CN113884491B - Carbon structural steel phase content determination method and application - Google Patents
Carbon structural steel phase content determination method and application Download PDFInfo
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- CN113884491B CN113884491B CN202111385876.9A CN202111385876A CN113884491B CN 113884491 B CN113884491 B CN 113884491B CN 202111385876 A CN202111385876 A CN 202111385876A CN 113884491 B CN113884491 B CN 113884491B
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Abstract
According to the invention, a laser confocal microscope is adopted to obtain the three-dimensional morphology of a region to be detected, three points with the same circle are selected in a ferrite region, a three-point leveling method is adopted to level the three-dimensional morphology, the leveling surface is used as the height reference of the three-dimensional morphology, the three-dimensional morphology of the region to be detected is cut off, a limited number of cross sections and cross section profile curves are obtained, whether the height standard deviation of the points with the continuous preset number of the cross section profile curves is smaller than or equal to a preset value is determined, the ferrite phase and the pearlite phase of the cross section where the cross section profile curves are located are divided according to whether the calculated height of the points with the continuous preset number is smaller than 0, and the ferrite phase and the pearlite phase of each cross section are respectively added to obtain the phase content of the region to be detected, so that the accuracy of phase content measurement is improved.
Description
Technical Field
The invention belongs to the technical field of steel phase content measurement, and particularly relates to a carbon structural steel phase content measurement method.
Background
Optical microscopy and scanning electron microscopy can be used to perform metallographic structure observations of steel. The optical microscope is a two-dimensional morphological tool, has lower effective resolution and smaller depth of field of resolution, and can not observe three-dimensional morphology in the longitudinal direction. Scanning electron microscopy is complex in sample preparation and sometimes causes sample damage, has limits on both the scanned area and the surface height of the material, and is also incapable of measuring surface area, volume, depth and other information. The confocal laser microscope can be used for observing the three-dimensional morphology and morphology of the surface of a sample in the submicron degree, and can also measure various tiny dimensions such as volume, area, crystal grain, film thickness, depth, length and width, line roughness, surface roughness and the like. Compared with other detection means, the laser confocal method has the unique advantages of improving the definition of pictures, having good depth of field, improving resolution and having certain advantages in the aspect of metallographic structure observation.
The normal metallographic structure of the medium-low carbon structural steel (carbon content is 15-50%) is ferrite and pearlite, the pearlite content has a certain correlation with the mechanical property, and the calculation of the pearlite content has important significance in estimating the carbon content and strength level. In the prior art, an optical gray scale method is mostly adopted, pearlite is a sheet-shaped mixed structure of ferrite and cementite, the gray scale method can mechanically classify the ferrite lamellar structure into ferrite rather than pearlite, meanwhile, certain pollution on a test surface can increase the gray scale, and the ferrite is classified into pearlite for calculation, so that the accuracy of phase content measurement is affected.
Disclosure of Invention
The invention aims to overcome the defect that the phase content of structural steel cannot be accurately estimated due to inaccurate and error gray level calculation on the measurement of the phase content of pearlite and ferrite when the phase content of medium-low carbon structural steel is measured by the existing optical gray level method, and provides a carbon structural steel phase content measuring method which does not estimate the phase content through gray level and improves the accuracy of phase content measurement.
In order to achieve the above object, a first aspect of the present invention provides a method for measuring the phase content of a carbon structural steel,
The method comprises the following steps: grinding and corroding the inspection surface of the steel sample, and then measuring the phase content by adopting a laser confocal microscope, wherein the phase content measurement comprises the following steps:
(1) A laser confocal microscope is adopted to obtain a three-dimensional stereomorphology map of the region to be detected on the surface of the sample;
(2) Leveling the three-dimensional morphology graph, wherein a leveling surface is used as a height reference surface of the three-dimensional morphology graph;
(3) In the direction parallel to the X axis or the Y axis, the three-dimensional stereomorphology graph is cut to obtain a limited number of cross sections and cross section profile curves;
(4) Dividing a section where the section profile curve is located into ferrite phase and pearlite phase according to whether the height standard deviation of the continuous preset number of points of the section profile curve is smaller than or equal to a preset value, wherein the area smaller than or equal to the preset value is ferrite phase;
(5) And respectively adding ferrite phase and pearlite phase of each section to obtain the phase content of the region to be measured.
Preferably, the resolution of the three-dimensional stereomorphology is above 0.125 μm, the spacing of the finite cross-sections is below 0.125 μm, the points in the cross-sectional profile curve, the abscissa or ordinate of adjacent points being spaced below 0.125 μm.
Preferably, the preset number is 5 or more.
Preferably, the preset value is 0.025-0.035 μm.
Preferably, three points with the same circle are selected in the ferrite region, and a three-dimensional morphology graph is leveled by adopting a three-point leveling method;
after the section profile curve is obtained, the basis for dividing the section where the section profile curve is located into ferrite phase and pearlite phase also comprises the step of calculating the average height of each point of the section profile curve, wherein the calculated height of each point is obtained by subtracting the average height from the original height of each point on the section profile curve, and the area with the calculated height of the points with continuous preset numbers smaller than 0 is ferrite.
Preferably, the etching liquid is 4% nitrate alcohol, and the etching time is 3-6s.
Preferably, the grinding includes a coarse grinding process, a fine grinding process, a3 μm polishing process, and a 1 μm polishing process.
Preferably, the time of the rough grinding process is 50-70 s, the force is 90-110 Nm, the rotating speed is 90-100 rpm, the time of the fine grinding process is 11-13 min, the force is 145-155 Nm, and the rotating speed is 300-320 rpm.
Preferably, the rotation speed of the 3 μm polishing procedure is 140-160 revolutions/min, the force is 145-155 Nm, the liquid spraying frequency is 25-30 s/time, the polishing time is 3-4 min, the rotation speed of the 1 μm polishing procedure is 140-160 revolutions/min, the force is 85-95N/m, the liquid spraying frequency is 25-30 s/time, and the polishing time is 2-3 min.
The second aspect of the application provides an application of the carbon structural steel phase content determination method of the first aspect of the application in carbon structural steel phase content detection.
The beneficial effects of the application include:
According to the invention, a laser confocal microscope is adopted to obtain a three-dimensional topography after sample corrosion, the three-dimensional topography is cut off after leveling to obtain a section and a section profile curve, and the section where the section profile curve is positioned is divided into ferrite and pearlite according to whether the height standard deviation of the continuous preset number of points of the section profile curve is smaller than or equal to a preset value, so that the defect that the phase content is measured by an optical gray scale method is avoided, the pearlite and the ferrite can be accurately distinguished, thereby obtaining accurate phase content, and estimating the carbon content and strength of steel.
By leveling, the height of adjacent ferrite in the cross section is prevented from being stepped, thereby affecting the distinction between ferrite and pearlite according to the standard deviation of the height of points of the cross section profile curve for a continuous preset number.
Through grinding, scratches on the surface of the sample can be reduced, the corrosion effect of the scratches is different from that of non-scratches, the scratches can influence the corrosion effect of the sample, and the complexity of the corrosion effect is increased. Usually, after corrosion, the scratch is lower in the height of the three-dimensional topography, and the height of the midpoint of the profile curve of the cross section is affected, so that the ferrite and the pearlite are accurately distinguished.
The deformation layer on the surface of the sample can be reduced by grinding, the complexity of corrosion action can be increased if the deformation layer exists, ferrite after corrosion has poor flatness, a concave-convex structure exists, the height of the middle point of the profile curve of the section can be influenced, and therefore the ferrite and pearlite can be accurately distinguished.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of the method for measuring the phase content of the carbon structural steel.
Fig. 2 is a three-dimensional perspective view of the region to be measured on the surface of the sample obtained by using a laser confocal microscope in example 1.
FIG. 3 is a schematic diagram of the leveling process of the present application.
Fig. 4 is a schematic view of the length of the profile cut of the characteristic tissue of example 1 and a cross-sectional profile curve illustrating a cross-section, fig. 4a is a schematic view of the length of the profile cut of the characteristic tissue, and fig. 4b is a cross-sectional profile curve illustrating the cross-section shown in fig. 4 a. Wherein the dashed line in fig. 4a represents a cross section, showing only a part of the cross section, and the image darkness change of fig. 4a represents a different phase, wherein both ends of the dashed line are respectively in ferrite phase, and the middle spans pearlite. In fig. 4b, the horizontal axis corresponds to the X-axis, the vertical axis corresponds to the Z-axis, and the vertical axis represents the calculated height obtained by subtracting the average height from the original height.
Fig. 5 is a schematic view of the length of the profile cut of the characteristic tissue of example 2 and a cross-sectional profile curve illustrating a cross-section, fig. 5a is a schematic view of the length of the profile cut of the characteristic tissue, and fig. 5b is a cross-sectional profile curve illustrating the cross-section shown in fig. 5 a.
Fig. 6 is a schematic view of the length of the profile cut of the characteristic tissue of example 3 and a cross-sectional profile curve illustrating a cross-section, fig. 6a is a schematic view of the length of the profile cut of the characteristic tissue, and fig. 6b is a cross-sectional profile curve illustrating the cross-section shown in fig. 6 a.
Fig. 7 is a schematic view of the length of the characteristic tissue profile cut of the ferrite scratch-containing region of example 4 and a cross-sectional profile curve illustrating a cross section, fig. 7a is a schematic view of the length of the characteristic tissue profile cut, and fig. 7b is a cross-sectional profile curve illustrating a cross section shown in fig. 7 a.
Fig. 8 is a schematic view of the sectional profile of the pearlite colony area according to example 4, showing the length of the sectional profile of the cross section, fig. 8a shows the length of the sectional profile of the pearlite colony area, and fig. 8b shows the sectional profile of the cross section shown in fig. 8 a.
Fig. 9 is a three-dimensional profile of the region to be measured on the surface of the sample obtained by using a laser confocal microscope in example 5, a schematic drawing of the length of the profile of the feature tissue and a profile curve of the cross section of the graph, fig. 9a is a three-dimensional profile of the region to be measured on the surface of the sample, fig. 9b is a schematic drawing of the length of the profile of the feature tissue, and fig. 9c is a profile curve of the cross section shown in fig. 9 b.
Fig. 10a is a schematic view of the length of the profile of the characteristic tissue of example 6, and fig. 10b is a cross-sectional profile curve of the cross-section shown in fig. 10 a.
Detailed Description
Embodiments of the present application will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only for illustrating the present application and should not be construed as limiting the scope of the present application. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention. The detection method used is not particularly specified, and is carried out according to national standards or conventional detection methods.
Because pearlite is a sheet-shaped mixed structure of ferrite and cementite, in order to overcome the defect that when the phase content of the medium-low carbon structural steel is measured by an optical gray scale method by adopting a laser confocal microscope in the prior art, the ferrite lamellar structure is classified as ferrite instead of pearlite, thereby influencing the accuracy of phase content measurement and further influencing the accuracy of carbon content and strength evaluation.
In order to facilitate understanding of the specific implementation of the above measurement method, the method for measuring the phase content of the carbon structural steel in the present invention will be described below.
A flow chart of a method for measuring the phase content of the carbon structural steel is shown in fig. 1.
A method for determining the phase content of carbon structural steel, comprising the following steps: grinding and corroding the inspection surface of the steel sample, and then measuring the phase content by adopting a laser confocal microscope, wherein the phase content measurement comprises the following steps:
(1) A laser confocal microscope is adopted to obtain a three-dimensional stereomorphology map of the region to be detected on the surface of the sample;
(2) Leveling the three-dimensional morphology graph, wherein a leveling surface is used as a height reference surface of the three-dimensional morphology graph;
(3) In the direction parallel to the X axis or the Y axis, the three-dimensional stereomorphology graph is cut to obtain a limited number of cross sections and cross section profile curves;
(4) Dividing a section where the section profile curve is located into ferrite phase and pearlite phase according to whether the height standard deviation of the continuous preset number of points of the section profile curve is smaller than or equal to a preset value, wherein the area smaller than or equal to the preset value is ferrite phase;
(5) And respectively adding ferrite phase and pearlite phase of each section to obtain the phase content of the region to be measured.
In the present invention, it should be understood that the operation mode of the laser confocal microscope is a normal temperature mode. A laser confocal microscope was selected from zeiss LSM800/imager.z2m. And grinding the sample by adopting an ATM full-automatic metallographic grinding and polishing machine. The software adopts Zeiss ZEN2.6 (metallographic image observation and laser 3D mapping) and ConfoMap ST (data processing of laser 3D mapping, and has the functions of leveling, noise reduction, 3D composition, appearance profile extraction and the like).
The measuring method of the invention can be suitable for measuring the phase content of the carbon structural steel (including low alloy) with 20, 30, 40Cr, 45, 50 and the like in rolled state and metallographic phase of ferrite and pearlite.
The three-dimensional morphology of the region to be measured on the surface of the sample is obtained by a laser confocal microscope, the region to be measured of the sample after grinding and corrosion is placed on a laser confocal microscope stage, and the stage is rotated, so that the length direction of the region to be measured is parallel to an X axis, and the width direction of the region to be measured is parallel to a Y axis. And focusing the region to be detected under the visible light mode, so that the image clearly appears in the image display region, and switching the visible light mode into a laser mode. In the channel column of the operation interface, the laser intensity of 405nm is 5%, and the pinhole is 1AU to ensure the highest resolution. And respectively focusing the highest point and the lowest point of the inspection view field, setting a scanning height range, adjusting a gain value during preview to exactly eliminate red points (noise points) appearing when the image is scanned from the highest point to the lowest point, and then scanning layer by layer to obtain three-dimensional shape data of the region to be detected, wherein the three-dimensional physical shape of the region to be detected is shown in figure 2.
Preferably, the laser intensity can be adjusted to obtain clear signals, and white spots do not appear during drawing.
Optionally, leveling the three-dimensional topography map can be achieved by adopting a three-point leveling method to level the three-dimensional topography map, wherein the leveling surface is used as a height reference surface of the three-dimensional topography map, and as ferrite is uniformly corroded, the corrosion degree is relatively close, the ferrite area is relatively smooth, three points with the same circle are selected on adjacent ferrite far away. The leveling process may refer to fig. 3, where three points are located on the ferrite, respectively.
The method comprises the steps of intercepting the three-dimensional stereomorphology map in the direction parallel to the X axis or the Y axis to obtain a limited number of cross sections and cross section profile curves, switching to a laser confocal three-dimensional measurement mode, intercepting the three-dimensional stereomorphology map of a region to be detected in sequence with a certain resolution in the direction parallel to the X axis or the Y axis to complete intercepting the whole three-dimensional stereomorphology map, and intercepting the three-dimensional stereomorphology map to obtain a cross section and a cross section profile curve once, wherein the shape of the cross section profile curve represents the surface morphology of a sample at the cross section position.
It is understood that the corrosion process uses chemical corrosion, and is mainly electrochemical dissolution process for carbon structural steel. The main structure of the carbon structural steel is ferrite and pearlite. Pearlite is a flaky mixed structure of ferrite and cementite, the potential of the ferrite is between-0.5V and-0.4V, the cementite is slightly lower than +0.37V, the ferrite is an anode in the corrosion process, the cementite is a cathode in the electrochemical dissolution process, the ferrite is uniformly dissolved out of a layer, the cementite is basically insoluble, and the phase boundary is large in dissolution amount due to large potential difference and high etching speed, so that a deeper groove is formed. Therefore, ferrite and pearlite of the carbon structural steel are corroded uniformly, a region with a high approximation is shown on the surface morphology of the three-dimensional stereomorphology graph, and pearlite corrosion is not uniform, a region with a high oscillation is shown, so that ferrite phase and pearlite phase can be distinguished according to the surface morphology change. The surface topography variations can be characterized by variations in the standard deviation of the height of successive points of the cross-sectional profile curve. However, the ferrite sheet in pearlite is uniformly dissolved, and for the ferrite sheet in pearlite, the surface morphology thereof is uniform, and the standard deviation of the height of the continuous point corresponding to the ferrite sheet in the cross-sectional profile curve is similar to the standard deviation of the height of the continuous point corresponding to the ferrite phase. However, the thickness of ferrite sheets in the equilibrium pearlite is about 0.25 μm to 0.5 μm, and the number of continuous points corresponding to ferrite sheets in the cross-sectional profile curve is limited, that is, when the number of points involved in calculation is large and exceeds a certain value, the standard deviation of the height of continuous points corresponding to pearlite phase in the cross-sectional profile curve will be different from the standard deviation of the height of ferrite phase. Therefore, ferrite phase and pearlite phase can be distinguished according to the height standard deviation of the continuous preset number of points of the cross section profile curve, when the height standard deviation is smaller than or equal to a preset value, the cross section where the cross section profile curve is located is ferrite phase, and when the height standard deviation is larger than the preset value, the cross section where the interface profile curve is located is pearlite phase.
It is understood that the process of adding ferrite phase and pearlite phase of each section to obtain the phase content of the region to be measured is to sequentially obtain the amounts of ferrite phase and pearlite phase of each section according to whether the height standard deviation of the points of the continuous preset number of section profile curves is less than or equal to a preset value, cut out the three-dimensional stereotopography of the region to be measured sequentially, have obtained a limited number of sections, add ferrite phase of each section, obtain the amount of ferrite phase of the region to be measured, add pearlite phase of each section, obtain the amount of pearlite phase of the region to be measured, and thus obtain the phase content of the region to be measured.
Pearlite is a flaky mixed structure of ferrite and cementite, a gray scale method can mechanically classify the ferrite lamellar structure into ferrite rather than pearlite, meanwhile, certain pollution on a test surface can increase the gray scale, and classification of ferrite into pearlite can influence the determination of the phase content. According to the invention, the phase content is estimated without using an optical gray scale method, a laser confocal microscope is adopted to obtain the three-dimensional morphology of the region to be measured, the three-dimensional morphology of the region to be measured is sequentially intercepted, a limited number of cross sections and cross section profile curves are obtained, and the cross section where the cross section profile curve is located is divided into ferrite phase and pearlitic phase according to whether the height standard deviation of the continuous preset number of points of the cross section profile curves is smaller than or equal to a preset value or not, so that the accuracy of phase content measurement is improved. Since the phase content is determined according to the height standard deviation, the accuracy of the measurement result is affected by the accurate quantification of the height, and meanwhile, the accuracy of the result is affected by the corrosion effect of pearlite and ferrite, which is the difference of the height standard deviation of points of a continuous preset number in the profile curve. It is therefore necessary to ensure a high degree of accurate quantification and difference in the corrosion effects of pearlite and ferrite, and to accurately embody the difference in the corrosion effects of pearlite and ferrite. Through leveling, the leveling surface is used as a height reference surface of the three-dimensional stereomorphology graph, so that the height measurement reference of the region to be measured can be consistent, the height can be accurately quantified, and in addition, the condition that the height of adjacent ferrite in the section is in a step shape can be avoided, so that the reflection of the corrosion effect difference of pearlite and ferrite is influenced. Through grinding, scratches on the surface of the sample can be reduced, the corrosion effect of the scratches is different from that of non-scratches, the scratches can affect the corrosion effects of ferrite and pearlite, and the complexity of the corrosion effect can be increased. After corrosion, the height of the scratch in the three-dimensional topography is low, which can affect the height of the midpoint of the profile curve of the cross section, thereby affecting the accurate distinction of ferrite and pearlite according to the difference of the corrosion effects of pearlite and ferrite. The deformation layer on the surface of the sample can be reduced by grinding, the complexity of corrosion action can be increased if the deformation layer exists, ferrite after corrosion has poor flatness, a concave-convex structure can exist, the height of the middle point of a section profile curve can be influenced, and ferrite and pearlite can be accurately distinguished according to the difference of corrosion effects of pearlite and ferrite.
In a preferred embodiment of the present invention, the resolution of the three-dimensional stereomorphology is above 0.125 μm, the spacing of the finite cross-sections is below 0.125 μm, and the points in the cross-sectional profile are spaced apart by below 0.125 μm on the abscissa or ordinate of adjacent points.
The resolution of the three-dimensional morphology is embodied as the three-dimensional coordinate spacing of adjacent points in the three-dimensional morphology grid graph, the three-dimensional morphology graph is intercepted according to the coordinate spacing of the adjacent points, the spacing of a limited section is equal to the value of the resolution, and the abscissa or ordinate spacing of the adjacent points in the section profile curve is equal to the value of the resolution. The higher the resolution of the three-dimensional morphology is, the smaller the spacing of the limited cross sections and the abscissa or ordinate interval of the adjacent points are, the higher the accuracy of phase content calculation is, and when the resolution of the three-dimensional morphology is more than 0.125 mu m, the spacing of the limited cross sections and the abscissa or ordinate interval of the adjacent points are less than 0.125 mu m, the higher the accuracy of phase content calculation is. The thickness of ferrite sheets in pearlite is 0.25 μm to 0.5 μm, when the interval between adjacent points in the cross-sectional profile curve is determined, the number of continuous points corresponding to ferrite sheets in the cross-sectional profile curve can be determined, and when pearlite and ferrite are distinguished, the value of the continuous preset number can be determined, for example, when the interval between adjacent points in the cross-sectional profile curve is 0.125 μm, the number of continuous points corresponding to ferrite sheets in the cross-sectional profile curve is 2 to 4 points, and when pearlite and ferrite are distinguished, the value of the continuous preset number is 5 or more.
In a preferred embodiment of the present invention, the preset number is 5 or more.
When the resolution is 0.125 μm, the spacing between the finite sections is 0.125 μm, the points in the profile curve of the section, and the abscissa or ordinate of adjacent points are spaced by 0.125 μm, the numerical value of the continuous preset number is 5 or more, when pearlite and ferrite are distinguished. When the resolution is higher, the pitch of the finite number of sections and the abscissa or ordinate interval of the points in the section profile are smaller, and the minimum value of the preset number is a minimum integer greater than the ratio of the thickness of the ferrite sheet in the pearlite (0.25 μm to 0.5 μm) to the abscissa or ordinate interval, and the minimum integer is 5 or more.
In a preferred embodiment of the invention, the preset value is 0.025-0.035 μm.
When the resolution of the three-dimensional morphology is 0.125 mu m, the spacing between the limited sections is 0.125 mu m, and the interval between the abscissa and the ordinate of the points in the section profile curve is 0.125 mu m, the ferrite phase and the pearlite phase of the section where the section profile curve is located can be accurately divided according to whether the standard height difference of the continuous 5 points of the section profile curve is less than or equal to 0.025-0.035 mu m, and the phase content calculation has higher accuracy. When the resolution of the three-dimensional morphology is larger than 0.125 mu m, when the height standard deviation is calculated, the calculation range, namely the total abscissa or ordinate difference value of continuous preset number points, is consistent with the calculation range with the resolution of 0.125 mu m and the preset number of 5, and the preset value is also 0.025-0.035 mu m.
In a preferred embodiment of the invention, three points with the same circle are selected in the ferrite region, and a three-dimensional morphology graph is leveled by adopting a three-point leveling method; after the section profile curve is obtained, the basis for dividing the section where the section profile curve is located into ferrite phase and pearlite phase also comprises the step of calculating the average height of each point of the section profile curve, wherein the calculated height of each point is obtained by subtracting the average height from the original height of each point on the section profile curve, and the area with the calculated height of the points with continuous preset numbers smaller than 0 is ferrite.
The main structure of the carbon structural steel is ferrite and pearlite. Pearlite is a lamellar mixed structure of ferrite and cementite. The potential of ferrite is-0.5V to-0.4V, cementite is slightly lower than +0.37V, ferrite is an anode in the corrosion process, cementite is a cathode in the electrochemical dissolution process, ferrite is uniformly dissolved, and cementite is basically insoluble. Ferrite and pearlite of the carbon structural steel are corroded uniformly, a region with a high degree is displayed on the surface morphology of the three-dimensional stereomorphology graph, and pearlite corrosion is not uniform, and a region with a high degree of oscillation is displayed. In addition, since ferrite is easy to corrode, a region with lower height is presented in the surface morphology of the three-dimensional stereomorphology graph, ferrite and pearlite can be distinguished on the basis of whether the standard deviation of the height of points with continuous preset numbers is smaller than or equal to a preset value or not, and further, ferrite and pearlite are distinguished according to the heights of points with continuous preset numbers on a section profile curve. After the height reference plane is defined, the original heights of all points on the cross section contour curve are obtained, the average heights of all points can be obtained by averaging the original heights of all points, the calculated heights of all points are obtained by subtracting the average heights from the original heights of all points, and the area with the calculated heights of all points with continuous preset numbers smaller than 0 is ferrite. The basis is a specific method of distinguishing ferrite from pearlite phases according to the heights of points of a predetermined number in succession on the cross-sectional profile curve. And (3) selecting three points with the same circle in the ferrite region, leveling the three-dimensional morphology graph by adopting a three-point leveling method, wherein the leveling surface is a height reference surface of the three-dimensional morphology graph, and the height of the height reference surface is 0, so that the height of the point corresponding to the ferrite in the section profile curve is close to the height of the height reference surface, namely, is close to 0, and the average height is subtracted from the original height of the point corresponding to the section profile curve of the ferrite and is smaller than 0.
In a preferred embodiment of the invention, the etching solution is 4% nitroalcohol and the etching time is 3-6s.
Preferably, after the corrosion is finished, the test surface of the steel sample is washed by clean water, ultrasonic cleaning is carried out for 1-2 minutes, and the test surface of the steel sample is washed and dried by alcohol.
When 4% nitroalcohol is adopted, the corrosion time is 3-6s, the corrosion effect difference of the pearlite phase and the ferrite phase is obvious, the corrosion degree of the pearlite is weaker, the ferrite and the pearlite can be distinguished through the corrosion effect difference, namely, the section where the section profile curve is located can be divided into the ferrite phase and the pearlite phase through whether the height standard deviation of the points with continuous preset numbers is smaller than or equal to a preset value and whether the calculated height of the points with continuous preset numbers is smaller than 0.
Alternatively, the etching time may be 3s, 4s, 5s, 6s.
In a preferred embodiment of the present invention, the grinding includes a coarse grinding process, a fine grinding process, a 3 μm polishing process, and a 1 μm polishing process.
When the sample is cut, a deformation layer and scratches are generated on the test surface of the steel sample. If the deformation layer is provided, the complexity of corrosion action is increased, ferrite after corrosion has poor flatness, a concave-convex structure is formed, the height of the middle point of the profile curve of the section is influenced, and ferrite and pearlite are accurately distinguished according to the difference of corrosion effects of the pearlite and the ferrite. If there is a scratch, the corrosion effect at the scratch and the non-scratch are different, the scratch affects the corrosion effect of ferrite and pearlite, and the complexity of the corrosion effect is increased. After corrosion, the height of the scratch in the three-dimensional topography is low, which can affect the height of the midpoint of the profile curve of the cross section, thereby affecting the accurate distinction of ferrite and pearlite according to the difference of the corrosion effects of pearlite and ferrite. By grinding, scratches and deformation layers on the surface of the sample can be reduced. In the polishing step, the efficiency of removing the deformed layer is higher than that of the polishing step, but a new deformed layer may be generated, and the larger the abrasive grain size in the polishing liquid in the polishing step, the higher the efficiency of removing the deformed layer is, but a new deformed layer may be generated, and in order to simultaneously ensure the polishing efficiency and prevent the generation of the new deformed layer, the polishing is performed by combining the rough polishing step, the fine polishing step, the 3 μm polishing step and the 1 μm polishing step. Up to 100 times lower surface visible scratch no more than 3 mirror surfaces, and no plastic deformation layer is basically arranged on the surface.
Alternatively, the grinding process may be sequentially subjected to coarse grinding, fine grinding, 3 μm polishing, and 1 μm polishing.
In a preferred embodiment of the present invention, the time of the rough grinding process is 50 to 70 seconds, the force is 90 to 110Nm, the rotation speed is 90 to 100 rpm, the time of the fine grinding process is 11 to 13 minutes, the force is 145 to 155Nm, and the rotation speed is 300 to 320 rpm.
The rough grinding is to level the inspection surface by using a grinding wheel, remove the deformation layer caused by cutting, and has the advantages of large deformation layer caused by the inspection surface due to thicker grinding wheel and quick grinding, short selection time and small strength; the fine grinding is to remove the deformation layer brought by coarse grinding by using the abrasive particles of 18um, and the deformation layer is ground layer by layer, so that the efficiency is considered, the selection strength is high, the rotating speed is high, and the time is long.
In a preferred embodiment of the present invention, the rotation speed of the 3 μm polishing process is 140 to 160 revolutions/min, the force is 145 to 155Nm, the spray frequency is 25 to 30 s/time, the polishing time is 3 to 4min, the rotation speed of the 1 μm polishing process is 140 to 160 revolutions/min, the force is 85 to 95N/m, the spray frequency is 25 to 30 s/time, and the polishing time is 2 to 3min.
The size of abrasive particles in the polishing solution, the applied pressure and the polishing time have influence on the polishing effect, the mechanical grinding degree of the abrasive particles with the size of 1 mu m to 3 mu m on the inspection surface is smaller, the deformation layer caused on the inspection surface is basically eliminated, and the deformation layer is reflected on the metallographic definition degree; the pressure applied by the abrasive particles with the size of 1um is correspondingly reduced, and the deformation layer generated by 3um is ground off instead of adding a new deformation layer; the time is correspondingly reduced, the time is too long, the deformation layer generated by 3um is abraded, 1um is added, the scratch number is increased, and the scratch is not lost.
The polishing rotation speed is selected to balance the rotation speed and the spraying frequency, the spraying frequency is selected continuously to ensure that abrasive particles are in a lubrication state and grinding products are discharged, and if the spraying is insufficient, more scratches can be generated in a dry grinding state to accurately distinguish ferrite from pearlite according to the difference of corrosion effects of pearlite and ferrite.
The second aspect of the application provides an application of the carbon structural steel phase content determination method of the first aspect of the application in carbon structural steel phase content detection.
According to the invention, the phase content is estimated without using an optical gray scale method, a laser confocal microscope is adopted to obtain the three-dimensional morphology of the region to be measured, the three-dimensional morphology of the region to be measured is sequentially intercepted, a limited number of cross sections and cross section profile curves are obtained, and the cross section where the cross section profile curve is located is divided into ferrite phase and pearlitic phase according to whether the height standard deviation of the continuous preset number of points of the cross section profile curves is smaller than or equal to a preset value or not, so that the accuracy of phase content measurement is improved. And selecting three points with the same circle in the ferrite region, leveling the three-dimensional morphology graph by adopting a three-point leveling method, taking the leveled surface as the height reference of the three-dimensional morphology graph, calculating the average height of each point of the cross-section profile curve after obtaining the cross-section profile curve, subtracting the average height from the original height of each point on the cross-section profile curve to obtain the calculated height of each point, and distinguishing ferrite and pearlite according to whether the calculated height of the points with continuous preset numbers is smaller than 0 or not. By combining the two distinguishing methods, whether the height standard deviation of the points with the continuous preset number is smaller than or equal to a preset value or not is judged, and whether the calculated height of the points with the continuous preset number is smaller than 0 or not is judged, so that the accuracy of the phase content measurement can be further improved. Meanwhile, through a specific grinding process, deformation layers and scratches on the test surface of the steel sample can be reduced, the complexity of corrosion action is reduced, the influence of the deformation layers and the scratches on the height of the middle point of the profile curve of the section is reduced, and the influence on accurately distinguishing ferrite from pearlite according to the difference of corrosion effects of the pearlite and ferrite is reduced.
The following examples take the measurement of the phase (matrix structure is ferrite + pearlite in the rolled state) content of 50 carbon structural steel as an example.
Example 1
Step 1: the method comprises the steps of coarse grinding, fine grinding, 3 mu m polishing working procedures and 1 mu m polishing working procedures sequentially acting on the inspection surface of a carbon structural steel sample, wherein the time of the coarse grinding working procedure is 60s, the force is 100Nm, the rotating speed is 90 turns/min, the time of the fine grinding working procedure is 12min, the force is 150Nm, the rotating speed is 300 turns/min, the rotating speed of the 3 mu m polishing working procedure is 150 turns/min, the force is 150Nm, the liquid spraying frequency is 30 s/time, the polishing time is 3min, the rotating speed of the 1 mu m polishing working procedure is 150 turns/min, the force is 90N/m, the liquid spraying frequency is 30 s/time, and the polishing time is 2min;
Step 2: the test surface of the carbon structural steel is corroded by chemical corrosion, the corrosive liquid is 4% nitrate alcohol, and the corrosion time is 4s. After corrosion is finished, the inspection surface of the steel sample is washed by clean water, ultrasonic cleaning is carried out for 1-2 minutes, and the inspection surface of the steel sample is washed and dried by alcohol.
Step 3: and placing the polished and corroded region to be tested of the sample on a laser confocal microscope objective table, and rotating the objective table to enable the length direction of the region to be tested to be parallel to the X axis and the width direction to be parallel to the Y axis. And focusing the region to be detected under the visible light mode, so that the image clearly appears in the image display region, and switching the visible light mode into a laser mode. In the channel column of the operation interface, the laser intensity of 405nm is 5%, and the pinhole is 1AU to ensure the highest resolution. The focus knob is adjusted clockwise until the blue screen appears and the black color substantially covers the image, the upper limit point is determined by clicking the [ set start point ] button, the focus knob is adjusted slowly and anticlockwise, and when the image appears a red dot, reducing the main gain value of the channel column until the red dot does not appear, stopping the process until the blue screen appears, and basically covering the image by black, and clicking a [ set wire harness point ] button to determine a lower limit point. To obtain 3D data of full height (lowest, highest measurable). Clicking the Stop to Stop the preview mode, clicking the optimal optimization button to automatically set the optimal scanning step length. And in a laser mode, scanning the region to be detected layer by layer to obtain a two-dimensional topography map of the region to be detected, after the two-dimensional topography map is obtained, adopting a Gaussian operator method to reduce noise images, flattening the images, removing noise peaks, and then switching the two-dimensional topography map into a three-dimensional topography map to obtain the three-dimensional physical topography of the region to be detected, wherein the resolution ratio of the three-dimensional topography map is 0.125 mu m.
Step 4: and selecting three points with the same circle on adjacent far ferrite, and leveling the three-dimensional morphology graph by adopting a three-point leveling method, wherein the leveling surface is used as a height reference surface of the three-dimensional morphology graph.
Step 5: the three-dimensional stereographic map is taken in a direction parallel to the X-axis to obtain a finite number of sections and section profile curves, the spacing of the finite number of sections being 0.125 μm, the abscissa interval of the points in the section profile curves being 0.125 μm.
Step 6: and calculating the standard deviation of the heights of the continuous 5 points of the profile curve of the section, and judging whether the standard deviation of the heights of the continuous 5 points is smaller than 0.025-0.035 mu m.
Step 7: and obtaining the original heights of all points on the section profile curve by taking the leveling surface as a reference, calculating the average heights of all points of the section profile curve by the original heights of all points, subtracting the average heights of all points on the section profile curve to obtain the calculated heights of all points, and judging whether the calculated heights of continuous 5 points on the section profile curve are smaller than 0.
Fig. 4b shows calculated heights of points corresponding to ferrite in the cross-sectional profile curves, the calculated heights being all smaller than 0, the cross-sectional profile curves corresponding to ferrite having small fluctuation in height.
Table 1 shows the standard deviations of the original heights of the AB segment, the CD segment and the EF segment in FIG. 4b at 5 points in succession, and it can be found from Table 1 that the AB segment and the EF segment are located in pearlite with a standard deviation between 0.014 and 0.403, and the CD segment is located in ferrite with a standard deviation between 0.002 and 0.029.
| AB | CD | EF | |
| Minimum value (um) | 0.014 | 0.002 | 0.014 |
| Maximum value (um) | 0.403 | 0.029 | 0.225 |
| Average value (um) | 0.108 | 0.006 | 0.074 |
| Standard deviation (um) | 0.049 | 0.002 | 0.032 |
TABLE 1
Example 2
The phase content determination method of example 1 was followed, except that the etching time was <3s.
Fig. 5a is a schematic view of the length of a characteristic tissue profile cut-out, and fig. 5b is a cross-sectional profile curve of the cross-section shown in fig. 5 a.
Table 2 shows the standard deviations of the original heights at 5 consecutive points for the AB, CD and EF segments of FIG. 5 b.
Comparative example 1, which has insufficient corrosion time, insufficient ferrite corrosion, uneven height, narrowed height difference between pearlite and ferrite, close dispersion, and insignificant two-phase contrast, is unfavorable for data analysis and determination of the area.
| AB | CD | EF | |
| Minimum value (um) | 0.012 | 0.022 | 0.008 |
| Maximum value (um) | 0.128 | 0.160 | 0.100 |
| Average value (um) | 0.057 | 0.022 | 0.040 |
| Standard deviation (um) | 0.017 | 0.019 | 0.017 |
TABLE 2
Example 3
The phase content determination method of example 1 was followed, except that the etching time was >6s.
Fig. 6a is a schematic view of the length of a characteristic tissue profile cut-out, and fig. 6b is a cross-sectional profile curve of the cross-section shown in fig. 6 a.
Table 3 shows the standard deviations of the original heights at 5 consecutive points for the AB, CD and EF segments of FIG. 6 b.
Compared with example 1, the peak-valley width of the pearlite area is increased as the corrosion time is longer, the relative maximum height is reduced, the ferrite area is excessively corroded to generate unevenness, the dispersion is increased, the relative average height is increased, and the reduction relative pearlite contrast is unfavorable for area judgment.
| AB | CD | EF | |
| Minimum value (um) | 0.022 | 0.001 | 0.017 |
| Maximum value (um) | 0.219 | 0.177 | 0.297 |
| Average value (um) | 0.085 | 0.011 | 0.102 |
| Standard deviation (um) | 0.036 | 0.008 | 0.044 |
TABLE 3 Table 3
Example 4
According to the phase content measuring method of example 1, the different grinding processes are rough grinding, fine grinding, 3 μm polishing process and 1 μm polishing process sequentially act on the test surface of the carbon structural steel sample, wherein the time of the rough grinding process is 60s, the force is 130Nm, the rotation speed is 90 turns/min, the time of the fine grinding process is 10min, the force is 160Nm, the rotation speed is 300 turns/min, the rotation speed of the polishing process is 140 turns/min, the force is 130Nm, the liquid spraying frequency is 30 s/time, the polishing time is 3min, the rotation speed of the 1 μm polishing process is 170 turns/min, the force is 80N/m, the liquid spraying frequency is 30 s/time, and the polishing time is 3min.
Fig. 7a shows that scratches appear in the ferrite region. It can be seen from fig. 7b that the ferrite region curve shows a valley, increasing the dispersion. It can be seen from fig. 8a that scratches occur in the pearlite area, and from fig. 8b that the pearlite area curve has valleys, the mean value is lowered, the dispersion is increased, and a width exceeding 5 points will lead to erroneous judgment.
Example 5
According to the phase content measuring method of example 1, the different grinding processes are rough grinding, fine grinding, 3 μm polishing process and 1 μm polishing process sequentially act on the test surface of the carbon structural steel sample, wherein the time of the rough grinding process is 60s, the force is 100Nm, the rotation speed is 90 turns/min, the time of the fine grinding process is 12min, the force is 150Nm, the rotation speed is 300 turns/min, the rotation speed of the polishing process is 140 turns/min, the force is 170Nm, the liquid spraying frequency is 30 s/time, the polishing time is 2min, the rotation speed of the 1 μm polishing process is 170 turns/min, the force is 100N/m, the liquid spraying frequency is 30 s/time, and the polishing time is 1min.
As can be seen from fig. 9, when the polishing was poor, the structure was not clear, the ferrite region was rough, the contour line was very rough, and the effect of comparative example 1 was poor.
Example 6
The phase content measurement method of example 1 was followed except that the type of the carbon structural steel was changed, and the carbon structural steel was SWRCH22A steel.
Table 4 shows the standard deviations of the original heights at 5 consecutive points for the AB, CD and EF segments of FIG. 10 b.
It can be seen from table 4 that the method of example 1 has a better adaptability to different steel grades.
| AB | CD | EF | |
| Minimum value (um) | 0.007 | 0.001 | 0.011 |
| Maximum value (um) | 0.123 | 0.020 | 0.109 |
| Average value (um) | 0.034 | 0.004 | 0.048 |
| Standard deviation (um) | 0.025 | 0.002 | 0.022 |
Table 4.
Claims (9)
1. A method for determining the phase content of carbon structural steel, comprising the following steps: grinding and corroding the inspection surface of the steel sample, and then measuring the phase content by adopting a laser confocal microscope, wherein the phase content measurement comprises the following steps:
(1) A laser confocal microscope is adopted to obtain a three-dimensional stereomorphology map of the region to be detected on the surface of the sample;
(2) Leveling the three-dimensional morphology graph, wherein a leveling surface is used as a height reference surface of the three-dimensional morphology graph;
(3) In the direction parallel to the X axis or the Y axis, the three-dimensional stereomorphology graph is cut to obtain a limited number of cross sections and cross section profile curves;
(4) Dividing a section where the section profile curve is located into ferrite phase and pearlite phase according to whether the height standard deviation of the continuous preset number of points of the section profile curve is smaller than or equal to a preset value, wherein the area smaller than or equal to the preset value is ferrite phase;
(5) And respectively adding ferrite phase and pearlite phase of each section to obtain the phase content of the region to be measured.
2. The measurement method according to claim 1, wherein the resolution of the three-dimensional topography is 0.125 μm or more, the pitch of the limited number of cross sections is 0.125 μm or less, and the abscissa or ordinate of points in the cross-sectional profile is 0.125 μm or less apart.
3. The method according to claim 2, wherein the predetermined number is 5 or more.
4. The method according to claim 3, wherein the predetermined value is 0.025 to 0.035. Mu.m.
5. The measurement method according to claim 1, wherein three points of the same circle are selected in the ferrite region, and a three-dimensional topography is leveled by a three-point leveling method;
after the section profile curve is obtained, the basis for dividing the section where the section profile curve is located into ferrite phase and pearlite phase also comprises the step of calculating the average height of each point of the section profile curve, wherein the calculated height of each point is obtained by subtracting the average height from the original height of each point on the section profile curve, and the area with the calculated height of the points with continuous preset numbers smaller than 0 is ferrite.
6. The method according to claim 1, wherein the etching liquid is 4% nitroalcohol and the etching time is 3 to 6s.
7. The measurement method according to claim 1, wherein the grinding includes a coarse grinding process, a fine grinding process, a 3 μm polishing process, and a 1 μm polishing process.
8. The method according to claim 7, wherein the time of the rough grinding step is 50 to 70 seconds, the force is 90 to 110Nm, the rotational speed is 90 to 100 rpm, the time of the fine grinding step is 11 to 13 minutes, the force is 145 to 155Nm, and the rotational speed is 300 to 320 rpm.
9. The method according to claim 7, wherein the rotation speed of the 3 μm polishing step is 140 to 160 revolutions/min, the force is 145 to 155Nm, the liquid spraying frequency is 25 to 30 s/time, the polishing time is 3 to 4min, the rotation speed of the 1 μm polishing step is 140 to 160 revolutions/min, the force is 85 to 95N/m, the liquid spraying frequency is 25 to 30 s/time, and the polishing time is 2 to 3min.
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