Processamento e caracterização dos aços inoxidáveis austenítico AISI 316L e duplex SAF 2205 obtidos por solidificação rápida

Abstract

Austenitic stainless steels and duplex stainless steels have good mechanical and corrosion resistance characteristics that make them applicable in various industries. The objective of this work was to process the steels by rapid solidification, with subsequent heat treatment. Microstructural characterizations were carried out under conditions as received, by rapid solidification and in heat treatments. Microstructural characterization was performed using techniques such as: optical microscopy, scanning electron microscopy with energy dispersion analysis and X-ray diffraction. Microhardness, thermal analysis by differential scanning calorimetry and thermogravimetry and polarization corrosion tests cyclic potentiodynamics. The AISI 316L steels in the condition as received and after the heat treatments the obtained microstructures were similar, varying the grain size with the temperature increase. AISI 316L steel in the fast set condition showed a microstructure with columnar dendrite, acircular dendrite and equiaxed dendrite. After the heat treatments of the steel in the condition by rapid solidification, it was observed the formation of equiaxed grains, increase in grain size and the formation of phases such as sigma and chi which are undesirable because they promote the embrittlement and corrosion of the steel. The fast set condition of the AISI 316L steel showed better resistance to pitting corrosion. The duplex stainless steel SAF2205 in the condition as received and after the solubilization treatments presented a ferritic matrix with dispersed lamellae of austenite and the increase of the grain size was observed with the increase of the solubilization temperature. The microstructure in the condition by rapid solidification was of equiaxed ferrite grains and austenite in the contours of the ferrite grains. After the solubilization treatment in the condition by rapid solidification, a ferritic matrix with equiaxed grains, austenite in grain contour, austenite widmänstten and intragranular austenite was obtained. For SAF2205 duplex stainless steel there was no significant variation of pitting potential between the processing routes and the passivation started faster, in the condition as received.