LONG TERM ATMOSPHERIC EXPOSURE OF STABILIZED FERRITIC STAINLESS STEELS

摘要

Ferritic stainless steels are attractive considering metallurgical and economical features when compared to the austenitic stainless steels. The atmospheric corrosion resistance of ferritic stainless steels with chemical compositions ranging from AISI 430 to AISI 444 was evaluated. Tested materials had 16 to 18% chromium, increasing concentrations of molybdenum from 0 to 2%, low C and N, and were stabilized with titanium and niobium. Four different locations were chosen and the samples were exposed for 2 years and submitted to marine, urban and industrial atmospheres. The "in-situ" collected data includes sample appearance, electrode potential, environment temperature, rainfall and chemical composition of the rain water. It was done X-Ray diffraction analysis of the oxides and particles found at the 4 locations and metallographic analysis of the samples using optic microscope and Scanning Electron Microscope (SEM). This paper shows all the results obtained and emphasises the relation with the austenitic stainless steels AISI 304 and AISI 316. It is shown that a stabilized 17%-18% Cr ferritic stainless steels with addition of 2%Mo can be a reasonable substitute material for AISI 304.