A welding wire for ferritic stainless steel resistant to high-temperature molten salt-liquid Cd corrosion and its application

Abstract

This invention discloses a high-temperature molten salt-liquid Cd corrosion resistant ferritic stainless steel welding wire and its application. This welding wire is suitable for welding spent fuel dry reprocessing electrolytic refining / extraction vessels, belonging to the field of metal materials (welding consumables) technology. The chemical composition of the welding wire (wt.%) is: C: <0.05%, Si: 1.5-2.5%, Ti: 0.1-0.7%, C+N: 0.02-0.07%, Al: 0.2-0.6%, Cr: 15.5-18.5%, Mo: 0.2-0.6%, with the balance being Fe and unavoidable impurity elements. The weld obtained by welding with the wire of this invention exhibits excellent resistance to high-temperature molten salt corrosion and liquid Cd corrosion. It also possesses high strength and toughness, making it suitable for welding spent fuel dry reprocessing electrolytic refining / extraction vessels, ensuring their service safety in the complex corrosive environment of high-temperature molten salt-liquid Cd.

Description

Technical Field

[0001] This invention relates to the field of metal materials (welding materials), specifically to a high-temperature molten salt-liquid Cd corrosion resistant ferritic stainless steel welding wire, which is suitable for welding spent fuel dry reprocessing electrolytic refining / extraction vessels. Background Technology

[0002] With the support of a closed fuel cycle, the utilization rate of uranium resources in integrated fast reactors can be increased from 1% in pressurized water reactors to over 60%. Dry reprocessing technology is a key component of the closed fuel cycle in integrated fast reactors and a practical technological choice for it. It is currently the only feasible technology to solve the problems of uranium resource supply and nuclear waste disposal. Electrolytic refining / extraction in dry reprocessing technology is a crucial step in realizing the recovery and utilization of uranium and transuranic elements from spent fuel. This step takes place in an electrolytic refining / extraction vessel, but the harsh and complex environment of high temperature (550℃) and corrosion (molten chloride-liquid Cd coupling environment) poses significant challenges to the mechanical and corrosion resistance properties of the materials used in the transuranic electrolytic refining / extraction vessel components and their welded joints. Currently, there is no mature material selection experience for such equipment worldwide, and the research and development of related materials and technologies is one of the limiting factors for the engineering and industrialization of dry reprocessing technology. Summary of the Invention

[0003] This invention relates to the field of metal materials (welding consumables), specifically to a high-temperature molten salt-liquid Cd corrosion resistant ferritic stainless steel welding wire. This welding wire is suitable for welding spent fuel dry reprocessing electrolytic refining / extraction vessels. To achieve the above objective, the technical solution adopted by this invention is as follows:

[0004] A high-temperature molten salt-liquid Cd corrosion resistant ferritic stainless steel welding wire, the chemical composition of which is as follows by weight percentage:

[0005] C: <0.05%, Si: 1.5-2.5%, Ti: 0.1-0.7%, C+N: 0.02-0.07%, Al: 0.2-0.6%, Cr: 15.5-18.5%, Mo: 0.2-0.6%, with the balance being Fe and unavoidable impurity elements (including one or more of O, H, B, etc.). The chemical composition of this welding wire is: P <0.01% (mass fraction), S <0.01% (mass fraction).

[0006] The welding wire can be produced by vacuum induction furnace smelting or by electric furnace smelting and ladle refining. The final chemical composition of the welding wire should meet the requirements of the above range.

[0007] This welding wire is used for welding of electrolytic refining / extraction containers for dry reprocessing of spent fuel. The welding process is as follows: take a Φ1.2mm welding wire, use tungsten inert gas (TIG) welding, the joint type is butt joint, and the welding parameters are: welding current 80-160A, current type / polarity DC positive, welding speed 0.07-0.12m / min, arc protection using high purity argon gas with a purity ≥99.995%, and gas flow rate 12-18L / min.

[0008] The present invention has the following advantages:

[0009] 1. Experimental verification shows that the welding wire of this invention can be used for welding of electrolytic refining / extraction containers for dry reprocessing of spent fuel. The welding process is simple and highly feasible. Welding can be carried out using the commonly used tungsten inert gas (TIG) welding method. The welding current is 120-160A, the current type / polarity is DC positive, the welding speed is 0.07-0.12m / min, and the arc protection uses high-purity argon gas with a purity of ≥99.995% and a gas flow rate of 12-18L / min.

[0010] 2. When using the ferritic stainless steel welding wire of the present invention to obtain welds with excellent resistance to molten salt corrosion and liquid Cd corrosion, the welding process is stable, with few defects and good process performance.

[0011] 3. The ferritic stainless steel welding wire of the present invention can produce welds with excellent resistance to molten salt corrosion and liquid Cd corrosion, and the welds have excellent resistance to molten salt corrosion and liquid Cd corrosion at 550°C.

[0012] 4. The weld obtained by welding ferritic stainless steel using the high-temperature molten salt-liquid Cd corrosion resistant welding wire of this invention exhibits a corrosion depth ≤10μm after 200h in a molten salt environment (system: 93.8wt.% (45wt.% LiCl-55wt.% KCl)-6wt.% CeCl3-0.1wt.% SrCl2-0.1wt.% CsCl) at 550℃ (100ppm O2+18ppm H2O), and a corrosion depth ≤4μm after 200h in a liquid Cd corrosion environment at 550℃. The weld has a room temperature yield strength >380MPa, a tensile strength >550MPa, a 550℃ yield strength >165MPa, and a tensile strength >210MPa. The room temperature V-shaped impact energy is >10.6J / cm². 2

[0013] The main ideas and mechanisms of this invention are as follows:

[0014] Ferritic stainless steel welds resistant to high-temperature molten salt-liquid Cd corrosion require excellent resistance to molten salt corrosion and liquid metal dissolution. Ni-based materials exhibit good resistance to molten salts but are highly soluble in liquid metals such as liquid Cd, Pb, and Bi. Fe-based materials offer relatively good resistance to liquid metals but poor resistance to molten salt corrosion. Therefore, Fe-based materials are selected based on a comprehensive evaluation, and their corrosion resistance is enhanced by adding corrosion-resistant elements. Thus, the welding wire of this invention uses an Fe-based alloy with 17% Cr added as an oxide film performance element, along with a small amount of Si. Utilizing Si's "third component" effect on the Cr oxide film, the film-forming ability of the oxide film is improved, resisting external corrosion. To further improve corrosion resistance, the welding wire of this invention removes austenitizing elements such as Mn, Ni, and reduces C, thereby designing a single ferrite matrix to avoid accelerated corrosion due to multiple matrix components within the material. However, the single ferrite structure results in coarse weld structure and poor weld impact toughness. Therefore, the welding wire of this invention further adds a small amount of Ti, N, and Al to form Ti(C,N). AlN acts as a grain nucleating agent, thereby refining the grains, improving impact toughness, and playing a certain role in improving strength. Attached Figure Description

[0015] Figure 1 Schematic diagram of sampling for mechanical and corrosion specimens;

[0016] Figure 2 The image shows a cross-sectional view of the corrosion layer after molten chloride corrosion at 550°C for 200 hours, as described in Example 1.

[0017] Figure 3 The image shows a cross-sectional view of the corrosion layer after Cd etching at 550°C for 200 hours, as described in Example 1.

[0018] Figure 4 The cross-sectional photographs of the corrosion layer after molten chloride corrosion at 550℃ for 200h are used to characterize the corrosion layer of Comparative Example 1.

[0019] Figure 5 The image shows a cross-sectional photograph of the corrosion layer after Cd corrosion at 550℃ for 200 hours, which is used to characterize the corrosion layer of Comparative Example 1. Detailed Implementation

[0020] The ferritic stainless steel welding wire in this invention can be produced by vacuum induction furnace smelting or by electric furnace refining, as long as the final chemical composition of the welding wire meets the above requirements. Furthermore, the entire smelting and processing of the welding wire is not significantly different from that of ordinary stainless steel welding wire, and there are no additional special technical requirements. The base material used in the welding tests of this invention is 1Cr17 ferritic stainless steel.

[0021] The following are preferred embodiments of the present invention. In the following embodiments and comparative examples, the welding wires were all produced using a vacuum induction furnace. The welding wire specification was Φ1.2mm, and manual tungsten inert gas (TIG) welding was employed. The joint type was a butt weld of a 15mm thick plate (the maximum thickness of the full weld tensile test specimen and impact test specimen is 10mm, therefore the thickness of the welding plate must be greater than 10mm to meet the sampling size requirements). The bottom gap of the butt plates was 15mm, and the bevel angle on one side was 22.5°. See [link to relevant documentation]. Figure 1 The welding parameters are as follows: welding current 140A, current type DC positive polarity, welding speed 0.1m / min, arc shielding atmosphere argon, molar purity ≥99.995%, and shielding gas flow rate 16L / min during welding.

[0022] After welding, the weld is subjected to post-weld heat treatment at 900℃ for 1 hour followed by air cooling. Corrosion and mechanical tests are performed on the entire weld. Sampling locations are as follows: Figure 1 As shown. Since the base material used in the welding test of this invention is 1Cr17 ferritic stainless steel, the content of its main elements such as Fe and Cr is consistent with that of the welding material of this invention, which belongs to homogeneous welding. Moreover, the bottom gap width is 15mm during welding, which further eliminates the dilution effect of the base material on the weld. In addition, the argon arc welding has excellent protection and very low element burn-off rate. Therefore, the chemical composition of the weld can be considered to be consistent with the composition of the welding wire.

[0023] The corrosion sample dimensions were 10mm × 8mm × 2mm. The six surfaces of the sample were sequentially polished and chamfered using 400#, 800#, 1200#, and 2000# sandpaper. The samples were then ultrasonically cleaned for 10 minutes each with deionized water and ethanol, respectively, for molten salt immersion corrosion tests and liquid Cd immersion corrosion tests. High-purity Cd particles were used for the liquid Cd immersion test, while a mixed salt system of 93.8 wt.% (45 wt.% LiCl - 55 wt.% KCl) - 6 wt.% CeCl3 - 0.1 wt.% SrCl2 - 0.1 wt.% CsCl was used for the molten salt immersion test. The high-purity Cd particles and the mixed salt were placed sequentially in a corundum crucible. The samples for the molten salt immersion corrosion test and the liquid Cd immersion corrosion test were suspended at corresponding heights, placing them in either the mixed salt or the Cd particles, respectively. Because Cd has a higher density than the mixed salt and the two are immiscible, in the high-temperature molten state, liquid Cd is at the bottom of the crucible, and the mixed salt is at the top. This provides convenient conditions for simultaneously conducting molten salt immersion corrosion tests and liquid Cd immersion corrosion tests. The crucible containing the mixed salt and Cd was placed in an atmosphere furnace, and then a vacuum was drawn and an Ar-O2 mixed gas (O2 content of 100.35 ppm) was introduced to ensure that the oxygen content in the furnace was 100 ppm O2. The water content in the furnace was measured to be 18 ppm using a dew point meter. In addition, the water and oxygen contents were monitored using a dew point meter and an oxygen analyzer during the test to ensure the accuracy of the experimental atmosphere. The crucible was heated from room temperature to 550℃ over 2.5 hours, and the corrosion test was conducted at 550℃ for 200 hours.

[0024] The room temperature tensile test specimens are full weld specimens, meaning the specimen is completely located within the weld, with its length parallel to the weld length direction. A schematic diagram of the sampling location is shown below. Figure 1 The specimen dimensions and test methods for room temperature tensile testing shall be in accordance with GB / T 228.1-2021 "Metallic materials, tensile testing—Part 1: Test method at room temperature". The specimen dimensions and test methods for 550℃ tensile testing shall be in accordance with GB / T228.2-2021 "Metallic materials, tensile testing—Part 2: Test method at high temperature". Both room temperature and high temperature tensile specimens shall be circular cross-section specimens with a parallel section diameter of 5 mm and a parallel section length of 30 mm.

[0025] The notch of the room temperature impact specimen was located at the centerline of the weld. The specimen size and test method were in accordance with GB / T229-2020 "Metallic Materials Charpy Pendulum Impact Test Method". A schematic diagram of the sampling location is shown below. Figure 1 The sample size is 55×10×10mm.

[0026] Example 1

[0027] The basic chemical composition (by weight) of this type of high-temperature molten salt-liquid Cd corrosion resistant ferritic stainless steel welding wire is as follows:

[0028] C: 0.041%, Si: 2.16%, Ti: 0.29%, N: 0.016%, Al: 0.3%, Cr: 16.69%, Mo: 0.4%, S: 0.0028%, P: 0.005%, with the balance being Fe and unavoidable impurity elements (including one or more of O, H, B, etc.).

[0029] Example 2

[0030] The basic chemical composition (by weight) of this type of high-temperature molten salt-liquid Cd corrosion resistant ferritic stainless steel welding wire is as follows:

[0031] C: 0.045%, Si: 2.16%, Ti: 0.62%, N: 0.012%, Al: 0.29%, Cr: 16.65%, Mo: 0.41%, S: 0.0029%, P: 0.005%, with the balance being Fe and unavoidable impurity elements (including one or more of O, H, B, etc.).

[0032] Example 3

[0033] The basic chemical composition (by weight) of this type of high-temperature molten salt-liquid Cd corrosion resistant ferritic stainless steel welding wire is as follows:

[0034] C: 0.041%, Si: 2.22%, Ti: 0.37%, N: 0.0028%, Al: 0.32%, Cr: 16.84%, Mo: 0.41%, S: 0.0027%, P: 0.004%, with the balance being one or more of Fe and unavoidable impurity elements (including O, H, B, etc.).

[0035] Comparative Example 1

[0036] The basic chemical composition (by weight) of this type of high-temperature molten salt-liquid Cd corrosion resistant ferritic stainless steel welding wire is as follows:

[0037] C: 0.047%, Si: 0.017%, Ti: 0.006%, N: 0.0020%, Al: 0.003%, Cr: 16.88%, Mo: 0.2%, S: 0.0027%, P: 0.005%, with the balance being Fe and unavoidable impurity elements (including one or more of O, H, B, etc.).

[0038] Comparative Example 2

[0039] The basic chemical composition (by weight) of this type of high-temperature molten salt-liquid Cd corrosion resistant ferritic stainless steel welding wire is as follows:

[0040] C: 0.038%, Si: 2.2%, Ti: 0.29%, N: 0.016%, Al: 0.020%, Cr: 16.96%, Mo: 0.42%, S: 0.0026%, P: 0.005%, with the balance being Fe and unavoidable impurity elements (including one or more of O, H, B, etc.).

[0041] Comparative Example 3

[0042] The basic chemical composition (by weight) of this type of high-temperature molten salt-liquid Cd corrosion resistant ferritic stainless steel welding wire is as follows:

[0043] C: 0.013%, Si: 2.20%, Ti: 0.0018%, N: 0.026%, Al: 0.32%, Cr: 16.85%, Mo: 0.0003%, S: 0.0026%, P: 0.004%, with the balance being Fe and unavoidable impurity elements (including one or more of O, H, B, etc.).

[0044] Comparative Example 4

[0045] The basic chemical composition (by weight) of this type of high-temperature molten salt-liquid Cd corrosion resistant ferritic stainless steel welding wire is as follows:

[0046] C: 0.040%, Si: 0.97%, Ti: 0.30%, N: 0.018%, Al: 0.32%, Cr: 16.79%, Mo: 0.42%, S: 0.0029%, P: 0.004%, with the balance being Fe and unavoidable impurity elements (including one or more of O, H, B, etc.).

[0047] The molten salt corrosion and liquid Cd corrosion section depth of the welds in the above embodiments and comparative examples at 550℃ / 200h are shown in Table 1. The results of room temperature tensile and impact properties are shown in Table 2, and the results of tensile properties at 550℃ are shown in Table 3.

[0048] Table 1. Depth of molten salt corrosion and liquid Cd corrosion of welds at 550℃ / 200h in the examples and comparative examples.

[0049] Molten salt corrosion depth (μm) Liquid Cd corrosion depth (μm) Design Specifications ≤10 ≤4 Example 1 9 3.2 Example 2 9.3 3.8 Example 3 8.9 4 Comparative Example 1 43 7.2 Comparative Example 2 9.2 3.6 Comparative Example 3 8.8 2.9 Comparative Example 4 18 4.8

[0050] Table 2. Results of room temperature tensile strength and impact energy tests on welds in the examples and comparative examples.

[0051]

[0052]

[0053] Table 3. Tensile strength test results of welds in the examples and comparative examples at 550℃.

[0054]

[0055] The weld obtained by the welding wire designed in this invention has the following performance design indicators: ≤10μm corrosion depth after 200h in a molten salt environment (system: 93.8wt.% (45wt.% LiCl-55wt.% KCl)-6wt.% CeCl3-0.1wt.% SrCl2-0.1wt.% CsCl) at 550℃ (100ppm O2 + 18ppm H2O); ≤4μm corrosion depth after 200h in a liquid Cd corrosion environment at 550℃. Regarding mechanical properties: after heat treatment, the weld exhibits a room temperature yield strength >380MPa, tensile strength >550MPa, a 550℃ yield strength >165MPa, and a tensile strength >210MPa. Room temperature impact toughness >10.6J / cm². 2 From Examples 1, 2, 3 and Comparative Examples 1, 2, 3, 4, and Tables 1 to 3, it can be seen that:

[0056] Examples 1, 2, and 3 employ the chemical composition of the welding wire designed according to the present invention. The composition range meets the preferred composition of the welding material as described in claim 1 or 2, and the performance meets the performance design requirements of the present invention. The welding process is stable, with few defects detected by X-ray non-destructive testing, and the process performance is good.

[0057] In Comparative Example 1, the contents of Si, Ti, and Al are not within the scope of the technical solution of this invention. The Si element mainly plays the role of improving the film-forming ability of the protective oxide film. Therefore, its weld seam resistance to molten salt corrosion and liquid Cd corrosion does not meet the design requirements of this invention. Ti and Al play the role of refining grains and improving impact toughness and strength. Therefore, its room temperature yield strength, room temperature tensile strength, room temperature impact toughness, and 550℃ yield strength do not meet the design requirements of this invention.

[0058] In Comparative Example 2, the Al content was not within the scope of the technical solution of the present invention, and the room temperature yield strength, room temperature tensile strength, and room temperature impact toughness of its weld did not meet the design requirements of the present invention.

[0059] In Comparative Example 3, the Ti and Mo contents are not within the scope of the technical solution of the present invention. Mo plays a solid solution strengthening role and can improve strength. Therefore, its weld room temperature yield strength, room temperature tensile strength, room temperature impact toughness, 550℃ yield strength and 550℃ tensile strength do not meet the design requirements of the present invention.

[0060] In Comparative Example 4, the Si content was not within the range of the technical solution of the present invention, and the weld's resistance to molten salt corrosion and resistance to liquid Cd corrosion did not meet the design requirements of the present invention.

[0061] The above embodiments merely illustrate several implementation methods of the present invention and should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. An application of a high-temperature molten salt-liquid Cd corrosion resistant ferritic stainless steel welding wire, characterized in that: This welding wire is used for fusion welding of spent fuel dry reprocessing electrolytic refining / extraction vessels or for welding components in high-temperature molten salt and liquid Cd coupled corrosion environments. The chemical composition of this welding wire, by weight percentage, is as follows: C: 0.02-0.05%, Si: 1.5-2.5%, Ti: 0.2-0.6%, N: 0.01-0.02%, Al: 0.2-0.4%, Cr: 16-18%, Mo: 0.2-0.6%, with the balance being Fe and unavoidable impurity elements; The welding process for this welding wire is as follows: Take a Φ 1.2mm welding wire, use tungsten inert gas (TIG) welding, the joint type is butt joint, and the welding parameters are: welding current 80-160A, current type is DC positive polarity, welding speed 0.07-0.12m / min, arc shielding atmosphere is argon, molar purity ≥99.995%, and shielding gas flow rate during welding is 12-18 L / min.

2. The application of the ferritic stainless steel welding wire according to claim 1, characterized in that: The chemical composition of this welding wire contains: P mass fraction < 0.01%, S mass fraction < 0.01%.

3. The application of the ferritic stainless steel welding wire according to claim 1, characterized in that: The corrosion depth of the weld seam in a molten salt environment at 550℃ for 200 h is ≤ 10 μm. The molten salt consists of 93.8 wt.% of 45 wt.% LiCl and 55 wt.% KCl, with the remainder being 6 wt.% CeCl3, 0.1 wt.% SrCl2, and 0.1 wt.% CsCl. The molten salt environment is 100 ppm O2 + 18 ppm H2O. The corrosion depth in a liquid Cd corrosion environment at 550℃ for 200 h is ≤ 4 μm. In terms of mechanical properties: After heat treatment, the weld exhibits a room temperature yield strength > 380 MPa, a tensile strength > 550 MPa, a 550℃ yield strength > 165 MPa, and a tensile strength > 210 MPa; room temperature impact toughness > 10.6 J / cm². 2 .

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