Nano investigation on the grain boundary periodic segregation based on the divorced coincident segregation in 5% Ni steels

The segregation mechanism of alloying elements in prior austenitic grain boundaries in the improved 5% Ni steels with no or almost no intergranular fracture was studied for the first time by applying FE-TEM in the previous study. It has been consequently elucidated that alloying elements tend to segregate coincidently to grain boundaries, showing the asymmetric segregation according to solute interactions. The observed behavior was defined as the 'divorced coincident segregation' in the previous paper. The result also shows the effect of soluble Al on the suppression of temper embrittlement and hydrogen embrittlement. In the present study, the mechanism of the divorced coincident segregation is further investigated by employing FE-TEM-EDS along grain boundaries. First is found the periodic segregation of Al and Si, which vary alternately by the cycle of about 3 nm along grain boundaries investigated. It is also shown that Al has the repulsive interaction with Si both in grain boundaries and in matrices.