Silicon influence on corrosion properties of austenitic stainless steels

In the present paper there are presented results concerning comparative corrosion resistance of some austenitic stainless steels, with or without silicon content. The silicon content is varying in the range of 1-5 %, in a matrix of alloyed austenite, containing 20% Cr and 15-18%Ni and with very low carbon contents (lower than 0,03% C). There are investigated different types of corrosion resistance: intergranular corrosion in nitrogen media, stress corrosion resistance in chloride media, and transpassive behaviour in sulphuric media. The testing media contained nitrogen, as it follows: Huey test (65% HNO3, at boiling temperature, 244 hours maintain), and 5N HNO3 +1g/l Cr6+ (144 h, at boiling temperature). The media containing chloride is 45% MgCl2 at boiling temperature, with a period of 1000 hours. The transpassive behaviour is tested in 10% HSO4. The investigations were made by optic and electronic microscope, and the corroded surfaces were examined by scanning electron microscopy.