Method for accurately measuring influence of third component on carbon diffusion coefficient in steel

Abstract

The invention discloses a method for accurately measuring influence of a third component on a carbon diffusion coefficient in steel, and belongs to the technical field of steel and iron materials. The method comprises the following steps: firstly, preparing a series of target steel blocks with different carbon concentrations and with or without a third component, then traceless constructing two or more target steel blocks with or without the third component into diffusion couples at high temperature and high pressure, and immediately performing rapid quenching after high-temperature diffusion, then testing a surface scanning graph of the carbon concentration of a diffusion couple on a construction interface by using an electronic probe, obtaining a carbon concentration curve in the carbon diffusion direction after integral smoothing, and finally reversely solving the diffusion coefficient of carbon in the to-be-tested steel with or without a third component. A direct means is provided for studying the influence of the addition of the third component on the carbon diffusion behavior in the steel, basic data is provided for the influence of alloy elements on the precipitation behavior, phase change kinetics and the like, and a series of problems existing in carbon diffusion measurement are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel materials, and particularly relates to a method for accurately measuring the influence of a third component on the carbon diffusion coefficient in steel. Background Art

[0002] Carbon is one of the most important alloying elements in steel materials. Its diffusion behavior in steel will directly affect macro and micro segregation, precipitation of second phases, hardenability / hardness, etc., and thus play a decisive role in the service performance of steel materials. With the development of steel materials towards multi-component and micro-alloying directions, it is difficult to accurately and quickly quantify the influence of the currently added third alloy component on the carbon diffusion coefficient in steel, and thus it is impossible to provide basic data for carrying out kinetic calculations related to the element partitioning and precipitation behavior of the third component alloy.

[0003] In the test experiment, in addition to affecting the carbon diffusion coefficient in the steel solid, when using atmosphere carburization (gas-solid), the "catalytic diffusion mechanism" of the precipitated phases or oxides formed by the third component on the adsorption and enrichment of carbon atoms and the decomposition of the enriched gas affects the shape of the carbon distribution curve in the sample to be measured, bringing greater interference factors in the subsequent inversion of the influence of rare earth on the carbon diffusion coefficient in steel. At the same time, when using solid-solid diffusion, problems such as the flatness, oxidation, and uneven grain size of the interface during the preparation of the diffusion couple may also bring a series of effects. In addition, carbon atoms are low-atomic-number atoms, with a low solid solubility content in steel, carbide precipitation and micro-segregation. When using electron probe (EPMA) dot or line scanning methods to measure the carbon concentration distribution, the accuracy is limited or the number of parallel samples is too small, etc. Eventually, the influence of the third alloy component on the carbon diffusion coefficient cannot be accurately measured, resulting in the lack of data on the influence of some elements (such as rare earths, etc.) on the carbon diffusion coefficient in the steel (TCFE8) thermodynamic database in current software such as Thermo-Calc, and it is impossible to provide reliable guidance for composition design and heat treatment process formulation. Patent CN112557136A discloses a multi-component alloy diffusion couple device and a method for measuring the multi-component alloy diffusion coefficient, which is mainly aimed at measuring the diffusion coefficients of alloying elements (such as high-atomic-number elements like Al, Cu, Ni, etc.) at the interfaces of liquid-liquid / liquid-solid / solid-solid, etc. under ultra-high temperature or high temperature conditions, and cannot accurately measure the influence of the addition of the third component on the volume diffusion coefficient of carbon (low-atomic-number) elements in steel.

[0004] Therefore, developing a method with characteristics such as simple equipment, good result repeatability, and high precision not only provides a direct means for studying the influence of the addition of the third component on the carbon diffusion behavior in steel, but also provides basic data for the influence of alloying elements on precipitation behavior, phase transformation kinetics, etc. Summary of the Invention

[0005] To solve the above problems, the object of the present invention is to provide a method for accurately measuring the influence of the third component on the carbon diffusion coefficient in steel, including the preparation of carbon diffusion elements, the seamless construction of diffusion couples, vacuum packaging, high-temperature diffusion, and computational simulation. The method of the present invention has the characteristics of simple equipment, good result repeatability, and high precision, providing a direct means for studying the influence of the addition of the third component on the carbon diffusion behavior in steel, and also providing basic data for the influence of alloying elements on precipitation behavior, phase transformation kinetics, etc.

[0006] To achieve the above object, the technical solution of the present invention is:

[0007] A method for accurately measuring the influence of the third component on the carbon diffusion coefficient in steel, comprising the following steps:

[0008] (1) Smelt a series of target steel blocks with different carbon concentrations and third component concentrations; regulate the composition uniformity and grain size of the target steel blocks through homogenization diffusion, forging, and heat treatment; in the target steel blocks, the carbon concentrations in different third component concentrations are the same, and among them, the minimum third component concentration is 0.

[0009] (2) Using the regulated target steel blocks without the third component and with different carbon concentrations as elements, seamlessly construct diffusion couples by respectively combining two or more target steel blocks with different third component concentrations.

[0010] (3) Place the diffusion couple in a protective atmosphere for packaging to prevent its oxidation.

[0011] (4) Place the packaged diffusion couple at a set temperature for high-temperature diffusion. After the diffusion is completed, immediately perform rapid quenching.

[0012] (5) Use an electron probe to test the surface scan map of the carbon concentration at the construction interface of the diffusion couple. After integral smoothing treatment, obtain the carbon concentration curve in the carbon diffusion direction.

[0013] (6) Inversely calculate the carbon diffusion coefficient in the steel to be measured with and without the third component.

[0014] The third component added to the steel block in step (1) is one of solid solution alloying elements, inclusions, carbides, or other strengthening phases.

[0015] The size of the series of target steel blocks is length × width × height of (2 mm × 2 mm × 3 mm) to (10 mm × 8 mm × 12 mm).

[0016] In step (2), during the process of constructing a diffusion couple without traces, it can be carried out on a Gleeble testing machine. The temperature is 1000°C to 1150°C, the pressure is 10 MPa to 50 MPa, and the compressive strain is not more than 5%. There are no obvious microcracks, oxides, overburning of the specimen, and abnormal grain phenomena around the interface of the diffusion couple. After the construction and heat preservation for 3 s to 15 s are completed, it is immediately cooled to room temperature.

[0017] In step (3), the prepared diffusion couple is encapsulated using a quartz glass tube, or the specimen is directly placed in a vacuum or protective atmosphere furnace for treatment;

[0018] In step (4), the set temperature and heat preservation time are determined according to the size of the diffusion target block. It is preferred that the length of the carbon diffusion influence zone is 1 / 6 to 1 / 3 of the length of the target steel block of the specimen, ensuring that the carbon content at the 1 / 2 position of the target steel block is the initial carbon concentration value, which is convenient for electron probe calibration; after the diffusion is completed, it is immediately quenched. The quenching transfer time is short (≤15 s), and the cooling rate is moderate (30°C / s to 200°C / s), so as to ensure that during the quenching process, the redistribution of carbon is minimized and no obvious quenching cracks appear;

[0019] In step (5), during the electron probe metallographic sample preparation process, carbon pollution interference is minimized as much as possible, and ion surface cleaning treatment is used; to ensure the accuracy of carbon quantification, the carbon content measurement of the electron probe is calibrated with the known carbon concentration in the non-diffusion zone of the target steel block or a standard test block; when the integral of the electron probe surface scan result becomes a curve along the carbon concentration gradient direction: the interface is perpendicular to the integral curve direction, and the surface scan area is not less than 4 mm 2 , reducing the fluctuation of the carbon concentration curve obtained after integration;

[0020] In step (6), Fick's second law is used or the carbon diffusion coefficient as a function of carbon concentration is inversely obtained through a series of carbon gradient diffusion couples containing a third component;

[0021] Among them, when inversely obtaining the carbon diffusion coefficient in the steel to be measured with or without a third component using Fick's second law, it is necessary to consider that the carbon diffusion coefficient changes with the carbon concentration or the influence of carbon on the diffusion coefficient;

[0022] Among them, Fick's second law is Among them, D 0 is the diffusion coefficient constant, Q is the activation energy for diffusion, R is the Boltzmann constant, and T is the thermodynamic temperature;

[0023] The influence of carbon on the diffusion coefficient Among them, C is the percentage of carbon content, R is the Boltzmann constant, and T is the thermodynamic temperature.

[0024] The beneficial effects of the method for accurately measuring the influence of a third component on the carbon diffusion coefficient in steel according to the present invention are as follows:

[0025] The invention provides a method for accurately measuring the influence of a third component on the carbon diffusion coefficient in steel, and solves a series of problems existing in carbon diffusion measurement.

[0026] 1. In step (1), the process of the present invention prepares a series of target steel blocks with different carbon concentrations and with or without a third component, and controls the composition uniformity and grain size of the target steel blocks through homogenization diffusion, multi-directional forging and heat treatment. Among them, high-temperature diffusion, multi-pass forging and heat treatment reduce the influence of composition segregation and coarse or uneven grains on carbon diffusion behavior;

[0027] 2. The process of the present invention seamlessly constructs two or more target steel blocks with or without the addition of a third component into diffusion couples under high temperature and high pressure, thereby avoiding the effects of gas-solid carburizing surface catalytic effect and solid-solid interface oxidation. At the same time, multiple steel blocks are constructed into a diffusion couple, which can ensure consistent test conditions and reduce sample preparation time.

[0028] 3. The present invention uses an electron probe to test the diffusion couple to construct a surface scan of the carbon concentration at the interface, and performs line integration of the surface scan along the vertical interface, thereby reducing the precipitation of carbon carbides and the large dispersion of the carbon concentration curve caused by experimental errors. The non-diffusion-affected area (such as 1 / 2) of the target test block to be tested or the standard test block is used to correct the carbon content measurement of the electron probe, thereby further improving the accuracy of the electron probe detection results;

[0029] 4. Since the process of the present invention utilizes Fick's second law The formula is used to inversely calculate the diffusion coefficient of carbon in the steel to be tested with or without the third component. When measuring the diffusion coefficient of the sample to be tested with or without the third component, the carbon diffusion coefficient changes with the carbon concentration, and the influence of carbon on the diffusion coefficient can also be considered. Or, the carbon diffusion coefficient can be inversely calculated by using a series of carbon gradient diffusion couples containing a third component to change with carbon concentration. According to the influence of carbon concentration on the diffusion coefficient of steel, different inverse formulas can be selected to improve the efficiency and calculation accuracy of the carbon diffusion coefficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic flow chart of a method for measuring the influence of the third component on the carbon diffusion coefficient in steel according to the present invention;

[0031] Figure 2 The carbon concentration curves are obtained by different methods; (a) the carbon concentration curve is obtained by the traditional method, and (b) the carbon concentration curve is obtained by the process of the present invention;

[0032] Figure 3 The process of the present invention measures the influence of trace solid-solution rare earth on the carbon diffusion coefficient in steel. DETAILED DESCRIPTION

[0033] It has been widely recognized in the industry that dissolved rare earths have a strong microalloying effect in steel materials. However, how dissolved rare earths affect the diffusion and phase transformation behaviors of steel materials has not been clarified. Therefore, the process of the present invention can be used to quantitatively study the effect of dissolved rare earth states on the carbon diffusion coefficient in steel.

[0034] The method flow for accurately measuring the influence of the third component on the carbon diffusion coefficient in steel provided by the present invention is as Figure 1 shown.

[0035] In the present invention, there are no obvious microcracks, oxides, specimen overburning, and abnormal grain phenomena around the diffusion couple interface constructed.

[0036] In the present invention, when the encapsulated diffusion couple is placed at a set temperature for high-temperature diffusion, the set temperature and holding time are determined according to the size of the diffusion target block. Preferably, the length of the carbon diffusion influence zone is 1 / 6 to 1 / 3 of the length of the specimen target steel block, ensuring that the carbon content at the 1 / 2 position of the target steel block is the initial carbon concentration value, which is convenient for electron probe calibration; immediately quench after diffusion is completed. The quenching transfer time should be short (≤15 s) and the cooling rate should be moderate (30 °C / s to 200 °C / s), so as to ensure that carbon redistribution is minimized during quenching and no obvious quenching cracks appear.

[0037] In the present invention, carbon pollution interference is minimized during the electron probe metallographic sample preparation process, and ion surface cleaning treatment is used; to ensure the accuracy of carbon quantification, the carbon content measurement of the electron probe is calibrated with the known carbon concentration in the non-diffusion zone of the target steel block or a standard test block; when the integral of the electron probe surface scan result becomes a curve along the carbon concentration gradient direction: the interface is perpendicular to the integral curve direction, and the surface scan area is not less than 4 mm 2 , reducing the fluctuation of the carbon concentration curve obtained after integration.

[0038] Next, the present invention will be further described in conjunction with the drawings and embodiments.

[0039] Example 1:

[0040] In this example, high-purity rare earths (oxygen content in rare earths is less than 100 ppm) and high-purity purification smelting technology are used to prepare two steel ingots of Fe-0.14 wt.% C and Fe-0.6 wt.% C with and without about 300 ppm of rare earth added respectively. Then, the above steel ingots are subjected to homogenization diffusion, multi-directional forging, and heat treatment to ensure uniform composition and structure in the specimens, and target steel blocks of Fe-0.14 wt.% C, Fe-0.14 wt.% C-300 ppm RE, Fe-0.6 wt.% C, and Fe-0.6 wt.% C-300 ppm RE are obtained respectively. The grain size is about grade 6, and the compositions of different steel blocks are measured as shown in Table 1.

[0041] Table 1 Detection Results of Steel Compositions with Different Carbon Contents and the Third Component in the Smelting Series

[0042] Number / Element C RE(La+Ce) Others Fe - 0.14wt.%C 0.14wt.% / Fe Fe - 0.14wt.%C - 300ppm RE 0.14wt.% 290ppm Fe Fe - 0.6wt.%C 0.6wt.% / Fe Fe - 0.6wt.%C - 300ppm RE 0.6wt.% 300ppm Fe

[0043] Steel blocks of Fe-0.14wt.% C, Fe-0.14wt.% C-300ppm RE, Fe-0.6wt.% C and Fe-0.6wt.% C-300ppm RE were prepared into specimens of 3mm×3mm×6mm. Then, using a Gleeble thermal simulation testing machine, Fe-0.14wt.% C / Fe-0.6wt.% C and Fe-0.14wt.% C-300ppm RE / Fe-0.6wt.% C-300ppm RE were quickly heated pairwise to 1100℃±50℃, and a pressure of 10MPa was applied for heat preservation for 15s. The compression strain was within 2%. Then, it was immediately quenched in water to room temperature to complete the construction of diffusion couples with and without rare earth addition without traces. There were no obvious microcracks, oxides, specimen overburning, and abnormal grain phenomena around the interface of the prepared diffusion couples.

[0044] The above-prepared diffusion couples were encapsulated using a quartz glass tube, and argon gas was filled in the tube for protection.

[0045] Then, it was placed in a muffle furnace and diffused at a high temperature of 920℃ for 5 hours. After the diffusion was completed, it was transferred within 10s and immediately quenched rapidly. The cooling rate during the quenching process was 50℃ / s. The length of the carbon diffusion affected zone was 1 / 6 - 1 / 3 of the length of the specimen target block, and the carbon content at 1 / 2 of the target block was the initial carbon concentration value.

[0046] The test block was cut from the center plane to prepare a metallographic specimen, and an electron probe was used to perform carbon concentration surface scanning in multiple selected areas near the constructed interface of the diffusion couple. The surface scanning area was 4.5mm 2 , and after appropriate integral smoothing treatment, a carbon concentration curve of carbon along the diffusion direction was obtained. To compare the process advantages of the present invention, this embodiment also used an electron probe to directly perform line scanning and used surface scanning integration to obtain the carbon concentration curve of Fe-0.14wt.% C / Fe-0.60wt.% C along the diffusion direction as shown in Figure 2 (b). It can be seen that compared with the traditional method (as shown in Figure 2 (a)), the carbon concentration curve of carbon measured by the process of the present invention along the diffusion direction is smoother and more accurate;

[0047] Using the empirical relationship between the carbon diffusion coefficient and the carbon concentration: All the tested data of the prepared diffusion couples were fitted, and the results are shown in Table 2 and Figure 3 . It is not difficult to find that the average carbon diffusion coefficients at both ends of 0.14wt.% C and 0.6wt.% C in the diffusion couple with rare earth addition are: D (0.14wt.％C-RE)= 0.65 ± 0.025×10 -11 m 2 / s -1 ; D (0.6wt.％C-RE) = 1.11 ± 0.03×10 -11 m 2 / s -1 , the carbon diffusion coefficients at both ends of 0.14 wt.% C and 0.6 wt.% C in the diffusion couple without rare earth addition are respectively: D (0.14wt.％C) = 0.85 ± 0.035×10 -11 m 2 / s -1 ; D (0.6wt.％C) = 1.50 ± 0.035×10 -11 m 2 / s -1 . It can be seen that the standard deviations of the carbon diffusion coefficient calculated by the inverse solution using the process of the present invention and the selected fitting formula are both small (<5%), and the errors are very small (<5%) when the experiment is repeated many times, indicating that the accuracy and repeatability of the process of the present invention for testing the carbon diffusion coefficient are both very good. It can also be seen from Table 2 that the carbon diffusion coefficients in the Fe-C alloy after adding trace rare earths become smaller, thus confirming that the dissolved rare earth significantly inhibits the diffusion coefficient of carbon elements in the Fe-C alloy.

[0048] Table 2 Fitted D (0.14wt.％C) and D (0.6wt.％C) results

[0049] Test Specimen Number <![CDATA[D 0.6C (10 -8 cm 2 / s)]]> <![CDATA[D 0.14C (10 -8 cm 2 / s)]]> <![CDATA[Standard deviation (10 -2 )]]> 1 - 0.6wt.%C - 0.14wt.%C - RE 11.40 6.61 0.72 2 - 0.6wt.%C - 0.14wt.%C - RE 11.20 6.50 0.97 3 - 0.6wt.%C - 0.14wt.%C - RE 10.78 6.26 1.17 1 - 0.6wt.%C - 0.14wt.%C 15.26 8.85 0.83 2 - 0.6wt.%C - 0.14wt.%C 15.06 8.73 0.98 3 - 0.6wt.%C - 0.14wt.%C 14.65 8.50 1.57

[0050] Example 2:

[0051] The influence of alloying element Mn on the carbon diffusion coefficient will directly affect the carbon partitioning and stability during the austenite reverse transformation process. Therefore, in this example, the process of the present invention is used to quantitatively study the influence of different manganese contents on the carbon diffusion coefficient in Fe-C-Mn-Si-Al steel. In this example, Fe-C-Mn-Si-Al steel ingots with different carbon contents or manganese contents are prepared by vacuum induction melting, and then the above steel ingots are subjected to high-temperature homogenization diffusion, multi-directional forging and heat treatment to ensure that the composition and structure in the specimens are uniform, and the grain size is controlled at grade 8. The measured compositions are shown in Table 1.

[0052] Table 3 Detection results of steel compositions with different carbon contents and manganese contents in the smelting series

[0053] Number / Element C Mn Si Al Others Fe - 0.2wt.%C - 1wt.%Mn 0.20wt.% 0.97 0.32 2.10 Fe Fe - 0.2wt.%C - 3wt.%Mn 0.20wt.% 3.05 0.33 2.08 Fe Fe - 0.4wt.%C - 1wt.%Mn 0.65wt.% 1.03 0.32 2.11 Fe Fe - 0.4wt.%C - 3wt.%Mn 0.65wt.% 3.10 0.33 2.12 Fe Fe - 0.65wt.%C - 1wt.%Mn 0.65wt.% 1.03 0.32 2.11 Fe Fe - 0.65wt.%C - 3wt.%Mn 0.65wt.% 3.10 0.33 2.12 Fe

[0054] Steel blocks of Fe-0.2wt.%C-1wt.%Mn, Fe-0.2wt.%C-3wt.%Mn, Fe-0.6wt.%C-1wt.%Mn and Fe-0.6wt.%C-3wt.%Mn were prepared into specimens of 4mm×4mm×12mm. Then, using a Gleeble thermal simulation testing machine, Fe-0.2wt.%C-1wt.%Mn / Fe-0.4wt.%C-1wt.%Mn / Fe-0.65wt.%C-1wt.%Mn and Fe-0.2wt.%C-3wt.%Mn / Fe-0.4wt.%C-3wt.%Mn / Fe-0.65wt.%C-3wt.%Mn were rapidly heated to 1100°C ± 20°C in pairs, and a pressure of 25 MPa was applied and held for 5 s. The compression strain was approximately 3.5%. Then, it was immediately quenched in water to room temperature to complete the construction of two diffusion couples with different manganese contents without traces. There were no obvious microcracks, oxides, specimen overburning, and abnormal grain phenomena around the interface of the prepared diffusion couples.

[0055] The above-prepared diffusion couples were encapsulated using a quartz glass tube, and argon gas was filled in the tube for protection.

[0056] Then, it was placed in a muffle furnace and diffused at a high temperature of 940°C for 8 hours. After the diffusion was completed, it was transferred within 12 s and immediately rapidly quenched. The cooling rate during the quenching process was 80°C / s. The length of the carbon diffusion affected zone was 1 / 6 - 1 / 3 of the length of the specimen target block, and the carbon content at 1 / 2 of the target block was the initial carbon concentration value.

[0057] The test block was cut from the central plane to prepare a metallographic specimen. The approximate interfaces of the three samples with different carbon contents were constructed without traces. An electron probe was used to perform a carbon concentration area scan on multiple selected areas near the constructed interface of the diffusion couple. The area scan area was 8 mm 2 After appropriate integral smoothing treatment, a carbon concentration curve of carbon along the diffusion direction was obtained.

[0058] According to Fick's second law It is considered that the carbon diffusion coefficient does not change with the carbon concentration in the steel. The carbon diffusion coefficients near each constructed interface were calculated as shown in Table 4. It can be seen that the standard deviations of the carbon diffusion coefficients calculated by the process of the present invention and the selected fitting formula are both small (<2%). It can also be seen from Table 4 that the carbon concentration near the diffusion interface has a certain influence on the diffusion coefficient. The higher the carbon concentration, the higher the measured carbon diffusion coefficient. Under the condition of the same carbon content, the diffusion coefficient of the steel containing 3wt.% Mn at 940°C is significantly smaller than that in the steel containing 1wt.% Mn.

[0059] Table 4 Results of carbon diffusion coefficients in different diffusion couples

[0060] Test Specimen Number <![CDATA[D(10 -8 cm 2 / s)]]> <![CDATA[Standard deviation (10 -2 )]]> 0.2wt.%C - 1wt.%Mn / 0.4wt.%C - 1wt.%Mn 2.15 1.42 0.4wt.%C - 1wt.%Mn / 0.65wt.%C - 1wt.%Mn 2.69 1.67 0.65wt.%C - 1wt.%Mn / 0.2wt.%C - 1wt.%Mn 2.48 1.45 0.2wt.%C - 3wt.%Mn / 0.4wt.%C - 3wt.%Mn 1.05 1.64 0.4wt.%C - 3wt.%Mn / 0.65wt.%C - 3wt.%Mn 1.31 1.31 0.65wt.%C - 3wt.%Mn / 0.2wt.%C - 3wt.%Mn 1.24 1.73

[0061] Example 3:

[0062] There is still controversy over whether rare earth inclusions or the second phase in steel, as the third component, have a certain impact on the carbon diffusion behavior. In this example, it is explored whether the carbon diffusion coefficient of steel at high temperature will be affected when rare earth exists in the form of chemical compounds (commonly RE 2 O 2 S) in steel. In this example, powder metallurgy technology is used to prepare two steel blocks with carbon concentrations of Fe-0.14wt.% C and Fe-0.65wt.% C, with and without the addition of about 400ppm high-purity RE 2 O 2 S powder. Then, the above steel blocks are subjected to homogenization diffusion, multi-directional forging and heat treatment to ensure that the composition and structure in the specimens are uniform, and the grain size is about grade 7. The compositions of different steel blocks are measured as shown in Table 5.

[0063] Table 5 Detection results of the compositions of steels with different carbon contents and the third component in the smelting series

[0064] Number / Element C RE(La+Ce) Others Fe - 0.14wt.%C 0.14wt.% / Fe <![CDATA[Fe - 0.14 wt.% C - 400 ppm RE 2 O 2 S]]> 0.14wt.% 320ppm Fe Fe - 0.6wt.%C 0.6wt.% / Fe <![CDATA[Fe-0.6 wt.% C-400 ppm RE 2 O 2 S]]> 0.6wt.% 325ppm Fe

[0065] The powder metallurgy Fe-0.14wt.% C, Fe-0.14wt.% C-400ppm RE 2 O 2 S, Fe-0.6wt.% C and Fe-0.6wt.% C-400ppm RE 2 O 2 S steel blocks are made into 4mm×4mm×8mm specimens. Then, using a Gleeble thermal simulation testing machine, Fe-0.14wt.% C / Fe-0.6wt.% C and Fe-0.14wt.% C-400ppm RE 2 O 2 S / Fe-0.6wt.% C-400ppm RE 2 O 2 S are paired up at 1050°C ± 50°C, and a pressure of 30MPa is applied and held for 12s. The compression strain is 4.5%. Then, it is immediately quenched in water to room temperature to complete the construction of diffusion couples with and without rare earth addition without obvious microcracks, oxides, specimen overburning and abnormal grain phenomena around the interface of the prepared diffusion couples.

[0066] Place the diffusion couple in a vacuum heat treatment furnace;

[0067] Perform high-temperature diffusion treatment. The diffusion temperature is 920°C, and the diffusion time is 3 hours. After the diffusion is completed, it is transferred within 15s and immediately quenched rapidly; the cooling rate during the quenching process is 100°C / s. The length of the carbon diffusion affected area is 1 / 6 to 1 / 3 of the length of the target block of the specimen, and the carbon content at the 1 / 2 of the target block is the initial carbon concentration value.

[0068] Cut the specimen block from the central plane to prepare a metallographic specimen, and use an electron probe to perform multiple area scans of the carbon concentration near the built interface of the diffusion couple. The area of the area scan is 6 mm 2 . After appropriate integral smoothing treatment, multiple curves of carbon concentration with the diffusion direction are obtained.

[0069] Using the empirical relationship between the carbon diffusion coefficient and the carbon concentration: Fit all the tested data of the prepared diffusion couples. The results are shown in Table 6. It is found that the average carbon diffusion coefficients at both ends of 0.14 wt.% C and 0.6 wt.% C in the diffusion couples with rare earth compounds added are respectively: The carbon diffusion coefficients at both ends of 0.14 wt.% C and 0.6 wt.% C in the diffusion couples without rare earth compounds added are respectively: D (0.14wt.％C) = 0.67 ± 0.02 × 10 -11 m 2 / s -1 ; D (0.6wt.％C) = 1.70 ± 0.02 × 10 -11 m 2 / s -1 . It can be seen that the standard deviations of the carbon diffusion coefficients calculated by the process of the present invention and the selected fitting formula are all within ±1%, and the errors are all within ±5% when repeating the experiment multiple times, indicating that the accuracy and repeatability of the process of the present invention for testing the carbon diffusion coefficient are both very good. It can also be seen from Table 2 that after adding trace rare earth compounds (modifying rare earth inclusions), the carbon diffusion coefficient in the Fe-C alloy basically does not change, thus confirming that rare earth inclusions do not change the diffusion coefficient of carbon elements in the Fe-C alloy.

[0070] Table 6 Fitted D (0.14wt.％C) and D (0.6wt.％C) results

[0071]

Claims

1. A method for accurately measuring the influence of a third component on the carbon diffusion coefficient in steel, characterized in that: The following steps are involved: Step 1. Smelting a series of target steel blocks with different carbon concentrations and third component concentrations; regulating the component uniformity and grain size of the target steel blocks through homogenization diffusion, forging and heat treatment; in the target steel blocks, the carbon concentration in the third component with different concentrations is consistent, wherein the minimum concentration of the third component is 0; Step 2. Using the regulated target steel blocks without the third component and with different carbon concentrations as the primitives, two or more target steel blocks with different third component concentrations are seamlessly constructed into diffusion couples; Step 3. Encapsulate the diffusion couple in a protective atmosphere; Step 4. Place the packaged diffusion couple at a specific temperature for high-temperature diffusion, and immediately perform rapid quenching after the diffusion is completed; Step 5. Use an electron probe to test the surface scan of the carbon concentration of the diffusion couple at the construction interface, and after integral smoothing, obtain the carbon concentration curve in the carbon diffusion direction; Step 6. Inversely calculate the diffusion coefficient of carbon in the steel to be tested with and without the third component.

2. The method for accurately measuring the influence of the third component on the carbon diffusion coefficient in steel according to claim 1, characterized in that: In step 1, the third component added to the steel block is one of a solid solution alloy element, an inclusion, a carbide or other strengthening phase; The target steel block size is length×width×height (2mm×2mm×3mm) to (10mm×8mm×12mm).

3. The method for accurately measuring the influence of the third component on the carbon diffusion coefficient in steel according to claim 1, characterized in that: In step 2, during the traceless construction of the diffusion couple, the temperature is 1000° C. to 1150° C., the pressure is 10 MPa to 50 MPa, and the compression strain does not exceed 5%; After the construction is completed and the temperature is kept for 3s to 15s, it is immediately cooled to room temperature.

4. The method for accurately measuring the influence of the third component on the carbon diffusion coefficient in steel according to claim 1, characterized in that: In step 3, the well-prepared diffusion couple is encapsulated using a quartz glass tube, or the sample is directly placed in a vacuum or protective atmosphere furnace for treatment.

5. The method for accurately measuring the influence of the third component on the carbon diffusion coefficient in steel according to claim 1, characterized in that: In step 4, the set temperature and holding time are determined according to the diffusion target block size; After diffusion is completed, quench immediately, the quenching transfer time is ≤15s, and the cooling rate is 30℃ / s~200℃ / s.

6. The method for accurately measuring the influence of the third component on the carbon diffusion coefficient in steel according to claim 1, characterized in that: In step 4, the length of the carbon diffusion affected zone is 1 / 6 to 1 / 3 of the length of the target steel block of the sample, ensuring that the carbon content at 1 / 2 of the target steel block is the initial carbon concentration value.

7. The method for accurately measuring the influence of the third component on the carbon diffusion coefficient in steel according to claim 1, characterized in that: In step 5, the electron probe carbon content measurement is calibrated with the known carbon concentration in the non-diffusion zone of the target steel block or a standard test block during the electron probe metallographic sample preparation process; When the electron probe surface scanning result is integrated into a curve along the carbon concentration gradient direction: the interface is perpendicular to the direction of the integral curve, and the surface scanning area is not less than 4mm 2 .

8. The method for accurately measuring the influence of the third component on the carbon diffusion coefficient in steel according to claim 1, characterized in that: In step 6, the carbon diffusion coefficient is inversely calculated as a function of carbon concentration using Fick's second law or through a series of carbon gradient diffusion couples containing a third component; Among them, when using Fick's second law to inversely calculate the diffusion coefficient of carbon in the steel to be tested with or without the third component, it is necessary to consider that the carbon diffusion coefficient changes with the carbon concentration, or the influence of carbon on the diffusion coefficient.

9. The method for accurately measuring the influence of the third component on the carbon diffusion coefficient in steel according to claim 8, characterized in that: In step 6, Fick’s second law is Where D0 is the diffusion coefficient constant, Q is the thermal activation energy of diffusion, R is the Boltzmann constant, and T is the thermodynamic temperature; Effect of carbon on diffusion coefficient Wherein, C is the carbon content percentage, R is the Boltzmann constant, and T is the thermodynamic temperature.

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