Low magnetic permeability austenitic stainless steel hot-rolled plate and bolt for vacuum chamber of nuclear fusion reactor

Abstract

The application relates to the technical field of nuclear fusion vacuum chamber preparation, and discloses a low-magnetic permeability austenitic stainless steel hot-rolled plate and a bolt for a nuclear fusion reactor vacuum chamber, the chemical components of the hot-rolled plate are as follows in percentage by mass: C 0.025%, Mn 1.80%, Si 0.27%, Ni 13.52%, Cr 16.74%, Mo 2.06%, Nb 0.018%, Co 0.050%, N 0.076%, P<=0.045%, S<=0.030%, and the rest is Fe and inevitable impurities; the chemical components of the bolt are as follows in percentage by mass: C 0.021%, Mn 1.849%, Si 0.395%, Ni 10.01%, Cr 17.9%, Mo 2.204%, N 0.16%, P<=0.045%, S<=0.030%, and the rest is Fe and inevitable impurities. The content of the Ni element in the chemical components of the 316L stainless steel is increased, so that the stainless steel hot-rolled plate still has low magnetic permeability after processing and welding; the content of the N element in the chemical components of the 316L stainless steel is increased to reduce the magnetic permeability of the bolt; the magnetic permeability of the obtained hot-rolled plate and bolt is <=1.03, and the requirements of the nuclear fusion vacuum chamber can be met.

Description

Technical Field

[0001] This invention relates to the field of nuclear fusion vacuum chamber preparation technology, and in particular to a low-permeability austenitic stainless steel hot-rolled plate and bolts for a nuclear fusion reactor vacuum chamber. Background Technology

[0002] Research in cutting-edge interdisciplinary fields such as materials science, energy, and life sciences is a key and hot topic against the backdrop of the current accelerated evolution of a new round of technological revolution and industrial transformation. Large scientific facilities, as important platforms for basic and cutting-edge scientific research, play a crucial role in developing new functions, technologies, and key future technologies. A typical large scientific facility is the China Future Fusion Engineering Experimental Reactor (CFEP), a tokamak device that uses magnetic confinement to achieve controlled nuclear fusion in a toroidal container. The vacuum chamber and magnets are its main components, with the vacuum chamber being a core safety component, playing a vital role in ensuring the stable and safe operation of the plasma beam. The materials used in most near-magnetic field structural components must meet permeability requirements. Excessive permeability in components or assemblies can distort the actual magnetic field conditions during device operation, causing localized damage to the magnetic field, or even sudden changes, leading to turbulent or broken particle flows. The accuracy of the magnetic field distribution is a key performance indicator for the CFEP. If the permeability of the vacuum chamber's structural materials exceeds the standard, it will alter the theoretical iron content of the vacuum chamber, thus causing magnetic field distortion.

[0003] Austenitic stainless steel, with its excellent corrosion resistance, high strength, toughness, low outgassing rate, non-magnetic properties, and good weldability, has become one of the most commonly used structural materials in the vacuum chambers of nuclear fusion experimental devices and accelerators. In the design of near-magnetic field vacuum chamber components and their supporting structures in fusion experimental reactors, stringent requirements are placed on magnetic permeability, requiring the relative permeability μ of the finished product to be ≤1.03. Considering the requirements for design strength, load, thermal stability, and magnetic permeability, austenitic stainless steel 316L(N) is commonly used as the material for vacuum chambers.

[0004] The manufacturing of vacuum chambers generally involves a series of processes, including material preparation, rough machining, welding, heat treatment, and finish machining. The microstructure of austenitic stainless steel 316L consists of equiaxed austenite crystals. Austenite is paramagnetic; however, under high-temperature induction, austenitic stainless steel may generate δ-ferrite, or undergo a phase transformation to generate martensite under cold working or ion irradiation. Martensite and δ-ferrite are ferromagnetic. Therefore, due to the large deformation during processing, high cutting temperatures, and the ease with which unstable austenite phases transform into magnetic ferrite or martensite phases during welding, the magnetic permeability of austenitic stainless steel exceeds the standard after processing, resulting in a permeability μ > 1.03.

[0005] In addition, a large number of 316L(N) austenitic stainless steel bolts are needed in the vacuum chamber assembly process, but the magnetic permeability of 316L stainless steel bolts available on the market generally does not meet the requirements. Summary of the Invention

[0006] Based on the technical problems existing in the background technology, the present invention proposes a hot-rolled plate and bolts of low magnetic permeability austenitic stainless steel for use in the vacuum chamber of nuclear fusion reactor.

[0007] The present invention proposes a hot-rolled austenitic stainless steel plate with low magnetic permeability for use in the vacuum chamber of a nuclear fusion reactor. Its chemical composition, by mass percentage, is as follows: C 0.025%, Mn 1.80%, Si 0.27%, Ni 13.52%, Cr 16.74%, Mo 2.06%, Nb 0.018%, Co 0.050%, N 0.076%, P≤0.045%, S≤0.030%, with the remainder being Fe and unavoidable impurities.

[0008] This invention also proposes a method for preparing the above-mentioned hot-rolled austenitic stainless steel plate with low magnetic permeability for the vacuum chamber of a nuclear fusion reactor, the steps of which are as follows:

[0009] S1. Electric furnace smelting: Adding furnace charge into an electric furnace for smelting to obtain molten steel;

[0010] S2, AOD refining: The molten steel is treated by slag removal, and the molten steel after slag removal is added into the AOD furnace. A nitrogen-oxygen mixed gas is blown into the molten steel to refine it. During the blowing process, the content of each element is adjusted to the target composition, and the steel is tapped to obtain AOD refined molten steel.

[0011] S3, LF Refining: AOD refined molten steel is deoxidized, desulfurized and alloy element fine-tuned in an LF furnace to obtain LF refined molten steel;

[0012] S4. Continuous casting: LF refined steel is poured into a mold to cast flat ingots, resulting in molded flat ingots.

[0013] S5. Hot rolling: The die-cast flat ingot is heated and hot-rolled into a plate of the required specifications. After pickling, the hot-rolled plate is obtained.

[0014] Preferably, in S1, the tapping temperature is 1600–1640°C.

[0015] Preferably, in S2, the O2:N2 ratio in the nitrogen-oxygen mixture is 7 to 9.

[0016] Preferably, in S5, the final rolling temperature of hot rolling is between 800 and 950°C.

[0017] The present invention also proposes an austenitic stainless steel bolt for vacuum chamber assembly, characterized in that its chemical composition by mass percentage is: C 0.021%, Mn 1.849%, Si 0.395%, Ni 10.01%, Cr 17.9%, Mo 2.204%, N 0.16%, P≤0.045%, S≤0.030%, with the remainder being Fe and unavoidable impurities.

[0018] The present invention also proposes a method for preparing the above-mentioned austenitic stainless steel bolts for vacuum chamber assembly, characterized in that stainless steel plates are laser-cut and machined into bolts.

[0019] Preferably, the bolt is a hexagonal head fully threaded bolt.

[0020] Compared with the prior art, the beneficial effects of this application are reflected in:

[0021] 1. This invention increases the Ni content in the chemical composition of 316L stainless steel, so that the hot-rolled stainless steel plate maintains a low magnetic permeability after processing and welding, with a magnetic permeability ≤1.03, which meets the requirements of nuclear fusion vacuum chambers, and the Ni content does not exceed the upper limit specified in the national standard for 316L.

[0022] 2. This invention increases the nitrogen content in the chemical composition of 316L stainless steel, so that the magnetic permeability of the stainless steel bolts processed from it is ≤1.03, which can meet the requirements for bolts used in vacuum chamber assembly, and the nitrogen content meets the requirements of the national standard for 316L. Attached Figure Description

[0023] Figure 1 The graph shows the magnetic permeability of a test plate made from the hot-rolled plate of Example 1.

[0024] Figure 2 This is a magnetic permeability test chart of a processed plate made from the hot-rolled plate of Example 1;

[0025] Figure 3 This is a magnetic permeability test diagram of the weld seam of a finished product processed from the hot-rolled plate of Example 1;

[0026] Figure 4 This is a magnetic permeability test diagram of the bolt shank portion of the bolt in Example 2;

[0027] Figure 5 This is a magnetic permeability test diagram of the bolt head portion of the bolt in Example 2;

[0028] Figure 6 This is a graph showing the magnetic permeability test results of the bolt shank portion of the bolt in Comparative Example 2.

[0029] Figure 7This is a graph showing the magnetic permeability test results of the bolt head portion of the bolt in Comparative Example 2. Detailed Implementation

[0030] The technical solution of the present invention will now be described in detail through specific embodiments.

[0031] Example 1

[0032] A 20mm thick 316L hot-rolled sheet has the following chemical composition by mass percentage: C 0.025%, Mn 1.80%, Si 0.27%, Ni 13.52%, Cr 16.74%, Mo 2.06%, Nb 0.018%, Co 0.050%, N 0.076%, P 0.023%, S 0.0039%;

[0033] The preparation method involves conventional electric furnace + AOD + LF heating and smelting, die casting into flat ingots, and then hot rolling to obtain the final product; the specific operation is as follows:

[0034] S1. Electric furnace smelting: Add furnace charge into the electric furnace for smelting, and tap the steel at a temperature of 1620-1630℃.

[0035] S2, AOD refining: The molten steel is slag-removed and then poured into the AOD furnace. A nitrogen-oxygen mixture (O2:N2=8) is blown into the molten steel to refine it. During the refining process, the content of each element is adjusted to the target composition, and the steel is tapped.

[0036] S3, LF Refining: AOD refined molten steel is deoxidized, desulfurized and alloy element fine-tuned in an LF furnace to obtain LF refined molten steel;

[0037] S4. Continuous casting: LF refined steel is poured into a mold to cast flat ingots, resulting in molded flat ingots.

[0038] S5. Hot rolling: The die-cast flat ingot is heated and hot rolled into a plate of the required specifications. The hot rolling temperature is 870-880℃. After pickling, the hot-rolled plate is obtained.

[0039] Example 2

[0040] An austenitic stainless steel bolt, characterized in that its chemical composition, by mass percentage, is: C 0.021%, Mn 1.849%, Si 0.395%, Ni 10.01%, Cr 17.9%, Mo 2.204%, N 0.16%, P 0.012%, S 0.0122%, with the remainder being Fe and unavoidable impurities;

[0041] The preparation method is as follows: Purchased 316LN plates that meet national standards are laser-cut into appropriate sizes and then machined by turning and other machining methods. The precision and dimensions meet the requirements of "GBT 5783-2016 Hexagonal Head Bolt Full Thread".

[0042] The magnetic permeability performance of the products prepared in Examples 1-2 was tested using a magnetic permeability tester. Commercially available hot-rolled steel plate was used as Comparative Example 1, and bolts made from commercially available 316LN steel plate were used as Comparative Example 2 for magnetic permeability testing and comparison.

[0043] The chemical compositions of the purchased hot-rolled steel sheet and 316LN sheet were tested using a spectrometer, and are as follows:

[0044] Comparative Example 1: A commercially available 20mm thick 316L hot-rolled sheet, with the following chemical composition by mass percentage: C 0.020%, Mn 1.17%, Si 0.49%, Ni 10.13%, Cr 16.95%, Mo 2.05%, Nb 0.017%, Co 0.046%, N 0.05%, P 0.027%, S 0.001%, with the remainder being Fe and unavoidable impurities; its magnetic permeability μ≤1.03;

[0045] Comparative Example 2: Commercially available 316LN sheet, whose chemical composition by mass percentage is: C 0.020%, Mn 1.068%, Si 0.371%, Ni 10.36%, Cr 17.9%, Mo 2.013%, P 0.016%, S < 0.0005%, with the remainder being Fe and unavoidable impurities.

[0046] The specific procedures for permeability testing are as follows:

[0047] 1. Hot-rolled plate: The magnetic permeability of the hot-rolled plate raw material is measured, and then a test plate is obtained by plasma cutting. Its magnetic permeability is measured. Then, the test plate is processed by lathe, planer and milling machine to obtain the processed plate, and its magnetic permeability is measured. Finally, the sample is welded in steps, and the magnetic permeability of the finished product after welding is measured.

[0048] The measurement results are shown in Table 1 and Figure 1-3 .

[0049] 2. Assembly bolts: The magnetic permeability of the bolt studs and nuts was measured separately; the test results are shown in Table 2 and... Figure 4-7 .

[0050] Table 1. Magnetic permeability data of hot-rolled plates

[0051]

[0052] Table 2. Magnetic permeability data of bolts

[0053]

[0054] From Table 1 and Figure 1-3 As can be seen, increasing the nickel content in the hot-rolled plate can effectively control the magnetic permeability of 316L austenitic stainless steel hot-rolled plate before and after processing and welding to be ≤1.03.

[0055] From Table 2 and Figure 4-7 As can be seen, using austenitic stainless steel bolts in the vacuum chamber increases the nitrogen content in the composition, which can reduce the magnetic permeability of the product.

[0056] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A hot-rolled austenitic stainless steel plate with low magnetic permeability for use in the vacuum chamber of a nuclear fusion reactor, characterized in that, Its chemical composition by mass percentage is as follows: C 0.025%, Mn 1.80%, Si 0.27%, Ni 13.52%, Cr 16.74%, Mo 2.06%, Nb 0.018%, Co 0.050%, N 0.076%, P≤0.045%, S≤0.030%, with the remainder being Fe and unavoidable impurities; The preparation method of the low-permeability austenitic stainless steel hot-rolled plate for the vacuum chamber of the nuclear fusion reactor includes the following steps: S1. Electric furnace smelting: Adding furnace charge into an electric furnace for smelting to obtain molten steel; S2, AOD refining: The molten steel is treated by slag removal, and the molten steel after slag removal is added into the AOD furnace. A nitrogen-oxygen mixed gas is blown into the molten steel to refine it. During the blowing process, the content of each element is adjusted to the target composition, and the steel is tapped to obtain AOD refined molten steel. S3, LF Refining: AOD refined molten steel is deoxidized, desulfurized and alloy element fine-tuned in an LF furnace to obtain LF refined molten steel; S4. Continuous casting: LF refined steel is poured into a mold to cast flat ingots, resulting in molded flat ingots. S5. Hot rolling: The die-cast flat ingot is heated and hot-rolled into a plate of the required specifications. After pickling, the hot-rolled plate is obtained.

2. The low-permeability austenitic stainless steel hot-rolled plate for the vacuum chamber of a nuclear fusion reactor according to claim 1, characterized in that, In S1, the tapping temperature is 1600~1640℃.

3. The low-permeability austenitic stainless steel hot-rolled plate for the vacuum chamber of a nuclear fusion reactor according to claim 1, characterized in that, In S2, the ratio of O2 to N2 in the nitrogen-oxygen mixture is 7 to 9.

4. The low-permeability austenitic stainless steel hot-rolled plate for the vacuum chamber of a nuclear fusion reactor according to claim 1, characterized in that, In S5, the hot rolling final rolling temperature is 800–950℃.

5. An austenitic stainless steel bolt for assembling a vacuum chamber, characterized in that, Its chemical composition by mass percentage is as follows: C 0.021%, Mn 1.849%, Si 0.395%, Ni 10.01%, Cr 17.9%, Mo 2.204%, N 0.16%, P≤0.045%, S≤0.030%, with the remainder being Fe and unavoidable impurities; The bolt is made by laser cutting stainless steel sheet and then machining it into a bolt; the magnetic permeability of the bolt is ≤1.

03.

6. The austenitic stainless steel bolt for vacuum chamber assembly according to claim 5, characterized in that, The bolt is a hexagonal head fully threaded bolt.

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