Spectrographic analysis of cast iron for silicon by high voltage spark discharge with graphite as upper electrode

Abstract

A study was made on the metallographic effect on spectrographic analysis of cast iron for silicon and an analytical method without the influence was found out. A cylindrical rod of chilled casting which was solidified in unidirection from the chilled side was devided into two parts vertically. It was found by means of a microscope that the metallurgical structure of the cross section of the sample varied successively with distance from the chilled side. Then, silicon in the sample was determined at the positions on the cross section 10, 20, 30, 40 and 55 mm form the chilled side as follow; the sample was excited by high voltage spark discharge with a graphite electrode and an analytical line pair, Si I 2516.123Å/Fe II 2714.142 Å was used. When discharged in air, spectral line intensity ratio was stronger to a certain extent as apart from the chilled side, although silicon content was uniform in the sample. On the other hand, when discharged in argon, there was the intensity ratio in the same level at every position and its reproducibility was desirable. From these results, it was expected for metallic matrix to have no influence on the intensity ratio, if sparked in argon. Actually, for the chilled casting sample, gray cast and ductyle iron having indistinct metallurgical history, spectrographic results calibrated by the use of NBS standard samples were in good agreement with chemical results.