Method for measuring original austenite grain size of low-alloy quenched steel by X-ray diffractometer method

Abstract

The invention discloses a method for determining the original austenite grain size of low-alloy quenched steel by an X-ray diffractometer method, and belongs to the technical field of metal material detection. According to the method provided by the invention, nondestructive testing is realized by establishing the quantitative relation model of the martensite phase change product and the original grain size, chemical erosion and mechanical damage of a traditional metallographic method to a sample are avoided, and the problems of large destructiveness, complex operation, limited application range and the like of a traditional detection means are solved; the method can be directly used for quality inspection of finished products, and a new technical means is provided for whole-process quality control of steel products. An optimized diffraction peak analysis algorithm is combined, so that the measurement precision is remarkably improved; the detection process is simple, convenient and efficient, the single detection time can be shortened to be within 30 minutes, the detection efficiency is greatly improved, and the method is particularly suitable for rapid detection requirements of batch samples.

Description

Technical Field

[0001] This invention belongs to the field of metal material testing technology, specifically relating to a method for determining the original austenite grain size of low alloy quenched steel using X-ray diffraction. Background Technology

[0002] Austenite grain size is one of the key factors affecting the mechanical properties of steel (such as strength, toughness, and fatigue life). Traditional methods for determining the original austenite grain size mainly include metallography, electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM), but each of these methods has its limitations. Metallographic method: The sample needs to be ground, polished, and etched. It is destructive, and the etching reagents, such as picric acid, are toxic. The temperature and time of etching have a significant impact on the results, resulting in poor reproducibility.

[0003] Electron backscatter diffraction (EBSD): Relies on a high-precision scanning electron microscope (SEM), resulting in high equipment costs and complex sample preparation (grinding, electropolishing). The analytical area is limited, making it difficult to represent the overall grain distribution of the material. Extremely high surface flatness is required for the sample; even slight tilting can lead to data distortion.

[0004] Transmission electron microscopy (TEM): Sample preparation is difficult and the observation area is extremely small, resulting in insufficient statistical representativeness. The equipment is expensive, the testing cycle is long, and it is not suitable for rapid on-site industrial testing.

[0005] In recent years, X-ray diffraction (XRD) technology has been explored for grain size analysis due to its non-destructive, rapid, and statistically accurate characteristics. Existing XRD methods primarily calculate grain size based on the Scherrer formula, but they suffer from the following problems: They are only applicable to the existing phase; traditional XRD methods can only measure the grain size of the current phase (such as martensite and ferrite) and cannot directly reflect the original austenite grain size. They are also susceptible to interference from micro-stress: high-density dislocations and residual stresses in quenched or deformed steel lead to broadening of diffraction peaks, affecting the accuracy of grain size calculations. Furthermore, XRD cannot directly observe grain boundaries and requires indirect calculation models.

[0006] Therefore, how to develop a rapid, non-destructive, and high-precision method for determining the original austenite grain size based on XRD technology to make up for the shortcomings of existing technologies and meet the quality control and material research needs of the steel industry has become an important issue that urgently needs to be addressed. Summary of the Invention

[0007] Therefore, the purpose of this invention is to provide a method for determining the original austenite grain size of low-alloy quenched steel using X-ray diffraction. By optimizing the XRD diffraction peak analysis algorithm, a quantitative relationship model between austenite phase transformation products and the original grain size is established. This method enables non-destructive, rapid, and accurate determination of austenite grain size, providing a new and reliable grain size detection solution for the steel industry.

[0008] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a method for determining the original austenite grain size of low-alloy quenched steel by X-ray diffraction, comprising the following steps: S1, After the sample is cut, it is kept warm and water-quenched; S2, after water quenching, the sample is ground and polished to obtain a diffraction sample; after cutting, the sample is inlaid, ground and polished to obtain a metallographic sample. S3, X-ray diffraction of the diffracted sample to obtain the spectrum; etching of the metallographic sample with picric acid to obtain the interdendritic boundaries; S4. Fit the spectral lines of the spectrum to obtain the required parameters, and use the Scherrer formula to calculate the martensite grain size; calculate the average original austenite grain size based on the dendrite boundaries. S5. Fit the martensite grain size and the average original austenite grain size to obtain the fitting equation; S6. Based on the fitting equation and the martensite grain size of the sample to be tested, the original austenite grain size is obtained.

[0009] In S1, there are 3 samples, each of which is kept at a different temperature. The Fit Profile function of HighScore Plus is used to obtain an accurate fitting equation after 3 fittings.

[0010] In S1, wire cutting is used to cut the sample to a length of 10mm, a width of 10mm, and a height of 5mm.

[0011] The Scherrer formula refers to the Debye-Scherrer-Scherrer formula.

[0012] Picric acid is a saturated aqueous solution of picric acid.

[0013] The spectrum obtained from S3 was analyzed using HighscorePlus software.

[0014] The average original austenite grain size was calculated using Image J.

[0015] For the fitting of S5, Origin was used to build the model, and the fitting correlation coefficient R was [value missing]. 2 =1, indicating a good fit.

[0016] The sample is composed of the following chemical components by mass percentage: C 0.45%, Si 0.20%, Mn 0.52%, S ≤0.035%, P ≤0.035%, balance is iron and unavoidable impurities.

[0017] The sample was 45# steel, which refers to steel containing 0.45% C.

[0018] Based on the above technical solution, the insulation temperature in S1 is further 850℃-1050℃.

[0019] The heat preservation time is 30 minutes.

[0020] Based on the above technical solution, further, the grinding in S2 is done with 180#-1200# sandpaper, and the polishing is done with polishing paste.

[0021] The sample characterization surfaces were successively polished with 180#, 400#, 800#, and 1200# sandpaper.

[0022] Among them, the polishing paste is diamond polishing paste.

[0023] Based on the above technical solution, furthermore, the X-ray diffraction in S3 uses a Cu target and the test range is 20°-120°.

[0024] The X-ray diffraction used a tube voltage of 40kV, a tube current of 40mA, and a scanning time of 10 minutes.

[0025] Based on the above technical solution, the parameters in S4 further include the incident angle of the martensitic main peak crystal plane, the measured broadening value, and the standard broadening value.

[0026] The crystal plane index of the main martensite peak crystal plane is 110.

[0027] Based on the above technical solution, the Scherrer formula in S4 is further as follows: (1); In the formula, k is the shape factor, λ is the target wavelength of Cu, B1 is the measured broadening value, B2 is the standard broadening value, and θ is the incident angle.

[0028] Based on the above technical solution, further, when the martensite grain size calculated in S4 is between 18.3 nm and 26.6 nm, the fitting equation in S5 is the following numerical calculation formula: y=31.63-2 x+0.07 x2 (2); In the formula, y is the original austenite grain size in μm and x is the martensite grain size in nm.

[0029] Compared with the prior art, the present invention has the following beneficial effects: 1. The method provided by this invention achieves non-destructive testing by establishing a quantitative relationship model between martensitic phase transformation products and original grain size, avoiding the chemical erosion and mechanical damage to samples caused by traditional metallographic methods. It solves the problems of high destructiveness, complex operation, and limited applicability of traditional testing methods, and can be directly used for quality inspection of finished parts, providing a new technical means for the whole process quality control of steel products.

[0030] 2. The method provided by this invention, combined with an optimized diffraction peak analysis algorithm, significantly improves measurement accuracy.

[0031] 3. The method provided by this invention is simple and efficient in the detection process, and the detection time for a single test can be shortened to less than 30 minutes, which greatly improves the detection efficiency and is particularly suitable for the rapid detection needs of batch samples. Attached Figure Description

[0032] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.

[0033] Figure 1 The following are the spectra of three samples from Example 1 of the present invention, which were kept at temperatures of 850°C, 950°C, and 1050°C: A is the spectrum at a temperature of 850°C, B is the spectrum at a temperature of 950°C, and C is the spectrum at a temperature of 1050°C. Figure 2 The following are dendrite boundary diagrams for three samples of Example 1 of the present invention, with holding temperatures of 850℃, 950℃, and 1050℃ respectively: A is the dendrite boundary diagram at a holding temperature of 850℃, B is the dendrite boundary diagram at a holding temperature of 950℃, and C is the dendrite boundary diagram at a holding temperature of 1050℃. Figure 3 This is a fitting diagram of Embodiment 1 of the present invention; Figure 4 This is the spectrum of Embodiment 2 of the present invention; Figure 5 This is a dendrite boundary diagram of Embodiment 2 of the present invention; Figure 6 This is a fitting diagram of Embodiment 3 of the present invention; Figure 7 This is a dendrite boundary diagram of Embodiment 3 of the present invention. Detailed Implementation

[0034] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0035] Example 1 This embodiment describes the process of establishing the fitting equation for the method of determining the original austenite grain size of low alloy quenched steel using the X-ray diffraction method provided by this invention. The specific process is as follows.

[0036] Step 1: 45# steel was selected as the experimental steel. The samples were cut into 10mm long, 10mm wide, and 5mm high sections using wire cutting. The key chemical composition of 45# steel is: C 0.45 wt.%, Si 0.20 wt.%, Mn 0.52 wt.%, S ≤0.035 wt.%, P≤0.035 wt.%. The samples were held in a muffle furnace for 30 minutes, followed by water quenching. The holding temperatures for the three samples were 850℃, 950℃, and 1050℃, respectively.

[0037] Step 2: Grind the sample characterization surface sequentially with 180#, 400#, 800#, and 1200# sandpaper, and then polish it with a high-efficiency polishing agent.

[0038] Step 3: The equipment used is an X`PERT PRO X-ray diffractometer. A Cu target is used, with a tube voltage of 35kV, a tube current of 40mA, and a test range of 20°-120°.

[0039] Step 4: Use HighscorePlus software to analyze the obtained spectrum, as shown in the image. Figure 1 The required parameters (incident angle of the martensitic main peak (110) crystal plane, measured broadening value, and standard broadening value) are obtained by fitting the spectral lines. The grain size is calculated using the Scherrer formula, as shown in Table 1.

[0040] We can calculate the average grain size using the Debye-Scherrer formula, as shown in equation (1): (1) In the formula, k is the shape factor, λ is the target wavelength of Cu, B1 is the measured broadening value, B2 is the standard broadening value, and θ is the incident angle.

[0041] Step 5: Prepare metallographic specimens. After mounting, grinding, and polishing the specimens, etch them with picric acid to reveal the interdendritic boundaries. The average original austenite grain size (Y) is calculated using Image J. Figure 2 Table 1.

[0042] Step Six: A model is built using Origin to fit the martensite grain size (D) calculated by XRD with the actual average original austenite grain size (Y) calculated using ImageJ. The correlation coefficient R0 is used for fitting. 2 =1 indicates a very good fit. The fitting graph is shown below. Figure 3 The fitting equation is as follows: y=31.63-2 x+0.07 x 2 (2); In the formula, y is the original austenite grain size in μm; x is the martensite grain size in nm.

[0043] Y represents the original austenite grain size in μm, and D represents the martensite grain size in nm.

[0044] This equation is applicable to as-cast samples of 45# steel. XRD calculations show that the martensite grain size is between 18.3 nm and 26.6 nm.

[0045] Table 1 shows the results of martensite grain size and average original austenite grain size in Example 1.

[0046]

[0047] Example 2 This embodiment is a verification embodiment of the method for determining the original austenite grain size of low alloy quenched steel using the X-ray diffraction method provided by the present invention. The specific process is as follows.

[0048] Step 1: 45# steel was selected as the experimental steel and machined to dimensions of 10mm in length, 10mm in width, and 5mm in height. The key chemical composition of 45# steel is: C 0.45 wt.%, Si 0.20 wt.%, Mn 0.52 wt.%, S ≤0.035 wt.%, P ≤0.035 wt.%. The sample was held in a muffle furnace for 30 minutes, followed by water quenching at 900℃.

[0049] Step 2: Grind the sample characterization surface sequentially with 180#, 400#, 800#, and 1200# sandpaper, and then polish it with high-efficiency polishing paste.

[0050] Step 3: The equipment used is an X`PERT PRO X-ray diffractometer. A Cu target is used, with a tube voltage of 35kV, a tube current of 40mA, and a test range of 20°-120°.

[0051] Step 4: Use HighscorePlus software to analyze the obtained spectrum and perform spectral fitting. Figure 4) Obtain the required parameters (incident angle of the martensite main peak (110) crystal plane, measured broadening value, standard broadening value, Table 2, and calculate the grain size using the Scherrer formula (1), D=18.7 nm.

[0052] Step 5: The original austenite grain size Y = 18.7 μm was calculated using formula (2), as shown in Table 2.

[0053] Step Six: Prepare metallographic specimens. After mounting, grinding, and polishing, the specimens are etched with picric acid to reveal the interdendritic boundaries. Image J calculations show that the average original austenite grain size (Y) is 19.0 μm. Figure 5 .

[0054] Example 3 This embodiment is a verification embodiment of the method for determining the original austenite grain size of low alloy quenched steel using the X-ray diffraction method provided by the present invention. The specific process is as follows.

[0055] Step 1: 45# steel was selected as the experimental steel and machined to dimensions of 10mm in length, 10mm in width, and 5mm in height. The key chemical composition of 45# steel is: C 0.45 wt.%, Si 0.20 wt.%, Mn 0.52 wt.%, S ≤0.035 wt.%, P ≤0.035 wt.%. The sample was held in a muffle furnace for 30 minutes, followed by water quenching at 1000℃.

[0056] Step 2: Grind the sample characterization surface sequentially with 180#, 400#, 800#, and 1200# sandpaper, and then polish it with a high-efficiency polishing agent.

[0057] Step 3: The equipment used is an X`PERT PRO X-ray diffractometer. A Cu target is used, with a tube voltage of 35kV, a tube current of 40mA, and a test range of 20°-120°.

[0058] Step 4: Use HighscorePlus software to analyze the obtained spectrum and perform spectral fitting. Figure 6 To obtain the required parameters (the incident angle of the martensite main peak (110) crystal plane, the measured broadening value, and the standard broadening value, Table 2), the grain size was calculated using the Scherrer formula (1), with D = 26.3 nm.

[0059] Step 5: The original austenite grain size Y = 27.4 μm was calculated using formula (2), as shown in Table 2.

[0060] Step Six: Prepare metallographic specimens. After mounting, grinding, and polishing, the specimens are etched with picric acid to reveal the interdendritic boundaries. Image J calculations show that the average original austenite grain size (Y) is 27.3 μm. Figure 7 .

[0061] Table 2 shows the results of martensite grain size and average original austenite grain size for Examples 2 and 3.

[0062]

[0063] As can be seen from Examples 2 and 3, the original austenite grain size of 45# steel after quenching calculated using the equation of the present invention is very close to the actual grain size obtained by metallographic method, with an error of less than 2%. Therefore, within a certain range, the equation designed in this invention can be used to estimate the original austenite grain size of 45# steel after quenching.

[0064] 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 determining the original austenite grain size of low-alloy quenched steel using X-ray diffraction, characterized in that, Includes the following steps: S1, After the sample is cut, it is kept warm and water-quenched; S2, after water quenching, the sample is ground and polished to obtain a diffraction sample; after cutting, the sample is inlaid, ground and polished to obtain a metallographic sample. S3, X-ray diffraction of the diffracted sample to obtain the spectrum; etching of the metallographic sample with picric acid to obtain the interdendritic boundaries; S4. Fit the spectral lines of the spectrum to obtain the required parameters, and use the Scherrer formula to calculate the martensite grain size; calculate the average original austenite grain size based on the dendrite boundaries. S5. Fit the martensite grain size and the average original austenite grain size to obtain the fitting equation; S6. Based on the fitting equation and the martensite grain size of the sample to be tested, the original austenite grain size is obtained.

2. The method for determining the original austenite grain size of low-alloy quenched steel by X-ray diffraction according to claim 1, characterized in that, The insulation temperature in S1 is 850℃-1050℃.

3. The method for determining the original austenite grain size of low-alloy quenched steel by X-ray diffraction according to claim 1, characterized in that, The grinding in S2 is done with 180#-1200# sandpaper, and the polishing is done with polishing paste.

4. The method for determining the original austenite grain size of low-alloy quenched steel by X-ray diffraction according to claim 1, characterized in that, The X-ray diffraction in S3 uses a Cu target and has a test range of 20°-120°.

5. The method for determining the original austenite grain size of low-alloy quenched steel by X-ray diffraction according to claim 1, characterized in that, The parameters in S4 include the incident angle of the martensitic main peak crystal plane, the measured broadening value, and the standard broadening value.

6. The method for determining the original austenite grain size of low-alloy quenched steel by X-ray diffraction according to claim 1, characterized in that, The Scherrer formula in S4 is as follows: （1）； In the formula, k is the shape factor, λ is the target wavelength of Cu, B1 is the measured broadening value, B2 is the standard broadening value, and θ is the incident angle.

7. The method for determining the original austenite grain size of low-alloy quenched steel by X-ray diffraction according to claim 2, characterized in that, When the martensite grain size calculated in S4 is between 18.3 nm and 26.6 nm, the fitting equation in S5 is the following numerical calculation formula: y=31.63-2 x+0.07 x 2 (2); In the formula, y is the original austenite grain size in μm and x is the martensite grain size in nm.

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