Caracterização de óxido produzido em aços maraging com Nb durante envelhecimento em atmosfera controlada de N2

Abstract

This work addresses the production and characterization of an oxide film on maraging 300 steels with the addition of niobium, obtained throug h an aging heat treatment under a controlled nitrogen (N₂) atmosphere. The formation of oxide films containing, especially, magnetite spinel (Fe₃O₄) has proven to be effective for surface protection, delaying the progression of corrosive processes in aggre ssive environments. The study investigated two types of maraging 300 steels doped with niobium: one with total substitution of titanium by niobium (Nb), and another with partial substitution of titanium by niobium (Ti + Nb). The samples were solution treat ed at 840 °C and cooled inside the furnace after shutdown. Subsequently, they were prepared by progressive grinding and subjected to an aging heat treatment at 500 °C for 3 (three) hours under a controlled N₂ atmosphere, in order to promote the formation o f a surface oxide layer. The characterization of the oxide films was carried out using different techniques, such as X ray Diffraction (XRD), Focused Ion Beam (FIB) combined with EDS analysis, and Raman spectroscopy. The results revealed a predominance of magnetite spinel, although small amounts of other oxides, such as wüstite (FeO) and goethite [FeO(OH)], were also detected. This may be related to the XRD characterization which, despite being performed in grazing incidence mode, can still slightly penetra te beyond the sample surface. It was concluded that the employed method is efficient for the formation of an oxide film predominantly composed of magnetite spinel, presenting adequate adhesion for handling and for the execution of non destructive tests. Th e objective was achieved for both samples: maraging 300 steel with niobium totally replacing titanium (Nb), and maraging 300 steel with niobium partially replacing titanium (Ti + Nb), resulting in the formation of magnetite spinel over most of their surfac es.