In this study, 9-12 wt.% Cr steels P91 and HCM12A were coated with an aluminium diffusion coating by a slurry method and examined in terms of microstructure. Elevated-temperature corrosion behavior of the uncoated and aluminized steels was studied and compared under biomass combustion conditions in the laboratory. The test materials were covered by KCl and exposed to the temperatures of 560 degrees C and 610 degrees C in atmospheres containing varying amounts of HCl, SO2, H2O and O-2 in N-2. The tests were continued for 336 h, after which the test materials were characterized in terms of weight changes, phase structure and elemental distribution. The results showed that both uncoated and aluminized steels underwent active oxidation process. For the uncoated steels, corrosion was essentially uniform all through the surface, whereas for the aluminized steels it was not uniform: some occasional areas of the coating were seemingly unaffected by the surrounding environment, while most of the coatings were completely destroyed. The results clearly demonstrated that the slurry aluminium coating did not improve the corrosion resistance of P91 and HCM12A beneath KCl deposit. These results are presented and discussed in this paper. (C) 2014 Elsevier Ltd. All rights reserved.