JP2014020839A - Segregation evaluation method and segregation evaluation device by emission spectrometric analysis - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a segregation evaluation method and a segregation evaluation device by emission spectrometric analysis capable of quickly and quantitatively evaluating the degree of segregation of C or a low concentration element of 0.01 wt% or less which is difficult to evaluate by an EPMA (Electron Probe Micro Analyzer) method.SOLUTION: There is provided a method for quantitatively evaluating segregation by performing the concentration mapping analysis of a segregation element by the spark discharge emission spectrometric analysis of a region including a portion to be evaluated on segregation while allowing steel materials including the portion to be evaluated on segregation to continuously scan with respect to an electrode which generates spark discharge, in which scanning is repeatedly performed two or more times on the same scanning line, and at least one of discharge energy and a scanning speed is changed in preliminary scanning and main scanning for quantitative analysis. Thus, it is possible to quickly and quantitatively evaluate the degree of segregation of C or a low concentration element of 0.01 wt% or less which is difficult to evaluate by the EPMA method.

Description

  The present invention relates to a segregation evaluation method and segregation evaluation apparatus by emission spectroscopic analysis for evaluating the internal quality of a steel material, particularly a continuous cast slab of steel or a thick steel plate.

  In the field of steel continuous cast slabs (hereinafter abbreviated as slabs) and thick steel plates made from cast slabs, segregation at the center of the slab formed during continuous casting (center segregation) has a significant effect on product quality. It is known to do. Therefore, many techniques for reducing this center segregation have been developed. On the other hand, several techniques are known for evaluating the center segregation. Specifically, center segregation is evaluated by applying a macro print method, a drill analysis method, a slice analysis method, a spark discharge emission analysis method, or the like to a sample collected for each slab.

  In the macro printing method, the cut surface of the slab is polished, the segregated part is corroded with a corrosive liquid such as picric acid, and then ink is soaked. Then, the ink on the surface is once wiped off, and the ink remaining in the corroded part This is a method of visualizing the occurrence of segregation by copying the material on cellophane paper. However, the macro print method is effective in that it can grasp the segregation of the entire slab sample, but the segregation of the segregation is difficult because the concentration of the obtained print depends on the state of corrosion and polishing.

  The drill analysis method is a method in which a center segregation part is specified by a macro print method or the like, a chip sample is collected from a plurality of analysis points of the center segregation part with a drill, and the chip is analyzed. The slice analysis method is a method of obtaining a concentration distribution of components in the thickness direction by analyzing the components of chips obtained by sequentially slicing a slab or the like in the thickness direction. However, according to the drill analysis method and the slice analysis method, it is possible to quantitatively evaluate the segregation, but it takes a long time for preprocessing such as sampling.

  Patent Document 1 discloses a technique for analyzing a plurality of analysis points on a slab analysis surface using a spark discharge emission analysis method and quantitatively evaluating the degree of segregation. However, according to this technique, since the entire analysis surface is not measured, there is a possibility that the degree of segregation cannot be accurately evaluated.

  As described above, it is difficult to quickly and quantitatively evaluate the degree of segregation with various conventional evaluation methods. For this reason, in recent years, an evaluation method using a mapping analysis technique using an EPMA (electron probe X-ray microanalyzer) or a spark discharge emission analysis described in Patent Document 2 and Non-Patent Document 1 has been proposed.

JP 2007-178321 A JP 2009-236842 A

Wang Haizhou, “Original position statistic distribution analysis (original position analysis)”, SCIENCE IN CHINA (Series B), Vol. 46 No. 2, Page119-123 (2003)

  In the segregation degree evaluation by the mapping analysis technique using the EPMA method described in Patent Document 2, there is an advantage that the entire surface of the slab sample can be analyzed to grasp the macro view of segregation and the result can be quantified. However, in the EPMA method, the effect of depositing carbon (C) on the sample surface by electron beam irradiation has a great influence on the strength of the steel material, and it is difficult to quantitatively analyze C, which is an important segregation element in the segregation degree evaluation. Moreover, there is a limit to the quantification of low concentration elements of 0.01 wt% or less.

  On the other hand, mapping analysis technology (OPA (Original Position statistic distribution Analysis) method) that performs spark discharge emission analysis while continuously scanning the sample described in Non-Patent Document 1 is a technology that can evaluate macrosegregation quickly and quantitatively. As expected. However, in order to quantitatively evaluate the degree of segregation by the OPA method, the same analysis surface is repeatedly scanned multiple times, and the emission data after reducing the effects of surface contamination such as contamination and initial unstable discharge are obtained. Since it needs to be used, analysis takes a long time.

  The present invention has been made in view of the above. Segregation evaluation by emission spectroscopic analysis capable of quickly and quantitatively evaluating the segregation degree of C and low concentration elements of 0.01 wt% or less which are difficult to evaluate by the EPMA method. An object is to provide a method and a segregation evaluation apparatus.

  In order to solve the above-described problems and achieve the object, the method for evaluating segregation by emission spectroscopic analysis according to the present invention continuously applies a steel material including a portion to be evaluated for segregation to an electrode that generates a spark discharge. This is a method of quantitatively evaluating segregation by performing concentration mapping analysis of segregation elements by spark discharge emission spectroscopic analysis of a region including a portion to be evaluated for segregation while scanning, and repeatedly performing segregation on the same scanning line twice or more. The scanning is performed, and at least one of the discharge energy and the scanning speed is changed between the preliminary scanning and the main scanning for quantification.

  Further, the segregation evaluation method by emission spectroscopic analysis according to the present invention is the above invention, wherein, in the above invention, after the preliminary scanning in which the total discharge energy amount per 1 mm of the scanning distance exceeds 60 J, at least one of the discharge energy and the scanning speed is changed. And performing density mapping analysis by scanning.

  Moreover, the segregation evaluation method by emission spectroscopic analysis according to the present invention is the above invention, wherein the segregation element includes at least one of C, P, Mn, Nb, S, Ti, Cu, Mo, V, and Ni. It is characterized by containing elements.

  Further, the segregation evaluation apparatus by emission spectroscopic analysis according to the present invention includes a part to be evaluated for segregation while continuously scanning a steel material including a part to be evaluated for segregation with respect to an electrode that generates a spark discharge. An apparatus for quantitatively evaluating segregation by performing concentration mapping analysis of segregated elements by spark discharge optical emission spectrometry of the included area, repeatedly scanning the same scanning line two or more times, and for preliminary scanning and quantification It is characterized by comprising means for changing at least one of the discharge energy and the scanning speed during the main scanning.

  According to the present invention, it is possible to quickly and quantitatively measure the segregation degree of C or a low concentration element of 0.01 wt% or less which is difficult to evaluate by the EPMA method.

FIG. 1 is a diagram showing changes in calibration curves of C, P, and Mn accompanying changes in discharge energy. FIG. 2 is a diagram showing the relationship between the number of scans and the C emission intensity. FIG. 3 is a diagram showing the C and P concentration distribution of the slab by the measurement method of the present embodiment. FIG. 4 is a diagram showing the relationship between the number of scans and the C emission intensity (discharge energy at the first scan: 240 mJ, discharge energy at the second and subsequent scans: 75 mJ). FIG. 5 is a diagram showing the C and P concentration distribution of the slab by the measurement method of the present embodiment. FIG. 6 is a diagram showing the C and P concentration distribution of the slab by the measurement method of the present embodiment.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited by this embodiment.

  The present invention has an effect on quantitative evaluation of element concentration in an analysis method that performs mapping analysis by a spark discharge emission spectrometry method on a region including a segregation part while continuously scanning a sample with respect to an electrode that generates a spark discharge. The quantitative mapping analysis of each element is made possible by clarifying the factor that gives the effect and performing mapping analysis under the optimum scanning conditions and discharge conditions in order to suppress the influence of each factor.

  In the spark discharge emission analysis, usually, a spark discharge is repeatedly performed in an area of several mmφ without scanning a sample, and a light emission signal generated by discharge several hundred times or more is processed. At this time, a preliminary discharge of about 1 second is carried out in order to reject defective data until the sample surface is decontaminated and a stable discharge is reached.

  On the other hand, when performing spark discharge emission analysis while scanning the sample, the first to several scans are the initial discharge for the undischarged region of the sample, and thus the emission information includes information on the surface contamination of the sample. It is inevitable. Therefore, by repeatedly scanning the same analysis surface many times, using the emission data after reducing the effects of surface contamination and initial unstable discharge, obtain stable emission intensity, and from the obtained emission intensity The concentration of each element can be quantitatively evaluated by a calibration curve method or the like. However, repeated scanning on the same analysis surface many times improves the accuracy of quantitative analysis, but requires a long time for the analysis, and the segregation degree over a wide area cannot be evaluated quickly.

  Therefore, in order to evaluate the segregation degree quickly and quantitatively, it is important that the analysis surface of the sample is made free from the influence of surface contamination and the influence of the initial unstable discharge with as few scans as possible. In addition, since the light emission signal due to the discharge during the scanning until the analysis surface is stabilized is not used for the evaluation of the segregation degree, it is possible to set the conditions different from the optimum discharge conditions for the analysis.

  Here, when the discharge energy is increased, depending on the element, the background is increased and the emission intensity is saturated. Therefore, it is not an optimal condition for quantitative analysis. However, when the discharge energy is high, the amount of sample evaporation per discharge increases, and surface contamination can be quickly removed (surface cleaning).

  Therefore, in the initial preliminary scan for surface cleaning, discharge conditions with high discharge energy are used, the effects of surface contamination and initial unstable discharge are quickly removed, and in the main scan for subsequent determination, each element is quantitatively analyzed. By setting the discharge conditions with the optimum discharge energy, quantitative mapping analysis of elements can be performed quickly. Furthermore, as for the scanning speed, preliminary processing can be performed by preliminary scanning at a scanning speed faster than the scanning speed optimum for quantification to remove surface contamination and the like. Rapid and accurate segregation evaluation becomes possible by emission spectroscopic analysis by such a method.

  FIGS. 1A to 1C are diagrams showing changes in calibration curves (relationship between concentration and emission intensity ratio) of C, P, and Mn with changes in discharge energy. In order to clean the surface of the analysis portion, the discharge treatment was repeated for 10 seconds at a discharge energy of 75 mJ and a discharge repetition frequency of 200 Hz for the same place without scanning the sample (preliminary treatment). Thereafter, the discharge energy was changed to 75 mJ, 200 mJ, and 240 mJ for the analyzed portion, and C, P, and Mn were quantified (this measurement).

  As shown in FIG. 1A, in C, the emission intensity ratio increases as the discharge energy increases during quantification. On the other hand, as shown in FIG. 1 (b), in P, the accuracy in the low-concentration region decreases due to an increase in the background as the discharge energy increases, and as shown in FIG. 1 (c), the discharge energy increases in Mn. Accordingly, the saturation in the emission intensity ratio decreases the accuracy in the high concentration range. In general, if the discharge energy becomes too low, the analysis sensitivity is lowered. Therefore, from the results shown in FIG. 1, the discharge energy at the time of quantification (during this measurement) is preferably about 75 mJ. This is also a preferable condition in the analysis method of the present invention in which mapping analysis is performed on a region including a segregation part while continuously scanning a sample, and it is desirable to apply this.

  The spark discharge emission analysis method according to the present invention was applied to mapping analysis of a slab. As a specific measurement method, a slab C cross section perpendicular to the casting direction is subjected to spark discharge emission analysis while continuously scanning a sample using a stepping motor driven arm, and emission data for each discharge is recorded, Quantitative analysis was performed by the calibration curve method. As a sample scanning method, 15 mm was scanned in the plate thickness direction of the slab, and the measurement was performed 20 times while shifting the scanning position at a pitch of 3 mm in the plate width direction of the slab, and a 15 mm × 60 mm region was measured. Prior to the measurement, the analysis surface was finished by belt polishing with a roughness of # 100. In addition, the optimum discharge conditions that can quantitatively analyze each segregated element such as C, P, and Mn in this scan are as described above in consideration of the influence of background on the calibration curve and the influence of quantitative analysis such as saturation of emission intensity. The same discharge energy was 75 mJ, the discharge repetition frequency was 200 Hz, and the scanning speed was 30 mm / min. The measurement time of the main scan for a 15 mm × 60 mm region under the above measurement conditions was about 15 minutes.

  FIG. 2 is a diagram showing a change in the light emission intensity of C when the same scanning line is scanned a plurality of times under the optimal discharge conditions (discharge energy 75 mJ, discharge repetition frequency 200 Hz, scanning speed 30 mm / min) for the above quantitative determination. . As shown in FIG. 2, the C emission intensity gradually decreases with each scanning. This is presumably because surface contamination decreases with every scanning. In FIG. 2, the light emission intensity is almost constant after the fourth scan. Therefore, in order to sufficiently reduce the influence of surface contamination under the optimum discharge conditions for the above-described quantification, three or more preliminary scans are necessary, and the scan time for actual quantification after the fourth time (this time) When combined with (measurement time), the total measurement time is 60 minutes or more. At this time, the total discharge energy discharged per scanning distance of 1 mm in the three preliminary scans was 90 J (= 75 mJ × 200 Hz (times / second) × 2 seconds × 3 times).

  FIG. 3 (a) is a diagram showing a C-thickness direction concentration profile of slab when measured under the above conditions, and FIG. 3 (b) is a thickness direction of P of slab measured under the above conditions. It is a figure which shows a density profile. In the measurement shown in FIGS. 3A and 3B, the first to third scans are pre-scanned, the discharge energy amount is 75 mJ, the discharge repetition frequency is 200 Hz, and the scan speed is 30 mm / min. Scanning was performed with a discharge energy of 75 mJ, a discharge repetition frequency of 200 Hz, and a scanning speed of 30 mm / min. As shown in FIG. 3 (a), by performing spark discharge emission analysis continuously while scanning a sample, it becomes possible to measure the concentration distribution of C, which is difficult to determine by the EPMA method, and to evaluate the degree of segregation. did it. Further, as shown in FIG. 3 (b), it was possible to measure the concentration distribution of P, which is difficult to determine by the EPMA method, and the segregation degree could be evaluated.

  Next, the discharge energy at the first scan is increased to 240 mJ and discharged at a discharge repetition frequency of 200 Hz and a scan speed of 30 mm / min. The discharge energy at the second and subsequent scans is 75 mJ, which is the optimum discharge condition for quantitative determination. The repetition frequency was 200 Hz and the scanning speed was 30 mm / min. FIG. 4 is a diagram showing a change in C emission intensity under these conditions. As shown in FIG. 4, by increasing the discharge energy during the first scan, the influence of surface contamination can be sufficiently reduced by one scan, and effective analysis can be performed by the second scan. It became. Therefore, the total measurement time could be shortened to 30 minutes. The total amount of discharge energy discharged per 1 mm of scanning distance at the time of the first scanning at this time was 96 J (= 240 mJ × 200 Hz (times / second) × 2 seconds × 1 time).

  Furthermore, the discharge energy at the first scanning is 240 mJ, the discharge repetition frequency is 200 Hz, the scanning speed is changed to 45 mm / min, 60 mm / min, and the discharge energy at the second scanning is 75 mJ, which is the optimal discharge condition for quantification. The repetition frequency was 200 Hz and the scanning speed was 30 mm / min. FIG. 4 also shows changes in C emission intensity under these conditions. As shown in FIG. 4, when the first scanning speed is increased to 60 mm / min, the surface contamination cannot be sufficiently reduced. However, when the first scanning speed is 45 mm / min, the surface contamination is sufficiently reduced. It was possible to reduce. When the scanning speed was 45 mm / min, the scanning time was about 10 minutes, and the total measurement time including the second scanning under the optimal discharge conditions for quantification could be shortened to 25 minutes. The total amount of discharge energy discharged per 1 mm of scanning distance at the first scanning is 64 J (= 240 mJ × 200 Hz (times / second) × 1.33 seconds × 1 time) at a scanning speed of 45 mm / min, scanning speed 60 mm. 48 J (= 240 mJ × 200 Hz (times / second) × 1 second × 1 time) at / min.

  According to the investigations by the inventors including the above-mentioned experiment, usually, in the preliminary scan, after performing the preliminary scan such that the total discharge energy amount per 1 mm of the scanning distance exceeds 60 J, the quantification by the main scan can be performed. It turned out to be preferable.

  The total discharge energy amount per 1 mm scanning distance in the preliminary scanning is expressed by the product of the discharge energy, the discharge repetition frequency, the time required for 1 mm scanning (the reciprocal of the scanning speed), and the number of scans. Therefore, in the preliminary scanning, it is preferable to set each factor to be adjusted so that the total discharge energy amount per 1 mm of the scanning distance is 60 J or more. However, there are also restrictions on the apparatus, and it is usually selected from the range of discharge energy 20 to 1000 mJ, discharge repetition frequency 100 to 500 Hz, and scanning speed 10 to 200 mm / min. Further, in order to uniformly clean the surface without missing the pre-scanned portion, it is necessary to discharge 250 times or more per 1 mm, and therefore, the discharge repetition frequency and the scanning speed are limited from these viewpoints.

  In general, when the scanning speed of a sample is increased, the number of discharges per unit scanning area decreases, so that the statistical error increases and the accuracy of quantitative analysis decreases, but the scanning time can be shortened. Therefore, by performing the preliminary scan for surface cleaning without performing quantitative analysis, the scanning speed is increased, and in subsequent main scans, the scanning speed is set so that the number of discharges necessary for quantitative analysis can be ensured. Analysis can be performed quickly. In a normal apparatus, it is preferable to select a preliminary scan for surface cleaning at a scanning speed exceeding 30 mm / min, and a main scanning for performing quantitative analysis from a scanning speed of 30 mm / min or less. .

  Further, as the element for quantitatively evaluating the concentration, it is preferable to use an element whose concentration in steel can be evaluated by an ordinary spark discharge optical emission spectrometry, and an element that tends to segregate in a cast slab or a thick steel plate. , Mn, Nb, S, Ti, Cu, Mo, V, Ni and the like. In particular, it can be suitably used for segregation degree evaluation using C having a large influence on the material such as steel strength or P having a large difference (distribution difference) between the concentration in the molten metal and the concentration in the solidified metal. .

  As described above, according to the segregation evaluation method and the segregation evaluation apparatus based on the emission spectroscopic analysis of the present embodiment, C or 0.01 wt% or less at the center of a continuous cast slab or a thick steel plate that is difficult to evaluate by the EPMA method. Segregation of low-concentration elements can be measured quickly and quantitatively. Thereby, evaluation of center segregation can be performed accurately and rapidly, and it can greatly contribute to quality improvement of continuous cast slabs and thick steel plates.

[Example]
The spark discharge emission analysis method according to the present invention was applied to slab mapping analysis and compared with the measurement results obtained by the conventional mapping analysis method. Table 1 shows steel materials of [C]: 0.023 wt%, [Si]: 0.30 wt%, [Mn]: 1.26 wt%, [P]: 0.003 wt%, [S]: 0.002 wt%. The measurement conditions and measurement results of the respective examples measured in the same manner as described above with various conditions changed are shown. As shown in Table 1, for each example, for all of C, P, and Mn, the measurement result error is within ± 5% of the above composition, and the total of the pretreatment time and the main measurement time. When the total measurement time is shorter than the measurement by the conventional mapping analysis method (60 minutes), it was evaluated as effective. As a result, it was able to be evaluated as effective in Examples 7 to 10 in Table 1 to which the present invention was applied.

  5 (a) and 6 (a) are diagrams showing the concentration distribution of C in the slab by the measurement method according to the present invention, and FIGS. 5 (b) and 6 (b) show the measurement according to the present invention. It is a figure which shows density | concentration distribution of P of the slab by a method. In the measurements shown in FIGS. 5A and 5B, the first scan is a preliminary scan, the discharge energy is 240 mJ, the discharge repetition frequency is 200 Hz, and the scan speed is 30 mm / min (total discharge energy amount per scan distance of 1 mm: 96 J). ) The second scanning was performed with a discharge energy of 75 mJ, a discharge repetition frequency of 200 Hz, and a scanning speed of 30 mm / min. In the measurements shown in FIGS. 6A and 6B, the first scan is a preliminary scan, the discharge energy is 240 mJ, the discharge repetition frequency is 200 Hz, and the scan speed is 45 mm / min (total discharge energy amount per 1 mm of scanning distance: 64 J). ) The second scanning was performed with a discharge energy of 75 mJ, a discharge repetition frequency of 200 Hz, and a scanning speed of 30 mm / min. As shown in FIG. 5A and FIG. 6A, the concentration distribution of C was measured under each condition. Further, as shown in FIGS. 5B and 6B, the concentration distribution of P could be measured under each condition. The results of FIG. 5 and FIG. 6 are in good agreement with the results of FIG. 3, and the degree of segregation could be evaluated quickly and quantitatively by the spark discharge emission analysis method according to the present invention.

  Although the embodiment to which the invention made by the present inventor is applied has been described above, the present invention is not limited by the description and the drawings that form a part of the disclosure of the present invention according to this embodiment. That is, other embodiments, examples, operational techniques, and the like made by those skilled in the art based on this embodiment are all included in the scope of the present invention.

Claims (4)

  Segregation element concentration mapping analysis by spark discharge optical emission spectrometry of the region including the part to be evaluated for segregation while continuously scanning the steel material including the part to be evaluated for segregation with respect to the electrode that generates the spark discharge. In which the segregation is quantitatively evaluated, wherein the same scanning line is repeatedly scanned two or more times, and at least the discharge energy and the scanning speed in the preliminary scanning and the main scanning for the quantitative determination. A segregation evaluation method by emission spectroscopic analysis, characterized in that one is changed.   A density mapping analysis is performed by performing a main scan for quantification by changing at least one of the discharge energy and the scanning speed after a preliminary scan in which the total discharge energy amount per 1 mm of scanning distance exceeds 60 J. The segregation evaluation method by the emission spectroscopic analysis according to claim 1.   The emission spectrum according to claim 1 or 2, wherein the segregation element includes at least one element of C, P, Mn, Nb, S, Ti, Cu, Mo, V, and Ni. Segregation evaluation method by analysis.   Segregation element concentration mapping analysis by spark discharge optical emission spectrometry of the region including the part to be evaluated for segregation while continuously scanning the steel material including the part to be evaluated for segregation with respect to the electrode that generates the spark discharge. The apparatus for quantitatively evaluating segregation, wherein the same scanning line is repeatedly scanned two or more times, and at least the discharge energy and the scanning speed in the preliminary scanning and the main scanning for the quantitative determination. An apparatus for evaluating segregation by emission spectroscopic analysis, comprising means for changing one of the two.

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