Polycrystalline modeling of the cyclic hardening/softening behavior of an austenitic-ferritic stainless steel

P EVRARD; I ALVAREZ; V AUBIN; S DEGALLAIX

MECHANICS OF MATERIALS

Elsevier

Lugar: Cambridge; Año: 2010 vol. 42 p. 395 - 404

0167-6636

In order to simulate the cyclic hardening/softening curves in low-cycle fatigue of an austenitic-ferritic or duplex stainless steel (DSS), a new polycrystalline model is proposed. The polycrystalline model developed by Cailletaud [1] and Pilvin [2] and modified by Hoc et al. [3] was previously extended in [4] in order to take into account the bi-phased character of the DSS. This model correctly accounts for the cyclic hardening, but it is not able to simulate the cyclic softening. Consequently, the stabilized state and hysteresis loop are overestimated. TEM observations of the dislocation structures show that during the cyclic hardening, planar arrangements are observed in austenitic grains and no significant evolution is observed during the subsequent cyclic softening and stabilization stage. On the contrary, in ferritic grains, dislocations are homogeneously distributed during cyclic hardening, and the microstructure evolves during the subsequent cyclic softening and stabilization stage. Dislocation structures build progressively consisting of hard zones or walls, separed by soft zones or channels. Consequently we propose to model the cyclic softening through dislocation structure evolution within ferritic grains. The single crystal law used by [3] is modified in order to take into account the heterogeneous distribution of dislocations in the ferrite. The model is compared with experimental data. A good agreement is observed between experimental and calculated harden-ing/softening curves and stabilized hysteresis loops.