CN113176181A - Grain size testing method - Google Patents
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- 238000012360 testing method Methods 0.000 title claims abstract description 44
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- 238000000227 grinding Methods 0.000 claims abstract description 8
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- 238000011065 in-situ storage Methods 0.000 claims abstract description 4
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- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 4
- 229910001566 austenite Inorganic materials 0.000 description 4
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- OXNIZHLAWKMVMX-UHFFFAOYSA-N picric acid Chemical class OC1=C([N+]([O-])=O)C=C([N+]([O-])=O)C=C1[N+]([O-])=O OXNIZHLAWKMVMX-UHFFFAOYSA-N 0.000 description 2
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
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Abstract
The invention provides a grain size testing method, which comprises the following steps: step S1, processing the sample into a test sample with a proper size, and grinding and polishing the surface to be tested of the test sample to obtain the test sample to be tested; step S2, placing a sample to be tested into a high-temperature furnace for heating, heat preservation and cooling treatment, wherein the high-temperature furnace is connected with a high-speed image acquisition CCD system, carrying out in-situ real-time observation on the surface of the sample to be tested in the heat preservation process through the high-speed image acquisition CCD system, and acquiring and storing a crystal boundary morphology picture; and step S3, adopting size measurement software to import the picture collected in the step S2, measuring and analyzing the grain size in the stored picture, and obtaining average grain size information. The testing method can obtain the grain sizes under different temperatures and heat preservation times, is simple and convenient to operate, does not use any chemical reagent, has wide adaptability and short time consumption, and obtains more comprehensive and accurate grain size data compared with the existing grain size grading method.
Description
Technical Field
The invention belongs to the technical field of analysis and test of microstructure of metal materials, and particularly relates to a grain size test method.
Background
The development of new materials and new processes is accompanied with the acquisition of materials with various tissue morphologies and structures to improve the service performance of the materials, how to accurately and precisely determine the internal tissue structure of the standard materials has great reference value for material application customers, and very important test means and basis can be provided for material process optimization and component improvement of material scientists, so that corresponding novel detection means can be continuously developed along with the continuous development of material research and development, and the current actual detection requirements are met. The main standards for detecting the grain size currently include GB/T6394-. However, evaluation using these criteria requires a clear, complete grain boundary geometry, which is difficult to achieve for many materials.
In the prior art, the 'method for nondestructive rapid detection of grain size of metal polycrystal' of Chinese patent application No. 03136604.X can only obtain the number of grains within a certain size range, and the result is not accurate enough; application No. 201310612064.2 'preparation method of a wear-resistant steel austenite actual grain size detection sample', the grain size is detected by high-temperature tempering, grinding and polishing and etching, the operation process is complex, and only one material can be detected; application No. 201510148112.6 'detection and display method of austenite grain size of quenched and tempered steel for gears at room temperature', adopts saturated picric acid, sodium dodecyl benzene sulfonate and concentrated hydrochloric acid mixed solution to display austenite grain boundary, but the saturated picric acid belongs to limited purchased chemical reagent at present, the method is limited, and only can be used for the type of steel. Application No. 201310217350.9 "a method for rapidly detecting grain size of a material" utilizes a method of quenching in a vacuum furnace and tempering and then observing by a microscope to analyze the grain size, which is not suitable for a material with unclear grain boundaries caused by phase change at the later stage, and the heat preservation at a higher temperature may cause the growth of austenite grain size in the heat preservation process, the real-time observation of the grain size and the real-time collection of photos cannot be performed, so that the grain size of the material after the final quenching and tempering is not consistent with the actual result, and the grain size detection is still performed by the traditional method, so that the information of each grain size cannot be given, and the result is not accurate. The grain size testing method in the prior art is complex to operate and the testing result is not accurate enough.
Therefore, there is a need to provide an improved solution to the above-mentioned deficiencies of the prior art.
Disclosure of Invention
The invention aims to provide a grain size testing method, which at least solves the problems that the grain size is limited by a corrosive agent in the process of measuring the grain size by the conventional grain size grading method, the operation is complex, the testing data is incomplete, and the testing result is inaccurate.
In order to achieve the above purpose, the invention provides the following technical scheme:
a grain size testing method comprises the following steps:
step S1, processing the sample into a test sample with a proper size, and grinding and polishing the surface to be tested of the test sample to obtain the test sample to be tested;
step S2, placing a sample to be tested into a high-temperature furnace for heating, heat preservation and cooling treatment, wherein the high-temperature furnace is connected with a high-speed image acquisition CCD system, carrying out in-situ real-time observation on the surface of the sample to be tested in the heat preservation process through the high-speed image acquisition CCD system, and acquiring and storing a crystal boundary morphology picture;
and step S3, introducing the grain boundary morphology picture collected in the step S2 by adopting size measurement software, measuring and analyzing the grain size in the grain boundary morphology picture, and obtaining average grain size information.
In the grain size test method as above, preferably, the sample is processed into a test piece satisfying the thickness dimension of less than 4mm and the length and width dimensions of less than 7mm in step S1.
In the above method for testing the grain size, preferably, in step S1, all surfaces of the sample are finely ground to prevent the surface foreign matter from volatilizing during the high-temperature heating process and contaminating the surface to be tested;
preferably, the step S1 further includes: carrying out ultrasonic cleaning on the sample after polishing and before obtaining the sample to be measured, and then carrying out light polishing treatment on the surface to be measured;
still preferably, the time of the light polishing process is 5 s.
In the above method for testing the grain size, preferably, the high-temperature furnace is provided with a temperature control system, so that the adjustment setting of the heating rate, the heat preservation time, the heat preservation temperature and the cooling rate can be realized; inert protective gas is introduced into the high-temperature furnace.
In the above method for testing the grain size, preferably, in step S2, the rate of heating the sample to be tested in the high temperature furnace is 100 ℃/min to 800 ℃/min;
preferably, the heating is carried out in a high temperature furnace at a rate of 100 ℃/min to 500 ℃/min.
In the above grain size test method, preferably, in step S2, the holding temperature of the sample to be tested in the high temperature furnace is set to 800 ℃ to 1400 ℃;
preferably, the holding temperature in the high temperature furnace is set to 900 ℃ -1350 ℃.
In the above grain size test method, preferably, in step S2, the holding time in the high temperature furnace should satisfy 0.5min to 10 min.
In the above method for testing die size, preferably, in step S2, a plurality of pictures of the field of view are stored during the heat preservation process, and each picture contains at least five dies.
In the grain size test method, preferably, the grain boundary morphology picture has a total number of complete grains ranging from 5 to 200;
preferably, the grain boundary morphology picture has a total number of complete grains in the range of 20-150.
In the grain size testing method, preferably, the size data of each grain in the picture, including the maximum size, the minimum size and the average size of each grain, is obtained through the size measuring software, and the average size of the grains, the maximum size of the grains and the minimum size of the grains in the whole field range are finally obtained after averaging the values in all the measured grain size data.
Has the advantages that:
the invention provides a grain size testing method, a sample to be detected is ground and polished and then placed into a high-temperature heating furnace (namely a high-temperature furnace) which is filled with protective gas and can realize temperature and time control, the high-temperature heating furnace is connected with a high-speed image acquisition CCD system, and the high-speed image acquisition CCD system is utilized to realize high-definition real-time capture and recording of dynamic pictures in the heat preservation process; then, the grain size in the sample to be measured is measured by using relevant software, so that the size information of a single grain, the statistical result of the size information of all grains and the grain sizes under different temperatures and heat preservation times can be obtained.
The testing method of the invention obtains the crystal boundary morphology by a thermal etching method, has simple and convenient operation, does not use any chemical reagent, can avoid the problem that the crystal boundary can not be clearly displayed due to improper selection of the chemical reagent and improper corrosion process, and can obtain the data of the maximum size, the minimum size and the average size of each crystal grain and the statistical result data of all crystal grains. Compared with the common method, the method can completely avoid using dangerous reagents and a sample preparation method with overlong display time, reduces the exploration of the corrosion process, has wide adaptability and short time consumption, and obtains more comprehensive and accurate grain size data compared with the existing grain size grading method.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention. Wherein:
FIG. 1 is a graph showing the crystal grain morphology of low carbon steel in example 1 of the present invention after heat preservation at 1350 ℃ for 2 min;
FIG. 2 is a tissue morphology map obtained after the picture in FIG. 1 is processed by software;
FIG. 3 is a graph showing the morphology of grains of the low alloy steel in example 2 of the present invention after heat preservation at 950 ℃ for 9.5 min;
FIG. 4 is a graph showing the morphology of grains of the low alloy steel in example 3 of the present invention after heat preservation at 1200 ℃ for 5 min;
FIG. 5 is a graph showing the morphology of grains of the low alloy steel of comparative example 1 of the present invention after heat preservation at 1200 ℃ for 1 second.
Detailed Description
The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings. It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.
In the description of the present invention, the terms "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, which are for convenience of description of the present invention only and do not require that the present invention must be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention. The terms "connected" and "connected" used herein should be interpreted broadly, and may include, for example, a fixed connection or a detachable connection; they may be directly connected or indirectly connected through intermediate members, and specific meanings of the above terms will be understood by those skilled in the art as appropriate.
The invention provides an accurate grain size testing method for solving the problems that a plurality of materials are difficult to obtain the appearance of grains through corrosion and the grain size detection cannot be realized.
For ease of understanding, the terms in the present invention are explained as follows:
the maximum dimension of each grain refers to the maximum length through the grain centroid;
the minimum size of each grain refers to the minimum length through the grain centroid;
the average size of each grain refers to the average of the length through the grain centroid.
The grain size of the present invention refers to average grain size information of grains in the whole view field range (i.e. in the grain boundary morphology picture), and specifically, the average grain size information includes the maximum size of grains in the whole view field range, the minimum size of grains in the whole view field range, and the average size of grains in the whole view field range. Wherein:
the maximum size of the crystal grains in the whole view field range refers to the average value of the maximum sizes of all the crystal grains, and correspondingly;
the minimum size of the crystal grains in the whole view field range refers to the average value of the minimum sizes of all the crystal grains;
the average size of the crystal grains in the whole visual field range refers to the ratio of the sum of the average sizes of each crystal grain to the number of the crystal grains. The grain size testing method has wide adaptability and simple and convenient operation; compared with the conventional metallographic etching sample preparation method, the metallographic etching sample preparation method is not limited by the etchant. Compared with the existing grain size grading method, the obtained data is more comprehensive and accurate.
The grain size testing method specifically comprises the following steps:
and step S1, processing the sample into a sample with a proper size, and grinding and polishing the surface to be measured of the sample by adopting sand paper with different particle sizes according to the metallographic sample preparation method to obtain the sample to be measured.
In an embodiment of the present invention, in step S1, the sample is processed to obtain a test specimen having a thickness dimension of less than 4mm and length and width dimensions of less than 7 mm. If the sample is processed into a cylindrical sample, the diameter of the cylindrical sample is less than 7 mm. Because the sample is placed in the crucible, the current crucible size is basically 9mm in diameter and 4mm in height, so the sample size is smaller than this size.
All surfaces of the sample are subjected to fine grinding treatment to prevent surface foreign matters from volatilizing in the high-temperature heating process to pollute the surface of the sample to be detected; and after the surface of the sample to be tested is ground and polished, the sample to be tested is placed in a high-temperature furnace after being ensured to be clean and pollution-free.
Preferably, after the sample to be measured polished in step S1 is subjected to ultrasonic cleaning, the surface to be measured is subjected to light polishing for 5S, the light polishing serves to remove surface dust, and the sample to be measured is placed in a high temperature furnace after being subjected to light polishing.
And S2, placing the sample to be tested into a high-temperature furnace for heating, heat preservation and cooling treatment, connecting the high-temperature furnace with a high-speed image acquisition CCD system, carrying out in-situ real-time observation on the surface of the sample to be tested in the heat preservation process through the high-speed image acquisition CCD system, and collecting and storing the grain boundary morphology picture.
In the specific embodiment of the invention, inert protective gas such as argon is introduced into the high-temperature furnace, so as to prevent the surface of the sample material to be detected from being oxidized in the processes of temperature rise and heat preservation, deteriorate the image quality and reduce the definition. The high-temperature furnace is provided with a temperature control system, and the adjustment setting of heating rate, heat preservation time, heat preservation temperature and cooling rate can be realized.
The temperature of the sample to be tested in the high temperature furnace is set to 800-1400 ℃ (such as 850 ℃, 900 ℃, 950 ℃, 1000 ℃, 1050 ℃, 1100 ℃, 1150 ℃, 1200 ℃, 1250 ℃, 1300 ℃, 1350 ℃); preferably, the holding temperature in the high temperature furnace is set to 900 ℃ -1350 ℃. The heat preservation time in the invention is 0.5min-10min (such as 40s, 50s, 1min, 2min, 3min, 4min, 5min, 6min, 7min, 8min and 9min), so that the sample can display complete grains at the temperature, meanwhile, the heat preservation time cannot be overlong, the grains are prevented from growing, and the heat preservation time in the high-temperature furnace is less than 10 min. Too short a heat preservation time will result in unclear crystal boundary display and failure to obtain a complete grain microstructure picture. Meanwhile, in order to save time and prevent the crystal grains from growing up in the heating process, the heating rate cannot be too slow, and the heating rate of the sample to be measured in the high-temperature furnace is generally set to be 100 ℃/min-800 ℃/min (such as 150 ℃/min, 200 ℃/min, 250 ℃/min, 300 ℃/min, 350 ℃/min, 400 ℃/min, 450 ℃/min, 500 ℃/min, 550 ℃/min, 600 ℃/min, 650 ℃/min, 700 ℃/min and 750 ℃/min); preferably, the heating is carried out in a high temperature furnace at a rate of 100 ℃/min to 500 ℃/min.
In the embodiment of the invention, pictures of a plurality of view fields are stored in the heat preservation process, and the magnification is manually changed according to the actual grain size, so that the grains can be clearly seen, the number of the grains is not too small, and each picture contains at least five grains. Meanwhile, the total number of the complete grains in the stored grain boundary morphology pictures is ensured to be 5-200 (such as 10, 15, 20, 30, 50, 60, 80, 100, 110, 120, 130, 140, 150, 160, 170, 180 and 190), and more accurate average grain size values can be obtained in a plurality of pictures, so that size measurement errors are reduced. Preferably, the grain boundary morphology picture has a total number of complete grains in the range of 20-150.
And step S3, adopting size measurement software to import the picture collected in the step S2, measuring and analyzing the grain size in the stored picture, and obtaining average grain size information.
In the embodiment of the present invention, the dimension measurement software is image-Pro plus, but may be other dimension measurement software in other embodiments, and may be any software capable of realizing the measurement of the grain size. And obtaining size data of each crystal grain in the picture through size measurement software, wherein the size data comprises the maximum size, the minimum size and the average size of each crystal grain, and averaging the values in all the measured crystal grain size data to finally obtain the average size, the maximum size and the minimum size of the crystal grains in the whole field range.
Example 1
The grain size of the low-carbon steel after heat preservation at 1350 ℃ for 2min is measured, and the test result is shown in figure 1 and figure 2.
The embodiment of the invention provides a method for testing the grain size of low-carbon steel after heat preservation at 1350 ℃ for 2min, which comprises the following steps:
processing a sample to be detected into a cylindrical sample with the diameter of 6 multiplied by 4mm, grinding and polishing a surface to be observed (namely the surface to be detected of the sample) by using abrasive paper with different particle sizes after fine grinding, wherein a polishing agent with the particle size of 1 mu m is used for ensuring the optimal surface effect, the polished surface is ensured to be bright and pollution-free, then putting the sample into a beaker filled with acetone for ultrasonic cleaning for 20min, and lightly polishing for 5s after cleaning is finished to obtain the sample to be detected.
Placing the prepared sample to be tested into an alumina crucible, placing the alumina crucible into a high-temperature furnace, introducing argon, setting a temperature control program, setting the heating rate to be 100 ℃/min, the heat preservation temperature to be 1350 ℃ and the heat preservation time to be 2min, then quickly cooling to the room temperature, and clicking to start executing the temperature control program after the setting program is finished.
After the temperature of the crystal grains is kept, the crystal grains are manually focused to ensure that the image is clear, the size change of the crystal grains in the heat preservation process is observed, and the crystal grain shape images at a plurality of positions can be stored by moving the sample table (the sample table is a device which is arranged on the high-temperature furnace and is controlled to move by software). After the program is executed, selecting the grain to be analyzed by using the picture or video stored in the equipment, and as shown in fig. 1, obtaining a grain boundary morphology picture after heat preservation for 2 min.
And opening the image analysis software image-Pro plus, importing the obtained grain boundary morphology picture, identifying the grain boundary in the picture, wherein the result is shown in figure 2, the picture analysis software can automatically count and calculate the crystal grains, and size data and statistical result data of each crystal grain are formed, and are shown in the following table 1.
Table 1 statistical results of grain sizes in fig. 2
From the data in table 1, statistical data of all the grains in fig. 1 can be obtained, and the average size of the grains, the maximum size of the grains, and the minimum size of the grains in the whole field range (i.e. in the grain boundary morphology picture fig. 1) can be obtained. By the same method, the grain size data in other pictures collected and stored can be obtained.
Example 2
The embodiment of the invention provides a test method for measuring the grain size of low alloy steel wheel steel after heat preservation at 950 ℃ for 9.5min, and the test result is shown in figure 3.
The sample preparation method and the operation steps of the embodiment are the same as those of the embodiment 1, except that the heat preservation temperature and the heat preservation time are different, and are not described again.
As can be seen from the figure, the grain boundary of the example is clearly visible after the temperature is kept at 950 ℃ for 9.5min, the measurement requirement of the grain size can be met, the average size of the grains in the whole field range is about 32 μm, the maximum size of the grains is about 90 μm, and the minimum size of the grains is about 7 μm.
Example 3
The embodiment of the invention provides a test method for measuring the grain size of low alloy steel wheel steel after heat preservation for 5min at 1200 ℃, and the test result is shown in figure 4.
The sample preparation method and the operation steps in this embodiment are the same as those in embodiment 1, except that the heat preservation temperature and the heat preservation are different, and are not described herein again.
As can be seen from the figure, the grain boundary of the embodiment is clearly visible after the temperature is kept at 1200 ℃ for 5min, the measurement requirement of the grain size can be met, the average size of the grains in the whole field range is about 13 μm, the maximum size of the grains is about 50 μm, and the minimum size of the grains is about 5 μm.
Comparative example 1
The difference between the comparative example and the example 3 is that the holding time is changed to 1s, other steps and operation methods are the same as those of the example 3, and the picture of the grain boundary morphology obtained in the comparative example is shown in fig. 5.
As can be seen from the figure, the surface of the sample has a large number of scratches, the heat preservation time is too short, the appearance of the grain boundary is unclear, and the stable grain size at the temperature is not suitable for grain size measurement.
In summary, according to the grain size testing method provided by the invention, a sample to be tested is ground and polished and then placed into a high-temperature heating furnace (i.e. a high-temperature furnace) which is filled with protective gas and can realize temperature and time control, the high-temperature heating furnace is connected with a high-speed image acquisition CCD system, and the high-speed image acquisition CCD system is used for realizing high-definition real-time capture and recording of a dynamic picture in a heat preservation process; then, the grain size in the sample to be measured is measured by using relevant software, so that the size information of a single grain, the statistical result of the size information of all grains and the grain sizes under different temperatures and heat preservation times can be obtained.
The testing method of the invention obtains the crystal boundary morphology by a thermal etching method, has simple and convenient operation, does not use any chemical reagent, can avoid the problem that the crystal boundary can not be clearly displayed due to improper selection of the chemical reagent and improper corrosion process, and can obtain the data of the maximum size, the minimum size and the average size of each crystal grain and the statistical result data of all crystal grains. Compared with the common method, the method can completely avoid using dangerous reagents and a sample preparation method with overlong display time, reduces the exploration of the corrosion process, has wide adaptability and short time consumption, and obtains more comprehensive and accurate grain size data compared with the existing grain size grading method.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A method of testing grain size, the method comprising the steps of:
step S1, processing the sample into a test sample with a proper size, and grinding and polishing the surface to be tested of the test sample to obtain the test sample to be tested;
step S2, placing a sample to be tested into a high-temperature furnace for heating, heat preservation and cooling treatment, wherein the high-temperature furnace is connected with a high-speed image acquisition CCD system, carrying out in-situ real-time observation on the surface of the sample to be tested in the heat preservation process through the high-speed image acquisition CCD system, and acquiring and storing a crystal boundary morphology picture;
and step S3, introducing the grain boundary morphology picture collected in the step S2 by adopting size measurement software, measuring and analyzing the grain size in the grain boundary morphology picture, and obtaining average grain size information.
2. The grain size test method of claim 1, wherein in step S1, the sample is processed to obtain a test specimen having a thickness dimension of less than 4mm and length and width dimensions of less than 7 mm.
3. The method for testing the grain size according to claim 1, wherein in the step S1, all surfaces of the sample are finely ground to prevent the surface foreign matter from volatilizing during the high-temperature heating process and polluting the surface to be tested;
preferably, the step S1 further includes: carrying out ultrasonic cleaning on the sample after polishing and before obtaining the sample to be measured, and then carrying out light polishing treatment on the surface to be measured;
still preferably, the light polishing process is performed for 5 seconds.
4. The grain size test method according to claim 1, wherein the high temperature furnace is provided with a temperature control system to achieve adjustment settings of heating rate, holding time, holding temperature, and cooling rate; and inert protective gas is introduced into the high-temperature furnace.
5. The method for testing the grain size according to claim 4, wherein in the step S2, the sample to be tested is heated in the high temperature furnace at a rate of 100 ℃/min to 800 ℃/min;
preferably, the heating is carried out in a high temperature furnace at a rate of 100 ℃/min to 500 ℃/min.
6. The grain size test method according to claim 4, wherein in the step S2, the holding temperature of the sample to be tested in the high temperature furnace is set to 800-1400 ℃;
preferably, the holding temperature in the high temperature furnace is set to 900 ℃ -1350 ℃.
7. The grain size test method according to claim 4, wherein the holding time in the high temperature furnace in step S2 is 0.5min-10 min.
8. The die size testing method of claim 1, wherein in step S2, a plurality of visual field pictures are stored during the heat preservation process, each picture containing at least five dies.
9. The grain size test method according to claim 8, wherein the grain boundary morphology picture has a total number of complete grains in the range of 5 to 200;
preferably, the grain boundary morphology picture has a total number of complete grains ranging from 20 to 150.
10. The grain size testing method according to claim 1, wherein the size measuring software obtains the size data of each grain in the picture, including the maximum size, the minimum size and the average size of each grain, and averages the values in the measured size data of all the grains to finally obtain the average size, the maximum size and the minimum size of the grains in the whole field of view.
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