Quenching and tempering-induced molybdenum segregation to grain boundaries in a 2.25Cr–1Mo steel

Molybdenum is one of the major alloying elements in low-alloy structural steels and is beneficial for mitigating temper embrittlement. Enhancement of the grain boundary cohesion by molybdenum segregation is one of the mechanisms for molybdenum to alleviate the temper embrittlement. To understand clearly the segregation behaviour of molybdenum in low-alloy structural steels, examination of molybdenum grain boundary segregation during quenching and tempering in a 2.25Cr–1Mo steel is conducted experimentally by virtue of field emission gun scanning transmission electron microscopy. There is some molybdenum segregation during quenching. Supersaturated vacancies created by quenching play a certain role in the segregation. Combined equilibrium and non-equilibrium segregation of molybdenum is the nature of segregation in the tempered steels.