Method for reducing false alarm rate of magnetic flux leakage testing of bearing steel bar

Abstract

The present application relates to the technical field of nondestructive flaw detection of bars, and particularly to a method for reducing false alarm rate of magnetic flux leakage detection of bearing steel bars, which comprises the following steps in sequence: peeling and magnetic flux leakage detection; in the peeling step, the surface of the bar to be detected is peeled by using a multi-stage sand wheel combination to reduce the roughness of the surface of the bar to be detected, and a finished bar is obtained, and the multi-stage sand wheel combination adopts a three-stage layout of a coarse sand wheel, a fine sand wheel and a polishing sand wheel, wherein the roughness Ra of the surface of the finished bar is 2.8-3.7 microns. By limiting the roughness Ra of the surface of the finished bar to 2.8-3.7 microns, the false alarm rate in the magnetic flux leakage detection process of the bearing steel bar is significantly reduced, thereby improving the accuracy of the detection result, which effectively reduces unnecessary scrapping, downgrading or rework caused by misjudging qualified products as defective products, directly improves the yield of bearing steel products, and reduces waste loss and processing cost.

Description

Technical Field

[0001] This invention relates to the field of nondestructive testing technology for bars, and in particular to a method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars. Background Technology

[0002] Bearing steel is a key steel material used in the manufacture of balls, rollers, and bearing rings. It is widely used in automotive bearings, machinery bearings, and other fields. It possesses high and uniform hardness and wear resistance, as well as a high elastic limit, meeting the requirements of bearings under high-speed, high-load, and complex operating conditions. With the rapid development of my country's economy, the domestic and international automotive manufacturing industries are also progressing rapidly. Against this backdrop, the consumption and variety of automotive steel are increasing daily, and the requirements for steel surface quality are constantly rising. As one of the steel grades with the most stringent production standards among all steel products, bearing steel has extremely high requirements regarding the uniformity of its chemical composition, the content and distribution of non-metallic inclusions, the distribution of carbides, and surface quality.

[0003] Magnetic flux leakage (MFL) testing is currently a reliable non-destructive testing technology for bar stock surface quality. MFL testing refers to the application of magnetic flux leakage detection technology specifically used to detect, locate, and evaluate surface and near-surface discontinuities (i.e., "scratches") on workpieces (especially ferromagnetic materials). It is a method for detecting defects in ferromagnetic materials and their products, similar to magnetic particle testing (MPI). When a steel pipe or bar is magnetized to saturation using one or more magnetizers, defects present in the bar or pipe will generate leaking magnetic fields, magnetic lines of force, or magnetic flux (these are parameters describing the magnetic field). These are detected by magnetically sensitive elements or components, and the quantity of these leaked magnetic fields is then described to obtain the defect detection signal. However, bearing steel differs from other steels in microstructure, mechanical properties, and surface condition. This difference leads to higher surface noise during MFL testing, easily causing false alarms and seriously affecting the accuracy and reliability of defect detection. Effectively reducing noise interference caused by material characteristics remains a technical challenge for the industry.

[0004] To date, there are few reports on research into reducing false alarms during magnetic flux leakage testing of bearing steel bars. Therefore, developing a method to reduce the false alarm rate of magnetic flux leakage testing of bearing steel bars, thereby improving the accuracy of testing results and reducing unnecessary scrapping, downgrading, or rework caused by misjudging qualified products as defective products (false alarms), is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the aforementioned shortcomings in existing technologies, the present invention aims to provide a method for reducing the false alarm rate of magnetic flux leakage testing (MFLP) on bearing steel bars. This invention significantly reduces the false alarm rate during MFLP by limiting the surface roughness Ra of the finished bar to 2.8–3.7 μm, thereby improving the accuracy of the testing results. This effectively reduces unnecessary scrapping, downgrading, or rework caused by misclassifying qualified products as defective (false alarms), directly increasing the yield of bearing steel products and reducing scrap losses and processing costs.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars. The method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars includes the following steps in sequence: peeling and magnetic flux leakage testing. In the peeling process, a multi-stage grinding wheel combination is used to peel the surface of the bar to be tested in order to reduce the surface roughness of the bar and obtain the finished bar. The multi-stage grinding wheel combination adopts a three-stage layout of coarse grinding wheel, fine grinding wheel and polishing grinding wheel, wherein the surface roughness Ra of the finished bar is 2.8 to 3.7 μm.

[0007] Furthermore, the number of coarse grinding wheels is 9, the number of fine grinding wheels is 1, the number of polishing grinding wheels is 2, and the total number of coarse grinding wheels, fine grinding wheels and polishing grinding wheels is 12; And / or, the method of using a multi-stage grinding wheel combination to peel off the surface of the bar to be inspected includes: firstly, using the coarse grinding wheel to coarsely grind the surface of the bar to be inspected, secondly, using the fine grinding wheel to finely grind, and finally using the polishing wheel to polish. And / or, the coarse grinding wheel is a 16-18 mesh coarse grinding wheel, the fine grinding wheel is a 46-60 mesh fine grinding wheel, and the polishing grinding wheel includes a flap grinding wheel; And / or, in the peeling process, a multi-stage grinding wheel combination in the peeling machine is used to peel the surface of the bar to be inspected. The peeling machine includes 12 grinding wheels, the first to ninth grinding wheels are the coarse grinding wheels, the tenth grinding wheel is the fine grinding wheel, and the eleventh and twelfth grinding wheels are the polishing grinding wheels.

[0008] Furthermore, in the magnetic flux leakage testing process, an automated magnetic flux leakage testing machine is used for magnetic flux leakage testing. The filter in the automated magnetic flux leakage testing machine has a correction coefficient of 0 and a bandwidth of 2Hz.

[0009] Furthermore, the finished bar is a GCr15 bearing steel bar with a specification of Φ50~Φ130mm; And / or, the preparation method of the bar to be inspected includes the following steps in sequence: heating, descaling, rough rolling, continuous rolling, bar sizing and finishing rolling, and slow cooling.

[0010] Furthermore, in the heating process, the continuously cast billet is heated in a walking beam furnace. The heating is divided into four stages: a preheating stage, a first heating stage, a second heating stage, and a soaking stage. The temperature of the preheating stage is 300-650℃, the temperature of the first heating stage is 800-850℃, the temperature of the second heating stage is 1180-1200℃, and the temperature of the soaking stage is 1200-1210℃. And / or, in the descaling process, high-pressure water is used to remove the surface iron oxide scale, and the pressure of the high-pressure water is 20-30 MPa.

[0011] Furthermore, the continuously cast billet is a GCr15 continuously cast billet; And / or, in the heating process, the heating time of the preheating section is 100-240 min, the heating time of the first heating section is 120-270 min, the heating time of the second heating section is 150-300 min, and the heating time of the homogenization section is 120-360 min.

[0012] Furthermore, in the roughing process, the inlet temperature is 1100-1150℃, the number of roughing passes is 4-7, and the final rolling temperature is 950-1000℃.

[0013] Furthermore, the continuous rolling process includes an intermediate rolling process and a pre-finishing rolling process. After continuous rolling, a suitable material for entering the bar reduction and sizing mill is obtained. The inlet temperature of the intermediate rolling process is 900-950℃, the intermediate rolling passes are 5-7, and the final rolling temperature of the intermediate rolling process is 870-920℃. In the pre-finishing rolling process, the initial rolling temperature of the pre-finishing rolling process is 870-920℃, the final rolling temperature of the pre-finishing rolling process is 840-890℃, and the pre-finishing rolling passes are 2-4.

[0014] Furthermore, in the finishing rolling process of the bar reduction and sizing mill, the finishing rolling of the bar reduction and sizing mill is KOCKS rolling, with an initial rolling temperature of 830-880℃, a final rolling temperature of 800-850℃, and 3-6 rolling passes.

[0015] Furthermore, in the slow cooling process, the bars obtained after finishing rolling by the bar reduction and sizing mill are air-cooled on the cooling bed and then air-cooled on the lower cooling bed to room temperature, with the temperature of the lower cooling bed being ≥180℃.

[0016] Compared with the prior art, the beneficial effects of the present invention include at least one of the following: (1) By limiting the surface roughness Ra of the finished bar to 2.8 to 3.7 μm, the present invention significantly reduces the false alarm rate in the magnetic flux leakage test of bearing steel bars, thereby improving the accuracy of the test results. This effectively reduces unnecessary scrapping, downgrading or rework caused by misjudging qualified products as defective products (false alarm), directly improves the "yield" of bearing steel products, and reduces scrap loss and processing costs.

[0017] (2) By optimizing the filter parameters, the present invention further reduces noise interference and false alarm rate during magnetic flux leakage testing of bearing steel bars, thereby improving the accuracy of the testing results. Attached Figure Description

[0018] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 This is a surface view of a bar obtained after peeling with a grinding wheel in Comparative Example 1 of the present invention; Figure 2 This is a surface view of a bar obtained after peeling with a grinding wheel in Embodiment 1 of the present invention; Figure 3 This is a flaw detection noise diagram corresponding to the parameters of the magnetic flux leakage flaw detection filter in Comparative Example 1 of the present invention; Figure 4 This is a flaw detection noise diagram corresponding to the parameters of the magnetic flux leakage flaw detection filter in Embodiment 1 of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions. Unless otherwise specified, the experimental materials used in the following embodiments are all obtainable through conventional commercial channels.

[0021] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0022] This invention provides a method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars. The method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars includes the following steps in sequence: peeling and magnetic flux leakage testing. In the peeling process, a multi-stage grinding wheel combination is used to peel the surface of the bar to be tested in order to reduce the surface roughness of the bar and obtain the finished bar. The multi-stage grinding wheel combination adopts a three-stage layout of coarse grinding wheel, fine grinding wheel and polishing wheel. The surface roughness Ra of the finished bar is 2.8 to 3.7 μm, for example, it can be 2.8 μm, 2.9 μm, 3.0 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.5 μm or 3.7 μm.

[0023] Here, a false positive refers to identifying harmless material noise (such as a large carbide) as a harmful defect, causing qualified products to be wrongly judged as unqualified, resulting in unnecessary scrapping and cost losses.

[0024] By limiting the roughness Ra to 2.8–3.7 μm, this invention can ensure that the roughness is low enough to significantly reduce the "lift-off effect noise" caused by surface micro-undulations, and also avoid unnecessary over-polishing in pursuit of ultimate smoothness. Over-polishing not only drastically increases processing costs and time, but also reduces the leakage magnetic field strength, making defects more difficult to detect, thus increasing the risk of missed detection.

[0025] This invention significantly reduces noise interference and false alarm rate during magnetic flux leakage testing of bearing steel bars by limiting the surface roughness Ra of the finished bar to 2.8–3.7 μm, thereby improving the accuracy of the testing results. This effectively reduces unnecessary scrapping, downgrading, or rework caused by misjudging qualified products as defective products (false alarms), directly improving the yield of bearing steel products and reducing scrap losses and processing costs.

[0026] With noise effectively suppressed, the magnetic flux leakage signal generated by real defects becomes more clearly visible. This enables the system to more accurately distinguish between noise and real defect signals, reducing false alarms and enhancing the detection capability and qualitative judgment accuracy of small and critical-sized defects, thereby effectively improving the "pass rate" (i.e., the correct judgment rate of qualified products) of the flaw detection results.

[0027] The method provided by this invention is simple to operate and easy to promote. It reduces false alarms in bearing steel noise without changing the microstructure and properties of the steel, greatly increasing the yield of bearing steel, improving the pass rate of flaw detection and reducing the scrap rate.

[0028] In the above-mentioned method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars, as an optional implementation, the number of coarse grinding wheels is 9, the number of fine grinding wheels is 1, the number of polishing grinding wheels is 2, and the total number of coarse grinding wheels, fine grinding wheels and polishing grinding wheels is 12.

[0029] The peeling machine has 12 grinding heads. Conventionally, grinding heads 1-10 are equipped with coarse grinding wheels, grinding head 11 with a fine grinding wheel, and grinding head 12 with a polishing wheel. To improve the surface roughness of the bearing steel, this invention adjusts the conventional grinding wheel configuration, increasing the number of polishing wheels and reducing the number of coarse grinding wheels. By optimizing the peeling process, this invention reduces the surface roughness of the bearing steel, reducing magnetic noise (lift-off noise) caused by microscopic surface undulations at its physical source. This significantly reduces the background noise level of the detection system, directly and significantly reducing the "false alarm rate" caused by noise misjudgment, thereby improving the accuracy of flaw detection results. A lower false alarm rate directly means fewer qualified products misjudged as scrap or requiring rework. This effectively reduces unnecessary scrapping, downgrading, or rework caused by misjudging qualified products as defective products (false alarms). More qualified bars can smoothly enter subsequent processing stages, directly improving the "yield rate" of bearing steel products and reducing scrap losses and processing costs.

[0030] In the above-mentioned method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars, as an optional implementation, the method of using a multi-stage grinding wheel combination to peel off the surface of the bar to be tested includes: firstly, using the coarse grinding wheel to perform coarse grinding on the surface of the bar to be tested, secondly, using the fine grinding wheel to perform fine grinding, and finally using the polishing wheel to perform polishing.

[0031] In the above-mentioned method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars, as an optional embodiment, the coarse grinding wheel is a 16-18 mesh (e.g., 16 mesh, 17 mesh or 18 mesh) coarse grinding wheel, the fine grinding wheel is a 46-60 mesh (e.g., 46 mesh, 48 mesh, 50 mesh, 52 mesh, 54 mesh, 56 mesh, 58 mesh or 60 mesh) fine grinding wheel, and the polishing grinding wheel includes a flap grinding wheel.

[0032] Here, "mesh count" is a unit for measuring the fineness of abrasive (the particles on a grinding wheel that perform cutting action). The lower the mesh count, the larger the sieve opening, and the coarser the abrasive particles that can pass through. The higher the mesh count, the smaller the sieve opening, and the finer the abrasive particles.

[0033] In the above-mentioned method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars, as an optional implementation, in the peeling process, a multi-stage grinding wheel combination in the peeling machine is used to peel the surface of the bar to be tested. The peeling machine includes 12 grinding wheel heads, the first to ninth grinding heads are the coarse grinding wheels, the tenth grinding head is the fine grinding wheel, and the eleventh and twelfth grinding heads are the polishing grinding wheels.

[0034] In the above-mentioned method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars, as an optional implementation, the raw materials of the grinding wheel include brown corundum, resin liquid and resin powder, wherein the resin liquid is alkaline phenolic resin (stage A), which provides the grinding wheel with formability and initial adhesion, and the resin powder is linear phenolic resin (stage B), which provides final strength and filling space.

[0035] In one optional implementation of the above-mentioned method for reducing the false alarm rate of magnetic flux leakage (MFL) testing of bearing steel bars, an automated MFL testing machine is used in the MFL testing process. The automated MFL testing machine has a filter correction coefficient of 0 and a bandwidth of 2Hz. This invention, by specifically adjusting the filter parameters, effectively suppresses inherent material noise and electromagnetic interference at the signal processing level, further reducing noise interference and false alarm rate during MFL testing of bearing steel bars, thereby improving the accuracy of the testing results.

[0036] In the above-mentioned method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars, as an optional implementation, the finished bar is a GCr15 bearing steel bar with a specification of Φ50~Φ130mm (diameter of circular cross-section) (for example, it can be Φ50, Φ60, Φ70, Φ80, Φ90, Φ100, Φ110, Φ120 or Φ130).

[0037] In the above-mentioned method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars, as an optional implementation method, the preparation method of the bar to be tested includes the following steps in sequence: heating, descaling, rough rolling, continuous rolling, bar sizing and finishing rolling, and slow cooling.

[0038] In one optional implementation of the above-mentioned method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars, the continuously cast billet is heated in a walking beam furnace during the heating process. The heating is divided into four stages: a preheating stage, a first heating stage, a second heating stage, and a soaking stage. The temperature of the preheating stage is 300-650℃ (e.g., 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, or 650℃), the temperature of the first heating stage is 800-850℃ (e.g., 800℃, 830℃, or 850℃), the temperature of the second heating stage is 1180-1200℃ (e.g., 1180℃, 1185℃, 1190℃, 1195℃, or 1200℃), and the temperature of the soaking stage is 1200-1210℃ (e.g., 1200℃, 1205℃, or 1210℃).

[0039] In the above-mentioned method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars, as an optional implementation, the continuous casting billet is a GCr15 continuous casting billet.

[0040] In the above-mentioned method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars, as an optional implementation, the heating time for the four heating stages in the heating process is as follows: the heating time for the preheating stage is 100-240 min (e.g., 100 min, 120 min, 140 min, 160 min, 180 min, 200 min, 220 min, or 240 min), and the heating time for the first heating stage is 120-270 min (e.g., 120 min, 140 min, or 160 min). The heating time of the second heating stage is 150-300 min (e.g., 150 min, 200 min, 220 min, 240 min, or 270 min), and the heating time of the heat spreader is 120-360 min (e.g., 120 min, 150 min, 180 min, 210 min, 250 min, 300 min, 320 min, 340 min, or 360 min).

[0041] In the above-mentioned method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars, as an optional implementation, high-pressure water is used to remove the surface iron oxide scale in the descaling process. The pressure of the high-pressure water is 20-30 MPa (for example, it can be 20 MPa, 22 MPa, 24 MPa, 26 MPa, 28 MPa or 30 MPa), preferably 25-30 MPa.

[0042] In the above-mentioned method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars, as an optional implementation, in the roughing process, the inlet temperature is 1100-1150℃ (for example, it can be 1100℃, 1110℃, 1120℃, 1130℃, 1140℃ or 1150℃), the number of roughing passes is 4-7 (for example, it can be 4 passes, 5 passes, 6 passes or 7 passes), preferably 6 passes, and the final rolling temperature is 950-1000℃, for example, it can be 950℃, 960℃, 970℃, 980℃, 990℃ or 1000℃.

[0043] In one optional implementation of the above method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars, the continuous rolling process includes an intermediate rolling process and a pre-finishing rolling process. After continuous rolling, the incoming material is suitable for entering the bar reduction and sizing mill. The inlet temperature of the intermediate rolling process is 900-950℃ (e.g., 900℃, 930℃, or 950℃), and the number of intermediate rolling passes is 5-7 (e.g., 5, 6, or 7 passes), preferably 6 passes. The finishing rolling temperature of the intermediate rolling process is 870-920℃ (e.g., 870℃, 880℃, or 920℃). The pre-finishing rolling temperature is 870-920℃ (e.g., 870℃, 880℃, 890℃, 900℃, 910℃, or 920℃), and the final rolling temperature is 840-890℃ (e.g., 840℃, 850℃, 860℃, 870℃, 880℃, or 890℃). The number of pre-finishing rolling passes is 2-4 (e.g., 2, 3, or 4 passes), preferably 4 passes.

[0044] In the above-mentioned method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars, as an optional implementation, in the finishing rolling process of the bar reducing and sizing mill, the finishing rolling of the bar reducing and sizing mill is KOCKS rolling, with an initial rolling temperature of 830-880℃ (for example, 830℃, 840℃, 850℃, 860℃, 870℃ or 880℃), a final rolling temperature of 800-850℃ (for example, 800℃, 830℃ or 850℃), and 3-6 rolling passes (for example, 3 passes, 4 passes, 5 passes or 6 passes), preferably 3 passes.

[0045] In the above-mentioned method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars, as an optional implementation, in the slow cooling process, the bars obtained after finishing rolling by the bar reducing and sizing mill are air-cooled on the cooling bed and then air-cooled on the lower cooling bed to room temperature, with the temperature of the lower cooling bed being ≥180℃, preferably ≥200℃.

[0046] In the above-mentioned method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars, as an optional implementation, the temperature of the lower cooling bed is 180-300℃, for example, it can be 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃ or 300℃.

[0047] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0048] In the following embodiments and comparative examples: The method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars provided by the present invention uses GCr15 continuous casting billet as raw material. The raw material continuous casting billet of the present invention is obtained through conventional smelting, refining and continuous casting processes, which will not be described in detail here.

[0049] The raw materials for the grinding wheel are conventional materials in the art, such as brown corundum, resin liquid and resin powder, wherein the resin liquid is an alkaline phenolic resin (stage A), which provides the grinding wheel with formability and initial adhesion, and the resin powder is a linear phenolic resin (stage B), which provides final strength and filling space.

[0050] A missed detection refers to a situation where a defect or target feature that actually exists in the object being tested is not identified and correctly alarmed by the detection system or method.

[0051] A false alarm refers to a situation where a defect or target feature that does not actually exist in the object being tested is incorrectly identified as existing by the detection system or method, triggering an alarm.

[0052] Example 1 The method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars provided in this embodiment includes the following steps: (1) Billet heating: GCr15 continuous casting billet is placed in a four-stage walking beam furnace for heating. The billet size is 300*400mm (rectangular cross-sectional size). The mass percentage of each component in the billet is: C: 1.01%, Si: 0.25%, Mn: 0.30%, Cr: 1.58%, and the remainder is Fe and unavoidable impurities. The heating includes a preheating section, a first heating section, a second heating section, and a soaking section. The temperature of the preheating section is 600℃, the temperature of the first heating section is 835℃, the temperature of the second heating section is 1195℃, and the temperature of the soaking section is 1205℃. The heating times for the four sections are as follows: 200min for the preheating section, 180min for the first heating section, 150min for the second heating section, and 120min for the soaking section.

[0053] (2) Dephosphorization of steel billet: High pressure water is used to remove the iron oxide scale on the surface. The pressure of the high pressure water is 26 MPa.

[0054] (3) Steel billet rough rolling: After descaling, the steel billet enters the rough rolling mill with an inlet temperature of 1135℃. It is rolled into a rough billet by a large reduction rough rolling mill (the maximum reduction reaches 60mm). The rough rolling passes are 6, and the final rolling temperature is 990℃.

[0055] (4) Continuous rolling of billet: The obtained roughing billet is fed into the continuous rolling mill for rolling. The continuous rolling process includes intermediate rolling and pre-finishing rolling. After continuous rolling, the material suitable for entering the bar reduction and sizing mill is obtained. The intermediate rolling inlet temperature is 938℃, the intermediate rolling passes are 6, and the intermediate rolling end temperature is 910℃. The pre-finishing rolling start temperature is 882℃, the end rolling temperature is 860℃, and the pre-finishing rolling passes are 4.

[0056] (5) Bar reduction sizing mill finishing: Finishing is KOCKS rolling. The rolled material obtained after pre-finishing is KOCKS rolling. The initial rolling temperature is 846℃ and the final rolling temperature is 822℃. The number of KOCKS rolling passes is 3.

[0057] (6) Slow cooling: The bars obtained after finishing rolling by the bar reduction and sizing mill are air-cooled on the cooling bed and then air-cooled on the lower cooling bed to room temperature. The temperature of the lower cooling bed is 192℃.

[0058] (7) Grinding wheel peeling: A peeling machine is used to peel the surface of the bar to reduce the surface roughness of the bar and finally obtain the finished bar. The specification of the finished bar is Φ75mm (the diameter of the circular cross-section of the finished bar is 75mm). The peeling machine includes 12 grinding wheels. The first to ninth grinding wheels are coarse grinding wheels, the tenth grinding wheel is a fine grinding wheel, and the eleventh and twelfth grinding wheels are polishing grinding wheels. First, the first to ninth coarse grinding wheels are used to coarsely grind the surface of the bar. Then, the tenth fine grinding wheel is used to finely grind the surface. Finally, the eleventh and twelfth polishing wheels are used to polish the surface. The coarse grinding wheel is a 16-mesh coarse grinding wheel, the fine grinding wheel is a 46-mesh fine grinding wheel, and the polishing grinding wheel is a bladed grinding wheel. The grinding wheel material is composed of brown corundum, resin liquid (alkaline phenolic resin (A-stage)) and resin powder (linear phenolic resin (B-stage)).

[0059] (8)Magnetic flux leakage testing: Using an automated magnetic flux leakage testing machine (the model of the magnetic flux leakage testing machine is RO130), the 136 bars obtained in step (7) are subjected to automated magnetic flux leakage testing according to the corresponding magnetic flux leakage testing standard. The calibration coefficient of the filter in the automated magnetic flux leakage testing machine is 0, and the bandwidth is 2 Hz (filter: separates the useful signal from the noise, improves the anti-interference ability and signal-to-noise ratio of the signal, filters out the frequency components that are not of interest, improves the analysis progress, and separates a single frequency component from the complex frequency components). The magnetic flux leakage testing standard and results are shown in Table 1. A total of 136 samples are involved in this test, of which 126 pieces of steel are judged to be qualified, and 10 pieces of steel are detected to have defects. The flaw detection noise diagram corresponding to the parameters of the magnetic flux leakage testing filter is as Figure 4 shown, and it can be seen from Figure 4 that during the magnetic flux leakage testing process, the surface noise is low and the noise interference is small.

[0060] A total of 136 finished bars are prepared by the method of this embodiment. After grinding and peeling with a grinding wheel, the surface roughness Ra of the steel is 2.803 μm - 3.642 μm. The surface diagram of one bar after grinding and peeling with a grinding wheel is as Figure 2 shown.

[0061] Comparative Example 1 The method for reducing the false alarm rate of flaw detection noise of bearing steel provided in this comparative example is basically the same as that of Example 1, except that in step (7), the peeling machine includes 12 grinding wheels. The 1st to 10th grinding wheels are coarse grinding wheels, the 11th grinding wheel is a fine grinding wheel, and the 12th grinding wheel is a polishing grinding wheel; first, the surface of the bar is coarsely ground with the 1st to 10th coarse grinding wheels, then finely ground with the 11th fine grinding wheel, and finally polished with the 12th polishing grinding wheel; in step (8), the calibration coefficient of the filter in the automated magnetic flux leakage testing machine is -2, and the bandwidth is -2 Hz.

[0062] The magnetic flux leakage testing standard and results are shown in Table 1. A total of 136 samples are involved in this test, of which 61 pieces of steel are judged to be qualified, and 75 pieces of steel are detected to have defects. The flaw detection noise diagram corresponding to the parameters of the magnetic flux leakage testing filter is as Figure 3 shown, and it can be seen from Figure 3 that during the magnetic flux leakage testing process, the surface noise is relatively high and the noise interference is large.

[0063] A total of 136 finished bars are prepared by the method of this comparative example. After grinding and peeling with a grinding wheel, the surface roughness Ra of the steel is 4.853 μm - 6.883 μm. The surface diagram of one bar after grinding and peeling with a grinding wheel is as Figure 1 shown.

[0064] Example 2 The method for reducing the false alarm rate of bearing steel flaw detection noise provided in this embodiment includes the following steps: (1) Billet heating: GCr15 continuous casting billet is placed in a four-stage walking beam furnace for heating. The billet size is 300*400mm (rectangular cross-sectional size). The mass percentage of each component in the billet is: C: 1.01%, Si: 0.25%, Mn: 0.30%, Cr: 1.58%, with the remainder being Fe and unavoidable impurities. The heating process includes a preheating section, a first heating section, a second heating section, and a soaking section. The temperature of the preheating section is 500℃, the temperature of the first heating section is 800℃, the temperature of the second heating section is 1180℃, and the temperature of the soaking section is 1200℃. The heating times for the four sections are as follows: 150min for the preheating section, 220min for the first heating section, 200min for the second heating section, and 200min for the soaking section.

[0065] (2) Dephosphorization of steel billet: High pressure water is used to remove the iron oxide scale on the surface. The pressure of the high pressure water is 20 MPa.

[0066] (3) Steel billet rough rolling: After descaling, the steel billet enters the rough rolling mill with an inlet temperature of 1100℃. It is rolled into a rough billet by a large reduction rough rolling mill (the maximum reduction reaches 60mm). The rough rolling passes are 6, and the final rolling temperature is 950℃.

[0067] (4) Continuous rolling of billet: The obtained roughing billet is fed into the continuous rolling mill for rolling. The continuous rolling process includes intermediate rolling and pre-finishing rolling. After continuous rolling, the material suitable for entering the bar reduction and sizing mill is obtained. The intermediate rolling inlet temperature is 920℃, the intermediate rolling passes are 6, and the intermediate rolling finishing temperature is 890℃. The pre-finishing rolling start temperature is 870℃, the finishing rolling temperature is 850℃, and the pre-finishing rolling passes are 4.

[0068] (5) Bar reduction sizing mill finishing: Finishing is KOCKS rolling. The rolled material obtained after pre-finishing is KOCKS rolling. The initial rolling temperature is 830℃ and the final rolling temperature is 800℃. The number of KOCKS rolling passes is 3.

[0069] (6) Slow cooling: The bars obtained after finishing rolling by the bar reduction and sizing mill are air-cooled on the cooling bed and then air-cooled on the lower cooling bed to room temperature. The temperature of the lower cooling bed is 261℃.

[0070] (7) Grinding wheel peeling: A peeling machine is used to peel the surface of the bar to reduce the surface roughness of the bar and finally obtain the finished bar. The specification of the finished bar is Φ75mm (the diameter of the circular cross-section of the finished bar is 75mm). The peeling machine includes 12 grinding wheels. The first to ninth grinding wheels are coarse grinding wheels, the tenth grinding wheel is a fine grinding wheel, and the eleventh and twelfth grinding wheels are polishing grinding wheels. First, the first to ninth coarse grinding wheels are used to coarsely grind the surface of the bar. Then, the tenth fine grinding wheel is used to finely grind the surface. Finally, the eleventh and twelfth polishing wheels are used to polish the surface. The coarse grinding wheel is a 16-mesh coarse grinding wheel, the fine grinding wheel is a 46-mesh fine grinding wheel, and the polishing grinding wheel is a bladed grinding wheel. The grinding wheel material is composed of brown corundum, resin liquid (alkaline phenolic resin (A-stage)) and resin powder (linear phenolic resin (B-stage)).

[0071] (8) Magnetic flux leakage testing: According to the corresponding magnetic flux leakage testing standards, an automated magnetic flux leakage testing machine (model RO130) was used to perform automated magnetic flux leakage testing on the 152 bars obtained in step (7). The correction coefficient of the filter in the automated magnetic flux leakage testing machine was 0, and the bandwidth was 2 Hz (filter: to separate the useful signal from the noise, improve the anti-interference and signal-to-noise ratio of the signal, filter out the frequency components of no interest, improve the analysis progress, and separate a single frequency component from the complex frequency components). The magnetic flux leakage testing standards and results are shown in Table 1. A total of 152 samples were involved in this test, of which 122 steels were judged to be qualified and 30 steels were found to have defects.

[0072] Using the method described in this embodiment, a total of 152 finished bars were prepared. After peeling with a grinding wheel, the surface roughness Ra of the steel obtained was 2.852μm-3.632μm.

[0073] Comparative Example 2 The method for reducing the false alarm rate of bearing steel flaw detection noise provided in this comparative example is basically the same as that in Example 2. The difference is that in step (7), the peeling machine includes 12 grinding wheels. The first to tenth grinding wheels are coarse grinding wheels, the eleventh grinding wheel is a fine grinding wheel, and the twelfth grinding wheel is a polishing grinding wheel. First, the first to tenth coarse grinding wheels are used to coarsely grind the surface of the bar, then the eleventh fine grinding wheel is used to finely grind it, and finally the twelfth polishing wheel is used to polish it. In step (8), the correction coefficient of the filter in the automated magnetic flux leakage flaw detector is -2, and the bandwidth is -2 Hz.

[0074] The standards and results of magnetic flux leakage testing are shown in Table 1. A total of 152 samples were tested, of which 64 were deemed qualified and 88 were found to have defects.

[0075] Using this comparative method, a total of 152 finished bars were prepared. After peeling with a grinding wheel, the surface roughness Ra of the steel was 4.832 μm-6.848 μm.

[0076] Comparative Example 3 The method for reducing the false alarm rate of bearing steel flaw detection noise provided in this comparative example is basically the same as that in Example 1. The difference is that in step (7), the peeling machine includes 12 grinding wheels. The first to tenth grinding wheels are coarse grinding wheels, the eleventh grinding wheel is a fine grinding wheel, and the twelfth grinding wheel is a polishing grinding wheel. First, the first to tenth coarse grinding wheels are used to coarsely grind the surface of the bar, then the eleventh fine grinding wheel is used to finely grind it, and finally the twelfth polishing wheel is used to polish it.

[0077] The standards and results of magnetic flux leakage testing are shown in Table 1. A total of 136 samples were tested, of which 79 were deemed qualified and 57 were found to have defects.

[0078] Using this comparative method, a total of 136 finished bars were prepared. After peeling with a grinding wheel, the surface roughness Ra of the steel was 4.853 μm-6.883 μm.

[0079] Table 1 Performance testing The accuracy of the magnetic flux leakage testing results obtained from the examples and comparative examples was verified: The finished bars prepared in the examples and comparative examples were 100% visually inspected by professionals with extensive experience in identifying defects in bearing steel to confirm the presence of actual defects. The professionals' judgments will serve as the baseline for calculating the false alarm rate and false negative rate of the automated magnetic flux leakage (MFL) testing system. By comparing the MFL testing results with the inspection results, and statistically comparing the following two core performance indicators, the accuracy of the MFL testing results can be clearly and quantitatively evaluated. The results are shown in Table 2. False alarms in magnetic flux leakage testing: This refers to the number of bars that the magnetic flux leakage testing system identifies as defective (alarms) but are actually defect-free upon re-inspection. The lower this value, the fewer false alarms the system generates due to noise interference, and the stronger its specificity. Number of missed tests in magnetic flux leakage testing: This refers to the number of bars that were deemed qualified by the magnetic flux leakage testing system (no alarm was triggered), but were actually found to have defects upon re-inspection. The lower this value, the stronger the system's ability to detect real defects, and the higher its sensitivity and reliability.

[0080] The formula for calculating the false alarm rate is: False alarm rate = Number of false alarms in magnetic flux leakage testing / Number of tests conducted.

[0081] Table 2 Table 2 shows at least the following: The number of false alarms in the embodiments of this invention is significantly lower than that in the comparative example, proving that the present invention effectively suppresses noise interference by optimizing surface roughness and filter parameters, significantly reducing false alarms and making the "qualified" determination more accurate. This improves the accuracy of flaw detection results and effectively reduces unnecessary scrapping, downgrading, or rework caused by misjudging qualified products as defective products (false alarms). It directly improves the "yield rate" of bearing steel products and reduces scrap losses and processing costs. The method provided by the embodiments of this invention has higher accuracy and superior overall performance.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars, characterized in that, The method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars includes the following steps in sequence: peeling and magnetic flux leakage testing; In the peeling process, a multi-stage grinding wheel combination is used to peel the surface of the bar to be tested in order to reduce the surface roughness of the bar and obtain the finished bar. The multi-stage grinding wheel combination adopts a three-stage layout of coarse grinding wheel, fine grinding wheel and polishing grinding wheel, wherein the surface roughness Ra of the finished bar is 2.8 to 3.7 μm.

2. The method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars according to claim 1, characterized in that, The number of coarse grinding wheels is 9, the number of fine grinding wheels is 1, the number of polishing grinding wheels is 2, and the total number of coarse grinding wheels, fine grinding wheels and polishing grinding wheels is 12. And / or, the method of using a multi-stage grinding wheel combination to peel off the surface of the bar to be inspected includes: firstly, using the coarse grinding wheel to coarsely grind the surface of the bar to be inspected, secondly, using the fine grinding wheel to finely grind, and finally using the polishing wheel to polish. And / or, the coarse grinding wheel is a 16-18 mesh coarse grinding wheel, the fine grinding wheel is a 46-60 mesh fine grinding wheel, and the polishing grinding wheel includes a flap grinding wheel; And / or, in the peeling process, a multi-stage grinding wheel combination in the peeling machine is used to peel the surface of the bar to be inspected. The peeling machine includes 12 grinding wheels, the first to ninth grinding wheels are the coarse grinding wheels, the tenth grinding wheel is the fine grinding wheel, and the eleventh and twelfth grinding wheels are the polishing grinding wheels.

3. The method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars according to claim 1, characterized in that, In the magnetic flux leakage testing process, an automated magnetic flux leakage testing machine is used for magnetic flux leakage testing. The correction coefficient of the filter in the automated magnetic flux leakage testing machine is 0, and the bandwidth is 2Hz.

4. The method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars according to claim 1, characterized in that, The finished bar stock is GCr15 bearing steel bar stock with a specification of Φ50~Φ130mm; And / or, the preparation method of the bar to be inspected includes the following steps in sequence: heating, descaling, rough rolling, continuous rolling, bar sizing and finishing rolling, and slow cooling.

5. The method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars according to claim 4, characterized in that, In the heating process, the continuously cast billet is heated in a walking beam furnace. The heating is divided into four sections: a preheating section, a first heating section, a second heating section, and a soaking section. The temperature of the preheating section is 300-650℃, the temperature of the first heating section is 800-850℃, the temperature of the second heating section is 1180-1200℃, and the temperature of the soaking section is 1200-1210℃. And / or, in the descaling process, high-pressure water is used to remove the surface iron oxide scale, and the pressure of the high-pressure water is 20-30 MPa.

6. The method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars according to claim 5, characterized in that, The continuously cast billet is a GCr15 continuously cast billet; And / or, in the heating process, the heating time of the preheating section is 100-240 min, the heating time of the first heating section is 120-270 min, the heating time of the second heating section is 150-300 min, and the heating time of the homogenization section is 120-360 min.

7. The method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars according to claim 4, characterized in that, In the roughing process, the inlet temperature is 1100-1150℃, the number of roughing passes is 4-7, and the final rolling temperature is 950-1000℃.

8. The method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars according to claim 4, characterized in that, The continuous rolling process includes an intermediate rolling process and a pre-finishing rolling process. After continuous rolling, the material is suitable for entering the bar reduction and sizing mill. The inlet temperature of the intermediate rolling process is 900-950℃, the intermediate rolling passes are 5-7, and the final rolling temperature of the intermediate rolling process is 870-920℃. In the pre-finishing rolling process, the initial rolling temperature of the pre-finishing rolling process is 870-920℃, the final rolling temperature of the pre-finishing rolling process is 840-890℃, and the pre-finishing rolling passes are 2-4.

9. The method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars according to claim 4, characterized in that, In the finishing rolling process of the bar reduction and sizing mill, the finishing rolling of the bar reduction and sizing mill is KOCKS rolling, with an initial rolling temperature of 830-880℃, a final rolling temperature of 800-850℃, and 3-6 rolling passes.

10. The method for reducing the false alarm rate of magnetic flux leakage testing of bearing steel bars according to claim 4, characterized in that, In the slow cooling process, the bars obtained after finishing rolling by the bar reduction and sizing mill are air-cooled on the cooling bed and then air-cooled on the lower cooling bed to room temperature, with the temperature of the lower cooling bed being ≥180℃.

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