Production and Characterization of Oxides Formed on Grade 300 and 350 Maraging Steels Using two Oxygen/Steam Rich Atmospheres

Abstract

The growing process of a spinel-like oxide film can be obtained through different atmospheres; in this sense Air, O 2 , steam, and nitrogen atmospheres were used in different steps during the aging heat treatment at 490ºC of maraging 300 and 350 alloys. The oxidation layer produced under different atmospheres was chemically, microstructurally and mechanically characterized by means of advanced techniques. The results showed (in both alloys) a non-homogeneous mix oxide formed by magnetite, nickel and cobalt ferrites and MoO 3 heterogeneously distributed along the oxide thickness. It was also founded TiO 2 in the innermost areas and a particularly important quantify of hematite on the external surface. A nickel-rich austenite phase was produced at the interphase due to the combination of nickel stability and the preference of cobalt, molybdenum, and iron diffuses through the film as ions. The highest thickness values were found in the oxides produced in maraging 300 steels which could indicate greater susceptibility to oxidation comparing with grade 350 maraging steel. The oxide films produced in both maraging alloys using air atmosphere presents excellent adherence, and the results show the capability for being used for tribological applications under sliding contact tests.

Microstructural and mechanical characterization of additively manufactured parts of maraging 18Ni300M steel with water and gas atomized powders feedstock

“…These oxides exhibit microcracks likely nucleated and propagated due to their high fragility, which partially explains the previously discussed tensile results. Similar findings regarding protuberances, cracks, ridges, and oxide decohesion on the fracture surfaces of maraging steels and Fe-Cr-Mo and Fe-Cr-Y alloys were reported in the studies referenced by [36,50,61,62].…”

“…One possible explanation for this result is the increased concentration of nitrogen and oxygen observed in the 18Ni300M steel processed from the WA batch. The presence of these elements leads to the formation of nitrides and oxides of cobalt, aluminum, titanium, and molybdenum, which are known for their high hardness but also come with a notable degree of brittleness [36,50]. It is worth mentioning that the average percentage variation in hardness for samples processed from the GA and WA batches was approximately 1.5%.…”

“…As expected, the concentration of pores (indicated by white arrows) within the pools and at their edges is more pronounced in the WA batch due to the bimodal distribution and lower circularity of the powder particles mentioned earlier. Additionally, the micrograph of the WA batch shows the presence of large inclusion particles (marked by black arrows) [32,36]. In contrast, the GA micrograph exhibits a lack of fusion defect (pointed by a dashed arrow), which is characteristic of the LPBF process [4].…”