A sample, apparatus and method for high temperature molten salt slow strain rate tensile testing

Abstract

The present application belongs to the technical field of material environmental corrosion and mechanical property coupling test, and provides a sample, device and method for high-temperature molten salt slow strain rate tensile test. The sample provided by the present application has a dumbbell-shaped structure, the inside center of the dumbbell-shaped structure has a through cavity, and the dumbbell-shaped structure is sequentially divided into an upper clamping section, an upper transition section, a parallel section, a lower transition section and a lower clamping section along the axial direction. In the parallel section, the diameter of the cavity is 2-6 mm. Two annular positioning protrusions are symmetrically arranged on the outside of the parallel section of the sample, and the annular positioning protrusions are used for fixing the extensometer. The sample provided by the present application can accurately simulate the corrosion environment of the inner wall of the sample in contact with the molten salt, and the coupling test precision of corrosion and mechanical property is high.

Description

Technical Field

[0001] This invention relates to the field of coupled testing technology of environmental corrosion and mechanical properties of materials, and in particular to a specimen, apparatus and method for high-temperature molten salt slow strain rate tensile testing. Background Technology

[0002] In fields such as molten salt energy storage and concentrated solar power generation, molten salt storage tank materials operate for extended periods in high-temperature molten salt environments while simultaneously bearing certain loads, making them susceptible to stress corrosion cracking and other damage, which severely impacts the safe and stable operation of the equipment. Slow strain rate tensile (SSRT) testing is a core method for evaluating the stress corrosion susceptibility of materials in corrosive environments, effectively simulating the coupling effect of plastic deformation and corrosion during actual service.

[0003] Currently, slow strain rate tensile tests in high-temperature molten salt corrosion environments mostly use solid specimens. However, solid specimens have significant limitations: corrosion only acts on the surface of solid specimens, failing to simulate the corrosion environment of the inner wall of actual equipment containing molten salt, leading to significant deviations between test results and actual service conditions. Furthermore, slow strain rate tensile tests on solid specimens rely on a moving crossbeam at the top of the slow strain rate tensile testing machine to achieve longitudinal tension. This results in the obtained tensile data representing the longitudinal strain of the entire specimen, leading to inaccurate strain data acquisition and difficulty in accurately capturing the interaction between corrosion and mechanical load, thus affecting the accuracy of coupled corrosion and mechanical property testing. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a specimen, apparatus, and method for high-temperature molten salt slow strain rate tensile testing. The specimen provided by the present invention can accurately simulate the dual corrosion environment of the specimen's inner wall in contact with molten salt.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a specimen for a high-temperature molten salt slow strain rate tensile test. The specimen has a dumbbell-shaped structure with a through cavity at its center. The dumbbell-shaped structure is divided into an upper clamping section, an upper transition section, a parallel section, a lower transition section, and a lower clamping section along the axial direction. The diameter of the cavity in the parallel section is 2-6 mm. Two annular positioning protrusions are symmetrically arranged on the outer side of the parallel section of the sample, and the annular positioning protrusions are used to fix the extensometer.

[0006] Preferably, the surface roughness Ra of the outer wall of the parallel section of the sample is ≤1.6μm.

[0007] Preferably, the distance between the two annular positioning protrusions is 20~30mm.

[0008] Preferably, the height of the annular positioning protrusion is 1 / 5 to 1 / 3 of the outer diameter of the parallel segment.

[0009] The present invention also provides an apparatus for high-temperature molten salt slow strain rate tensile testing, comprising the specimen, extensometer and slow strain rate tensile testing machine described in the above technical solution; The extensometer is fixed by two annular positioning protrusions on the sample; The slow strain rate tensile testing machine includes a moving crossbeam; The upper pull rod is threadedly connected to the upper clamping section of the sample. A pull rod, wherein the pull rod is threadedly connected to the lower clamping section of the sample; A heating furnace, which encloses the sample.

[0010] Preferably, the system further includes a strain acquisition system connected to the extensometer.

[0011] Preferably, the extensometer is made of ceramic.

[0012] The present invention also provides a method for conducting high-temperature molten salt slow strain rate tensile tests using the apparatus described above, comprising the following steps: After heating the molten salt, it is placed in the through cavity of the specimen, and a moving crossbeam is loaded to obtain the slow strain rate tensile test results when the specimen is in contact with the molten salt on the inner wall.

[0013] Preferably, the molten salt includes one or more of solar salt, Hitec salt, and ternary nitrate, and the molten salt is heated to a temperature of 220~700℃.

[0014] Preferably, the loading and moving crossbeam includes sequential preloading and stretching; The preloaded tensile stress is 500N, the temperature is 290~565℃, and the heat preservation time is 24h; The stretching rate is 10 -6 ~10 -7 s -1 .

[0015] This invention provides a specimen for high-temperature molten salt slow strain rate tensile testing.

[0016] The present invention sets the internal center of the dumbbell-shaped sample as a through cavity, which can simulate the corrosion of the sample in the corrosive environment of molten salt in contact with the inner wall, so that the test results deviate little from the actual service conditions.

[0017] The present invention also provides an apparatus for high-temperature molten salt slow strain rate tensile testing. The present invention fixes the extensometer by an annular positioning protrusion on the parallel section of the specimen, which can obtain the strain data of the parallel section, making the data acquisition accurate and accurately capturing the interaction between corrosion and mechanical load, thus improving the accuracy of corrosion and mechanical property coupling test.

[0018] The present invention also provides a method for conducting high-temperature molten salt slow strain rate tensile tests using the apparatus described above. The method provided by the present invention can accurately capture the interaction between corrosion and mechanical load, thereby improving the accuracy of coupled corrosion and mechanical property testing. Attached Figure Description

[0019] Figure 1 A schematic diagram of the structure of a specimen used in a high-temperature molten salt slow strain rate tensile test; Figure 2 A schematic diagram of an apparatus used for high-temperature molten salt slow strain rate tensile testing; Figure 3 This is a force-displacement curve of the specimen in Example 1 under slow strain rate tensile test in air; Figure 4 This is a force-displacement curve of a slow strain rate tensile test of the specimen in Example 2 with the specimen in contact with molten salt 1 on the inner wall; Figure 5 This is a force-displacement curve of a slow strain rate tensile test of the specimen in Example 3 with the specimen in contact with molten salt 2 on the inner wall. Detailed Implementation

[0020] This invention provides a specimen for a high-temperature molten salt slow strain rate tensile test. The specimen has a dumbbell-shaped structure with a through-cavity at the center of the internal structure. The dumbbell-shaped structure is divided into an upper clamping section, an upper transition section, a parallel section, a lower transition section, and a lower clamping section along the axial direction. The diameter of the cavity in the parallel section is 2-6 mm. Two annular positioning protrusions are symmetrically arranged on the outer side of the parallel section of the sample, and the annular positioning protrusions are used to fix the extensometer.

[0021] The following is combined with Figure 1 The sample provided by the present invention will be described.

[0022] The specimen for high-temperature molten salt slow strain rate tensile testing provided by this invention has a dumbbell-shaped structure. The dumbbell-shaped structure has a through-cavity at its center, which is used to load molten salt to simulate corrosion of the specimen's inner wall in contact with the molten salt. Preferably, the cross-sectional shape of the through-cavity is circular. The dumbbell-shaped structure is sequentially divided along the axial direction into an upper clamping section, an upper transition section, a parallel section, a lower transition section, and a lower clamping section. Preferably, the upper and lower transition sections are tapered structures. The upper transition section connects the upper clamping section and the parallel section, and the lower transition section connects the lower clamping section and the parallel section to avoid stress concentration. Preferably, the diameter of the through-cavity in the lower transition section, the parallel section, and the upper transition section is smaller than the diameter of the through-cavity in the upper and lower clamping sections.

[0023] In this invention, the dimensions of the specimen are the same as those used in slow strain rate tensile tests, the only difference being the presence of a through cavity; and two annular positioning protrusions are symmetrically arranged on the outer side of the parallel section. In this invention, the diameter of the cavity in the parallel section is 2-6 mm, preferably 2 mm, 3 mm, 4 mm, 5 mm, or 6 mm; the outer diameter of the parallel section is preferably 10 mm.

[0024] In this invention, the surface roughness Ra of the outer wall of the parallel section of the sample is preferably ≤1.6 μm. Maintaining a surface roughness (Ra) ≤1.6 μm ensures secure clamping of the extensometer, prevents slippage during stretching, and reduces damage to the sample during clamping.

[0025] In this invention, two annular positioning protrusions are symmetrically arranged on the outer side of the parallel section of the sample. These annular positioning protrusions are used to fix the extensometer. In this invention, the distance between the two annular positioning protrusions ( Figure 1 The height of d) shown is preferably 20-30 mm, more preferably 25 mm. In this invention, the height of the annular positioning protrusion is preferably 1 / 5 to 1 / 3 of the outer diameter of the parallel section. This application places the extensometer on the parallel section, which can accurately obtain plastic deformation, making strain data acquisition accurate and improving the accuracy of corrosion and mechanical property coupling tests. In addition, the annular positioning protrusion can prevent the extensometer from slipping or falling off, achieving real-time and accurate strain data acquisition.

[0026] The sample provided by this invention can accurately simulate the corrosive environment of molten salt in contact with the inner wall of the sample.

[0027] The present invention also provides an apparatus for high-temperature molten salt slow strain rate tensile testing, comprising the specimen, extensometer and slow strain rate tensile testing machine described in the above technical solution; The extensometer is fixed by two annular positioning protrusions on the sample; The slow strain rate tensile testing machine includes a moving crossbeam; The upper pull rod is threadedly connected to the upper clamping section of the sample. A pull rod, wherein the pull rod is threadedly connected to the lower clamping section of the sample; A heating furnace, which encloses the sample.

[0028] The following is combined with Figure 2 The apparatus of the present invention will be described.

[0029] The device provided by the present invention includes the sample described in the above technical solution.

[0030] The device provided by this invention includes an extensometer, which is fixed by two annular positioning protrusions on the sample. In this invention, the extensometer is preferably made of ceramic.

[0031] The apparatus provided by the present invention preferably further includes a strain acquisition system, which is connected to the extensometer. In the present invention, the strain acquisition system is preferably located outside the heating furnace.

[0032] The apparatus provided by the present invention includes a slow strain rate tensile testing machine; the slow strain rate tensile testing machine includes a movable crossbeam for slow strain tensile testing of a specimen; an upper pull rod connected to an upper clamping section of the specimen by a thread; a lower pull rod connected to the upper clamping section of the specimen by a thread; and a heating furnace enclosing the specimen.

[0033] The present invention also provides a method for conducting high-temperature molten salt slow strain rate tensile tests using the apparatus described above, comprising the following steps: After heating the molten salt, it is placed in the through cavity of the specimen. A moving crossbeam is loaded, and the results of the slow strain rate tensile test when the specimen is in contact with the molten salt on the inner wall are obtained by an extensometer.

[0034] In this invention, the molten salt preferably includes one or more of solar salt, Hitec salt, and ternary nitrates. In this invention, the solar salt preferably includes sodium nitrate and potassium nitrate; the mass content of sodium nitrate is preferably 60%, and the mass content of potassium nitrate is preferably 40%. In this invention, the Hitec salt preferably includes potassium nitrate, sodium nitrite, and sodium nitrate; the mass content of potassium nitrate is preferably 53%, the mass content of sodium nitrite is preferably 40%, and the mass content of sodium nitrate is preferably 7%. In this invention, the ternary nitrate preferably includes 40% lithium nitrate + 15% sodium nitrate + 45% potassium nitrate; the mass content of lithium nitrate is preferably 40%, the mass content of sodium nitrate is preferably 15%, and the mass content of potassium nitrate is preferably 45%. In this invention, the molten salt preferably also includes chloride salts, which are preferably added in the form of sodium chloride or potassium chloride; this invention does not specifically limit the content of chloride salts in the molten salt, and those skilled in the art can set it according to actual needs.

[0035] In this invention, the heating temperature of the molten salt is preferably 220~700℃, and more preferably 565℃.

[0036] In this invention, the loading and moving crossbeam preferably includes preloading and stretching in sequence.

[0037] In this invention, the preloaded tensile stress is preferably 500N, the temperature is preferably 290~565℃, and the heat preservation time is 24h.

[0038] In this invention, the stretching rate is preferably 10. -6 ~10 -7 s -1 .

[0039] This invention addresses the technical challenges of slow strain rate tensile (SSRT) testing under high-temperature molten salt corrosion conditions. By designing a dedicated hollow specimen and an integrated loading scheme with an extensometer, it constructs a precise coupling testing system for corrosion and mechanical properties, enabling performance evaluation of the specimen under simulated actual service conditions.

[0040] (1) Sample structure design principle: A hollow structure (divided into clamping section, transition section and parallel section) is adopted. The inner cavity of the parallel section can be sealed to contact the high temperature molten salt, so that the inner wall of the sample can contact the high temperature molten salt and simulate the corrosion condition of the inner wall.

[0041] (2) Extensometer loading principle: An annular positioning protrusion is set in the parallel section, and a high temperature and corrosion resistant extensometer is used to solve the problems of extensometer slippage, detachment and corrosion in high temperature molten salt environment, so as to realize the real-time and accurate acquisition of strain data.

[0042] (3) Adaptability principle: Optimized sample size and extensometer compatibility design can be adapted to different materials, molten salt types and existing testing machines without special modification, reducing costs and improving versatility.

[0043] The following detailed description of the specimen, apparatus, and method for high-temperature molten salt slow strain rate tensile testing provided by the present invention, with reference to the embodiments, should not be construed as limiting the scope of protection of the present invention.

[0044] Example 1 use Figure 2 The apparatus shown is used for a slow strain rate tensile test method, which includes the following steps: S1. Sample Preparation: The sample with a through cavity (made of austenitic stainless steel of grade TP347H) is surface-treated to ensure that the surface of the parallel section is smooth, without obvious scratches or oil stains. The sample is then dimensionally measured, and the inner and outer diameters of the parallel section are recorded as 6 mm and 10 mm, respectively.

[0045] S2. The specimen is mounted on the slow strain rate tensile testing machine using the upper and lower pull rods. The high-temperature and corrosion-resistant ceramic extensometer is installed on the specimen through the annular positioning protrusions of the parallel section (the annular positioning protrusions are symmetrically arranged, with a distance of 25 mm between them; the height of the annular positioning protrusions is 1 / 5 of the outer diameter of the parallel section), and is firmly clamped to prevent slippage or falling off during the tensile process. In this embodiment, the cavity of the specimen is not filled with molten salt, but only with air.

[0046] S3. Perform slow strain rate tensile tests according to Part VII of GB / T-15970: Load a moving crossbeam, preload a tensile stress of 500 N, and maintain at 565 °C for 24 hours to ensure uniform temperature inside and outside the specimen. Set the tensile rate to 10. -6 ~10 -7 s -1 Slow strain rate tensile tests are conducted, and strain data of the specimen is collected in real time by an extensometer. The testing machine collects load data in real time and dynamically adjusts the tensile rate to ensure stable strain rate and avoid test deviations in material stress corrosion cracking (SCC) caused by rate fluctuations.

[0047] S4. Test Completion and Data Processing: After the specimen fractures, stop the test, remove the specimen, observe the fracture morphology, and analyze the plastic deformation under no-load conditions in conjunction with the collected strain and load data to clarify the correlation law of strain evolution.

[0048] Example 2 The difference from Example 1 is that solar salt was added to the sample. The specific process is as follows: S1. Sample Preparation: The sample with a through cavity (made of austenitic stainless steel of grade TP347H) is surface-treated to ensure that the surface of the parallel section is smooth, without obvious scratches or oil stains. The sample is then dimensionally measured, and the inner and outer diameters of the parallel section are recorded as 6 mm and 10 mm, respectively.

[0049] S2. Prepare solar salt (60wt% sodium nitrate + 40wt% potassium nitrate, denoted as molten salt 1).

[0050] S3. Heat the solar salt to about 220°C until it is in a molten state. Fix one end of the sample and fill the molten solar salt into the through cavity of the sample.

[0051] S4. Mount the sample containing molten salt onto the slow strain rate tensile testing machine using the upper and lower pull rods. Install the high-temperature and corrosion-resistant ceramic extensometer onto the sample through the annular positioning protrusions of the parallel section (the annular positioning protrusions are symmetrically arranged, with a distance of 25 mm between them; the height of the annular positioning protrusions is 1 / 5 of the outer diameter of the parallel section), and clamp it firmly to prevent slippage or detachment during the tensile process.

[0052] S5. Perform slow strain rate tensile tests according to Part VII of GB / T-15970: Load a moving crossbeam, preload a tensile stress of 500 N, and maintain at 565 °C for 24 hours to ensure uniform temperature inside and outside the specimen and that the molten salt is at the set temperature. Set the tensile rate to 10. -6 ~10 -7 s -1 Slow strain rate tensile tests are conducted, and strain data of the specimen is collected in real time by an extensometer. The testing machine collects load data in real time and dynamically adjusts the tensile rate to ensure stable strain rate and avoid test deviations in material stress corrosion cracking (SCC) caused by rate fluctuations. By utilizing the characteristics of corrosion on the inner wall of the specimen and combining the strain data measured by the extensometer, the interaction between molten salt corrosion and plastic deformation can be accurately captured.

[0053] S6. Test Completion and Data Processing: After the sample fractures, stop the test, remove the sample, observe the corrosion and fracture morphology, and analyze the interaction between high-temperature molten salt corrosion and plastic deformation in conjunction with the collected strain and load data. Clarify the correlation between corrosion rate and strain evolution, and evaluate the stress corrosion cracking sensitivity and damage evolution law of the material.

[0054] Example 3 The difference from Example 2 is that 0.5% sodium chloride (denoted as molten salt 2) by mass of solar salt is added to the solar salt, otherwise it is the same as Example 2.

[0055] Figure 3 This is a force-displacement curve of the specimen in Example 1 under slow strain rate tensile test in air. Figure 4 This is a force-displacement curve of a slow strain rate tensile test of the specimen in Example 2 with the inner wall in contact with molten salt 1. Figure 5 This is a force-displacement curve from a slow strain rate tensile test of the specimen in Example 3, where the specimen was in contact with molten salt 2 on the inner wall. From... Figures 3-5 It can be seen that: in Example 1, the elongation after fracture A of the sample is 7.5% and the reduction of area Z is 58%; in Example 2, the elongation after fracture A of the sample is 9.0% and the reduction of area Z is 49%; in Example 3, the elongation after fracture A is 7.0% and the reduction of area Z is 40%.

[0056] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A specimen for high-temperature molten salt slow strain rate tensile testing, characterized in that, The sample has a dumbbell-shaped structure with a through cavity at its center. The dumbbell-shaped structure is divided into an upper clamping section, an upper transition section, a parallel section, a lower transition section, and a lower clamping section along the axial direction. The diameter of the cavity in the parallel section is 2-6 mm. Two annular positioning protrusions are symmetrically arranged on the outer side of the parallel section of the sample, and the annular positioning protrusions are used to fix the extensometer.

2. The sample according to claim 1, characterized in that, The surface roughness Ra of the outer wall of the parallel section of the sample is ≤1.6μm.

3. The sample according to claim 1, characterized in that, The distance between the two annular positioning protrusions is 20~30mm.

4. The sample according to claim 1 or 3, characterized in that, The height of the annular positioning protrusion is 1 / 5 to 1 / 3 of the outer diameter of the parallel section.

5. An apparatus for high-temperature molten salt slow strain rate tensile testing, characterized in that, Includes the specimen, extensometer, and slow strain rate tensile testing machine as described in any one of claims 1 to 4; The extensometer is fixed by two annular positioning protrusions on the sample; The slow strain rate tensile testing machine includes a moving crossbeam; The upper pull rod is threadedly connected to the upper clamping section of the sample. A pull rod, wherein the pull rod is threadedly connected to the lower clamping section of the sample; A heating furnace, which encloses the sample.

6. The apparatus according to claim 5, characterized in that, It also includes a strain acquisition system, which is connected to the extensometer.

7. The apparatus according to claim 5, characterized in that, The extensometer is made of ceramic.

8. A method for conducting high-temperature molten salt slow strain rate tensile tests using the apparatus described in any one of claims 5 to 7, characterized in that, Includes the following steps: After heating the molten salt, it is placed in the through cavity of the specimen. A moving crossbeam is loaded, and the results of the slow strain rate tensile test when the specimen is in contact with the molten salt on the inner wall are obtained by an extensometer.

9. The method according to claim 8, characterized in that, The molten salt includes one or more of solar salt, Hitec salt, and ternary nitrate, and the molten salt is heated to a temperature of 220~700℃.

10. The method according to claim 8 or 9, characterized in that, The loading and moving crossbeam includes sequential preloading and stretching; The preloaded tensile stress is 500N, the temperature is 290~565℃, and the heat preservation time is 24h; The stretching rate is 10 -6 ~10 -7 s -1 .

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