Estudo da influência da fase sigma nas propriedades mecânicas de dureza e resistência ao impacto de um aço inoxidável superduplex

Abstract

Superduplex stainless steels have excellent combinations of mechanical properties and high corrosion resistance, for these reasons they are applied in the oil and gas industries, offshore platforms and other extremely aggressive environments. When subjected to high temperatures they seek the thermodynamic equilibrium and can precipitate different types of phases. The sigma phase can be considered the most important precipitate because of the large fraction found in the microstructure of the super duplex stainless steels and because it impairs the mechanical and corrosion resistance properties. In this work, after the heat treatment of aging at temperatures of 700, 800 and 900°C, the volume of ferrite was reduced due to precipitation of the sigma phase in the microstructure of grade 6 superduplex stainless steel. Because sigma is a hard intermetallic, the increase of its volumetric fraction in the microstructure generated an increase in the hardness of the material as a whole, reaching values of 348,9 and 398,5 HV at temperatures of 800 and 900°C, respectively. The energy absorbed in the impact test for the solubilized sample was 91.5 J, falling to 10 J for the sample aged at 900°C. The scanning electron microscope images of the fracture surfaces of the aged samples presented cleavage facets, showing a fragile fracture and low energy absorption, while the fracture surface of the solubilized sample presented alveoli, which is characteristic of a fracture with high fracture energy absorption