Ultralarge-size metal billet ultrasonic detection method based on multi-probe combination

Abstract

The invention belongs to the technical field of nondestructive testing, and relates to a high-sensitivity ultrasonic testing method for an oversized metal billet based on multi-probe combination. According to the method, the bimorph longitudinal wave normal probes and the single-wafer longitudinal wave normal probes with different parameters are jointly used, and reasonable selection of detection partitions, detection surfaces and sensitivity adjustment modes is combined, so that high-sensitivity detection of the oversized metal billets with the thickness of 500-1000mm is realized, and meanwhile, relatively high near-surface resolution is ensured. According to the invention, the background noise of the material is reduced, the detection signal-to-noise ratio is improved, effective detection of the metal billet with the maximum thickness of 1m can be realized, the detection sensitivity can reach the equivalent weight of a flat-bottomed hole with the diameter of 1.2 mm, meanwhile, the near-surface resolution is superior to 2-5mm, a large number of reference blocks are not required to be manufactured, the cost is reduced, and field operation is facilitated. According to the method, the problem that ultrasonic detection of the oversized metal billets cannot be detected or the detection sensitivity is low at present can be solved, and an effective means is provided for controlling the internal quality of raw materials for large metal parts.

Description

Technical Field

[0001] The invention belongs to the technical field of nondestructive testing and relates to a high-sensitivity ultrasonic testing method for ultra-large-sized metal ingots based on the combination of multiple probes. Background Art

[0002] Large metal parts are important basic components necessary for major national technical equipment and major engineering construction. They play an important role in the shipbuilding, power, engineering machinery, petrochemical, metallurgy, aerospace and other industries. As the basic raw material for manufacturing large metal parts, the quality of super-large metal billets directly determines the quality of the parts. Super-large (thickness above 500mm) metal billets usually have the characteristics of large size and weight, long production cycle, high cost, and high internal quality requirements. Due to the large size and weight, the manufacturing process of super-large metal billets is also different from that of traditional small and medium-sized billets. The particularity and complexity of this forming technology make it more prone to defects inside, which directly affects the product qualification rate. Therefore, effective measures must be taken at the raw material stage to conduct internal quality monitoring to prevent defective raw materials from entering subsequent processes and reduce unnecessary time and economic costs.

[0003] Nondestructive testing technology has the advantage of evaluating the quality of the object under inspection without destroying it. It is an effective method for controlling product quality in the field of industrial production. Among them, ultrasonic testing technology is the main means for detecting internal defects of raw materials for large metal parts. For super-large metal ingots, the currently commonly used ultrasonic testing method is based on the full-sound range detection method, which uses a low-frequency (as low as 0.5-1MHz) single-crystal straight probe, and uses the full-sound range test block comparison method or the bottom wave calculation method to adjust the sensitivity and complete the detection. This detection method has the characteristics of large detection sound range, low signal-to-noise ratio, and large near-surface blind area; and this method is usually only applicable to materials with a thickness of less than 400mm. For super-large metal ingots with a thickness of more than 500mm, there is often a problem of being unable to detect; at the same time, due to the low detection frequency and the long ultrasonic wavelength, the existing method is not capable of detecting small defects (the minimum defect diameter that can be detected by a 0.5MHz probe is theoretically about 6mm), and the detection capability is difficult to meet the detection requirements of metal ingots for internal quality, and it is easy to cause missed detection. Summary of the invention

[0004] The purpose of the present invention is to provide an ultrasonic detection method for ultra-large-sized metal ingots based on multi-probe combination, so as to realize the detection of ultra-large-sized (thickness above 500mm) metal ingots.

[0005] To solve this technical problem, the technical solution of the present invention is:

[0006] An ultrasonic detection method for ultra-large metal ingots based on multi-probe combination includes the following steps:

[0007] S1: Pre-treat the surface of the metal ingot, and the surface roughness Ra value of the inspected part is not greater than 3.2μm;

[0008] S2: Select ultrasonic detector and coupling agent;

[0009] S3: Use the contact type longitudinal wave direct incidence method to detect the metal ingot. The detection surface and the ultrasonic sound beam incident direction are determined according to the forming process of the metal ingot. The sound beam incident direction is perpendicular to the detection surface.

[0010] S4: Determine the detection partition and corresponding probe according to the thickness of the metal ingot. The selected probes include contact double-chip longitudinal wave straight probes and contact single-chip longitudinal wave straight probes with different frequencies and chip diameters. The deviation between the peak frequency of the selected probe and the nominal value should be within ±10% of the nominal value. The specific selection of partitions and probes is as follows:

[0011] 1) For metal billets with a thickness of 800-1000 mm, they are divided into four regions: 2-10 mm in depth for region I, 10-100 mm in depth for region II, 100-T / 4 mm in depth for region III, and T / 4-T / 2 mm in depth for region IV, where T is the billet thickness;

[0012] The region I uses a contact type double-chip longitudinal wave straight probe A with a frequency of 5 to 10 MHz and a chip diameter of 8 to 20 mm; the regions II and III use a contact type single-chip longitudinal wave straight probe B with a frequency of 3.5 to 5 MHz and a chip diameter of 10 to 15 mm; the region IV uses a contact type single-chip longitudinal wave straight probe C with a frequency of 3.5 to 5 MHz and a chip diameter of 15 to 20 mm;

[0013] 2) The metal ingot with a thickness of 500-800 mm is divided into three regions: the depth of 2-10 mm is region i, and the probe A is used; the depth of 10-150 mm is region ii, and the probe B is used; the depth of 150-T / 2 mm is region iii, and the probe C is used;

[0014] S5: For different detection zones, the bottom wave calculation method and the test block comparison method are used to adjust the sensitivity;

[0015] S6: Determine the detection parameters such as scanning interval, scanning speed, pulse repetition frequency, etc.;

[0016] S7: Use the selected probe and detection parameters to scan the detection areas respectively, and record and evaluate the scanning results.

[0017] In step S5, the sensitivity adjustment method is specifically as follows:

[0018] 1) Use the test block comparison method to adjust the sensitivity of areas Ⅰ, Ⅱ, ⅰ and ⅱ, and select ultrasonic testing comparison test blocks with the same or similar sound permeability, sound velocity and sound impedance as the inspected billet. The test blocks contain flat-bottomed holes with different buried depths. The aperture of the flat-bottomed holes is the same as the aperture specified in the acceptance grade of the inspected billet. The minimum buried depth value of the test block should meet the requirements of machining allowance or near-surface resolution, and the maximum buried depth value should be at least the same as the depth of the detection partition. Use the probe corresponding to the area to make the amplitude of the reflected signal from any flat-bottomed hole on the selected test block reach 80% of the full scale of the fluorescent screen, and take the gain value of the one with the lowest amplitude as the scanning sensitivity to scan the area;

[0019] 2) For area III, use the bottom wave calculation method to adjust the 1 / 4 sound path scanning sensitivity, adjust the amplitude of the first bottom wave reflection signal to 80% of the full scale of the fluorescent screen, then increase the instrument gain value by the value of ΔdB, and then reduce it by 24dB, and use this gain value as the scanning sensitivity to scan the area; the calculation method of ΔdB is:

[0020]

[0021] Where: ΔdB is the gain value adjustment, Φ is the minimum equivalent flat-bottom hole diameter required to be detected in the acceptance grade of the inspected billet, λ is the ultrasonic wavelength in the inspected billet, and x is the total thickness of the inspected billet;

[0022] 3) For areas IV and III, use the bottom wave calculation method to adjust the 1 / 2 sound path scanning sensitivity, adjust the amplitude of the first bottom wave reflection signal to 80% of the full scale of the fluorescent screen, then increase the instrument gain value by the value of ΔdB, and then reduce it by 12dB. Use this gain value as the scanning sensitivity to scan the area; the ΔdB is calculated according to formula (1).

[0023] In step S2, the ultrasonic detector includes a frequency band range of 1 to 20 MHz, the pulse repetition frequency should be adjustable to a lower value of 50 to 100 Hz, and the gain adjustment range should be no less than 100 dB.

[0024] In step S3, the detection surface is determined according to the forming process of the billet, specifically as follows:

[0025] 1) For forging and extrusion forming ingots, select the surface closest to the parallelism of the metal flow line as the detection surface;

[0026] 2) For bars, the circumferential surface should be selected as the testing surface;

[0027] 3) For hot isostatic pressed ingots, all surfaces are inspected;

[0028] 4) For the additively manufactured billet, the surface perpendicular to the deposition direction is selected as the detection surface.

[0029] In step S4, the areas I and I are candidate inspection areas, and whether to conduct inspection is determined according to technical requirements or the surface machining allowance of the inspected billet.

[0030] In step S6, the scanning interval is no greater than half of the effective acoustic beam width of the probe, the scanning speed should be no greater than 50 mm / s, and the pulse repetition frequency is selected to be 50 to 100 Hz.

[0031] In step S7, after the inspection surfaces I to IV or I to III are scanned, the billet is turned over and scanned again from the opposite side with the same inspection parameters to achieve full coverage of the entire thickness range.

[0032] Preferably, in step S2, the coupling agent is engine oil, glycerine or hydraulic oil. For the billet with a convex incident surface, a coupling agent with a higher viscosity should be selected as much as possible.

[0033] Preferably, in step S1, loose oxide scale, burrs, oil stains, etc. that may affect ultrasonic detection are removed.

[0034] The oversized metal billet refers to a metal billet with a thickness of more than 500 mm.

[0035] The beneficial effects of the present invention are:

[0036] The present invention proposes a high-sensitivity ultrasonic detection method for ultra-large-sized metal ingots based on multi-probe combination, and its advantages and beneficial effects are manifested in the following aspects:

[0037] (1) For ultra-large (500-1000mm thick) metal ingots, the use of dual-chip longitudinal wave straight probes and single-chip longitudinal wave straight probes with different parameters, combined with the reasonable selection of detection partitions, detection surfaces and sensitivity adjustment methods, can effectively solve the problem of low signal-to-noise ratio in thick ingot detection, resulting in undetectable or low detection sensitivity. This method can achieve a detection sensitivity level of Φ1.2mm flat-bottom hole equivalent on metal ingots with a maximum thickness of 1 meter, thereby discovering smaller defects and greatly improving the ultrasonic detection capability of ultra-large metal ingots;

[0038] (2) By adjusting the sensitivity of each area and using a dual-chip longitudinal wave straight probe, a near-surface resolution of better than 2 to 5 mm can be achieved on ultra-large metal ingots, effectively reducing the near-surface blind area, maximizing the detectable range, and avoiding the waste of raw materials;

[0039] (3) The sensitivity is adjusted by using the test block comparison method combined with the bottom wave calculation method. Only a flat-bottom hole comparison test block with a buried depth of less than 150 mm is needed to complete the comprehensive scanning of the super-large billet. There is no need to make a thicker comparison test block, thereby reducing the test block production cost and time. It is also easy to carry and facilitate on-site testing.

[0040] (4) This method can provide an effective means for controlling the internal quality of raw materials used in large metal parts. Through early monitoring of the raw material stage, defective raw materials can be prevented from entering the next process, thereby reducing unnecessary time and economic costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions implemented in the present invention, the following is a brief explanation of the drawings required to be used in the examples of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0042] Figure 1 It is a flow chart of high-sensitivity ultrasonic testing of super-large metal billets based on multi-probe combination;

[0043] Figure 2 It is a schematic diagram of the detection division of metal ingots with a thickness of 800 to 1000 mm;

[0044] Figure 3 It is a schematic diagram of the detection zones for metal ingots with a thickness of 500 to 800 mm. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0046] The features of various aspects of the embodiments of the present invention will be described in detail below. In the detailed description below, many specific details are proposed to fully understand the present invention. However, it is obvious to those skilled in the art that the present invention can also be implemented without these specific details. The following description of the embodiments is only for a better understanding of the present invention by illustrating examples of the present invention. The present invention is not limited to any specific settings and methods provided below, but covers all product structures, any improvements, replacements, etc. of the methods covered without departing from the spirit of the present invention. In the various drawings and the following description, known structures and technologies are not shown to avoid unnecessary ambiguity of the present invention.

[0047] Example 1

[0048] The alloy steel ring-shaped parts made by additive manufacturing using directed energy deposition process are of material grade ZG27CrNi2MoA, with an outer diameter of 520mm, an inner diameter of 100mm, a height of 700mm, a single-side machining allowance of 3mm, and a deposition direction in the height direction of the ring. The required detection sensitivity is Φ1.2mm flat-bottom hole equivalent. The detection is carried out using a high-sensitivity ultrasonic detection method for ultra-large-sized metal billets based on a combination of multiple probes. The main steps are as follows:

[0049] S1: The surface of the additively manufactured alloy steel parts shall be treated. Loose oxide scale, burrs and oil stains that may affect ultrasonic testing are not allowed to exist. The surface roughness Ra value shall not be greater than 3.2μm.

[0050] S2: Use ultrasonic flaw detector for testing, the frequency band range is 1 to 20 MHz, and the coupling agent is engine oil;

[0051] S3: The contact-type longitudinal wave direct incidence method is used to detect the additively manufactured alloy steel parts. Considering that the parts are formed by additive manufacturing process and the deposition direction is the height direction of the ring, the upper and lower end surfaces perpendicular to the deposition direction are selected as the main detection surfaces for detection;

[0052] S4: The total height of the additively manufactured alloy steel part is 700mm, and the single-side machining allowance is 3mm. Therefore, the detection partitions and probes are selected as follows:

[0053] Area i (depth 3-10 mm) uses a DDR contact dual-element longitudinal wave straight probe (frequency 5 MHz, element diameter 13 mm);

[0054] Area ii (depth 10-150 mm) uses a contact single-element longitudinal wave straight probe model V109 (frequency 5 MHz, element diameter 13 mm);

[0055] Area iii (depth 150-350 mm) uses a contact single-element longitudinal wave straight probe model V108 (frequency 5 MHz, element diameter 19 mm);

[0056] The peak frequency of the selected probe should deviate from the nominal value within ±10% of the nominal value;

[0057] S5: For different detection zones, the bottom wave calculation method and the test block comparison method are used to adjust the sensitivity. The comparison test block used should be the same or similar to the sound permeability, sound velocity and acoustic impedance of the test piece. It is recommended to use the material with the same material grade, forming process and deposition direction as the alloy steel part to make the comparison test block. The aperture of the flat bottom hole is Φ1.2mm. The specific sensitivity adjustment method is as follows:

[0058] 1) For area i (depth 3-10mm), couple the DDR probe to the comparison test blocks with burial depth of 3-10mm, so that the reflection signal amplitude from any flat-bottom hole reaches 80% of the full scale of the fluorescent screen. Among them, the reflection amplitude of the flat-bottom hole with burial depth of 3mm is the lowest, and its gain value is 60dB. Therefore, 60dB is used as the scanning sensitivity to scan area i;

[0059] 2) For area ii (depth 10-150mm), the V109 probe was coupled to the comparison test blocks with buried depths of 10-150mm, so that the reflection signal amplitude from any flat-bottom hole reached 80% of the full scale of the fluorescent screen. Among them, the reflection amplitude of the flat-bottom hole with a buried depth of 150mm was the lowest, and its gain value was 75dB. Therefore, 75dB was used as the scanning sensitivity to scan area ii.

[0060] 3) For area iii (depth 150-350 mm), the bottom wave calculation method is used to adjust the 1 / 2 sound path scanning sensitivity. The V108 probe is coupled to the upper end surface of the alloy steel part to be inspected, and the amplitude of the first bottom wave reflection signal is adjusted to 80% of the full scale of the fluorescent screen. At this time, the gain value is 42 dB. The ΔdB value at the full sound path thickness calculated by formula (1) is 51 dB. Therefore, the scanning sensitivity at the 1 / 2 sound path is determined to be 42+51-12=81 dB;

[0061] S6: Use the scanning sensitivity of each partition determined in S5 and the corresponding probe to scan respectively, with a scanning interval of 3mm, a scanning speed of no more than 50mm / s, and an instrument pulse repetition frequency of 60Hz;

[0062] S7: After completing the scanning of areas i to iii, turn over the alloy steel part to be inspected, and scan again from the other end face according to the scanning sensitivity of each partition and the corresponding probe determined in S5 to achieve full coverage of the entire thickness range. During the scanning process, record the plane position, buried depth and amplitude of defects with a size exceeding the Φ1.2mm flat-bottom hole equivalent.

[0063] Example 2

[0064] Silicon carbide particles reinforced aluminum matrix (SiC p / Al) composite material billet, formed by hot isostatic pressing using powder metallurgy process, with a diameter of 560mm, a height of 1000mm, a single-side machining allowance of 10mm, and the required detection sensitivity is Φ1.2mm flat-bottom hole equivalent. The detection is carried out using a high-sensitivity ultrasonic detection method based on multi-probe combination for ultra-large-sized metal billets. The main steps are as follows:

[0065] S1: The surface of the aluminum-based composite material ingot is treated. Loose oxide scale, burrs and oil stains that affect ultrasonic testing are not allowed to exist. The surface roughness Ra value should not be greater than 3.2μm;

[0066] S2: Use ultrasonic flaw detector for testing, the frequency band range is 1 to 20 MHz, and the coupling agent is engine oil;

[0067] S3: The aluminum-based composite material ingot is tested by contact longitudinal wave direct incidence method. Considering that the part is formed by hot isostatic pressing process, the defect distribution has no obvious directionality, so all surfaces need to be tested, and the circumferential surface and upper and lower end surfaces are selected as the test surfaces;

[0068] S4: Selection of detection partitions and probes:

[0069] 1) End face detection: The total axial height of the aluminum-based composite material billet is 1000mm, and the single-side machining allowance is 10mm. Therefore, the detection of area I (depth 2-10mm) is not required. Use V109 probe to detect area II (depth 10-100mm) and area III (depth 100-250mm), and use V108 probe to detect area IV (depth 250-500mm). The deviation of the peak frequency of the selected probe from the nominal value should be within ±10% of the nominal value;

[0070] 2) Circumferential surface detection: The diameter of the aluminum-based composite material ingot is 560mm, and the single-side machining allowance is 10mm. Therefore, the detection of area i (depth 2-10mm) is not required. Use V109 probe to detect area ii (depth 10-150mm), and use V108 probe to detect area iii (depth 150-280mm). The deviation of the peak frequency of the selected probe from the nominal value should be within ±10% of the nominal value;

[0071] S5: For different detection zones, the bottom wave calculation method and the test block comparison method are used to adjust the sensitivity. The comparison test block used should be the same or similar to the sound permeability, sound velocity and acoustic impedance of the test piece. It is recommended to use the same material grade and forming process as the aluminum-based composite material billet to make the comparison test block. The diameter of the flat bottom hole is Φ1.2mm. The specific sensitivity adjustment method is as follows:

[0072] 1) For area II (end face depth 10-100mm), the V109 probe was coupled to the comparison test blocks with burial depths of 10-100mm, so that the reflection signal amplitude from any flat-bottom hole reached 80% of the full scale of the fluorescent screen. Among them, the reflection amplitude of the flat-bottom hole with a burial depth of 100mm was the lowest, and its gain value was 69dB. Therefore, 69dB was used as the scanning sensitivity for scanning area II.

[0073] 2) For area III (end face depth 100-250 mm), the bottom wave calculation method is used to adjust the 1 / 4 sound path scanning sensitivity. The V109 probe is coupled to the upper end face of the inspected billet, and the amplitude of the first bottom wave reflection signal is adjusted to 80% of the full scale of the fluorescent screen. At this time, the gain value is 50 dB. The ΔdB value at the full sound path thickness is calculated by formula (1) to be 55 dB. Therefore, the scanning sensitivity at 1 / 4 sound path is determined to be 50+55-24=81 dB;

[0074] 3) For area IV (end face depth 250-500 mm), the bottom wave calculation method is used to adjust the 1 / 2 sound path scanning sensitivity. The V108 probe is coupled to the upper end face of the inspected billet, and the amplitude of the first bottom wave reflection signal is adjusted to 80% of the full scale of the fluorescent screen. At this time, the gain value is 46 dB. The ΔdB value at the full sound path thickness calculated by formula (1) is 55 dB. Therefore, the scanning sensitivity at the 1 / 2 sound path is determined to be 46+55-12=89 dB;

[0075] 4) For area ii (circumferential surface depth 10-150mm), the V109 probe was coupled to the comparison test blocks with buried depths of 10-150mm, so that the reflection signal amplitude from any flat-bottom hole reached 80% of the full scale of the fluorescent screen. Among them, the reflection amplitude of the flat-bottom hole with a buried depth of 150mm was the lowest, and its gain value was 72dB. Therefore, 72dB was used as the scanning sensitivity to scan area ii.

[0076] 5) For area iii (circumferential surface depth 150-280 mm), the bottom wave calculation method is used to adjust the 1 / 2 sound path scanning sensitivity. The V108 probe is coupled to the upper end surface of the inspected billet, and the amplitude of the first bottom wave reflection signal is adjusted to 80% of the full scale of the fluorescent screen. At this time, the gain value is 45 dB. The ΔdB value at the full sound path thickness is calculated by formula (1) to be 49 dB. Therefore, the scanning sensitivity at the 1 / 2 sound path is determined to be 45+49-12=82 dB;

[0077] S6: Use the scanning sensitivity of each partition determined in S5 and the corresponding probe to scan respectively, with a scanning interval of 3mm, a scanning speed of no more than 50mm / s, and an instrument pulse repetition frequency of 60Hz;

[0078] S7: After completing the scanning of areas II to IV, the aluminum-based composite material ingot to be inspected is turned over, and the scanning sensitivity of each partition and the corresponding probe determined in S5 are used to scan again from the other end face to achieve full coverage of the entire thickness range. During the scanning process, the plane position, buried depth and amplitude of the defects with a size exceeding the equivalent of a Φ1.2mm flat-bottom hole are recorded.

[0079] In summary, the high-sensitivity ultrasonic detection method for ultra-large-sized metal billets based on multi-probe combination proposed in the present invention can detect the equivalent defect of Φ1.2mm flat-bottom hole on the large-sized alloy steel and aluminum-based composite billets with a thickness of 700-1000mm as described in Examples 1 and 2. While the prior art cannot detect billets of the above size or has a low detection capability (Φ3.2mm), the method of the present invention greatly improves the ultrasonic detection capability of ultra-large-sized metal billets.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the field can easily think of various equivalent modifications or substitutions within the technical scope disclosed by the present invention, and these modifications or substitutions should all be covered within the protection scope of the present invention.

Claims

1. A method for ultrasonic testing of oversized metal ingots based on multi-probe combination, characterized in that: The steps include: S1: Pre-treat the surface of the metal ingot, and the surface roughness Ra value of the inspected part is not greater than 3.2μm; S2: Select ultrasonic detector and coupling agent; S3: Use the contact type longitudinal wave direct incidence method to detect the metal ingot. The detection surface and the ultrasonic sound beam incident direction are determined according to the forming process of the metal ingot. The sound beam incident direction is perpendicular to the detection surface. S4: Determine the detection partition and corresponding probe according to the thickness of the metal ingot. The selected probes include contact double-chip longitudinal wave straight probes and contact single-chip longitudinal wave straight probes with different frequencies and chip diameters. The deviation between the peak frequency of the selected probe and the nominal value should be within ±10% of the nominal value. The specific selection of partitions and probes is as follows: 1) For metal billets with a thickness of 800-1000 mm, they are divided into four regions: 2-10 mm in depth for region I, 10-100 mm in depth for region II, 100-T / 4 mm in depth for region III, and T / 4-T / 2 mm in depth for region IV, where T is the billet thickness; The region I uses a contact type double-chip longitudinal wave straight probe A with a frequency of 5 to 10 MHz and a chip diameter of 8 to 20 mm; the regions II and III use a contact type single-chip longitudinal wave straight probe B with a frequency of 3.5 to 5 MHz and a chip diameter of 10 to 15 mm; the region IV uses a contact type single-chip longitudinal wave straight probe C with a frequency of 3.5 to 5 MHz and a chip diameter of 15 to 20 mm; 2) The metal ingot with a thickness of 500-800 mm is divided into three regions: the depth of 2-10 mm is region i, and the probe A is used; the depth of 10-150 mm is region ii, and the probe B is used; the depth of 150-T / 2 mm is region iii, and the probe C is used; S5: For different detection zones, the bottom wave calculation method and the test block comparison method are used to adjust the sensitivity; S6: Determine the detection parameters such as scanning interval, scanning speed, pulse repetition frequency, etc.; S7: Use the selected probe and detection parameters to scan the detection areas respectively, and record and evaluate the scanning results.

2. The method according to claim 1, characterized in that In step S5, the sensitivity adjustment method is specifically as follows: 1) For areas Ⅰ, Ⅱ, ⅰ and ⅱ, the sensitivity is adjusted by using the test block comparison method. The ultrasonic testing comparison test blocks with the same acoustic permeability, acoustic velocity and acoustic impedance as the inspected billet are selected. The test blocks contain flat-bottomed holes with different buried depths, and the aperture of the flat-bottomed holes is the same as the aperture specified in the acceptance grade of the inspected billet. The probe corresponding to the area is used to make the amplitude of the reflected signal from any flat-bottomed hole on the selected test block reach 80% of the full scale of the fluorescent screen. The gain value of the one with the lowest amplitude is taken as the scanning sensitivity to scan the area. 2) For area III, use the bottom wave calculation method to adjust the 1 / 4 sound path scanning sensitivity, adjust the amplitude of the first bottom wave reflection signal to 80% of the full scale of the fluorescent screen, then increase the instrument gain value by the value of ΔdB, and then reduce it by 24dB, and use this gain value as the scanning sensitivity to scan the area; the calculation method of ΔdB is: Where: ΔdB is the gain value adjustment, Φ is the minimum equivalent flat-bottom hole diameter required to be detected in the acceptance grade of the inspected billet, λ is the ultrasonic wavelength in the inspected billet, and x is the total thickness of the inspected billet; 3) For areas IV and III, use the bottom wave calculation method to adjust the 1 / 2 sound path scanning sensitivity, adjust the amplitude of the first bottom wave reflection signal to 80% of the full scale of the fluorescent screen, then increase the instrument gain value by the value of ΔdB, and then reduce it by 12dB. Use this gain value as the scanning sensitivity to scan the area; the ΔdB is calculated according to formula (1).

3. The method according to claim 1, characterized in that The minimum buried depth value of the test block should meet the processing allowance or near-surface resolution requirements, and the maximum buried depth value should be at least the same as the test partition depth.

4. The method according to claim 1, characterized in that: In step S2, the ultrasonic detector includes a frequency band range of 1 to 20 MHz, the pulse repetition frequency should be adjustable to a lower value of 50 to 100 Hz, and the gain adjustment range should be no less than 100 dB.

5. The method according to claim 1, characterized in that In step S3, the detection surface is determined according to the forming process of the billet, specifically as follows: 1) For forging and extrusion forming ingots, select the surface closest to the parallelism of the metal flow line as the detection surface; 2) For bars, the circumferential surface should be selected as the testing surface; 3) For hot isostatic pressed ingots, all surfaces are inspected; 4) For the additively manufactured billet, the surface perpendicular to the deposition direction is selected as the detection surface.

6. The method according to claim 1, characterized in that In the step S4, the areas I and I are candidate inspection areas, and whether to perform inspection is determined according to the surface machining allowance of the inspected billet.

7. The method according to claim 1, characterized in that In step S6, the scanning interval is no greater than half of the effective acoustic beam width of the probe, the scanning speed should be no greater than 50 mm / s, and the pulse repetition frequency is selected to be 50 to 100 Hz.

8. The method according to claim 1, characterized in that In step S7, after the inspection surfaces I to IV or I to III are scanned, the billet is turned over and scanned again from the opposite side with the same inspection parameters to achieve full coverage of the entire thickness range.

9. The method according to claim 1, characterized in that: In the step S1, loose oxide scale, burrs, oil stains, etc. that may affect ultrasonic detection are removed.

10. The method according to claim 1, characterized in that In step S2, the coupling agent is engine oil, glycerin or hydraulic oil.

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