Preparation method for positioning and intercepting metallographic specimen at non-joint defect position of steel plate flaw detection

Abstract

The invention relates to a method for positioning, cutting and preparing a metallographic specimen at a flaw detection incompatibility defect of a steel plate. The method comprises the following steps: 1) determining a flaw detection incompatibility center position; 2) cutting and segmenting a metallographic sample; (3) preparing a sample; and 4) performing metallographic microscopic observation and inspection. The flaw detection mismatching center position is determined through flaw detection positioning, the metallographic specimen is cut by taking the flaw detection mismatching center position as the center, a coloring agent is added to corrode the surface of the specimen after polishing, the segregation position is displayed, the flaw detection mismatching defect position can be accurately positioned, and the flaw detection mismatching reason is further analyzed.

Description

Technical Field

[0001] The invention relates to the technical field of microstructure analysis, characterization and detection, and in particular to a method for positioning, cutting and preparing a metallographic sample at a non-conforming defect of a steel plate during flaw detection. Background Art

[0002] As the service environment and technical requirements of steel plates become more and more stringent, users' requirements for steel plate quality are constantly increasing. In addition to requiring good surface quality and mechanical properties, they must also have good internal quality. Using ultrasonic flaw detectors to inspect steel plates can detect quality defects inside the steel plates. In the actual production process, the phenomenon of product re-judgment or scrapping due to unqualified flaw detection (abbreviated as flaw detection failure) often occurs, which to a certain extent affects the product delivery time and contract fulfillment rate.

[0003] For products that fail to meet the flaw detection criteria, ultrasonic flaw detectors can only locate the locations of quality defects inside them, but cannot determine the specific types of defects. Optical microscopes and scanning electron microscopes are required to observe and analyze the locations of steel plates that fail to meet the flaw detection criteria. Flaw detection failures caused by internal quality issues of steel plates are mainly of two types: cracks and inclusions. After flaw detection and positioning, inspection is required to determine the specific reasons for the failure.

[0004] At present, the commonly used method for preparing non-metallic phase samples for flaw detection is: cut the metallographic sample near the flaw detection non-conforming area, grind the cross section of the metallographic sample, and observe whether there are defects that may cause flaw detection non-conforming. If no defects are observed, continue to grind and polish the metallographic sample until they are found.

[0005] This conventional sampling and sample preparation method is inefficient. On the one hand, since the ultrasonic flaw detector has a relatively large probe, it can only locate the non-conforming area, and the specific location of the defect (the location of the accurate interception of the metallographic observation surface) is difficult to determine, and whether the defect can be observed quickly is somewhat accidental; on the other hand, if the non-conforming is caused by small stress cracks and small aggregated inclusions, it is difficult to observe in the metallographic sample and is easy to miss.

[0006] Therefore, it is necessary to address the problems of inaccurate positioning of metallographic specimens and easy missed detection of small defects. When conducting microscopic inspection of metallographic specimens, it is necessary to start from the sample preparation and innovate a new preparation method for positioning the inspection section of metallographic specimens and displaying small defects. Summary of the invention

[0007] The present invention provides a method for positioning, cutting and preparing a metallographic sample at a non-conforming defect of a steel plate. The non-conforming center position is determined by non-conforming positioning, and the metallographic sample is cut with the non-conforming center position as the center. After polishing, a colorant is added to etch the sample surface to display the segregation position. The non-conforming defect position can be accurately located and the cause of the non-conforming defect can be further analyzed.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for positioning, cutting and preparing a metallographic sample at a defective part of a steel plate for flaw detection comprises the following steps:

[0010] 1) Determine the non-center position of the flaw detection:

[0011] Use ultrasonic flaw detector to detect and analyze the size, direction and severity of defect distribution. For the non-conforming position that needs metallographic microscope inspection, select the highest point of the flaw detection amplitude curve to locate and mark it;

[0012] 2) Cutting and segmenting of metallographic samples:

[0013] According to the defect depth displayed by the ultrasonic flaw detector, the defect depth is taken as the thickness center of the metallographic sample to be cut, and the center of the mark in step 1) is taken as the center point to cut the metallographic sample; the metallographic sample is cut into 4 samples of the same size by a wire cutting machine;

[0014] 3) Preparation of samples:

[0015] The sample is corroded after pretreatment, which includes grinding and polishing. The polished surface of the sample is corroded with a colorant until the polished surface changes color. At this time, a segregation band visible to the naked eye will appear at the defect position, which is the location of the defect.

[0016] 4) Metallographic microscopic observation and inspection:

[0017] Place the defect location on the test surface of the sample at the center of the observation area of ​​the metallographic microscope stage, determine the defect type, and observe the morphology and distribution of the defect.

[0018] In the step 2), the side length of the cut metallographic sample is 2 to 6 cm, and the thickness is 1.5 to 3 cm; the cut sample is a cube with a side length of 1 to 3 cm.

[0019] In the step 3), the pretreatment process of the sample is: firstly, the wire cutting section of the sample is roughly ground with water sandpaper on a metallographic pre-grinding machine, and sandpaper from coarse to fine is selected and ground with water to remove the wire cutting interference layer; and then the ground sample surface is polished with a mechanical polishing machine.

[0020] In the step 4), the defect types include inclusions and cracks.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1) The center position of the non-conformity of the flaw detection is determined by flaw detection positioning, and the metallographic sample is cut with the center position of the non-conformity of the flaw detection as the center. After polishing, the surface of the sample is etched with a colorant to show the segregation position, which can accurately locate the defect position of the non-conformity of the flaw detection and further analyze the cause of the non-conformity of the flaw detection.

[0023] 2) Particularly suitable for thick hot-rolled steel plates. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1a FIG1 is a microscopic morphology of microcracks in a metallographic sample taken from a non-conforming portion of a steel plate detected in Example 1 of the present invention.

[0025] Figure 1b FIG2 is a microscopic morphology of microcracks in a metallographic sample taken from a non-conforming portion of a steel plate in accordance with Example 1 of the present invention.

[0026] Figure 2a FIG1 is a microscopic morphology of fine aggregated inclusions in a metallographic sample taken from a non-conforming portion of a steel plate subjected to flaw detection in Example 2 of the present invention.

[0027] Figure 2b FIG2 is a microscopic morphology of fine aggregated inclusions in a metallographic sample taken from a non-conforming portion of a steel plate subjected to flaw detection in Example 2 of the present invention. DETAILED DESCRIPTION

[0028] The method for positioning, cutting and preparing a metallographic sample at a non-conforming defect of a steel plate according to the present invention comprises the following steps:

[0029] 1) Determine the non-center position of the flaw detection:

[0030] Use ultrasonic flaw detector to detect and analyze the size, direction and severity of defect distribution. For the non-conforming position that needs metallographic microscope inspection, select the highest point of the flaw detection amplitude curve to locate and mark it;

[0031] 2) Cutting and segmenting of metallographic samples:

[0032] According to the defect depth displayed by the ultrasonic flaw detector, the defect depth is taken as the thickness center of the metallographic sample to be cut, and the center of the mark in step 1) is taken as the center point to cut the metallographic sample; the metallographic sample is cut into 4 samples of the same size by a wire cutting machine;

[0033] 3) Preparation of samples:

[0034] The sample is corroded after pretreatment, which includes grinding and polishing. The polished surface of the sample is corroded with a colorant until the polished surface changes color. At this time, a segregation band visible to the naked eye will appear at the defect position, which is the location of the defect.

[0035] 4) Metallographic microscopic observation and inspection:

[0036] Place the defect location on the test surface of the sample at the center of the observation area of ​​the metallographic microscope stage, determine the defect type, and observe the morphology and distribution of the defect.

[0037] In the step 2), the side length of the cut metallographic sample is 2 to 6 cm, and the thickness is 1.5 to 3 cm; the cut sample is a cube with a side length of 1 to 3 cm.

[0038] In the step 3), the pretreatment process of the sample is: firstly, the wire cutting section of the sample is roughly ground with water sandpaper on a metallographic pre-grinding machine, and sandpaper from coarse to fine is selected and ground with water to remove the wire cutting interference layer; and then the ground sample surface is polished with a mechanical polishing machine.

[0039] In the step 4), the defect types include inclusions and cracks.

[0040] In order to more intuitively embody the present invention, the embodiments of the present invention are further described in conjunction with examples. The following examples are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any technical solution that can be obviously obtained by a person skilled in the art within the technical scope disclosed in the present invention, including simple changes or equivalent replacements, is within the protection scope of the present invention.

[0041] [Example 1]

[0042] This embodiment adopts the method of the present invention to locate the non-conforming defects of 45mm thick Q355B steel plate and cut out metallographic samples for inspection. The specific process is as follows:

[0043] 1. Determine the non-center position of the flaw detection:

[0044] According to the test results of the ultrasonic flaw detector, the center point of the flaw detection is calibrated; from the flaw detection amplitude curve, the position where the defect is relatively serious is 22mm deep from the steel plate surface, and a circle with a diameter of 1cm is drawn on the steel plate surface corresponding to the center point of the flaw detection for calibration.

[0045] 2. Take metallographic specimens at the non-center position of the flaw detection:

[0046] Taking the marked non-conforming center point as the center, a metallographic sample with a side length of 4 cm and a thickness of 2 cm was cut at a depth of 21 to 23 mm (corresponding to the thickness of the metallographic sample) from the surface of the steel plate, and the metallographic sample was divided into 4 samples with a side length of 2 cm using a wire cutting machine.

[0047] 3. Grind and polish the sample, and use a positioning etchant to show the defect location:

[0048] (1) Use mechanical polishing to first coarsely grind the wire-cut section of the sample with water sandpaper on a metallographic pre-grinder to remove the wire-cut interference layer. Select sandpaper from coarse to fine and add water to grind until the finest sandpaper is polished; then use a mechanical polishing machine to polish the surface of the sample after grinding.

[0049] (2) Corrosion of the sample: Use a 2% sodium bicarbonate aqueous solution to corrode the polished surface of the sample until there is no obvious reflection on the polished surface. After corrosion, segregation bands visible to the naked eye will appear at locations with larger defects. The defect location can be quickly located under a metallographic microscope.

[0050] 4. Metallographic microscopic observation and inspection:

[0051] Place the defect position of the sample inspection surface at the center of the observation area of ​​the metallographic microscope stage, and then conduct metallographic microscopic observation and inspection. After inspection, micro cracks exist in the darker segregation zone on the sample surface, such as Figure 1a , Figure 1b shown.

[0052] [Example 2]

[0053] This embodiment uses the method of the present invention to locate the non-conforming defects of the 40mm thick AH32 steel plate and cut out the metallographic specimen for inspection. The specific process is as follows:

[0054] 1. Determine the non-center position of the flaw detection:

[0055] According to the test results of the ultrasonic flaw detector, the center point of the flaw detection is calibrated; from the flaw detection amplitude curve, the position where the defect is relatively serious is 19.5mm deep from the steel plate surface. A circle with a diameter of 1cm is drawn on the steel plate surface corresponding to the center point of the flaw detection for calibration.

[0056] 2. Take metallographic specimens at the non-center position of the flaw detection:

[0057] Taking the marked non-conforming center point as the center, a metallographic sample with a side length of 4 cm and a thickness of 2 cm was cut at a depth of 18.5 to 20.5 mm (corresponding to the thickness of the metallographic sample) from the surface of the steel plate, and the metallographic sample was divided into 4 samples with a side length of 2 cm using a wire cutting machine.

[0058] 3. Grind and polish the sample, and use a positioning etchant to show the defect location:

[0059] (1) Use mechanical polishing to first coarsely grind the wire-cut section of the sample with water sandpaper on a metallographic pre-grinder to remove the wire-cut interference layer. Select sandpaper from coarse to fine and add water to grind until the finest sandpaper is polished; then use a mechanical polishing machine to polish the surface of the sample after grinding.

[0060] (2) Corrosion of the sample: Use a 2% sodium bicarbonate aqueous solution to corrode the polished surface of the sample until there is no obvious reflection on the polished surface. After corrosion, segregation bands visible to the naked eye will appear at locations with larger defects. The defect location can be quickly located under a metallographic microscope.

[0061] 4. Metallographic microscopic observation and inspection:

[0062] After positioning the defect position of the sample inspection surface, place it at the center of the observation area of ​​the metallographic microscope stage, and then conduct metallographic microscopic observation and inspection. After inspection, it is found that there are small aggregated inclusions in the darker segregation band on the surface of the sample, such as Figure 2a , Figure 2b shown.

[0063] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for positioning, cutting and preparing metallographic samples at non-conforming defects of steel plates, characterized in that: The steps include: 1) Determine the non-center position of the flaw detection: Use ultrasonic flaw detector to detect and analyze the size, direction and severity of defect distribution. For the non-conforming position that needs metallographic microscope inspection, select the highest point of the flaw detection amplitude curve to locate and mark it; 2) Cutting and segmenting of metallographic samples: According to the defect depth displayed by the ultrasonic flaw detector, the defect depth is taken as the thickness center of the metallographic sample to be cut, and the center of the mark in step 1) is taken as the center point to cut the metallographic sample; the metallographic sample is cut into 4 samples of the same size by a wire cutting machine; 3) Preparation of samples: The sample is corroded after pretreatment, which includes grinding and polishing. The polished surface of the sample is corroded with a colorant until the polished surface changes color. At this time, a segregation band visible to the naked eye will appear at the defect position, which is the location of the defect. 4) Metallographic microscopic observation and inspection: Place the defect location on the test surface of the sample at the center of the observation area of ​​the metallographic microscope stage, determine the defect type, and observe the morphology and distribution of the defect.

2. The method for positioning, cutting and preparing metallographic samples at non-conforming defects of steel plates according to claim 1, characterized in that: In the step 2), the side length of the cut metallographic sample is 2 to 6 cm, and the thickness is 1.5 to 3 cm; the cut sample is a cube with a side length of 1 to 3 cm.

3. The method for positioning, cutting and preparing metallographic samples at non-conforming defects of steel plates according to claim 1, characterized in that: In the step 3), the pretreatment process of the sample is: firstly, the wire cutting section of the sample is roughly ground with water sandpaper on a metallographic pre-grinding machine, and sandpaper from coarse to fine is selected and ground with water to remove the wire cutting interference layer; and then the ground sample surface is polished with a mechanical polishing machine.

4. The method for positioning, cutting and preparing metallographic samples at non-conforming defects of steel plates according to claim 1, characterized in that: In the step 4), the defect types include inclusions and cracks.

Images