High-Temperature Oxidation of Fe-12Cr-0.3C-4Mn-(13-15)Cu Composite Alloys

Abstract

Alloys of Fe-12Cr-0.3C-4Mn-(13, 14, 15)Cu (wt%) were cast using an induction furnace. They were structurally heterogeneous composites that consisted of a relatively stiff α-Fe matrix and a soft (Cu, Mn)-rich secondary phase. They were developed as self-lubricating, wear-resistant metals. Since the formation of oxides plays an important role in wear, understanding the oxidation behavior of two-phase, multi-component composites is of practical interest. This study was undertaken to understand the effect of varying Cu concentration on the formation of oxide scales. When the concentration of Cu in the alloys was increased to 13, 14, and 15 wt%, the volume fraction of the secondary phase also increased from 10.3, 11.2, and 13.3 vol%. When oxidized at 700 ℃ for 30 h, the secondary phase preferentially oxidized to oxide nodules due to Cu and Mn, which could not form a protective scale. The matrix was uniformly oxidized, forming a thin surface scale, due mainly to oxidation-resistant Cr in the matrix. When oxidized at 800-900 ℃ for 30 h, not only the secondary phase but also the α-Fe matrix oxidized rapidly, because of the increased reaction and diffusion rates, resulting in the formation of thick, bi-layered oxide scales. An Fe-rich outer scale was formed by the outward diffusion of Fe, Cr, Mn, and Cu, while a Cr-rich inner scale was formed by the inward diffusion of oxygen. Mn and Cu were rather uniformly distributed in the outer and inner oxide scales. The oxidation rates increased with increasing amounts of Cu, and significantly more with increasing temperature. (Received April 18, 2019; Accepted June 28, 2019)