Method for measuring volume fraction of Cr23C6 in steel through X-ray diffraction method

Abstract

The invention relates to the technical field of carbide detection, in particular to a method for measuring the volume fraction of Cr23C6 in steel by an X-ray diffraction method, which comprises the following steps: machining a high-chromium low-carbon quenched steel sample into a standard sample, and measuring sample components; oxide skin on the surface of the standard sample is removed; experiment parameters are set, a standard sample with the structure of martensite + austenite + Cr23C6 is placed in an instrument, and a systematic diffraction experiment is carried out to obtain a diffraction spectral line; the diffraction spectral lines are analyzed, and peak position parameter information of martensite and austenite in the phase is obtained; searching data of Cr23C6 in a crystallography database, and fitting the obtained diffraction spectral lines by adopting a Rietveld refinement method to obtain the mass fractions of martensite, Cr23C6 and austenite; establishing a model to convert the mass fraction into a volume fraction; therefore, the M23C6 volume fraction of a multiphase coexisting sample with preferred orientation can be measured.

Description

Technical Field

[0001] This invention relates to the field of carbide detection technology, and more particularly to an X-ray diffraction method for determining Cr in steel. 23 The C6 volume fraction method. Background Technology

[0002] M in steel 23 C6 type carbides (such as Cr) 23 C6, (Cr,Fe) 23 C6 is a key reinforcing phase in stainless steel, heat-resistant steel and high alloy steel. Its composition, size, distribution and volume fraction have a decisive influence on the high-temperature strength, corrosion resistance and toughness of the material.

[0003] Nanoscale intracrystalline dispersion can enhance strength through the Orowan mechanism, while continuous precipitation at grain boundaries forms a brittle network and induces Cr-depleted zones, leading to an increased corrosion rate. Among existing methods, chemical analysis (acid extraction + gravimetric method) requires sample destruction and takes 8-24 hours, failing to preserve the original sample; metallographic methods struggle to identify nano-carbide and have significant errors in area fraction conversion; traditional XRD methods (K-value method / internal standard method) suffer from insufficient matrix absorption correction, difficulty in peak separation due to multiphase coexistence (e.g., martensite + carbide), preferred orientation interference, and low detection limits, failing to meet the requirements for M. 23 C6 quantitative requirements. Summary of the Invention

[0004] This invention provides an X-ray diffraction method for determining Cr in steel. 23 The C6 volume fraction method enables M-phase analysis of multiphase coexisting samples with preferred orientations. 23 The determination of C6 mass fraction and the establishment of a conversion relationship between XRD data acquisition and actual sample volume fraction are achieved. The refined mass fraction is automatically converted into the volume fraction required for mechanistic analysis, solving the parameter matching problem of precipitation strengthening model. This method provides quantitative support for material composition design, process control and service evaluation.

[0005] To achieve the above objectives, the present invention employs the following technical solution: An X-ray diffraction method for determining Cr in steel 23 The method for C6 volume fraction includes the following steps: Step 1: Machin the high-chromium, low-carbon quenched steel sample into a standard sample and measure the composition of the standard sample. Step 2: Remove the oxide scale from the surface of the standard sample; Step 3: Set experimental parameters to determine the microstructure as martensite + austenite + Cr. 23 The standard C6 sample is placed in the instrument to conduct a systematic diffraction experiment in order to obtain the diffraction pattern. Step 4: Analyze the diffraction lines to obtain the peak position parameters of martensite and austenite in the phase. Step 5: Search for martensite, austenite, and Cr in crystallography databases. 23 The C6 data were fitted with the obtained diffraction lines using the Rietveld refinement method to obtain martensite and Cr. 23 C6 and austenite mass fraction; Step 6: Build a model to convert mass fraction into volume fraction; ; in, Cr obtained after refinement 23 C6 volume fraction, Cr obtained after refinement 23 C6 mass fraction; The density of steel; Let be the density of the i-th element, in g / cm³. 3 n is the number of different types of elements in the alloy; For Cr 23 Density of C6, g / cm³ 3 .

[0006] Furthermore, the standard sample is a high-chromium, low-carbon quenched steel sample with a length of 10–20 mm, a width of 10–20 mm, and a height of 1–5 mm.

[0007] Furthermore, the experimental parameters are as follows: the experiment is conducted using an X`PERTPROX optical diffractometer, a Cu target is used, and the tube voltage is adjusted to 35-40kV and the tube current is set to 35-40mA.

[0008] Furthermore, the obtained diffraction lines are fitted using the Rietveld refinement method, and the fitting formula is as follows: ; Among them, Y1 and Y bt For the measured intensity and background intensity of the diffraction curve; I pk J pk F pk These represent the multiplicity factor, angular factor, and structural amplitude including the temperature factor of the k-th diffraction line of a certain phase in the standard sample to be tested; G pki It is a peak-shaped function; This is the weighting factor for phase P.

[0009] Compared with the prior art, the beneficial effects of the present invention are: A non-destructive measurement method based on Rietveld full-spectrum refinement is proposed: enabling M-mode analysis of multiphase coexisting samples with preferred orientations. 23The determination of C6 mass fraction; at the same time, the connection between XRD data acquisition and actual sample volume fraction is established, and the refined mass fraction is automatically converted into the volume fraction required for mechanism analysis, solving the parameter matching problem of precipitation strengthening model. This method provides quantitative support for material composition design, process control and service evaluation, and has significant engineering application value and scientific innovation significance. Solving the problem of Cr in high-chromium, low-carbon quenched steel 23 The presence of orientational and austenitic mass peaks in C6 leads to the inability to determine its content via XRD. This paper proposes a model based on the conversion between mass fraction and volume fraction in XRD patterns, providing a reliable basis for material mechanism research and offering an efficient, accurate, and convenient solution for determining the volume fraction of carbides in steel, thereby promoting technological progress in the steel industry. Attached Figure Description

[0010] Figure 1 This is the diffraction pattern of the sample in Example 1 of the present invention.

[0011] Figure 2 This is an image obtained by fitting the diffraction spectrum of the sample using the Rietveld method in Embodiment 1 of the present invention.

[0012] Figure 3 This is the diffraction pattern of the sample in Example 2 of the present invention.

[0013] Figure 4 This is an image obtained by fitting the diffraction spectrum of the sample using the Rietveld method in Embodiment 2 of the present invention. Detailed Implementation

[0014] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings: This invention provides an X-ray diffraction method for determining Cr in steel. 23 The method for C6 volume fraction includes the following steps: Step 1: Machin the high-chromium, low-carbon quenched steel sample to a size of 20mm in length, 20mm in width, and 5mm in height. The composition is determined by chemical methods.

[0015] Step 2: Grind the test surface with 800# and 1200# sandpaper in turn to remove the oxide scale on the sample surface.

[0016] Step 3: Experimental parameters: The experiment was conducted using an X'PERT PRO X-ray diffractometer with a Cu target. The tube voltage was adjusted to 40kV and the tube current was set to 40mA. The high-chromium, low-carbon quenched steel sample (microstructure consisting of martensite + austenite + Cr) was used. 23 C6) is placed in the instrument to conduct a systematic diffraction experiment in order to obtain clear diffraction lines.

[0017] Step 4: Use HighscorePlus software to analyze the obtained sample diffraction patterns and obtain the peak position parameters of martensite and austenite in the phase.

[0018] Step 5: Search for martensite, austenite, and Cr in crystallography databases. 23 The C6 data were fitted with the obtained diffraction lines using the Rietveld refinement method to obtain martensite and Cr. 23 C6 and austenite mass fraction; The Rietveld method is a full-spectrum linear fitting method. First, the structural model and linear function are determined. The structural model is derived from the crystal parameters, which are then used to derive the parameters required for the linear function. An expression is used to fit the entire diffraction pattern. The goal is to find an appropriate functional form and specific parameters for this expression that best approximates the reference pattern. The fitting formula is as follows: ; Among them, Y1 and Y bt For the measured intensity and background intensity of the diffraction curve; I pk J pk F pk These represent the multiplicity factor, angular factor, and structural amplitude including the temperature factor of the k-th diffraction line of a certain phase in the standard sample to be tested; G pki It is a peak-shaped function; This is the weighting factor for phase P.

[0019] Step 6: Build a model to convert mass fraction into volume fraction; ; in, Cr obtained after XRD refinement 23 C6 volume fraction, Cr obtained after XRD refinement 23 C6 mass fraction; The density of steel; Let be the density of the i-th element, in g / cm³. 3 n is the number of different types of elements in the alloy; For Cr 23 Density of C6, g / cm³ 3 .

[0020] The following embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments. Unless otherwise specified, the methods used in the following embodiments are conventional methods.

[0021] Example 1 Step 1: The sample material is high-chromium low-carbon steel, and it is machined to a size of 20mm in length, 20mm in width and 5mm in height. The chemical composition of high-chromium low-carbon steel is as follows: C: 0.18 wt.%, Cr: 17.00 wt.%, Si: 0.15 wt.%, Mn: 0.45 wt.%, S≤0.153 wt.%, P≤0.153 wt.%, Fe: Bal.

[0022] Step 2: Grind the test surface with 800# and 1200# sandpaper in turn to remove the oxide scale on the sample surface.

[0023] Step 3: Experimental parameters: The experiment was conducted using an X`PERT PRO X-ray diffractometer with a Cu target. The tube voltage was adjusted to 40kV and the tube current was set to 40mA. The high-chromium, low-carbon quenched steel sample was placed in the instrument, and a systematic diffraction experiment was conducted to obtain clear diffraction lines.

[0024] Step 4: Use HighscorePlus software to analyze the diffraction lines to determine that the sample is composed of α-Fe and γ-Fe. Figure 1 As shown.

[0025] Step 5: Search for martensite, austenite, and Cr in crystallography databases. 23 The C6 data were fitted with the obtained diffraction lines using the Rietveld refinement method, as shown below. Figure 2 As shown, martensite and Cr were obtained. 23 The mass fractions of C6 and austenite were 88.2 wt.%, 4.2 wt.%, and 7.6 wt.%, respectively.

[0026] Step 6: Convert the mass fraction into a volume fraction using the established model; ; in, Cr obtained after XRD refinement 23 C6 volume fraction, Cr obtained after XRD refinement 23 C6 mass fraction; The density of steel; Let be the density of the i-th element, in g / cm³. 3 n is the number of different types of elements in the alloy; For Cr 23 Density of C6, g / cm³ 3 Therefore, calculate Cr 23 The volume fraction of C6 was 4.46 vol%.

[0027] Example 2 Step 1: The sample material is high-chromium low-carbon steel, and it is machined to a size of 20mm in length, 20mm in width and 5mm in height. The chemical composition of high-chromium low-carbon steel is as follows: C: 0.18 wt.%, Cr: 17.00 wt.%, Si: 0.15 wt.%, Mn: 0.45 wt.%, S≤0.153 wt.%, P≤0.153 wt.%, Fe: Bal.

[0028] Step 2: Grind the test surface with 800# and 1200# sandpaper in turn to remove the oxide scale on the sample surface.

[0029] Step 3: Experimental parameters: The experiment was conducted using an X`PERT PRO X-ray diffractometer with a Cu target. The tube voltage was adjusted to 40kV and the tube current was set to 40mA. The high-chromium, low-carbon quenched steel sample was placed in the instrument, and a systematic diffraction experiment was conducted to obtain clear diffraction lines.

[0030] Step 4: Using HighscorePlus software, obtain the diffraction spectrum of the sample to determine that the sample is composed of α-Fe and γ-Fe. Figure 3 As shown.

[0031] Step 5: Search for martensite, austenite, and Cr in crystallography databases. 23 The C6 data were fitted with the obtained diffraction lines using the Rietveld refinement method, as shown below. Figure 4 As shown, martensite and Cr were obtained. 23 The mass fractions of C6 and austenite were 87.3 wt.%, 3.4 wt.%, and 9.3 wt.%, respectively.

[0032] Step 6: Convert the mass fraction into a volume fraction using the established model; ; in, Cr obtained after XRD refinement 23 C6 volume fraction, Cr obtained after XRD refinement 23 C6 mass fraction; The density of steel; Let be the density of the i-th element, in g / cm³. 3 n is the number of different types of elements in the alloy; For Cr 23 Density of C6, g / cm³ 3 Therefore, calculate Cr 23 The volume fraction of C6 is 3.61 vol.

Claims

1. An X-ray diffraction method for determining Cr in steel 23 The C6 volume fraction method is characterized by... Includes the following steps: Step 1: Machin the high-chromium, low-carbon quenched steel sample into a standard sample and measure the composition of the standard sample. Step 2: Remove the oxide scale from the surface of the standard sample; Step 3: Set experimental parameters to determine the microstructure as martensite + austenite + Cr. 23 The standard C6 sample is placed in the instrument to conduct a systematic diffraction experiment in order to obtain the diffraction pattern. Step 4: Analyze the diffraction lines to obtain the peak position parameters of martensite and austenite in the phase. Step 5: Search for martensite, austenite, and Cr in crystallography databases. 23 The C6 data were fitted with the obtained diffraction lines using the Rietveld refinement method to obtain martensite and Cr. 23 C6 and austenite mass fraction; Step 6: Build a model to convert mass fraction into volume fraction; ； in, Cr obtained after refinement 23 C6 volume fraction, Cr obtained after refinement 23 C6 mass fraction; The density of steel; Let be the density of the i-th element, in g / cm³. 3 n is the number of different types of elements in the alloy; For Cr 23 Density of C6, g / cm³ 3 .

2. The X-ray diffraction method for determining Cr in steel according to claim 1 23 The C6 volume fraction method is characterized by... The standard sample is a high-chromium, low-carbon quenched steel sample with a length of 10-20 mm, a width of 10-20 mm, and a height of 1-5 mm.

3. The X-ray diffraction method for determining Cr in steel according to claim 1 23 The C6 volume fraction method is characterized by... The experimental parameters were as follows: an X`PERT PRO X-ray diffractometer was used, a Cu target was employed, and the tube voltage was adjusted to 35-40 kV and the tube current was set to 35-40 mA.

4. The X-ray diffraction method for determining Cr in steel according to claim 1 23 The C6 volume fraction method is characterized by... The obtained diffraction lines are fitted using the Rietveld refinement method, and the fitting formula is as follows: ； Among them, Y1 and Y bt For the measured intensity and background intensity of the diffraction curve; I pk J pk F pk These represent the multiplicity factor, angular factor, and structural amplitude including the temperature factor of the k-th diffraction line of a certain phase in the standard sample to be tested; G pki It is a peak-shaped function; This is the weighting factor for phase P.

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