TW202022373A - Method for detecting central porosity of steel slab - Google Patents

Abstract

The present invention relates to a method for detecting central porosity of a steel slab. A test sheet of the steel slab is first provided, and a detecting process is performed to the test sheet. The test sheet is scanned by an ultrasonic wave, and an echo signal of a bottom wave of the ultrasonic wave is detected, thereby obtaining a C-scan image. And then, the central porosity of the test sheet is determined according to the C-scan image. The central porosity of the steel slab can be rapidly and nondestructively determined by the method of the present invention.

Description

Method for detecting density of core of steel blank

The invention relates to a detection method, in particular to a detection method for the density of the core of a steel blank.

Generally, the core of the steel billet produced by the continuous casting process is prone to form hollow defects such as shrinkage cavity, which reduces its quality. When these hollow defects are shrinkage defects with a size of 2 mm to 20 mm, these hollow defects can be easily detected with the naked eye after flame cutting of the steel blank or thiopickling inspection. However, for micro-shrinkage cavities of smaller size (for example, the size is less than 1 mm), it cannot be detected by the above-mentioned inspection method, so it is not easy to be found.

Furthermore, when the steel billet is to be made into large-size steel bars or extra-thick steel plates, the thickness of the finished product is relatively large and the rolling is relatively low, so the subsequent rolling process cannot heal the shrinkage cavity (size Hollow defects such as 2mm to 20mm) and micro-shrinkage holes (less than 1mm in size). These defects will reduce the fatigue life and tensile strength of the steel core. Even when the produced steel is used in a low-temperature environment, these hollow defects will embrittle the core structure and reduce the low-temperature impact toughness of the steel, so that it cannot meet the specification requirements of the steel, and become high-grade large-size steel bars and The production technology bottleneck of ultra-thick steel plate.

Generally, the detection methods for the density of the core of the steel billet include sulfur printing, pickling, pickling and penetrant detection, radiation detection, specific gravity method, and in-situ analyzer detection. However, these methods cannot quickly and accurately detect hollow defects in the heart. In the aforementioned methods, sulfur stamping and pickling cannot detect defects such as micro-shrinkage, so they cannot be used in the continuous casting process of process improvement; pickling and penetrant detection cannot quantify the size and number of defects, and cannot accurately measure The number of hollow defects; the resolution of radiation detection is poor, and the results obtained cannot be quantified; although the specific gravity method can accurately measure the density of the heart, it must prepare a large number of test pieces, and the processing requirements of the test pieces are extremely high. The core density of the steel billet can be quickly detected, and the detection result of the defect distribution cannot be provided. Although the in-situ analyzer can quickly detect the core density, its detection accuracy is poor, so it is impossible to make a finer comparison.

Therefore, the conventional detection method cannot quickly and accurately measure the core density of the steel blank, and cannot be used as a quality control tool for the continuous casting process, and it is difficult to control the quality of the steel blank.

In view of this, it is urgent to provide a method for detecting the density of the core of the steel blank to improve the defects of the conventional method of detecting the density of the core of the steel blank.

Therefore, one aspect of the present invention is to provide a method for detecting the density of the core of the steel billet, which is based on the emission of ultrasonic waves to the steel billet test piece, and the steel billet test piece can be judged by the reflected echo signal The heart is dense.

According to one aspect of the present invention, a method for detecting the density of the core of a steel blank is provided. This detection method is to provide the steel blank test piece first, and perform the surface processing process on the steel blank test piece. After the surface processing process, the steel blank test piece is inspected. This inspection process is to first transmit ultrasonic waves to a plurality of detection positions on the cross section of the steel blank test piece, and detect the echo signal of the bottom wave at each detection position, to obtain a depth profile below the cross section. The C-scan image. Wherein, the C-scan image has a gradation distribution. The color gradation distribution corresponds to a plurality of intensity values of the echo signal, these intensity values are 0% to 100%, and the cross section is parallel to the cross section. Then, according to this C-scan image, determine the density of the core of the steel blank test piece. Among them, the region where the intensity value corresponding to the gradation distribution is less than 40% has hollow defects.

According to an embodiment of the present invention, the aforementioned depth is not greater than 15 mm.

According to another embodiment of the present invention, the thickness of the aforementioned steel blank test piece is 10 mm to 50 mm.

According to another embodiment of the present invention, before performing the aforementioned operation of providing the steel blank test piece, the detection method may optionally perform the continuous casting process to obtain the steel blank. Then, a cutting process is performed on the steel blank to form a steel blank test piece. Among them, the cutting direction of the cutting process is perpendicular to the continuous casting direction of the continuous casting process.

According to another embodiment of the present invention, the emission direction of the aforementioned ultrasonic wave is parallel to the continuous casting direction.

According to still another embodiment of the present invention, the focus of the aforementioned ultrasonic wave is located at the middle position of the thickness of the steel blank test piece.

According to still another embodiment of the present invention, the frequency of the aforementioned ultrasonic wave is 10 MHz to 20 MHz.

According to still another embodiment of the present invention, the aforementioned detection process is performed using submerged ultrasonic waves.

According to still another embodiment of the present invention, the aforementioned hollow defects include pore defects, shrinkage defects and/or micro shrinkage defects.

Applying the method for detecting the density of the core of the steel blank of the present invention, by emitting ultrasonic waves to the steel blank test piece, the intensity of the echo signal of the reflected bottom wave can be used to accurately and non-destructively judge the heart of the test piece Department density. Furthermore, the operator can improve the process of the steel blank based on the obtained core density, and can improve the quality of the steel blank.

100‧‧‧Method

110/121/123/130‧‧‧Operation

120‧‧‧Testing process

200‧‧‧Press roller device

210‧‧‧Press roller

220‧‧‧Fixed roller

230‧‧‧Steel blank

231‧‧‧surface

231a‧‧‧Three-point

233‧‧‧Semi-condensed casting embryo

α ₁ / α ₂ / α ₃ / α ₄ ‧‧‧Included angle

A‧‧‧Scope

In order to have a more complete understanding of the embodiments of the present invention and its advantages, please refer to the following description and cooperate with the corresponding drawings. It must be emphasized that the various features are not drawn to scale and are for illustration purposes only. The contents of the related drawings are described as follows: [Figure 1] is a flow chart showing a method for detecting the density of the core of a steel blank according to an embodiment of the present invention.

[Fig. 2] is a three-dimensional schematic diagram showing a steel blank produced by a continuous casting process according to an embodiment of the present invention.

[Fig. 3A] shows a C-scan image of a steel blank test piece according to an embodiment of the present invention.

[Figure 3B] is a radiographic image showing the range A of the steel blank test piece corresponding to [Figure 3A].

[Fig. 4] is a graph showing the variation of the total area where the bottom wave strength of steel blanks of different processes according to an embodiment of the present invention is less than 20%.

The manufacture and use of embodiments of the present invention are discussed in detail below. However, it can be understood that the embodiments provide many applicable inventive concepts that can be implemented in a variety of specific contents. The specific embodiments discussed are for illustration only and are not intended to limit the scope of the invention.

In the present invention, ultrasonic waves are emitted into the steel blank test piece, and the echo signal of the ultrasonic reflection is used to determine the core density of the steel blank test piece. Among them, when ultrasonic waves pass through hollow defects (such as: pore defects, shrinkage defects (size 2 mm to 20 mm), micro shrinkage defects (size less than 1 mm) and/or other hollow defects, etc.), 99 More than% of the ultrasonic signal will be reflected by the hollow defect (that is, less than 1% of the ultrasonic signal can penetrate the hollow defect), forming an echo signal of the hollow defect; when the ultrasonic wave passes through the solid defect (for example: When intermediary materials, manganese sulfide and/or other appropriate solid defects, etc.), about 6.2% of the ultrasonic signal will be reflected (that is, about 93.8% of the ultrasonic signal can penetrate the solid defect), and the echo of the defect is also formed Signal: When the ultrasonic wave is transmitted to the bottom of the steel blank test piece, due to the change of the interface, the ultrasonic wave will be reflected to form the echo signal of the bottom wave. According to the foregoing content, it can be seen that most of the ultrasonic waves cannot be transmitted to the bottom of the steel blank due to the hollow defect. Therefore, based on the intensity value of the echo signal of the bottom wave, the core of the steel blank can be dense. quickly Be judged. Among them, the weaker the strength of the echo signal of the bottom wave, the more hollow defects exist in the core of the steel blank test piece, and the lower the density of the core of the steel blank test piece. It is understandable that although both hollow defects and solid defects reflect ultrasonic waves and reduce the ultrasonic waves transmitted to the bottom of the test piece, the penetration of ultrasonic waves for the two is still different, so the echo of the bottom wave The intensity value of the signal, hollow defects and solid defects can still be easily distinguished.

It should be noted that although the hollow defect of the steel blank is generally formed in the core, the detection method of the present invention is not limited to detecting the hollow defect of the core.

Please refer to FIG. 1, which shows a flowchart of a method for detecting the density of the core of a steel blank according to an embodiment of the present invention. In the method 100, the steel blank test piece is provided first, as shown in operation 110. Then, the inspection process 120 is performed on the steel blank test piece. Among them, the inspection process 120 is to first emit ultrasonic waves to the steel blank test piece, and then detect the echo signal of the bottom wave of the ultrasonic wave to obtain the C-scan image of the steel blank test piece, such as operation 121 and Operation 123 is shown. The ultrasonic detection method of the detection process 120 of the present invention is not particularly limited. In some embodiments, the inspection process 120 may be performed by using submerged ultrasonic waves.

The size of the steel blank test piece of the present invention is not particularly limited. It only needs to ensure that the ultrasonic wave injected into the steel blank test piece can be transmitted to the bottom surface of the steel blank test piece and return the reflected signal under the condition of no hollow defect. OK. In some embodiments, the thickness of the steel blank test piece may be 10 mm to 50 mm, preferably 20 mm to 30 mm.

In some embodiments, before performing operation 110, the method 100 may optionally perform a continuous casting process to produce a steel blank. Among them, the process and equipment of the continuous casting process are well-known to those with ordinary knowledge in the technical field to which the present invention belongs, so only the pressing roller steps of the continuous casting process are described here. Please refer to FIG. 2, which is a three-dimensional schematic diagram of a steel blank produced by a continuous casting process according to an embodiment of the present invention. The semi-condensed casting blank 233 after continuous casting is rolled by the upper roller 210 and the lower roller 220 of the pressing roller device 200 to form the steel blank 230. Wherein, the continuous casting direction of the steel blank 230 is parallel to the x-axis, and the produced steel blank 230 has a surface 231 and two three-pointed points 231a. The "three-pointed point 231a" mentioned here refers to a virtual line drawn on the surface 231 from two corners of a narrow side, and the intersection of the two virtual lines is the three-pointed point 231a. Wherein, the angles α ₁ and α ₂ between the virtual line and the narrow side are both about 45 degrees. Similarly, on the other narrow side of the surface 231 of the steel blank 230, by the intersection of two virtual lines drawn at the corners (the angles α ₃ and α ₄ between the virtual line and the narrow side are both approximately 45 degrees), namely Another trident point 231a can be obtained. Then, a cutting process (for example, a flame cutting process) is performed on the steel blank produced by the continuous casting process to form a steel blank test piece. Among them, the cutting direction of the cutting process is perpendicular to the continuous casting direction of the continuous casting process. In other words, as shown in FIG. 2, the cutting process is to cut the steel blank 230 along a plane (ie, the yz plane) perpendicular to the x-axis (ie, the continuous casting direction). It can be understood that this plane is parallel to the surface 231. In these embodiments, when the inspection process is performed on the steel blank test piece, the emission direction of the ultrasonic wave is parallel to the continuous casting direction. In other words, the emission direction of the ultrasonic wave is perpendicular to the surface 231 of the steel blank 230.

In some embodiments, the steel blank test piece obtained by cutting the steel blank 230 can be further cut to obtain a smaller volume steel blank test piece, which is convenient For handling. In these embodiments, the steel blank test piece can be cut along a plane perpendicular to the y-axis (ie, the x-z plane). Similarly, when the detection process is performed, the emission direction of the ultrasonic wave is perpendicular to the surface 231.

Please continue to refer to Figure 1. When the inspection process 120 is performed, the focus of the ultrasonic wave can be located at the middle position of the thickness of the steel blank test piece (that is, the size of the test piece along the x-axis of FIG. 2). In some embodiments, the frequency of the ultrasonic wave can be 10MHz to 20MHz. When the frequency of the ultrasonic wave is in the aforementioned range, the detection depth of the ultrasonic wave can be improved, and it has a good resolution, which can improve the applicability of the detection method of the present invention. For example, the effective detection depth of ultrasound is not more than 15 mm. In addition, according to the size of the steel blank test piece and the desired resolution, a person with ordinary knowledge in the technical field of this case can appropriately adjust the moving distance of the ultrasonic probe. For example, when the frequency of the ultrasonic wave is 15MHz and the moving distance of the ultrasonic probe is 0.3 mm, the minimum size of the hollow defect that can be measured by this inspection method is 0.09 mm.

During operation 121 and operation 123, the ultrasonic probe emits ultrasonic waves to a plurality of detection positions on the surface of the steel blank test piece (that is, the surface 231 in FIG. 2), and uses the reflected bottom wave at each detection position The echo signal obtained from the C-scan image of the steel blank test piece. Among them, corresponding to the intensity value of the echo signal, the C-scan image has a gradation distribution. In other words, corresponding to the different intensities of the echo signal, the C-scan image is represented by a different gradation distribution. Therefore, based on the color scale performance of a position in the C-scan image, the operator can correspondingly determine the intensity value of the echo signal at the detected position. It is understandable that the intensity value of the echo signal is 0% to 100%. In some embodiments, the ultrasonic probe scans the entire surface of the aforementioned steel blank test piece to obtain the entire surface of the steel blank test piece. Image of a plane. It is understandable that this image is a C-scan image of the internal section of the steel blank test piece (cut along the y-z plane in Figure 2). In some embodiments, the ultrasonic probe does not need to scan the entire surface of the steel blank test piece, and the operator can adjust the scanning range of the ultrasonic probe according to requirements.

In some embodiments, before performing the inspection process, the inspection method 100 may perform a surface processing process on the surface of the steel blank test piece (that is, the incident surface of the ultrasonic wave and the opposite bottom surface). For example, the surface accuracy of the steel blank test piece is controlled by three processing symbols (▽▽▽). It is understandable that, according to the general knowledge in the mechanical processing field, the three processing symbols are used to standardize the surface roughness of the steel blank test piece, which are already well known by those with general knowledge in the relevant field, so they will not be repeated here. When the surface accuracy of the steel blank test piece is controlled to three processing symbols, the defect wave of the steel blank test piece is not easily disturbed, and the accuracy of the detection method of the present invention can be improved. In some embodiments, when the steel blank system is divided into multiple test pieces, in order to ensure that each steel blank test piece can have the same detection standard, the surface accuracy of each steel blank test piece is controlled to three processing symbols .

Please continue to refer to FIG. 1, after operation 123 is performed, the core density of the steel blank test piece is determined according to the C-scan image, as shown in operation 130. When the ultrasonic wave passes through the steel blank test piece, the intensity of the echo signal of the returned bottom wave will change according to whether there is a hollow defect in the steel blank test piece. Therefore, the core density of the steel blank test piece can be quickly judged. Among them, when the color gradation of the C-scan image corresponding to the detection position represents the intensity value of the echo signal of the bottom wave is less than 40%, the area of the detection position has a hollow defect. Preferably, the detection area corresponding to the color gradation with a representative intensity value not greater than 20% has a hollow defect.

The following uses embodiments to illustrate the application of the present invention, but it is not intended to limit the present invention. Anyone who is familiar with this art can make various modifications and retouching without departing from the spirit and scope of the present invention.

Steel blank test piece detection

Please refer to FIG. 3A and FIG. 3B at the same time. FIG. 3A shows a C-scan image of a steel blank test piece according to an embodiment of the present invention, and FIG. 3B shows a radiographic image of the range A of the steel blank test piece corresponding to FIG. 3A.

In the ultrasonic detection method of Fig. 3A, the thickness of the steel blank test piece is 19.5 mm to 20.5 mm. The ultrasonic detection frequency is 15MHz, the ultrasonic focus is set at a distance of 10 mm from the surface of the steel blank test piece, and the gain of the bottom wave is set to 68db.

According to the comparison of Fig. 3A and Fig. 3B, it can be seen that the hollow defect (that is, the white hollow area in the test piece of Fig. 3A (the intensity value of the echo signal of the bottom wave is less than 40) measured by the ultrasonic detection method of the present invention The position of %)) is consistent with the position of the hollow defect measured by the radiation inspection in Fig. 3B. Accordingly, the core density detection method of the present invention can accurately and quickly detect the hollow defect of the steel blank test piece.

Continuous casting steel blank inspection

The detection of the continuous casting steel blank applies the detection method of the present invention to the continuous casting process under different process conditions. Among them, the continuous casting process of sprue 1 uses the conventional continuous casting process (that is, the distance between the upper and lower rollers is fixed, and the taper of the distance between the rollers is less than 2mm/m) to produce the steel blank to be tested; casting Daojiyuki The continuous casting process is a continuous casting process with heavy reduction (that is, the pressing roller step uses heavy reduction technology. In other words, the pressure roller can move and press the shell, and the reduction of a single roller is more than 4mm ).

Please refer to FIG. 4, which is a graph showing the variation of the total area where the bottom wave strength of steel blanks of different processes according to an embodiment of the present invention is less than 20%. Both sprues produce three furnaces (Heat 1, Heat 2 and Heat 3). A test piece (Slab) is taken for each furnace of the sprue, two of which are taken from the second furnace and one for the rest, a total of four steel blanks are taken for inspection and comparison. The second sprue also takes test pieces for each furnace, but two pieces are taken for the first and third furnaces, and one piece is taken for the second furnace, for a total of five specimens.

According to the foregoing description, since the sprue 1 uses traditional technology without additional pressure on the shell of the semi-condensed steel blank, the steel blank produced by the sprue 1 is more likely to have hollow defects. The pressure roller of the second runner will put a heavy pressure on the shell, so those with ordinary knowledge in the technical field to which this case belongs can expect that the hollow defect of the steel blank produced by the second runner will be effectively eliminated.

According to the change in the total area where the bottom wave strength is less than 20% in Figure 4, it can be seen that the total area where the bottom wave strength of the steel billet is less than 20% of the sprue 1 is greater than 45 square mm, but the sprue 2 is made The total area of the resulting steel billet with a bottom wave strength of less than 20% is less than 1.5 square millimeters. It should be noted that since the heavy pressure in the embodiment in Figure 4 is static heavy pressure, and the third furnace in Figure 4 is the finishing furnace, Slab 3 and Slab 4 are the last two finishing embryos. Due to the advancement of the liquid center position in the finishing stage, the metallurgical effect under heavy pressure is attenuated. Therefore, the total area of the bottom wave strength of the two steel blanks in the last section is less than 20%, especially the last one (ie Slab 4).

Accordingly, the core density detection method of the present invention can effectively and quickly detect the hollow defects in the core of the steel blank, and can improve the continuous casting process of the steel blank, thereby reducing the hollow defects of the steel blank, and Improve the quality of the produced steel blanks.

According to the foregoing description, the method for detecting the density of the core of the steel blank of the present invention can accurately and non-destructively detect the hollow defect in the core of the test piece, and can detect the density of the core, and then According to improve the process of steel billet.

Although the present invention has been disclosed as above in the embodiments, it is not intended to limit the present invention. Anyone with ordinary knowledge in the technical field to which the present invention belongs can make various changes without departing from the spirit and scope of the present invention. Retouching, therefore, the protection scope of the present invention shall be subject to the scope defined in the appended patent application.

100‧‧‧Method

110/121/123/130‧‧‧Operation

120‧‧‧Testing process

Claims (9)

A method for detecting the density of the core of a steel billet includes: providing a steel billet test piece and subjecting the steel billet test piece to a surface processing process; after performing the surface processing process, performing a surface processing process on the steel billet test piece A detection process, wherein the detection process includes: respectively transmitting an ultrasonic wave to a plurality of detection positions of a cross section of the steel blank test piece; and detecting an echo signal of a bottom wave of each of the detection positions To obtain a C-scan image of a cross-section at a depth below the cross-sectional plane, wherein the C-scan image has a gradation distribution corresponding to a plurality of intensity values of the echo signal, The intensity values are 0% to 100%, and the cross section is parallel to the cross section; and according to the C-scan image, the core density of the steel blank test piece is judged, wherein the color gradation distribution corresponds to the intensity value Less than 40% of an area has a hollow defect. The method for detecting the density of the core of a steel blank as described in item 1 of the scope of patent application, wherein the depth is not more than 15 mm. The method for detecting the density of the core of the steel blank as described in item 1 of the scope of patent application, wherein one of the steel blank test pieces has a thickness of 10 mm to 50 mm. For example, the method for detecting the density of the core of the steel blank described in item 1 of the scope of patent application, before the operation of providing the steel blank test piece, the detection method further includes: performing a continuous casting process to obtain a steel blank And performing a cutting process on the steel blank to form the steel blank test piece, wherein a cutting direction of the cutting process is perpendicular to a continuous casting direction of the continuous casting process. The method for detecting the density of the core of the steel blank as described in item 4 of the scope of patent application, wherein one of the emission directions of the ultrasonic waves is parallel to the continuous casting direction. According to the method for detecting the density of the core of the steel blank as described in item 1 of the patent application, a focal point of the ultrasonic wave is located at an intermediate position of a thickness of the steel blank test piece. According to the method for detecting the density of the core of the steel blank as described in item 1 of the scope of patent application, one of the frequencies of the ultrasonic wave is 10MHz to 20MHz. The method for detecting the density of the core of a steel blank as described in item 1 of the scope of patent application, wherein the detection process is performed by a water-immersion ultrasonic wave. According to the method for detecting the density of the core of the steel blank as described in the first item of the patent application, the hollow defect includes a pore defect, a shrinkage defect and/or a micro shrinkage defect.

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