Test method for evaluating recrystallization completion degree of steel and iron material

Abstract

The invention relates to the technical field of metal material detection, in particular to a test method for evaluating the recrystallization completion degree of a steel material. The method comprises the following steps: dividing a to-be-detected steel plate into a plurality of blocky steel plate samples; preliminarily determining the range of the recrystallization temperature of the steel plate to be measured according to experience, setting a plurality of temperature gradients in the range, respectively heating a plurality of steel plate samples at different temperatures, carrying out heat preservation for a period of time, and then cooling to room temperature; grinding and polishing the cooled steel plate sample; putting the polished steel plate sample into an X-ray diffractometer sample table, and starting an X-ray diffractometer for scanning to obtain diffraction patterns of the steel plate sample at different temperatures; and judging the recrystallization completion degree of the steel plate sample according to the separation condition of the diffraction peaks K alpha1 and K alpha2 in the diffraction pattern. The method has the advantages of simple sample preparation and inspection methods, and results are representative and are basically not influenced by subjective effects of operators due to a large test area.

Description

Technical Field

[0001] The present invention relates to the technical field of metal material testing, and particularly relates to a test method for evaluating the recrystallization completion degree of steel materials. Background Art

[0002] During the hot working process of metals, due to the increase in the dislocation density in the material during the high-temperature deformation process of the material, the plastic deformation resistance of the material increases, resulting in "cold working hardening". In order to reduce the influence brought by cold working hardening, recrystallization occurs as an annealing behavior during the hot working process of metal materials. That is to say, during the hot deformation process of metal materials, when the temperature reaches a certain value, cold working hardening will disappear, dislocations will be rearranged, and new small grains will be formed, and this process is called recrystallization. Through recrystallization, structural defects such as dislocations, vacancies, sub-boundaries, and mixed grains caused by cold deformation can be eliminated, which is also an effective method for industrially controlling the microstructure and properties of metal materials. Therefore, determining the recrystallization temperature is of great significance for the production, processing, and industrial application of metal materials.

[0003] Traditional methods for measuring the recrystallization temperature mainly include the metallographic method, the hardness method, etc., by observing the change in the grain size of the sample or measuring the change in the hardness of the sample to determine the recrystallization temperature. In recent years, related patented technologies have tried to improve this problem: for example, in 201210185480.4, a method for measuring the recrystallization temperature of stamping steel, this patent proposes to combine a thermal simulation compression test with microscopic structure observation, and use the characteristic points of the stress-strain curve combined with grain size analysis to determine the recrystallization temperature. However, this method still needs to rely on multiple physical tests and microscopic observations, and the test process is complex and time-consuming. Another example is 202010210554.X, a device and method for quickly determining the recrystallization temperature of metal materials. This technology uses a laser scanning confocal microscope to monitor the grain evolution in real time, and combines a temperature-stress synchronous acquisition system to achieve rapid determination. However, this device is costly, and the locality of laser scanning may lead to insufficient representativeness of the results, and at the same time, the requirements for the surface state of the sample are extremely high. Although the existing technology has improved the measurement efficiency to a certain extent, it still has not solved the core problems of complex operation, long test cycle, and strong subjectivity. Summary of the Invention

[0004] To solve the problems in the existing technology, the purpose of the present invention is to provide a test method for evaluating the recrystallization completion degree of steel materials. This method has simple sample preparation and inspection methods. Due to the large test area, the results are representative and are basically not affected by the subjectivity of the operator.

[0005] To achieve the above purpose, the present invention is realized through the following technical solutions:

[0006] The present invention provides a test method for evaluating the recrystallization completion degree of steel materials, comprising the following steps:

[0007] (1) Divide the steel plate to be tested into multiple block-shaped steel plate specimens;

[0008] (2) Preliminarily determine the range of the recrystallization temperature of the steel plate to be tested according to experience, set multiple temperature gradients within this range, heat and hold multiple steel plate specimens at different temperatures for a period of time, and then cool them down to room temperature;

[0009] (3) Grind and polish the steel plate specimens after cooling;

[0010] (4) Place the polished steel plate specimens on the sample stage of an X-ray diffractometer, start the X-ray diffractometer for scanning, and obtain the diffraction patterns of the steel plate specimens at different temperatures;

[0011] (5) Judge the recrystallization completion degree of the steel plate specimens according to the separation situation of diffraction peaks K α1 and K α2 in the diffraction pattern.

[0012] As a further optimized scheme of the present invention, in step (1), the deformation amount of the steel plate to be tested is 70-90%.

[0013] As a further optimized scheme of the present invention, in step (2), the setting step size of the temperature gradient is 5-10°C.

[0014] In step (2), setting the step size of the temperature gradient to 5-10°C can more carefully study the influence of different temperatures on recrystallization. While ensuring the test accuracy, it will not lead to excessive test workload due to too small a step size.

[0015] As a further optimized scheme of the present invention, in step (3), during the grinding and polishing process, cold water is used to cool the steel plate specimens.

[0016] In step (3), using cold water to cool the steel plate specimens during the grinding and polishing process ensures that there is no decarburization, no oxidation, and no heat-affected zone on the test surface of the specimens, guarantees the original state of the specimens, and avoids interference of these factors on the test results.

[0017] As a further optimized scheme of the present invention, in step (4), the voltage of the X-ray diffractometer is 40-50 kV, and the current is 40-50 mA.

[0018] As a further optimized scheme of the present invention, in step (4), the X-ray diffractometer uses a cobalt target or a copper target.

[0019] As a further optimized scheme of the present invention, in step (4), the optical path of the X-ray diffractometer uses a focusing optical path.

[0020] As a further optimized solution of the present invention, in step (4), the 2θ scanning range of the X-ray diffractometer is 95° - 105°, and the scanning speed is not greater than 5° / min.

[0021] In step (4), parameters such as the voltage, current, target material, optical path, scanning range, and scanning speed of the X-ray diffractometer are optimized. For example, the voltage is 40 - 50 kV, the current is 40 - 50 mA, a cobalt target or a copper target is used, the optical path is a focusing optical path, the 2θ scanning range is 95° - 105°, and the scanning speed is not greater than 5° / min. These parameter settings are beneficial for obtaining clear and accurate diffraction patterns, thereby better judging the degree of recrystallization completion.

[0022] As a further optimized solution of the present invention, in step (5), if there is no diffraction peak K α2 sign in the diffraction pattern, it indicates that the recrystallization of the steel sample has not started yet; if there is a diffraction peak K α2 sign in the diffraction pattern but it is not completely separated from the diffraction peak K α1 , it indicates that only partial recrystallization of the steel sample has been completed; if the diffraction peaks K α1 and K α2 in the diffraction pattern are completely separated, it indicates that the steel sample has completely completed recrystallization at the corresponding heating temperature.

[0023] As a further optimized solution of the present invention, in step (5), if the intensity ratio of diffraction peak K α1 and diffraction peak K α2 is 2:1, it indicates that the diffraction peaks K α1 and K α2 are completely separated.

[0024] In step (5), the standard for judging the degree of recrystallization completion according to the separation situation of diffraction peaks K α1 and K α2 in the diffraction pattern is clarified. If there is no sign of diffraction peak K α2 , it indicates that recrystallization has not started yet; if there is a K α2 sign but it is not completely separated from K α1 , it indicates that only partial recrystallization has been completed; K α1 and K α2 are completely separated, and when the intensity ratio of diffraction peak K α1 and diffraction peak K α2 is 2:1, it indicates that recrystallization has been completely completed. This precise judgment basis makes the determination of test results more scientific and accurate.

[0025] Compared with the prior art, the present invention brings beneficial effects in many aspects:

[0026] Simple sample preparation: In step (1), the steel plate to be tested is divided into multiple block-shaped steel plate specimens. Only wire cutting or other conventional means are required to cut the specimens into blocks with a length and width of 10-20 mm. The thickness of the specimen is determined according to the configuration of the diffractometer. The operation is simple and the requirements for equipment and technology are not high. Compared with the traditional metallographic method that may require complex sample preparation steps such as slicing and embedding, the present invention greatly simplifies the sample preparation process and reduces the sample preparation time and cost.

[0027] Simple inspection method and representative results: Detection is carried out using a common X-ray diffractometer. The test area is large (i.e., the test area is dozens to hundreds of square millimeters), and a large number of grains can be statistically analyzed, and the obtained results have statistical significance. Different from some traditional methods (such as a single field of view of a microscope being only a few hundred square micrometers) that only detect local areas, the results may deviate greatly due to local differences. For example, when determining the recrystallization temperature range, multiple specimens are heated and tested by setting multiple temperature gradients to reflect the recrystallization situation of the material at different temperatures as a whole.

[0028] Little influence from subjective factors: During the whole test process, mainly rely on the X-ray diffractometer to obtain the diffraction pattern, and then objectively judge the degree of recrystallization completion according to the separation of diffraction peaks K α1 and K α2 in the diffraction pattern. It avoids the differences caused by different subjective judgment criteria of experimental personnel when observing the change of grain size by the traditional metallographic method and measuring the hardness change by the hardness method. For example, differences in the judgment of grain boundaries by different experimental personnel and the selection of hardness measurement positions will not occur in the present invention, ensuring the accuracy and reliability of the test results. Description of the Drawings

[0029] Figure 1 It is the diffraction pattern of the 211 crystal plane of sample 211 after annealing at 680°C in Example 1 of the present invention.

[0030] Figure 2 It is the diffraction pattern of the 211 crystal plane of sample 211 after annealing at 690°C in Example 1 of the present invention.

[0031] Figure 3 It is the diffraction pattern of the 211 crystal plane of sample 211 after annealing at 700°C in Example 1 of the present invention.

[0032] Figure 4 It is the diffraction pattern of the 211 crystal plane of sample 211 after annealing at 710°C in Example 1 of the present invention.

[0033] Figure 5 It is the diffraction pattern of the 211 crystal plane of sample 211 after annealing at 720°C in Example 1 of the present invention. Detailed Embodiments

[0034] To enable those skilled in the art to better understand the technical solution of the present invention, the preferred implementation of the present invention will be described below in conjunction with specific embodiments. However, it should be understood that the drawings are only for illustrative purposes and should not be construed as a limitation of this patent.

[0035] The present invention proposes a method for judging the recrystallization temperature of steel materials by using an X-ray diffractometer. The principle is that the X-ray generator equipped with a conventional X-ray diffractometer obtains X-rays by bombarding the anode target surface with electrons of cathode rays. When the voltage is high enough, characteristic X-rays or characteristic X-rays are generated. In the actual test process of the diffractometer, K-series characteristic X-rays (K-series radiation) are generally used. The K-series characteristic X-rays include K α and K β series. Since the wavelengths of the two differ by an angle, the K β series can be filtered out by a filter or a monochromator. However, the K α series also includes two K α1 and K α2 radiations with very small wavelength differences. Generally, the intensity ratio is 2:1. Therefore, on the diffraction pattern, two diffraction peaks that are very close in position but have an intensity ratio of 2:1 will be formed. According to Bragg's formula 2dsinθ = λ, in the diffraction spectrum, the angular difference at low angles is small and not obvious (K α1 and K α2 almost overlap), while the diffraction angle difference at high angles is large and obvious.

[0036] At a certain temperature, if the recrystallization process is completed, the macroscopic stress, microscopic stress, crystal defects, and dislocations caused by strain are eliminated. K α1 and K α2 can be clearly separated. That is, on the X-ray diffraction pattern of the material that has undergone sufficient recrystallization, two separated diffraction peaks K α1 and K α2 will appear, and the intensity ratio of K α1 and K α2 is 2:1. If the recrystallization has not been completed, the stress, dislocations, and crystal defects cause the interplanar spacing of the same crystal planes in a small area to increase, decrease, or remain unchanged. The diffraction angles generated by the three are slightly different, making the diffraction peak broader. After broadening, it is equivalent to submerging K α1 and K α2 , so that K α1 and K α2 cannot be separated, indicating that the recrystallization has not been completed.

[0037] The technical solution of the present invention includes the following steps:

[0038] (1) Select obviously deformed steel, and use wire cutting or other means to cut the steel into block specimens with a length and width of 10-20 mm. The thickness of the specimen is determined according to the configuration of the diffractometer used.

[0039] (2) Determine the approximate range of recrystallization temperature based on experience, heat to different temperatures, keep them for a period of time, and then cool them down to room temperature.

[0040] (3) Grind and polish the specimens. Use cold water to cool the specimens continuously during the grinding and polishing process to ensure that there is no decarburization, oxidation, or heat-affected zone on the test surface of the specimens.

[0041] (4) Place the sample on the sample stage of the diffractometer. The voltage and current of the diffractometer are 40 kV and 40 mA respectively. A cobalt target is used (a copper target can also be used if the diffractometer is equipped with a high-energy detector). The optical path adopts a focusing optical path. The 2θ scanning range should completely include the diffraction peak of the 211 crystal plane of Fe, specifically 95°-105°. The scanning speed is not more than 5° / min.

[0042] (5) Determine K by observing the diffraction pattern of the 211 crystal plane α1 and K α2 Determine whether recrystallization is complete.

[0043] Example 1

[0044] See also Figures 1 - 5 , a test method for evaluating the degree of recrystallization completion of steel materials, comprising the following steps:

[0045] (1) Select Q235 steel plates that have been cold deformed with a deformation amount of 80%, cut the cold deformed Q235 steel plates into 10 mm*10 mm specimens, anneal at 680°C, 690°C, 700°C, 710°C, and 720°C and keep them warm for 20 minutes, and then slowly cool to room temperature.

[0046] (2) Based on past experience, it can be confirmed that under the condition of 10 minutes of insulation, the recrystallization temperature range of Q235 steel plate is between 680℃ and 720℃; the sample is ground and polished, and the sample is continuously cooled with cold water during the grinding and polishing process to ensure that there is no decarburization, oxidation, or heat-affected zone on the test surface of the sample.

[0047] (3) Place the sample on the sample stage of an X-ray diffractometer with a voltage and current of 40 kV and 40 mA, respectively. Use a cobalt target (copper target can also be used if the diffractometer is equipped with a high-energy detector). Use a focusing optical path. The 2θ scanning range should completely include the diffraction peak of the 211 crystal plane of Fe, specifically 95°-105°. The scanning speed should not exceed 5° / min. Obtain the diffraction peak spectra of the 211 crystal plane of the sample at different temperatures.

[0048] (4) Whether the diffraction peak of Fe 211 crystal plane in the diffraction spectrum appears as two separate diffraction peaks K α1 and K α2 To judge whether recrystallization is fully completed, if the diffraction spectrum shows obvious separation of K α1and K α2 , indicating that recrystallization has been completed. From Figures 1 through 5 it can be seen that the diffraction patterns at 680 °C and 690 °C cannot separate K α1 and K α2 , indicating that recrystallization has not yet started. At 700 °C, the diffraction pattern shows the appearance of K α2 signs, indicating that the specimen has started the recrystallization process, but only some grains have started recrystallization. At 710 °C and 720 °C, the diffraction pattern shows obvious K α2 , indicating that the specimen has completed the recrystallization process between 710 °C and 720 °C.

[0049] The present invention has been described in detail above in connection with the embodiments, but the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the gist of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims

1. A test method for evaluating the degree of recrystallization completion of steel materials, characterized in that, It includes the following steps: (1) Divide the steel plate to be measured into multiple block-shaped steel plate specimens; (2) Preliminarily determine the recrystallization temperature range of the steel plate to be measured according to experience, set multiple temperature gradients within this range, heat multiple steel plate specimens at different temperatures and hold for a period of time, and then cool them to room temperature; (3) Grind and polish the steel plate specimens after cooling; (4) Place the polished steel plate specimens on the sample stage of the X-ray diffractometer, start the X-ray diffractometer for scanning, and obtain the diffraction patterns of the steel plate specimens at different temperatures; (5) Based on the separation of diffraction peaks K α1 and K α2 in the diffraction pattern, determine the degree of recrystallization completion of the steel plate specimen.

2. The test method for evaluating the degree of recrystallization completion of steel materials according to claim 1, characterized in that, In step (1), the deformation amount of the steel plate to be measured is 70-90%.

3. The test method for evaluating the degree of recrystallization completion of steel materials according to claim 1, characterized in that, In step (2), the set step size of the temperature gradient is 5-10°C.

4. The test method for evaluating the degree of recrystallization completion of steel materials according to claim 1, characterized in that, In step (3), cold water is used to cool the steel plate specimens during the grinding and polishing process.

5. The test method for evaluating the recrystallization completion degree of steel materials according to claim 1, characterized in that, In step (4), the voltage of the X-ray diffractometer is 40-50 kV, and the current is 40-50 mA.

6. The test method for evaluating the degree of recrystallization completion of steel materials according to claim 1, characterized in that, In step (4), the X-ray diffractometer uses a cobalt target or a copper target.

7. The test method for evaluating the degree of recrystallization completion of steel materials according to claim 1, wherein In step (4), the optical path of the X-ray diffractometer uses a focusing optical path.

8. The test method for evaluating the degree of recrystallization completion of steel materials according to claim 1, wherein, In step (4), the 2θ scanning range of the X-ray diffractometer is 95°-105°, and the scanning speed is not greater than 5° / min.

9. The test method for evaluating the recrystallization completion degree of steel materials according to claim 1, characterized in that In step (5), if no diffraction peak K appears in the diffraction pattern α2 sign, it indicates that the recrystallization of the steel sample has not yet started; If a diffraction peak K appears in the diffraction pattern α2 but is not completely separated from the diffraction peak K α1 it indicates that only partial recrystallization has occurred in the steel sample. If the diffraction peaks K α1 and K α2 are completely separated in the diffraction pattern, it indicates that the steel sample has fully completed recrystallization at the corresponding heating temperature.

10. The test method for evaluating the recrystallization completion degree of steel materials according to claim 9, characterized in that, In step (5), if the intensity ratio of diffraction peak K α1 and diffraction peak K α2 is 2:1, it indicates that diffraction peak K α1 and K α2 are completely separated.

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