Determination of Nitrogen in Steel by Spark Emission Spectrometry

Abstract

A co-laboratory research was carried out in order to apply the spark emission spectrometry to the determination of nitrogen in steel. The atomic emission line of nitrogen at 149.263 nm is used as the analytical line. It is found that the conventional types of spark emission spectrometer is considerably useful to determine nitrogen concentration in steel down to 20 ppm level with rather high precision the sensitivity represented as BEC value is 350 ppm, and the analytical precision is 2ppm (1σ) at 20 ppm level. Spectral interferences originated from Fe(II) 149.258 nm and Si based continuous emission are found, but there is no interference from the possible metallic elements such as Cr, Ni, Mo, and Mn. Those ieterferences can be easily corrected by the co-existing elements correction method, in which the correction factor of Fe is 0.00013 × [Fe] % and that of Si is 0.007 x [Si] %. There is no effect of co-existing Ti on the sensitivity and the analytical precision of nitrogen determination, because the TiN may not grow enough to disturb the normal sparks in these heating pretreatment conditions. Grain size of sample has no effect on nitrogen determination. This point is of great advantage to its application to the ladle analysis. It is because the microstructure is strongly affected by sample heating and quenching patterns and is quite different from sample to sample at the production site.