Effect of grain boundary segregation of carbon on critical grain boundary strength of ferritic steel

The critical shear stress for dislocation emission at grain boundary was directly measured by nanoindentation technique. The change in the grain boundary strength with low-temperature aging was then discussed. It was found that the critical grain boundary shear stress increased, and the increment was correlated to the amount of carbon segregated at the grain boundary. From the relationship between the lower yield point and the amount of segregated carbon, it was concluded that the Hall–Petch coefficient (k_y) increased with grain boundary segregation. The validity of the pile-up theory explaining k_y, which depends on the grain boundary strength, was demonstrated.