Susceptibility to the intergranular attack in austenitic stainless steels

Abstract

Intergranular corrosion is very dangerous local corrosion form that often leads to the dislodgment of individual grains and to the intensive negative influence on the mechanical properties of the material. The susceptibility of the austenitic stainless steels to the intergranular corrosion is connected with their exposition in the temperature range of 500-800 °C ("critical temperatures") and with consequent slow cooling in the air which leads to the precipitation of chromium-rich carbides at the grain boundaries. This process consumes chromium from a narrow band along the grain boundaries and the steel becomes to be sensitized and susceptible to the intergranular corrosion in aggressive environments. This article deals with the susceptibility to the intergranular corrosion of three austenitic stainless steels (AISI 304, 316L, 316Ti). Both "as received" and improperly heat treated specimens (sensitization for 10 hours at 650 °C, cooling in the air) were tested by ASTM A262 standard method, A and E practices. Optical microscopy and SEM analysis were used for the assessment of the obtained results.