JPH09257761A - Ultrasonic inspection of cast piece - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inspect the distribution of the nonmetal enclosure present in a cast piece from the surface thereof to a specific depth in a depth direction by scanning a probe on the inclined plane having a specific angle of inclination formed by grinding the surface of the case piece. SOLUTION: When the nonmetal enclosure or air bubble present within a case piece 1 is inspected by a vertical ultrasonic flaw detection method using ultrasonic waves of 10MHz or more, a part of the surface 2 of the case piece 1 is ground to form an inclined plane 3 having a definite angle θ of inclination with respect to the surface 2. A probe is scanned on the inclined plane 3 to perform ultrasonic flaw detection. The angle θ of inclination is appropriately selected within a range of 0.03-0.2 radian (about 1.7-11.5 deg.) corresponding to the purpose of inspection. By this method, a flaw present within the region from the surface of the cast piece 1 to a depth of about 20mm can be inspected by using one inspection surface and inspection labor is reduced and a required time is shortened. By forming an image showing whether a flaw at each measuring point is detected, the distribution of the flaw in a depth direction can be displayed obviously.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slab ultrasonic inspection method for inspecting non-metallic inclusions or bubbles present inside a steel slab, particularly a continuous cast slab.

[0002]

2. Description of the Related Art When rolling slabs cast by continuous casting or other methods to produce steel products, defects such as non-metallic inclusions and bubbles existing near the surface of the slabs are the cause of surface defects. Become. In particular, surface defects of thin plate products often occur due to nonmetallic inclusions existing within a depth of 20 mm from the surface layer of the continuous cast slab, and the distribution of nonmetallic inclusions near the surface layer can be rapidly inspected. A method is needed.

In recent years, ultrasonic flaw detection technology has advanced, and it has become possible to detect minute inclusions of about 10 μ by using high frequency ultrasonic waves, but high frequency ultrasonic waves have large attenuation, A certain depth from the surface (for example 0.5
It is possible to inspect only up to the range of ~ 5mm).

Therefore, in order to inspect non-metallic inclusions existing at a deeper position than this, a slab is cut to form, for example, a cross section perpendicular to the surface, and ultrasonic waves are incident from this vertical cross section to make a non-inclusion. It is necessary to inspect metal inclusions. However, in this case, the surface of the slab becomes the side surface of the material to be inspected, and in the range up to about 3 mm from the surface, the influence of scattering echo from the side surface (the surface of the slab) is large during ultrasonic flaw detection, and accurate flaw detection is performed. There is a problem that you cannot do it.

For this reason, there is no conventional ultrasonic flaw detection method capable of inspecting all non-metallic inclusions existing at a depth of up to about 20 mm from the surface of the slab by a single measurement. Is.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides a simple method for inspecting minute non-metallic inclusions or bubbles present near the surface of a slab by a vertical ultrasonic flaw detection method using high frequency ultrasonic waves. For the purpose of providing a method, in particular, by scanning the probe on one inspection surface and ultrasonic flaw detection,
It is an object of the present invention to provide an ultrasonic inspection method capable of inspecting the distribution in the depth direction of nonmetallic inclusions or bubbles existing up to a depth of about 20 mm from the surface of a slab.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and its gist is the inside of a slab by a vertical ultrasonic flaw detection method using ultrasonic waves having a frequency of 10 MHz or more. When inspecting non-metallic inclusions or air bubbles present in the slab, the surface of the slab is ground to form an inclined plane having an inclination angle of 0.03 to 0.2 radian with respect to the surface of the slab, and the inclination is It is an ultrasonic inspection method for a cast product, characterized by performing ultrasonic flaw detection by scanning a probe on a flat surface.

[0008]

FIG. 1 is an explanatory view showing an example of the shape of an inspection surface for ultrasonic flaw detection according to the present invention.
Is partially ground to form an inclined flat surface 3 having a constant inclination angle θ with respect to the surface 2, and this is used as an inspection surface for vertical ultrasonic flaw detection.

Whether defects such as non-metallic inclusions inside the slab cause surface defects in the rolled product depends on the depth of the defective portion from the surface, and generally the depth from the surface is about 5 mm. Although the influence of defects within the range is the largest, depending on the case, a defect having a depth of about 20 mm from the surface may be a problem.

Therefore, the depth h from the surface of the tip of the inspection surface in FIG. 1 is set to about 5 to 20 mm depending on the purpose of the inspection. The length 1 of the inclined plane is determined in consideration of the scanning pitch of ultrasonic flaw detection and the time required for flaw detection.
Usually, it is suitable to set the thickness to about 50 to 200 mm. The inclination angle θ is appropriately selected within the range of 0.03 to 0.2 radian (angle is about 1.7 ° to 11.5 °) according to the purpose of inspection.

The reason why the inclination angle θ of the inclined plane (inspection surface) with respect to the surface of the slab is limited to the above range is that when θ is 0.2 radian or more, the inspectable range for a certain depth becomes too narrow. This is because if θ is 0.03 radians or less, the inspection surface is too wide, and the time required to scan the probe becomes too long, which is not suitable for the purpose of the ultrasonic inspection method of the present invention. .

Generally, in the ultrasonic inspection method using a high frequency of 10 MHz or more, the depth from the surface where defects can be detected is up to about 5 mm due to the attenuation of ultrasonic waves. Therefore, when it is attempted to inspect a depth of about 20 mm from the surface by the conventional ultrasonic inspection method, it is necessary to grind several steps from the surface over several steps and perform ultrasonic flaw detection on each surface. I had a lot of time. On the other hand, when the method of the present invention is used, defects up to a depth of about 20 mm from the surface can be inspected with one inspection surface, which reduces inspection time and drastically reduces the required time.

Further, as shown in the following embodiment, the ultrasonic probe is scanned on the inclined plane to perform ultrasonic flaw detection at predetermined time intervals, and whether or not a defect is detected at each measurement point. By imaging, the distribution in the depth direction of defects such as non-metallic inclusions can be displayed at a glance. Particularly in continuous cast slabs, an accumulated layer of non-metallic inclusions is often formed at a certain depth from the surface layer. The density can be easily determined.

Further, since the defect reflected wave signal at each measurement point on the inclined plane contains information on the depth of the defect,
By processing this signal with a computer,
The density distribution of defects in the depth direction of the slab can be calculated. In this case, the inspection method of the present invention is characterized in that the range in the depth direction that can be inspected by one inspection surface is significantly wider than that of the conventional ultrasonic flaw detection method.

[0015]

EXAMPLE An ultrasonic inspection method according to the present invention was carried out using a measuring device in which an ultrasonic flaw detector and an image processing device were combined. FIG. 2 is a diagram showing the configuration of the measuring apparatus in this embodiment.

As shown in FIG. 2, the material to be inspected 4 is immersed and left in the water tank 5 with the inclined plane 3 being horizontal, and the ultrasonic probe 6
Are scanned in the XY directions on the inclined plane 3 and pulsed ultrasonic waves are transmitted from the probe 6 at each lattice point to perform flaw detection. The signal wave reflected from the surface of the material to be inspected and the interface between the defective parts (non-metallic inclusions, etc.) and received by the probe 6 is amplified by the ultrasonic flaw detector 7, processed by the microcomputer 8 and stored in the memory. It is recorded in a copy and displayed in a predetermined format on the image display device 9.

The material to be inspected was a continuously cast slab of low carbon aluminum killed steel for producing thin plates, which was sampled from the surface layer portion of the L surface (the inner surface of the curve of the curved continuous casting machine) of the slab at the continuous seam.

FIG. 3 is a diagram showing the shape of the ground surface of the material to be inspected and the inspection result in this embodiment. As shown in FIG. 3, a material of 50 × 50 mm including the surface layer of the slab is inspected from the surface. Grinding was performed to form an inclined plane having an inclination angle θ of 0.11 radian (6.3 °). The material to be inspected was immersed in water with the inclined plane being horizontal and allowed to stand still, and the inclined plane was used as an inspection surface, and the probe was scanned on this to perform ultrasonic flaw detection on the entire inspection surface. The conditions of ultrasonic flaw detection are as follows.

Ultrasonic frequency: 75 MHz Depth flaw detection range: 0.5 to 1.5 mm below the surface Scanning pitch: 50 μm Ultrasonic flaw detection is performed at each scanning point, and the reflected signal wave is analyzed by a computer to detect the flaw detection range. FIG. 3 shows a result in which it is determined whether or not there is a defect and the defective portion is displayed as a black dot by image processing. As can be seen in the figure, many defects such as non-metallic inclusions are present at depths of 2 to 3 mm and 4 to 5 mm from the surface of the cast slab.

As described above, it is one of the effects of the present invention that the position where the defects such as non-metal inclusions are accumulated and the density of the accumulation can be displayed at a glance so that they can be judged at a glance. In the present embodiment, the test was conducted only up to a depth of about 5 mm from the surface of the slab, but it is needless to say that the test can be conducted to a deeper range by further increasing the length or the tilt angle of the inclined plane. Nor.

[0021]

According to the present invention, it becomes possible to easily and quickly inspect the distribution in the depth direction of defects such as non-metallic inclusions existing up to about 20 mm from the surface of the cast slab. As a result, it becomes easier to predict the rate of occurrence of flaws during rolling at the stage of slab, and it becomes possible to determine whether maintenance of the slab is necessary and to specify the purpose or direction of the slab at an early stage.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of the shape of an inspection surface for ultrasonic flaw detection according to the present invention.

FIG. 2 is a diagram showing a configuration of a measuring device according to the present embodiment.

FIG. 3 is a diagram showing a shape of a ground surface of a material to be inspected and an inspection result in this example.

[Explanation of symbols]

 1 cast piece 2 surface 3 inclined plane 4 material to be inspected 5 water tank 6 probe 7 ultrasonic flaw detector 8 microcomputer 9 image display device h depth from the surface of the tip of the inspection surface 1 length of inclined plane θ inclination angle

Claims (1)

[Claims] 1. When inspecting for non-metallic inclusions or bubbles present inside a slab by a vertical ultrasonic flaw detection method using ultrasonic waves with a frequency of 10 MHz or more, the surface of the slab is ground by grinding the surface of the slab. The ultrasonic inspection of the slab is characterized in that an inclined plane having an inclination angle of 0.03 to 0.2 radians is formed with respect to, and ultrasonic flaw detection is performed by scanning the probe on the inclined plane. Method.