Double loop electrochemical potentiodynamic reactivation test (DL-EPR) study of the influence of microstructure on the susceptibility of AISI 430 stainless steel to sensitization

Abstract

AISI 430 is a ferritic stainless steel grade very popular due to its interesting properties and attractive cost. The sensitization of ferritic and semi-ferritic steels has been much less investigated than austenitic types. In this work, the microstructure of AISI 430 steel processed by industrial annealing were characterized by optical microscopy and double-loop electrochemical polarization reactivation tests (DL-EPR). Starting from the as received material several heat treatments between 900 °C and 1150 °C followed by different cooling procedures (water, air and furnace) were performed. Other samples were treated at 600 °C, 700 °C and 800 °C for one hour with water cooling. The resulting microstructures were characterized by optical and scanning electron microscopy. The DL-EPR tests were conducted to identify the microstructures and heat treatment conditions more resistant to intergranular corrosion. The specimen treated at 950 °C for one hour followed by water cooling, and the specimen re-heated at 700 °C from the as received condition were the two samples which presented the lowest intergranular corrosion susceptibility, although their microstructures were completely different one from the other.