Steel crack opening method
By using metallographic sample preparation and wire cutting equipment, the problem of steel cracks less than 1 mm deep was solved, enabling high-quality observation of crack surfaces and ensuring the comprehensiveness of test data.
Patent Information
- Application Number
- CN202511694696.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-18
- Publication Date
- 2026-02-13
AI Technical Summary
Existing technologies are insufficient to effectively open steel cracks less than 1 mm deep, which leads to inconvenience in subsequent crack surface testing.
The process involves metallographic sample preparation, wire cutting, cryogenic liquid nitrogen treatment, and ultrasonic cleaning to ensure reliable opening and observation of cracked samples.
It has achieved reliable opening of steel cracks with a depth of less than 1 mm, providing high-quality test data to meet the needs of scientific research and precision inspection.
Smart Images
Figure CN121521918A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of material analysis, and relates to a steel crack opening method. BACKGROUND
[0002] In the production process of steel materials, cracks are usually generated. After the steel material appears crack defects, the use of the product is damaged. For different types of crack information, the crack formation mechanism is different, which is the result of the comprehensive action of mechanical factors and metallurgical characteristics in the formation process. Sometimes, in order to take more effective measures to prevent cracks, the causes of the cracks need to be clarified, so that the cracks need to be further opened for analysis, and the crack surface is observed to provide a hair-like crack under a microscope.
[0003] At present, the micron-level crack is difficult to open. Generally, the crack with a depth of more than 5 mm is easy to open, and the crack with a depth of less than 1 mm is difficult to open, which brings inconvenience for subsequent crack surface testing. SUMMARY
[0004] To solve the above technical problems, the application provides a steel crack opening method, so as to realize the opening of a crack sample and display the crack surface, solve the problem that the crack surface of the sample cannot be tested, and ensure the comprehensiveness of the test data.
[0005] The technical scheme adopted by the application is a steel crack opening method, comprising the following steps:
[0006] S1: preparing a metallographic sample, observing the crack size and morphology, and recording the crack with a depth of less than 1 mm and in a hair-like shape;
[0007] S2: marking the crack position, marking the crack observed in S1 in the region and ensuring that the marked part is more than 5 mm away from the crack;
[0008] S3: cutting the marked region in S2 by using a wire cutting device to ensure that the mark is exposed after cutting;
[0009] S4: placing the sample cut in S3 in liquid nitrogen at-196 DEG C, clamping out the sample with tweezers after standing for 5 minutes, fixing one end of the sample on a suitable clamp, using pliers to take the crack as a crack source, then gently prying the crack along the crack propagation direction with the pliers, placing the cracked surface upward in alcohol for 5 minutes of ultrasonic cleaning, taking out the sample, and blowing dry with a hair dryer;
[0010] S5: after blowing dry, placing the sample cracked surface upward in a scanning electron microscope for observation.
[0011] Further, the step of preparing the metallographic sample comprises:
[0012] Sampling: select the effective part of the analyzed material or part to represent the overall state of the cutting;
[0013] Grinding and rough grinding: on the coarse-grained metallographic sandpaper, each time the sandpaper is changed, the grinding mark generated by the previous sandpaper needs to be completely removed, and the sample moving direction is perpendicular to the previous grinding mark direction;
[0014] Fine grinding: using manual grinding or automatic grinding method;
[0015] Polishing: using mechanical polishing method, on the rotating disc covered with polishing cloth, and using polishing agent;
[0016] Coarse polishing: using alumina suspension to quickly remove the grinding mark;
[0017] Fine polishing: using finer polishing agent to finally eliminate small scratches and obtain mirror surface.
[0018] Further, the cutting uses a metallographic special cutting machine equipped with water-based cooling liquid.
[0019] Further, the coarse-grained metallographic sandpaper is 180# to 360#.
[0020] Further, fine grinding uses manual grinding method, and finer number of water sandpaper is used in turn, and each time the sandpaper is changed, the sample is rotated 90° and cooled with water.
[0021] Further, fine grinding uses an automatic grinding and polishing machine.
[0022] Further, the wire cutting equipment in S3 cuts the marked area in S2 according to the following steps:
[0023] Check the verticality of the electrode wire, turn on the wire running switch, and check whether the electrode wire is shaking;
[0024] Before processing, simulate the processing and check the program to ensure that it is correct before formal processing and cutting;
[0025] According to the selected coordinate direction and the cutting point of the processing program, fix the sample in the appropriate position, avoid the crack surface area that needs to be reserved, avoid the key area and the clear analysis surface when clamping the sample, and set the lead-in line and the exit line on the non-key area or the part that can be discarded later;
[0026] Check whether the working liquid is full;
[0027] Turn on the power and let the machine preheat for 20-30 minutes;
[0028] Turn on the cooling pump, the wire electrode, and input the program, and run for 10 minutes before processing;
[0029] Processing in turn opens the wire, the pump, the pulse power switch, the processing key;
[0030] After processing, first turn off the pulse power and the stepping power, and then turn off the machine tool liquid pump and the wire barrel.
[0031] The beneficial effects of the present application are: the present application cuts the sample with cracks through the wire cutting equipment, and processes the cut sample, so as to realize the purpose of opening one crack sample and showing the crack surface, solve the problem that the crack surface of the sample cannot be tested, and ensure the comprehensiveness of the test data. Through the above strict process control, a "steel material opened crack surface" with minimal damage, high quality and sufficient for scientific research and precision inspection can be provided. BRIEF DESCRIPTION OF DRAWINGS
[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.
[0033] Figure 1 is the scanning electron microscope graph of the opened crack provided by the embodiment 1 of the present application;
[0034] Figure 2 is the scanning electron microscope graph of the opened crack provided by the embodiment 2 of the present application;
[0035] Figure 3 is the scanning electron microscope graph of the opened crack provided by the comparative example 1 of the present application;
[0036] Figure 4 is the scanning electron microscope graph of the opened crack provided by the comparative example 2 of the present application;
[0037] Figure 5 is the scanning electron microscope graph of the opened crack provided by the comparative example 3 of the present application. DETAILED DESCRIPTION
[0038] In order to facilitate the understanding of those skilled in the art, the present application will be further described below in combination with the embodiments and drawings. The content mentioned in the embodiments is not a limitation of the present application.
[0039] A steel crack opening method, comprising the following steps:
[0040] S1: metallographic sample preparation, observing crack size and morphology, recording the cracks with a depth of less than 1mm and in the form of hair;
[0041] Specifically, the metallographic sample preparation step is as follows:
[0042] Sampling: Select the effective part of the material or part to be analyzed to represent the overall state of the material or part. The cutting is done using a metallographic cutting machine equipped with a cooling liquid such as water-based cooling liquid to prevent the sample from changing its structure due to overheating. Common cutting methods include abrasive wheel cutting and wire cutting. Pay attention to the cutting process, which should be slow and smooth to ensure sufficient cooling and avoid sample burning, and to preserve the true state of the part or material to be analyzed.
[0043] Flat grinding and rough grinding: Remove the deep damage and deformation layer caused by sampling to obtain a relatively flat surface. Usually done on a coarse-grained (such as 180# to 360#) metallographic sandpaper. Each time a new sandpaper is used, the scratches on the previous sandpaper must be completely removed, and the sample should be rotated 90° to observe the scratch removal.
[0044] Fine grinding: Gradually eliminate the deep scratches left by rough grinding to prepare for polishing. Use manual grinding methods, and use finer-grained water sandpaper (such as 400#, 600#, 1000#, 2000#) in sequence. Similarly, each time a new sandpaper is used, the sample should be rotated 90° and cooled with water.
[0045] Or use automatic grinding methods, use automatic grinding and polishing machines, which are efficient and have good reproducibility.
[0046] Polishing: Remove the fine scratches left after fine grinding to obtain a scratch-free, smooth, mirror-like observation surface, which is the most critical and skillful step in the preparation process. Use mechanical polishing methods on a rotating disc covered with polishing cloth and use polishing agents (polishing liquid).
[0047] Coarse polishing: Use an aluminum oxide suspension to quickly remove scratches.
[0048] Fine polishing: Use finer polishing agents to finally eliminate micro-scratches and obtain a mirror surface. Pay attention to applying appropriate pressure during polishing and keeping the sample clean to prevent contamination by different particle sizes of abrasive.
[0049] S2: Mark the crack location, mark the crack observed in S1 in the area, and ensure that the marked area is at least 5 mm away from the crack;
[0050] S3: Use a wire cutting device to cut the marked area in S2, and ensure that the cut exposes the mark;
[0051] Specifically, the cutting is operated according to the following steps:
[0052] When winding, ensure that the electrode wire has a certain pre-tightening force to reduce the vibration amplitude of the wire electrode during processing and improve the processing accuracy. Check and adjust the electrode wire perpendicularity, turn on the wire running switch, and check whether the electrode wire is shaking.
[0053] Before processing, simulate the operation and check the program to make sure it is correct. Fix the sample in the right position according to the coordinate direction and starting point selected in the processing program. The sample must be fixed firmly and stably to prevent it from moving or deforming during processing. The clamping position should avoid the crack surface area that needs to be reserved. Pay attention to avoid the key area, clear analysis surface, lead-in line and exit line when clamping the sample. Set the lead-in line and exit line in the non-key area or the part that can be discarded later. Make sure the processing sample is within the travel range to prevent collision with the wire rack and damage to the rotating parts such as screw rod and nut. Confirm the clamping position with the operator to ensure that important marks and crack surfaces are not damaged.
[0054] Check if the working fluid is full to ensure that there is no lack of working fluid during processing, which may cause wire breakage.
[0055] Turn on the power and let the machine preheat for 20-30 minutes.
[0056] During the EDM sample processing, the working fluid must fully surround the electrode wire to prevent wire breakage caused by heat generated by the electrode wire passing through the large pulse current.
[0057] Turn on the cooling pump, wire electrode, and input program. After 10 minutes of idling, the processing can begin.
[0058] Turn on the wire, water pump, pulse power switch, and processing key in sequence. Adjust the pulse width, interval, frequency modulation, and other parameters according to the material, thickness, and processing accuracy.
[0059] Do not touch the sample and workbench simultaneously during processing to prevent electric shock.
[0060] Carefully observe the electrical processing values during processing to prevent wire breakage, short circuits, and insufficient working fluid. If wire breakage occurs more than three times, check if the machine tool wire guide and conductive block are jammed to ensure the normal operation of the machine tool, tools, and sample processing quality.
[0061] Turn on / off the pulse power and step power before and after processing, and then turn on / off the machine tool liquid pump and wire drum.
[0062] If the working fluid circulation system is blocked, it should be unblocked in time. Pay special attention to prevent working fluid from seeping into the machine tool and causing electrical failure.
[0063] Clean the entire work area after processing is complete.
[0064] S4: opening the crack; after cutting in S3, the sample was placed in liquid nitrogen at -196°C, and after 5 minutes, it was taken out with tweezers. One end of the sample was fixed on a suitable clamp, which must be firm and stable to prevent the sample from moving or deforming during clamping. The clamping position should avoid the area of the crack surface that needs to be retained. When clamping the sample, attention should be paid to avoiding the marked key area and the clear analysis surface. The other end was gripped with pliers, taking the crack as the crack source. Then the crack was gently pried open along the crack propagation direction with pliers. The open crack surface was immersed in alcohol, and ultrasonic cleaning was performed for 5 minutes. The sample was taken out and dried with a hair dryer;
[0065] S5: after drying, the sample was placed crack surface up in a scanning electron microscope for observation.
[0066] The following examples are further described.
[0067] Example 1:
[0068] This example relates to opening a crack with a depth of 100 microns or less, and the steps are as follows:
[0069] S1: metallographic sample preparation, observing the crack size and morphology, and recording the cracks with a depth of 100 microns or less and a hair-like shape;
[0070] S2: marking the crack position, marking the cracks observed in S1 in the area, ensuring that the marked part is more than 5 mm away from the crack;
[0071] S3: linear cutting of the marked area in S2, ensuring that the mark is exposed after cutting;
[0072] S4: after cutting in S3, the sample was placed in liquid nitrogen at -196°C, and after 5 minutes, it was taken out with tweezers. One end of the sample was fixed on a suitable clamp, which must be firm and stable to prevent the sample from moving or deforming during clamping. The clamping position should avoid the area of the crack surface that needs to be retained. When clamping the sample, attention should be paid to avoiding the marked key area and the clear analysis surface. The other end was gripped with pliers, taking the crack as the crack source. Then the crack was gently pried open along the crack propagation direction with pliers. The open crack surface was immersed in alcohol, and ultrasonic cleaning was performed for 5 minutes. The sample was taken out and dried with a hair dryer;
[0073] S5: after drying, the sample was placed crack surface up in a scanning electron microscope for observation.
[0074] As shown in Figure 1 the crack opening surface is mainly quasi-cleavage and dimple morphology, with a large amount of MnS precipitation locally, with a size of 60 microns to 100 microns, and a small amount of NbTi precipitation locally, with a maximum size of 15 microns, which is a thermal crack generated during cutting.
[0075] Example 2:
[0076] This embodiment involves crack opening with a depth of less than 200 micrometers. The specific steps are as follows:
[0077] S1: Metallographic sample preparation, observation of crack size and morphology, and recording of cracks with a depth of less than 200 micrometers and hair-like appearance;
[0078] S2: Mark the location of the crack. Mark the crack observed in S1 in the area, ensuring that the marked part is more than 5 mm away from the crack;
[0079] S3: Perform line cutting on the marked area in S2 to ensure that the marking is exposed after cutting;
[0080] S4: Place the sample after S3 cutting in liquid nitrogen at -196℃ and let it stand for 5 minutes. Then, use tweezers to remove the sample and fix one end of the sample to a suitable clamp. It must be firm and stable to prevent the sample from moving or deforming during clamping. The clamping position should avoid the crack surface area that needs to be preserved. When clamping the sample, pay attention to avoiding the marked key areas and clearly defining the analytical surface. Use pliers to gently pry open the other end, taking the crack as the crack source. Then, use pliers to gently pry open the crack along the crack propagation direction. Immerse the cracked surface upward in alcohol and perform ultrasonic cleaning for 5 minutes. Remove the sample and dry it with a hair dryer.
[0081] S5: After drying, place the sample with the cracked side facing up in a scanning electron microscope for observation.
[0082] like Figure 2 As shown, the crack initiation site is mainly intergranular, while the propagation zone has quasi-cleavage and dimple morphology. There are a large number of NbTi precipitates in some areas, with a maximum size of 23 micrometers, which are thermal cracks generated during the cutting process.
[0083] Comparative Example 1:
[0084] This comparative example involves crack opening within a depth of 100 micrometers. The specific steps are as follows:
[0085] S1: Metallographic sample preparation, observation of crack size and morphology, and recording of cracks with a depth of more than 1000 micrometers and hair-like appearance;
[0086] S2: Mark the location of the crack. Mark the crack observed in S1 in the area, ensuring that the marked part is more than 5 mm away from the crack;
[0087] S3: Perform line cutting on the marked area in S2 to ensure that the marking is exposed after cutting;
[0088] S4: The sample after S3 cutting is placed in liquid nitrogen at -196°C, and after standing for 5 minutes, it is clamped out with tweezers. One end of the sample is fixed on a suitable clamp, which must be firm and stable to prevent the sample from moving or deforming during clamping. The clamping position should avoid the area of the crack surface that needs to be retained. When clamping the sample, attention should be paid to avoid the key areas marked and to clearly define the analysis surface. The other end is clamped with pliers, taking the crack as the crack source. Then the crack is gently pried open along the crack propagation direction with pliers, and the cracked surface is immersed in alcohol with the cracked surface facing up. Ultrasonic cleaning is performed for 30 minutes. The sample is taken out and dried with a hair dryer;
[0089] S5: After drying, the sample is placed in a scanning electron microscope with the cracked surface facing up for observation.
[0090] As shown in Figure 3 , because of ultrasonic cleaning for 30 minutes, the cracked surface of the crack has an over-washed appearance, and the crack initiation position near the surface cannot observe the true morphology.
[0091] Comparative Example 2:
[0092] This comparative example involves opening a crack with a depth of 100 microns or less. The specific steps are as follows:
[0093] S1: Metallographic sample preparation, observe the crack size and morphology, and record the cracks with a depth of 1000 microns or less and a hair-like shape;
[0094] S2: Mark the crack position. The cracks observed in S1 are marked in the area, ensuring that the marked part is more than 5 mm away from the crack;
[0095] S3: Linear cutting of the marked area in S2 to ensure that the mark is exposed after cutting;
[0096] S4: The sample after S3 cutting is placed in liquid nitrogen at -196°C, and after standing for 5 minutes, it is clamped out with tweezers. One end of the sample is fixed on a suitable clamp, which must be firm and stable to prevent the sample from moving or deforming during clamping. The clamping position should avoid the area of the crack surface that needs to be retained. When clamping the sample, attention should be paid to avoid the key areas marked and to clearly define the analysis surface. The other end is clamped with pliers, taking the crack as the crack source. Then the crack is gently pried open along the crack propagation direction with pliers, and the cracked surface is immersed in alcohol with the cracked surface facing up. Ultrasonic cleaning is performed for 5 minutes. The sample is taken out and dried with a hair dryer;
[0097] S5: After drying, the sample is placed in a scanning electron microscope with the cracked surface facing up for observation.
[0098] As shown in Figure 4 , because the crack is opened with the crack tip as the crack source, the cracked surface of the crack has a damaged and deformed appearance, and the crack initiation position near the surface cannot observe the true morphology.
[0099] Comparative Example 3:
[0100] The present comparative example relates to crack opening within a depth of 100 microns, and the specific steps are as follows:
[0101] S1: metallographic sample preparation, observation of crack size, morphology, and recording of cracks with a depth of 1000 microns or more and in the form of hair;
[0102] S2: marking the crack position, marking the cracks observed in S1 in the area, and ensuring that the marked part is more than 5 mm away from the crack;
[0103] S3: line cutting of the marked area in S2, and ensuring that the mark is exposed after cutting;
[0104] S4: directly fixing one end of the sample after cutting in S3 on a suitable clamp, which must be firm and stable to prevent the sample from moving or deforming during clamping, the clamping position should avoid the crack surface area that needs to be reserved, and the other end should be clamped with pliers, taking the crack as the crack source, then gently prying the crack along the crack propagation direction with pliers, if the crack cannot be opened, a greater bending force and tearing force need to be applied to open the crack, and the cracked surface is upward in alcohol for 5 minutes of ultrasonic cleaning, the sample is taken out and dried with a hair dryer;
[0105] S5: after drying, the sample is placed crack surface upward in a scanning electron microscope for observation.
[0106] As shown in Figure 5 , because the cut sample is not placed in liquid nitrogen, there is serious damage and deformation morphology on the crack opening surface, and the crack initiation position near the surface cannot observe the true morphology.
[0107] In summary, by using the technical scheme of the present application, crack opening within a depth of 100 microns can be achieved through strict process control, and the purpose of displaying the crack surface is achieved.
[0108] The above embodiment is a preferred implementation scheme of the present application, in addition to this, the present application can also be implemented in other ways, and any obvious replacement without departing from the technical scheme concept of the present application is within the protection scope of the present application.
[0109] In order to make the ordinary skilled in the art more conveniently understand the improvement of the present application over the prior art, some drawings and descriptions of the present application have been simplified, and some other elements have been omitted in the present application file for the sake of clarity, and the person skilled in the art should realize that these omitted elements can also constitute the content of the present application.
Claims
1. A method for opening cracks in steel, characterized in that, Includes the following steps: S1: Metallographic sample preparation, observation of crack size and morphology, and recording of cracks less than 1 mm in depth and hair-like in shape; S2: Mark the location of the crack. Mark the crack observed in S1 in the area and ensure that the marked part is more than 5 mm away from the crack; S3: Use a wire cutting device to wire cut the marked area in S2 to ensure that the mark is exposed after cutting; S4: After the sample is cut by S3, place it in liquid nitrogen at -196℃ and let it stand for 5 minutes. Then, take it out with tweezers, fix one end of the sample on a suitable fixture, and use pliers to gently pry open the other end along the crack direction, with the crack as the crack initiation point. Place the cracked side up in alcohol and perform ultrasonic cleaning for 5 minutes. Take out the sample and dry it with a hair dryer. S5: After drying, place the sample with the cracked side facing up in a scanning electron microscope for observation.
2. The method for opening cracks in steel as described in claim 1, characterized in that, The steps for preparing the metallographic sample include: Sampling: Select a valid part that can represent the overall state of the material or part being analyzed and cut it; Grinding and coarse grinding: This is done on coarse metallographic sandpaper. Each time you change sandpaper, you need to completely remove the grinding marks produced by the previous sandpaper. The direction of sample movement is perpendicular to the direction of the previous grinding marks. Fine grinding: using manual or automatic grinding methods; Polishing: Mechanical polishing is performed on a turntable covered with polishing cloth, using a polishing compound; Rough polishing: Uses an alumina suspension to quickly remove abrasion marks; Fine polishing: Using a finer polishing compound to ultimately eliminate minor scratches and achieve a mirror finish.
3. The method for opening cracks in steel as described in claim 2, characterized in that, The cutting is performed using a metallographic-specific cutting machine equipped with water-based coolant.
4. The method for opening cracks in steel as described in claim 3, characterized in that, The coarse-grained metallographic sandpaper is 180# to 360#.
5. The method for opening cracks in steel as described in claim 4, characterized in that, Fine grinding is done by hand, using progressively finer grit wet sandpaper. Each time a new grit of sandpaper is used, the sample is rotated 90° and cooled with water.
6. The method for opening cracks in steel as described in claim 4, characterized in that, Fine grinding is performed using an automatic grinding and polishing machine.
7. A method for opening cracks in steel as described in any one of claims 2-6, characterized in that, In step S3, the marked area in step S2 is wire-cut using a wire cutting device according to the following steps: Check and adjust the verticality of the electrode wire, turn on the wire feed switch, and check if the electrode wire vibrates. Before actual processing, simulate the processing and check that the program is correct before proceeding with the actual cutting. According to the coordinate direction and starting point selected by the processing program, fix the sample in a suitable position. Avoid the crack surface area that needs to be retained. Avoid the marked key areas and clearly defined analysis surfaces when clamping the sample. Set the lead-in line and exit line on non-critical areas or parts that can be discarded later. Check if the working fluid is full; Turn on the power and let the machine preheat for 20-30 minutes; Turn on the cooling pump, wire feed electrode, input the program, and run idle for 10 minutes before processing; The machining process involves sequentially turning on the wire feeder, water pump, pulse power switch, and machining key; After processing is completed, turn off the pulse power supply and stepper power supply first, then turn off the machine tool hydraulic pump and wire drum.