AGING EFFECTS ON THE CYCLIC DEFORMATION MECHANISMS OF A DUPLEX STAINLESS-STEEL

Aging effects on the cyclic deformation mechanisms of an AISI-329 dupl ex stainless steel have been studied on the basis of the cyclic harden ing-softening response, cyclic stress-strain curve and substructure ev olution within the individual phases. The cyclic behavior of an unaged and two aged materials shows, in terms of plastic strain amplitude (e psilon(pl)), three well-defined stages. In the first regime, at low ep silon(pl), no differences are observed among the response of the three materials as a consequence of the dominance of ''austenitic-like'' de formation mechanisms for all the materials. In the second regime, al i ntermediate epsilon(pl), the cyclic behavior of unaged material is ass ociated with a mixed ''austenitic/ferritic-like'' character, mainly du e to plastic activity of both phases. On the other hand, the cyclic re sponse of aged material within this intermediate epsilon(pl) range is rather correlated to ''austenitic-like'' cyclic deformation mechanisms because of the intrinsic brittleness of the ferritic matrix. A third regime, at relatively large epsilon(pl), suggests a synergetic phenome non of dislocation activity, deformation twinning and demodulation of spinodal microstructure in ferrite that enables this phase to sustain plastic deformation. Thus, in this epsilon(pl) interval, the observed mechanical and substructural behavior within ferrite may be considered as relatively similar to that observed in unaged material at much low er stress levels; and therefore is amenable to be associated with ''fe rritic-like'' cyclic deformation mechanisms. Finally, based on the res ults presented, the prevalence of ''austenitic-like'' or ''ferritic-li ke'' cyclic deformation mechanisms, for a given plastic strain range, is discussed in terms of the different role played by the ferritic mat rix in each material investigated, depending upon its embrittlement de gree. Copyright (C) 1996 Acta Metallurgica Inc.