LAUSR

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) was employed for an analysis of the rare earth element Ce in pure iron and steel. Secondary ion images showed that the amount of the segregation of Ce and its oxides was much less as the concentration of Ce decreased to about 11 ppm in the pure iron. In terms of depth profiling from the surface to the matrix, variation of the CeO+/Ce+ ratio in a Ce oxides sample and a pure Ce sample exhibited difference between oxidized state and metallic state. It was demonstrated that metallic Ce was presented when the ratio of CeO+/Ce+ decreased to approximately 2 and even smaller. Oxygen content with concentration of tens of ppm may influence the ratio obviously. Such ToF‐SIMS analysis was also feasible to discern the states of cerium in a Q345E steel with concentration in ppm level.