THE EMBRITTLEMENT AND DE-EMBRITTLEMENT OF GRAIN-BOUNDARIES IN AN FE-MN-NI ALLOY DUE TO GRAIN-BOUNDARY SEGREGATION OF MN

A ductile-brittle-ductile (DBD) transition behavior in an age-hardenab le Fe-8Mn-7Ni alloy has been analyzed in light of segregation and dese gregation of alloying elements at prior austenite grain boundaries. Th e DBD transition in the alloy can be distinguished by two C-type curve s: one corresponding to the start of zero tensile elongation and the o ther to the finish. The activation energies for ductile-to-brittle and brittle-to-ductile transitions are in close agreement with that for a ge hardening. Manganese content at the prior austenite grain boundarie s was analyzed by Auger electron spectroscopy, and intergranular fract ure strength at the brittle fracture region showed inverse trends with Mn concentration at the grain boundaries. All these observations stro ngly suggest that manganese segregation and its desegregation are resp onsible for the DBD transition of this alloy.