MECHANISM OF DYNAMIC CONTINUOUS RECRYSTALLIZATION DURING SUPERPLASTICDEFORMATION IN A MICRODUPLEX STAINLESS-STEEL

Microstructural evolution during the cyclic cold-rolling and annealing process in an (alpha + gamma) microduplex stainless steel, which cons ists of alpha subgrains and fine gamma particles, has been studied in detail with the aim of clarifying the mechanism of dynamic continuous recrystallization. A continuous increase in a subgrain boundary misori entation is obtained by the present processing where grain boundary sl iding does not occur and the effect of increasing boundary misorientat ion with cumulative strain is comparable to those observed in dynamic continuous recrystallization of superplastic aluminium alloys. The inc rease in boundary misorientation is accounted for by the absorption of dislocations into subgrain boundaries during annealing, dislocations which had operated to accommodate the plastic strain incompatibility o f the neighboring phases undergoing slip deformation. The present resu lts show that grain boundary sliding is not indispensable but the diff erence in accommodation deformation between adjacent subgrains is of g reat importance for the dynamic continuous recrystallization during su perplastic deformation. Copyright (C) 1996 Acta Metallurgica Inc.