Corrosion behaviour of AISI 304L and 316L stainless steels prepared by powder metallurgy in the presence of sulphuric and phosphoric acid

The corrosion rates of AISI 304L and 316L stainless steels prepared by powder metallurgy (P/M) have been studied by continuous electrochemical methods, in different concentrations of inorganic acid solutions (sulphuric and phosphoric) at room temperature (T = 298 K). For comparison purposes, a simultaneous study was carried out on similar composition cast AISI 304L and AISI 316L stainless steels specially prepared for this study. For the latter part of this investigation, polarisation resistance and an intersection method were applied to obtain values for the Tafel slopes and the Stern-Geary constant B. The sintered AISI 304L and 316L stainless steels had the highest corrosion rates, these being much higher in sulphuric acid. Subsequently, a kinetic study of the corrosion process has been carried out. The most pronounced attack was observed in those steels prepared by powder metallurgy due to a generalised mechanism of crevice corrosion taking place in the pores. On the other hand, as is already well known, the cast stainless steels generally showed a strong resistance to corrosion in the media tested.