TEM-EDX analysis of spinodal decomposition in fatigued duplex stainless steel

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

Beaune

Conferencia; 8th Duplex Stainless Steels Conference; 2010

Abstract. The increased use of duplex stainless steel (DSS) has rekindled the interest in the study of the phenomenon known as “475 oC embrittlement”, ascribed to the spinodal decomposition (SD) of its ferrite phase. It has been reported that the reaction by which á and ᒠare formed leads to important changes in the fatigue properties of DSS. Nevertheless, the relationship during fatigue between dislocation structure and spinodal decomposition is not well understood. In this context, the cyclic softening observed in aged DSS needs further investigation. The present work 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 aged 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.