JPH09304363A - Method for ultrasonically detecting flaw in austenitic steel casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for ultrasonically detecting flaws in austenitic steel castings, which enables flaw detection in a certain ultrasonic wave incident direction, without being affected by the direction of the crystal growth of a structure. SOLUTION: A probe 1 which causes longitudinal ultrasonic waves containing a wide band of frequencies incident perpendicularly on the flaw detection surface of a subject for flaw detection, so as to search for any internal flaw 3. Flaw evaluation is, made based on a distance-amplitude characteristic curve chart obtained from the received waveforms of the reflected waves, to determine whether or not any internal flaw 3 exists. The frequencies of the probe 1 should preferably contain at least 0.5 to 4Mhz. A flaw detection limit distance is within at least 60mm from the flaw detection surface, or within at least 120mm, when the top and bottom surfaces 2a, 2b of the subject for flaw detection are parallel. Determination of whether or not the internal flaw 3 exists, performed during the flaw evaluation, is made based on the distance- amplitude characteristic curve chart in which the reception level at a predetermined flaw detection distance of 80%, when sensitivity is 46dB and the size of the internal flaw is ϕ6.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an ultrasonic flaw detection method for austenitic stainless castings.

[0002]

2. Description of the Related Art The detection of internal defects by ultrasonic flaw detection of austenitic stainless castings has hitherto been taken up as an important issue, but until now, the internal defect detection by ultrasonic flaw detection has been due to the following problems. Is said to be impossible. 1) There are large variations in the attenuation of ultrasonic waves depending on the flaw detection point,
Stable measurement results cannot be obtained. 2) The difference in the flaw detection surface, that is, the difference in the attenuation and speed of sound of the ultrasonic wave is remarkable depending on the direction in which the ultrasonic wave is incident. 3) There is acoustic anisotropy (difference in sound velocity) inside the object to be inspected, and as a result, echoes (reflected waves) are exchanged, and attenuation and forest echo are large, making measurement difficult. It is said that the above-mentioned problems are mainly caused by scattering and attenuation of ultrasonic waves due to scattering factors such as crystal grain boundaries in the tissue.

Conventionally, various research institutions and manufacturers have been researching the above problems, and it has been pointed out that it is necessary to confirm the relationship between the crystal structure of austenitic stainless castings and ultrasonic characteristics. Then, some flaw detection methods that have solved this problem have been proposed. For example, Japanese Examined Patent Publication No. 57-1788 proposes an ultrasonic flaw detection method that enables flaw detection of an austenitic stainless casting under specific conditions. According to the publication, an ultrasonic probe that emits a longitudinal wave having a frequency of 0.3 to 2 MHz is used, and the propagation direction of the ultrasonic pulse to the object to be inspected is 40 ° to 50 ° with respect to the crystal growth direction of the tissue. The oblique angle flaw detection is performed by injecting ultrasonic waves so as to form a crossing angle. At this time, it has been confirmed that the height of the echo reception signal becomes maximum near the crossing angle of 45 °, so that if the crossing angle is in the range of 40 ° to 50 °, the height of the echo signal is determined by the flaw detection method. It is considered to be sufficiently practical.

[0004]

However, in the conventional flaw detection method as described above, the crossing angle between the propagation direction of the ultrasonic pulse incident on the object to be inspected and the crystal growth direction of the tissue is determined from the measurement result. Since it is a very important factor that affects the accuracy of internal defect detection, strict process control regarding the regularity of the crystal growth direction of the structure is required when manufacturing austenitic stainless cast products. . That is, the crystal growth direction of the structure at the time of product manufacturing is made to be a direction perpendicular to the surface over the entire product in the case of a plate-shaped product, or in the direction toward the central axis of the tube in the case of a tubular product. Therefore, a certain regularity is given. Such process management work becomes very complicated, which makes it difficult to streamline the manufacturing process of an austenitic stainless cast product that enables ultrasonic flaw detection.

The present invention has been made by paying attention to the above-mentioned problems, and it is an ultra-high-quality austenitic stainless casting that enables flaw detection in an arbitrary ultrasonic wave incident direction regardless of the crystal growth direction of the structure. It is intended to provide a method for ultrasonic flaw detection.

[0006]

In order to achieve the above-mentioned object, the invention according to claim 1 uses a probe to inject ultrasonic waves into an austenitic stainless cast product to cause internal defects. In the ultrasonic flaw detection method for austenitic stainless castings for flaw detection of No. 3, longitudinal ultrasonic waves including a wide band frequency are made to enter perpendicularly to the flaw detection surface of the flaw detection target.

According to the first aspect of the present invention, since the wideband probe which emits the longitudinal ultrasonic wave including the wideband frequency is used, the crystal growth direction of the tissue is increased as compared with the conventional ultrasonic flaw detection method. The S / N ratio for noise such as forest echo is improved regardless of the flaw detection direction regardless of the flaw detection direction. Therefore, it is possible to perform flaw detection in an arbitrary ultrasonic wave incident direction with respect to the crystal direction without being influenced by the crystal growth direction of the texture. Further, since the ultrasonic wave incident direction is not affected by the crystal growth direction, the ultrasonic wave incident direction can be made perpendicular to the flaw detection surface. Therefore, the work of connecting the above-mentioned broadband probe to the flaw detection surface becomes easy, and the workability at the time of flaw detection is improved. As a result, it is not necessary to control the regularity of the crystal growth direction of the structure of the product when manufacturing the austenitic stainless cast product, and the work efficiency of the manufacturing process and the flaw detection process is improved.

The invention according to claim 2 is an ultrasonic flaw detection method for an austenitic stainless casting in which ultrasonic waves are incident on the austenitic stainless casting using a probe to detect internal defects 3. As a method of making longitudinal ultrasonic waves incident perpendicularly to the flaw detection surface of the flaw detection target, performing defect evaluation based on the distance amplitude characteristic curve diagram obtained from the received waveform of this reflected wave, and determining the presence or absence of the internal defect 3 There is.

According to the second aspect of the present invention, since the wideband probe which emits the longitudinal ultrasonic wave including the wideband frequency is used, the crystal growth direction of the tissue is larger than that of the conventional ultrasonic flaw detection method. The S / N ratio for noise such as forest echo is improved regardless of the flaw detection direction regardless of the flaw detection direction. Therefore, it is possible to perform flaw detection in an arbitrary ultrasonic wave incident direction with respect to the crystal direction without being influenced by the crystal growth direction of the texture. Further, since the ultrasonic wave incident direction is not affected by the crystal growth direction, the ultrasonic wave incident direction can be made perpendicular to the flaw detection surface. Therefore, the work of connecting the above-mentioned broadband probe to the flaw detection surface becomes easy, and the workability at the time of flaw detection is improved. As a result, it is not necessary to control the regularity of the crystal growth direction of the structure of the product when manufacturing the austenitic stainless cast product, and the work efficiency of the manufacturing process and the flaw detection process is improved. Further, the presence / absence of an internal defect at the time of defect evaluation is determined based on a distance-amplitude characteristic curve diagram showing the relationship between the size of the internal defect, the flaw detection distance and the reception level thereof. At this time, the reception level of the actual reflected wave is plotted, and it is determined based on the comparison between the plotted point and the distance amplitude characteristic curve, so that the size (area) of the internal defect can be estimated at the time of defect evaluation, Pass / fail judgment becomes easy. Therefore, the flaw detection workability is improved.

[0010] The invention described in claim 3 is the invention according to claim 1 or 2.
In the ultrasonic flaw detection method for austenitic stainless castings described in (3), it is preferable that the wide band frequency of the probe includes at least a frequency of 0.5 to 4 MHz.

According to the third aspect of the invention, the frequency of the broadband probe is at least 0.5 to 4 MHz. As a result, the ultrasonic transmission in any flaw detection direction is improved without being affected by the crystal growth direction of the structure of the austenitic stainless casting, and there are few forest-like echoes and clear echoes from the internal defects and the bottom surface can be obtained. .
As a result, the S / N ratio is improved, and the presence / absence of an internal defect can be easily determined.

[0012] The invention according to claim 4 is the invention according to claim 1 or 2.
In the ultrasonic flaw detection method for austenitic stainless castings described in (3) above, the limit distance for flaw detection of the internal defect 3 is at least 60 mm from the flaw detection surface.

According to the invention described in claim 4, the thickness of the austenitic stainless cast product is at least 60 mm.
If it is within the range, by performing vertical flaw detection using a broadband probe that emits longitudinal ultrasonic waves including broadband frequencies,
It is possible to detect flaws without the ultrasonic incident angle being influenced by the crystal growth direction of the tissue. Therefore, it is not necessary to control the regularity of the crystal growth direction of the structure of the product when manufacturing the austenitic stainless cast product, and the work efficiency is improved.

The invention described in claim 5 is the invention according to claim 1 or 2.
In the ultrasonic flaw detection method for austenitic stainless castings described in (3) above, when the upper surface 2a and the bottom surface 2b of the flaw detection target are parallel to each other, the flaw detection limit distance of the internal defect 3 is at least 120 mm or less.

According to the fifth aspect of the present invention, if the austenitic stainless cast product has a top surface and a bottom surface parallel to each other and a thickness of at least 120 mm, a wide band ultrasonic wave including a wide band frequency is emitted. By performing flaw detection on the top surface and the bottom surface of the probe vertically, flaw detection is possible without the ultrasonic wave incident angle being influenced by the crystal growth direction of the tissue. Therefore, it is not necessary to control the regularity of the crystal growth direction of the structure of the product when manufacturing the austenitic stainless cast product, and the work efficiency is improved.

The invention according to claim 6 is the ultrasonic flaw detection method for an austenitic stainless casting according to claim 2, wherein the presence / absence of the internal defect 3 in the defect evaluation is 46 dB and the internal defect 3 is judged. When the size is φ6, the determination method is based on the distance amplitude characteristic curve diagram in which the reception level at the predetermined flaw detection distance is 80%.

According to the invention of claim 6, the sensitivity 46
In dB, the presence / absence of an internal defect at the time of defect evaluation can be determined based on the distance amplitude characteristic curve diagram created when the reception level at a predetermined flaw detection distance is 80% when the size of the internal defect is φ6. Done. At this time, the reception level of the actual reflected wave is plotted, and the judgment is made based on the comparison between the plotted point and the distance amplitude characteristic curve of φ6, so the size (area) of the internal defect 3 is estimated at the time of defect evaluation. It will be possible.
Therefore, the pass / fail judgment of the defect evaluation becomes easy, and the flaw detection workability is improved.

[0018]

DETAILED DESCRIPTION OF THE INVENTION Embodiments will be described below with reference to the drawings. FIG. 1 is an explanatory view of an ultrasonic flaw detection method for an austenitic stainless casting according to the present invention.
The steel material 2 to be inspected is composed of an austenitic stainless casting, and is, for example, SCS14 material. Either one of the upper surface 2a and the bottom surface 2b of the flaw detection target steel material 2 is used as a measurement surface for flaw detection (hereinafter referred to as flaw detection surface), and the probe 1 that emits ultrasonic waves is connected to this flaw detection surface. This probe 1
A wide band probe is used as the ultrasonic wave, and the ultrasonic wave is a longitudinal wave including at least a frequency of 0.5 to 4 MHz. Then, the probe 1 is connected so that ultrasonic waves are incident vertically to the flaw detection surface of the flaw detection target steel material 2. Further, this flaw detection surface may be flaw-detected from any direction regardless of the crystal growth direction of the steel material 2 to be flaw-detected. Here, as shown in FIG. 1, the flaw detection surface is an upper surface 2a. The ultrasonic waves emitted from the probe 1 travel straight inside the steel material 2 to be flaw-detected at the speed of sound, causing internal defects 3
Bottom surface 2 that is reflected by or is facing the flaw detection surface
reflected by b. This reflected wave is received by the probe 1, and the reception time of this reception signal (elapsed time from the time of emission)
Based on the above, the depth of the internal defect 3 from the flaw detection surface and the height to the bottom surface 2b can be measured. Here, the propagation sound velocity V in the flaw detection target steel material 2 depends on the crystal grain size and the crystal growth direction of the structure in the flaw detection target steel material 2.

At the time of defect evaluation, evaluation is carried out by using a distance amplitude characteristic curve diagram as shown in FIG. In the figure, the horizontal axis represents the flaw detection distance, and the vertical axis represents the reception level of the reflected wave with respect to the amplitude of the wave emitted from the probe 1. This distance amplitude characteristic curve 20 shows the relationship between the reception level of the reflected wave and the flaw detection distance when flaw detection is performed on the internal defect 3 having a diameter of 6 mm (hereinafter referred to as φ6). The effective area of flaw detection is shown inside the department. When actually evaluating a defect, first, with respect to a workpiece of an austenitic stainless casting to be inspected, first, in order to temporarily detect an approximate defective position, a flaw measuring device at the time of creating the distance amplitude characteristic curve 20. The flaw detection is performed with a sensitivity of 58 dB which is greater than the sensitivity of, for example, greater than 46 dB. Next, at the time of this defect evaluation, under the condition that the internal defect 3 of φ6 at the position of the flaw detection distance of 20 mm is received with the sensitivity of 46 dB and the level of 80% with the same sensitivity as when the distance amplitude characteristic curve 20 was created. The flaw detection is carried out with, and the reception level of the reflected wave at this time is plotted in the distance amplitude characteristic curve diagram of FIG.
Based on this flaw detection result, the φ6 distance amplitude characteristic curve 20
When plotted above, it can be determined that there is an internal defect 3 having a size (area) of about φ6 at the flaw detection distance corresponding to this plot point, and when plotted above the distance amplitude characteristic curve 20 of φ6. Can be determined to have an internal defect 3 larger than φ6 at the corresponding flaw detection distance. Further, when plotted in the shaded area in FIG. 2 and below the distance amplitude characteristic curve 20 of φ6, it can be seen that there may be an internal defect 3 smaller than φ6.

Next, the operation of the above flaw detection method will be described in detail. First, the reason why flaw detection is possible from any direction regardless of the crystal growth direction will be described. FIG. 3 shows an example of the received reflection waveform described above. This figure shows an example of a reflection waveform when the crystal growth direction of the austenitic stainless cast structure is parallel to the ultrasonic wave incident direction, that is, when it is perpendicular to the flaw detection surface.
In the figure, the horizontal axis represents the above-mentioned reception time t, and the vertical axis represents the reception level (signal intensity) of the reflected wave. The present inventor, in the conventional probe of a specific frequency used for flaw detection of conventional austenitic stainless castings, since the received signal of the reflected wave and the noise signal are observed mixedly at the same level, the bottom surface It was confirmed that the reflected wave from 2b (hereinafter referred to as the bottom echo) cannot be clearly distinguished. After this confirmation, if a probe 1 for a wide band, for example, a frequency of 0.5 to 4 MHz is used, the S / N ratio is improved, and the bottom surface echo is observed very clearly under certain measurement conditions as described later. I was confirmed. The waveform at this time is a reflection waveform similar to that obtained when ultrasonically flaw-detecting a general metal member other than an austenitic stainless casting, that is, a waveform B representing a bottom echo is clearly observed as shown in FIG. . If there is an internal defect 3 in the steel material 2 to be inspected, a waveform representing the reflected wave from the internal defect 3 between the position of the reception time t = 0 (corresponding to the inspection surface) and the position of the above waveform B. A is observed. Thus, when the waveform A is observed, it can be determined that there is an internal defect 3, and the reception time Ta of the waveform A is Ta.
The distance to the internal defect 3 and the distance to the bottom surface 2b can be calculated from the reception time Tb of the waveform B and the propagation sound velocity V described above.

On the other hand, when an ultrasonic wave is applied in a direction orthogonal to the crystal growth direction of the structure of the austenitic stainless cast product, the waveform A and the waveform B are the received signals which can be easily discriminated as shown in FIG. However, the waveform is such that a large number of noise signals are observed. FIG. 4 shows an example of the reception reflection waveform in this case, and the probe 1 at this time also uses the same wideband probe having a frequency of 0.5 to 4 MHz as described above. As can be seen from the figure, a noise signal waveform is observed in a scattered manner in the received waveform, and such a noise signal waveform is conventionally called a forest echo. This forest-like echo is generated because the ultrasonic waves are scattered by the crystal grain boundaries that form the structure of the steel material 2 to be flaw-detected as described above. Therefore, it becomes very difficult to identify the internal defect 3 and the bottom echo based on the received waveform in which the forest echo is observed.

As described above, the received waveform of the reflected wave is very different depending on the angle formed by the crystal growth direction of the structure of the austenitic stainless casting and the incident direction of the ultrasonic wave, and the state of this received waveform is an internal defect. This affects the quality of detection accuracy. Therefore, there is a demand for a flaw detection method capable of obtaining stable detection accuracy without being affected by the ultrasonic wave incident direction, and the present inventor has found that, based on some test results, under specific conditions. We propose a flaw detection method that can obtain such stable detection accuracy. This will be described in detail below.

In order to confirm the relationship between the crystal growth direction of the structure of the austenitic stainless cast product, the ultrasonic wave incident direction, and the internal defect, the present inventor has prepared a test piece having a certain crystal growth direction. I made some. That is,
A test material 10 having a constant crystal growth direction is made by the casting direction 14 of the SCS14 stainless steel hot water as shown in FIG. 5, and from this test material 10, the casting direction 14
A cubic test piece 11 having two surfaces orthogonal to and four surfaces parallel to the casting direction 14 was manufactured. This test piece 1
1, one of the planes orthogonal to the casting direction 14 is a plane P, and the planes parallel to the casting direction 14 are orthogonal to each other,
The planes orthogonal to the plane P are referred to as the plane Q and the plane R, respectively. Here, the length of one side of the test piece 11 is 70 mm. Each of the surface P, the surface Q, and the surface R of the test piece 11 was used as a flaw detection surface, and the above-described probe 1 was connected, and the received waveform of the reflected wave at this time was observed. When the surface P is used as a flaw detection surface, the waveform has a forest echo as shown in FIG. 4, and it is difficult to observe the waveform B which is the bottom echo. When the surface Q is used as the flaw detection surface, a clear bottom surface echo as shown in FIG. 3 can be confirmed, and the forest-like echo at this time is very small (the reception level is 20% or less even if large). there were.
Further, when the surface R was used as the flaw detection surface, about 20% of the forest-like echo was observed as compared with the above-mentioned flaw detection on the Q surface, but the bottom echo was clear and could be confirmed easily.

From the above, it was found that the direction of the crystal grain boundary of the test piece 11 differs depending on the pouring direction of the molten metal, and the ultrasonic wave transmission varies depending on the difference in the directionality of the crystal grain boundary. Generally, it is well known that the pouring direction and the solidification direction of the molten metal are orthogonal to each other and the crystal grains grow in this solidification direction. Therefore, on the surfaces Q and R, the crystal growth direction is orthogonal to the flaw detection surface, so that the ultrasonic wave incident direction is parallel to the crystal growth direction, and the ultrasonic wave transmittance is good. Therefore, for Q-face inspection and R-face inspection, test piece 1 with 70 mm thickness
Since the bottom echo of 1 can be clearly observed, flaw detection is possible. Further, since the crystal growth direction is parallel to the flaw detection surface on the surface P, the ultrasonic wave incident direction is perpendicular to the crystal growth direction, and the ultrasonic wave transmittance varies. Therefore, in the P-plane flaw detection, since the bottom surface echo cannot be observed in the test piece 11 having a thickness of 70 mm, flaw detection is impossible. As a result, regarding the flaw detection direction, it can be understood that the worst condition is the direction perpendicular to the crystal growth direction.

Therefore, the inventor of the present invention experimentally finds the limit value of the flaw detection distance under the above-mentioned worst condition. FIG.
Shows the manufacturing procedure of the test material for this test, and FIG. 7 shows the test distance when ultrasonic waves are injected in the direction perpendicular to the crystal growth direction using this test material, that is, the flaw detection distance by P-plane flaw detection. And the reception level of the bottom echo. In FIG. 6, the test material 12 has two surfaces orthogonal to the pouring direction 14 of the molten metal, and has at least 100 mm in this pouring direction.
It is a square columnar test material having the above length. If one of the two surfaces orthogonal to the casting direction 14 is referred to as the surface P as in the above, the P-plane flaw detection is a flaw detection direction perpendicular to the crystal growth direction. Based on this surface P, for example, 60 mm, 70 m
Cut the test material 12 like m, 80mm, 90mm ...
Specimens of different length are made at 0 mm intervals. Then, the bottom surface echo was observed by P-face flaw detection of each of the test pieces, and the flaw detection distance was measured. This result is shown in FIG. 7, in which the horizontal axis represents the flaw detection distance (here,
(Corresponding to the distance to the bottom surface), and the vertical axis represents the reception level of the bottom surface echo when the signal level of the emitted wave is 100%. The curve 23 in the figure is created as follows. That is, the reception level of the bottom echo is observed for each of the above-mentioned test pieces at intervals of 10 mm, and the relationship between the length of the test piece and this reception level at this time is shown in FIG. Create by plotting the relationship. As a result, it can be estimated that the limit of the flaw detection distance with which the bottom echo can be clearly observed is within 60 mm. Therefore, it was judged that the flaw detection direction under the worst condition, that is, the limit value of the flaw detection distance in P-face flaw detection is within 60 mm. Conversely, if it is within 60 mm, flaw detection is possible when the crystal growth direction is arbitrary.

Next, the present inventor seeks the minimum value of the size of the internal defect which can be detected under the condition of 60 mm or less as described above. That is, in order to confirm the size of the internal defect that can be distinguished from the forest echo, the relationship between the size of the internal defect, the reception level at that time, and the flaw detection distance is examined. Figure 8 shows this relationship,
In the figure, the horizontal axis represents the distance from the flaw detection surface, and the vertical axis represents the ratio of the received level of the amplitude of the reflected wave to the amplitude of the emitted wave. The present invention is based on the above-mentioned worst condition, that is, it is premised that an internal defect within a flaw detection distance of 60 mm can be detected by P-face flaw detection.
The reception level at 60 mm or more is measured as well as the reception level within, and the curve 21 of FIG. 8 regarding the smallest detectable internal defect is created based on the measurement result. Therefore, in FIG. 8, in order to measure the reception level at the flaw detection distance of 60 mm or more, the reception level of the internal defect is measured by flaw detection from the direction orthogonal to the casting direction (the above-mentioned Q-plane flaw detection). . The present inventor has confirmed that the reception level within 60 mm is similar between the above-described P-plane flaw detection and Q-face flaw detection.

In FIG. 8, a curve 21 represents the reception level of the reflected wave from the φ6 circular hole for each flaw detection distance. Further, FIG. 9 shows a test piece used at this time, and in order to measure the reception level at a flaw detection distance of 60 mm or more as described above, a test piece capable of Q-face flaw detection is used. A hole 25 having a predetermined size of, for example, φ6 is opened from the bottom surface of the test piece, and the test piece is processed so that the distance between the end surface of the hole 25 and the upper surface of the test piece becomes a predetermined flaw detection distance. The upper surface of this test piece is used as a flaw detection surface, the reception level of the reflected wave from the hole 25 of φ6 or the like provided at a predetermined flaw detection distance is plotted for each flaw detection distance, and each plot point is connected to the curve 21.
Has been created. Here, although the reception level of the forest echo is also shown in FIG. 8, the reception sensitivity of the flaw measuring device is adjusted so that the reception level of the forest echo does not exceed a predetermined level. In FIG. 8, the sensitivity is set to 46 dB so that the reception level of this forest echo does not exceed, for example, 30%. At this time, the reception level from the hole 25 of φ6 or the like at a position with a flaw detection distance of 20 mm is 80%. Has been adjusted to be. Such a curve 21 was created for each hole having a predetermined size, for example, φ3, 4, 5, 6 or the like.
It should be noted that FIG. 8 shows only the curve relating to the φ6 hole. Then, considering the difference in the reception level between the forest echo and the reflected wave of each hole 25 based on these curves 21, in order to determine the presence or absence of the hole 25 within a flaw detection distance of 60 mm, an area of φ6 or more is required. It turned out that hole 25 is needed. From this, when the flaw detection distance is within 60 mm, the minimum detectable size of the internal defect is φ6.
And The distance amplitude characteristic curve 20 used in the above-described defect evaluation is created in this way.

Since the flaw detection method is as described above, flaw detection can be performed from any direction without being influenced by the crystal growth direction of the flaw detection surface of the austenitic stainless casting, and the flaw detection distance at that time is within 60 mm. can do.
As a result, when manufacturing the austenitic stainless cast product, no special process control is required so as to give a certain regularity to the crystal growth direction of the structure of this product, and the manufacturing process is simplified and becomes efficient. . Further, since the special process as described above can be omitted, it is advantageous in terms of manufacturing cost. Further, at the time of actual flaw detection work, a so-called vertical flaw detection method is used in which an arbitrary surface that is not affected by the crystal growth direction of the product can be used as the flaw detection surface and the ultrasonic wave incident direction from the probe 1 is perpendicular to the flaw detection surface. Therefore, the workability can be improved.

In the above description, the flaw detection limit thickness of the flaw detection steel material 2 is 60 mm, but the invention is not limited to this. For example, when the top surface 2a and the bottom surface 2b of the flaw detection steel material 2 are configured to be parallel to each other. Has a limit thickness of 1 by performing flaw detection from the upper surface 2a and the bottom surface 2b in the same manner as described above.
It becomes possible to make it 20 mm. It is easy to see that the action and effect in this case are the same.

[Brief description of drawings]

FIG. 1 is an explanatory view of an ultrasonic flaw detection method for an austenitic stainless casting according to the present invention.

FIG. 2 is a distance amplitude characteristic curve diagram of an ultrasonic flaw detection method according to the present invention.

FIG. 3 shows an example of received waveforms when the ultrasonic wave incident direction and the crystal growth direction are parallel to each other in the ultrasonic flaw detection method according to the present invention.

FIG. 4 shows an example of a received waveform in the ultrasonic flaw detection method according to the present invention when the ultrasonic wave incident direction and the crystal growth direction are vertical.

FIG. 5 is a diagram showing the relationship between the casting direction of hot water and each surface of the test piece during the production of the test material.

FIG. 6 shows a test material manufacturing procedure in a test for determining a flaw detection distance limit value under the worst condition.

FIG. 7 shows the relationship between the flaw detection distance by P-face flaw detection and the reception level of the bottom surface echo.

FIG. 8 shows the relationship between the size of an internal defect, its reception level, and the flaw detection distance.

9 shows a test piece for making the relationship diagram of FIG.

[Explanation of symbols]

 1 probe 2 steel material for flaw detection 2a upper surface 2b bottom surface 3 internal defect 10, 12 test material 11 test piece 14 casting direction 20 distance amplitude characteristic curve 21, 23 curve 25 hole A internal defect echo waveform B bottom echo waveform P casting Surface orthogonal to the casting direction Q Surface parallel to the casting direction R Surface parallel to the casting direction

Claims (6)

[Claims] 1. An ultrasonic flaw detection method for an austenitic stainless casting in which ultrasonic waves are incident on the austenitic stainless casting using a probe to detect internal defects (3). An ultrasonic flaw detection method for an austenitic stainless casting, which is characterized in that the flaw is incident perpendicularly to the flaw detection surface of the flaw detection target. 2. An ultrasonic flaw detection method for an austenitic stainless casting, in which ultrasonic waves are incident on the austenitic stainless casting using a probe to detect internal defects (3). The defect is evaluated based on the distance-amplitude characteristic curve diagram obtained from the received waveform of this reflected wave by making it incident perpendicularly to the flaw detection surface of the flaw detection target.
An ultrasonic flaw detection method for austenitic stainless castings, which comprises determining the presence or absence of (3). 3. The ultrasonic flaw detection method for an austenitic stainless casting according to claim 1, wherein the probe has a broadband frequency of at least 0.5 to 0.5.
Ultrasonic flaw detection method for austenitic stainless castings containing 4 MHz. 4. The ultrasonic flaw detection method for an austenitic stainless casting according to claim 1 or 2, wherein the flaw detection limit of the internal defect (3) is at least 60 mm from the flaw detection surface. Ultrasonic flaw detection method for austenitic stainless castings. 5. The ultrasonic flaw detection method for an austenitic stainless casting according to claim 1 or 2, wherein the upper surface (2a) and the bottom surface (2b) of the flaw detection target are parallel to each other, and the internal defect is present. (3) The ultrasonic flaw detection method for austenitic stainless castings, wherein the flaw detection limit distance is at least 120 mm or less. 6. The ultrasonic flaw detection method for an austenitic stainless casting according to claim 2, wherein the presence / absence of the internal defect (3) in the defect evaluation is a sensitivity 46.
In dB, when the size of the internal defect (3) is φ6, the determination is made based on the distance amplitude characteristic curve diagram in which the reception level at a predetermined flaw detection distance is 80%, and the superposition of austenitic stainless castings is characterized. Sonic flaw detection method.