Masahiko Morita

Auger electron spectroscopy of boron nitride in hot-rolled graphitized steel sheet

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 x 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 to in situ Ar + ion sputtering. Anger electron spectroscopy colour mapping images showed stringers of BN precipitates in the area 2 μm x 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.