AFM observations of intergranular corrosion of 304 stainless steels
Liu Li; Mitamura Tohru; Terasawa Mititaka; Takatani Yasuyuki; Fukumoto Shinji; Tsubakino Harushige
Abstract:Grain boundary corrosion of SUS 304 and SUS 304 L stainless steels sensitized for 0.1 to 24 h at 675 degree C was studied by atomic force microscopy (AFM) and an electrochemical potentiokinetic reactivation (EPR) technique. The specimens for AFM observations were polished carefully and exposed to 10% oxalic acid. The width, depth and angle of the grain boundary grooves of variously sensitized specimens were measured from the profile of grain boundary groove observed by AFM. It is shown that both the depth and width of grain boundary grooves increase and the angles of grooves become narrower with an increase in sensitizing time. The relationship between the degree of intergranular corrosion, profiles of grain boundary groove and estimated grain boundary energy of the sensitized stainless steels was discussed. It is suggested that the grain boundary energy obtained from the grooves angle becomes large with an increase in sensitizing time. This result coincides with that obtained from EPR measurement. AFM is a powerful technique for investigating the mechanism of grain boundary corrosion. Key Words:AFM, EPR, Austenitic stainless steel, Intergranular corrosion, Grain boundary groove