On appearance of pittings on grain boundaries of stainless steel

The pitting corrosion of steels Kh18N10T and S3Kh25N5M2 in a solution of in HClO+0.1n NaCl and in a solution of 0.05n NaCl was investigated. The pitting topography was studied metallographically after taking potentiodynamic curves. In chloride solutions, pittings on hardened steel 03Kh25N5M2 appear in sulphide inclusions located in austenite and at the austenite-ferrite interfaces, and on steel Kh18N10T in particles of complex oxides and titanium-containing oxisylphites. A decrease in grain size of steel Kh18N10T promotes the nucleation of pittings. Sensibilizing annealing does not affect the pitting potential, but in a coarser-grain steel, inclusions at the grain boundaries become more preferable centers of pitting than inclusions in grains