Formation of Al2O3/Fe-Al layers on SS 316 surface by pack aluminizing and heat treatment

Formation of different iron aluminide (Fe-Al) layers during pack aluminizing of stainless steel 316, and subsequent heat treatments has been studied in detail. The single Fe2Al5 layer formed during pack aluminization carried out in the temperature regime 450-650 °C is transformed into FeAl/Fe(Al) layers in the course of post aluminizing heat treatments conducted at higher temperatures. The iron aluminide layers were characterized using SEM, BSE, EDS and EBSD techniques. The precipitates of Cr5Al8 are formed mainly in the Al-rich Fe2Al5 layer, and they get completely dissolved in FeAl layer developed after heat treatment at 1050 °C. The concentration of porosities in the FeAl or Fe(Al) is reduced when the heat treatment temperature is lowered from 1050 to 900 °C. Controlled oxidation approach has been adopted to study the formation and phase transition (γ → θ → α) behavior of alumina (Al2O3) scale in the temperature regime of 700-1050 °C.