Estudo de resistência à corrosão de aços maraging 300 e 350 com e sem recobrimento de óxido tipo espinélio em meio de ácido fluorídrico

Abstract

Maraging steels are extremely versatile and widely used materials due to their high mechanical strength characteristics. These steels have a martensitic microstructure and can be subjected to aging heat treatment to improve their mechanical properties through the precipitation of ultrafine intermetallic compounds. An important application of this material is in the manufacture of rotors for ultracentrifuges used in the isotopic enrichment of uranium, an application that can expose the metal to erosion and a Fluor-rich atmosphere. It is known that some special atmospheres induce the formation of surface oxides with spinel-type microstructure (cubic or tetragonal symmetry structure with a centered body with interstitial atoms occupying the tetrahedral and octahedral sites), which improve corrosion resistance. New projects are being developed to better understand this type of corrosion protection mechanism in maraging steels. The research aimed to study the effects of such oxides on the electrochemical behavior of maraging 300 and 350 steels in comparison with the uncoated material, with the help of techniques such as Open Circuit Potential (OCP), Electrochemical Impedance Spectroscopy and Linear Polarization. In addition, the coating surface was observed by Scanning Electron Microscopy to analyze the degradation caused during the Linear Polarization test. It was found that the presence of spinel oxides of Fe, Ni and Co significantly improves the corrosion resistance of the material in a solution containing hydrofluoric acid. The amount of spinel present in the coatings was directly proportional to the corrosion resistance of the material.