Ultrasonic detection method for residual stress of hot-rolled steel plate

Abstract

The invention relates to an ultrasonic detection method for residual stress of a hot-rolled steel plate, belongs to the technical field of mechanical property testing of metal materials, and solves the problems that a destructive measurement technology for the residual stress of the hot-rolled steel plate in the prior art can damage materials, and a non-destructive detection technology is huge in equipment and high in cost. The invention provides an ultrasonic testing method for residual stress of a hot-rolled steel plate, which comprises the following steps of: S1, measuring a stress coefficient and a calibration function by using a zero-stress stretching standard block; S2, measuring a zero-stress processing reference standard block and calibrating the calibration function; S3, actually measuring the residual stress of a to-be-tested steel plate; and S4, correcting the data to obtain final residual stress data. According to the method, the distribution condition and the specific value of the residual stress of the hot-rolled steel plate can be rapidly and accurately obtained, operation is easy, equipment is relatively easy to obtain, cost is low, and powerful support and reference can be provided for size stability improvement in the processes of plate shape control, component manufacturing end forming and the like in the hot-rolled steel plate production process.

Description

Technical Field

[0001] The invention relates to the technical field of nondestructive testing of metal materials, and in particular to an ultrasonic testing method for residual stress of a hot-rolled steel plate. Background Art

[0002] With the increasing strengthening and widening of hot-rolled steel plate products, they have broad application prospects in the current modern engineering field. However, due to various factors in the manufacturing and processing process, such as rolling, heat treatment, etc., hot-rolled steel plates often have residual stress problems. These residual stresses may have an important impact on the surface quality of the steel plate and the mechanical properties, durability and safety of subsequent components. They are the key to the shape problems of hot-rolled steel plates and the poor stability of subsequent component processing performance. Therefore, the residual stress in the production and manufacturing process of hot-rolled steel plates and the processing of components needs to be accurately and quickly characterized and controlled.

[0003] At present, there are two main types of residual stress measurement technologies: destructive and non-destructive. Destructive detection methods are also called lossy (mechanical) methods, such as blind hole method, strip cutting method, etc., which mainly release the local stress of the material under test by mechanical means. The release of stress in the material will produce a certain strain. The strain produced can be measured by means such as strain gauges, and the stress value released by the material can be calculated using the principle of elastic mechanics; non-destructive detection methods are also called non-destructive (physical) methods, such as neutron diffraction method, X-ray diffraction method, ultrasonic method, etc., which mainly complete the residual stress detection without damaging the material by determining the relationship between certain physical quantities and stress. For steel plate products, non-destructive testing can ensure normal delivery. At present, the commonly used non-destructive testing methods include neutron diffraction method, X-ray diffraction method and ultrasonic method, among which neutron diffraction method currently has no small portable equipment and is not open to the public; X-ray diffraction method characterizes residual strain by measuring the displacement of diffraction lines, and then calculates residual stress by Hooke's law, but the penetration ability of X-rays is relatively weak, so it is only used to measure residual stress on the surface of materials and the test efficiency is low. Summary of the invention

[0004] In view of the above analysis, an embodiment of the present invention aims to provide an ultrasonic detection method for residual stress of hot-rolled steel plates, so as to solve at least one of the problems that the existing destructive measurement technology of residual stress of hot-rolled steel plates may damage the material and the non-destructive detection technology equipment is bulky and costly.

[0005] The present invention provides an ultrasonic testing method for residual stress of a hot-rolled steel plate, comprising the following steps:

[0006] S1: processing a number of rolling direction and transverse tensile test blocks of the steel plate to be tested, subjecting the test blocks to zero stress treatment and then subjecting them to tensile tests, and measuring calibration functions and stress coefficients of the rolling direction and transverse tensile calibration test blocks;

[0007] S2: cutting a reference test block at a certain depth of the steel plate to be tested and performing zero stress treatment to obtain a zero stress reference test block, performing an ultrasonic residual stress test on the zero stress reference test block after zero stress reference calibration, and recording the ultrasonic time and corresponding residual stress value of the zero stress reference test block in the rolling direction and transverse direction;

[0008] S3: setting an array of measured points on the measured steel plate, and for any measured point, completing the residual stress test in the corresponding direction of the measured point and recording the acoustic time and the corresponding residual stress value of the measured point;

[0009] S4: After correcting the data measured in S3, the final results of the residual stress values ​​in the rolling direction and the transverse direction of the steel plate to be tested are obtained.

[0010] Specifically, for the same batch or model of tested steel plates, only steps S1 and S2 need to be performed on a small number of samples and relevant functions and databases need to be established; in actual large-scale testing, only step S3 needs to be implemented without causing damage to the steel plates.

[0011] Specifically, the specific operations of step S1 are:

[0012] Several rolling direction and transverse tensile calibration test blocks of the tested steel plates were processed, and zero stress treatment and surface quality treatment were performed on the tensile calibration test blocks. Tensile tests were carried out on a universal tensile testing machine to simulate loading stress. Within the elastic limit range of the processed tensile calibration test blocks, multi-level loading was performed with a certain force as a step length. The ultrasonic critical refracted longitudinal wave propagation time and stress were output on the oscilloscope to obtain the calibration function and stress coefficient of the rolling direction and transverse tensile calibration test blocks, that is, the quantitative relationship between the acoustic time value and the corresponding stress value.

[0013] Specifically, for any tensile calibration specimen to be tested, the ultrasonic critical refraction longitudinal wave propagation time t under each level of loading stress is taken relative to the acoustic time t under zero stress according to multiple calibration results. 0 The average value of the sound time difference Δt=tt 0 The stress difference Δσ with the corresponding loading step 0 =σ-σ 0 Fitting calibration function, where σ represents the residual stress of the corresponding loading step, σ 0 It is a set value and does not affect the slope of the calibration function.

[0014] Specifically, the specific operations of the surface quality treatment are: grinding off the oxide scale on the surface of the tensile calibration test block to be measured and wiping the test piece with anhydrous ethanol to remove surface stains, applying a coupling agent between the parallel parts of the tensile calibration test block to be measured, and axially attaching the ultrasonic probe to the middle measured area of ​​the tensile calibration test block to be measured.

[0015] Specifically, the sampling depth of the zero stress reference test block in step S2 is the near-surface area of ​​the steel plate, and the sampling depth does not exceed 1 / 10 of the total thickness of the steel plate.

[0016] Specifically, the zero stress processing method is the zero stress processing method in the national standard GB / T 32073-2015 "Non-destructive Testing of Residual Stress by Ultrasonic Critical Refraction Longitudinal Wave Testing Method".

[0017] Specifically, the array of measured points in step S3 is obtained by equally dividing the measured steel plate into rolling direction and transverse dimensions.

[0018] Specifically, the array of measured points is obtained by dividing the measured steel plate into five equal parts in the rolling direction and the transverse direction, and the distance between the outermost measured points in the rolling direction and the transverse direction and the edge of the corresponding steel plate, that is, the trimming length, is not less than 200 mm.

[0019] Specifically, the correction operation in step S4 is:

[0020] The residual stress values ​​of the zero stress reference test block in the rolling direction and the transverse direction measured in step S2 are respectively taken as the zero values ​​of the residual stress in the rolling direction and the transverse direction of the steel plate, that is, the stress difference Δσ 0 =σ 实测 -σ 0 σ 0 , where σ 实测 is the measured stress value in step S3;

[0021] The residual stress results of the steel plate in the rolling direction and transverse direction are corrected, and the stress difference Δσ is obtained. 0 That is the final test result of the residual stress value at the corresponding point σ 最终 .

[0022] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0023] 1. The present invention firstly performs zero-stress treatment on the tensile test block to preliminarily measure the calibration function and stress coefficient, and then obtains the accurate relationship between residual stress and acoustic time difference through secondary calibration of the zero-stress reference block and establishes a corresponding database, thereby being able to perform large-scale non-destructive treatment on steel plates of the same batch / model, with simple operation, accurate results and low cost.

[0024] 2. The present invention measures and calibrates stress coefficients and functions in the rolling direction and the transverse direction respectively according to the actual situation that the rolling direction and the transverse extension characteristics of the steel plate to be tested are different. The accuracy and confidence of the correlation coefficients and functions are higher, thereby more comprehensively displaying the residual stress conditions of each point to be tested (i.e., the transverse and rolling direction residual stresses).

[0025] 3. The present invention can more comprehensively display the residual stress of the steel plate to be tested through the reasonable design of the array of test points, which is helpful to provide support and reference for subsequent steps such as steel plate shaping. Especially for thicker steel plates, the present invention provides a better sampling depth limit. When the above limit is met, the measured residual stress is more accurate.

[0026] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0028] Figure 1 is the rolling direction calibration function fitting result of the embodiment;

[0029] Figure 2 is the lateral calibration function fitting result of the embodiment;

[0030] Figure 3 is a schematic diagram of a possible array of measured points for residual stress of a steel plate;

[0031] Figure 4 Schematic diagram of sampling position / depth of the zero stress reference block in the embodiment. DETAILED DESCRIPTION

[0032] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0033] The present invention provides an ultrasonic testing method for residual stress of a hot-rolled steel plate, comprising the following steps:

[0034] S1: processing a number of rolling direction and transverse tensile test blocks of the steel plate to be tested, subjecting the test blocks to zero stress treatment and then subjecting them to tensile tests, and measuring calibration functions and stress coefficients of the rolling direction and transverse tensile calibration test blocks;

[0035] S2: cutting a reference test block at a certain depth of the steel plate to be tested and performing zero stress treatment to obtain a zero stress reference test block, performing an ultrasonic residual stress test on the zero stress reference test block after zero stress reference calibration, and recording the ultrasonic time and corresponding residual stress value of the zero stress reference test block in the rolling direction and transverse direction;

[0036] S3: setting an array of measured points on the measured steel plate, and for any measured point, completing the residual stress test in the corresponding direction of the measured point and recording the acoustic time and the corresponding residual stress value of the measured point;

[0037] S4: After correcting the data measured in S3, the final results of the residual stress values ​​in the rolling direction and the transverse direction of the steel plate to be tested are obtained.

[0038] Furthermore, the ultrasonic method has a large detection depth due to the propagation characteristics of ultrasonic waves, and can characterize the residual stress on the surface and inside of the material. In addition, the ultrasonic method is simple to operate and highly efficient when testing, and is applicable to most materials. Therefore, the ultrasonic method has the feasibility of rapid and non-destructive detection of residual stress in the production site environment. Ultrasonic detection of residual stress is based on the acoustoelastic effect. By measuring the propagation speed of sound waves, it can better reflect the surface and internal residual stress of the component. The acoustoelastic effect refers to the fact that when ultrasonic waves propagate in a stressed medium, their shear waves are polarized along the two principal stress directions. The two polarized waves propagate at different speeds. It is found that the speed difference of the two ultrasonic shear waves along the principal stress direction is proportional to the difference between the two principal stresses.

[0039] Specifically, the present invention firstly performs zero-stress treatment on the tensile test block to preliminarily measure the calibration function and stress coefficient, and then obtains the precise relationship between residual stress and acoustic time difference through secondary calibration of the zero-stress reference block and establishes a corresponding database, thereby being able to perform large-scale non-destructive treatment on the same batch / model of steel plates, with simple operation, accurate results and low cost. The present invention measures and calibrates stress coefficients and functions in the rolling direction and the transverse direction respectively in view of the actual situation that the rolling direction and transverse extension characteristics of the steel plate to be tested are different, and the accuracy and confidence of the correlation coefficient and function are higher, thereby more comprehensively displaying the residual stress situation of each point to be tested (i.e., transverse and rolling direction residual stress).

[0040] Specifically, for the same batch or model of tested steel plates, only steps S1 and S2 need to be performed on a small number of samples and relevant functions and databases need to be established; in actual large-scale testing, only step S3 needs to be implemented without causing damage to the steel plates.

[0041] Specifically, the specific operations of step S1 are:

[0042] Several rolling direction and transverse tensile calibration test blocks of the tested steel plates were processed, and zero stress treatment and surface quality treatment were performed on the tensile calibration test blocks. Tensile tests were carried out on a universal tensile testing machine to simulate loading stress. Within the elastic limit range of the processed tensile calibration test blocks, multi-level loading was performed with a certain force as a step length. The ultrasonic critical refracted longitudinal wave propagation time and stress were output on the oscilloscope to obtain the calibration function and stress coefficient of the rolling direction and transverse tensile calibration test blocks, that is, the quantitative relationship between the acoustic time value and the corresponding stress value.

[0043] Specifically, for any tensile calibration specimen to be tested, the ultrasonic critical refraction longitudinal wave propagation time t under each level of loading stress is taken relative to the acoustic time t under zero stress according to multiple calibration results. 0 The average value of the sound time difference Δt=tt 0 The stress difference Δσ with the corresponding loading step 0 =σ-σ 0 Fitting calibration function, where σ represents the residual stress of the corresponding loading step, σ 0 is the set value and does not affect the slope of the calibration function, that is, the ultrasonic stress coefficient K. The specific process is to draw a coordinate diagram of the tensile stress value and the acoustic time difference, perform a linear fit on the data, and the inverse of the slope of the obtained straight line is the ultrasonic stress coefficient K.

[0044] Specifically, the specific operations of the surface quality treatment are: grinding off the oxide scale on the surface of the tensile calibration test block to be measured and wiping the test piece with anhydrous ethanol to remove surface stains, applying a coupling agent between the parallel parts of the tensile calibration test block to be measured, and axially attaching the ultrasonic probe to the middle measured area of ​​the tensile calibration test block to be measured.

[0045] It is worth mentioning that during the ultrasonic stress coefficient calibration test and the zero stress reference block calibration test, the surface of the sample was treated to promote the coupling effect between the probe and the steel plate, reduce the loss during ultrasonic propagation, and improve the measurement accuracy of ultrasonic critical refracted longitudinal wave propagation sound.

[0046] Specifically, the sampling depth of the zero stress reference test block in step S2 is the near surface area of ​​the steel plate, and the sampling depth does not exceed 1 / 10 of the total thickness of the steel plate. This depth can better maintain the accuracy of ultrasonic measurement, and can also basically reflect the residual stress inside the thick steel plate. If the zero stress reference test block is sampled too shallowly, it will not be able to reflect the residual stress inside the steel plate, and if it is too deep, it will cause the ultrasonic wave to be unable to penetrate, thereby affecting the measurement accuracy and confidence.

[0047] Specifically, the zero stress treatment method is the zero stress treatment method in the national standard GB / T 32073-2015 "Nondestructive Testing of Residual Stress Ultrasonic Critical Refraction Longitudinal Wave Testing Method". There are two main zero stress treatment methods: one is to perform stress relief annealing on the test block, and the metallographic structure state of the test block after annealing should be the same as the structure state of the material being tested; the other is to perform vibration aging stress relief treatment on the test block to approximately obtain a test block with zero stress.

[0048] Specifically, the array of measured points in step S3 is obtained by equally dividing the measured steel plate into rolling direction and transverse dimensions.

[0049] Specifically, the array of measured points is obtained by dividing the measured steel plate into five equal parts in the rolling direction and the transverse direction, and the distance between the outermost measured points in the rolling direction and the transverse direction and the edge of the corresponding steel plate, that is, the trimming length, is not less than 200 mm. The present invention can more comprehensively display the residual stress of the steel plate to be measured through the reasonable design of the array of measured points, which is helpful to provide support and reference for subsequent steps such as steel plate shaping.

[0050] Specifically, the correction operation in step S4 is:

[0051] The residual stress values ​​of the zero stress reference test block in the rolling direction and the transverse direction measured in step S2 are respectively taken as the zero values ​​of the residual stress in the rolling direction and the transverse direction of the steel plate, that is, the stress difference Δσ 0 =σ 实测 -σ 0 σ 0 , where σ 实测 is the measured stress value in step S3;

[0052] The residual stress results of the steel plate in the rolling direction and transverse direction are corrected, and the stress difference Δσ is obtained. 0 That is the final test result of the residual stress value at the corresponding point σ 最终 .

[0053] Examples and Comparative Examples

[0054] The present invention is further described in detail below in conjunction with an embodiment. A method for ultrasonic testing residual stress of a hot-rolled steel plate, wherein the sample is a 60 mm thick Q390 seismic grade steel plate, comprises the following steps:

[0055] Calibration experiment

[0056] (a) According to the national standard GB / T 32073-2015 "Non-destructive testing of residual stress by ultrasonic critical refraction longitudinal wave detection method", 5 Q390 steel plate calibration test blocks were processed near the surface, 1 / 4 of the thickness direction, and 1 / 2 of the thickness direction in the rolling direction and transverse tensile calibration test blocks, with a total length of 215 mm, a width of 30 mm, a middle parallel length of 83.8 mm, a width of 20 mm, a transition arc radius of 20 mm, and a thickness of 6 mm;

[0057] (b) performing stress relief annealing on the tensile test block, grinding off the oxide scale on the surface of the annealed tensile calibration test block, and wiping the test piece with anhydrous ethanol to remove surface stains, and clamping the treated zero stress tensile calibration test block axially onto the tensile testing machine;

[0058] (c) Coating a coupling agent on the parallel area of ​​the zero stress tensile calibration block, and attaching the ultrasonic probe to the measured area of ​​the zero stress tensile calibration block along the axial direction;

[0059] (d) Prestress the tensile calibration test block within the elastic limit range to eliminate the gap between the tensile testing machine fixture and the test block to ensure more accurate loading stress;

[0060] (e) Within the elastic limit range of the tensile calibration block to be tested, a certain force is used as a step length, and multiple loading is performed. The ultrasonic critical refraction longitudinal wave propagation time change Δt and stress Δσ output on the oscilloscope are recorded to obtain the calibration function and stress coefficient of the rolling direction and transverse direction tensile calibration block;

[0061] The original data records of the rolling direction and transverse calibration tests sampled at different thickness positions are shown in Tables 1 and 2. The calibration function is as follows: Figure 2 and Figure 3 As shown in the figure, the calibration coefficients K in the rolling direction and transverse direction are 22.83, 22.99, 23.04 and 21.55, 21.60, 21.60, respectively, which are somewhat different, indicating the necessity of calibrating the ultrasonic stress coefficients in the rolling direction and transverse direction separately. After the calibration test, the ultrasonic stress coefficients in the rolling direction and transverse direction are recorded in the ultrasonic residual stress tester.

[0062] Table 1 Rolling direction calibration information of three sampling positions

[0063]

[0064] Table 2 Transverse calibration information of three sampling positions

[0065]

[0066] Residual stress testing

[0067] (1) A hot-rolled Q390 steel plate with a length of 9 m in the rolling direction and a width of 1.2 m in the transverse direction was selected, and the measured points were set on the surface of the steel plate. The distribution of the measured points was designed according to the rolling direction and transverse dimensions of the steel plate. Figure 3 As shown, a total of 25 points were tested;

[0068] (2) Select the channel information connected to the probe and the database of the steel plate to be tested in the ultrasonic residual stress tester. This time, the calibration data near the surface in the thickness direction of the steel plate is selected;

[0069] (3) Coat the surface of the zero stress reference test block with coupling agent and collect the acoustic time t of the zero stress reference test block. 0 and stress σ 0 , and test other positions of the zero stress reference test block, the stress change does not exceed ±10MPa, this time the reference test block taken near the surface in the thickness direction of the steel plate is selected;

[0070] (4) Apply coupling agent to any measured point and attach the ultrasonic probe parallel to the surface of the measured steel plate in the corresponding direction;

[0071] (5) Complete the rolling direction and transverse residual stress tests at 25 test points one by one, and record the acoustic time t and residual stress σ value of the corresponding points;

[0072] (6) Based on the self-test data of the zero stress reference test block in step (3), the acoustic time t and residual stress σ value of the corresponding point recorded in step (5) are corrected. The stress test results are shown in Table 3;

[0073] (7) According to the above test steps, the residual stress test of the calibration test block and the reference test block was completed at the sampling positions of 1 / 4 and 1 / 2 of the thickness direction, and the acoustic time t and residual stress σ values ​​at the corresponding points were recorded. The stress test results are shown in Tables 4 and 5.

[0074] Table 3 Corrected stress measured by sampling near the surface (1 / 10)

[0075]

[0076] Table 4 Corrected stress measured by sampling at 1 / 4

[0077]

[0078] Table 5 Corrected stress measured by sampling at 1 / 2

[0079]

[0080] It can be seen from the experimental data that the corrected stress values ​​obtained at different sampling depths are quite different. However, based on the analysis of the ultrasonic test depth and comparison with other residual stress test methods, it can be obtained that the error of ultrasonic residual stress measurement for near-surface sampling is no more than 5%. Too deep a sampling depth will lead to uncontrollable errors.

[0081] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. An ultrasonic testing method for residual stress of hot-rolled steel plate, characterized in that: The following steps are involved: S1: processing a number of rolling direction and transverse tensile test blocks of the steel plate to be tested, subjecting the test blocks to zero stress treatment and then subjecting them to tensile tests, and measuring calibration functions and stress coefficients of the rolling direction and transverse tensile calibration test blocks; S2: cutting a reference test block at a certain depth of the steel plate to be tested and performing zero stress treatment to obtain a zero stress reference test block, performing an ultrasonic residual stress test on the zero stress reference test block after zero stress reference calibration, and recording the ultrasonic time and corresponding residual stress value of the zero stress reference test block in the rolling direction and transverse direction; S3: setting an array of measured points on the measured steel plate, and for any measured point, completing the residual stress test in the corresponding direction of the measured point and recording the acoustic time and the corresponding residual stress value of the measured point; S4: After correcting the data measured in S3, the final results of the residual stress values ​​in the rolling direction and the transverse direction of the steel plate to be tested are obtained.

2. The ultrasonic testing method according to claim 1, characterized in that: For the tested steel plates of the same batch or model, only steps S1 and S2 need to be performed on a small number of samples. When testing a large number of samples, only step S3 needs to be performed without causing damage to the steel plates.

3. The ultrasonic testing method according to claim 1, characterized in that: The specific operations of step S1 are: Several rolling direction and transverse tensile calibration test blocks of the tested steel plates were processed, and zero stress treatment and surface quality treatment were performed on the tensile calibration test blocks. Tensile tests were carried out on a universal tensile testing machine to simulate loading stress. Within the elastic limit range of the processed tensile calibration test blocks, multi-level loading was performed with a certain force as a step length. The ultrasonic critical refracted longitudinal wave propagation time and stress were output on the oscilloscope to obtain the calibration function and stress coefficient of the rolling direction and transverse tensile calibration test blocks, that is, the quantitative relationship between the acoustic time value and the corresponding stress value.

4. The ultrasonic testing method according to claim 3, characterized in that: For any tensile calibration specimen under test, the calibration function is fitted by taking the average value of the acoustic time difference Δt=t-t0 of the ultrasonic critical refracted longitudinal wave propagation time t under each level of loading stress relative to the acoustic time t0 under zero stress and the stress difference Δσ0=σ-σ0 of the corresponding loading step according to multiple calibration results, where σ represents the residual stress of the corresponding loading step, σ0 is the set value and does not affect the slope of the calibration function.

5. The ultrasonic testing method according to claim 3, characterized in that: The specific operation of the surface quality treatment is: grinding off the oxide scale on the surface of the tensile calibration test block to be measured and wiping the test piece with anhydrous ethanol to remove surface stains, coating a coupling agent between the parallel parts of the tensile calibration test block to be measured, and axially attaching the ultrasonic probe to the middle measured area of ​​the tensile calibration test block to be measured.

6. The ultrasonic testing method according to claim 1, characterized in that: The sampling depth of the zero stress reference test block in step S2 is the near surface area of ​​the steel plate, and the sampling depth does not exceed 1 / 10 of the total thickness of the steel plate.

7. The ultrasonic testing method according to claim 1, characterized in that: The zero stress processing method is the zero stress processing method in the national standard GB / T 32073-2015 "Non-destructive Testing of Residual Stress Ultrasonic Critical Refraction Longitudinal Wave Testing Method".

8. The ultrasonic testing method according to claim 1, characterized in that: The array of measured points in step S3 is designed to be equally divided according to the rolling direction and transverse dimensions of the measured steel plate.

9. The ultrasonic testing method according to claim 8, characterized in that: The array of measured points is obtained by dividing the measured steel plate into five equal parts in the rolling direction and the transverse direction, and the distance between the outermost measured points in the rolling direction and the transverse direction and the edge of the corresponding steel plate, that is, the trimming length, is not less than 200 mm.

10. The ultrasonic testing method according to claim 1, characterized in that: The correction operation in step S4 is: The residual stress values ​​of the zero stress reference test block in the rolling direction and the transverse direction measured in step S2 are respectively taken as the zero values ​​of the residual stress in the rolling direction and the transverse direction of the steel plate, that is, the stress difference Δσ0=σ 实测 -σ0 in σ0, where σ 实测 is the measured stress value in step S3; The residual stress results of the steel plate in the rolling direction and transverse direction are corrected, and the obtained stress difference Δσ0 is the final test result σ of the residual stress value at the corresponding point 最终 .

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