THEORY OF NONEQUILIBRIUM SEGREGATION IN AN FE-MN-NI TERNARY ALLOY ANDA DUCTILE-BRITTLE-DUCTILE TRANSITION

In an Fe-8Mn-7Ni ternary alloy, age-hardened by coherently formed face -centered tetragonal MnNi intermetallic compounds within the matrix, a modeling based on a regular solution model is performed to formulate the nonequilibrium grain boundary segregation behaviors of the alloyin g elements, followed by a ductile-brittle-ductile transition [1, 2] in the alloy. An equation is derived representing the segregation kineti cs. It is confirmed from the calculations that the segregation behavio rs of the elements are directly controlled by the precipitation reacti on in the matrix. The nonequilibrium segregation behaviors are charact erized by time-temperature diagrams, which show maximum segregation le vels of the elements in an intermediate aging time and temperature ran ge. The calculated results explain theoretically and semiquantitativel y the relationship between the nonequilibrium segregation of the eleme nts and the ductile-brittle-ductile transition. Copyright (C) 1996 Act a Metallurgica Inc.