BEHAVIOUR OF PASSIVE FILMS ON STAINLESS STEEL EXPOSED IN VARIOUS CORROSIVE CONDITIONS

Abstract

Corrosion behavior of different steel grades such as 304 and 445NF types with passive films formed under various corrosive environments was examined according to ASTM G61-86 (2014). The distinctive susceptibility of the steel grades to local corrosion in chloride solutions was also discussed. A distinction in corrosion of these steel grades was defined by different austenitic and ferritic natures as well as their elemental compositions. Besides, a corrosion survey of these materials was also conducted for constructions exposed in various atmospheric natural areas ranging from benign rural to aggressive marine conditions. Damages were detected at surfaces of popularly used constructions made of Type 304 stainless steel, where more severe deterioration was observed in the area with higher airborne salinity; examination on Type 445 stainless steel in the same environmental conditions gave results of less severe deterioration and milder damages on surfaces in comparison to Type 304. Different states of passive films also affect the result of the experiments. Corrosion appearance and corrosion products examined by visual inspection and EPMA techniques for steel surfaces showed the influence of airborne salinity on the degree of damage. Corrosion of the steel surfaces was attributed to the combined effect of atmospheric airborne salinity and high time-of-wetness (TOW).