Emission spectroscopic analysis method for Sb in metallic materials, method for measuring Sb concentration in molten steel during refining, and method for manufacturing steel materials

Abstract

To provide an emission spectral analysis method for quickly and highly accurately measuring the concentration of Sb contained in a metal material (especially, the metal material containing a lot of iron such as a steel material).SOLUTION: Disclosed is an emission spectral analysis method of Sb in a metal material, which includes the steps of: generating the excitation light emission by repeatedly generating the spark discharge between the metal material and an electrode facing the metal material; dispersing the excitation light emission; and measuring the emission intensity IM and the emission intensity ISb in order to obtain the ratio ISb / IM of the light emission intensity ISb of Sb contained in the metal material to the light emission intensity IM of a matrix element of the metal material. The spark discharge is performed with discharge energy of less than 0.10 J.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an emission spectroscopic analysis method for Sb in metallic materials, a method for measuring the Sb concentration in molten steel during refining, and a method for manufacturing a steel material. [Background technology]

[0002] Adding trace amounts of specific elements to steel materials is effective in improving properties and developing new functions, and has been put to practical use.

[0003] For example, in the field of high-tensile steel, Nb and Ti are added to steel materials at levels of several hundred ppm by mass because the Nb and Ti added to steel materials form fine carbides, which have a precipitation strengthening effect. In the field of bearing steel, Sb is added to steel materials at levels of several tens of ppm by mass because Sb added to steel materials suppresses the decrease in fatigue strength caused by surface decarburization during hot processes such as hot forming and quenching.

[0004] For this reason, it is necessary to control the concentration of elements in steel materials just enough to obtain the desired properties.

[0005] The concentration of elements in steel materials is adjusted during the refining of molten steel. That is, a portion of the molten steel being refined is taken to prepare a sample, the concentration of the target element (for convenience, referred to as "element A") contained in the prepared sample is quickly analyzed, and based on the analysis results, the amount of element A to be added to bring the concentration of element A in the molten steel to the target concentration is calculated, and element A is added to the molten steel in the calculated amount.

[0006] Methods used to quantify elements in steel materials include spark discharge optical emission spectroscopy and laser ablation ICP (inductively coupled plasma) mass spectrometry (LA-ICP-MS). In spark discharge optical emission spectroscopy, spark discharges are repeatedly generated between a metal material and an electrode, and the excited luminescence generated by each spark discharge is separated into spectra and the luminescence intensity is measured. Patent Document 1 discloses a method for quickly and accurately measuring the concentration of carbon contained in a metal material containing a large amount of iron, such as a steel material, using spark discharge optical emission spectroscopy. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-215113 Summary of the Invention [Problem to be solved by the invention]

[0008] However, when measuring the Sb concentration in steel material using the method disclosed in Patent Document 1, the sensitivity is low and Sb concentrations at the level of several tens of ppm by mass cannot be measured. Therefore, in order to accurately measure the Sb concentration in steel materials, it is necessary to carry out a separate wet chemical analysis. However, because wet chemical analysis takes a long time, it is not possible to measure the Sb concentration in molten steel during refining. Therefore, the Sb concentration in molten steel is adjusted using a predicted value based on past performance and refining parameters as a guideline, without the Sb concentration in molten steel being unknown. As a result, the Sb concentration in the final steel product may deviate from the target concentration, resulting in a decrease in yield.

[0009] The present invention has been made in view of the above points, and aims to provide an optical emission spectroscopic analysis method for quickly and accurately measuring the concentration of Sb contained in metal materials (particularly, metal materials containing a large amount of iron, such as steel materials). [Means for solving the problem]

[0010] As a result of extensive research, the present inventors have found that the above object can be achieved by employing the following configuration, and have completed the present invention.

[0011] That is, the present invention provides the following [1] to [6]. [1] Spark discharge is repeatedly generated between a metal material and an electrode facing the metal material to generate excited luminescence, and the excited luminescence is analyzed by spectroscopy to determine the luminescence intensity I of the matrix element of the metal material. M The emission intensity I of Sb contained in the above metal materials Sb Ratio of I Sb / I M In order to calculate the emission intensity I M and the above emission intensity I Sb The method for analyzing Sb in a metal material by optical emission spectroscopy, wherein the spark discharge is carried out with a discharge energy of less than 0.10 J. [2] The method for analyzing Sb in a metal material according to [1] above, wherein the spark discharge is carried out with a discharge energy of 0.07 J or less. [3] The method for analyzing Sb in a metal material according to [1] or [2] above, wherein the emission intensity is measured with a delay time. [4] The method for analyzing Sb in a metal material according to [3] above, wherein the delay time is equal to or longer than the time required for the emission intensity of Sb from each spark discharge to decrease to 60% of its maximum value. [5] A portion of the molten steel is collected during refining to prepare an analytical sample, and the emission intensity I of the matrix element of the analytical sample is measured using optical emission spectroscopy. M and the emission intensity I of Sb contained in the above analytical sample Sb Measure the above emission intensity I M The above emission intensity I Sb Ratio of I Sb / I M Using the previously calculated ratio I Sb / I M and the Sb concentration, the Sb concentration of the analysis sample is obtained based on the relationship between the Sb concentration and the Sb concentration, wherein the optical emission spectroscopic analysis method is the optical emission spectroscopic analysis method for Sb in a metallic material according to any one of [1] to [4] above. [6] A method for producing a steel material, comprising: obtaining an Sb concentration in molten steel during refining using the method for measuring the Sb concentration in molten steel during refining described in [5] above; determining an amount of Sb to be added to the molten steel during refining based on the obtained Sb concentration; and adding Sb to the molten steel during refining based on the determined amount of Sb to be added. [Effects of the Invention]

[0012] According to the present invention, the concentration of Sb contained in a metal material (particularly a metal material containing a large amount of iron, such as a steel material) can be measured quickly and with high accuracy. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a graph showing an example of the relationship between BEC and discharge energy. [Figure 2] 10 is a graph showing an example of the relationship between BEC and delay time. [Figure 3] 1 is a graph showing the luminescence behavior of Fe and Sb for each spark discharge. [Figure 4] 1 is a graph showing the relationship between the emission intensity of Sb and BEC. DETAILED DESCRIPTION OF THE INVENTION

[0014] [Findings Obtained by the Inventors] The present inventors have focused on spark discharge optical emission spectrometry and investigated the conditions for quantifying Sb at the level of several tens of ppm by mass in steel materials.

[0015] To increase the sensitivity of spark discharge optical emission spectrometry, it is effective to lower the background equivalent concentration (BEC), which is believed to be correlated with the lower limit of quantitation. BEC is the concentration-converted signal intensity obtained from a sample that does not contain the target element (i.e., the content of the target element is zero), and is calculated from the absolute value (|b / a|) obtained by dividing the intercept b by the slope a of the calibration curve (y=ax+b).

[0016] In spark discharge optical emission spectroscopy, the emission intensity I of the matrix element is used to reduce the variation caused by the sample. M Emission intensity I of analyte element A relative to A The ratio (I A / I M ) is used as the signal strength. Therefore, in order to reduce BEC, it is necessary to increase the slope a, that is, the ratio (I A / I M It is preferable to increase the value of

[0017] Therefore, the present inventors changed various analytical conditions and calculated and compared the BECs each time. As a result, we found that behavior specific to Sb appears in the relationship between the spark discharge energy (discharge energy) and BEC, and in the relationship between the delay time set when measuring the excited luminescence after each spark discharge and BEC.

[0018] FIG. 1 is a graph showing an example of the relationship between BEC and discharge energy. As shown in Figure 1, when the target elements were Cr, Ti, V, and Zr, the BEC value hardly changed even when the discharge energy (unit: J) was changed. In contrast, when the target element was Sb, the BEC value decreased when the discharge energy was lowered.

[0019] FIG. 2 is a graph showing an example of the relationship between BEC and delay time. As shown in FIG. 2, when the target element of analysis was Sb, the BEC decreased by providing a delay time (unit: n seconds).

[0020] The present invention was made based on the above findings. A preferred embodiment of the present invention is described below.

[0021] [Analysis of Sb in metallic materials by optical emission spectroscopy] First, the emission spectroscopic analysis of Sb in a metal material according to this embodiment (hereinafter also referred to as "this analysis method") is carried out.

[0022] <Device used for emission spectroscopic analysis of Sb in metal materials> The apparatus used in this analysis method is not particularly limited as long as it is a spark discharge optical emission spectrometer, but a solid-state optical emission spectrometer capable of simultaneously measuring multiple elements is preferred.

[0023] <Metal materials> Although there are no particular limitations on the metallic material used as the sample in this analytical method, this analytical method is particularly effective for metallic materials that contain a lot of iron, and therefore metallic materials that contain a lot of iron are preferred. In other words, the matrix element of the metallic material is preferably iron (Fe). Furthermore, the metallic material that is the sample for this analytical method may contain antimony (Sb) as an element to be analyzed. Examples of such samples (metallic materials) include samples obtained by taking samples from molten steel during refining, solidifying them, shearing them, and polishing the sheared surface; and samples obtained by shearing steel materials and polishing the sheared surface.

[0024] Spark discharge An electrode is placed opposite the metal material, and spark discharge is generated multiple times between the metal material and the electrode in an inert gas or vacuum to generate excited luminescence. The spark discharge may be generated by a known method. The number of spark discharges (number of pulses) may be set to an appropriate number that allows for highly accurate analysis. Preliminary discharges may be performed as necessary. The number of spark discharges required to collect data for analysis is preferably about 1,000 to 2,000. The repetition frequency of the spark discharge does not particularly contribute significantly to analytical performance, so a general range of 200 to 400 Hz is preferred.

[0025] In this embodiment, the energy of the spark discharge (discharge energy) is less than 0.10 J. This reduces the luminescence intensity I M Sb emission intensity I Sb The ratio (ISb / I M ) value increases, and BEC can be reduced. The discharge energy is preferably 0.07 J or less, and more preferably 0.05 J or less.

[0026] On the other hand, if the discharge energy is too low, the ratio (I Sb / I M ) may vary greatly, resulting in a decrease in accuracy. For this reason, the discharge energy is preferably 0.01 J or more, and more preferably 0.02 J or more.

[0027] <Spectroscopy> The excitation light emitted by the spark discharge is then analyzed to obtain the characteristic spectral lines of each element.

[0028] <Measurement of luminescence intensity> Next, the emission intensity of the element-specific spectral lines obtained by spectroscopy of the excited emission is measured, thus measuring the emission intensities of Sb and the matrix elements. Sb emission intensity I Sb When measuring the emission line, there is no particular limitation, but when the sample is a metal material containing a large amount of iron, it is preferable to use an emission line of 217.58 nm, which has a wavelength with little spectral interference. Emission intensity of matrix elements I M The emission lines to be measured are not particularly limited as long as they are emission lines originating from the matrix element, are not overlapped with other elements, and have sufficient intensity. For example, when the sample (metal material) is a steel material, emission lines of the matrix element Fe include Fe(I) 287.2 nm and Fe(II) 271.4 nm.

[0029] <Delay time> We investigated the effect of the delay time when capturing the excitation luminescence after each spark discharge. As a result, when the luminescence intensity was measured after a certain delay time from the spark discharge, the BEC was lower than when the luminescence intensity was measured immediately after the spark discharge (Figure 2).

[0030] FIG. 3 is a graph showing the luminescence behavior of Fe and Sb for each spark discharge, with the horizontal axis representing the elapsed time (unit: μsec) from the spark discharge and the vertical axis representing the normalized luminescence intensity. Regarding the vertical axis in Figure 3, in order to compare elements with different absolute values ​​of emission intensity, the emission intensity of each element is corrected so that the minimum value is zero and the maximum value is 1. In other words, the emission intensity is normalized. As shown in the graph in Figure 3, Sb tends to emit light with a slight delay compared to the matrix element iron (Fe). This suggests that adding a delay time reduces the background by reducing the Fe emission, and at the same time, the Sb emission becomes relatively dominant, resulting in a decrease in the BEC.

[0031] FIG. 4 is a graph showing the relationship between the emission intensity of Sb and BEC. In the case of a metal material containing a large amount of iron, the delay time can be set to the time it takes for the emission intensity of Sb per spark discharge to drop below its maximum value (maximum emission intensity). Specifically, the delay time is preferably equal to or longer than the time required for the emission intensity of Sb per spark discharge to decrease to 90% of its maximum value (maximum emission intensity), more preferably equal to or longer than the time required for the emission intensity to decrease to 80%, and even more preferably equal to or longer than the time required for the emission intensity to decrease to 60%.

[0032] On the other hand, if the delay time is too long, the BEC decreases, but the emission intensity varies, which may result in a decrease in the accuracy of Sb quantification. Therefore, the delay time is preferably equal to or shorter than the time it takes for the emission intensity of Sb per spark discharge to drop to 20% of its maximum value (maximum emission intensity), and more preferably equal to or shorter than the time it takes for it to drop to 30%.

[0033] The time (gate width) for capturing the excited luminescence after the delay time has elapsed is not particularly limited as long as sufficient luminescence intensity can be measured for quantifying Sb. A gate width of a fixed time may be set after the delay time has elapsed, or a gate width may be set from the time the delay time has elapsed until the luminescence is completely extinguished.

[0034] [Method for measuring Sb concentration in molten steel during refining] Next, a method for measuring the Sb concentration of molten steel during refining according to this embodiment (hereinafter also referred to as "this measuring method") will be described.

[0035] <Preparation of analytical samples> In this measurement method, first, an analytical sample is prepared from molten steel during refining. Specifically, a portion of the molten steel is taken from the molten steel being refined, solidified, and then sheared to an appropriate size.The sheared surface is then polished to prepare an analytical sample.

[0036] <Measurement of emission intensity of Sb and matrix elements> Next, the emission intensity I of the matrix element was measured using the optical emission spectroscopy. M and Sb emission intensity I Sb Measure. In this measurement method, the above-described present analytical method is used as the emission spectroscopic analysis method.

[0037] <Measurement of Sb concentration> Then, the measured emission intensity I M and emission intensity I Sb From the ratio (I Sb / I M ) and calculate the ratio (I Sb / I M ) to obtain the ratio (I Sb / I M ) and Sb concentration, the Sb concentration of the analytical sample is obtained. Specifically, for example, a metal material (such as a steel material) with a known Sb concentration that falls within the range of the Sb concentration to be analyzed is prepared as a reference sample. At this time, two or more types of reference samples with different Sb concentrations are prepared. Next, the ratio (I Sb / I M The measurement conditions using emission spectroscopy should be the same for the reference sample and the analytical sample. The obtained ratio (I Sb / I M A calibration curve is created from the relationship between the Sb concentration and the ion concentration. Such a calibration curve is prepared in advance, and the ratio of the analytical sample (I Sb / I M ) is substituted into this calibration curve to calculate the Sb concentration.

[0038] [Method of manufacturing steel materials] Next, a method for producing a steel material according to this embodiment (hereinafter also referred to as "this production method") will be described. In this manufacturing method, first, the Sb concentration of molten steel during refining is obtained using the above-described measurement method. Next, the amount of Sb to be added to the molten steel during refining is determined based on the obtained Sb concentration. In other words, the amount of Sb to be added is determined so that the Sb concentration of the molten steel during refining becomes the target concentration. Thereafter, Sb is added to the molten steel during refining based on the determined amount of Sb to be added, thereby producing a steel material. According to this manufacturing method, the amount of Sb added to molten steel during refining can be controlled with high precision, making it possible to manufacture steel materials with stable properties at a good yield. [Example]

[0039] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples described below.

[0040] <Invention Examples 1 and 2 and Comparative Example 1> For the analysis samples (12 samples) collected from molten steel during refining, the emission intensity I of the matrix element Fe was measured using spark discharge optical emission spectroscopy. Fe and Sb emission intensity I Sb and measure the Fe emission intensity I Fe Sb emission intensity I Sb The ratio (I Sb / I Fe ) was determined and the Sb concentration (unit: mass ppm) was calculated.

[0041] In Examples 1 and 2 of the present invention, the above-described present analytical method was used as the spark discharge optical emission spectrometry. Specifically, in Inventive Example 1, spark discharge (integrated discharge) was performed with a discharge energy of 0.02 J. The delay time was set to a time required for the emission intensity of Sb to reach 50% of the maximum emission intensity. In Example 2, spark discharge (integrated discharge) was carried out with a discharge energy of 0.05 J. The delay time was set to a time required for the emission intensity of Sb to reach 40% of the maximum emission intensity.

[0042] On the other hand, in Comparative Example 1, conventional spark discharge optical emission spectrometry under standard measurement conditions was used as the spark discharge optical emission spectrometry.

[0043] In each example, a steel sample with a known Sb concentration was used as a reference sample, and the Fe emission intensity I Fe Sb emission intensity I Sb The ratio (I Sb / I Fe A calibration curve of the relationship between the Sb concentration and the Sb content was prepared, and the Sb concentration was calculated using this calibration curve.

[0044] The Sb(I)217.58 nm emission line was used as the Sb emission line. The Fe(I) 287.2 nm emission line was used as the Fe emission line.

[0045] The analytical samples used were cylindrical cast samples taken from molten steel during refining. The cast sample was cut into a cross section at the center to obtain the sheared surface, which was then polished using a belt sander (grain size: #80). The Sb emission intensity I Sb and Fe emission intensity I Fe was measured. The Sb emission intensity I Sb After measuring the Sb concentration, a chip sample of about several grams was taken from the sample, a part of which was dissolved in acid, and the chemical analysis value of the Sb concentration (unit: ppm by mass) was determined.

[0046] Emission Intensity Using Emission Spectroscopy I Fe and emission intensity I Sb The measurement conditions are shown in Table 1 below. Also, the ratio (I Sb / I Fe The Sb concentrations (unit: mass ppm) calculated from the above are shown in Table 2 below. Table 2 below also shows chemical analysis values.

[0047] [Table 1]

[0048] [Table 2]

[0049] <Summary of evaluation results> As shown in Table 2 above, the measurement result of the Sb concentration in Comparative Example 1 deviated significantly from the chemical analysis value. Specifically, when σD was calculated as an index representing the accuracy (inaccuracy) of the measurement result, σD in Comparative Example 1 was 5.1 ppm by mass. In Comparative Example 1, the deviation was particularly large at an Sb concentration of 30 mass ppm or less. The reason for this is thought to be that under the measurement conditions of Comparative Example 1, the lower limit of quantitation was around 40 ppm by mass, making it difficult to quantify Sb at concentrations below 40 ppm by mass.

[0050] In contrast, the quantitative Sb concentration results for Invention Examples 1 and 2 were in excellent agreement with the chemical analysis values. Specifically, σD for Invention Example 1 was 1.2 ppm by mass, and σD for Invention Example 2 was 1.9 ppm by mass. The lower limit of quantitation under the measurement conditions of Example 1 was approximately 8 mass ppm, and the lower limit of quantitation under the measurement conditions of Example 2 was approximately 24 mass ppm, so it is believed that more accurate measurement results were obtained.

[0051] Conventionally, Sb has been quantified using wet chemical analysis, which requires about a day from sample collection to obtaining quantitative results, but in Invention Examples 1 and 2, it took only about 15 minutes. Therefore, in Examples 1 and 2, it was demonstrated that trace amounts of Sb contained in steel materials can be determined quickly and with high precision.

Claims

1. Spark discharge is repeatedly generated between a metal material and an electrode facing the metal material to generate excited luminescence, and the excited luminescence is spectroscopically analyzed to determine the luminescence intensity I of the matrix element of the metal material. Ｍ The emission intensity I of Sb contained in the metal material Ｓｂ Ratio I Ｓｂ / I Ｍ In order to calculate the emission intensity I Ｍ and the luminescence intensity I Ｓｂ An emission spectroscopic analysis method for Sb in a metal material, comprising measuring The spark discharge is carried out with a discharge energy of 0.05 J or less.

2. measuring the luminescence intensity after a delay; 2. The method for analyzing Sb in a metal material according to claim 1, wherein the delay time is equal to or longer than the time required for the emission intensity of Sb from each spark discharge to decrease to 60% of its maximum value.

3. A portion of the molten steel is taken during refining to prepare an analytical sample. Using optical emission spectroscopy, the emission intensity I of the matrix element of the analysis sample is Ｍ and the emission intensity I of Sb contained in the analysis sample Ｓｂ Measure The light emission intensity I Ｍ The luminescence intensity I Ｓｂ Ratio I Ｓｂ / I Ｍ Using the previously calculated ratio I Ｓｂ / I Ｍ and the Sb concentration of the analysis sample is obtained based on the relationship between the Sb concentration and the Sb concentration, A method for measuring the Sb concentration in molten steel during refining, wherein the optical emission spectroscopy is the optical emission spectroscopy for Sb in a metallic material according to claim 1 or 2.

4. The Sb concentration of molten steel during refining is obtained using the method for measuring the Sb concentration of molten steel during refining according to claim 3, Based on the obtained Sb concentration, an amount of Sb to be added to the molten steel during refining is determined; A method for producing a steel material, comprising adding Sb to the molten steel during refining based on the determined amount of Sb to be added.

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