Examination of the intergranular corrosion sensitivity of austenitic stainless steel with physical simulation

Abstract

As known, the austenitic stainless steels, if their carbon content exceeding 0,03-0,04%, with slow cooling from higher temperature, or tempering between 500-900 °C, a non-homogeneous microstructure evolved. Addition to the austenite, a number of intermetallic compounds can be precipitated, among these the M₂₃C₆ carbide is the most determining, in terms of intergranular corrosion. Around the precipitated, high chromium content (approximately 65%) phase, the austenite Cr content could be decreases under 10,5%, so the steel became sensitive to intergranular corrosion. This undesirable effect could be evolved during the welding heat cycle, in case of austenitic steels with intergranular corrosion sensitivity. The sensitivity properties of these austenitic stainless steels can be described by sensitivity diagrams, which can display the location and occurrence area of carbides, as a function of the holding temperature and time. Given that, the welding heat cycle significantly different from the constant tempering heat treatment, the sensitivity of austenitic stainless steels should be analysed in the fucniton of the different parameters of welding heat cycle. In this research work, experiments were done on test specimens with physical simulated welding heat cycles on a Gleeble 3500 equipment, where different maximum temperatures were used, alongside with variable cooling profiles. With the gained test results the welding circumstances were determined, which can cause intergranular corrosion in the tested austenitic steels.