Influencia del movimiento de las dislocaciones en la descomposición espinodal de aceros inoxidables duplex fatigados

S. HEREÑÚ,; M. SENNOUR; M. BALBI; I. ALVAREZ-ARMAS, ; A. F. ARMAS

Rosario

Conferencia; 5ª CONFERENCIA SOBRE USOS DEL ACERO DEL IAS; 2010

Instituto Argentino de Sidururgia

Despite the attractiveness of duplex stainless steel grades (DSS), they have limitations. The well-known 475°C embrittlement that these steels present sets an upper limit to the temperature range recommended during service. This phenomenon is ascribed to the spinodal decomposition (SD) in its ferrite phase. Several authors have studied the influence of spinodal decomposition on fatigue properties of DSS. Nevertheless, the relationship during fatigue between dislocation structure and spinodal decomposition needs further investigation. In this context, the cyclic softening observed in aged DSS S32750 has been ascribed to the development of the localized dislocations bands from a homogenous distribution of linear dislocation arrangements or to a demodulation of the spinodal decomposition in the ferrite phase enhanced by dislocations motion. The last propose could not be confirmed by conventional transmission electron microscopy (TEM) observations. The present investigation is focused on assessing the influence of dislocation movement on spinodal decomposition through scanning electron transmission microscopy (STEM) in combination with energy dispersive X-ray spectroscopy (EDX) analysis in aged DSS S32750. Microbands are the prominent dislocation arrangements observed in samples cyclic tested at large plastic strains. By EDX measurements it was found that the spinodal decomposition was dissolved inside these microbands. Therefore, the mechanism of microband formation developed during cycling in the ferritic phase seems to be responsible for the demodulation of the spinodal decomposition. This fact could be involved in the cyclic softening displayed by aged DSS(EDX) analysis in aged DSS S32750. Microbands are the prominent dislocation arrangements observed in samples cyclic tested at large plastic strains. By EDX measurements it was found that the spinodal decomposition was dissolved inside these microbands. Therefore, the mechanism of microband formation developed during cycling in the ferritic phase seems to be responsible for the demodulation of the spinodal decomposition. This fact could be involved in the cyclic softening displayed by aged DSS