High Temperature Oxidation Behavior of Aluminized Austenitic Stainless Steels

High temperature oxidation of metallic alloys is a complex phenomenon involving multiple processes, e.g., arrival of gaseous species at the surface of the materials, solid state diffusion, creation and movement of defects in the material, initial oxidation state, etc. One of the limitations in using stainless steels for high temperature service is the formation of a volatile, non-protective CrO3 scale at temperatures above 900??C. For these elevated temperatures, alloys that form aluminum oxide scales afford better protection due to their higher stability and slower growth rates. High temperature coatings have been developed to form a protective Al2O3 oxide scale on substrates at these elevated temperatures, while at the same time, retaining the mechanical properties of the chromium-containing alloy. Simulating high temperature service environments in the laboratory enables the development of insights into the formation and stability of oxide films on metallic substrates. In this project, we are examining the oxidation behavior of uncoated and coated type 304 stainless steels in air. Coated samples were prepared by pack aluminizing type 304 stainless steels using an aluminum chloride activator for nine hours at temperatures of 650??C, 750??C, and 850??C. Coated and base samples were then subjected to isothermal as well as cyclic oxidation testing under atmospheric pressure at 1000??C for various time intervals. Results based on macro-photography, mass change data and X-ray diffraction, optical microscopy and micro-hardness tests will be reported