of the steel and causes cracks during forging and rolling. Therefore, the lower the content of both is better, but considering the steelmaking conditions and cost, the present invention requires that P in the steel be ≤ 0.010% and S: 0.005% - 0.015%.

[0026] (4) Nickel: A certain content of Ni element can reduce the dislocation movement resistance in steel. As the dislocation movement resistance decreases, the stress in the steel will relax. The present invention precisely uses the Ni element to change the dislocation and substructure of the matrix structure, thereby improving the toughness of the steel. The Ni content in the present invention is controlled at 0.67% - 1.50%.

[0027] (5) Chromium: It can produce solid solution strengthening in steel and increase the corrosion resistance of steel. Chromium cooperates with manganese element to form an Mn-Cr alloy system, improving the overall performance and uniform stability of the steel plate. However, if the chromium content is too high, it will increase the brittle transition temperature of the steel. The present invention controls Cr ≤ 0.75%.

[0028] (6) Molybdenum: It is a strong hardenability element, which helps to improve the hardenability of thick steel plates along the thickness direction, improves the performance stability of the steel plates, and can also temper the steel plates at a higher temperature, thereby improving the plasticity and toughness of the steel plates; at the same time, it can increase the solubility of microalloying elements in austenite, reduce the precipitation of carbonitrides of microalloying elements, and make the microalloying elements precipitate from ferrite at a lower temperature, enhancing the precipitation strengthening effect. Therefore, the present invention requires Mo: 0.3% - 1.0%.

[0029] (7) Niobium: Nb can effectively refine the microstructure by inhibiting austenite recrystallization during the controlled rolling process. At the same time, it can partially dissolve into the solid solution to play a role in solid solution strengthening and improve the high-temperature strength of the steel. Niobium can also reduce the overheating sensitivity and temper brittleness of the steel. Therefore, the Nb content in the present invention is controlled at 0.02% - 0.12%.

[0030] (8) Boron: B can lower the transformation temperature from austenite to ferrite phase, promote the formation of acicular ferrite within grains, and play a role in refining grains. Therefore, in this invention, B is controlled at 0.0005% - 0.006%.

[0031] (9) Vanadium: In quenched and tempered steels, it mainly plays the roles of increasing the strength and yield ratio of the steel, refining grains, and improving strength and toughness. However, vanadium has a strong affinity with carbon and oxygen, and when it exists in the form of carbides, it will affect hardenability. Therefore, in this invention, V is controlled at 0.002% - 0.050%.

[0032] (10) Titanium: It can exert a nitrogen fixation effect, form precipitation phases mainly composed of TiN, inhibit the grain growth of austenite under high-temperature conditions, and can also improve the toughness of the heat-affected zone after welding; during the welding process, TiN particles can prevent the grain growth in the coarse-grained heat-affected zone and improve the low-temperature toughness of the welded joint. In addition, due to its low solubility, Ti is likely to appear in the form of interphase precipitation during the transformation from austenite to ferrite, thereby increasing strength. However, excessive Ti will reduce the toughness of the steel. Therefore, in this invention, Ti is controlled ≤0.10%.

[0033] (11) Copper: It can improve the hardenability of the steel, can significantly increase the core strength of thick steel plates, and is also an important element for improving weather resistance. During the slow cooling process of thick steel plates, appropriate amount of Cu can precipitate ε-Cu through self-tempering, thereby increasing the strength of the steel plate. In this invention, Cu is controlled at 0.12% - 0.53%.

[0034] The manufacturing method of the steel plate for nuclear power CB20 module described in this invention includes the following steps:

[0035] (1) Smelting: Use a converter or an electric furnace for melting;

[0036] (2) Continuous casting: Pour the molten steel after smelting into slab billets through continuous casting;

[0037] (3) Rolling: The heating temperature of the slab billet is 1150 - 1300 °C, the starting rolling temperature is 1150 - 1280 °C, and the finishing rolling temperature is 900 - 1150 °C; Through rolling, ensure that the carbonitrides of Nb, V, and Ti are fully dissolved to provide conditions for subsequent dynamic precipitation. During the rolling process in the non-recrystallization zone (T < 950 °C), utilize the strain-induced precipitation of Nb to refine austenite grains, and finally obtain a uniform and fine ferrite / acicular ferrite structure.

[0038] (4) Quenching and tempering treatment: The quenching temperature is 850 °C - 960 °C, and the holding time is 1 - 10 min / mm; The tempering temperature is 580 °C - 680 °C, and the holding time is 1 - 10 min / mm.

[0039] Quenching in the two-phase region can retain some undissolved carbides and inhibit the growth of austenite grains; quenching in the full austenite region ensures maximum solution strengthening. High-temperature tempering promotes the precipitation of nano-phases such as ε-Cu and Mo2C, eliminates quenching stress, and maintains strength through "secondary hardening" (precipitation of Mo and V carbides).

[0040] The manufacturing method of the steel plate for nuclear power CB20 module described in the present invention has the following mechanism of action:

[0041] 1) Strength and toughness matching: The low-carbon + Mn-Cr-Mo-B composition design synergistically improves hardenability. Combining thermo-mechanical control process (TMCP) and quenching and tempering treatment realizes the multi-mechanism synergistic effect of fine grain strengthening (grain size ≥ ASTM 10 grade) + precipitation strengthening + dislocation strengthening.

[0042] 2) Weldability guarantee: Low P / S (P ≤ 0.010%, S ≤ 0.015%) + TiN grain control reduces HAZ embrittlement; adding Cu and Ni improves the toughness of the weld.

[0043] 3) Weather resistance guarantee: The combined action of Cr-Cu-Mo forms a stable passivation film to adapt to the long-term service environment of nuclear power modules.

[0044] According to the chemical composition and manufacturing method described in the present invention, the mechanical properties of the obtained finished steel plate are as follows: (1) At room temperature, the yield strength ≥ 620 MPa, the tensile strength is 730 - 1000 MPa; the elongation ≥ 16%, and the reduction of area ≥ 35%; (2) At 360 °C, the yield strength ≥ 530 MPa, the tensile strength ≥ 730 MPa, the elongation ≥ 10%, and the reduction of area ≥ 50%; the impact energy at -20 °C ≥ 34 J.

[0045] The metallographic structure photos of the steel plate for nuclear power CB20 module described in the present invention are as Figure 1 shown.

[0046] To more intuitively illustrate the present invention, the implementation manners of the present invention will be further described in combination with embodiments. The following embodiments are only the preferred specific implementation manners of the present invention, but the protection scope of the present invention is not limited thereto. Any technical solutions that can be obtained obviously by those skilled in the art within the technical scope disclosed by the present invention, including simple changes or equivalent replacements, are within the protection scope of the present invention.

[0047]

Embodiment

[0048] The chemical compositions of the steels in each embodiment are shown in Table 1.

[0049] Table 1 Chemical compositions of the steels in each embodiment (wt%)

[0050] Example C Mn Ni Cr Mo Nb B V Ti Cu 1 0.08 1.10 0.67 0.70 0.90 0.12 0.0005 0.019 0.001 0.53 2 0.21 1.00 1.30 0.20 0.40 0.03 0.004 0.005 0.003 0.49 3 0.18 0.65 0.80 0.65 0.50 0.09 0.001 0.035 0.030 0.24 4 0.14 0.85 1.20 0.40 0.60 0.07 0.0035 0.015 0.090 0.39 5 0.16 0.75 0.90 0.50 0.85 0.06 0.003 0.002 0.010 0.33 6 0.12 0.80 1.00 0.55 0.80 0.05 0.0009 0.025 0.005 0.29 7 0.20 0.70 1.10 0.60 0.30 0.08 0.005 0.029 0.050 0.41 8 0.09 0.90 0.85 0.30 0.35 0.04 0.0025 0.009 0.070 0.19 9 0.10 0.60 0.75 0.10 0.70 0.11 0.002 0.048 0.007 0.51 10 0.22 0.55 1.50 0.75 1.00 0.02 0.006 0.050 0.100 0.12

[0051] The main production process (rolling and heat treatment) parameters of each embodiment are shown in Table 2.

[0052] Table 2 Main production process parameters of the steel plates of each embodiment

[0053]

[0054] The main properties of the finished steel plates of each embodiment are shown in Table 3. The process parameters of the simulated post-weld heat treatment (mock welding) are: holding temperature 605°C, holding time 16 h, heating and cooling rate ≤ 55°C / h above 400°C.

[0055] Table 3 Main properties of the finished steel plates of each embodiment

[0056]

[0057] As described above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its inventive concept, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A steel plate for nuclear power CB20 module, characterized in that, The chemical composition by weight percentage is: C: 0.08% - 0.22%, Mn: 0.55% - 1.10%, P ≤ 0.010%, S: 0.005% - 0.015%, Ni: 0.67% - 1.50%, Cr ≤ 0.75%, Mo: 0.3% - 1.0%, Nb: 0.02% - 0.12%, B: 0.0005% - 0.006%, V: 0.002% - 0.050%, Ti ≤ 0.10%, Cu: 0.12% - 0.53%, and the balance is Fe and unavoidable impurities.

2. The steel plate for a nuclear power CB20 module according to claim 1, characterized in that, The mechanical properties of the finished steel plate are as follows: at room temperature, the yield strength ≥ 620 MPa, the tensile strength is 730 - 1000 MPa; the elongation ≥ 16%, and the reduction of area ≥ 35%; at 360 °C high temperature, the yield strength ≥ 530 MPa, the tensile strength ≥ 730 MPa, the elongation ≥ 10%, and the reduction of area ≥ 50%; The impact energy at -20 °C ≥ 34 J.

3. A manufacturing method of a steel plate for a nuclear power CB20 module according to any one of claims 1 or 2, characterized in that, It includes the following steps: (1) Smelting: Using a converter or an electric furnace for melting; (2) Continuous casting: Pouring the molten steel after smelting into a slab through continuous casting; (3) Rolling: The heating temperature of the slab is 1150 - 1300 °C, the starting rolling temperature is 1150 - 1280 °C, and the finishing rolling temperature is 900 - 1150 °C; (4) Quenching and tempering treatment: The quenching temperature is 850 °C - 960 °C, and the holding time is 1 - 10 min / mm; the tempering temperature is 580 °C - 680 °C, and the holding time is 1 - 10 min / mm.

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