Application of EIS to the study of corrosion behaviour of sintered ferritic stainless steels before and after high-temperature exposure

Two types of ferritic stainless steel powders (AISI 409LNb and 434L) have been sintered in vacuum at three different temperatures (1225, 1250 and 1275 °C). The corrosion behaviour of the six materials produced has been studied through polarization curves and electrochemical impedance spectroscopy (EIS) measurements. The electrochemical tests have been carried out for the six materials before and after a high-temperature exposure at 800 °C. A new parameter, the active area factor (AAF), deduced from EIS measurements, has been proposed. This AAF quantifies approximately the relationship between the apparent surface of the powder metallurgical (PM) stainless steel specimens and the real surface exposed to corrosion.