JPH03135752A - Method and apparatus for emission spectrochemical analysis of sulfur in steel - Google Patents

Abstract

PURPOSE:To make simultaneous analysis with good accuracy even if steel kinds vary by determining the min. value of the quadratic curve obtd, by subjecting the relation between the emission intensity and emission time of sulfur to secondary regression by a method of least squares as a sulfur intensity characteristic value. CONSTITUTION:The secondary regression is executed by regarding the attenuation curve as a quadratic curve when the emission intensity of the sulfur is designated as IS and the discharge time as T at the time of subjecting an element in steel to stimulated light emission and analyzing the intrinsic spectra. The min. value of the intensity IS of the resulted regression curve coincides with the stable emission intensity existing on the extension of the attenuation curve and exhibits a high correlation with the content of the sulfur in the steel. The emission intensity is merely necessitated to be measured for about ten to some tens seconds after the preliminary discharge for several seconds in the initial period of discharge by dealing with the contamination on the surface of a sample in this case. The relation with the discharge is the same even if the ratio (IS/IFe) between the intensity IS and the emission intensity IFe of the iron as an internal standard is used. The factors acting simultaneously on the iron and sulfur such as the fluctuation in the discharge conditions and a temp. change of the sample or the fluctuation of a measuring system, are eventually corrected in this case and the accuracy of the measurement is additionally improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] In the simultaneous and rapid analysis of multiple elements in steel, one of the components whose analytical values are particularly susceptible to the effects of the elements coexisting in the sample, the thermal history of the sample, etc. This invention relates to improving the precision and accuracy of sulfur analysis.

[Conventional technology] At steelworks, analysis values are fed back through rapid analysis that takes just a few seconds in order to highly control steel components during the steelmaking process. One of these rapid analysis methods is optical emission spectroscopy, in which energy is applied to a solid sample of steel by means of an electrical discharge to excite the elements in the steel, causing them to emit light, and the unique spectra are analyzed. Component analysis is performed, and this analysis method can simultaneously analyze dozens of elements in steel. However, regarding sulfur, coexisting elements in steel and thermal history affect the luminescence value,
The correlation with the content rate is not sufficient.

For this reason, it is not possible to obtain sufficiently reliable analytical values using the above-mentioned emission spectroscopy alone, and it is necessary to avoid using it in combination with other methods that require a check using the combustion method, which is not affected by tissue or history. There wasn't. The disadvantages of the combustion method are that the time required for analysis is several times longer than that of emission spectroscopy, and that simultaneous analysis of multiple elements is impossible and requires a corresponding amount of man-hours. It was hoped to obtain accurate analytical values excluding the

Generally, in emission spectrometry, repeated discharges are performed and analytical values are determined from the luminescence intensities obtained one after another. However, the luminescence intensity obtained at the beginning of the discharge often differs from the luminescence intensity after that. This is due to the luminescence of sulfur. This tendency is seen not only in the luminescence of other elements, but for some elements this difference is constant, while for others it is not, and sulfur is the most prominent example of the latter.

The very initial luminescence intensity is affected by dirt on the surface of the sample, so it is common practice to use the luminescence intensity that excludes these as the measured value. JIS also requires that the luminescence intensity be measured for 2 to 50 seconds before measurement. It is stipulated that preliminary discharge be performed. In addition, in order to ensure analytical accuracy for measurement, the emission intensity collection time is specified from 2 seconds to 30 seconds (JIS-G-1
253 [revised 1983]).

Conventionally, sulfur has been analyzed simultaneously with many other elements based on the above-mentioned JIS, and the measurement has been carried out for about 5 seconds after a preliminary discharge of about 5 seconds. In this case, the luminescence intensity is integrated over the measurement time, or, using the luminescence intensity of iron as an internal standard, the intensity ratio obtained by dividing the luminescence intensity of the measured element by the luminescence intensity of iron is integrated over the measurement time. It was optimal to use the intensity characteristic value as the intensity characteristic value (hereinafter referred to as the constant time integration method).

On the other hand, in the case of sulfur, there is research that it is insufficient to eliminate the light emission caused by the above-mentioned preliminary discharge, and that a longer and higher-energy preliminary discharge is required. For example, Analytical Chemistry v01゜33, No. 10. p.515
~519. In this case, by performing a high energy predischarge for 30 seconds or more, the MnS crystals, which have different states of existence depending on coexisting elements and thermal history, become finer, and these influences are removed, and the emission intensity becomes a constant value that corresponds only to the sulfur content. (hereinafter referred to as the high-energy pre-discharge method).

On the other hand, instead of using the integral value as the characteristic value of the emission intensity, −
A method of capturing and analyzing the luminescence intensity of each discharge to improve analysis accuracy has also been introduced (for example, Funseki, 198
5, No. 6, p430-434). According to this method,
It has been reported that analysis accuracy can be improved by examining the frequency distribution of intensity values for each emission and using the median value as the characteristic value of the emission intensity (Rishita, referred to as pulse distribution measurement method).

[Problem to be solved by the invention] However, with the constant time integration method, the correlation between the luminescence intensity characteristic value and the sulfur content is not sufficient when the steel types are different.
There is a problem with analysis accuracy.

Although accuracy is improved with the high energy pre-discharge method, this method requires a long pre-discharge of 30 seconds or more.

Several problems arise with this long pre-discharge.
The greatest feature of emission spectrometry is the simultaneous analysis of multiple elements.
Moreover, in general analysis of steel, about 30 other elements can be measured in a very short time of about 10 seconds, including the preliminary discharge time. One of the problems with long pre-discharge is that for sulfur analysis, long-time pre-discharge also prolongs the analysis time for many other elements, which is a disadvantage for process control analysis, and also has the advantage of simultaneous analysis. If we abandon the method and analyze only sulfur, it will remain in the same role as the combustion method mentioned above.
Another problem is that the electrodes are severely worn out due to long-term high-energy discharge, and the intensity of sulfur emission changes greatly each time the number of analyzes is increased, so the device must be calibrated frequently.

In the pulse distribution measurement method, the measurement time is not particularly long and simultaneous analysis of multiple elements is possible within a short period of time, but the effect of improving analysis accuracy is small and is not sufficient.

This invention was made to solve such problems, and it is possible to simultaneously analyze the content of sulfur in steel with high precision even for different steel types in the same short time as that of many other elements. purpose.

[Means and effects for solving the problem] The means to achieve this objective is to minimize the relationship between the emission intensity and emission time of sulfur in a component analysis method in which elements in steel are excited to emit light and their characteristic spectra are analyzed. This is an emission spectroscopic analysis method for sulfur in steel in which the minimum value of the quadratic curve obtained by quadratic regression using the multiplicative method is used as the sulfur intensity characteristic value and the standard for the analytical value. This is an emission spectroscopic analysis method of sulfur in steel, which is the emission intensity ratio divided by the emission intensity of iron. The analyzer used to carry out this emission spectrometry method also achieves its purpose. This device is a component analyzer that excites elements in steel to emit light and analyzes their characteristic spectra. This is an optical emission spectrometer for sulfur in steel, which has a regression processing device that performs quadratic regression using the least squares method and further calculates the minimum value of the luminescence intensity in the obtained regression quadratic curve.

In the analysis of sulfur in steel, the characteristic spectrum of sulfur is 180.
73 is used for measurement, but this luminous intensity is high at the beginning of the discharge, and settles down to a smaller value as the discharge continues.The number of discharges is generally a constant periodic discharge, so However, the relationship between the number of discharges or the discharge time and the luminescence intensity differs slightly depending on the coexisting elements and thermal history. This is because, in particular, the shape and size of the sulfide are related to the amounts of coexisting Mn and C, and the size of the sulfide crystal is also related to the cooling rate, etc. This situation is investigated for steel types A and B, which have significantly different Mn and C contents, as shown in FIG. 6. In the figure,
The vertical axis is the emission intensity of sulfur, and the horizontal axis is the discharge time. Steel type B
The luminescence intensity of sulfur is higher than that of steel type A at the beginning of the discharge, but this relationship reverses when the discharge time is approximately 10 seconds, and the luminescence intensity of sulfur is stable for both steel types when the discharge time is approximately 30 seconds. I've been doing it. In the high-energy pre-discharge method, this stable emission intensity is the object of measurement. This stable luminescence intensity is certainly not affected by the structure or thermal history, and shows a very good correlation with the sulfur content in the steel, but only after stabilizing the luminescence intensity. does not have a high correlation with the sulfur content, and the luminescence intensity, which is decreasing from the high luminescence intensity before stabilizing, is also closely related to the sulfur content. That is, the stable luminescence intensity in the latter half can be estimated from the luminescence intensity in the first half without performing a long preliminary discharge. As a method of estimation, it has been found that the accuracy is insufficient when using a linear regression curve, but sufficient accuracy can be obtained using a quadratic regression curve.

When the emission intensity Is of sulfur and the discharge time are T, this attenuation curve is regarded as a quadratic curve and quadratic regression is performed. Assuming that the obtained regression curve is 5=αT2+βT+γ, the minimum value of Is γ−β2/4α corresponds to the stable emission intensity on the extension of the attenuation curve, and has a very high correlation with the sulfur content in the steel. In the case of , it is not necessary to continue measuring the luminescence intensity for more than 30 seconds, and as is done in general emission spectrometry, after a few seconds of preliminary discharge in order to prevent contamination on the sample surface, It is sufficient to measure the emission intensity of dirt or sand for a period of about 10 seconds.

The above was described in terms of the relationship between the emission intensity of sulfur and the discharge time, but
The relationship with the discharge time is the same even if the ratio (Is/Ip-) between the emission intensity Is of sulfur and iron as an internal standard (Is/Ip-) is used instead of the emission intensity Is of sulfur. That is, if the regression curve is Is/Ipe=αT2+βT+γ, then the minimum value of Is/Ipe (γ−β2/4α
) corresponds to a stable emission intensity on the extension of the decay curve. Moreover, by using the emission intensity ratio, factors that act simultaneously on sulfur and iron, such as variations in discharge conditions, changes in sample temperature, and fluctuations in the measurement system, can be corrected. The measurement accuracy will be better than in the case of

As described above, if the minimum value of the sulfur emission intensity or intensity ratio obtained from the regression curve is taken as the characteristic value of the sulfur emission intensity, and the analytical value is determined using the calibration curve created from this characteristic value, the sample Accurate analytical values can be obtained that are not affected by the structure or thermal history of the device.

A method in which the ratio to the emission intensity of iron is used as a standard for analysis values is often used, and general emission spectrometers have this calculation circuit and can quickly perform calculations.

However, in order to analyze the minimum value of the regression curve as a characteristic value of the luminescence intensity, the relationship between the luminescence intensity of sulfur or the sulfur/iron luminescence intensity ratio and the discharge time is quadraticly regressed, and the luminescence intensity or luminescence intensity of the regression curve is requires a regression processing device that calculates the minimum value of the emission intensity ratio, and the analysis can be performed by an emission spectrometer equipped with this regression processing device.

[Example] (Example 1) A regression processing device was added to a general emission spectrometer to perform quadratic regression on the relationship between emission intensity and discharge time to find the inflection point of the regression curve, and sulfur analysis was performed. . First, an overview of the device.
In the figure 0 shown in the figure, 1 is the power supply section, 2 is the spectroscopic section, 3 is the sample,
4 is an electrode, 5 is a diffraction grating, 6 is a photometric tube, 7 is a readout device, 8 is a central processing unit, 9 is a regression processing device, and 10 is a display/recording device. A 400 Hz discharge was caused between the sample 3 and the electrode 4 by the power supply unit 1, the generated spectrum was separated by the diffraction grating 5, and the intensity was measured by the photometer tube 6. The measured luminescence intensities of sulfur and iron are read out by the readout device 7.
The 0 regression processing device 9 reads out the ratio of the sulfur emission intensity and the iron emission intensity for the emission intensity accumulated over 100 discharges, stores it in the central processing unit 8, and sends it to the regression processing device 9. A regression curve was created by performing quadratic regression on the relationship between the ratios, and the minimum value of the emission intensity ratio was determined for this regression curve, and this was sent back to the central processing unit 8. The preliminary discharge time was 5 seconds, and the measurement time of luminescence intensity was 10 seconds. The central processing unit 8 performs the commonly performed spectral overlap correction for this minimum value, calculates the analytical value using the calibration curve, and sends the result to the display/recording device 10 for recording and displaying at the same time. The data sent to the zero regression processing device 9 is shown in FIG. 2, and the regression curve and minimum value obtained by the regression processing device are shown in FIG. 3.
Steel type A with less n had a smaller initial strength ratio than steel type B, but also had smaller damping. In Figure 3, the minimum value of strength pressure is
The steel type was expressed in mA, and the steel type B was expressed in mB.
mA is larger than ma, which means that the sulfur content of the AI type is larger. Table 1 shows the results of chemical analysis of these steel types. The results of the examples agree with the results of chemical analysis and demonstrate the validity of using the minimum value as the characteristic value of the emission strength.

Table 1 (Example 2) Using the apparatus shown in Example, the major sulfur content of steel types A and B was varied from 0.015wt% to 0035w1. ',;n
Ten samples with different ranges were analyzed and compared with the constant time integration method of the 66-bundle technique. The Mn content in the sample is Q,
The content ranged from 4wt% to 1.4wt%. These results are shown in Figures 4 and 5. Figure 4 shows the results of the example, and Figure 5 shows the results of the conventional example. In the example shown in FIG. 4, both steel types A and B lie on a single 45° line, and it is clear that the sulfur content and the sulfur analysis value have a one-to-one correspondence. On the other hand, in the conventional example shown in FIG. 5, only steel type A lies on the 45° line, and steel type B deviates from this line, which shows that the characteristic value of luminescence intensity differs depending on the steel type even if the content is the same.

(Example 3) Other conventional examples were also measured in the same manner as in Example 2, and their analysis accuracy was determined. The results are shown in Table 2.

Table 2 (%) However, d = [Σ (analytical value - content rate)] / nn = 2
0, σ, -[(Σd2)/(n-1)]I/2 The method of the present invention and the high-energy pre-discharge method are superior in both accuracy and precision, while the other conventional methods are inferior. Moreover, in the method of this invention, the analysis time was 20 seconds including the pre-discharge, which was the same as the analysis time for other elements.

[Effects of the Invention] As described above, according to the present invention, the luminescence intensity of sulfur in steel is determined by using the minimum luminescence intensity value of the regression curve obtained by quadratic regression of the luminescence intensity of sulfur as the luminescence intensity characteristic value. Spectroscopic analysis is performed, and therefore highly accurate and precise analysis values can be obtained even between different steel types without being affected by the coexisting elements or thermal history of the sample. It is now possible to analyze. In process control analysis of steelmaking, it is extremely important to shorten the time for feeding back analysis results by even one second, and this invention has a great effect by realizing simultaneous multi-element analysis, including sulfur, in a short time.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of an emission spectrometer that is an embodiment of the present invention, Figure 2 is a diagram showing the relationship between luminescence intensity and discharge time, which is quadratic regression data, and Figure 3 is a diagram showing the quadratic regression curve. Figure 4 shows the relationship between the analytical value and content rate obtained by the method of the present invention; Figure 5 shows the relationship between the analytical value and content rate obtained by the method of the prior art. FIG. 6 is a graph of luminescence intensity showing the difference in variation in luminescence intensity depending on the type of steel. 1...Power supply section, 2...Spectroscopy section, 3...Sample, 4.
...electrode, 5...diffraction grating, 6...photometer tube, 7...
Reading device, 8... Central processing unit, 9. Regression processing device, 10... Display recording device. Figure 2

Claims (3)

[Claims] (1) In the elemental analysis method in which the elements in steel are excited to emit light and their characteristic spectra are analyzed, the minimum value of the quadratic curve obtained by performing quadratic regression on the relationship between the emission intensity and emission time of sulfur using the least squares method is An optical emission spectroscopic analysis method for sulfur in steel characterized by its characteristic strength value. (2) The method for emission spectroscopic analysis of sulfur in steel according to claim 1, wherein the emission intensity of sulfur is an intensity ratio obtained by dividing the emission intensity of sulfur by the emission intensity of iron. (3) In a component analyzer that excites elements in steel to emit light and analyzes their characteristic spectra, quadratic regression is applied to the relationship between luminescence intensity and luminescence time using the least squares method, and the minimum value of luminescence intensity in the regression quadratic curve is calculated. An optical emission spectrometer for sulfur in steel, characterized by having a regression processing device.