A study of grain boundary nucleated widmanstätten precipitates in a two-phase stainless steel

Abstract

The factors which control the nucleation and growth of Widmanstätten precipitates at grain boundaries in a two-phase stainlesss steel, have been studied by transmission electron microscopy. Widmanstätten precipitates usually involves a separate nucleation and growth event at prior austenite films or allotriomorphs, which are the first phase to form at grain boundaries. The Widmanstätten precipitates have a preferred orientation relationship with both the prior grain boundary γ-phase and with the α matrix. The particular γ variant which forms has a near Kurdjumov-Sachs relationship with the α-grain and the invariant line assciated with the variant is nearly normal to the grain boundary plane. The orientation relationship changes during growth, towards an exact K-S relationship, with the growth direction (which is parallel to the invariant line) also rotating to be nearly parallel to the common close-packed direction associated with the transformation.