Abstract: An aluminide (AlFe and α-(FeAl)) surface layer containing lower-Al was formed on ferritic-martensitic steel P92 by means of surface mechanical attrition treatment (SMAT) combined with a duplex aluminization process at lower temperatures, i.e. a packed aluminization followed by a diffusion annealing treatment below its tempering temperature. Indentation tests indicated that the lower-Al surface layer formed on the SMAT sample is more resistant to cracking and has better adhesion to the substrate in comparison with the Al₅Fe₂ layer formed on the as-received sample after the duplex aluminization process. Isothermal steam oxidation measurements showed that the oxidation resistance is increased significantly by the lower-Al surface layer due to the formation of a protective (Fe,Cr)Al₂O₄ layer. The rate constant of oxidation was estimated to decrease from ~0.849 mg² cm^-4 h^-1 of the as-received material to ~0.011 mg² cm^-4 h^-1 of the AlFe layer at 700 °C.

Key words: Surface mechanical attrition treatment (SMAT), Ferritic-martensitic steel, Lower-temperature aluminization, Aluminide, Steam oxidation