Intergranular Corrosion of AISI 304 Heat Treated at 800 °C Varying Range Times

Abstract

Austenitic stainless steels, when exposed to welding conditions or aging for length of service, it's observed the formation of numerous deleterious phases, such as several kinds of carbides type MC, M 6 C, M 7 C 3 , M 23 C 6 , and intermetallic secondary phases (sigma, chi, laves), which cause the process of intergranular corrosion. The aim of this work was verifying the formation of the types of carbides and/or intermetallic phases existing in the stainless AISI 304 at 800 ºC, varying the timing of heat treatment between 30, 360 and 1,440 min. The optical microscopy analysis revealed the predominant formation of the carbide type M 23 C 6 . The results of DL-EPR (double loop electrochemical potentiokinetic reactivation) tests showed a gradual increase in the precipitation of this carbide with the increase of treatment time. The potentiodynamic polarization showed that the precipitation of this carbide reduce the formation of the Cr 2 O 3 passive layer, suggesting that the precipitate carbide to be predominantly of the Cr 23 C 6 type.