Deformation and Annealing Behavior of Nitrogen Alloyed Duplex Stainless Steels. Part II: Annealing

Abstract

The softening behavior of ferritic-austenitic duplex stainless steels (DSS) was investigated separately for both phases by means of microstructure investigations and texture analysis. The results were compared to those of similar single phase materials in order to unveil the influence of the second phase on the specific softening mechanisms during annealing after cold rolling. The microstructure and texture development during hot and cold rolling of the investigated duplex steels was subject of a previous paper.¹⁾ Based on those results this part describes the softening behavior observed during annealing in both a salt bath furnace and a conventional furnace. During annealing the rolled microstructure changes to a more isotropic morphology without pronounced coarsening of the constituent phases. Due to the layer character of the microstructure generated during rolling the recrystallization of the austenite phase is shown to be subject to constrained nucleation conditions and thus leads to textures different from textures of fcc single phase materials. Depending on the degree of deformation and on the initial cold rolling texture the ferrite phase undergoes recovery or recrystallization, but recovery dominates the softening of the bcc phase. Despite of the layered microstructure the active softening mechanisms of ferrite are the same as known from bulk single phase materials and obviously are negligibly influenced by the presence of the austenite phase.