Analysis of minute carbide in 25 chromium-20 nickel casting steel by microprobe Auger electron spectroscopy

Abstract

A newly developed Auger electron spectrometer equipped with a field emission electron gun was used for the quantitative analyses of carbides in 25Cr-20Ni casting steel containing 0.4% titanium, 0.3% niobium and 0.4 % carbon. The gun is possible to focus its electron beam on an extremely small spot of down to 20 nm in diameter. The emission current of the gun is 100μA and is stable over a period of 8 h. Standard stainless steels (NBS) were used for the preparation of calibration curves for chromium, iron and nickel. An identical, linear relation was obtained for the three elements between contents (mol % of the respective element) and intensity ratios. The ratios are those of the peak intensities of the respective element to the sum of the peak intensities of the three elements; chromium 489 eV, iron 651 eV, and nickel 848 eV. This technique was applied to analyze carbides in the casting steel. Two different carbides were found, and their compositions were estimated to be (Nb_0.2Ti_0.8)C and (Fe_0.27Cr_0.73)₂₃C₆, respectively.