JP5998801B2 - Method for quantitative analysis of alumina in steel - Google Patents

Description

  The present invention relates to an analysis method for quickly and accurately quantifying alumina in a steel material using a spark discharge type emission spectroscopic analysis method.

A part of the aluminum (hereinafter referred to as Al) added to the molten steel in the steelmaking refining process reacts with oxygen in the steel and floats as alumina (Al ₂ O ₃ ) and is removed from the molten steel. The reaction Al is dissolved in the molten steel. After the solidification of the steel, the alumina that has not been levitated and removed remains in the steel as it is, and the unreacted Al is present in the steel mainly as solute Al.

  With the recent increase in strength and quality of steel products, it is necessary to control the amount and composition of inclusions. In high clean steel applied to bearing materials and the like, a slight amount of remaining alumina deteriorates the fatigue characteristics of the product, so efforts are made to reduce alumina, and the amount of alumina is suppressed to about several ppm. In addition, in high-strength line pipe materials and the like, in order to suppress the formation of inclusions that become crack initiation points, Ca is added in the final process of refining to fix S as CaS, or a composite inclusion of Ca and alumina. Is formed. In the former case, the amount of alumina is an indicator of material properties, and in the latter case, the Ca addition amount needs to be optimized according to the S concentration in the molten steel and the amount of alumina forming the composite inclusions.

  As described above, in solidified steel, Al is present as alumina, and unreacted Al is present in the steel mainly as solute Al. The solid solution Al dissolves together when the steel sample is dissolved with an acid, but the alumina is difficult to dissolve, so that they are separated from each other by acid dissolution. That is, the amount of alumina in the steel sample can be determined by filtering the solution and determining the amount of Al contained in the residue by chemical analysis and converting it. However, this chemical analysis method takes several hours to obtain an analysis result, and there is a problem that the process management analysis is not quick. Therefore, a rapid analysis method using a spark discharge emission spectroscopic analysis method that can quickly obtain a result with a short analysis time has been developed and widely spread.

  For example, in Non-Patent Document 1, in the frequency distribution diagram of the spectrum intensity of Al emission generated by applying a spark discharge to a solid sample many times, the normal distribution part on the low intensity side is solid solution Al, and the distribution on the high intensity side is alumina. It is disclosed that each can be separately quantified. Further, in Patent Document 1, without using the frequency distribution diagram of the spectrum intensity used in Non-Patent Document 1, light emission with biaxial spectral emission intensity of Fe and Al generated by applying a multiple number of spark discharges to a solid sample. Using a pulse distribution chart, a lower boundary line indicating the lower limit of the Al intensity is obtained, and light emission with a higher Al emission intensity than the upper boundary line obtained from the average value of the pulse emission intensity of Fe and the coefficient of the lower boundary line A method for obtaining the concentration of alumina in steel from the frequency of pulses is disclosed. Further, in Patent Document 2, using a diagram in which the spectrum intensity of Al emission is rearranged in ascending order, all Al is obtained by multiplying the 50% rank value by the number of discharges, and all Al is subtracted from the total spectrum intensity integrated value. A method for obtaining solid solution Al from the difference between the two and determining the amount of Al by form is disclosed.

Japanese Patent Laid-Open No. 08-29349 JP 2005-345127 A JP 2012-26745 A (described later)

KAMADA Hitoshi / Hen, “Latest steel state analysis”, Agne, P111-114

  However, in the method described in Non-Patent Document 1, there is a problem that if the alumina contained in the sample is small, the distinction point between solid solution Al and alumina becomes unclear, and sufficient analysis accuracy can be obtained. Absent. Further, in the method described in Patent Document 1, the frequency of emission pulses having a higher Al emission intensity than the upper boundary straight line is extremely low in a sample in a trace concentration range where the Al content in the form of alumina is 50 mass ppm or less. In addition, in order to obtain sufficient accuracy, the number of discharges has to be increased, and there is a problem that analysis time becomes long. Furthermore, in the method described in Patent Document 2, the amount of alumina is calculated from the difference between the total spectral intensity integrated value and the integrated value based on the 50% rank value, but the amount and ratio of solute Al and alumina are large. When it fluctuates, there is a problem that the degree of influence of solid solution Al and alumina on the emission intensity of the 50% rank value is not constant but causes variation.

  In view of such circumstances, the present invention uses a spark discharge emission spectroscopic analysis method, and the ratio of the solid solution Al to alumina is not constant, and even in a trace amount sample in which the Al content in the alumina form is 50 mass ppm or less. An object of the present invention is to provide a method for quantitative analysis of alumina in steel, which can be measured quickly and accurately.

  The present inventors have developed the technique described in Patent Document 3 as a method capable of analyzing in detail the discharge pulse in the spark discharge emission spectroscopic analysis method and analyzing the solute Al in the steel with high accuracy. In Patent Document 3, the mode value of the Al / Fe emission intensity ratio is obtained using a frequency distribution diagram with the horizontal axis representing the Al / Fe emission intensity ratio for each discharge pulse and the vertical axis representing the frequency. The amount of solid solution Al (sol. Al) is analyzed by using, as a correction coefficient, the ratio of the number of pulses included in the range within double to the total number of pulses. In the solid solution Al quantitative analysis method, since the solid solution Al can be quantified with high accuracy even in various samples in which the ratio of the solid solution Al and alumina is not constant, the Al / Fe emission intensity ratio is further increased. In particular, the inventors have focused on the relationship between the amount of solute Al and the amount of alumina, and have studied in detail to find the present invention.

The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] In a method of performing spark discharge a number of times between a steel sample and a counter electrode in an inert gas atmosphere, and determining the content of alumina in the steel sample based on the intrinsic spectral intensity of the obtained element A method for quantitative analysis of alumina in steel, comprising the following steps.
A) Intensity ratio calculation step for obtaining the emission intensity ratio of aluminum and iron for each discharge pulse by a number of discharge pulses Step a) A frequency distribution diagram is drawn with the horizontal axis as the emission intensity ratio and the vertical axis as the frequency. Alumina for calculating the mode value of the emission intensity ratio from the figure and obtaining the alumina fraction by the following formula using the threshold value α defined with reference to the standard deviation of the mode and the emission intensity ratio smaller than the mode value Fraction calculation step Alumina fraction = number of pulses whose emission intensity ratio is greater than threshold α / number of total pulses c) The emission intensity ratio for each discharge pulse obtained by the intensity ratio calculation step is arranged in ascending order, The emission intensity ratio is set as the representative Al intensity ratio, and then the alumina intensity ratio is calculated from the product of the alumina fraction obtained in the alumina fraction calculation step and the representative Al intensity ratio. Using the alumina strength ratio calculated in the alumina strength ratio calculating step, an alumina quantitative step for calculating the amount of alumina in the steel sample [2] In the alumina fraction calculating step, the threshold α is obtained by the following equation: The method for quantitative analysis of alumina in steel according to [1].
Threshold value α = mode value of emission intensity ratio + standard deviation of emission intensity ratio smaller than the mode value × f
Note that 10 ≦ f ≦ 22.
[3] In the alumina intensity ratio calculation step, when arranging the emission intensity ratio for each discharge pulse from the smaller one, the emission intensity ratio at any position within 30% of the total number of pulses is calculated from the smaller emission intensity ratio. The method for quantitative analysis of alumina in steel according to [1] or [2], wherein the aluminum is extracted as a representative aluminum strength ratio.
[4] The method for quantitative analysis of alumina in steel according to any one of [1] to [3], wherein the steel sample is a sample collected from molten steel after aluminum deoxidation in a refining process.
[5] The method for quantitative analysis of alumina in steel according to any one of [1] to [4], wherein the aluminum content of alumina in the steel sample is 50 ppm by mass or less.
[6] In plotting the frequency distribution chart in the alumina fraction calculation step, the horizontal axis is set to any value in the range of 2 to 5% of the median value of the emission intensity ratio of the discharge pulse. The method for quantitative analysis of alumina in steel according to any one of [1] to [5], wherein a mode value is obtained by smoothing a broken line connecting numerical values.

  According to the present invention, the amount of alumina in a steel material can be quickly and accurately detected even in a minute sample in which the ratio of solute Al to alumina is not constant and the Al content in the form of alumina is 50 ppm by mass or less. Can be measured.

It is a figure which shows Al / Fe luminescence intensity ratio for every discharge pulse of the steel sample with many amounts of aluminas in order of time series of discharge. It is a figure which shows Al / Fe luminescence intensity ratio for every discharge pulse of the steel sample with few alumina amounts in order of time series of discharge. It is a frequency distribution diagram of the Al / Fe emission intensity ratio of two samples having different amounts of alumina. It is a schematic diagram which shows a spark discharge type | mold emission-spectral-analysis apparatus. It is a figure which shows the relationship between f value and analysis accuracy ((sigma) d). It is a figure which shows the correlation of the alumina analysis value calculated | required by the method of this invention, and a chemical analysis value. It is a figure which shows the correlation of the alumina analysis value calculated | required by the conventional method, and a chemical analysis value.

  The method for quantitative analysis of alumina in steel according to the present invention is a spark discharge emission spectroscopic analysis method, in which a spark discharge is carried out many times between a steel sample and a counter electrode in an inert gas atmosphere, and is contained in the steel sample. It is characterized by accurately and quickly quantifying the amount of alumina to be produced. In particular, the ratio of the number of pulses attributed to alumina to the total number of pulses based on the mode value obtained using the frequency distribution diagram with the horizontal axis representing the emission intensity ratio of aluminum and iron for each discharge pulse and the vertical axis representing the frequency. That is, the alumina fraction is obtained, and the emission intensity ratio between aluminum and iron is arranged in ascending order, and the emission intensity ratio that is less affected by alumina is used as the representative Al intensity ratio. By using the ratio of numbers, the amount of alumina can be obtained with high accuracy.

Hereinafter, the background to the completion of the present invention will be described.
In the steelmaking refining process, the sample collected during the refining process after deoxidation and the sample collected at the end of the refining process were each made to emit light by spark discharge, and the ratio of the aluminum emission intensity to the iron emission intensity for each discharge pulse (aluminum Obtained by dividing the emission intensity by the emission intensity of iron, hereinafter referred to as the emission intensity ratio). Light emission by spark discharge was performed 2000 times, and the light emission intensity ratio was determined for each. The obtained results are shown in FIG. 1 and FIG. 2 in the order of time series of discharge pulses (spark discharge). FIG. 1 is a sample collected during the refining process, and the Al content in the alumina form is 43 ppm. FIG. 2 shows a sample at the end of the refining process, and the Al content in the alumina form is 23 ppm. In addition, the Al content in the form of alumina is converted from the oxygen analysis value in steel after confirming in advance that the oxide in the sample is a simple substance of alumina (alumina made of Al ₂ O ₃ instead of a complex oxide). And asked. In the sample collected during the refining process of FIG. 1 with a high amount of Al in the form of alumina, a lot of spike-like luminescence data is observed irregularly, and this is a discharge that contains alumina that is unevenly present in the steel. It is thought to come from. On the other hand, in the sample collected at the end of the refining process in FIG. 2 with a low Al content in the form of alumina, the frequency of spike-like light emission is less than that in FIG. It is thought that it was generated by a discharge containing alumina present.

  FIG. 3 is a frequency distribution diagram of the emission intensity ratio created based on the results of FIGS. 1 and 2. From FIG. 3, the sample with a larger amount of alumina has a distribution shifted to the higher emission intensity ratio side. That is, it is considered that the signal derived from alumina is dominant on the high emission intensity ratio side. On the other hand, it is considered that the signal amount derived from alumina decreases as it goes to the low emission intensity ratio side of the frequency distribution diagram of the emission intensity ratio, and the signal derived from solute Al is dominant. The inventors have tried to calculate the signal amount derived from alumina by various algorithms. As a result, the inventors considered that it is extremely rare that only alumina emits excitation light, and even in the data on the high emission intensity ratio side, it is considered that a component that excited and emitted solute Al was included. It was thought that the amount of alumina could be quantified with high accuracy by correcting the minute. Based on the mode value of the frequency distribution diagram of the emission intensity ratio, the discharge pulse included in the range within twice that is derived from solute Al, that is, the discharge pulse exceeding twice the mode value is alumina. The method described in Patent Document 3 was completed.

  In spark discharge optical emission spectrometry, changes in the discharge state occur due to subtle differences in the polishing state of the sample surface and changes in the wear state of the discharge counter electrode due to numerous analyzes over a long period of time, resulting in fluctuations in the analytical value. Bring. The method of Patent Document 3 is a method that is remarkably superior to other methods, but in such a case, it cannot be said that sufficient accuracy is still obtained.

  Therefore, as a result of intensive studies to further improve the analysis accuracy, the present inventors thought that in Patent Document 3, the threshold value α is simply set to twice the mode value, so that sufficient accuracy cannot be obtained. .

  As long as the processing conditions and measurement conditions are the same, the frequency distribution of the Al / Fe emission intensity ratio derived from solute Al is the same distribution state for any measurement sample as long as the sample has the same composition. Thus, it is considered that the standard deviation and the mode value ratio of the emission intensity ratio derived from the solute Al are the same. However, in the actual measurement, it is considered that the standard deviation of the emission intensity ratio derived from the solute Al slightly varies depending on the measurement sample depending on the polishing state of the sample surface, the wear state of the discharge counter electrode, and the like. For this reason, in the method of Patent Document 3 in which only the mode value is considered and the threshold value is set without considering the standard deviation, the degree of separation between the solute Al-derived discharge pulse and the alumina-derived discharge pulse is low. It became different for each measurement, and the accuracy was thought to be reduced.

Therefore, when determining the threshold value α, it is considered that the influence of the standard deviation of the emission intensity ratio derived from the solute Al should be taken into consideration, and the emission intensity ratio is more than the mode value of the frequency distribution diagram of the emission intensity ratio. Since small discharge pulses are mainly emitted from solute Al, the standard deviation of the luminescence intensity ratio is correlated with the standard deviation of the luminescence intensity ratio derived from solute Al, and the present invention is completed. did. That is, the threshold value α when determining the alumina fraction is the sum of the constant value of the standard deviation of the emission intensity ratio smaller than the mode value and the mode value as shown in the following formula, so that the emission intensity ratio of the solute Al is Considering the standard deviation, it was considered that the discharge pulse derived from alumina could be separated.
Threshold value α = mode value of emission intensity ratio + standard deviation of emission intensity ratio smaller than the mode value × f
Here, the value of f is preferably 10 ≦ f ≦ 22, more preferably 15 ≦ f ≦ 20. When the value of f is smaller than 10, since data derived from solute Al increases, the correlation with the amount of alumina becomes worse. On the other hand, when the value of f is larger than 22, the number of pulses including the signal derived from alumina to be extracted becomes too small, and the variation of the analysis value becomes large. As will be described later with reference to FIG. 5, in such a case, the analysis accuracy exceeds 4 ppm, which is not very accurate.

  As a result of reducing the above error factors by the method of the present invention, the measurement accuracy is further improved, and it is possible to accurately quantify even a very small amount of sample having an alumina Al content of 50 mass ppm or less.

  Below, the procedure of the quantitative analysis method of the alumina in the steel of this invention is demonstrated in detail. FIG. 4 is a schematic diagram showing a spark discharge type emission spectroscopic analyzer according to the present invention. The spark discharge emission spectroscopic analysis apparatus includes a light emitting unit 10 including a discharge device 1, an analysis sample 2 (also an electrode), and a counter electrode 3, and a diffraction grating 7 that splits emission spectrum lines into eigenspectral lines of each element, A spectroscope 11 comprising a detector (photomultiplier) 6 and the like for detecting a unique spectral line for each element, and a photometric device for digitally converting the analog amount of the spectral line emitted for each spark discharge and performing data processing 4 and an arithmetic processing unit 5 for converting the spectral line intensity into the element content and a display unit 9 for displaying the result.

A) Intensity ratio calculation step First, spark discharge is performed between the analytical sample 2 and the counter electrode 3 by a usual method, and the emission intensity values for each discharge pulse of aluminum and iron are measured, and each discharge pulse is measured. The emission intensity ratio between Al and Fe (hereinafter sometimes referred to as emission intensity ratio) is calculated. Here, if the discharge is repeated excessively, alumina in the steel is finely dispersed and it becomes difficult to distinguish it from solute Al. Therefore, the number of discharges is preferably within 2000 pulses.

B) Alumina fraction calculation step A frequency distribution chart is drawn with the horizontal axis representing the emission intensity ratio and the vertical axis representing frequency, and the mode value of the emission intensity ratio is calculated from the frequency distribution chart. Next, the alumina fraction is obtained by the following equation using the threshold value α determined based on the mode value.
Alumina fraction = number of pulses with emission intensity ratio greater than threshold α / number of total pulses First, the mode of emission intensity ratio is calculated by the following procedure.
1) Obtain the median value of the emission intensity ratio of all discharge pulses.
2) Obtain a value of 2 to 5% of the median value obtained in 1).
3) Create a frequency distribution diagram of the emission intensity ratio of the discharge pulse, with the horizontal axis representing the emission intensity ratio and the vertical axis representing the frequency.
4) A polygonal line connecting each frequency value is smoothed by data processing, and the emission intensity ratio giving the maximum value of the obtained curve is set as the mode value.

  The frequency distribution diagram has a completely different form depending on the setting of the horizontal axis, and a problem occurs in determining the mode value. For example, if the categorical value is too small, the unevenness of the distribution becomes significant and it becomes difficult to determine the mode value. Conversely, if the categorical value is too large, the unevenness of the distribution is reduced and the mode value becomes clear. Decreases. Therefore, as a result of investigations using several steel samples, the inventors categorized it by 2 to 5% of the median value of each, and said that it is appropriate to smooth the polygonal line connecting the numerical values. I came to a conclusion. The smoothing curve may be obtained by a general method such as a moving average method or a numerical differentiation method.

C) Alumina intensity ratio calculation step The emission intensity ratio for each discharge pulse obtained in the intensity ratio calculation step is sorted in ascending order, and the emission intensity ratio at a fixed position is extracted as the representative Al intensity ratio. In particular, it is preferable that the emission intensity ratio at a position within 30% of the total number of pulses, more preferably 5 to 25%, is set as the representative Al intensity ratio from the smaller emission intensity ratio that is less influenced by alumina. In the case of aluminum, 396.1 nm, 394.4 nm, and 308.2 nm are appropriate as analysis wavelengths, and in the case of iron, 187.7 nm, 271.4 nm, 281.3 nm, and 287.5 nm are appropriate. is there.
Next, the product of the alumina fraction obtained in the alumina fraction calculating step and the representative Al intensity ratio is defined as the alumina intensity ratio.

D) Alumina determination step The alumina concentration ratio calculated can be derived directly by substituting the calculated alumina strength ratio into the relational expression (calibration curve) between the alumina strength ratio and the alumina concentration in steel. it can.
The relational expression (calibration curve) between the alumina strength ratio and the alumina concentration in steel, for example, quantifies the alumina concentration (acid-insoluble aluminum) by a method such as JIS G1257 for a plurality of samples collected from the same refining process, On the other hand, it can be obtained by determining the alumina strength ratio according to the present invention and determining their correlation.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to the following Example at all.

  A steel sample collected and cooled from molten steel after deoxidation of aluminum in the refining process was used. The steel sample contains solute Al having the concentrations shown in Table 1 and alumina. The solid solution Al, alumina in the form of alumina, and alumina shown in Table 1 were obtained by chemical analysis according to Appendix 14 or Appendix 16 of JIS G1257 (1994) (hereinafter referred to as chemical analysis values). The steel sample was cut into an appropriate size and the surface was polished, and then analyzed by the following method.

Invention Example After polishing the steel sample shown in Table 1, 2000 pulses of discharge measurement were performed four times for each sample using the spark discharge emission spectroscopic analyzer shown in FIG. The discharge energy by one pulse was 0.2J. ARL4460 type (manufactured by Thermo Fisher Scientific Co.) was used as a spark discharge emission spectroscopic analyzer. Using the obtained 2000-pulse measurement data, a frequency distribution diagram of the emission intensity ratio was created to determine the mode value. Next, the alumina fraction was determined using the sum of the mode value of the frequency distribution diagram of the light emission intensity ratio and f times the standard deviation of the light emission intensity ratio smaller than the mode value as a threshold value.
As the representative Al intensity ratio, the emission intensity ratios of the obtained discharge pulses were arranged in ascending order, and the 400th emission intensity ratio corresponding to 20% of the total number of pulses was used from the smaller emission intensity ratio. The product of the alumina fraction and the representative Al intensity ratio was used as the alumina intensity ratio, and was substituted into a calibration curve prepared in advance with a steel sample having a known alumina concentration, and converted to the alumina concentration. This was obtained for every 2000 pulses of discharge measurement, and the average value for 4 times was taken as the alumina concentration of the sample.

  In this way, using various values of f = 6 to 30, the alumina concentrations (hereinafter referred to as alumina analysis values) by the spark discharge type emission spectroscopic analysis method for sample numbers 1 to 12 shown in Table 1 are respectively used. Asked. Moreover, the analytical accuracy with respect to the alumina analytical value calculated | required using f value was each derived | led-out. FIG. 5 shows the relationship between the f value and the analysis accuracy. FIG. 6 shows the correlation and analytical accuracy between the alumina analysis value and the chemical analysis value obtained by the method of the present invention when f = 10, 18, and 22.

  The analysis accuracy (σd) is the root mean square of the difference between the alumina analysis value and the chemical analysis value, and is generally represented by the following formula.

here,
σd: analysis accuracy N: number of samples in Table 1 (N = 12)
x _i : difference of the obtained analytical value with respect to the chemical analytical value for the sample number i in Table 1 (alumina analytical value−chemical analytical value)
And

Comparative Example As a comparative example, the alumina analysis value was determined by the conventional methods described in Patent Documents 1, 2, and 3. After polishing the steel sample shown in Table 1, 2000 pulses of discharge measurement were performed four times by the same method using the same apparatus as the invention example. The obtained measurement data of 2000 pulses were processed according to the methods of Patent Documents 1, 2, and 3, and converted into an alumina concentration by substituting into a calibration curve prepared in advance with a steel sample having a known alumina concentration. This was obtained for every 2000 pulses of discharge measurement, and the average value for 4 times was taken as the alumina concentration of the sample. FIG. 7 shows the correlation between the analytical value of alumina and the chemical analysis value obtained by the conventional methods of Patent Documents 1, 2, and 3, and the analytical accuracy.

  Moreover, about the sample numbers 1-12 of Table 1, the chemical analysis value of alumina, the alumina analysis value by the method of patent documents 1, 2, and 3, the alumina analysis value by the method of this invention (f = 18), analysis accuracy ( Table 2 shows values of σd).

  5-7 and Table 2, in the method of this invention and patent document 3, compared with patent document 1, 2, the ratio of solute Al and alumina is not constant, and Al content of an alumina form is 50 ppm or less It can be seen that an accurate analytical value is obtained even for a very small amount of sample.

  Next, the method of the present invention was compared with the method of Patent Document 3 with respect to the effect when the discharge state fluctuated. As described above, the discharge energy per minute surface area of the sample surface where discharge occurs due to changes in the polishing state of the sample surface, the wear state of the discharge counter electrode, and the like causes variation in analysis values. Since it is not easy to reproduce these fluctuations quantitatively, as a method for simulating them, pulse discharge was caused by changing the discharge energy (steady condition: 0.2 J) by ± 5%, and the results were compared.

  With respect to the samples shown in Table 1, analytical values were obtained when the discharge energy per pulse was increased by 5% and when the discharge energy was decreased by 5%. The measurement conditions other than the discharge energy were the same as those in Example 1, and f = 18. The analytical accuracy was also derived. Furthermore, an error average value (Δave) represented by the following formula was also calculated.

here,
Δave: error average value N: number of samples in Table 1 (N = 12)
x _i : difference of the obtained analytical value with respect to the chemical analytical value for the sample number i in Table 1 (alumina analytical value−chemical analytical value)
And

  Table 3 shows the results of analysis values, analysis accuracy, and error mean values.

  As shown in Table 3, in the method of Patent Document 3, the accuracy of analysis becomes larger and the accuracy is inferior with respect to the discharge energy fluctuation of ± 5% as compared with the steady state. On the other hand, in the method of the present invention, it is not so different from the value in the steady state. Therefore, the method of the present invention can accurately determine the alumina concentration in steel. And it turns out that the alumina concentration can be quantified stably with respect to the fluctuation | variation of a discharge state in the analysis method of this invention. Furthermore, it can be seen from the result of the average error value that the analysis method of the present invention has a small error.

DESCRIPTION OF SYMBOLS 1 Discharge apparatus 2 Analytical sample 3 Counter electrode 4 Photometry apparatus 5 Arithmetic processing apparatus 6 Detector 7 Diffraction grating 8 Slit 9 Display part 10 Light emission part 11 Spectrometer

Claims (6)

In an inert gas atmosphere, a spark discharge is performed many times between a steel sample and a counter electrode, and the content of alumina in the steel sample is obtained based on the intrinsic spectral intensity of the obtained element, A method for quantitative analysis of alumina in steel, comprising the following steps.
A) Intensity ratio calculation step for obtaining the emission intensity ratio of aluminum and iron for each discharge pulse by a number of discharge pulses Step a) A frequency distribution diagram is drawn with the horizontal axis as the emission intensity ratio and the vertical axis as the frequency. Alumina for calculating the mode value of the emission intensity ratio from the figure and obtaining the alumina fraction by the following formula using the threshold value α defined with reference to the standard deviation of the mode and the emission intensity ratio smaller than the mode value Fraction calculation step Alumina fraction = number of pulses whose emission intensity ratio is greater than threshold α / number of total pulses c) The emission intensity ratio for each discharge pulse obtained by the intensity ratio calculation step is arranged in ascending order, The emission intensity ratio is set as the representative Al intensity ratio, and then the alumina intensity ratio is calculated from the product of the alumina fraction obtained in the alumina fraction calculation step and the representative Al intensity ratio. Using the alumina strength ratio calculated in the alumina strength ratio calculating step, the alumina quantitative step for calculating the amount of alumina in the steel sample 2. The method for quantitative analysis of alumina in steel according to claim 1, wherein in the alumina fraction calculation step, the threshold value α is obtained by the following equation.
Threshold value α = mode value of emission intensity ratio + standard deviation of emission intensity ratio smaller than the mode value × f
Note that 10 ≦ f ≦ 22. In the alumina intensity ratio calculation step, when arranging the emission intensity ratio for each discharge pulse from the smaller one, the emission intensity ratio at any position within 30% of the total number of pulses from the smaller emission intensity ratio is represented as the representative aluminum intensity. The method for quantitative analysis of alumina in steel according to claim 1 or 2, wherein extraction is performed as a ratio. The method for quantitative analysis of alumina in steel according to any one of claims 1 to 3, wherein the steel sample is a sample collected from molten steel after aluminum deoxidation in a refining process. The method for quantitative analysis of alumina in steel according to any one of claims 1 to 4, wherein the aluminum content in the form of alumina in the steel sample is 50 ppm by mass or less. In drawing the frequency distribution chart in the alumina fraction calculation step, the horizontal axis segment value is set to any value in the range of 2 to 5% of the median value of the emission intensity ratio for each discharge pulse, and each frequency value is 6. The method for quantitative analysis of alumina in steel according to any one of claims 1 to 5, wherein the mode value is obtained by smoothing the connecting line to form a curved line.

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