Precipitates and Grain Boundary Strength of an Fe-Mn-Ni Alloy

Abstract

The effect of grain boundary (GB) precipitates on the GB strength of an age-hardened Fe-7.8Mn-8.2Ni alloy was investigated. Premature intergranular fracture was observed after age hardening due to the precipitation of theta-MnNi precipitates at prior austenite grain boundaries. However, the conversion of GB theta precipitates to austenite by a short second aging at 793 K (520 A degrees C) after peak aging at 713 K (440 A degrees C) resulted in a remarkable improvement of GB strength. The result strongly supports the proposition that the weak bonding of GB theta precipitates to the matrix is the main reason for GB embrittlement in age-hardened Fe-Mn-Ni alloys.