JP2009257896A - Method of evaluating surface flaw of steel material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of evaluating the surface flaw of a steel material capable of quantitatively evaluating the occurrence state of a flaw. <P>SOLUTION: An ultrasonic flaw detecting test, which rotates an ultrasonic flaw detecting probe around the steel material to spirally detect the flaw of at least one region of the cross section of the steel material over the longitudinal direction of the steel material, is performed with respect to at least one steel material to detect the flaw of the steel material. The flaw detected with respect to each steel material is arranged on the mesh in a data map wherein a first axis is set to the direction of rotation of the ultrasonic flaw detecting probe and a second axis is set to the longitudinal direction of the steel material. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for evaluating surface defects of steel materials, and more particularly, to a method for evaluating surface defects of steel materials capable of quantitatively evaluating the occurrence of defects.

  Round steel bar made of special steel is obtained by rolling a steel piece. Usually, multi-stage rolling is performed by a rough row rolling mill, a middle row rolling mill, and a finishing row rolling mill arranged in tandem. By this rolling, the steel slab is gradually reduced in diameter and lengthened to obtain a round bar steel. Depending on the user's request, the round bar steel obtained by rolling is further subjected to heat treatment, peeling processing, etc. to obtain round bar steel (product).

  The round steel bar manufactured in this way may have defects (hereinafter also referred to as wrinkles) on the surface and directly below the surface. Depending on the number of defects, the quality of the round bar steel is impaired. Therefore, it is necessary to inspect the surface defects according to the use of the round bar steel and to ship only high quality round bar steel.

  As a typical inspection method for defects on the surface of a round steel bar and directly under the surface, there is an inspection using a fully automatic ultrasonic flaw detector equipped with a probe for oblique flaw detection (see, for example, Patent Document 1).

  A general fully automatic ultrasonic flaw detector includes a probe for vertical flaw detection and a probe for oblique flaw detection, and a round bar material from the probe for vertical flaw detection and the probe for oblique flaw detection. An internal flaw in the material to be inspected is detected by making an ultrasonic beam enter the inside.

  Here, a defect inspection method using a fully automatic ultrasonic flaw detector will be briefly described. FIG. 1 is a diagram showing the principle of ultrasonic flaw detection by oblique flaw detection. A round bar steel surface gate (hereinafter also referred to as Lo) and a gate directly below the surface (hereinafter also referred to as Li) are inspected by an oblique probe. As shown in FIG. 1A, the ultrasonic wave incident from the surface of the round bar steel is refracted at an angle of 45 degrees, and as shown in FIG. The reflected echo is captured as a defect signal.

  FIG. 2 is a diagram showing the principle of ultrasonic flaw detection by vertical flaw detection. The center part and the middle part of the round bar steel are inspected with a vertical probe. As shown in FIG. 2 (a), the ultrasonic wave is incident as it is without being refracted from the surface of the round steel bar, and as shown in FIG. 2 (b), it is reflected by defects at the gates in the middle and central regions. Echoes are captured as defect signals.

The probe for vertical flaw detection and the probe for oblique flaw detection are set in holders filled with water, and rotate around the round steel bar in the direction A in FIGS. The entire area of the cross section of the round bar steel traveling inside is spirally detected over the entire length of the round bar steel.
JP 2007-271375 A

  FIG. 3 is a diagram illustrating an example of a defect detection result using a fully automatic ultrasonic flaw detector. As shown in FIG. 3 (a) and FIG. 3 (b), the Lo waveform and the Li waveform are inspected over the entire length (6.8 m in the figure) of one round bar steel, and the strength of the reflection and the presence of defects in the round bar steel A reflection intensity distribution is generated according to the position in the axial direction.

  FIG. 3C is a diagram in which when the intensity of the Lo waveform and the Li waveform exceeds a predetermined threshold value, it is determined that there is a defect and an event is set up, and the event is displayed at a position in the axial direction of the round bar steel. It is.

  However, from the chart shown in FIG. 3 (c), only the positional relationship in the longitudinal direction of the defective round steel bar is known. Conventionally, it is an evaluation method for the ratio of the number of round steel bars with one or more events in the same lot (hereinafter referred to as the defect rate), and the number of steel materials in the same lot is wrinkled. Although it was possible to determine whether or not there was any wrinkle per bottle, it was unclear. In addition, the number of wrinkles can be calculated if they do not overlap at one place, but if a plurality of wrinkles are duplicated at the same position in the axial direction of the round steel bar, the number of wrinkles will be reduced. There was a problem.

  Thus, conventionally, the presence / absence of defects in the surface portion (Lo) and directly under the surface (Li) of the steel material was evaluated by the defect number rate. However, even if the defect number rate is equivalent, the defect per steel material In some cases, the number may vary greatly, and an index capable of quantitative evaluation of the defect occurrence status has been desired.

  The present invention has been made to solve such a conventional problem, and is to provide a method for evaluating surface defects of a steel material capable of quantitatively evaluating the state of occurrence of defects.

  According to the method for evaluating surface defects of a steel material according to the present invention, an ultrasonic flaw detection inspection is performed in which a probe for ultrasonic flaw detection is rotated around the steel material and at least one gate region of the cross section of the steel material is spirally detected over the longitudinal direction of the steel material. The detection is performed on at least one steel material, and the detected defect is detected for each steel material, with the first axis as the rotation direction of the ultrasonic flaw detector and the second axis as the longitudinal direction of the steel material. It is arranged on the corresponding mesh in the data map.

  According to the method for evaluating surface defects of a steel material according to the present invention, the detected defects are defined in a data map in which the first axis is the rotation direction of the ultrasonic flaw detector and the second axis is the longitudinal direction of the steel material. By arranging them on the mesh, the position of the ridge and the depth of the ridge can be discriminated.

  Hereinafter, a steel surface defect evaluation method according to an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 4 is a diagram showing a data map used in the steel surface defect evaluation method of the present embodiment.

  The data map of the present embodiment shown in FIG. 4 shows the result of full-automatic ultrasonic flaw detection performed on the same steel material of steel number 1 with the probe for oblique flaw detection under the same conditions as the chart shown in FIG. This is output as map data.

  In the present embodiment, Lo is determined to be in the range of 0 to 5% D from the surface with respect to the diameter D of the round steel bar, and Li is determined to be in the range of 5 to 15% D with respect to the diameter D in the oblique flaw detection method shown in FIG. It is carried out.

  The vertical axis of the data map of the present embodiment shown in FIG. 4 shows the case where a defect is detected by rotating the probe for oblique flaw detection shown in FIG. 1 in the direction A in the drawing around the round steel bar. A detection result when one round of 360 ° is divided into 20 meshes and flaw detection is performed at each position (ie, every 18 °) is shown.

  In addition, the horizontal axis of the data map of this embodiment shown in FIG. 4 is a round bar steel when divided into 10 meshes per 1 m of round bar steel and flaw detection is performed at each position over the entire length of the round bar steel (6.8 m). The detection results in the axial direction are shown.

  For Lo and Li, an event is displayed at a corresponding position on the data map when a predetermined threshold value is exceeded.

  The event display is “1” when the threshold value is exceeded at Lo, “2” when the threshold value is exceeded at Li, and both the Lo and Li thresholds at the same position (same mesh). When the value is exceeded, “3” is displayed. Thereby, the data map of this embodiment is as follows. For each steel material, shallow wrinkles (Lo only), deep wrinkles (Lo + Li), and deep wrinkles that are not exposed on the surface due to pressure bonding during rolling. Only), and the position and depth of the eyelid can be discriminated. It is also possible to evaluate the quality of steel materials by the number of events.

  When FIG. 3C and FIG. 4 are compared, there is no particular problem when there is one wrinkle as in the area A in both figures. In the case where a plurality of wrinkles overlap at the same location as in the B area in both figures, it is displayed as one wrinkle data in FIG. 3 (c), whereas in FIG. The number is displayed correctly.

  In addition, in the case where a plurality of wrinkles are concentrated as in the C region in both figures, it can be seen that there are only long wrinkles in FIG. 3C, but from FIG. I understand. Further, in FIG. 4, since the index “3” exists, it can be seen that there is a deep flaw.

  As described above, with respect to the steel material of steel No. 1, an event occurs in the portion exceeding the threshold with respect to the Lo and Li waveforms, but according to this embodiment, the event occurrence position is 20 mesh in the circumference and long Each direction of steel No. 1 is obtained by obtaining an evaluation index as an area ratio where an event stands (hereinafter referred to as a defective area ratio) by acquiring a direction in a data map that is a development map of 10 mesh / m. It is possible to grasp the amount of soot generated quantitatively. In FIG. 4, the defective area rate is 2.72% (= 37 pieces / (20 mesh * 10 mesh / m * 6.8 m)), and the defective area rate particularly for deep wrinkles from the surface is 0.07% (= 1 mesh / (10 mesh / m * 6.8 m)).

  FIG. 5 is a diagram showing a result of conventional evaluation of a steel material of steel number 2 different from steel number 1 by detecting a defect using a fully automatic ultrasonic flaw detector. FIG. 6 is a diagram in which the data map of the present embodiment is created for the steel material of steel No. 2. As can be seen from FIG. 3 and FIG. 5, the steel material of steel No. 2 has more wrinkles than the steel material of steel No. 1.

  Table 1 is a table showing the result of evaluating the occurrence of defects from the detection results of a total of 130 steel materials of each steel number including the steel materials of FIGS. 3 and 5 using a conventional evaluation method. In addition, Table 2 uses the evaluation method based on the data map of the present embodiment to quantitatively determine the occurrence of defects from the detection results of a total of 130 steel materials including the steel materials shown in FIGS. 4 and 6. It is a table | surface which shows the result of having evaluated

  In Table 2, the “total area” is an area obtained by adding up the number of meshes in the data map of each steel material of steel numbers 1 and 2 shown in FIG. 4 and FIG. "Is the total of the number of meshes where the event" 1 "in the data map of each steel number 1 and 2 shown in FIGS. 4 and 6 stands for 130 steel materials, "" Is the total of the number of meshes where the event "2" in the data map of each steel number 1 and 2 shown in FIGS.

  From Table 1, although the number of Lo defects is a little worse at 94.6% and 97.7% between Steel No. 1 and Steel No. 2, a large difference cannot be recognized. Therefore, according to the conventional evaluation method, it is determined that the steel number 1 and the steel number 2 have substantially the same quality.

  On the other hand, according to Table 2, between Steel No. 1 and Steel No. 2, the Lo defective area ratio is almost doubled, 0.537% and 1.008%, and the total amount of wrinkles is very large. It can be seen that the load of the scraping work in the next process increases. Therefore, according to the evaluation method of the present embodiment, it is determined that there is a large difference in quality between steel No. 1 and steel No. 2, and it is possible to cope with this by issuing a warning in the previous process.

  In the above-described embodiment, the case where oblique flaw detection is performed has been described as an example. However, the same applies to the case where vertical flaw detection is performed. Instead of the surface gate (Lo) and the gate directly below the surface (Li), an intermediate gate (IAf, What is necessary is just to acquire the defect signal of IAB) and center gate (IB), create the data map of the said embodiment, and perform evaluation.

  Examples of the present invention will be described below. However, the present invention is not limited to the following examples.

  The bearing steel (SUJ2) was rolled into a billet with a diameter of 167-7m with a block mill, cooled, and subjected to ultrasonic testing with RUST.

  Data is aggregated in units of steel output in steelmaking (130 / C #).

  When data is aggregated, numerical values of the number of inspections, Lo defect number, Li defect number, inspection area, Lo defect area, Li defect area of the target material inspected after the previous aggregation until the current aggregation processing command is issued The Lo defect number rate, the Li defect number rate, the Lo defect area rate, and the Li defect area rate are calculated and printed out.

  In addition to the conventional Lo defect number rate and Li defect number rate as quality control data, in this embodiment, the Lo defect area rate and Li defect area rate are registered in the PC and evaluated whether there is an increase or decrease compared to the conventional value. To do.

  From Table 3, it can be seen that Steel No. 2 has a large number of scraps and a large amount of wrinkle generation area. In addition, it can be seen that steel material No. 8 has a smaller number of scraps than No. 6, but has a large area of scraping. In addition, it can be seen that Steel No. 11 has a large number of scraps and a large amount of wrinkles.

(Example of finding abnormal operation during normal operation)
In addition, as can be seen from Steel No. 1 and Steel No. 2 in Table 3, the number of Lo defects is almost the same as about 95% in the monthly total in August, but the Lo defect area ratio is 0.7% It has risen to 1.45%. In this way, the number of soot has not changed, but the total amount of soot is increasing, and it is possible to report to the upper process and the technical management department (management department) and start investigating the cause. . Further, as the state, there is no change in the number of scooping treatments, but the scooping area is large, and it can be determined that the load on the scooping processing is increasing.

  As described above, according to the surface defect evaluation method for a steel material of the present embodiment as described above, the ultrasonic flaw detection probe is rotated around the steel material, and the gate just below the surface of the cross section of the steel material, the surface gate, and the surface directly below Defects are detected by performing an ultrasonic flaw inspection in which both the gate and the surface gate are spirally detected over the longitudinal direction of the steel material, and the detected defects are arranged in the data map. By obtaining the rate, it is possible to quantitatively evaluate the defect occurrence status.

It is a figure which shows the principle of ultrasonic flaw detection by oblique flaw detection. It is a figure which shows the principle of the ultrasonic flaw detection by a vertical flaw detection. It is a figure which shows an example of the detection result of the defect using the conventional fully automatic ultrasonic flaw detector. It is a figure which shows an example of the data map using the surface defect evaluation method of the steel materials of this embodiment. It is a figure which shows the other example of the detection result of the defect using the conventional fully automatic ultrasonic flaw detector. It is a figure which shows the other example of the data map using the surface defect evaluation method of the steel materials of this embodiment.

Claims (3)

Detecting defects by performing ultrasonic flaw detection on at least one steel material by rotating the probe for ultrasonic flaw detection around the steel material and flaw-detecting at least one gate region of the cross section of the steel material in the longitudinal direction of the steel material. And
For each steel material, the detected defects are arranged in a corresponding mesh in a data map in which the first axis is the rotation direction of the ultrasonic flaw detection probe and the second axis is the longitudinal direction of the steel material. A method for evaluating surface defects of steel materials characterized by The number of meshes where the defects exist is totaled for all the steel materials to determine the defective area,
The total number of meshes of the data map is summed for all the steel materials to determine the total area,
2. The surface defect evaluation of a steel material according to claim 1, wherein a defective area ratio is obtained by dividing the defective area by the total area, and a quantitative evaluation of a defect generation amount is performed based on the defective area ratio. Method. The gate region in the steel material section is divided into a gate region directly under the surface and a surface gate region,
The detected defect is a defect detected in the gate region immediately below the surface, a defect detected in the surface gate region, and a defect detected in both the gate immediately below the surface and the surface gate. 3. The method for evaluating surface defects of steel materials according to claim 1 or 2, characterized in that the steel material is arranged on a mesh in the data map.

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