Abstract

The objective of this study is to characterize the microstructure of a sensitized AISI 304H steel subjected to a dissolution treatment at 900°C and to evaluate it through ultrasonic techniques. The monitoring of microstructural evolution was carried out by Scanning Electron Microscopy (SEM) and the determination of acoustic variables by ultrasound, using the pulse-echo detection technique. The results demonstrated the characteristic microstructure of these grain steels, exhibiting polygonal morphologies and highly contrasted zones along the grain boundaries. This was attributed to the presence of the sigma phase and chromium carbides, which were preferentially located in these high-energy zones. However, as the dissolution treatment time increased, the presence of small precipitates of chromium carbides were observed along the entire surface. This could be due to the dissolution of the sigma phase and the chromium carbide nucleation process, which occurs after three hours of treatment. Ultrasonic measurements revealed a variation in velocity as the treatment time increased, attributed to the influence of the fraction of sigma phase and carbides presented in the microstructure, as well as the material's inherent anisotropy. Conversely, the attenuation coefficient exhibited a tendency primarily associated with dispersion losses, resulting from the microstructural alterations observed in the material during dissolution treatments of the precipitates.