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

The growing process of a spinel-like oxide film can be obtained through different atmospheres; in this sense Air, O2, 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 MoO3 heterogeneously distributed along the oxide thickness. It was also founded TiO2 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.

Automated summary

The growing process of a spinel-like oxide film can be influenced by different atmospheres. The oxidation layer formed under different atmospheres was characterized chemically, microstructurally, and mechanically. The results showed a non-homogeneous mix oxide with uneven thickness. TiO2 was found in the inner areas and a significant amount of hematite on the external surface. A nickel-rich austenite phase was produced, with the highest thickness observed in maraging 300 steel. The oxide films produced in both alloys using air atmosphere exhibited excellent adherence and can be used for tribological applications.