Steelmaking slags have been widely used as aggregate for road and civil engineering. The slags sometimes expand as a result of hydration, which may cause evolution of cracks at surfaces of roads when used as aggregate. Free magnesium oxide (free-MgO) in the slags is a potential cause of the expansion as well as free calcium oxide is. Thus, analytical methods to determine the free-MgO in the slag have been required for the accurate evaluation of the expansion. We present an accurate method to determine the free-MgO in steelmaking slags based on the combination of chemical extraction and thermogravimetry (TG). Free-MgO and magnesium hydroxide (Mg(OH) 2) in steelmaking slags are dissolved into an ethyleneglycol solution containing iodine and ethanol when heated. The amount of the magnesium species dissolved in the solution is determined by inductively coupled plasma atomic emission spectrometry. The amount of Mg(OH) 2 in the slags determined by TG independently is subtracted from that of the dissolved in ethyleneglycol to yield the amount of free-MgO. The established method can quantify less than 0.1 wt% free-MgO in steelmaking slags.

For the steel making control with micro-alloyed elements, it is essential to accurately analyze the distribution of those elements between different metallurgical phases in steel. The micro-alloyed elements contained in precipitates have been analyzed by conventional chemical or electrochemical procedures, selectively dissolving the Fe matrix by electrolysis, and separating precipitates as insoluble particles from the matrix by filtration. But this method has become inadequate to analyze the fine precipitates because some of the fine precipitates extracted are unavoidably uncollected. Hence, we have developed a quantitative analysis for micro-alloyed elements containing in the solid solution phase of steel, named solute elements, by using of analyzing a portion of the electrolytic solution. By electrolysis, solute elements are dissolved into the electrolyte, and the precipitates remain on the surface of the sample as insoluble particles. So, the analysis of the electrolytic solution during or after electrolysis enables the determination of solute elements directly. For certified reference materials, the sum total of concentration of solute element analyzed by this method and the precipitate analyzed by conventional method suits a certified value substantially on the micro-alloyed element. However, for the samples that contain fine precipitates, they are not in agreement with the total content obtained by the spark-OES. It is estimated that the precipitates not collected by filtration in the conventional method cause the disagreement. It shows the proposed method, which analyzes solute elements directly, is useful for estimating the distribution of the microalloyed elements between different metallurgical phases.

緒言The electrolytic extraction -filtration method has been used to determine all precipitations in steel, and the content of solid solution is obtained by the subtraction of the precipitation content from total content. But it has become inadequate to analyze the fine precipitates because some of the fine precipitates are unavoidably uncollected. Hence, we have developed a quantitative analysis for solute elements in steel by using of analyzing a portion of the electrolytic solution. By electrolysis, solute elements are dissolved into the electrolyte, and the precipitates remains on the surface of the sample. So, the analysis of the electrolytic solution during or after electrolysis enables the determination of solid solution content directly. For certified reference materials, the sum of the total content of solid solution determined by this method and the precipitates determined by the conventional method substantially agrees with certified value. However, for the samples that contain fine precipitates, they are not in agreement with the total content obtained by the spark-OES. It is estimated that the precipitates not collected by filtration in the conventional method cause the disagreement. It shows the proposed method, which analyzes solute solution directly, is useful.

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Synopsis :We have developed an analytical method which enables highly precise and rapid quantitative analysis of ultra low sulfur contained in steel sample. The developed method is "ultraviolet fluorescence method after combustion", which combined high frequency induction furnace and the continuous UV fluorescence analyzer of sulfur dioxide. Despite easy operation like the conventional IR method, the newly developed method showed high sensitivity and good precision. The quantitation limit of sulfur in steel was 0.5 mass ppm. In addition, it was shown that this equipment has sufficient stability as a process control analysis apparatus of the iron mill which continues operation without resting.