The Embrittlement and De-Embrittlement of Grain Boundaries in an Fe-Mn-Ni Alloy Due to Grain Boundary Segregation of Mn

摘要

A ductile-brittle-ductile (DBD) transition behavior in an age-hardenable Fe-8Mn-7Ni alloy has been analyzed in light of segregation and desegregation of alloying elements at prior austenite grain boundaries. The DBD transition in the alloy can be distinguished by two C-type curves: one corresponding to the start of zero tensile elongation and the other to the finish. The activation energies for ductile-to-brittle and brittle-to-ductile transitions are in close agreement with that for age hardening. Manganese content at the prior austenite grain boundaries was analyzed by Auger electron spectroscopy, and intergranular fracture strength at the brittle fracture region showed inverse trends with Mn concentration at the grain boundaries. All these observations strongly suggest that manganese segregation and its desegregation are responsible for the DBD transition of this alloy.