An austenitic steel residual stress detection method capable of correcting grain size difference

Abstract

The present application relates to the technical field of residual stress detection, and particularly relates to an austenitic steel residual stress detection method capable of correcting grain size difference, which comprises the following steps: obtaining calibration samples of the same specification as the sample to be tested and having different grain sizes, obtaining surface wave attenuation coefficients and critical refracted longitudinal wave speeds of the calibration samples under different stress states, and then obtaining stress state functions under different grain sizes; obtaining surface wave attenuation coefficients and critical refracted longitudinal wave speeds of the sample to be tested by using a pre-constructed ultrasonic excitation probe, and calculating and obtaining residual stress values of a test area of the sample to be tested after microstructure correction according to the stress state functions. The austenitic steel residual stress detection method capable of correcting grain size difference can correct residual stress errors caused by different grain sizes, and improve detection accuracy.

Description

Technical Field

[0001] This invention relates to the field of residual stress detection technology, specifically a method for detecting residual stress in austenitic steel that can correct for differences in grain size. Background Technology

[0002] Austenitic steel is steel whose microstructure is a stable single-phase austenite at room temperature. Austenitic stainless steel is the most numerous and widely used type of stainless steel. Due to its comprehensive and excellent overall properties, austenitic stainless steel has gained widespread application in industry. The grain size of austenite is a crucial factor affecting the microstructure and properties of steel. The microstructure and composition of the steel, as well as factors such as the heating temperature, holding time, and heating rate during heat treatment, all influence the grain size of austenite.

[0003] Residual stress is a crucial basis for assessing the quality of engineering structures. The generation and release of residual stress often lead to decreased dimensional stability of structural components, and can even cause catastrophic failures in critical operational equipment. This stress-induced structural deformation is not negligible during component assembly and use. Therefore, rapid, efficient, and non-destructive monitoring and assessment of residual stress levels is of great industrial significance. Ultrasonic testing of residual stress has attracted widespread attention due to its advantages such as material penetrability, non-destructive nature, speed, high measurement efficiency, simple and portable equipment, and strong environmental adaptability. Ultrasonic measurement of residual stress is an indirect method. The propagation speed of ultrasound in the test sample has an acoustoelastic relationship with the residual stress in the sample; that is, the propagation speed of ultrasound in the test sample and the residual stress in the sample are essentially linearly related. Based on the relationship between ultrasound and the residual stress in the test sample, the residual stress of the test sample can be characterized. However, the propagation speed of ultrasound in the sample is not only related to the residual stress value of the test sample, but also affected by the microstructure of the test sample. For austenitic steel, the ultrasound velocity is affected by the austenite grain size. Current ultrasonic residual stress detection technologies do not consider the variation in ultrasonic velocity caused by differences in austenite grain size. Therefore, existing ultrasonic residual stress detection methods for austenitic steel have certain errors compared to the actual residual stress. Some studies have attempted to reduce the influence of microstructure by separately setting up an ultrasonic probe to detect the longitudinal wave attenuation in the test area during residual stress detection. However, setting up a separate probe is complex, has large coupling errors, and it is difficult to ensure that the test area for stress testing is the same as the test area for attenuation detection. Furthermore, longitudinal waves are volume waves, subject to both diffusion attenuation and medium attenuation, which is detrimental to the accurate detection of attenuation.

[0004] Laser ultrasound is a novel, high-precision, non-destructive ultrasonic testing technology that utilizes laser pulses to excite ultrasonic pulses on the surface of materials through thermoelastic or ablation effects, thereby obtaining information about the test sample. In existing technologies, residual stress detection using laser ultrasound typically involves directly irradiating the surface of the workpiece with a laser, using the thermoelastic effect to excite surface acoustic waves or guided waves to detect residual stress. However, the energy conversion efficiency of ultrasonic waves excited by the thermoelastic effect on austenitic steel surfaces is low. To obtain suitable ultrasonic signals for detection, the laser power density needs to be increased, which can easily damage the sample surface. Furthermore, directly exciting ultrasonic waves on the sample surface to detect residual stress generally utilizes the generated surface acoustic waves or guided waves, both of which are less sensitive to stress than longitudinal waves, limiting the development of laser ultrasound for residual stress detection. Summary of the Invention

[0005] The purpose of this invention is to provide a method for detecting residual stress in austenitic steel that can correct for differences in grain size. This method can detect the critical refractive longitudinal wave velocity and surface wave attenuation of the test sample without changing the probe or adjusting the probe angle, thereby correcting the residual stress error caused by different grain sizes and improving the detection accuracy.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for detecting residual stress in austenitic steel that can correct for grain size differences, comprising:

[0008] Obtain calibration samples with the same specifications as the sample to be tested but with different grain sizes;

[0009] The attenuation coefficient calibration test and tensile stress calibration test were carried out on the calibration sample to obtain the surface wave attenuation coefficient and the critical refracted longitudinal wave velocity under different stress states.

[0010] Using the surface wave attenuation coefficient and critical refracted longitudinal wave velocity under different stress states of the calibrated sample as independent variables and the stress value as the dependent variable, the stress state function under different grain sizes was obtained.

[0011] The surface wave attenuation coefficient and critical refractive longitudinal wave velocity of the test area of ​​the test sample were detected by using a pre-constructed ultrasonic excitation probe.

[0012] By substituting the surface wave attenuation coefficient and critical refracted longitudinal wave velocity of the test area of ​​the sample into the stress state function under different grain sizes, the residual stress value of the test area of ​​the sample after microstructure correction is calculated.

[0013] Furthermore, the ultrasonic excitation probe includes a glass wedge, one side of which has an arc-shaped top surface and the other side has a sloping top surface; both the arc-shaped top surface and the sloping top surface are coated with a thermoelastic material layer.

[0014] Furthermore, the angle between the top surface of the inclined plane and the horizontal plane is 5°-15°.

[0015] Furthermore, the thermoelastic material layer is a chromium layer, a tungsten layer, or a tin layer, and the thickness of the thermoelastic material layer is 250nm-400nm.

[0016] Furthermore, using a pre-constructed ultrasonic excitation probe, surface wave attenuation and critical refracted longitudinal wave velocity are measured in the test area of ​​the sample to obtain the surface wave attenuation coefficient and critical refracted longitudinal wave velocity of the test area of ​​the sample, including:

[0017] The ultrasonic excitation probe was characterized to obtain the relationship between the laser beam irradiating the ultrasonic excitation probe and the ultrasonic longitudinal wave it excites.

[0018] The ultrasonic excitation probe is fixed in the test area of ​​the sample to be tested, and the excitation is determined to be at the first critical angle. The laser beam that generates the longitudinal ultrasonic wave incident on the surface of the test sample is positioned at position A on the ultrasonic excitation probe, and the laser beam that generates the longitudinal ultrasonic wave incident on the surface of the test sample at an incident angle β is positioned at position C on the ultrasonic excitation probe.

[0019] Based on irradiation positions A and C, a pulsed laser with adjustable pulse width is used to emit a laser beam to irradiate the ultrasonic excitation probe and excite ultrasonic longitudinal waves. The surface wave attenuation and critical refractive longitudinal wave velocity of the test area of ​​the test sample are detected respectively to obtain the surface wave attenuation coefficient and critical refractive longitudinal wave velocity of the test area of ​​the test sample.

[0020] Among them, the first critical angle The incident positions of the ultrasonic longitudinal wave incident on the surface of the test sample and the ultrasonic longitudinal wave incident on the surface of the test sample at an incident angle β coincide, and are denoted as incident position B.

[0021] Furthermore, the ultrasonic excitation probe is characterized to obtain the relationship between the laser beam irradiating the ultrasonic excitation probe and the ultrasonic longitudinal wave it excites, including:

[0022] An array of piezoelectric crystals is arranged at the bottom of the ultrasonic excitation probe;

[0023] Ultrasonic longitudinal waves are generated by irradiating a thermoelastic material layer of an ultrasonic excitation probe with laser beams of different pulse widths and single pulse powers emitted by a pulsed laser.

[0024] The ultrasonic longitudinal wave is received by the piezoelectric crystal array and the signal is processed to determine the relationship between the center frequency of the ultrasonic longitudinal wave with the maximum amplitude excited by the laser beam and the pulse width of the laser beam, as well as the relationship between the sound pressure of the ultrasonic longitudinal wave with the maximum amplitude excited by the laser beam and the single pulse power of the laser beam.

[0025] Furthermore, the excitation at the first critical angle was determined. The irradiation position A of the laser beam that generates the longitudinal ultrasonic wave incident on the surface of the test sample and the irradiation position C of the laser beam that generates the longitudinal ultrasonic wave incident on the surface of the test sample at an incident angle φ include:

[0026] Determine the angle α between the line containing the maximum amplitude ultrasonic longitudinal wave excited by the laser beam and the perpendicular line to the plane at the laser beam irradiation position;

[0027] Combining the curvature of the arc-shaped top surface of the glass wedge and the first critical angle The irradiation position A is obtained based on geometric relationships, and the incident position B is further obtained.

[0028] The irradiation position C is obtained by combining the angle α between the line of the maximum amplitude ultrasonic longitudinal wave excited by the laser beam and the perpendicular line of the plane at the laser beam irradiation position, the incident position B, the incident angle φ, and the angle between the top surface of the inclined surface of the glass wedge and the horizontal plane, based on geometric relationships.

[0029] Furthermore, based on irradiation positions A and C, a pulsed laser beam emitted by a pulse width-adjustable laser is used to irradiate the ultrasonic excitation probe to generate ultrasonic longitudinal waves. Surface wave attenuation and critical refractive longitudinal wave velocity are then measured in the test area of ​​the sample to be tested, obtaining the surface wave attenuation coefficient and critical refractive longitudinal wave velocity of the test area of ​​the sample, including:

[0030] Preliminary experiments were conducted to determine the relationship between the surface wave detection depth and the surface wave center frequency, as well as the relationship between the critical refracted longitudinal wave detection depth and the critical refracted longitudinal wave center frequency.

[0031] Based on the relationship between surface wave detection depth and surface wave center frequency, and the relationship between critical refracted longitudinal wave detection depth and critical refracted longitudinal wave center frequency, the surface wave center frequency and critical refracted longitudinal wave center frequency are determined according to the required detection depth.

[0032] Based on the relationship between the center frequency of the ultrasonic longitudinal wave with the maximum amplitude excited by the laser beam and the pulse width of the laser beam, the pulse width of the laser beam for detecting the surface wave attenuation and the critical refractive longitudinal wave velocity in the test area of ​​the test sample is determined according to the determined surface wave center frequency and the critical refractive longitudinal wave center frequency.

[0033] Based on the determined pulse width, a laser beam is emitted from a pulsed laser with adjustable pulse width and irradiated at the irradiation position A, exciting an electron with a first critical angle. The incident ultrasonic longitudinal wave is collected at the detection point by an ultrasonic acquisition device to obtain the critical refracted longitudinal wave signal, and the critical refracted longitudinal wave signal is processed to obtain the critical refracted longitudinal wave velocity of the test area of ​​the sample to be tested.

[0034] Based on the determined pulse width, a laser beam is emitted from a pulsed laser with adjustable pulse width to irradiate the irradiation position C, thereby exciting an ultrasonic longitudinal wave incident at an incident angle φ. The surface wave signal is collected at the detection point by an ultrasonic acquisition device, and the surface wave signal is processed to obtain the surface wave attenuation coefficient of the test area of ​​the sample to be tested.

[0035] The detection depths for critical refractive longitudinal wave velocity detection and surface wave attenuation detection in the test area of ​​the test sample are the same.

[0036] Furthermore, the incident angle φ is 65°, the wavelength of the laser beam emitted by the pulsed laser is 1064nm, the pulse width is 10ns-10μs, the single pulse energy is 1mJ-10mJ, and the repetition frequency is 20Hz-500Hz.

[0037] Furthermore, the pulsed laser also includes a linear focusing unit for concentrating the energy of the laser beam to make the laser beam linearly distributed. When performing surface wave attenuation detection and critical refractive longitudinal wave velocity detection on the test area of ​​the test sample, the length direction of the linearly distributed laser beam illuminating the glass wedge is parallel to the axis of the glass wedge. The length of the linearly distributed laser beam is 5mm-15mm and the width is 200μm-500μm.

[0038] Compared with the prior art, the beneficial effects of the present invention are:

[0039] The present invention provides a method for detecting residual stress in austenitic steel that can correct for differences in grain size. For austenitic steel with significant differences in grain size due to different heat treatments, the method characterizes the grain size through the surface wave attenuation coefficient. Since surface waves do not diffuse and attenuate, the method can adapt to the attenuation detection of test areas of various sizes, resulting in more accurate grain size characterization. Based on accurate grain size detection, the method establishes stress state functions under different grain sizes to correct the residual stress detection error caused by different grain sizes, thereby reducing the ultrasonic residual stress detection error.

[0040] The ultrasonic excitation probe provided by this invention has a thermoelastic material layer on its top surface. Ultrasonic waves are excited through this layer, improving the energy conversion efficiency of the laser ultrasound. By adjusting the laser beam irradiation position, ultrasonic longitudinal waves in different directions can be obtained. A single ultrasonic excitation probe can simultaneously excite critically refracted longitudinal waves and surface waves. Furthermore, it ensures that during critically refracted longitudinal wave velocity detection, the ultrasonic longitudinal wave is precisely incident on the test sample surface at the first critical angle, eliminating the need to adjust the ultrasonic longitudinal wave incident direction to adapt to different test samples and frequently replace the probe wedge, making it convenient and flexible to use. By adjusting the laser beam irradiation position, the test area for critically refracted longitudinal wave velocity can be ensured to coincide with the test area for surface wave attenuation detection. Moreover, by controlling the pulse width of the pulsed laser, the test depth for critically refracted longitudinal wave velocity can be ensured to coincide with the detection depth for surface wave attenuation detection, further improving the accuracy of residual stress detection.

[0041] This invention uses a pulsed laser with adjustable pulse width. The pulse width of the laser beam determines the center frequency of the laser beam-induced sound wave. Therefore, by changing the pulse width of the laser beam, ultrasonic waves with different center frequencies can be obtained, enabling residual stress detection at different depths without the need to replace the probe. This invention is simpler and more efficient than existing technologies.

[0042] This invention will be used to excite at a first critical angle The top surface of the glass wedge for generating ultrasonic longitudinal waves incident on the surface of the test sample is set as an arc surface. The irradiation position of the laser beam can be adjusted according to the first critical angle of the specific test sample, thereby ensuring that the ultrasonic longitudinal waves excited by the laser are accurately incident on the surface of the test sample at the first critical angle. The top surface of the glass wedge used to excite ultrasonic longitudinal waves incident on the surface of the test sample at an angle α greater than the second critical angle is set as an inclined plane at 5°-15° with the horizontal plane. On the one hand, this ensures that the excited ultrasonic longitudinal waves are incident on the surface of the test sample at an angle of α+5° to α+15°, where α is generally 55°-60°. An incident angle of α+5° to α+15° can excite surface waves. On the other hand, the inclined plane allows the excitation position of the ultrasonic longitudinal waves that generate surface waves to be adjusted according to the incident position of the ultrasonic longitudinal waves detected by the critical refraction longitudinal wave velocity, ensuring that the first critical angle is reached. The incident positions of the ultrasonic longitudinal wave incident on the surface of the test sample and the ultrasonic longitudinal wave incident on the surface of the test sample at an angle of α+5° to α+15° coincide. Attached Figure Description

[0043] Figure 1 This is a flowchart of a method for detecting residual stress in austenitic steel that can correct for grain size differences, provided in an embodiment of the present invention.

[0044] Figure 2A schematic diagram of the propagation direction of ultrasonic longitudinal waves, which generate critical refracted longitudinal waves and surface waves within the cross section of an ultrasonic excitation probe, provided in an embodiment of the present invention.

[0045] Figure 3 This is a top view schematic diagram of the ultrasonic excitation probe provided in an embodiment of the present invention.

[0046] In the figure: 1-Laser beam, 2-Thermoelastic material layer, 3-Glass wedge, 4-Ultrasonic longitudinal wave excited by the laser beam to generate critical refractive longitudinal wave, 5-Ultrasonic longitudinal wave excited by the laser beam to generate surface wave, 6-Line of the highest position in the middle of the glass wedge, 7-Top surface of the inclined plane, 8-Arc-shaped top surface. Detailed Implementation

[0047] The technical solution of this patent will be further described in detail below with reference to specific embodiments.

[0048] The embodiments of this patent are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this patent, and should not be construed as limiting this patent. In the absence of conflict, the embodiments of this patent and the technical features in the embodiments can be combined with each other.

[0049] See Figure 1 The residual stress detection method for austenitic steel with correctable grain size differences provided in this embodiment specifically includes the following steps:

[0050] Step 1: Obtain calibration samples with the same specifications as the sample to be tested but with different grain sizes;

[0051] In this embodiment, calibration samples with different grain sizes are obtained by placing the samples at the grain growth temperature for different times. The national standard classifies austenite grain size into 8 levels. In this embodiment, at least 8 different grain sizes are set, corresponding to the national standard. It is preferable to set more to ensure the accuracy of the established stress state function, thereby ensuring the accuracy of the test results.

[0052] Step 2: Perform attenuation coefficient calibration test and tensile stress calibration test on the calibration sample to obtain the surface wave attenuation coefficient and critical refracted longitudinal wave velocity under different stress states.

[0053] Step 3: Using the surface wave attenuation coefficient and the critical refracted longitudinal wave velocity under different stress states of the calibrated sample as independent variables and the stress value as the dependent variable, obtain the stress state function under different grain sizes.

[0054] In this embodiment, the surface wave attenuation coefficient of the calibrated sample and the critical refracted longitudinal wave velocity under different stress states are used as independent variables, and the stress value is used as the dependent variable. The stress state function under different grain sizes is obtained by multivariate interpolation fitting.

[0055] Step 4: Using a pre-constructed ultrasonic excitation probe, the surface wave attenuation and critical refractive longitudinal wave velocity of the test area of ​​the test sample are detected to obtain the surface wave attenuation coefficient and critical refractive longitudinal wave velocity of the test area of ​​the test sample.

[0056] In this embodiment, as Figure 2 , Figure 3 As shown, the ultrasonic excitation probe includes a glass wedge 3, which is a cylinder with a rectangular or square base. The cross-section of the glass wedge 3 is high in the middle and low on both sides. Figure 2 , Figure 3 In the diagram, 6 represents the highest point of the glass wedge. One side of the top surface of the glass wedge 3 is an arc-shaped top surface 8, used to excite the glass wedge at the first critical angle. Ultrasonic longitudinal waves incident on the surface of the sample to be tested Figure 2 In the diagram, 4 represents the ultrasonic longitudinal wave excited by the laser beam, used to generate the critical refractive longitudinal wave; the other top surface of the glass wedge 3 is an inclined top surface 7, with an angle of 5°-15° between the inclined top surface 7 and the horizontal plane, used to excite ultrasonic longitudinal waves incident on the surface of the sample to be tested at an incident angle φ greater than the second critical angle. Figure 2 In the diagram, 5 represents the ultrasonic longitudinal wave excited by the laser beam to generate surface waves. Both the curved top surface 8 and the inclined top surface 7 are coated with a thermoelastic material layer 2, which is a chromium, tungsten, or tin layer, with a thickness of 250nm-400nm. The excitation principle of the ultrasonic waves excited by the laser beam 1 irradiating the thermoelastic material layer 2 is based on the thermoelastic principle.

[0057] In this embodiment, the glass wedge 3 is designed to enable the generation of ultrasonic longitudinal waves incident on the surface of the test sample at different incident angles by adjusting the irradiation position of the laser beam 1 on the thermoelastic material layer 2. Furthermore, it enables the generation of ultrasonic longitudinal waves at a first critical angle by adjusting the irradiation position of the laser beam 1 on the thermoelastic material layer 2. The incident positions of the ultrasonic longitudinal wave incident on the surface of the test sample and the ultrasonic longitudinal wave incident at an incident angle φ that can generate surface waves at an incident angle greater than the second critical angle can coincide on the surface of the test sample.

[0058] In this embodiment, the laser beam and the laser beam illumination position only represent the positions in the critical refraction longitudinal wave sound velocity detection and surface wave attenuation detection. In actual detection, the critical refraction longitudinal wave sound velocity detection and surface wave attenuation detection are performed sequentially.

[0059] The surface wave attenuation coefficient and critical refractive longitudinal wave velocity of the test area of ​​the test sample are obtained by using a pre-constructed ultrasonic excitation probe to detect the surface wave attenuation coefficient and critical refractive longitudinal wave velocity, respectively. The steps include the following:

[0060] Step ①: Characterize the ultrasonic excitation probe and obtain the relationship between the laser beam irradiating the ultrasonic excitation probe and the ultrasonic longitudinal wave it excites;

[0061] Characterizing the ultrasonic excitation probe and obtaining the relationship between the laser beam irradiating the ultrasonic excitation probe and the ultrasonic longitudinal wave it excites includes the following steps:

[0062] Step a: Arrange a piezoelectric crystal array at the bottom of the ultrasonic excitation probe;

[0063] Step b: Use a pulsed laser to emit laser beams with different pulse widths and different single pulse powers to irradiate the thermoelastic material layer of the ultrasonic excitation probe to excite ultrasonic longitudinal waves.

[0064] Step c: Receive ultrasonic longitudinal waves through a piezoelectric crystal array and perform signal processing to determine the relationship between the center frequency of the ultrasonic longitudinal wave with the maximum amplitude excited by the laser beam and the pulse width of the laser beam, as well as the relationship between the sound pressure of the ultrasonic longitudinal wave with the maximum amplitude excited by the laser beam and the single pulse power of the laser beam.

[0065] Step 2: Fix the ultrasonic excitation probe in the test area of ​​the sample to be tested, and determine the excitation angle at the first critical angle. The laser beam that generates the longitudinal ultrasonic wave incident on the surface of the test sample is positioned at position A on the ultrasonic excitation probe, and the laser beam that generates the longitudinal ultrasonic wave incident on the surface of the test sample at an incident angle φ is positioned at position C on the ultrasonic excitation probe.

[0066] In this embodiment, the first critical angle is used. The incident positions of the ultrasonic longitudinal wave incident on the surface of the test sample and the ultrasonic longitudinal wave incident on the surface of the test sample at the incident angle φ coincide, and are denoted as incident position B.

[0067] Determine the excitation at the first critical angle The irradiation position A of the laser beam that generates the longitudinal ultrasonic wave incident on the surface of the test sample and the irradiation position C of the laser beam that generates the longitudinal ultrasonic wave incident on the surface of the test sample at an incident angle φ include the following steps:

[0068] Step i: Determine the angle α between the line of the maximum amplitude ultrasonic longitudinal wave excited by the laser beam and the perpendicular line to the plane at the laser beam irradiation position;

[0069] Step ii: Combining the curvature of the curved top surface of the glass wedge with the first critical angle The irradiation position A is obtained based on geometric relationships, and the incident position B is further obtained.

[0070] Step iii: Based on the geometric relationships, combine the angle α between the line of the maximum amplitude ultrasonic longitudinal wave excited by the laser beam and the perpendicular line to the plane at the laser beam irradiation position, the incident position B, the incident angle φ, and the angle between the top surface of the inclined surface of the glass wedge and the horizontal plane, to obtain the irradiation position C.

[0071] Step 3: Based on the irradiation positions A and C, a laser beam is emitted from a pulsed laser with adjustable pulse width to irradiate the ultrasonic excitation probe and excite ultrasonic longitudinal waves. The surface wave attenuation and critical refractive longitudinal wave velocity of the test area of ​​the test sample are detected to obtain the surface wave attenuation coefficient and critical refractive longitudinal wave velocity of the test area of ​​the test sample.

[0072] Based on irradiation positions A and C, a laser beam is emitted using a pulsed laser with adjustable pulse width to irradiate the ultrasonic excitation probe, exciting ultrasonic longitudinal waves. Surface wave attenuation and critical refractive longitudinal wave velocity are then measured in the test area of ​​the sample to obtain the surface wave attenuation coefficient and critical refractive longitudinal wave velocity of the test area. The steps include:

[0073] Step 1: Determine the relationship between the surface wave detection depth and the surface wave center frequency, as well as the relationship between the critical refractive longitudinal wave detection depth and the critical refractive longitudinal wave center frequency through preliminary experiments;

[0074] Step II: Based on the relationship between the surface wave detection depth and the surface wave center frequency, and the relationship between the critical refractive longitudinal wave detection depth and the critical refractive longitudinal wave center frequency, determine the surface wave center frequency and the critical refractive longitudinal wave center frequency according to the required detection depth.

[0075] Step III: Based on the relationship between the center frequency of the ultrasonic longitudinal wave with the maximum amplitude excited by the laser beam and the pulse width of the laser beam, determine the pulse width of the laser beam for surface wave attenuation detection and critical refractive longitudinal wave velocity detection in the test area of ​​the sample to be tested, according to the determined surface wave center frequency and critical refractive longitudinal wave center frequency.

[0076] Step IV: Based on the determined pulse width, use a pulsed laser with adjustable pulse width to emit a laser beam to irradiate the irradiation position A, exciting a laser with a first critical angle. The incident ultrasonic longitudinal wave is collected at the detection point by an ultrasonic acquisition device to obtain the critical refracted longitudinal wave signal, and the critical refracted longitudinal wave signal is processed to obtain the critical refracted longitudinal wave velocity of the test area of ​​the sample to be tested.

[0077] Step V: Based on the determined pulse width, a laser beam is emitted from a pulsed laser with adjustable pulse width to irradiate the irradiation position C, thereby exciting an ultrasonic longitudinal wave incident at an incident angle φ. The surface wave signal is collected at the detection point by an ultrasonic acquisition device, and the surface wave signal is processed to obtain the surface wave attenuation coefficient of the test area of ​​the sample to be tested.

[0078] In this embodiment, the detection depth for critical refractive longitudinal wave velocity detection and surface wave attenuation detection is the same in the test area of ​​the test sample.

[0079] In this embodiment, the incident angle φ is 65°, the wavelength of the laser beam emitted by the pulsed laser is 1064nm, the pulse width is 10ns-10μs, the single pulse energy is 1mJ-10mJ, and the repetition frequency is 20Hz-500Hz.

[0080] In this embodiment, the pulsed laser also includes a linear focusing unit for concentrating the energy of the laser beam to make the laser beam linearly distributed. When the surface wave attenuation degree detection and critical refractive longitudinal wave velocity detection are performed on the test area of ​​the test sample, the length direction of the laser beam with linear distribution illuminating the glass wedge is parallel to the axis of the glass wedge. The length of the laser beam with linear distribution is 5mm-15mm and the width is 200μm-500μm.

[0081] Step 5: Substitute the surface wave attenuation coefficient and critical refracted longitudinal wave velocity of the test area of ​​the sample into the stress state function under different grain sizes to calculate the residual stress value of the test area of ​​the sample after microstructure correction.

[0082] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these should also be considered within the scope of protection of the present invention. These will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A method for detecting residual stress in austenitic steel that can correct for differences in grain size, characterized in that, include: Obtain calibration samples with the same specifications as the sample to be tested but with different grain sizes; The attenuation coefficient calibration test and tensile stress calibration test were carried out on the calibration sample to obtain the surface wave attenuation coefficient and the critical refracted longitudinal wave velocity under different stress states. Using the surface wave attenuation coefficient and critical refracted longitudinal wave velocity under different stress states of the calibrated sample as independent variables and the stress value as the dependent variable, the stress state function under different grain sizes was obtained. The surface wave attenuation coefficient and critical refractive longitudinal wave velocity of the test area of ​​the test sample were detected by using a pre-constructed ultrasonic excitation probe. Substitute the surface wave attenuation coefficient and critical refracted longitudinal wave velocity of the test area of ​​the test sample into the stress state function under different grain sizes to calculate the residual stress value of the test area of ​​the test sample after microstructure correction. The ultrasonic excitation probe includes a glass wedge, with one side of the top surface being an arc-shaped top surface and the other side being a sloping top surface; Both the curved top surface and the sloping top surface are coated with a thermoelastic material layer; Using a pre-constructed ultrasonic excitation probe, surface wave attenuation and critical refracted longitudinal wave velocity were detected in the test area of ​​the sample to obtain the surface wave attenuation coefficient and critical refracted longitudinal wave velocity in the test area of ​​the sample. The ultrasonic excitation probe was characterized to obtain the relationship between the laser beam irradiating the ultrasonic excitation probe and the ultrasonic longitudinal wave it excites. The ultrasonic excitation probe is fixed in the test area of ​​the sample to be tested, and the excitation is determined to be at the first critical angle. The laser beam that generates the longitudinal ultrasonic wave incident on the surface of the test sample is positioned at position A on the ultrasonic excitation probe, and the laser beam that generates the longitudinal ultrasonic wave incident on the surface of the test sample at an incident angle φ is positioned at position C on the ultrasonic excitation probe. Based on irradiation positions A and C, a pulsed laser with adjustable pulse width is used to emit a laser beam to irradiate the ultrasonic excitation probe and excite ultrasonic longitudinal waves. The surface wave attenuation and critical refractive longitudinal wave velocity of the test area of ​​the test sample are detected respectively to obtain the surface wave attenuation coefficient and critical refractive longitudinal wave velocity of the test area of ​​the test sample. Among them, the first critical angle The incident positions of the ultrasonic longitudinal wave incident on the surface of the test sample and the ultrasonic longitudinal wave incident on the surface of the test sample at the incident angle φ coincide, and are denoted as incident position B.

2. The method for detecting residual stress in austenitic steel with correctable grain size differences according to claim 1, characterized in that, The angle between the top surface of the inclined plane and the horizontal plane is 5°-15°.

3. The method for detecting residual stress in austenitic steel with correctable grain size differences according to claim 1, characterized in that, The thermoelastic material layer is a chromium layer, a tungsten layer, or a tin layer, and the thickness of the thermoelastic material layer is 250nm-400nm.

4. The method for detecting residual stress in austenitic steel with correctable grain size differences according to claim 1, characterized in that, Characterizing the ultrasonic excitation probe and obtaining the relationship between the laser beam irradiating the ultrasonic excitation probe and the ultrasonic longitudinal wave it excites includes: An array of piezoelectric crystals is arranged at the bottom of the ultrasonic excitation probe; Ultrasonic longitudinal waves are generated by irradiating a thermoelastic material layer of an ultrasonic excitation probe with laser beams of different pulse widths and single pulse powers emitted by a pulsed laser. The ultrasonic longitudinal wave is received by the piezoelectric crystal array and the signal is processed to determine the relationship between the center frequency of the ultrasonic longitudinal wave with the maximum amplitude excited by the laser beam and the pulse width of the laser beam, as well as the relationship between the sound pressure of the ultrasonic longitudinal wave with the maximum amplitude excited by the laser beam and the single pulse power of the laser beam.

5. The method for detecting residual stress in austenitic steel that can correct for grain size differences according to claim 1, characterized in that, Determine the excitation at the first critical angle The irradiation position A of the laser beam that generates the longitudinal ultrasonic wave incident on the surface of the test sample and the irradiation position C of the laser beam that generates the longitudinal ultrasonic wave incident on the surface of the test sample at an incident angle φ include: Determine the angle α between the line containing the maximum amplitude ultrasonic longitudinal wave excited by the laser beam and the perpendicular line to the plane at the laser beam irradiation position; Combining the curvature of the arc-shaped top surface of the glass wedge and the first critical angle The irradiation position A is obtained based on geometric relationships, and the incident position B is further obtained. The irradiation position C is obtained by combining the angle α between the line of the maximum amplitude ultrasonic longitudinal wave excited by the laser beam and the perpendicular line of the plane at the laser beam irradiation position, the incident position B, the incident angle φ, and the angle between the top surface of the inclined surface of the glass wedge and the horizontal plane, based on geometric relationships.

6. The method for detecting residual stress in austenitic steel with correctable grain size differences according to claim 1, characterized in that, Based on irradiation positions A and C, a pulsed laser beam emitted by a pulse width-adjustable laser is used to irradiate the ultrasonic excitation probe, exciting ultrasonic longitudinal waves. Surface wave attenuation and critical refractive longitudinal wave velocity are then measured in the test area of ​​the sample to be tested, obtaining the surface wave attenuation coefficient and critical refractive longitudinal wave velocity of the test area of ​​the sample, including: Preliminary experiments were conducted to determine the relationship between the surface wave detection depth and the surface wave center frequency, as well as the relationship between the critical refracted longitudinal wave detection depth and the critical refracted longitudinal wave center frequency. Based on the relationship between surface wave detection depth and surface wave center frequency, and the relationship between critical refracted longitudinal wave detection depth and critical refracted longitudinal wave center frequency, the surface wave center frequency and critical refracted longitudinal wave center frequency are determined according to the required detection depth. Based on the relationship between the center frequency of the ultrasonic longitudinal wave with the maximum amplitude excited by the laser beam and the pulse width of the laser beam, the pulse width of the laser beam for detecting the surface wave attenuation and the critical refractive longitudinal wave velocity in the test area of ​​the test sample is determined according to the determined surface wave center frequency and the critical refractive longitudinal wave center frequency. Based on the determined pulse width, a laser beam is emitted from a pulsed laser with adjustable pulse width and irradiated at the irradiation position A, exciting an electron with a first critical angle. The incident ultrasonic longitudinal wave is collected at the detection point by an ultrasonic acquisition device to obtain the critical refracted longitudinal wave signal, and the critical refracted longitudinal wave signal is processed to obtain the critical refracted longitudinal wave velocity of the test area of ​​the sample to be tested. Based on the determined pulse width, a laser beam is emitted from a pulsed laser with adjustable pulse width to irradiate the irradiation position C, thereby exciting an ultrasonic longitudinal wave incident at an incident angle φ. The surface wave signal is collected at the detection point by an ultrasonic acquisition device, and the surface wave signal is processed to obtain the surface wave attenuation coefficient of the test area of ​​the sample to be tested. The detection depths for critical refractive longitudinal wave velocity detection and surface wave attenuation detection in the test area of ​​the test sample are the same.

7. The method for detecting residual stress in austenitic steel with correctable grain size differences according to claim 6, characterized in that, The incident angle φ is 65°, the wavelength of the laser beam emitted by the pulsed laser is 1064nm, the pulse width is 10ns-10μs, the single pulse energy is 1mJ-10mJ, and the repetition frequency is 20Hz-500Hz.

8. The method for detecting residual stress in austenitic steel with correctable grain size differences according to claim 1, characterized in that, The pulsed laser also includes a linear focusing unit for concentrating the energy of the laser beam to make the laser beam linearly distributed. When the surface wave attenuation degree and critical refractive longitudinal wave velocity are detected in the test area of ​​the test sample, the length direction of the linearly distributed laser beam illuminating the glass wedge is parallel to the axis of the glass wedge. The length of the linearly distributed laser beam is 5mm-15mm and the width is 200μm-500μm.

Images