ABSTRACT ABSTRACT Aluminide coatings were applied by halide activated pack cementation to austenitic 304 stainless steel substrates. The evolution of coating microstructure as a function of coating process parameters, e.g., temperature, time, etc., was explored. Stainless steel type 304 was chosen as a model substrate to understand the kinetics of aluminizing and for the potential enhancement in high temperature corrosion resistance. The kinetics of the aluminizing process was studied at different temperatures in the 650 – 850°C range and times in the 1 – 25 h range. At 650°C, the coating consisted of a single layer containing two phases tentatively identified as Al5FeNi (Cr) as the matrix with a dispersed aluminide, Al86Fe14. At 850°C, the coatings initially consist of at least two layers containing three phases [with a preliminary identification as Al86Fe14, AlxFey(Ni,Cr) and Al5Fe Ni(Cr) which transitions to a single layer of possibly AlxFey(Ni,Cr) and intermetallic precipitates of undetermined composition. INTRODUCTION Stainless steels are known to have excellent resistance to attack from corrosive media at both room and elevated temperatures. High temperature corrosion is a potential problem for austenitic stainless steels, e.g., 304, used in chemical processing environments. Extension of the operating regime and the life of the base alloy can be achieved by the application of protective coatings. Aluminum-containing coatings form stable protective oxide scales, making aluminum a commonly used coating element and aluminizing a ubiquitous coating process. In the current study, the halide activated pack cementation process was used to apply aluminum diffusion coatings onto the surface of 304 SS. EXPERIMENTAL PROCEDURE Stainless steel samples were cut into 5 mm thick, 12.5 mm diameter coupons. The samples were then taken through standard metallographic preparation procedures by grinding the surface down to 600 grit using silicon carbide abrasive paper. Packs were prepared by mixing powders of aluminum oxide (“filler”), aluminum (“masteralloy”) and aluminum chloride (“activator”).