Quantitative analysis of grain boundaries in carbon- and nitrogen-added ferritic steels by atom probe tomography

Recent reports state that solute carbon increases the Hall–Petch coefficient in ferritic steel through grain boundary segregation, whereas solute nitrogen has hardly any affect. Atom probe analysis of grain boundaries was performed to investigate why nitrogen has negligible influence. Nitrogen segregation at the boundary was clearly observed with a similar amount of carbon segregation in ferritic steel containing 5C–54 N (mass ppm). Quantitative estimation of the coefficient increment per unit interfacial excess implies that grain boundary segregation of nitrogen barely influences the Hall–Petch coefficient.