Auger Electron Spectroscopy of Boron Nitride in Hot-rolled Graphitized Steel Sheet

Abstract

The distribution of elements in graphitized steel sheet was examined by Auger electron spectroscopy. The microstructure showed pronounced stringers of graphite with an area 6 μm×15 μm parallel to the rolling direction of the hot-rolled steel sheet after graphitization annealing at 933 K for 36 ks. Boron nitride (BN) precipitates were rarely detected in the graphite in polished specimens, but they were found on the graphite surface in specimens subjected toin situAr+ ion sputtering. Auger electron spectroscopy colour mapping images showed stringers of BN precipitates in the area 2 μm×0.5 μm parallel to the rolling direction at the interior of the graphite in the steel. The image was considered to present the first observation of BN precipitates in graphite. High-energy resolution Auger spectra obtained from the area of BN precipitation coincided well with spectra of hexagonal BN (h-BN), even in fine structures of B KLL and N KLL Auger transitions. It was deduced that h-BN precipitates exist inside the graphite and act as sites for the nucleation of graphitization. The distribution of h-BN precipitation in the graphite suggests that h-BN precipitates are formed at the unrecrystallized austenite grain boundaries during hot rolling.