JPH08211028A - Ultrasonic flaw detecting method and apparatus - Google Patents

Abstract

PURPOSE: To discriminate the nugget part and corona bond part of a welding member from the outside. CONSTITUTION: A dummy welding member is scanned using an ultrasonic probe 1 having an aperture angle equal to or more than the critical angle of a vertical wave and the ratio or difference of the propagation times of horizontal and vertical waves at every scanning position is calculated. Next, the dummy welding member is cut and the area and position of the nugget part of the welding member are confirmed by using a microscope and a reference value is calculated on the basis of the confirmed result and the ratio or difference of the propagation times to be stored in a memory 8. Next, the welding member 3 is scanned and the ratio or difference of the propagation times of horizontal and vertical waves is calculated at every scanning position to be collated with the reference value stored in the memory 8 to discriminate whether the present scanning point is a nugget part A or a corona bond part B. Since inspection is performed noticing that the propagation times of the horizontal and vertical waves are different between the nugget part A and the corona bond part B, both parts A, B can be accurately and simply judged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flaw detection method and apparatus for detecting the welding state of steel sheets and the like.

[0002]

2. Description of the Related Art When a plurality of steel plates are joined by so-called resistance welding such as spot welding or seam welding, as shown in FIG. 4, a nugget portion A where the steel plates 3 are completely welded,
Corona bond portion B where the steel sheets are in close contact with each other but not completely welded and unjoined portion C where the steel sheets are not joined
And occur. Since the corona bond portion B is not completely welded, it is desirable that the nugget portion A and the corona bond portion B be clearly distinguishable from the outside of the steel sheet 3.

As a method for identifying the nugget portion A and the corona bond portion B, for example, the welded steel plate 3 is cut and its cross section is observed with a microscope, and the nugget portion A and the corona bond portion B are identified by the shape of the cross section. There are possible ways to do this.
Alternatively, the welding state can be determined to some extent by irradiating the steel sheet 3 with ultrasonic waves and detecting the reflection echo from the bottom surface of the steel sheet or the welded portion.

Therefore, conventionally, a dummy welding member having a welding portion inside is prepared, and the dummy welding member is irradiated with ultrasonic waves from an ultrasonic probe of a non-focusing type and reflected from the bottom surface of the dummy welding member. While detecting the echo, the dummy welding member was cut and the range of the nugget portion A (hereinafter referred to as the nugget area) was detected by a microscope, and the calibration curve shown in FIG. 5 was created in advance from the relationship between the two. Then, the nugget area inside the welding member is estimated by collating this calibration curve with the result of detecting the reflected echo level by irradiating the welding member to be inspected with ultrasonic waves. In addition, the conventional apparatus mainly uses the unfocused ultrasonic probe,
This is because a wide range of welded members can be inspected at the same time.

[0005]

On the other hand, when an ultrasonic flaw detection test is performed using an ultrasonic probe, it can be relatively accurately and easily determined whether or not the unbonded portion C is present, whereas the nugget portion is There is a problem in that it cannot be accurately determined whether it is A or the corona bond portion B. This is because the corona bond portion B has the steel plates 3 closely attached to each other, so that the ultrasonic waves are transmitted to the same extent as the nugget portion A, and the nugget portion A and the corona bond portion B are accurately detected only by detecting the level of the reflection echo. This is because the identification accuracy cannot be improved. Therefore, even if a calibration curve as shown in FIG. 5 is created in advance, the identification accuracy does not increase so much.

Further, when welding is performed, the surface of the welding member becomes uneven or inclined, so that the signal level of the reflected echo and the time until the reflected echo is received may vary. It is difficult to distinguish between the corona bond part B and the corona bond part B.

An object of the present invention is to provide an ultrasonic flaw detection method and apparatus capable of accurately and easily discriminating a nugget portion and a corona bond portion from the outside of the welding member without cutting the welding member. is there.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to FIG. 1 showing an embodiment.
Focused ultrasonic waves are radiated from the welding member 3 toward the welding member 3, the reflected ultrasonic waves from the welding member 3 are received by the ultrasonic probe 1, and the ultrasonic flaw detection detects the welding state inside the welding member 3 by this received signal. Applied to the method, the ultrasonic wave propagating in the transverse direction inside the welding member 3 is reflected by the bottom surface of the welding member 3 and is received by the ultrasonic probe 1, and the ultrasonic wave propagates in the longitudinal direction inside the welding member 3. A completely welded nugget portion existing inside the welding member 3 based on the ratio of the time it takes for the propagating ultrasonic waves to be reflected by the bottom surface of the welding member 3 and received by the ultrasonic probe 1. The above object is achieved by discriminating the corona bond portion B which is in close contact with A but is not completely welded. The invention according to claim 2 provides an ultrasonic probe 1
Focused ultrasonic waves are radiated from the welding member 3 toward the welding member 3, the reflected ultrasonic waves from the welding member 3 are received by the ultrasonic probe 1, and the ultrasonic flaw detection detects the welding state inside the welding member 3 by this received signal. Applied to the method, the ultrasonic wave propagating in the transverse direction inside the welding member 3 is reflected by the bottom surface of the welding member 3 and is received by the ultrasonic probe 1, and the ultrasonic wave propagates in the longitudinal direction inside the welding member 3. A completely welded nugget portion existing inside the welding member 3 based on the difference between the propagation time of the propagating ultrasonic wave being reflected by the bottom surface of the welding member 3 and being received by the ultrasonic probe 1. The above object is achieved by discriminating the corona bond portion B which is in close contact with A but is not completely welded. The invention according to claim 3 is the ultrasonic flaw detection method according to claim 1 or 2, wherein the opening angle of the ultrasonic probe 1 is an angle equal to or greater than a critical angle of a longitudinal wave propagating inside the welding member 3. To be set to. The invention according to claim 4 is provided with an ultrasonic probe 1 that emits focused ultrasonic waves to the welding member 3 and receives reflected ultrasonic waves from the welding member 3. It is applied to an ultrasonic flaw detector that detects the welding state inside the welding member 3 based on the received reflected ultrasonic waves, and ultrasonic waves propagating as transverse waves inside the dummy welding member are reflected by the bottom surface of the dummy welding member and The propagation time until the ultrasonic probe 1 receives the ultrasonic wave and the ultrasonic waves propagating in the dummy welding member as longitudinal waves until the ultrasonic wave is reflected by the bottom surface of the dummy welding member and received by the ultrasonic probe 1. A reference value for discriminating between a completely welded nugget portion A existing inside the dummy welding member and a corona bond portion B which is in close contact but not completely welded, based on the ratio to the propagation time. Storage means 8 for storing in advance, and a welding part 3 the ultrasonic wave propagating in the transverse wave inside the welding member 3 until it is reflected by the bottom surface of the welding member 3 and received by the ultrasonic probe 1, and the ultrasonic wave propagating in the longitudinal direction inside the welding member 3 is the welding member. The ratio of the propagation time until the ultrasonic wave is reflected by the bottom surface of the ultrasonic probe 3 and received by the ultrasonic probe 1, and the nugget inside the welding member 3 is calculated based on this ratio and the reference value stored in the storage means 8. The above object is achieved by providing the identification means 7 for identifying the part A and the corona bond part B. According to a fifth aspect of the present invention, in the ultrasonic flaw detection apparatus according to the fourth aspect, the ultrasonic flaw detection device includes a scanning control unit that scans the ultrasonic probe 1 in at least one direction of the welding member 3 by a predetermined amount at a time. The opening angle of the probe 1 is set to an angle equal to or more than the critical angle of the longitudinal wave propagating inside the welding member 3, the ratio is obtained for each scanning position of the ultrasonic probe 1, and the nugget part A is obtained for each scanning position. The identifying means 7 is configured to identify the corona bond portion B and the corona bond portion B. The invention according to claim 6 is provided with an ultrasonic probe 1 that emits focused ultrasonic waves to the welding member 3 and receives reflected ultrasonic waves from the welding member 3. It is applied to an ultrasonic flaw detector that detects the welding state inside the welding member 3 based on the received reflected ultrasonic waves, and ultrasonic waves propagating as transverse waves inside the dummy welding member are reflected by the bottom surface of the dummy welding member and The propagation time until the ultrasonic probe 1 receives the ultrasonic wave and the ultrasonic waves propagating in the dummy welding member as longitudinal waves until the ultrasonic wave is reflected by the bottom surface of the dummy welding member and received by the ultrasonic probe 1. A reference value for discriminating between the completely welded nugget portion A existing inside the dummy welding member and the corona bond portion B which is in close contact but not completely welded, based on the difference from the propagation time. Storage means 8 for storing in advance, and a welding part 3 the ultrasonic wave propagating in the transverse wave inside the welding member 3 until it is reflected by the bottom surface of the welding member 3 and received by the ultrasonic probe 1, and the ultrasonic wave propagating in the longitudinal direction inside the welding member 3 is the welding member. The difference between the propagation time until the ultrasonic wave is reflected by the bottom surface of the ultrasonic probe 3 and received by the ultrasonic probe 1, and based on this difference and the reference value stored in the storage unit 8, the nugget inside the welding member 3 is obtained. The above object is achieved by providing the identification means 7 for identifying the part A and the corona bond part B. The invention according to claim 7 is the invention according to claim 6.
In the ultrasonic flaw detector described in 1 above, the ultrasonic probe 1
Is provided with scanning control means for scanning the welding member 3 in at least one direction by a predetermined amount, and the opening angle of the ultrasonic probe 1 is set to an angle equal to or greater than a critical angle of a longitudinal wave propagating inside the welding member 3. The discriminating means 7 is configured to obtain the difference for each scanning position of the acoustic probe 1 and discriminate between the nugget portion A and the corona bond portion B for each scanning position.

[0009]

In the invention described in claim 1, attention is paid to the fact that the structure of the nugget portion A inside the welding member 3 is enlarged as compared with the structure of the corona bond portion B, and the transverse wave is caused by the difference in the size of the structure. In consideration of the difference in the propagation time of the longitudinal wave and the propagation time of the longitudinal wave, the nugget part A and the corona bond part B are identified by the ratio of the propagation time of the transverse wave and the propagation time of the longitudinal wave. In the invention described in claim 2, attention is paid to the fact that the structure of the nugget part A inside the welding member 3 is enlarged compared to the structure of the corona bond part B, and the transverse wave and the longitudinal wave are different due to the difference in the size of the structure. The nugget portion A and the corona bond portion B are identified by the difference between the propagation time of the transverse wave and the propagation time of the longitudinal wave in consideration of the difference in the propagation time of the wave. In the invention according to claim 3, the opening angle of the ultrasonic probe 1 is set to an angle equal to or more than the critical angle of the longitudinal wave propagating inside the welding member 3, so that the ultrasonic wave from the entire range within the critical angle of the longitudinal wave is increased. Ultrasonic waves are incident on the welding member 3. As a result, the transverse wave and the longitudinal wave are generated most efficiently inside the welding member 3. In the invention according to claim 4, before inspecting the welding member 3 to be inspected, a dummy welding member is used to obtain the ratio of the transverse wave propagation time and the longitudinal wave propagation time, and based on this ratio Nugget part A and corona bond part B
A reference value for discriminating between and is stored in the storage means 8. Next, the ratio of the propagation time of the transverse wave to the propagation time of the longitudinal wave is obtained using the welding member 3 to be inspected, and the nugget portion A is calculated based on this ratio and the reference value stored in the storage means 8.
And corona bond part B are identified. In the invention according to claim 5, the ultrasonic probe 1 scans the welding member 3 by a predetermined amount, obtains the ratio of the propagation time of the transverse wave and the propagation time of the longitudinal wave at each scanning position, and obtains each scanning position. Nugget part A for each
And corona bond part B are identified. In the invention according to claim 6, before inspecting the welding member 3 to be inspected, the difference between the propagation time of the transverse wave and the propagation time of the longitudinal wave is obtained using the dummy welding member, and based on this difference A reference value for identifying the nugget portion A and the corona bond portion B is stored in the storage means 8. Next, the difference between the propagation time of the transverse wave and the propagation time of the longitudinal wave is obtained using the welding member 3 to be inspected, and based on this difference and the reference value stored in the storage means 8, the nugget portion A and the corona The bond portion B is identified. In the invention according to claim 7, the welding member 3 is scanned by the ultrasonic probe 1 by a predetermined amount, the difference between the propagation time of the transverse wave and the propagation time of the longitudinal wave is obtained for each scanning position, and each scanning position is obtained. Then, the nugget portion A and the corona bond portion B are identified.

Incidentally, in the section of means and action for solving the above problems for explaining the constitution of the present invention, the drawings of the embodiments are used for the purpose of making the present invention easy to understand. It is not limited to.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the ultrasonic flaw detector according to the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram showing an embodiment of an ultrasonic flaw detector according to the present invention. In this figure, reference numeral 1 denotes an ultrasonic probe, which irradiates the welding member 3 with ultrasonic waves which are excited by a pulsed voltage output from the transmitter 2 and are focused at a predetermined focal position, The ultrasonic echo reflected at 3 is received and converted into an electric signal. In this embodiment, the focus focusing type ultrasonic probe 1 is used in order to improve the lateral resolution. An acoustic lens 1a is provided at the tip of the ultrasonic probe 1, and the opening angle of the ultrasonic probe 1 is determined by the shape of the acoustic lens 1a.

Reference numeral 4 is a scanning control device for moving the ultrasonic probe 1 in the three directions of X, Y and Z axes, 5 is an amplifier for amplifying the electric signal converted by the ultrasonic probe 1, and 6 is an amplifier. It is a peak detector that detects the peak value of the received signal amplified by the amplifier 5. Reference numeral 7 is a control circuit for controlling the entire ultrasonic flaw detection apparatus, 8 is a memory for storing processing results by the control circuit 7, and 9 is a display device for displaying the ultrasonic flaw detection result.

Next, the setting of the opening angle of the ultrasonic probe 1 will be described. The ultrasonic waves that have entered the welding member 3 are generally propagated while being divided into longitudinal waves and transverse waves, but the ratio of generation of longitudinal waves and transverse waves differs depending on the incident angle of the ultrasonic waves. For example,
Ultrasonic waves incident from an angle larger than the critical angle of the longitudinal wave are totally reflected without traveling inside the welding member 3, and conversely, ultrasonic waves incident from an angle within the critical angle are welded without being reflected. It proceeds on the surface or inside of the member 3. Therefore, as shown in FIG. 2, when the opening angle of the ultrasonic probe 1 is equal to or greater than the critical angle of the longitudinal wave, ultrasonic waves from all ranges within the critical angle of the longitudinal wave are incident on the welding member 3. Therefore, the longitudinal wave and the transverse wave can be generated most efficiently. Therefore, in this embodiment, the opening angle of the ultrasonic probe 1 is set to an angle equal to or greater than the critical angle of the longitudinal wave propagating in the welding member 3.

In FIG. 2, the longitudinal wave propagating inside the welding member 3 is shown by a solid line and the transverse wave is shown by a one-dot chain line. As shown, the transverse wave has a slower propagation speed than the longitudinal wave, and therefore the transverse wave has a longer focal length than the longitudinal wave. .

Next, an outline of the welding state inspection method in this embodiment will be described. As a result of observing the welded part inside the welded member 3 with a microscope, the applicant has found that the structure of the nugget part A is coarse as shown in FIG.
It was found that the structure of the corona bond part B was densified as shown in FIG. Longitudinal waves are compressional waves that oscillate parallel to the direction of travel of ultrasonic waves, so they are unlikely to be affected by the size of tissue, and transverse waves oscillate in a direction perpendicular to the direction of travel of ultrasonic waves. It is considered to be easily affected. Therefore, in this embodiment, the nugget portion A and the corona bond portion B are identified by utilizing this property. Specifically, the nugget portion A and the corona bond portion B are distinguished from each other by the value of the ratio or the difference between the propagation times of the transverse and longitudinal waves of the ultrasonic wave propagating inside the welding member 3.

The operation of this embodiment will be described below with reference to FIG. The operation of the present embodiment is divided into two processes: a pre-process performed before the ultrasonic flaw inspection of the welding member 3 and an ultrasonic flaw inspection process performed thereafter.

First, the preprocessing will be described. A state in which a dummy welding member formed by welding two types of steel plates is submerged in a medium such as water, the ultrasonic probe 1 is placed above it, and the tip of the ultrasonic probe 1 is immersed in the medium. Then, the dummy welding member is irradiated with ultrasonic waves. Part of the ultrasonic waves emitted from the ultrasonic probe 1 is reflected by the dummy welding member and received by the ultrasonic probe 1. Hereinafter, this received signal is referred to as a surface echo. On the other hand, the other part of the ultrasonic waves radiated from the ultrasonic probe 1 is refracted on the surface of the dummy welding member, divided into longitudinal waves and transverse waves, and propagates inside the welding member. Both the longitudinal wave and the transverse wave are reflected by the bottom surface of the dummy welding member, and the reflected echoes are received by the ultrasonic probe 1. Hereinafter, this received signal is referred to as a bottom surface echo. If there is an unbonded portion C inside the dummy welding member, this portion is also reflected.

The bottom echoes of the longitudinal and transverse waves reflected by the bottom surface of the dummy welding member propagate at different velocities,
It is received by the ultrasonic probe 1 at different times. Therefore, the control circuit 7 of FIG. 1 discriminates whether the longitudinal wave or the transverse wave is received depending on the difference in the reception time of each bottom echo. Specifically, after the surface echo is detected, the bottom echo received first is determined to be a longitudinal wave, and the bottom echo received next is determined to be a transverse wave.

When the longitudinal and transverse wave bottom echoes are received, the control circuit 7 then determines the time difference between each bottom echo and the surface echo. Hereinafter, this time difference is referred to as a propagation time.
Then, after obtaining the ratio or difference between the propagation times of the longitudinal wave and the transverse wave, the scanning controller 4 is controlled to move the ultrasonic probe 1 in a predetermined direction by a predetermined amount. Then, the ratio or difference of the propagation times of the longitudinal wave and the transverse wave is obtained again. After that, the same processing is repeated.

When the scanning of the dummy welding member is completed, the dummy welding member used for the pretreatment is cut, and the area and position of the nugget portion A are confirmed by using a microscope (not shown). The reference value indicating the relationship between the ratio or difference between the longitudinal wave and the transverse wave and the nugget area is obtained by comparing the calculated result of the ratio or difference. The reference value thus obtained is stored in the memory 8 of FIG.

Next, the ultrasonic flaw detection inspection process will be described. The welding member 3 to be inspected is immersed in the medium similarly to the dummy welding member, and the ultrasonic probe 1 is placed above the welding member 3 to emit ultrasonic waves toward the welding member 3. The ultrasonic waves incident on the welding member 3 are divided into transverse waves and longitudinal waves and propagate like the dummy welding member, and are reflected by the bottom surface of the welding member 3.

The control circuit 7 receives the surface echo and the bottom echoes of the transverse wave and the longitudinal wave, and calculates the ratio or difference between the propagation time of the transverse wave and the propagation time of the longitudinal wave. Then, by comparing with the reference value stored in the memory 8, it is identified whether the point currently scanned by the ultrasonic probe 1 is the nugget portion A or the corona bond portion B. For example, if (transverse wave propagation time) / (longitudinal wave propagation time) is less than the reference value, it is determined as the nugget portion A, and (transverse wave propagation time) / (longitudinal wave propagation time) is greater than or equal to the reference value. For example, it is determined to be the corona bond part B.

As described above, according to this embodiment, attention is paid to the difference in the size of the structure between the nugget part A and the corona bond part B formed during welding, and the difference in the size of the structure Considering that there is a difference in the propagation time of the transverse wave and the longitudinal wave of the ultrasonic wave, it is determined whether the nugget portion A or the corona bond portion B is determined by the value of the ratio or the difference of the propagation time of the transverse wave and the longitudinal wave. The state can be detected accurately and easily. Further, in the present embodiment, since the ratio or the difference between the propagation times of the transverse wave and the longitudinal wave is calculated, even if the welding member 3 is made uneven by welding, it is not affected. That is, by taking the ratio or difference of the propagation times, it is possible to cancel the influence of unevenness. Further, in this embodiment, the scanning control device 4 scans the surface of the welding member by a predetermined amount, and the nugget portion A and the corona bond portion B are identified for each scanning position. The boundary position between A and the corona bond portion B can be accurately detected.

In the above embodiment, the nugget portion A and the corona bond portion B are distinguished from each other by the ratio or difference in the propagation time of the transverse wave and the longitudinal wave. Even if there is a difference, there is almost no difference in propagation time. Therefore, the nugget portion A and the corona bond portion B may be identified only by the propagation time of the transverse wave. However, in this case, if unevenness occurs in the welding member due to welding, the accuracy may deteriorate due to the influence. Further, in the above embodiment, it is not necessary to obtain both the ratio and the difference in the propagation time of the transverse wave and the longitudinal wave, and only one of them needs to be obtained.

In the embodiment thus constructed, the memory 8 corresponds to the storage means and the control circuit 7 corresponds to the identification means.

[0026]

As described in detail above, according to the present invention, it is noted that the structure of the nugget portion inside the welded member is enlarged compared to the structure of the corona bond portion, and the size of the structure is also increased. Considering that there is a difference in the propagation time of transverse wave and longitudinal wave due to the difference in the wave length, the nugget part and the corona bond part are identified by the ratio of the propagation time of transverse wave and the propagation time of longitudinal wave. Good and easy to detect. According to the invention of claim 2, the nugget portion and the corona bond portion are distinguished from each other by the difference between the propagation time of the transverse wave and the propagation time of the longitudinal wave. It can be done easily. According to the invention as set forth in claim 3, since the opening angle of the ultrasonic probe is set to an angle equal to or greater than the critical angle of the longitudinal wave propagating inside the welding member, the ultrasonic waves from the entire range within the critical angle of the longitudinal wave. Can be incident on the welding member, and transverse and longitudinal waves can be efficiently generated. According to the invention described in claim 4, the ratio of the propagation times of the longitudinal wave and the transverse wave is obtained using the dummy welding member, and the reference value for distinguishing the nugget part and the corona bond part is used in advance by using this ratio. Since the information is stored, the nugget portion and the corona bond portion inside the welding member to be inspected can be easily identified by using this reference value. According to the invention described in claims 5 and 7, the welding member is scanned by a predetermined amount,
Since the nugget portion and the nugget portion are identified for each scanning position, the boundary position between the nugget portion and the corona bond portion inside the welding member can be accurately detected. Claim 6
According to the invention described in (1), the difference between the propagation times of the longitudinal wave and the transverse wave is obtained using the dummy welding member, and the reference value for identifying the nugget part and the corona bond part is stored in advance using this difference. Therefore, by using this reference value, the nugget portion and the corona bond portion inside the welding member to be inspected can be easily identified.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of an ultrasonic flaw detector according to the present invention.

FIG. 2 is a diagram showing a transverse wave and a longitudinal wave propagating inside a welding member.

FIG. 3 is a diagram showing a state of a structure of a nugget portion and a corona bond portion.

FIG. 4 is a view showing a nugget portion, a corona bond portion, and an unbonded portion formed inside a steel plate.

FIG. 5 is a diagram showing a calibration curve showing a relationship between a nugget area and a reflected echo level.

[Explanation of symbols]

 1 Ultrasonic probe 2 Transmitter 3 Welding member 4 Scanning control device 5 Amplifier 6 Peak detector 7 Control circuit 8 Memory 9 Display device

Claims (7)

[Claims] 1. A focused ultrasonic wave is radiated from an ultrasonic probe toward a welding member, reflected ultrasonic waves from the welding member are received by the ultrasonic probe, and the received signal causes the inside of the welding member to be received. In the ultrasonic flaw detection method for detecting the welding state of, the propagation time until ultrasonic waves propagating in transverse waves inside the welding member are reflected by the bottom surface of the welding member and received by the ultrasonic probe, and Ultrasonic waves propagating in the welding member as longitudinal waves are reflected by the bottom surface of the welding member and are based on the ratio of the propagation time until received by the ultrasonic probe. An ultrasonic flaw detection method, characterized in that it is distinguished from a corona bond portion that is in close contact with the nugget portion that is welded to, but is not completely welded. 2. A focused ultrasonic wave is emitted from an ultrasonic probe toward a welding member, reflected ultrasonic waves from the welding member are received by the ultrasonic probe, and the received signal causes the inside of the welding member to be received. In the ultrasonic flaw detection method for detecting the welding state of, the propagation time until ultrasonic waves propagating in transverse waves inside the welding member are reflected by the bottom surface of the welding member and received by the ultrasonic probe, and Ultrasonic waves propagating in the welding member as longitudinal waves are reflected by the bottom surface of the welding member and are based on the difference from the propagation time until they are received by the ultrasonic probe. An ultrasonic flaw detection method, characterized in that it is distinguished from a corona bond portion that is in close contact with the nugget portion that is welded to, but is not completely welded. 3. The ultrasonic flaw detection method according to claim 1, wherein an opening angle of the ultrasonic probe is set to an angle equal to or greater than a critical angle of the longitudinal wave propagating inside the welding member. An ultrasonic flaw detection method characterized by the following. 4. An ultrasonic probe that emits focused ultrasonic waves to a welding member and receives reflected ultrasonic waves from the welding member, and the reflected ultrasonic waves received by the ultrasonic probe. In the ultrasonic flaw detector for detecting the welding state inside the welding member based on the above, ultrasonic waves propagating in transverse waves inside the dummy welding member are reflected by the bottom surface of the dummy welding member and received by the ultrasonic probe. The ratio of the propagation time until the ultrasonic wave propagating as a longitudinal wave inside the dummy welding member is reflected by the bottom surface of the dummy welding member and is received by the ultrasonic probe. Storage means for storing in advance a reference value for discriminating between a completely welded nugget portion existing inside the dummy welding member and a corona bond portion which is not completely welded, based on And before The ultrasonic wave propagating in the transverse direction inside the welding member is propagated until the ultrasonic wave is reflected by the bottom surface of the welding member and received by the ultrasonic probe, and the ultrasonic wave propagating in the longitudinal direction inside the welding member is the ultrasonic wave. The inside of the welding member is obtained based on the ratio of the propagation time until the ultrasonic wave is reflected by the bottom surface of the welding member and is received by the ultrasonic probe, and the reference value stored in the storage means. 2. An ultrasonic flaw detector, comprising: an identification unit that identifies the nugget portion and the corona bond portion. 5. The ultrasonic flaw detection apparatus according to claim 4, further comprising a scanning control unit that scans the ultrasonic probe in a predetermined amount in at least one direction of the welding member, the ultrasonic probe. The opening angle of is set to an angle equal to or greater than the critical angle of the longitudinal wave propagating inside the welding member, the identifying means obtains the ratio for each scanning position of the ultrasonic probe, and for each scanning position. An ultrasonic flaw detector, wherein the nugget portion and the corona bond portion are distinguished from each other. 6. A reflected ultrasonic wave received by the ultrasonic probe, comprising an ultrasonic probe that emits focused ultrasonic waves to the welding member and receives reflected ultrasonic waves from the welding member. In the ultrasonic flaw detector for detecting the welding state inside the welding member based on the above, ultrasonic waves propagating in transverse waves inside the dummy welding member are reflected by the bottom surface of the dummy welding member and received by the ultrasonic probe. The difference between the propagation time and the propagation time until ultrasonic waves propagating as longitudinal waves inside the dummy welding member are reflected by the bottom surface of the dummy welding member and received by the ultrasonic probe. Storage means for storing in advance a reference value for discriminating between a completely welded nugget portion existing inside the dummy welding member and a corona bond portion which is not completely welded, based on And before The ultrasonic wave propagating in the transverse direction inside the welding member is propagated until the ultrasonic wave is reflected by the bottom surface of the welding member and received by the ultrasonic probe, and the ultrasonic wave propagating in the longitudinal direction inside the welding member is the ultrasonic wave. Inside the welding member based on this difference and the reference value stored in the storage means, the difference between the propagation time until the ultrasonic wave is reflected by the bottom surface of the welding member and received by the ultrasonic probe. 2. An ultrasonic flaw detector, comprising: an identification unit that identifies the nugget portion and the corona bond portion. 7. The ultrasonic flaw detector according to claim 6, further comprising a scanning control unit that causes the ultrasonic probe to scan a predetermined amount in at least one direction of the welding member, the ultrasonic probe. The opening angle of is set to an angle equal to or greater than the critical angle of the longitudinal wave propagating inside the welding member, the identification means obtains the difference for each scanning position of the ultrasonic probe, for each scanning position An ultrasonic flaw detector, wherein the nugget portion and the corona bond portion are distinguished from each other.