Boron segregation to austenite grain boundary in low alloy steel measured by aberration corrected STEM–EELS

Boron concentration profile around prior austenite grain boundaries in Fe-0.05C–0.5Mo–0.001B (mass%) is examined by using aberration corrected STEM–EELS. Tilt series measurements of line analysis with a thin specimen (<30 nm) and the principal component analysis (PCA) are performed to obtain the precise distribution of boron around the boundary. The concentration on the grain boundary reaches beyond 8 at% and the distribution width is about 1.2 nm. The effects of the boundary inclination and the specimen thickness are also examined by calculation based on the Gaussian broadening model. The obtained concentration profile implies that the boron segregation in the present material is formed by ‘non-equilibrium segregation mechanism’.