JPH0617898B2 - Judgment method of defect type in ultrasonic flaw detection - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a long square bar having a square cross section (hereinafter referred to as square steel).
The present invention relates to a method of determining a defect type in ultrasonic flaw detection such as.

[Prior Art] Generally, as shown in FIG. 6, ultrasonic flaw detection of square steel is performed by fixing a saddle-shaped flaw detection head 10 having a plurality of probes 1 which are sensors for transmitting and receiving ultrasonic waves. 3 is conveyed in the longitudinal direction, and square steel 3 is flaw-detected over its entire length,
It is carried out by the method.

In this flaw detection method, the presence / absence of harmful defects existing in the square steel 3 is determined by on / off judgment based on whether there is a defect of a certain level or more, or as shown in FIG. The presence / absence of defects is detected for each detection pitch l, and if there are defects, the number of defects is counted, and the counted number is monitored to continuously detect defects (hereinafter referred to as continuity) or square steel 3 When the total number of defects appearing over the entire length of (1) (hereinafter referred to as “accumulation degree”) exceeds a preset value, it is determined that there is a harmful defect. Generally, l is about 5 mm.

In addition to the determination method based on the defect distribution in the longitudinal direction of these square steels, recently, as shown in FIG. 8, among the many probes 1 arranged in the circumferential direction of the square steel 3, a probe that detects a defect 11 is detected. A method of counting defects (1a, 1b, 1c, 1d in the figure) for each arbitrary length of the square steel 3 to determine the defect distribution in the cross-sectional direction of the square steel (hereinafter referred to as "density"), and further developing this method. Judgment by scoring defects in the cross-sectional direction of the square steel disclosed in Japanese Patent Laid-Open No. 58-24858 is also carried out in combination.

However, these methods are methods for judging the harmfulness of defects, and the type of defects cannot be judged. For this reason,
Although we could understand the frequency of defects, we could not obtain enough information to link them to quality improvement actions.

In the steel industry, it is known that there is a close correlation between the state of square steel production in the steelmaking process and the types of defects that occur, and it is very important to know the types of defects in order to improve the level of manufacturing technology. is important. Therefore, conventionally, square steel was cut and the type of defect was determined by macro and microscopic examination.

In addition, as a simple method, although it does not exist as patent information, the ultrasonic flaw detection condition of square steel is recorded in a chart (hereinafter referred to as flaw detection chart), and an expert determines the type of defect from this flaw detection chart. , Is also practiced.

Examples of defect types and flaw detection charts are shown in FIGS. 9a, 9b and 9c.

FIG. 9a shows a flaw detection chart for porosity and hair crack defects of square steel. The feature of this flaw is that the base level of the flaw detection chart is generally high and the signal level changes greatly.

FIG. 9b shows a flaw detection chart for pipe defects in square steel. In this defect, the base level of the flaw detection chart is generally high, and the signal is often white. Moreover, this defect is frequently generated at the front end or the rear end of the square steel.

FIG. 9c shows a flaw detection chart for inclusions of square steel. In this defect, signals are generated individually or sporadically.

Based on such defect characteristics, an expert determines the type of defect from the flaw detection chart, but since it is a human sensory judgment, ambiguity remains, and also from the viewpoint of recent labor saving and automation. There was a problem. Furthermore, the method of cutting the square steel and determining the defect type has a problem that it is not possible to inspect all of them because it takes time and labor.

[Problems to be Solved by the Invention]

The present invention has been made to solve such a problem, and an object thereof is to automatically identify the type of defect without relying on human sensory judgment.

[Means for Solving the Problems]

In order to achieve this object, in the present invention, the presence or absence of defects in the square steel is detected in a predetermined length unit, and the harmfulness of the defects is determined from the degree of continuity and the degree of accumulation of the defects and the density of defects in the cross section of the square steel. In ultrasonic flaw detection, the type of defect is determined based on the combination of these three pieces of information.

That is, in the ultrasonic flaw detection of square steel, the defect harmfulness such as the degree of continuity of defects, the degree of accumulation of defects and the density of defects is determined for each central area and surface area of the square steel, and, for example, porosity, pipes, inclusions, etc. The defect type can be accurately determined by associating the correlation with the defect type and combining these three pieces of information.

Specifically, (1) By combining the central continuity and the central cumulative degree of defects,
Wool cracks / porosity defects, pipe defects and inclusions are determined. (2) Surface deckle defects and inclusions are determined by the combination of surface continuity and surface cross-section density, and (3) central continuity of defects. The central deckle defect and the inclusion defect are determined by the combination of and the central cross-section density.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a method of dividing an ultrasonic flaw detection area of square steel into a center and a surface layer. The ultrasonic beam 2 transmitted from the probe 1 is reflected by the surface and the bottom surface of the square steel 3, and the surface echo 4 (hereinafter, referred to as S echo) and the bottom surface echo 5 (hereinafter, referred to as B echo) are caused by each reflected wave. ) Signal is obtained.

A signal reception area called a flaw detection gate is set based on the S echo 4. That is, of the flaw detection gates
For the center gate 6, a range from 10 mm after the S echo 4 to 10 mm before the B echo 5 is used, and as the surface layer gate 7,
On the S echo 4 side, there is an area where flaw detection cannot be performed, which is called avalanche, so the range from 10 mm before the B echo 5 to the front of the B echo is set.

By performing flaw detection with the probe 1 from four directions around the square steel 3, the flaw detection area of the square steel 3 can be divided into a surface layer area 8 having a depth of 10 mm from the surface and a central area 9 other than the surface area 8.

Figures 2, 3, and 4 show the results of ultrasonic flaw detection on square steel with various types of defects, with the index of continuity, accumulation, and density divided into the center and surface layers shown in Figure 1. It is a graph organized in.

FIG. 2 is a graph showing the hair continuity / porosity defect, pipe defect, and inclusion defect of square steel with the central continuity of the horizontal axis (hereinafter referred to as the x-axis) and the central cumulative degree of the vertical axis (hereinafter referred to as the y-axis) as indexes. It is a plot.

Here, the degree of continuity and the degree of accumulation of defects are the continuous number of defects counted for each predetermined length of the square steel and the total number of defects for the entire length of the square steel, respectively.

The type of each defect is specified by cutting the square steel at the defect position and performing macro examination and micro examination with a microscope.

From FIG. 2, the hair crack / porosity defect (A), pipe defect (B) and inclusion defect (E) of square steel can be determined by determining the combination of central continuity and central cumulative degree according to Table 1 below. The type can be identified.

FIG. 3 shows the results of ultrasonic flaw detection on the surface layer of square steel for square deckle defects and inclusion defects of square steel evaluated by the degree of defect continuity and cross-section density, and the surface continuity on the x-axis and the surface cross-section density on the y-axis. It is plotted using degrees as an index.

Here, the square steel surface layer portion, as shown in FIG.
Area 8 up to a depth of 10 mm from the surface of square steel. or,
As described above, the cross-sectional density of defects is, among the multiple probes arranged in the circumferential direction of the square steel, the number of probes in which defects are detected, counted for each arbitrary length of the square steel, and This is the defect distribution.

From FIG. 3, the surface deckle defect (C) and the inclusion defect (E) of the square steel can be classified according to the following judgment values.

Surface deckle defect: y ≧ −x + 4 Inclusion defect: x ≧ 1, y ≧ 1, y <−x + 4 FIG. 4 shows the center deckle defect and the inclusion defect of the square steel, as in FIG. 3. The ultrasonic flaw detection results of No. 1 are evaluated by the degree of continuity of defects and the cross-sectional density, and the results are plotted using the x-axis central continuity and the y-axis central cross-sectional density.

From FIG. 4, the central deckle defect (D) and inclusion defect (E) of the square steel can be identified by determining the x and y values according to the following equation (1).

Center deckle defect ... y ≧ -5x / 6 + 20/3 Inclusion defect ... x ≧ 1, y ≧ 1, y <-5x / 6 + 20/3 (1) The above-described FIGS. 2 and 3 When the contents of FIGS. 4 and 5 are summarized, as shown in Table 2 below, it is possible to determine the types of almost all defect types.

FIG. 5 shows a defect type determination flow according to the above determination method.

Hair cracks / porosity defects (A) and pipe defects (B) can be classified according to the combination of central continuity (x) and central cumulative degree (y). Degree x ≧ 3, central cumulative degree y ≧ 40 The pipe defect (B) is judged by central continuity degree x ≧ 10 and central cumulative degree y <40.

Surface deckle (C) and center deckle (D) can be classified by a combination of surface layer continuity (x) and surface layer cross-section density (y) and center layer continuity (x) and center cross-section density (y), The surface deckle (C) is determined as y ≧ −x + 4, and the center deckle (D) is determined as y ≧ −5x / 6 + 20/3.

The inclusions (E) are determined to be all defects other than the above A to D.

Of course, each of the above-mentioned judgment values has the property of changing if the machine conditions for steel making change.

〔The invention's effect〕

As described above, according to the method of the present invention, it is possible to accurately determine the types of defects existing in the square steel, and it is possible to automatically determine online with ultrasonic flaw detection of the square steel by using, for example, a microcomputer. It is possible, and the quality of square steel can be surely evaluated, and further, by reflecting this information in the steelmaking process, it has a great effect of promoting the improvement of the production level.

[Brief description of drawings]

FIG. 1 is a sectional view of a square steel showing a defect type determination area,
2, 3 and 4 are graphs showing the method of determining the defect type, FIG. 5 is a flowchart showing the determination process of the defect type, and FIGS. 6 and 8 are the flaw detector and the square steel. And FIG. 7 is a plan view showing the structure of a signal indicating the presence or absence of a defect, and FIGS. 9a, 9b and 9c show the contents of flaw detection charts for various defects. It is a waveform diagram. 1: Probe, 2: Ultrasonic beam 3: Square steel, 4: Surface echo 5: Bottom echo, 6: Center gate 7: Surface gate, 8: Surface area 9: Center area, 10: Inspection head 11: Defect

Claims (1)

[Claims] 1. A material to be inspected is subjected to ultrasonic flaw detection, defect positions are detected for each predetermined length, and the detected defect information is classified into a center information and a surface layer information, and The feature is that the type of defects such as hair cracks and inclusions is determined by obtaining the degree of continuity of defects in the longitudinal direction, the degree of accumulation of defects over the length of the material to be inspected, and the degree of density in the cross section of the material to be inspected, based on the combination of these. And a method of determining a defect type in ultrasonic flaw detection.