Influência da deformação a morno e recozimento na evolução microestrutural, microtextura e comportamento mecânico de um aço inoxidável duplex UNS S32205

Abstract

Due to the good combination of properties resulted from the presence of ferritic and austenitic phases, duplex stainless steels have been increasing their application on several industries sectors. However, there is a significant lack of knowledge on the phase transformations that occur during deformation and their effect on the mechanical behavior of the material, especially when they are processed in temperatures lower than the usual applied during hot working. In this context, the aim of this work was to investigate the microstructural and the texture evolution and the mechanical properties developed in a warm rolled and annealed UNS S32205 duplex stainless steel, with 60% and 80% thickness reduction. To do this, optical, scanning and transmission electron microscopy, and electron backscatter diffraction were used as main techniques. The microstructure evaluation revealed, after warm rolling and annealing processes, a transition of bamboo type into a pearl structure from the 60% WRA sample to the 80% WRA. Moreover, the ferrite phase presented a weakening of α-fiber, (<011>//RD), and a development of γ-fiber, (<111>//ND), as the level of thickness reduction increased. For the austenite, it was noted a weakening of {110}<112> Brass component and an increase in intensity of {110}<001> Goss and {112}<111> Copper components. The mechanical properties were assessed through tensile tests and Vickers microhardness, obtaining a tensile strength average of 794 MPa and microhardness of 255 HV between the analyzed conditions. Post deformation tests demonstrated an increase of microhardness towards the fractured regions, which according to TEM results was associated with the formation of deformation induced martensite. The orientation relationship developed between  and ’-martensite was the {111}γ//{110}α <110>γ//<001>α Nishiyama–Wassermann (N-W). It was also noticed, at regions distant from fracture, the formation of ε-martensite, consider as a precursor for α’, in a Shoji-Nishiyama (S-N) <110>γ//<2110>ε orientation relationship with γ phase. Multi-stage work hardening behavior was observed through Hollomon and Jaoul-Crussard analysis, which confirmed the presence of secondary deformation mechanisms during the plastic deformation of the steel.