Wide-range gradient controllable residual stress calibration test block and preparation method thereof

Abstract

This invention discloses a wide-range gradient controllable residual stress calibration block and its preparation method, belonging to the field of stress calibration technology. The preparation method includes processing a carburized steel substrate into a blank and sequentially performing carburizing and quenching, shot blasting, grinding to remove the surface oxide layer, and shot peening. The shot-peened blocks are divided into at least two groups, and tempered in different temperature ranges to obtain blocks with different residual compressive stress levels. The different temperature ranges are selected from at least two of the following: 50-150℃, 150-250℃, and 350-450℃. At least a portion of the tempered blocks undergoes surface corrosion treatment to remove the deformation layer of a predetermined depth and fine-tune the residual stress value. Finally, the blocks are rust-proofed and stored. This invention solves the problems of existing calibration blocks having single stress values, poor stability, and short shelf life. It achieves the acquisition of stable calibration blocks with different stress gradients within the same material batch.

Description

Technical Field

[0001] This invention relates to the field of stress calibration technology, specifically to a wide-range gradient controllable residual stress calibration block and its preparation method. Background Technology

[0002] In the automotive parts industry, residual internal stress is crucial, especially for critical load-bearing components such as gears and shafts. Appropriate residual internal stress can improve fatigue strength, wear resistance, and resistance to stress corrosion cracking. Therefore, monitoring the residual stress values ​​of critical components is essential. Ensuring the accuracy of residual stress detection results requires ensuring the precision of the testing equipment, necessitating regular calibration of residual stress testing equipment (X-ray diffractometers). Currently, commonly used calibration blocks are mechanically loaded blocks or shot peening / rolling blocks. Mechanically loaded blocks generate theoretical or simulated stress gradients through external loading. Their stress depends on continuous external force or elastic deformation; relaxation of the external force or changes in block size can cause nominal value drift, making long-term preservation and transmission difficult. Furthermore, the loading force of mechanically loaded blocks is fixed, producing only a single stress value. Shot peening / rolling blocks typically produce only one stress level using a single process, making it difficult to cover a wide range. Therefore, existing calibration blocks suffer from problems such as single stress value, poor stability, and short validity period. Moreover, traditional methods for preparing calibration blocks make it difficult to obtain calibration blocks with different gradients and stable performance from the same batch of materials. Summary of the Invention

[0003] The purpose of this invention is to overcome the problems in the prior art and provide a wide-range gradient controllable residual stress calibration block and its preparation method, which can obtain calibration blocks with different gradients and stable performance in the same batch of materials.

[0004] This invention provides a wide-range gradient controllable residual stress calibration block, comprising: Provide a carburized steel matrix and process it into a test block blank of predetermined size; The test block blank is subjected to carburizing treatment, followed by quenching, to form a high-carbon martensite hardened layer on the surface of the test block blank. The carburized and quenched test blocks were cleaned and shot-blasted, and the surface oxide layer was removed by grinding. The test blocks with the oxide layer removed were shot-peened to introduce a high-density dislocation structure and residual compressive stress field on their surface. The shot-peened specimens are divided into at least two groups, and tempered in different temperature ranges to obtain specimen groups with different residual compressive stress levels; wherein, the different temperature ranges are selected from at least two temperature ranges of 50-150℃, 150-250℃ and 350-450℃. At least a portion of the test blocks that have undergone the gradient tempering treatment are subjected to surface etching to remove the deformation layer of a predetermined depth on their surface and to fine-tune the residual stress value. The prepared test blocks were subjected to rust prevention treatment, and storage and use conditions were specified.

[0005] Preferably, the gradient tempering specifically includes: Tempering at the first temperature range of 350-450℃ yields the first group of specimens with residual compressive stress levels, which range from 261 to 332 MPa. Tempering at the second temperature range of 150-250℃ yields a second group of specimens with residual compressive stress levels ranging from 521 to 565 MPa. Tempering was performed in the third temperature range of 50-150℃ to obtain the third residual compressive stress level test block group.

[0006] Preferably, the selective corrosion treatment is mainly carried out on the third residual compressive stress level test block group, with a corrosion depth of 0.030 mm to 0.050 mm. After corrosion, the residual compressive stress range of the third residual compressive stress level test block group is finely adjusted to 760 MPa to 924 MPa.

[0007] Preferably, the carburizing steel is 8620RH steel; the carburizing temperature is 890℃-910℃, and the carbon potential is 1.0%; the quenching is oil cooling; and the depth of the hardened layer is 1.10-1.25mm.

[0008] Preferably, the shot used in the shot peening process has a diameter of 0.6 mm and a shot peening pressure of 0.5 MPa.

[0009] Preferably, the holding time for the tempering treatment is 1 hour, and after tempering, it is air-cooled and left to stand for 24 hours.

[0010] Preferably, the surface corrosion treatment is performed using a mixed solution containing hydrofluoric acid and hydrogen peroxide.

[0011] The present invention also provides a residual stress calibration test block, which is prepared by the above preparation method. Under the storage conditions of constant temperature of 20℃-25℃ and rust-preventive oil coating, the nominal residual stress value of the test block decreases by no more than 3.3% within one year.

[0012] Preferably, the test block comprises at least three stress gradient groups: The first stress gradient group has a nominal residual compressive stress range of 261-332 MPa. The second stress gradient group has a nominal residual compressive stress range of 521-565 MPa. The third stress gradient group has a nominal residual compressive stress range of 760-924 MPa. Furthermore, within the same stress gradient group, the residual stress fluctuation between different test blocks does not exceed 3%.

[0013] Preferably, the residual stress attenuation rate of the first stress gradient group after one year under storage conditions does not exceed 2.1%; the residual stress attenuation rate of the second stress gradient group after one year under storage conditions does not exceed 1.8%; and the residual stress attenuation rate of the third stress gradient group after one year under storage conditions does not exceed 3.3%.

[0014] Compared with the prior art, the beneficial effects of the present invention are: This invention forms an ultra-high strength martensitic substrate through carburizing and quenching, providing a high dislocation density and high stress field for shot peening. Shot peening induces plastic deformation and introduces metastable dislocation structures. Gradient tempering, through controlled thermal activation at different temperature zones, drives dislocation rearrangement and partial recovery, allowing the high-energy stress field to relax to a preset stable gradient level, while simultaneously achieving stress value gradation. Finally, selective corrosion is used to physically remove the surface damage layer formed by shot peening, eliminating the preferential occurrence points of stress relaxation and sealing the stable stress field beneath the smooth surface. Ultimately, residual stress calibration blocks covering three gradients—high (760-924 MPa), medium (521-565 MPa), and low (261-332 MPa)—were successfully prepared. The calibration blocks of this invention not only solve the problem of single stress values ​​in traditional calibration blocks, but also, through the interaction of the above processes, ensure that the stress attenuation rate of the blocks does not exceed 3.3% within a one-year storage period, and the stress fluctuation within a batch is ≤3%, which is significantly better than the existing technology (generally attenuation ≥8%). Thus, it achieves calibration capability with both excellent long-term stability and high consistency over a wide stress range. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the size and structure of the test block in an embodiment of the present invention.

[0016] Figure 2 This is a flowchart illustrating the preparation process of the calibration test block according to an embodiment of the present invention.

[0017] Figure 3 These are the residual stress test values ​​of the first group of test blocks after tempering in this embodiment of the invention.

[0018] Figure 4 These are the residual stress test values ​​of the second group of test blocks after tempering in this embodiment of the invention.

[0019] Figure 5 The values ​​are the residual stress values ​​detected after tempering and corrosion of the third group of test blocks in the embodiments of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0022] Example 1 Prepare 18 cylindrical test blocks in the normalized state of 8620RH, labeled as Group 1, Group 2, and Group 3, with 6 test blocks in each group. Machin the test blocks to a size of φ80mm × 15mm, ensuring the top and bottom surfaces are parallel.

[0023] The first, second, and third groups of test blocks were uniformly subjected to carburizing and quenching at a heating temperature of 900±10℃ for 20 minutes, followed by oil cooling. The carburized layer depth was 1.10mm~1.25mm. Carburizing was performed in an atmosphere with a carbon potential of 1.0%. In this embodiment, the above carburizing and quenching process can obtain a surface hardened zone with specific thickness, ultra-high hardness, and high micro-stress.

[0024] After carburizing and quenching, the first, second, and third groups of test blocks were cleaned and shot-blasted, and then ground to remove 0.10 mm of the surface layer to ensure that there was no oxide layer on the surface. The first, second, and third groups of test blocks were shot peened with steel shot diameter of 0.6 mm, shot peening pressure of 0.5 MPa, shot peening speed of 150 mm / min, shot peening time of 5 min, and coverage of 200%. Single shot peening was used to achieve uniform coverage. The first group of test blocks was tempered at 350~450℃. More specifically, the tempering temperature of test block No. 1 in the first group was 350℃, that of test block No. 2 in the first group was 370℃, that of test block No. 3 in the first group was 390℃, that of test block No. 4 in the first group was 410℃, that of test block No. 5 in the first group was 430℃, and that of test block No. 6 in the first group was 450℃. The heating time for all six test blocks was 1 hour. After air cooling, they were allowed to stand for 24 hours to obtain compressive stress test blocks with a stress of 261MPa~332MPa. The average stress attenuation rate after one year was 2.1%. Next, the second group of test blocks were tempered at 150℃~250℃. The tempering temperatures were as follows: Test block 1: 150℃; Test block 2: 170℃; Test block 3: 190℃; Test block 4: 210℃; Test block 5: 230℃; and Test block 6: 250℃. The heating time for all six test blocks was 1 hour. After air cooling and standing for 24 hours, compressive stress test blocks with stresses ranging from 521MPa to 565MPa were obtained. The average stress attenuation rate after one year was 1.8%.

[0025] The third group of test blocks was tempered at 50℃-150℃. The tempering temperatures were as follows: Test block 1 at 50℃, test block 2 at 70℃, test block 3 at 90℃, test block 4 at 110℃, test block 5 at 130℃, and test block 6 at 150℃. All blocks were then heated for 1 hour, air-cooled, and allowed to stand for 24 hours. Afterward, they were immersed in a solution of hydrofluoric acid, hydrogen peroxide, and deionized water in a specific ratio for 10 minutes, resulting in a surface corrosion depth of 0.030±0.005mm, yielding compressive stress test blocks ranging from 760MPa to 819MPa. To obtain even higher pressure stress test blocks, half of the test blocks were further immersed for 10 minutes, achieving a surface corrosion depth of 0.050±0.005mm, resulting in compressive stress test blocks ranging from 885MPa to 924MPa. Testing showed that the average stress attenuation rate of the third group of test blocks in this embodiment was 3.3% after one year. In this embodiment, the ratio of hydrofluoric acid, hydrogen peroxide, and deionized water is 1:17:2.

[0026] After the first, second, and third groups of test blocks are prepared, apply anti-rust oil to the surface and store them in a constant temperature oven at 24℃. Do not bump or knock the test blocks. The test blocks are valid for one year.

[0027] Before using the equipment for testing, select a test block with the corresponding stress value for calibration measurement. If the measured value deviates from the nominal value by ≥5%, the equipment parameters need to be corrected until the error is ≤±3%.

[0028] The heat treatment process sequence in Embodiment 1 of the present invention is specific. In this embodiment, the purpose of carburizing is to form a high-carbon martensite layer on the surface, providing a high-hardness substrate for subsequent shot peening. More specifically, the carburizing temperature in this embodiment is 890℃-910℃, the carbon potential is 1.0%, and the carburized layer depth is 1.10mm~1.25mm. The inventors also attempted to perform shot peening followed by carburizing, but research found that the dislocation structure introduced by shot peening would be completely recovered during the high-temperature carburizing process, and the stress substrate would disappear.

[0029] In this embodiment, quenching (oil cooling) forms high-density dislocations and twinned martensite to create a micro-stress field, facilitating subsequent stress control. Experiments show that the maximum residual compressive stress of unquenched 8620RH steel after shot peening is only about 400 MPa, which cannot meet the high stress requirements of over 800 MPa.

[0030] Furthermore, the essence of shot peening in this invention is to introduce dislocation entanglement and lattice distortion through plastic deformation, and its stress level is directly limited by the material's yield strength. High yield strength (≥1500MPa) of quenched martensite is a prerequisite for obtaining high shot peening stress. If tempering precedes shot peening, the martensite decomposes into tempered martensite or sorbite during tempering, resulting in a 30%-50% decrease in yield strength and a corresponding reduction in the upper limit of shot peening stress. Experimental results show that the maximum residual compressive stress of the specimen tempered (350℃) before shot peening is only 510MPa, failing to reach the required level of 565MPa or higher.

[0031] The reason for gradient tempering after shot peening is that the residual stress introduced by shot peening is in a metastable state and has a natural tendency to relax. Gradient tempering (50-450℃) promotes dislocation rearrangement and partial recovery through a controlled thermal activation process, achieving a balance between stress relaxation and stabilization.

[0032] In this invention, the tempering temperature and stress relaxation rate have an exponential relationship. By setting three temperature ranges (50℃~150℃, 150℃~250℃, 350℃~450℃), the stress relaxation rates can be controlled to be approximately 5%, 15%, and 40%, respectively, thereby obtaining three gradients of 760MPa~924MPa, 521MPa~565MPa, and 261MPa~332MPa.

[0033] If gradient tempering is cancelled, the shot peening stress is high (up to 1000 MPa or more), but the stability is extremely poor. The stress decay can reach 10% to 15% within 30 days of storage at room temperature, which does not meet the requirement of ≤±5% fluctuation of the calibration test block over one year.

[0034] In this embodiment, the selective etching solution uses a mixture of hydrofluoric acid and hydrogen peroxide to remove a micro-deformation layer of approximately 0.03 mm to 0.05 mm from the surface. This layer, due to the plastic deformation caused by shot peening, exhibits high dislocation density and microcracks, which facilitates stress attenuation. After etching, a smooth surface with low defect density is formed, effectively sealing the stable stress field beneath. If etching is performed before shot peening or tempering, the surface defects introduced by shot peening cannot be eliminated.

[0035] Furthermore, the study found a linear relationship between corrosion depth and stress fine-tuning; that is, for every 0.01 mm of corrosion removed, the surface stress can increase by approximately 30 MPa to 50 MPa. This effect provides high-stress specimens with a fine-tuning capability of ±50 MPa, which is impossible to achieve with traditional single shot peening processes.

[0036] To this end, the present invention also provides corresponding comparative examples 1-4: Comparative Example 1 The difference from Example 1 is that high-temperature tempering was used instead of gradient tempering. Specifically, the number of samples in Comparative Example 1 was 3, all of which were cylindrical test blocks in the 8620RH normalized state. They were machined to a size of φ80mm×15mm, ensuring that the top and bottom surfaces were parallel.

[0037] All three test blocks underwent uniform carburizing and quenching at a heating temperature of 900±10℃ for 20 minutes, followed by oil cooling. The depth of the hardened carburized layer was 1.10mm~1.25mm. Carburizing was performed in an atmosphere with a carbon potential of 1.0%.

[0038] After carburizing and quenching, the first, second and third test blocks were cleaned and shot blasted, and then ground to remove 0.10 mm of the surface layer to ensure that there was no oxide layer on the surface. Three test blocks were shot peening strengthened with steel shot diameter of 0.6 mm, shot peening pressure of 0.5 MPa, shot peening speed of 150 mm / min, shot peening time of 5 min, and coverage of 200%. Single shot peening was used to achieve uniform coverage.

[0039] The three samples were then tempered at 530℃, 580℃, and 630℃ for 1 hour each, followed by air cooling and 24 hours of rest. The measured residual compressive stresses were 382 MPa, 331 MPa, and 296 MPa, respectively. Due to carbide precipitation and significant dislocation recovery, the yield strength of the material was significantly reduced. Therefore, this process cannot cover the medium-to-high stress range.

[0040] Comparative Example 2 The difference from Example 1 is that nitriding is used instead of carburizing, and the same high-temperature tempering treatment as Comparative Example 1 is employed; specifically, in Comparative Example 2, three samples were used, all cylindrical specimens in the 8620RH normalized state. They were machined to dimensions of φ80mm × 15mm, ensuring the top and bottom surfaces were parallel. The specimens were nitrided at 900±10℃, followed by shot peening. The shot diameter was 0.6mm, the shot peening pressure was 0.5MPa, the shot peening speed was 150mm / min, the shot peening time was 5min, and the coverage was 200%. A single shot peening was used for uniform coverage.

[0041] The three samples were then tempered at 530℃, 580℃, and 630℃ respectively, with a heating time of 1 hour for each sample. After air cooling, they were left to stand for 24 hours. Accelerated aging tests (60℃ × 30 days) were then conducted. After the tests, the stress attenuation rate of the shot-peened nitrided sample was found to be 8.2%, which was higher than the 3.3% of the carburized sample.

[0042] Comparative Example 3 The difference from Example 1 is that induction hardening is used instead of integral hardening, as detailed below: A cylindrical specimen in the normalized state of 8620RH was machined to a size of φ80mm × 15mm, ensuring parallelism of the top and bottom surfaces. It was then subjected to high-frequency induction hardening at 150kHz for 6 seconds, followed by oil cooling and tempering at 250℃. After tempering, it was shot-peened with 0.6mm diameter steel shot at a pressure of 0.5MPa, a speed of 150mm / min, and a duration of 5 minutes, achieving 200% coverage in a single pass. Induction hardening resulted in a shallow hardened layer (typically <1mm), while the core remained soft and tough ferrite. After shot peening, the surface and core exhibited poor coordinated deformation, a steep stress gradient, and poor repeatability in calibration measurements; the standard deviation of three measurements on the same specimen reached ±25MPa.

[0043] Comparative Example 4 The difference from Example 1 is that tempering is omitted and shot peening is used directly; the details are as follows: A cylindrical 8620RH normalized specimen was machined to dimensions of φ80mm × 15mm, ensuring parallelism on both the top and bottom surfaces. The specimen was then carburized and quenched at 900±10℃ for 20 minutes, cooled by oil cooling, resulting in a carburized layer depth of 1.10mm~1.25mm. Carburizing was performed in an atmosphere with a carbon potential of 1.0%. After quenching, shot peening was performed directly using 0.6mm diameter steel shot at a pressure of 0.5MPa, a speed of 150mm / min, a duration of 5 minutes, and a coverage rate of 200%, using a single, uniform peening pass. The stress introduced by shot peening was in a high-energy state, exhibiting significant relaxation at room temperature. Experiments showed that the untempered specimen after shot peening experienced a stress attenuation of 12% within 30 days and over 20% after one year, completely failing to meet the stability requirements for calibration specimens.

[0044] Stability analysis of calibration blocks Attenuation rate test data and comparative analysis Experimental Design: Test block grouping: Six test blocks were prepared in each of the first, second, and third groups for this Example 1. A control group was also set up. Control group A: The only difference from Example 1 is the absence of the tempering step; otherwise, it is the same as Example 1. Control group B: The only difference from Example 1 is that it uses a single tempering temperature of 300°C; otherwise, it is the same as Example 1. Control group C: Commercially available shot peening calibration test block (a certain brand); Testing periods: 0 days, 30 days, 90 days, 180 days, 365 days Test method: X-ray diffraction Storage conditions: constant temperature of 24℃, protected with rust-preventive oil, and free from mechanical impact.

[0045] Table 1. Attenuation rate data of AC in Example 1 and the control group of the present invention. In Table 1, the attenuation rate at different time periods is the average attenuation rate of the same group of test blocks. Each test block in each group is within the fluctuation range of the corresponding initial stress and the stress fluctuation range after one year. The results in Table 1 show that the attenuation rate of this embodiment is significantly lower than that of the prior art. Among them, the attenuation rate of the highest stress group in Example 1, namely the third group, is 3.3% after one year, which is 15.4 percentage points lower than the control group without tempering (A) and 11.9 percentage points lower than the commercially available test block (C).

[0046] The attenuation rate of the low and medium stress groups (i.e., the first and second groups) is <2.1%, reaching the advanced level of international calibration blocks (ISO4965 standard recommends that the annual change rate of calibration blocks be ≤5%).

[0047] In this embodiment, the attenuation rate increases slightly with increasing stress level, but the increase is much smaller than that in the control group. This indicates that the stabilizing effect of gradient tempering plus corrosion remains effective in the high stress range.

[0048] Long-term stability verification: Extended tests (2-year follow-up) were conducted on the first, second, and third groups of test blocks. The attenuation rates were 3.0%, 2.7%, and 4.5%, respectively, which still met the technical requirement of ≤5%, proving that the stability of this embodiment is not a short-term effect.

[0049] Compared with industry standards: the nominal annual change rate of residual stress calibration blocks is ≤5% as recognized internationally, and all gradient blocks in this embodiment are superior to this index.

[0050] The annual variation rate of existing commercial test blocks in China is generally 8%-15%, while this embodiment improves the stability by 2-5 times.

[0051] The reason for the low attenuation rate in this embodiment is as follows: gradient tempering causes dislocations to transform from a tangled state into a stable cellular structure (confirmed by TEM observation), reducing the driving force for dislocation movement. The higher the tempering temperature, the larger the dislocation cell size (cell size ≈ 0.2 μm for tempering at 150℃, ≈ 0.5 μm for tempering at 450℃), and the stronger the resistance to stress relaxation.

[0052] Approximately 15%-20% of the austenite remaining in the carburized layer partially decomposes into cementite during tempering. The cementite pins dislocations at the phase interface with martensite, further suppressing stress relaxation. Grinding after shot peening removes a 0.10 mm surface layer, eliminating surface microcracks and the oxide layer. Subsequent corrosion further smooths the surface, reducing the surface roughness Ra from approximately 6.3 μm after shot peening to approximately 0.8 μm (measured with a white light interferometer). The low-roughness surface reduces stress concentration points and delays crack initiation, which is crucial for long-term stability.

[0053] Stress gradient design: The residual stress distribution along the depth in this embodiment is plateau-shaped (measured by X-ray sin²ψ method): the stress fluctuation from the surface to a depth of 0.1 mm is <5%, while traditional single shot peening is peak-shaped, with the highest stress at the surface but the fastest attenuation. The plateau-shaped distribution provides a supporting effect between the inner and outer layers during stress redistribution, slowing down the overall attenuation.

[0054] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a calibration specimen with wide-range gradient controllable residual stress, characterized in that, include: Provide a carburized steel matrix and process it into a test block blank of predetermined size; The test block blank is subjected to carburizing treatment, followed by quenching, to form a high-carbon martensite hardened layer on the surface of the test block blank. The carburized and quenched test blocks were cleaned and shot-blasted, and the surface oxide layer was removed by grinding. The test blocks with the oxide layer removed were then shot-peened. The shot-peened specimens are divided into at least two groups, and tempered in different temperature ranges to obtain specimen groups with different residual compressive stress levels; wherein, the different temperature ranges are selected from at least two temperature ranges of 50℃~150℃, 150℃~250℃ and 350℃~450℃. At least some of the test blocks that have undergone gradient tempering are subjected to surface etching treatment to remove the deformation layer of a predetermined depth on their surface in order to fine-tune the residual stress value. The prepared test blocks are then subjected to rust prevention treatment.

2. The method for preparing a wide-range gradient controllable residual stress calibration block as described in claim 1, characterized in that, The gradient annealing process specifically includes: Tempering at the first temperature range of 350℃~450℃ yields the first group of test blocks with residual compressive stress, which ranges from 261MPa to 332MPa. Tempering at the second temperature range of 150℃~250℃ yields a second set of test blocks with residual compressive stress levels ranging from 521MPa to 565MPa. Tempering was performed in the third temperature range of 50℃~150℃ to obtain the third residual compressive stress level test block group.

3. The method for preparing a wide-range gradient controllable residual stress calibration block as described in claim 2, characterized in that, The corrosion treatment is mainly carried out on the third residual compressive stress level test block group, with a corrosion depth of 0.030 mm to 0.050 mm. After corrosion, the residual compressive stress range of the third residual compressive stress level test block group is finely adjusted to 760 MPa to 924 MPa.

4. The method for preparing a wide-range gradient controllable residual stress calibration block as described in claim 1, characterized in that, The carburizing steel is 8620RH steel; the carburizing temperature is 900±10℃, and the carbon potential is 1.0%; the quenching is oil cooling; and the depth of the hardened layer is 1.10mm~1.25mm.

5. The method for preparing a wide-range gradient controllable residual stress calibration block as described in claim 1, characterized in that, The shot peening process uses steel shot with a diameter of 0.6 mm and a shot peening pressure of 0.5 MPa.

6. The method for preparing a wide-range gradient controllable residual stress calibration block as described in claim 1, characterized in that, The tempering process is held for 1 hour, followed by air cooling and standing for 24 hours.

7. The method for preparing a wide-range gradient controllable residual stress calibration block as described in claim 1, characterized in that, The surface corrosion treatment is carried out using a mixed solution containing hydrofluoric acid and hydrogen peroxide.

8. A residual stress calibration block, which is prepared by the preparation method of any one of claims 1 to 7, wherein the nominal residual stress value of the block decreases by no more than 3.3% within one year under the storage conditions of constant temperature at 20℃-25℃ and rust-preventive oil coating.

9. A residual stress calibration test block as described in claim 8, characterized in that, The test block includes at least three stress gradient sets: The first stress gradient group has a nominal residual compressive stress range of 261MPa~332MPa; The second stress gradient group has a nominal residual compressive stress range of 521MPa~565MPa. The third stress gradient group has a nominal residual compressive stress range of 760MPa~924MPa; Furthermore, within the same stress gradient group, the residual stress fluctuation between different test blocks does not exceed 3%.

10. A residual stress calibration test block as described in claim 9, characterized in that, The residual stress attenuation rate of the first stress gradient group after one year under storage conditions does not exceed 2.1%; the residual stress attenuation rate of the second stress gradient group after one year under storage conditions does not exceed 1.8%; and the residual stress attenuation rate of the third stress gradient group after one year under storage conditions does not exceed 3.3%.

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