IMPURITY SEGREGATION OF STAINLESS STEEL STUDIED BY ATOM-PROBE AND AUGER ELECTRON SPECTROSCOPY

The surface compositions of type 304 stainless steel heated in vacuum at 600-900°C were determined by an atom-probe and Auger electron spectroscopic analysis. In addition to enrichment and depletion of alloying elements in the surface of the stainless steel, segregation of impurity elements such as carbon, nitrogen, phosphorus and sulfur is known to occur. In this paper the atom-probe was used to measure the impurity segregation in the grains as well as in the grain boundary while the AES was used to measure the segregation in a single crystal. The atom-probe analysis shows that in the case of 5 min heating at 600°C, nitrogen segregates about 3 at% in the first atomic layer in the grains, while in the grain boundary nitrogen segregates 16 at% in the first layer and phosphorus 14 at% in the second layer. In the AES analysis, nitrogen and carbon are found to segregate about several at% for 5 min heating. The concentration of nitrogen and carbon decrease with further heating and phosphorus begins to segregate