Aplicação de diferentes técnicas de microscopia para quantificar fases deletérias presentes no aço inoxidável superduplex UNS S32750

Abstract

Superduplex stainless steels are used due to their characteristics are superior to those of ferritic and austenitic stainless steels, they have high mechanical strength and corrosion resistance. Its properties are closely linked to their crystalline two-phase microstructure, ferrite and austenite. The best volume ratio between these phases is 1: 1. Processes with extreme temperatures, such as welding, can modify the ideal proportion of the phases due to precipitation of secondary phases, which are detrimental to the properties of the material, hence the need to study different techniques of phase quantification in super duplex stainless steels. In this work, thermal treatments were performed on the stainless steel superduplex UNS S32750 in order to provide the precipitation of secondary phases, totaling 7 (seven) samples with different fractions of ferrite and austenite. Different techniques were used to quantify phases optical microscopy (OM), scanning electron microscopy (SEM) using BSE mode, backscattered electron diffraction (EBSD) and ferritescope. The results of the quantification of the volumetric fraction of the phases obtained by quantitative metallography were those expected for each technique used, giving importance and evaluating the advantages and limitations of each technique.