KR101951393B1 - Ultrasonic testing method for special steel - Google Patents

Abstract

In order to more accurately detect the internal defects of special steel, the process of ultrasonic inspection of special steel containing alloying elements other than carbon to check for defects and, if defects are found, Thereby providing a special steel ultrasonic flaw detection method.

Description

[0001] ULTRASONIC TESTING METHOD FOR SPECIAL STEEL [0002]

Disclosed is an ultrasonic flaw detection method for detecting an internal defect of a special steel produced by adding an alloy element other than carbon.

Generally, an ultrasonic inspection technique is used to detect defects in rigid inclusions existing in the inside of a thick plate. Ultrasonic flaw detection technology is a technology for detecting internal defects of a thick plate by using a phenomenon in which sound waves are reflected within a boundary of a medium having different characteristics (especially density).

Unlike ordinary carbon steel, specially alloyed steel may cause a flaw error depending on the components contained in the steel. For example, in the case of high manganese steel plate products, the sound velocity of ultrasound tends to be reduced compared to normal carbon steel depending on the content of manganese. Therefore, there is a high possibility that a defect detected due to the ultrasonic inspection is excessively or underestimated and a judgment error is generated.

A special steel ultrasonic flaw detection method capable of more accurately detecting internal defects of special steel is provided.

The ultrasonic flaw detection method of this embodiment may include a process of detecting a defect by ultrasonic flaw detection of a special steel to which an alloy element is added in addition to carbon, and a process of ultrasonic flaw detection of the identified special steel to determine whether or not the defect is defective.

The defect checking process includes a process of correcting the thickness measurement sensitivity of the ultrasonic flaw detector with a thickness correction ratio according to the content of the alloy element in the special steel, a process of ultrasonic flaw detection of the special steel based on the corrected thickness measurement sensitivity, And a process of determining whether or not there is a defect.

The thickness correction ratio according to the alloy element content can be prepared by calculating the thickness error between the measured thickness appearing by the attenuation of ultrasonic sound velocity and the actual thickness of the special steel according to the content of the special steel alloy element.

The thickness correction ratio according to the alloy element content is determined by preparing a contrast test specimen having different alloy element contents, ultrasonic testing each contrast specimen, comparing the actual thickness of the test specimen with the thickness difference between the measured thicknesses And calculating the thickness correction ratio according to the alloy element content of the special steel.

The process of correcting the thickness measurement sensitivity of the ultrasonic flaw detector may include the steps of confirming an alloy element content of the special steel to be ultrasonically inspected, selecting a thickness correction ratio corresponding to the content of the alloy element identified in the prepared thickness correction ratio, and setting the thickness correction factor in the ultrasonic flaw detector Process.

The defect determination process includes a process of correcting the defect size measurement sensitivity of the ultrasonic flaw detector to a defect size reference value according to an alloy element content of the special steel, a process of ultrasonic flaw detection of a defect portion of the special steel based on the corrected defect size measurement sensitivity, And comparing the defect size detected by the ultrasonic inspection with a predetermined defect determination value to determine whether the defect is defective.

The defect size reference value according to the alloy element content includes a process of preparing contrast test specimens having standardized artificial defects formed on one side and having different alloying element contents, a process of ultrasonically flawing artificial defects of each contrast test piece, And setting the measured size of the artificial defect of the test piece to the defect size reference value according to the alloy element content of the special steel.

The process of correcting the defect size measurement sensitivity of the ultrasonic flaw detector may include the steps of checking the content of the alloy element in the special steel to be ultrasonically inspected, selecting a defect size reference value corresponding to the identified alloy element content in the prepared defect size reference value, May include

In preparing the contrast test specimens, the contrast specimen may be prepared with different thicknesses, and may further include calculating a thickness correction ratio or a defect size reference value according to the thickness of the special steel.

The special steel may be high manganese steel to which manganese is added as an alloying element.

When the manganese content in the high manganese content is 24 wt%, the thickness correction ratio is 10%. When the manganese content is 22.5 wt%, the thickness correction ratio is 15% and the manganese content is 18 wt% , The thickness correction ratio can be set to 10%.

According to this embodiment, more accurate defect detection is possible regardless of the alloy element content of the special steel.

It is possible to more accurately detect quality defects in high manganese steel plate products.

FIG. 1 is a view showing an image obtained by performing thickness correction according to the present embodiment and comparing ultrasound images.
FIGS. 2 and 3 are schematic views showing a contrast test piece for high-manganese steel ultrasonic testing according to the present embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Wherever possible, the same or similar parts are denoted using the same reference numerals in the drawings.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms as used herein include plural forms as long as the phrases do not expressly express the opposite meaning thereto. Means that a particular feature, region, integer, step, operation, element and / or component is specified, and that other specific features, regions, integers, steps, operations, elements, components, and / And the like.

All terms including technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. Predefined terms are further interpreted as having a meaning consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or very formal meanings unless defined otherwise.

Hereinafter, the present invention will be described by taking as an example an ultrasonic inspection method for a high manganese steel plate containing manganese (Mn) in special steel. The present invention is not limited thereto. The present invention can be applied to a method for determining a defect by ultrasonic inspection of a special steel containing various alloy components including high nickel steel and high hardness steel in addition to high manganese steel.

The high manganese steel plate ultrasonic testing method according to the present embodiment includes a first firing step of checking the defect of the high manganese steel plate by ultrasonic flaw detection and a second fanning step of checking the defective part of the high manganese steel plate according to the first flaw, And a second flaw detection step of determining a second flaw detection step.

The primary flaw detection step can be performed using an automated ultrasonic flaw detector. The automated ultrasonic flaw detector performs the ultrasonic inspection on the entire surface by continuously passing the high manganese steel plate according to the set program.

The first flaw detection step can roughly judge only the presence or absence of defects in the high manganese steel plate and its position.

Here, the primary fusing step can be performed by correcting the thickness measurement error of the ultrasonic flaw detector generated according to the manganese content of the high manganese steel plate.

For this, the primary flawing step according to the present embodiment includes a step of correcting the measurement sensitivity of the ultrasonic flaw detector with a thickness correction ratio according to the manganese content of the high manganese steel plate, and a step of measuring the sensitivity of the ultrasonic flaw detection And checking the presence or absence of a defect by calculating an ultrasonic inspection result.

The manganese content of the high manganese steel plate can be confirmed by the detailed specification of the steel plate product. The high manganese steel plate is a heavy plate product containing 3 to 27% of manganese (Mn), and is manufactured with a manganese content determined according to the product standard. Thus, the manganese content can be confirmed by confirming the specification of each product of the manufactured high manganese steel plate.

The ultrasonic flaw detector is a non-destructive inspection device for measuring internal defects by applying ultrasonic waves to a flaw object. The ultrasonic tester can use the equipment for the detection of the defect in the normal plate. Ultrasonic waves refer to sound waves having a frequency of more than an audible frequency (several tens Hz to several tens of thousands of Hz), and have different propagation velocities depending on the characteristics of the medium. When the ultrasonic waves propagate inside the object, attenuation due to ultrasonic wave diffusion (diffusion attenuation) occurs, and attenuation of ultrasonic waves due to scattering due to crystal and internal friction occurs. In polycrystalline metals, ultrasonic waves are mainly caused by scattering attenuation by crystals or their tissues, and attenuation due to internal friction is very small. Therefore, manganese content is the main variable in high manganese steel plate, and the propagation speed of ultrasonic wave is changed according to manganese content. The sonic velocity of the ultrasonic wave propagating inside the high manganese steel plate is reduced by scattering and reflection by manganese inside the tissue. The sound velocity of ultrasonic waves is reduced by about 15 to 20% of that of normal carbon steel depending on the content of manganese steel manganese. Therefore, the thickness of the high manganese steel plate is different from the actual thickness because the bottom echo is delayed.

In ultrasonic inspection, the size of actual object and its measured value must be exactly the same. However, as mentioned above, in case of high manganese steel, the propagation speed of ultrasonic wave is changed by manganese, and the measured ultrasonic test value does not exactly coincide with the thickness of the high manganese steel plate, and an error occurs. If there is an error between the measured thickness and the actual thickness of the high manganese steel plate, the defect is not properly detected by the ultrasonic inspection and the position of the defect in the plate is also inaccurate. Therefore, it is impossible to judge whether there is an accurate defect through the ultrasonic inspection.

Therefore, it is necessary to calibrate the ultrasonic flaw measuring sensitivity according to the manganese content of the high manganese steel plate and reset it. By correcting the measurement sensitivity of the ultrasonic flaw detector according to the manganese content of the high manganese steel plate, the thickness of the ultrasonic flaw detection and the actual thickness of the thick plate are matched with each other. The measurement sensitivity can be understood as a detection standard of an ultrasonic flaw detector, for example, ultrasonic intensity, time axis interval, and the like.

The measurement sensitivity of the ultrasonic flaw detector can be corrected to the prepared thickness correction ratio according to the manganese content of the high manganese steel. The thickness correction factor can be prepared in advance through experiments.

In this embodiment, the thickness correction ratio can be prepared for each manganese content by calculating the thickness error between the thickness measured by attenuation of ultrasonic sound velocity and the actual thickness of the high manganese steel plate according to the manganese content of the high manganese steel plate.

To this end, the thickness correction factor is determined by preparing contrasting test specimens having different manganese contents, ultrasonic testing each contrast specimen, measuring the manganese content of the high manganese steel plate from the thickness error between the actual thickness and the measured thickness of the contrast specimen And calculating a thickness correction ratio according to the calculated thickness.

As described above, by providing the contrast test piece serving as a reference of the measurement sensitivity setting, it is possible to accurately detect the thickness of the high manganese steel.

Contrast test specimens can be prepared by thickness in addition to manganese content. In the case of high manganese steel plates with the same manganese content, sonic sound velocity decreases as the product thickness increases. Accordingly, each of the contrast test specimens prepared with different thicknesses can be ultrasonically inspected, and the thickness correction ratio according to the thickness of the high manganese steel plate can be calculated.

The contrast test specimen is a reference specimen having a standardized thickness or manganese content. The specific structure will be described later, and a detailed description thereof will be omitted.

When the thickness correction ratio according to the manganese content is prepared, the measurement sensitivity of the ultrasonic flaw detector is corrected according to the manganese content. To do this, first check the manganese content of the high manganese steel plate that is the object of actual inspection. Then, the thickness correction ratio corresponding to the manganese content of the actual high manganese steel plate among the prepared thickness correction rates is selected. When the thickness correction factor is selected, it is set in the ultrasonic flaw detector and the sensitivity of the ultrasonic flaw detector is set according to the manganese content of the high manganese steel plate.

In this embodiment, the process of preparing the thickness correction ratio from the test sample is as follows.

Table 1 below shows the attenuation ratio of ultrasonic sound velocity according to the manganese content of high manganese steel and the resulting thickness error.

Product (Thickness) Mn content
(weight%) Ultrasonic sound velocity
(m / sec) Decay rate
(%) Measured thickness
(mm) Thickness error
(%) POSM_CS400A (19T) About 24 5369 9.3 20.2 6.3 POSM_PM_350 (20T) Approximately 22.5 5288 10.7 22.3 11.5 POSM_XD_70 (18T) About 18 5560 4.4 19.5 8.3

A comparison test specimen was prepared for three representative product standards of high manganese steel plate, and a lot of experiments were performed on the contrast test specimens to obtain an average thickness error.

As shown in Table 1, for example, in the case of a 19 mm thick plate having a manganese content of about 24%, the ultrasonic sound velocity is 5369 m / sec, which is 9.3% attenuated compared to 5920 m / sec, Respectively. It was confirmed that an error of 6.3% occurred between the actual thickness and the measured thickness. Thus, it can be seen that a thickness error is generated depending on the content of manganese.

Through these experiments, the thickness correction ratio according to the manganese content can be prepared as shown in Table 2 below.

Product (Thickness) Mn content (% by weight) Sonic speed (m / sec) Thickness Correction Ratio POSM_CS400A (19T) About 24 5369 10 POSM_PM_350 (20T) Approximately 22.5 5288 15 POSM_XD_70 (18T) About 18 5560 10

As shown in Table 2, the ultrasonic flaw detection method of this embodiment corrects the measurement sensitivity of the ultrasonic flaw detector with a thickness correction ratio of 10% for a high manganese steel plate having a manganese content of about 24% It is possible to confirm whether or not the defect is defective. If the manganese content is about 22.5% or about 18%, the ultrasonic flaw measurement value can be corrected by setting the thickness correction ratio to 15% and 10%, respectively.

Thus, by preparing the thickness correction ratio for each manganese content, it is possible to set the measurement sensitivity of the ultrasonic flaw detector at the prepared thickness correction ratio. Therefore, by matching the thickness measurement value measured according to the manganese content of the high manganese steel plate with the actual thickness, it is possible to prevent the occurrence of coupling loss and accurately detect the defect.

FIG. 1 is a view showing a comparison of a test image obtained by performing ultrasonic inspection after correcting with a thickness correction ratio prepared according to the present embodiment.

In FIG. 1, the left photograph is an ultrasonic inspection image in which the thickness correction ratio is applied and not corrected as in the conventional method. In the case of the left photograph, it is confirmed that a coupling loss occurs and a very large amount of noise appears even though there is no defect. On the other hand, the photograph shown on the right side of FIG. 1 shows that a normal ultrasonic inspection image without defects appears by setting the thickness correction rate as in this embodiment.

Therefore, the presence and position of defects in the high manganese steel plate can be accurately detected by the accurate measurement sensitivity setting of the ultrasonic flaw detector according to the retention amount. Accordingly, the presence or absence of a defect can be accurately determined by calculating the measurement result of the defect that has been correctly detected.

The determination of the presence or absence of a defect is made, for example, by determining whether or not there is a defect. If it is judged that there is a defect, the defective portion of the high manganese steel plate is subjected to secondary ultrasonic wave inspection to judge whether it is defective or not.

The secondary flaw detection step can be performed using a manual ultrasonic flaw detector manually operated by an operator. The operator performs intensive ultrasonic inspection of defects on the detected high manganese steel plate using the probe of the manual ultrasonic flaw detector.

It is possible to judge whether the size of the detected defect is out of the preset determination value for the defect determination and whether the heavy plate product is a defective product or is within the set determination value and is acceptable product through the secondary inspection step.

For this purpose, the second flaw detection step according to the present embodiment includes a step of correcting the defect size measurement sensitivity of the ultrasonic flaw detector based on the defect size reference value according to the manganese content of the high manganese steel, the defect of high manganese steel based on the corrected defect size measurement sensitivity And comparing the size of the defect detected by the ultrasonic wave with a predetermined defect judgment value to judge whether the defect is defective or not.

In the secondary fusing stage, the measurement sensitivity of the ultrasonic flaw detector can be corrected to the prepared defect size reference value according to the manganese content of the high manganese steel. A different defect size reference value for the manganese content of the high manganese steel can be prepared through experiments.

In this embodiment, the defect size reference value according to the manganese content includes preparing a contrast test piece having a standardized artificial defect formed on one side and having a different manganese content, ultrasonic testing the artificial defect of each contrast test piece, And setting the measured value of the artificial defect of the contrast test piece to the defect size reference value according to the manganese content of the high manganese steel.

The defect size reference value can be understood as a measurement reference value depending on the manganese content for a certain size defect. In order to determine the size of the measurement value obtained from the ultrasonic flaw detector in the secondary flaw detection, there is a reference value for the size. Therefore, by providing a reference value for the accurate defect size for each manganese content through the contrast test piece, it is possible to accurately detect the actual defect size by setting an accurate detection sensitivity according to the reference value.

Contrast test specimens can be prepared by thickness in addition to manganese content. In the case of high manganese steel plates with the same manganese content, sonic sound velocity decreases as the product thickness increases. Thus, each of the contrast test specimens prepared with different thicknesses can be ultrasonically inspected, and the defect size reference value according to the thickness of the high manganese steel plate can be calculated.

When the defect size reference value according to the manganese content is prepared, the measurement sensitivity of the defect size of the ultrasonic flaw detector is corrected according to the manganese content of the target plate. To do this, first check the manganese content of the high manganese steel plate that is the object of actual inspection. The manganese content of the high manganese steel plate can be confirmed by the detailed specification of the steel plate product. Then, the defect size reference value corresponding to the manganese content of the actual high manganese steel plate among the prepared defect size reference values is selected. When the defect size reference value is selected, it is set in the ultrasonic flaw detector and the sensitivity of the defect size of the ultrasonic flaw detector is set according to the manganese content of the high manganese steel plate.

The defect size of the high manganese steel plate can be confirmed by the ultrasonic flaw detector set to the defect size reference value. Thus, it is possible to determine whether the defect is defective by comparing the finally measured defect size with a predetermined defect determination value.

The defect judgment value is a value which is used as a criterion of defect judgment with respect to the defect size and is set according to the standard of the high manganese steel plate. If the measured defect size is smaller than the defect judgment value, it is judged as acceptable. If it is larger than the defect judgment value, it can be judged as defectiveness.

Table 3 below shows an example of prepared contrast test specimens according to manganese content and thickness of high manganese steel.

Thickness (mm) Length (mm) Width (mm) Artificial defect diameter
(mm) Artificial defect thickness direction position (mm) 19 to 50 100 100 6 5 to 15

FIGS. 2 and 3 show contrast test specimens prepared according to this embodiment. Fig. 2 shows the bottom surface of the contrast test piece, and Fig. 3 shows the cross-sectional structure of the contrast test piece.

The contrast test piece 10 is made of high-manganese steel, and artificial defects 12 having a predetermined size are formed at the center of the surface. In this embodiment, the contrast test piece 10 has a square plate structure having a width and a length of 100 mm, and is formed variously between 19 and 50 mm in thickness. A circular groove-like artificial defect 12 is formed in the center of one side of the contrast test piece along the thickness direction. The artificial defect has a flat bottomed shape with a bottom of the groove, and a diameter of 6 mm and a depth of 10 mm.

Artificial defects can be formed in various sizes. For example, the artificial defects can be formed in accordance with the size of the high manganese steel plate to be a defect judgment standard. In the case of such a structure, the measurement result of the ultrasonic flaw detector can be directly compared with the reference value to judge whether or not it is defective.

The artificial defect sites of the contrast test specimens are used to prepare the defect size reference values, and the portions where artificial defects are not formed can be used to prepare the thickness correction rate.

In this embodiment, the above-mentioned contrast test piece is prepared for each manganese content of the high manganese steel plate. As mentioned above, the sound velocity of ultrasonic waves changes according to the content of manganese in the high manganese steel plate, so the reference value also changes. Therefore, according to the content of manganese in the high manganese steel plate, compared with each of the test specimens, an accurate thickness correction ratio and a reference value according to the manganese content can be obtained. In addition, the contrast test piece can be prepared for each thickness of the high manganese steel. As the thickness of the high manganese steel plate increases, the sound velocity of the ultrasonic wave decreases. Accordingly, by preparing the test specimens in accordance with the thickness of the high manganese steel plate, it is possible to obtain an accurate thickness correction ratio and a reference value according to the thickness.

Thus, it is possible to detect the defect of the thick plate and the defect size by preparing the correct thickness correction ratio and the defect size reference value according to the manganese content or thickness of the high manganese steel plate through the contrast test piece. If the defect of the thick plate is confirmed through the first ultrasonic inspection, the accurate defect size can be detected through the secondary ultrasonic inspection to finally judge the defect.

That is, the echo height of the ultrasonic flaw detector is calibrated using artificial defects formed on the contrast test piece as a reference value, and the sensitivity of measurement according to the content of manganese is appropriately set. With this measurement sensitivity setting, the measured value of the defects of the actual high manganese steel plates during the secondary flaw is shown to be the correct size. Thus, the echo height measured at the time of the secondary test is compared with the echo height of the previously determined failure judgment value. Whether or not the defect is defective can be determined by confirming whether the actually measured measured value is larger or smaller than the defect judgment value which is the judgment criterion.

For example, when the actual defect measurement value of the high manganese steel plate measured through the secondary flaw inspection is larger than the predetermined defect determination value, it is judged that the defect size is greater than the set limit and it can be judged as defective.

As described above, the accurate measurement value can be obtained through the contrast test piece, thereby making it possible to prevent errors in defect determination and increase defect detection capability.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, Of course.

10: contrast test piece 12: artificial defect

Claims (9)

A process of ultrasonic inspection of a special steel to which an alloy element is added in addition to carbon to confirm whether or not the steel is defective, and a process of ultrasonic inspection of a defective part of the identified special steel to judge whether or not the steel is defective.
The defect checking process includes a process of correcting the thickness measurement sensitivity of the ultrasonic flaw detector with a thickness correction ratio according to the content of the alloy element in the special steel, a process of ultrasonic flaw detection of the special steel based on the corrected thickness measurement sensitivity, And determining whether or not there is an abnormality,
Wherein the thickness correction ratio according to the alloy element content is prepared by calculating a thickness error between a measured thickness appearing by attenuation of ultrasonic sound velocity and an actual thickness of the special steel according to the content of the special steel alloy element. delete The method according to claim 1,
The thickness correction ratio according to the alloy element content is determined by preparing a contrast test specimen having different alloying element contents, ultrasonic testing each contrast specimen, and calculating a thickness error between the actual thickness of the specimen and the measured thickness And calculating a thickness correction ratio according to an alloy element content of the special steel. The method of claim 3,
The process of correcting the thickness measurement sensitivity of the ultrasonic flaw detector may include the steps of confirming an alloy element content of a special steel to be ultrasonically inspected and a thickness correction ratio corresponding to the content of the alloy element identified in the prepared thickness correction ratio, A method of ultrasonic testing of a special steel. The method according to any one of claims 1, 3, and 4,
The defect determination process includes a process of correcting the defect size measurement sensitivity of the ultrasonic flaw detector to a defect size reference value according to an alloy element content of the special steel, a process of ultrasonic flaw detection of a defect portion of the special steel based on the corrected defect size measurement sensitivity, And comparing the defect size detected by the ultrasonic wave with a predetermined defect judgment value to determine whether the defect is defective. 6. The method of claim 5,
The defect size reference value according to the alloy element content includes a process of preparing contrast test specimens having standardized artificial defects formed on one side and having different alloying element contents, a process of ultrasonically flawing artificial defects of each contrast test piece, A special steel ultrasonic flaw detection method which is prepared by setting a measured size of an artificial defect of a test piece to a defect size reference value according to an alloy element content of a special steel. 6. The method of claim 5,
The process of correcting the defect size measurement sensitivity of the ultrasonic flaw detector may include the steps of checking the content of the alloy element in the special steel to be ultrasonically inspected, selecting a defect size reference value corresponding to the identified alloy element content in the prepared defect size reference value, A method of ultrasonic testing of a special steel. The method according to claim 6,
Wherein the contrast test specimen is prepared in a different thickness in the process of preparing the contrast specimens, and further calculating a thickness correction ratio or a defect size reference value according to the thickness of the special steel. 6. The method of claim 5,
The special steel is a high manganese steel to which manganese is added as an alloying element.

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