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The erosion‐corrosion resistance of uncoated and aluminized 12% chromium ferritic steels under fluidized‐bed conditions at elevated temperature
Author(s) -
HuttunenSaarivirta E.,
Kalidakis S.,
Stott F.H.,
Rohr V.,
Schütze M.
Publication year - 2005
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.200503921
Subject(s) - materials science , spallation , metallurgy , corrosion , brittleness , chromium , high temperature corrosion , oxide , erosion , intergranular corrosion , atmospheric temperature range , composite material , paleontology , physics , quantum mechanics , meteorology , neutron , biology
Abstract In this paper, some results from a study of the erosion‐corrosion resistance of uncoated and aluminized 12% chromium steel in a fluidized‐bed rig are reported. The aims of the research are to establish and compare the erosion‐corrosion resistance of these materials for possible applications as heat exchangers in future power plants, and to obtain an increased understanding on their behaviour and mutual superiority in a range of conditions. Damage to the uncoated 12% chromium steel occurs by an oxidation‐affected erosion process under all the studied conditions, with spallation of scale being the primary mechanism of material wastage. At a temperature of 550°C, the uncoated steel follows the typical angle‐dependence of a brittle material, while, at temperatures above 550°C, it follows an angle‐dependence that is more typical of a ductile material. This change in the angle‐dependence with temperature is related to characteristics, i.e. uniformity, adhesion and density, of the formed oxide scales. The rate of material wastage increases with increase in speed and temperature, due to the development of thicker, more uniform and more dense oxide scales, that promote more severe scale spallation. The erosion‐corrosion behaviour of the aluminized 12% chromium steel changes in the temperature range from 600°C to 650°C. This is due to a shift from a brittle‐like to a ductile‐like angle‐dependence and to a more rapid oxide scale build‐up at temperatures above 600°C. At an impact angle of 30° and at 550°C and 600°C, the prevailing erosion‐corrosion process for the aluminized steel is oxidation‐affected erosion. At 650°C and 700°C for an impact angle of 90°, the primary erosion‐corrosion mode is essentially erosion‐enhanced oxidation. The results of the study have also demonstrated that the Al 5 Fe 2 coating deposited by pack aluminization offers enhanced protection against erosion‐corrosion at shallow impact angles at 550°C and 600°C and at steeper impact angles at 700°C.