Thick slab surface crack detection method and system for controlling thickness of transient ferromagnetic layer

Abstract

The invention discloses a thick slab surface crack detection method for controlling the thickness of a transient ferromagnetic layer, which comprises the following steps of: controlling the thickness of the transient ferromagnetic layer by locally performing short-time water cooling on the surface of a continuous casting slab, performing magnetic saturation on the transient ferromagnetic layer, and detecting the leakage magnetic field intensity of the transient ferromagnetic layer by adopting a magneto-sensitive effect element. Signals are quantitatively analyzed, crack defects are found out, quantitative analysis results are given, and quantitative depth detection of the surface cracks of the continuous casting billet is achieved. The invention also discloses a thick slab surface crack detection system for controlling the thickness of the transient ferromagnetic layer. According to the method, the treatment efficiency of defective continuous casting billet products can be improved, deep processing energy waste can be reduced, the treatment time of qualified continuous casting billet products can be shortened to the maximum extent, and energy conservation and emission reduction in the technical field of steelmaking can be promoted.

Description

Technical Field

[0001] The invention relates to a steelmaking product quality detection technology, and more specifically, to a thick slab surface crack detection method and system for controlling the thickness of a transient ferromagnetic layer. Background Art

[0002] At present, under the guidance of the strategic goals of "carbon peak" and "carbon neutrality", the online detection of various defects of continuous casting billet products in the steelmaking stage, especially surface crack defects in the high temperature stage, has received more and more attention. Since the defects of continuous casting billets cannot be detected in the hot state, the hot charging and hot delivery of continuous casting billets and the development of related quality control technologies are seriously affected. Public information shows that this problem has not yet been effectively solved. At present, the quality of continuous casting billets cannot be tested in the hot state, and products with high requirements have to be cooled down for testing, which consumes a lot of energy and is still ongoing.

[0003] In order to prevent problems before they occur, after cracks initiate in the continuous casting billet, the crack defects will be cleaned to avoid greater quality accidents during the subsequent rolling process due to stress concentration at the crack tip. It can be seen that despite the limitations of high temperature conditions (different parts of the continuous casting billet have different temperatures, usually above 800°C), if the defects can be detected online, the energy required for reheating will be greatly saved.

[0004] Currently, for Figure 1 There has long been a lack of effective means for online detection of crack defects on the surface of continuous casting billets and quantitative evaluation of cracks. There is no relevant online detection technology and equipment products in China. Internationally, only Russia's ULTRAKRAFT company has a product called "EQUIPMENT FOR AUTOMATED ULTRASONIC TESTING OF SLABS". According to the technical introduction, this technology uses electromagnetic acoustic (EMAT) imaging detection method, which has a good detection effect within the side surface range of continuous casting billets.

[0005] Although there are many existing non-destructive testing methods, there are also many non-destructive testing technologies for detecting metal surface cracks, such as coloring, electromagnetic, ultrasonic, eddy current, and radiation. However, compared with the effects of application under normal temperature conditions, various methods will encounter one or another technical obstacle that can no longer be applied under high temperature and large-size continuous casting conditions. For this reason, it is necessary to study and design new, more economical and efficient non-destructive testing methods and equipment without affecting the production process of high-temperature continuous casting. The following are the main non-destructive testing methods that can be considered in detecting metal surface cracking defects, but they are not suitable for detecting surface cracks of high-temperature continuous casting billets:

[0006] 1) Magnetic particle testing: It is widely used in military industries and special equipment such as aerospace, metallurgical tools, machinery manufacturing, atomic energy, weapons, etc. It is one of the most popular and convenient routine tests. Magnetic particle testing is mostly used for semi-finished products and raw materials, and bars, billets, forgings, castings, etc. are widely used. However, due to the high temperature of more than 800°C at the moving roller stage of the continuous casting billet, the magnetic method fails to detect and the sample is difficult to approach, so the method is not feasible;

[0007] 2) X-ray nondestructive testing: Currently, there are mainly computer-aided imaging (CR), digital ray (DR), computer tomography (CT), Compton imaging, neutron detection and other methods, which can be used for conventional defect detection, material organization, structure, residual stress, component cumulative damage and precise measurement of dimensions, component life assessment, etc. Since X-ray flaw detection is mostly a penetration method, it is not suitable for large-volume samples such as continuous casting billets, and the high-temperature site space is limited, so it is very inconvenient to implement;

[0008] 3) Penetrant testing: It is widely used to detect surface opening defects of most non-absorbent materials, such as steel and non-ferrous metals. It is the earliest conventional testing method to be widely used. It can also perform a one-time comprehensive test on complex-shaped defects and is suitable for field environments. Penetrant testing is also the same as the magnetic powder method. It is ineffective for high temperatures of 800°C or above in the roller stage of continuous casting billets.

[0009] 4) Electromagnetic testing: In the early days, electromagnetic nondestructive testing mainly included eddy current testing and magnetic flux leakage testing, which are methods of defect detection and performance testing of materials and components based on changes in the electromagnetic properties of materials. The metal magnetic memory detection, pulse eddy current detection, AC magnetic field detection, current disturbance detection, Barkhausen noise detection and magnetoacoustic emission technology that were developed later all fall within the scope of electromagnetic testing. This method is suitable for defect detection within a limited depth range on the surface. However, like the magnetic powder method, for the high temperature of the continuous casting billet at the moving roller stage, which is as low as 800°C, it is already higher than the Curie temperature of steel, the ferromagnetism disappears, and the electromagnetic detection fails;

[0010] 5) Acoustic emission detection: also known as stress wave emission, it is the phenomenon (AE) that local sources in materials quickly release energy to produce transient elastic waves. Acoustic emission is a natural phenomenon that occurs at any time in nature. Acoustic emission detection technology can be used for online dynamic detection, but cannot be used to evaluate depth;

[0011] 6) Infrared detection: It is a technology that receives infrared rays emitted by an object and obtains its surface temperature distribution in the form of an image, reflecting the temperature conditions inside and outside the object being detected, thereby determining whether there are defects. It is especially valuable for detecting defects in non-metallic materials. This method is more suitable for surface detection of continuous casting billets at temperatures above 800°C, but it is difficult to detect the depth of surface crack defects;

[0012] 7) Laser detection: Since the advent of lasers in 1960, laser holography technology has been put into practical use. Laser detection is mainly divided into three types according to the imaging principle: laser holography, laser speckle interferometry, and laser staggered speckle interferometry. The reasons for the inapplicability of laser holography are the same as above.

[0013] 8) Ultrasonic testing: There are many types of methods. Conventional ultrasonic testing is mainly aimed at discovering defects and evaluating them. Ultrasonic technologies that have made significant progress in recent years include: phased array technology, TOFT technology, laser ultrasonic technology, electromagnetic ultrasonic detection technology, ultrasonic guided wave detection technology, nonlinear ultrasonic technology, etc., and full consideration needs to be given to the on-site adaptability of detection methods and equipment. At present, existing ultrasonic high-temperature probes can be used for working conditions above 500°C, and there is still a gap from being used for high-temperature continuous casting billets above 800°C. At present, domestic technicians have used the EMAT method to conduct research and attempts on high-temperature continuous casting billets. Technical data shows that only Russia has commercial technology products.

[0014] In summary, under the current working conditions of high-temperature continuous casting billets, there is no ready-made detection technology for surface crack defects in this high-temperature product stage in the steelmaking field. Summary of the invention

[0015] In view of the defects existing in the prior art, the purpose of the present invention is to provide a method and system for detecting surface cracks in thick slabs by controlling the thickness of the transient ferromagnetic layer, which can improve the processing efficiency of problematic continuous casting products and reduce energy waste in deep processing, shorten the processing time of qualified continuous casting products to the greatest extent, and promote energy conservation and emission reduction in the field of steelmaking technology.

[0016] To achieve the above object, the present invention adopts the following technical solution:

[0017] The first aspect of the present invention provides a method for detecting surface cracks in thick slabs by controlling the thickness of a transient ferromagnetic layer:

[0018] The thickness of the transient ferromagnetic layer is controlled by short-term local water cooling on the surface of the continuous casting billet, and the transient ferromagnetic layer is magnetically saturated. A magneto-sensitive effect element is used to detect the leakage magnetic field intensity of the transient ferromagnetic layer, and the signal is quantitatively analyzed to detect crack defects and provide quantitative analysis results, thereby realizing quantitative depth detection of surface cracks in the continuous casting billet.

[0019] Preferably, the thick slab surface crack detection method specifically comprises the following steps:

[0020] S1. Positioning a continuous casting billet surface crack defect detection device at a starting point space position above the detection surface of the continuous casting billet;

[0021] S2, the water jet device of the continuous casting billet surface crack defect detection device sprays cooling water at the crack position on the surface of the continuous casting billet to form the transient ferromagnetic layer with controlled thickness;

[0022] S3, the magnetizing device of the continuous casting billet surface crack defect detection device magnetizes the transient ferromagnetic layer to form a leakage flux;

[0023] S4, the magnetosensitive effect element of the continuous casting billet surface crack defect detection device emits a magnetosensitive effect probe eddy current signal which is modulated by the leakage magnetic flux of the crack in the transient ferromagnetic layer;

[0024] S5. Establishing a relationship between the eddy current signal of the magnetic sensitive effect probe and the depth of the surface crack according to the influence of the density of the leakage magnetic flux;

[0025] S6. Determine the surface crack depth according to the relationship between the eddy current signal of the magnetic sensitive effect probe and the surface crack depth.

[0026] Preferably, the operation time of the magnetizing device is less than 1 second;

[0027] The magnetic field strength is greater than 3000mT;

[0028] The saturation value of the magnetic field strength is greater than 80%.

[0029] Preferably, the relationship between the eddy current signal of the magnetic sensitive effect probe and the surface crack depth is as follows:

[0030] Ф=A·d

[0031] Where Ф is the leakage flux, A is the coefficient, and d is the crack depth.

[0032] A second aspect of the present invention provides a thick slab surface crack detection system for controlling the thickness of a transient ferromagnetic layer, comprising:

[0033] A water jet device sprays cooling water on the surface cracks of the continuous casting billet to form a transient ferromagnetic layer of controlled thickness;

[0034] A magnetizing device, which magnetizes the transient ferromagnetic layer to form a leakage flux;

[0035] A magnetosensitive effect element emits a magnetosensitive effect probe eddy current signal, wherein the magnetosensitive effect probe eddy current signal is modulated by the leakage magnetic flux and establishes a relationship with the surface crack depth;

[0036] The thick slab surface crack detection system realizes the thick slab surface crack detection method for controlling the thickness of the transient ferromagnetic layer provided in the second aspect of the present invention.

[0037] The present invention provides a method and system for detecting surface cracks in thick slabs for controlling the thickness of transient ferromagnetic layers. The method controls the thickness of transient ferromagnetic layers by local short-term water cooling, and cooperates with the rapid magnetic saturation of the surface ferromagnetic layer, and uses a magnetic sensitive effect element to detect the leakage magnetic field intensity at a long distance, which is used for quantitative depth detection of surface cracks in high-temperature continuous casting slabs. Carry out research on detection technology for surface cracks in high-temperature continuous casting slabs, promote the development of quality control technology and equipment related to continuous casting slabs, improve the processing efficiency of problem continuous casting slab products and the energy waste of deep processing, minimize the processing time of qualified continuous casting slab products, and promote energy conservation and emission reduction in the field of steelmaking technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of surface cracks appearing on a continuous casting billet at room temperature;

[0039] Figure 2 It is a schematic diagram of the process of the thick slab surface crack detection method of the present invention;

[0040] Figure 3 It is a schematic structural diagram of a thick slab surface crack detection system of the present invention;

[0041] Figure 4 It is a schematic diagram of the operation of the water jet device in the thick slab surface crack detection system of the present invention;

[0042] Figure 5 It is a schematic diagram of the operation of the magnetization device in the thick slab surface crack detection system of the present invention;

[0043] Figure 6 It is a schematic diagram of the operation of the magnetic sensitive effect element in the thick slab surface crack detection system of the present invention;

[0044] Figure 7 It is a curve diagram showing the relationship between leakage magnetic field and magnetization degree of steel;

[0045] Figure 8 It is a curve diagram showing the relationship between leakage magnetic field and crack defect depth. DETAILED DESCRIPTION

[0046] In order to better understand the above technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0047] Considering the actual working condition of the continuous casting billet at a minimum temperature of more than 800°C in the moving roller stage, the present invention provides a thick slab surface crack detection method for controlling the thickness of the transient ferromagnetic layer as follows:

[0048] The thickness of the transient ferromagnetic layer is controlled by short-term local water cooling on the surface of the continuous casting billet, and the transient ferromagnetic layer is magnetically saturated. The leakage magnetic field intensity of the transient ferromagnetic layer is detected by a magnetosensitive effect element, and the signal is quantitatively analyzed to detect crack defects and give quantitative analysis results, thereby realizing quantitative depth detection of surface cracks in the continuous casting billet.

[0049] Combination Figure 2 As shown, the thick slab surface crack detection method of the present invention specifically comprises the following steps:

[0050] S1. Positioning a continuous casting billet surface crack defect detection device at a starting point space position above the detection surface of the continuous casting billet;

[0051] S2. The water jet device of the continuous casting billet surface crack defect detection device sprays cooling water at the crack position on the surface of the continuous casting billet to form a transient ferromagnetic layer of controlled thickness;

[0052] S3, the magnetizing device of the continuous casting billet surface crack defect detection device magnetizes the transient ferromagnetic layer to form a leakage flux;

[0053] S4, the magnetosensitive effect element of the continuous casting billet surface crack defect detection device emits a magnetosensitive effect probe eddy current signal which is modulated by the leakage magnetic flux of the crack in the transient ferromagnetic layer;

[0054] S5. According to the influence of the density of leakage magnetic flux on the eddy current signal of the magnetic sensitive effect probe, the relationship between the eddy current signal and the depth of the surface crack is established;

[0055] S6. Determine the surface crack depth based on the relationship between the eddy current signal of the magnetic sensitive effect probe and the surface crack depth.

[0056] Combination Figure 3 As shown, the thick slab surface crack detection system 100 for controlling the thickness of the transient ferromagnetic layer provided by the present invention can realize the relative position fixation of the functional components of the thick slab surface crack detection method of the present invention during detection, forming the overall functional arrangement of the thick slab surface crack detection method of the present invention. After the detection starts, the thick slab surface crack detection system of the present invention moves as a whole in a direction that can cover the surface of the continuous casting slab 200 that needs to be detected at a set reasonable speed. During the movement, scanning detection is performed, and when the covering movement above the surface of the continuous casting slab 200 that needs to be detected is completed, the surface crack defect detection task at this position is also completed.

[0057] Combination Figure 4As shown, during the scanning movement, the water jet device 1 sprays water on a certain area on the surface of the continuous casting billet 100, so that the position obtains a transient water cooling effect. At the same time, at the position of the water jet device 1, the surface material of the continuous casting billet 100 can be instantly restored to a ferromagnetic state (equivalent to the state after complete demagnetization). By controlling the cooling effect, the base material within a certain thickness range of the surface layer of the continuous casting billet 100 is below the Curie point temperature within a short time range (about 2 seconds), so that the material layer can restore ferromagnetism, which is convenient for non-destructive testing using magnetic methods. In this way, the thickness of the transient ferromagnetic layer 300 depends on the water volume, water speed, and movement speed controlled by the water jet device 1, and its purpose is to produce a transient ferromagnetic layer 300 of stable thickness in the detected surface area of ​​the continuous casting billet 200.

[0058] The water jet device 1 starts to operate. When the water column with designed flow rate and flow velocity continuously acts on the surface of the detection position of the continuous casting billet 200, a transient, stable ferromagnetic layer with a certain thickness can be established on the surface of the position within the designed time (time <1 second, determined by the minimum time required to establish the set transient ferromagnetic layer 300 thickness and the minimized jet flow). The thickness can be designed and determined according to actual needs. Of course, the thickness is achieved by controlling the parameters of the water jet.

[0059] The water volume, water velocity and movement speed of the water jet device 1 are mainly based on the experimental results, and can quickly cool the surface and be below the Curie temperature at a certain depth to provide enough time for the test. However, water cannot be sprayed excessively and quickly, so as not to have a negative impact on the on-site production environment, so there will be a more practical range of values, which is determined by the actual design situation.

[0060] Combination Figure 5 As shown, the magnetizing device 2 of the thick slab surface crack detection system 100 magnetizes the cracks in the transient ferromagnetic layer at the cracked position to form a leakage flux. Because the thick slab surface crack detection system 100 moves at a set speed, after the transient ferromagnetic layer 300 is established, the magnetizing device 2 of the thick slab surface crack detection system 100 immediately moves to the transient ferromagnetic layer 300 (such as Figure 5 As shown, time <1 second), the transient ferromagnetic layer 300 at this position is saturated magnetized, and the magnetization device 2 has a sufficiently strong magnetic field strength (>3000mT) so that the magnetic induction intensity of the surface steel material reaches more than 80% of the saturation value, so as to form a maximum leakage flux density at the crack when there is a surface crack. This is based on Figure 7 The law of leakage magnetic field and magnetization degree of steel shown in the figure shows that since the size of the leakage magnetic field of the defect is related to the magnetization degree of the workpiece, the experimental results show that, generally speaking, when the magnetic induction intensity of the steel reaches about 80% of the saturation value, the leakage magnetic field will increase rapidly.

[0061] Combination Figure 6 As shown, the eddy current signal of the magneto-sensitive effect probe 3 of the thick slab surface crack detection system 100 is modulated by the leakage flux of the crack in the transient ferromagnetic layer. During the movement, the magnetosensitive effect probe 3 of the thick slab surface crack detection system 100 immediately scans the position area where the transient ferromagnetic layer 300 has just completed saturation magnetization. The magnetosensitive effect probe 3 has established a stable alternating eddy current field around the probe (according to electromagnetic induction, that is, the same alternating magnetic field exists). When there are no cracks on the surface of the continuous casting billet 200, there is no leakage flux on the surface of the transient ferromagnetic layer 300, and there will be no modulation effect on the stable alternating eddy current field that already exists in the magnetosensitive effect probe 3. In the eddy current signal, the amplitude and phase of the eddy current vector signal remain unchanged; when there are cracks on the surface of the continuous casting billet 200, leakage flux will be formed on the surface of the transient ferromagnetic layer 300 at the crack. There are differences in the density of the leakage flux, which produces a modulation effect with different strengths on the stable alternating eddy current field around the magnetosensitive effect probe 3. In the eddy current signal, the amplitude and phase of the eddy current vector signal have changed significantly. The greater the leakage flux density, the more obvious the modulation effect, and the greater the changes in amplitude and phase. According to Figure 8 The existing relationship between leakage magnetic flux density and crack defect depth, combined with the amplitude and phase changes of the above-mentioned eddy current vector signal that reflect the size of the leakage magnetic flux density, has established a technical path for measuring the surface crack depth based on the amplitude and phase changes of the eddy current vector signal in the magnetosensitive effect probe in the present invention.

[0062] For surface defects of the same width, if the depth is different, the leakage magnetic field generated is also different. Within a certain range, the increase of leakage magnetic flux is almost linearly related to the increase of defect depth. That is, the relationship between the eddy current signal of the magnetic sensitive effect probe and the surface crack depth is as follows:

[0063] Ф=A·d

[0064] Where Ф is the leakage flux, A is the coefficient (since there is no clear formula relationship between the leakage flux and the crack depth, the coefficient will vary with the crack shape and steel type, and the value range needs to be determined based on experiments), and d is the crack depth.

[0065] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present invention, and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A method for detecting surface cracks in thick slabs by controlling the thickness of a transient ferromagnetic layer, characterized in that: The thickness of the transient ferromagnetic layer is controlled by short-term local water cooling on the surface of the continuous casting billet, and the transient ferromagnetic layer is magnetically saturated. A magneto-sensitive effect element is used to detect the leakage magnetic field intensity of the transient ferromagnetic layer, and the signal is quantitatively analyzed to detect crack defects and provide quantitative analysis results, thereby realizing quantitative depth detection of surface cracks in the continuous casting billet.

2. The thick slab surface crack detection method for controlling the thickness of the transient ferromagnetic layer according to claim 1 is characterized in that: The thick slab surface crack detection method specifically comprises the following steps: S1. Positioning a continuous casting billet surface crack defect detection device at a starting point space position above the detection surface of the continuous casting billet; S2, the water jet device of the continuous casting billet surface crack defect detection device sprays cooling water at the crack position on the surface of the continuous casting billet to form the transient ferromagnetic layer with controlled thickness; S3, the magnetizing device of the continuous casting billet surface crack defect detection device magnetizes the transient ferromagnetic layer to form a leakage flux; S4, the magnetosensitive effect element of the continuous casting billet surface crack defect detection device emits a magnetosensitive effect probe eddy current signal which is modulated by the leakage magnetic flux of the crack in the transient ferromagnetic layer; S5. Establishing a relationship between the eddy current signal of the magnetic sensitive effect probe and the depth of the surface crack according to the influence of the density of the leakage magnetic flux; S6. Determine the surface crack depth according to the relationship between the eddy current signal of the magnetic sensitive effect probe and the surface crack depth.

3. The thick slab surface crack detection method for controlling the thickness of the transient ferromagnetic layer according to claim 2 is characterized in that: The operation time of the magnetizing device is less than 1 second; The magnetic field strength is greater than 3000mT; The saturation value of the magnetic field strength is greater than 80%.

4. The thick slab surface crack detection method for controlling the thickness of the transient ferromagnetic layer according to claim 2 is characterized in that: The relationship between the eddy current signal of the magnetic sensitive effect probe and the surface crack depth is as follows: Ф=A·d Where Ф is the leakage flux, A is the coefficient, and d is the crack depth.

5. A thick slab surface crack detection system for controlling the thickness of the transient ferromagnetic layer, characterized in that: include: A water jet device sprays cooling water on the surface cracks of the continuous casting billet to form a transient ferromagnetic layer of controlled thickness; A magnetizing device, which magnetizes the transient ferromagnetic layer to form a leakage flux; A magnetosensitive effect element emits a magnetosensitive effect probe eddy current signal, wherein the magnetosensitive effect probe eddy current signal is modulated by the leakage magnetic flux and establishes a relationship with the surface crack depth; The thick slab surface crack detection system implements the thick slab surface crack detection method for controlling the thickness of the transient ferromagnetic layer as described in any one of claims 1-4.

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